DETECTOR FOR AN OPTICAL DETECTION OF AT LEAST ONE OBJECT

Abstract

Disclosed herein is a detector (110) containing: at least one longitudinal optical sensor (114), wherein the longitudinal optical sensor (114); and at least one evaluation device (140), wherein the evaluation device (140) is designed to generate at least one item of information on a longitudinal position of the object (112) by evaluating the longitudinal sensor signal of the longitudinal optical sensor (114). Also disclosed herein are articles containing the detector (110), and methods for optical detection of objects using the detector (110).

Claims

1. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region, wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the sensor region comprises at least one photoconductive material, wherein an electrical conductivity of the photoconductive material, given the same total power of the illumination, is dependent on the beam cross-section of the light beam in the sensor region, wherein the longitudinal sensor signal is dependent on the electrical conductivity; and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

2. The detector according to claim 1, wherein the photoconductive material is an inorganic photoconductive material.

3. The detector according to claim 2, wherein the chalcogenide is selected from the group consisting of: a sulfide chalcogenide, a selenide chalcogenide, a telluride chalcogenide, a ternary chalcogenide, a quaternary chalcogenide, a higher chalcogenide, and a solid solution and/or a doped variant thereof.

4. The detector according to claim 3, wherein the chalcogenide is selected from the group consisting of: lead sulfide (PbS), copper indium sulfide (CIS), copper indium gallium selenide (CIGS), copper zinc tin sulfide (CZTS), lead selenide (PbSe), copper zinc tin selenide (CZTSe), cadmium telluride (CdTe), mercury cadmium telluride (HgCdTe), mercury zinc telluride (HgZnTe), lead sulfoselenide (PbSSe), copper-zinc-tin sulfur-selenium chalcogenide (CZTSSe), and a solid solution and/or a doped variant thereof.

5. The detector according to claim 1, wherein the pnictogenide is selected from the group consisting of: nitride pnictogenides, phosphide pnictogenides, arsenide pnictogenides, antimonide pnictogenides, ternary pnictogenides, quarternary, and higher pnictogenides.

6. The detector according to claim 5, wherein the pnictogenide is selected from the group consisting of indium nitride (InN), gallium nitride (GaN), indium gallium nitride (InGaN), indium phosphide (InP), gallium phosphide (GaP), indium gallium phosphide (InGaP), indium arsenide (InAs), gallium arsenide (GaAs), indium gallium arsenide (InGaAs), indium antimonide (InSb), gallium antimonide (GaSb), indium gallium antimonide (InGaSb), indium gallium phosphide (InGaP), gallium arsenide phosphide (GaAsP), and aluminum gallium phosphide (AlGaP).

7. The detector according to claim 1, wherein the photoconductive material comprises doped silicon.

8. The detector according to claim 1, wherein the photoconductive material is provided as a colloidal film, wherein the colloidal film comprises quantum dots.

9. The detector according to claim 1, wherein the photoconductive material is an organic photoconductive material, wherein the organic photoconductive material comprises at least one conjugated aromatic molecule, in particular a dye or a pigment, and/or a mixture comprising an electron donor material and an electron acceptor material.

10. The detector according to claim 9, wherein the organic photoconductive material comprises a compound selected from the group consisting of: phthalocyanines, naphthalocyanines, subphthalocyanines, perylenes, anthracenes, pyrenes , oligo- and polythiophenes, fullerenes, indigoid dyes, bis-azo pigments, squarylium dyes, thiapyrilium dyes, azulenium dyes, dithioketo-pyrrolopyrroles, quinacridones, dibromoanthanthrone, polyvinylcarbazole, derivatives and combinations thereof.

11. The detector according to claim 9, wherein the electron donor material comprises an organic donor polymer.

12. The detector according to claim 9, wherein the electron acceptor material comprises a fullerene-based electron acceptor material.

13. The detector according to claim 9, wherein the electron acceptor material comprises an organic acceptor polymer.

14. The detector according to claim 1, wherein the optical detector is adapted to generate the longitudinal sensor signal by one or more of measuring an electrical resistance or a conductivity of at least one part of the sensor region.

15. The detector according to claim 14, wherein a bias voltage is applied across the material.

16. The detector according to claim 15, wherein a bias voltage source and a load resistor are arranged in series with the longitudinal optical sensor.

17. The detector according to claim 1, wherein the electrical conductivity of the sensor region, given the same total power of the illumination, decreases with decreasing beam width of a light spot generated by the light beam in the sensor region.

18. The detector according to claim 1, wherein the longitudinal optical sensor comprises at least one layer of the photoconductive material and at least two electrodes contacting the layer, wherein the at least two electrodes are applied at different locations of the layer of the photoconductive material.

19. The detector according to claim 18, wherein the at least two electrodes are applied to the same side of the layer.

20. The detector according to claim 18, wherein a Schottky barrier is formed at a boundary between the layer of the photoconductive material and at least one of the electrodes contacting the layer.

21. The detector according to claim 18, wherein the at least one layer of the photoconductive material is directly or indirectly applied to at least one substrate.

22. The detector according to claim 21, wherein the substrate is an insulating substrate.

23. The detector according to claim 21, wherein the substrate is at least partially transparent or translucent.

24. The detector according to claim 1, wherein the at least one longitudinal optical sensor comprises at least one transparent longitudinal optical sensor.

25. The detector according to claim 1, wherein the detector comprises at least one stack of at least two longitudinal optical sensors.

26. The detector according to claim 1, wherein the detector comprises at least one array of at least two longitudinal optical sensors, wherein the array is arranged perpendicular to the optical axis.

27. The detector according to claim 26, wherein the longitudinal optical sensors in the array are arranged as a matrix of individual resistors, wherein an aggregate resistance of the individual resistors in the matrix depends on a number N of the longitudinal optical sensors within the array which are illuminated by the incident light beam, wherein the evaluation device is adapted to determine a number N of the longitudinal optical sensors which are illuminated by the light beam, the evaluation device further being adapted to determine at least one longitudinal coordinate of the object by using the number N of the longitudinal optical sensors which are illuminated by the light beam.

28. The detector according to claim 1, wherein the longitudinal optical sensor is furthermore designed in such a manner that the illumination of the sensor region by the light beam additionally causes an increase in temperature of the sensor region, wherein the electrical conductivity in the sensor region, given the same total power of the illumination, is further dependent on the temperature of the sensor region, wherein the longitudinal sensor signal, given the same total power of the illumination, is further dependent on the temperature in the sensor region.

29. The detector according to claim 1, wherein the evaluation device is designed to generate the at least one item of information on the longitudinal position of the object from at least one predefined relationship between the geometry of the illumination and a relative positioning of the object with respect to the detector.

30. The detector according to claim 29, wherein the evaluation device is adapted to generate the at least one item of information on the longitudinal position of the object by determining a beam cross-section of the light beam from the longitudinal sensor signal.

31. The detector according to claim 30, wherein the evaluation device is adapted to compare the beam cross-section of the light beam with known beam properties of the light beam in order to determine the at least one item of information on the longitudinal position of the object.

32. The detector according to claim 1, wherein the light beam is a non-modulated continuous-wave light beam.

33. The detector according to claim 1, further comprising: at least one transversal optical sensor, the transversal optical sensor being adapted to determine a transversal position of the light beam traveling from the object to the detector, the transversal position being a position in at least one dimension perpendicular an optical axis of the detector, the transversal optical sensor being adapted to generate at least one transversal sensor signal, wherein the evaluation device is further designed to generate at least one item of information on a transversal position of the object by evaluating the transversal sensor signal.

34. The detector according to claim 33, wherein the transversal optical sensor is a photo detector having at least one first electrode, at least one second electrode and at least one layer of a photoconductive material embedded in between two separate layers of a transparent conductive oxide, wherein the transversal optical sensor has a sensor area, wherein the first electrode and the second electrode are applied to different locations of one of the layers of the transparent conductive oxide, wherein the at least one transversal sensor signal indicates a position of the light beam in the sensor area.

35. The detector according to claim 34, wherein at least one electrode is a split electrode having at least two partial electrodes, wherein electrical currents through the partial electrodes are dependent on a position of the light beam in the sensor area, wherein the transversal optical sensor is adapted to generate the transversal sensor signal in accordance with the electrical currents through the partial electrodes.

36. The detector according to claim 35, wherein the detector is adapted to derive the information on the transversal position of the object from at least one ratio of the currents through the partial electrodes.

37. The detector according to claim 33, wherein the at least one transversal optical sensor comprises at least one transparent transversal optical sensor.

38. The detector according to claim 1, furthermore comprising at least one illumination source.

39. The detector according to claim 1, wherein the detector further comprises at least one imaging device.

40. The detector according to claim 39, wherein the imaging device comprises a camera.

41. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the sensor region comprises at least one material capable of sustaining an electrical current, wherein at least one property of the material, given the same total power of the illumination, is dependent on the beam cross-section of the light beam in the sensor region, wherein the longitudinal sensor signal is dependent on the at least one property: and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

42. The detector according to claim 41, wherein the material capable of sustaining the electrical current is one of the group consisting of: amorphous silicon (a-Si), an alloy comprising amorphous silicon (a-Si), microcrystalline silicon (e-Si), germanium (Ge), cadmium telluride (CdTe), mercury cadmium telluride (HgCdTe), indium arsenide (InAs), indium gallium arsenide (InGaAs), indium antimonide (InSb), copper indium sulfide (CIS), copper indium gallium selenide (CIGS), copper zinc tin sulfide (CZTS), copper zinc tin selenide (CZTSe), copper-zinc-tin sulfur-selenium chalcogenide (CZTSSe), and solid solutions and/or doped variants thereof; wherein the property comprises an electrical conductivity of the material capable of sustaining the electrical current.

43. The detector according to claim 41, wherein the longitudinal optical sensor is a photo detector having at least one first electrode, at least one second electrode, and a layer of the material capable of sustaining an electrical current located between the first electrode and the second electrode, wherein at least one of the first electrode and the second electrode is a transparent electrode.

44. The detector according to claim 41, wherein the material capable of sustaining the electrical current is located between the first electrode and the second electrode is arranged as a PIN diode, wherein the PIN diode comprises an i-type semiconductor layer located between an n-type semiconductor layer and a p-type semiconductor layer, wherein the i-type semiconductor layer exhibits a thickness which exceeds the thickness of each of the n-type semiconductor layer and the p-type semiconductor layer.

45. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region, wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the longitudinal optical sensor, given the same total power of the illumination, is capable of generating at least one longitudinal sensor signal being dependent on the beam cross-section of the light beam in the sensor region such that an amplitude of the longitudinal sensor signal decreases with decreasing cross-section of a light spot generated by the light beam in the sensor region; and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

46. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region, wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the longitudinal optical sensor, given the same total power of the illumination, is capable of generating at least one longitudinal sensor signal being dependent on the beam cross-section of the light beam in the sensor region, wherein a minimum of the longitudinal sensor signal occurs under a condition in which the sensor region is impinged by a light beam with the smallest available beam cross-section; and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

47. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region, wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the longitudinal sensor is substantially frequency-independent in a range of a modulation frequency of the light beam of 0 Hz to 500 Hz; and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

48. A detector for an optical detection of at least one object, the detector comprising: at least one longitudinal optical sensor, wherein the longitudinal optical sensor has at least one sensor region, wherein the longitudinal optical sensor is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of the sensor region by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the longitudinal optical sensor comprises at least one photodiode driven in a photoconductive mode, wherein an electrical conductivity of the sensor region, given the same total power of the illumination, is dependent on the beam cross-section of the light beam in the sensor region, wherein the longitudinal sensor signal is dependent on the electrical conductivity; and at least one evaluation device, wherein the evaluation device is designed to generate at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

49. The detector according to claim 48, wherein the photodiode comprises at least one p-type absorber material, at least one n-type semiconductor layer, and at least one pair of electrodes.

50. The detector according to claim 49, wherein the p-type absorber material is selected from the group consisting of: III-V compounds, II-VI compounds, I-III-VI.sub.2 compounds, and I.sub.2-II-IV-VI.sub.4 compounds.

51. The detector according to claim 50, wherein the p-type absorber material is selected from the group consisting of: amorphous silicon (a-Si), an alloy comprising amorphous silicon (a-Si), microcrystalline silicon (c-Si), germanium (Ge), copper indium sulfide (CIS), copper indium gallium selenide (CIGS), copper zinc tin sulfide (CZTS), copper zinc tin selenide (CZTSe), copper-zinc-tin sulfur-selenium chalcogenide (CZTSSe), cadmium telluride (CdTe), mercury cadmium telluride (HgCdTe), indium arsenide (InAs), indium gallium arsenide (InGaAs), indium antimonide (InSb), an organic-inorganic halide perovskite, and solid solutions and/or doped variants thereof.

52. The detector according to claim 48, wherein a bias voltage is applied across the photodiode in a reverse biased mode.

53. A camera for imaging at least one object, the camera comprising at least one detector according to claim 1.

54. A human-machine interface for exchanging at least one item of information between a user and a machine, wherein the human-machine interface comprises at least one detector according to claim 1, wherein the human-machine interface is designed to generate at least one item of geometrical information of the user by means of the detector wherein the human-machine interface is designed to assign to the geometrical information at least one item of information.

55. An entertainment device for carrying out at least one entertainment function, wherein the entertainment device comprises at least one human-machine interface according to claim 54, wherein the entertainment device is designed to enable at least one item of information to be input by a player by means of the human-machine interface, wherein the entertainment device is designed to vary the entertainment function in accordance with the information.

56. A tracking system for tracking the position of at least one movable object, the tracking system comprising at least one detector according to claim 1, the tracking system further comprising at least one track controller, wherein the track controller is adapted to track a series of positions of the object, each position comprising at least one item of information on at least a longitudinal position of the object at a specific point in time.

57. A scanning system for determining at least one position of at least one object, the scanning system comprising at least one detector according to claim 1, the scanning system further comprising at least one illumination source adapted to emit at least one light beam configured for an illumination of at least one dot located at at least one surface of the at least one object, wherein the scanning system is designed to generate at least one item of information about the distance between the at least one dot and the scanning system by using the at least one detector.

58. A stereoscopic system, comprising at least one tracking system according to claim 57 and the at least one scanning system, wherein the tracking system and the scanning system each comprise at least one longitudinal optical sensor which are located in a collimated arrangement in a manner that they are aligned in an orientation parallel to the optical axis of the stereoscopic system and exhibit an individual displacement in the orientation perpendicular to the optical axis of the stereoscopic system.

59. A method for an optical detection of at least one object, the method comprising: generating at least one longitudinal sensor signal by using at least one longitudinal optical sensor, wherein the longitudinal sensor signal is dependent on an illumination of a sensor region of the longitudinal optical sensor by a light beam, wherein the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam in the sensor region, wherein the sensor region comprises at least one photoconductive material, wherein an electrical conductivity of the photoconductive material in the sensor region, given the same total power of the illumination, is dependent on the beam cross-section of the light beam in the sensor region, wherein the longitudinal sensor signal is dependent on the electrical conductivity; and generating at least one item of information on a longitudinal position of the object by evaluating the longitudinal sensor signal of the longitudinal optical sensor.

60. A detector according to claim 1, where the detector is adapted to function as a detector for at least one application selected from the group consisting of: a distance measurement; a position measurement; an entertainment application; a security application; a human-machine interface application; a tracking application; a scanning application; in stereoscopic vision; a photography application; an imaging application or camera application; a mapping application for generating maps of at least one space; a homing or tracking beacon detector for vehicles; a distance and/or position measurement of objects with a thermal signature; a machine vision application; a robotic application; a logistics application.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0540] Further optional details and features of the invention are evident from the description of preferred exemplary embodiments which follows in conjunction with the dependent claims. In this context, the particular features may be implemented alone or with features in combination. The invention is not restricted to the exemplary embodiments. The exemplary embodiments are shown schematically in the figures. Identical reference numerals in the individual figures refer to identical elements or elements with identical function, or elements which correspond to one another with regard to their functions.

[0541] Specifically, in the figures:

[0542] FIG. 1 shows an exemplary embodiment of a detector according to the present invention comprising a longitudinal optical sensor having a sensor region, wherein the sensor region comprises a photoconductive material;

[0543] FIGS. 2A and 2B show exemplary embodiments of the longitudinal optical sensor having a sensor region, wherein the sensor region comprises a photoconductive material in an arrangement as a photoconductor;

[0544] FIGS. 3A to 3C show experimental results demonstrating the negative FiP effect by using the longitudinal optical sensor having a sensor region, wherein the sensor region comprises lead sulfide (PbS) as photoconductive material;

[0545] FIGS. 4A to 4D show further experimental results demonstrating the negative FiP effect by using the longitudinal optical sensor having a sensor region, wherein the sensor region comprises lead sulfide (PbS) as the photoconductive material;

[0546] FIG. 5 shows further experimental results by using the longitudinal optical sensor having a sensor region, wherein the sensor region comprises lead sulfide (PbS) as photoconductive material, wherein the FiP effect is observed without applying a modulation to the incident light beam;

[0547] FIGS. 6A to 6H show further experimental results demonstrating the negative FiP effect by using the longitudinal optical sensor having a sensor region, wherein the sensor region comprises other photoconductive materials apart from lead sulfide (PbS), i.e. lead selenide (PbSe; FIG. 6A), a mixture of an organic donor polymer and a fullerene-based electron acceptor material (FIGS. 6B to 6D), antimony trisulfide (Sb.sub.2S.sub.3; FIGS. 6E to 6G), and p-type doped crystalline silicon comprising a low dopant concentration and a low defect density (FIG. 6H);

[0548] FIGS. 7A and 7B show further exemplary embodiments of a transversal optical sensor having a layer of a photoconductive material in the arrangement as a photoconductor;

[0549] FIG. 8 shows an exemplary embodiment of an optical detector, a detector system, a human-machine interface, an entertainment device, a tracking system and a camera according to the present invention.

[0550] FIG. 9 shows a simulation of a change in a resistance of a longitudinal sensor signal in a detector having an interconnected array of longitudinal optical sensors;

[0551] FIGS. 10A to 10G show a further exemplary embodiment of the longitudinal optical sensor in the arrangement as a photodiode (FIG. 10A) as well as experimental results demonstrating the positive FiP effect obtained by using this arrangement which comprises a layer of amorphous silicon (a-Si:H; FIGS. 10B to 10E), of microcrystalline silicon (c-Si; FIG. 10F), and of gallium phosphide (GaP; FIG. 10G);

[0552] FIGS. 11A to 11J show further exemplary embodiments of the longitudinal optical sensor in the arrangement as a thin-film solar cell being used as a photodiode within the sensor region of a longitudinal optical sensor (FIGS. 11A and 11B), experimental results which demonstrate the occurrence of the FiP effect in the photodiode comprising cadmium telluride (CdTe; FIG. 11C), zinc cadmium telluride (ZnCdTe; FIG. 11D), copper indium gallium selenide (CIGS; FIG. 11E) or copper zinc tin sulfide (CZTS; FIGS. 11F to 11H), as p-type absorber material; and a further exemplary embodiment of a detector according to the present invention, wherein the longitudinal optical sensor has a sensor region comprising a photodiode (FIG. 11J); and

[0553] FIGS. 12A to 12D show further exemplary embodiments of different arrangements of longitudinal optical sensors in which the photoconductive material within the photodiode is provided as a film comprising quantum dots (FIGS. 12A, 12C and 12D), and experimental results which demonstrate the occurrence of the FiP effect in the longitudinal optical sensor according to FIG. 12A (FIG. 12B).

EXEMPLARY EMBODIMENTS

[0554] FIG. 1 illustrates, in a highly schematic fashion, an exemplary embodiment of an optical detector 110 according to the present invention, for determining a position of at least one object 112. The optical detector 110 may preferably be adapted to be used as an infrared detector. However, other embodiments are feasible. The optical detector 110 comprises at least one longitudinal optical sensor 114, which, in this particular embodiment, is arranged along an optical axis 116 of the detector 110. Specifically, the optical axis 116 may be an axis of symmetry and/or rotation of the setup of the optical sensors 114. The optical sensors 114 may be located inside a housing 118 of the detector 110. Further, at least one transfer device 120 may be comprised, preferably a refractive lens 122. An opening 124 in the housing 118, which may, particularly, be located concentrically with regard to the optical axis 116, preferably defines a direction of view 126 of the detector 110. A coordinate system 128 may be defined, in which a direction parallel or antiparallel to the optical axis 116 is defined as a longitudinal direction, whereas directions perpendicular to the optical axis 116 may be defined as transversal directions. In the coordinate system 128, symbolically depicted in FIG. 1, a longitudinal direction is denoted by z and transversal directions are denoted by x and y, respectively. However, other types of coordinate systems 128 are feasible.

[0555] Further, the longitudinal optical sensor 114 is designed to generate at least one longitudinal sensor signal in a manner dependent on an illumination of a sensor region 130 by a light beam 132. Thus, according to the FiP effect, the longitudinal sensor signal, given the same total power of the illumination, is dependent on a beam cross-section of the light beam 132 in the respective sensor region 130, as will be outlined in further detail below. According to the present invention, the 130 sensor region comprises at least one photoconductive material 134, in particular a chalcogenide 136, preferably lead sulfide (PbS) or lead selenide (PbSe). However, other photoconductive materials 134, in particular other chalcogenides 136, may be used. As a result of the use of the photoconductive material 134 in the sensor region 130, an electrical conductivity of the sensor region 130, given the same total power of the illumination, depends on the beam cross-section of the light beam 132 in the sensor region 130. Consequently, the resulting longitudinal sensor signal as provided by the longitudinal optical sensor 114 upon impingement by the light beam 132 depends on the electrical conductivity of the photoconductive material 134 in the sensor region 130 and thus allows determining the beam cross-section of the light beam 132 in the sensor region 130. Via a longitudinal signal lead 138, the longitudinal sensor signal may be transmitted to an evaluation device 140, which will be explained in further detail below. Preferably, the sensor region 130 of the longitudinal optical sensor 114 may be transparent or translucent with respect to the light beam 132 travelling from the object 112 to the detector 110. However, this feature may not be required since the sensor region 130 of longitudinal optical sensor 114 may also be intransparent.

[0556] In a preferred embodiment, the longitudinal optical sensor 114 may be located at a focal point 142 of the transfer device 120. Additionally or alternatively, in particular in embodiment in which the optical detector 110 may not comprise a transfer device 120, the longitudinal optical sensor 114 may be arranged in a movable fashion along the optical axis 116, such as by means of an optional actuator 144, which may be controllable by using an actuator control unit 146, which may be placed within the evaluation device 136. However, other kinds of setups are feasible.

[0557] The evaluation device 140 is, generally, designed to generate at least one item of information on a position of the object 112 by evaluating the sensor signal of the transversal optical sensor 114. For this purpose, the evaluation device 140 may comprise one or more electronic devices and/or one or more software components, in order to evaluate the sensor signals, which are symbolically denoted by a longitudinal evaluation unit 148 (denoted by z). As will be explained below in more detail, the evaluation device 140 may be adapted to determine the at least one item of information on the longitudinal position of the object 112 by comparing more than one longitudinal sensor signals of the longitudinal optical sensor 114.

[0558] As explained above, the longitudinal sensor signal as provided by the longitudinal optical sensor 114 upon impingement by the light beam 132 depends on the electrical conductivity of the photoconductive material 134 in the sensor region 130. In order to determine a variation of the electrical conductivity of the photoconductive material 134 it may, as schematically depicted in FIG. 1, therefore be advantageous to measure a current, which may also be denominated a photocurrent, through the longitudinal optical sensor 114. For this purpose, in a particularly preferred embodiment, a bias voltage source 150 may be provided which may be configured to provide a bias voltage above ground 152. Further, the longitudinal sensor signal as provided by the longitudinal optical sensor 114 may first be amplified by application of an amplifier 154 before supplying it to the longitudinal evaluation unit 148.

[0559] The light beam 132 for illumining the sensor region 130 of the longitudinal optical sensor 114 may be generated by a light-emitting object 112. Alternatively or in addition, the light beam 132 may be generated by a separate illumination source 156, which may include an ambient light source and/or an artificial light source, such as a light-emitting diode 158, being adapted to illuminate the object 112 that the object 112 may be able to reflect at least a part of the light generated by the illumination source 156 in a manner that the light beam 132 may be configured to reach the sensor region 130 of the longitudinal optical sensor 114, preferably by entering the housing 118 of the optical detector 110 through the opening 124 along the optical axis 116. In a specific embodiment, the illumination source 156 may be a modulated light source 160, wherein one or more modulation properties of the illumination source 156 may be controlled by at least one optional modulation device 162. Alternatively or in addition, the modulation may be effected in a beam path between the illumination source 156 and the object 112 and/or between the object 112 and the longitudinal optical sensor 114. Further possibilities may be conceivable. In this specific embodiment, it may be advantageous taking into account one or more of the modulation properties, in particular the modulation frequency, when evaluating the sensor signal of the transversal optical sensor 114 for determining the at least one item of information on the position of the object 112. For this purpose, the respective property as provided by the modulation device 162 may also be supplied to the amplifier 154, which, in this specific embodiment, may be a lock-in amplifier 164.

[0560] Generally, the evaluation device 140 may be part of a data processing device 166 and/or may comprise one or more data processing devices 166. The evaluation device 140 may be fully or partially integrated into the housing 118 and/or may fully or partially be embodied as a separate device which is electrically connected in a wireless or wire-bound fashion to the longitudinal optical sensor 114. The evaluation device 140 may further comprise one or more additional components, such as one or more electronic hardware components and/or one or more software components, such as one or more measurement units and/or one or more evaluation units and/or one or more controlling units (not depicted here).

[0561] FIGS. 2A and 2B show exemplary embodiments of the longitudinal optical sensor 114 in an arrangement of a photoconductor. Accordingly, the longitudinal optical sensor 114 comprises a layer 168 of at least one photoconductive material 134, in particular a chalcogenide 136, preferably lead sulfide (PbS), lead selenide (PbSe), or another photoconductive material as described elsewhere herein. The occurrence of the above-mentioned negative FiP effect in the longitudinal optical sensor 114 comprising the layer 168 of lead sulfide (PbS), lead selenide (PbSe), and or other photoconductive materials has been experimentally demonstrated as illustrated in FIGS. 3A to 6, respectively. Preferably, the photoconductive material 134 is placed on an insulating substrate 170, preferably on a ceramic substrate 172, in particular for providing mechanical stability to the layer 168 of the photoconductive material 134, which may exhibit a thickness from 10 nm to 1000 m, in particular from 100 nm to 10 m.

[0562] As described above, the illumination of the photoconductive material 134 in the sensor region 130 by the incident light beam 132 results in a variation of the electrical conductivity of the photoconductive material 134 which, given the same total power of the illumination, depends on a beam cross-section 174 of the light beam 132 in the sensor region 130. Consequently, upon impingement of the sensor region 130 by the light beam 132 at least two separated electrodes 176, 178 provide the longitudinal sensor signal which depends on the electrical conductivity of the photoconductive material 134 and, thus, allows determining the beam cross-section 174 of the light beam 132 in the sensor region 130. Preferably, the optically intransparent electrodes 176, 178 each comprise a metal electrode, in particular one or more of a silver (Ag) electrode, a platinum (Pt) electrode, an aluminum (Al) electrode, or a gold (Au) electrode, or, alternatively, a graphene electrode. Herein, the electrodes 176, 178 are, preferably, placed on different locations on top of the layer 168 of the photoconductive material 134, in particular in form of bars which may be spaced apart a distance between 1 mm and 10 cm, such as about 1 cm.

[0563] Whereas in the exemplary setup of the longitudinal optical sensor 114 according to FIG. 2A the incident light beam 132 may directly impinge on the photoconductive material 134, in the exemplary setup of the longitudinal optical sensor 114 according to FIG. 2B the incident light beam 132 may first impinge on the substrate 170 until it may reach the sensor region 130 in the photoconductive material 134. In this particular embodiment pursuant FIG. 2B, the insulating substrate 170, therefore, may advantageously be a transparent substrate 180 or at least a translucent substrate 182, such as a glass substrate or a quartz substrate. In this case, a part of the material may not be covered with the photoconductive material. Further, in the case a gold (Au) electrode may be used, a thin layer of Ni/Cr or Ti/Ni may be employed in order to bond the gold strongly to the glass substrate, thus, making it bondable for wires.

[0564] In an alternative embodiment, the layer 168 of the photoconductive material 134 within the longitudinal optical sensor 114 comprises a mixture of an organic donor polymer as electron donor material and a fullerene-based electron acceptor material. In a particular example, the organic donor polymer comprises a 80:20 wt % mixture of poly(3-hexylthiophene-2,5.diyl) (P3HT) as the electron donor material and of [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) as the electron acceptor material. However, other kinds of mixture ratios and/or organic photoconductive materials 134 may also be suitable. Preferably, the single layer 168 of the photoconductive material 134 comprising the mixture of P3HT: PC60BM is similarly placed on the insulating substrate 170, preferably on the transparent or translucent substrate 180, 182, such as a glass or a quartz substrate. For this purpose, the mixture of P3HT:PC60BM may, preferably, be cast from a solution, in particular from a chlorobenzene solution, by using a deposition method, preferably a coating method, more preferred a spin-coating method, a slot-coating method, or a blade-coating method, or, alternatively, by evaporation, into the single layer 168 which may exhibit a thickness from 100 m to 2000 m, in particular from 200 m to 750 m.

[0565] Irrespective whether the embodiment according to FIG. 2A or to FIG. 2B may actually be selected for the optical detector 110, both embodiments exhibit a comparatively simple and cost-efficient setup of the longitudinal optical sensor 114, for example when compared to the longitudinal optical sensor as exemplary depicted in WO 2012/110924 A1 or WO 2014/097181 A1. This result may, in particular, be attributed to a lower number of layers which may here be used in order to still provide a working embodiment for the longitudinal optical sensor 114. However, other embodiments not depicted here may also be appropriate as the setup for the longitudinal optical sensor 114 according to the present invention.

[0566] In FIGS. 3A to 3C, the occurrence of the above-mentioned negative FiP effect in the exemplary embodiments of FIGS. 1 and 2 shall be experimentally demonstrated.

[0567] Herein, FIG. 3A shows a so-called FiP curve as the experimental results in a setup in which the sensor region 130 of the longitudinal optical sensor 114 comprised lead sulfide (PbS) as the photoconductive material 134. Herein, the setup of the optical detector 110 comprised a green light-emitting diode (LED) 158 which was placed 80 cm in front of the refractive lens 122 and which was simultaneously employed as both the illumination source 156 for the light beam with an optical wavelength of 530 nm and the object 112. The sensor region 130 of the longitudinal optical sensor 114 comprised the commercially available lead sulfide (PbS) photoconductive material 134, which was operated under a 10 mV bias voltage provided by the bias voltage source 150. In this particular experiment, the light-emitting diode as the illumination source 156 was modulated with a modulation frequency of 375 Hz by using the modulation device 162. Consequently, the longitudinal sensor signal was measured by using the lock-in amplifier 164.

[0568] During the experiment, the longitudinal optical sensor 114 was moved along the z-axis of the optical detector 110 by using the actuator 144 and the resulting voltage in millivolts (mV) was measured. Herein, the focal point 142 of the refractive lens 122 was located at a distance of 43.5 mm, whereby the refractive lens 122 and the light-emitting diode 158 serving as the illumination source 156 were placed at larger z-values. Moving the sensor along the z-axis of the optical detector 110 during the experiment resulted in a variation of the beam cross-section (spot size) of the incident light beam 132 at the position of the sensor region 130, thus yielding a z-dependent voltage signal.

[0569] As can be seen in FIG. 3A, the FiP curve comprising the observable voltage which may be attributed as the longitudinal sensor signal varied with the varying distance of the longitudinal optical sensor 114 from the object 112 and comprises a distinct minimum in an event in which the object 112 was focused on the longitudinal optical sensor 114. Thus, the optical detector 110 according to the present invention may be arranged in a manner that it clearly exhibits the above-described negative FiP effect, i.e. the observation of a minimum of the longitudinal sensor signal under a condition in which the material in the sensor region 130 is impinged by the light beam 132 with the smallest possible cross-section, which occurs in this setup when the sensor region 130 is located at the focal point 142 as effected by the refractive lens 122, i.e. here at a distance of approximately 43.4 mm from the refractive lens 122.

[0570] In the experiment according to FIG. 3B, the same setup as in the previous experiment pursuant to FIG. 3A was used. Herein, the experiment as performed above with respect to FIG. 3A was repeated several times, wherein the light-emitting diode 158 serving as the illumination source 156 was being placed at different distances from the refractive lens 122. The recorded FiP curves are presented in FIG. 3B. As a result, the minimum of the recorded voltage attributed as the longitudinal sensor signal varied with varying distance of the light-emitting diode 158 from the refractive lens 122.

[0571] As can be, furthermore, extracted from FIG. 3B, the absolute values of the recorded voltage also increases with increasing distance of the light-emitting diode 158 from the refractive lens 122. Therefore, it may be useful to divide all values of an individual observed FiP curve by the value of the observed FiP curve acquired for a condition in which the sensor region 130 is located at a distance where the z-coordinate equals the focal distance of the refractive lens 122. As a result, the following graph as displayed in FIG. 3C is obtained. Herein, all normalized FiP curves have a minimum value of approximately 0.55 mV, and a value of 1.0 at a value of the z-coordinate of 43.4 mm, i.e. where the z-coordinate equals the focal distance of the refractive lens 122. This observation clearly demonstrates that the so-called Iso-FiP relation still holds in the case the photoconductive material 134 is used for sensing in the sensor region 130. As used herein, the Iso-FiP relation refers to a presentation in which the longitudinal sensor signal curves for different focus positions may be normalized to a corresponding longitudinal sensor signal of the focal longitudinal optical sensor. On further details, reference may be made to the European patent application, EP 14 176 112.2, filed Aug. 07, 2014, whose contents are included herein by reference. Consequently, two to three longitudinal optical sensors are sufficient to detect a distance without any ambiguity.

[0572] FIGS. 4A to D show experimental results of further measurements in which the sensor region 130 of the longitudinal optical sensor 114 comprised lead sulfide (PbS) as the photoconductive material 134. Again, the setup of the optical detector 110 comprised a green light-emitting diode (LED) 158 which was placed 80 cm in front of the refractive lens 122 and which was, again, simultaneously employed as both the illumination source 156 for the optical wavelength of 530 nm and the object 112. The longitudinal optical sensor 114 with the photoconductive material 134 lead sulfide (PbS) was operated under a 10 V bias voltage provided by the bias voltage source 150. In this particular experiment, the light-emitting diode 158 was again used as the illumination source 156 which was modulated with a modulation frequency by means of the modulation device 162, wherein, however in contrast to the experiments as performed according to FIGS. 3A to C, different values for one of the photocurrent and the modulation frequency were applied. Consequently, the longitudinal sensor signal was, again, measured by using the lock-in amplifier 164.

[0573] Whereas FIG. 4A shows the actual FiP curves as recorded under these conditions, wherein the modulation frequency was set to 375 Hz and the photocurrents have been varied between a minimum value of 1 mA and a maximum value of 1000 mA, FIG. 4B displays the respective normalized actual FiP which, again, demonstrate the validity of the Iso-FiP relation under these circumstances.

[0574] In FIGS. 4C and 4D, the FiP currents in focus (FIG. 4C) and out of focus (FIG. 4D) are recorded at a varying modulation frequency. The modulation frequencies are plotted on the x-axis in Hertz. The FiP-currents in focus are plotted on the y-axis. All curves were normalized to the value at 0 Hz. Both axis are plotted on a logarithmic scale. The different curves were recorded at varying currents which were applied for the LED-target (1 mA-1000 mA). Additionally, an organic sensor curve is shown for comparison in FIG. 4C. The curves show that the FiP-signals are not substantially affected by increasing the modulation frequency to more than 500 Hz. This result is independent of the light intensity and the focus position.

[0575] In measurement according to FIG. 5 the same setup as for the measurement pursuant to FIGS. 3A to 3C was employed, wherein, however, no modulation was applied so that the green light-emitting diode 158 emitted a light beam 132 which exhibited an optical wavelength of 530 nm in a continuous intensity. Herein, the longitudinal sensor signal was recorded by using the amplifier 154 and an oscilloscope. Thereby, the observable residual modulation in the photocurrent in FIG. 5 may be caused by an electromagnetic interference into the amplifier circuit through the power line and not by the non-existing modulation of the incident light beam 132. The observable decreasing of the intensity at both sides of the curve as shown in FIG. 5 may be attributed to the fact that, by increasing the spot size at the sensor region 130, at some point the spot size exceeds the area of the sensor region 130. Nevertheless, FIG. 5 clearly demonstrates that the occurrence of the FiP effect does not require the presence of a modulation.

[0576] FIG. 6 demonstrates that the measurements according to FIGS. 3 to 5 which have been performed in lead sulfide (PbS) as the applied photoconductive material 134 in the arrangement of the photoconductor within the sensor region 130 of the longitudinal optical sensor 114 may also be performed by using another photoconductive material 134 apart from PbS.

[0577] Accordingly, the photoconductive material 134 as used for the experiments as shown in FIG. 6A comprises the selenide chalcogenide lead selenide (PbSe) in the sensor region 130. Similar to the measurements according to FIG. 3A, again, the setup of the optical detector 110 comprised a light-emitting diode 158 which was placed 80 cm in front of the refractive lens 122 and which was, again, simultaneously employed as both the object 112 and the illumination source 156. This time, however, and in accordance with the known absorption spectrum of lead selenide (PbSe), the optical wavelength of 1050 nm which is located in the near infrared (NIR) spectral range was applied. The longitudinal optical sensor 114 with the photoconductive material 134 lead selenide (PbSe) was operated under a 10 V bias voltage which was provided by the bias voltage source 150. Again, the light-emitting diode 158 as the illumination source 156 was modulated with the modulation frequency of 375 Hz by using the modulation device 162. Consequently, the longitudinal sensor signal was, again, measured by using the lock-in amplifier 164. The result is the FiP curve as depicted in FIG. 6A which, again, demonstrates the occurrence of the negative FiP effect in this kind of materials.

[0578] FIGS. 6B and 6C show experimental results in which the layer 168 in the sensor region 130 of the longitudinal optical sensor 114 comprised the above-mentioned 80:20 wt % mixture of P3HT:PC60BM as the organic photoconductive material 134. Herein, three different samples were used being distinguishable from each other by the corresponding thickness of the layer 168 of the organic photoconductive material 134. As indicated in the Figures, the respective thickness of the layer 168 amounted to d=430 m, d=580 m, and d=1500 m.

[0579] Similar to the measurements according to FIGS. 3A and 6A, the setup of the optical detector 110 comprised a light-emitting diode 158 emitting an optical wavelength of 530 nm which was placed in front of the refractive lens 122 and which was simultaneously employed as both the object 112 and the illumination source 156. The longitudinal optical sensor 114 comprising the organic photoconductive material 134 was operated under a 10 V bias voltage which was provided by the bias voltage source 150. Further, the light-emitting diode 158 as the illumination source 156 was modulated by using a modulation frequency of 43 Hz provided by the modulation device 162, while the longitudinal sensor signal was, consequently, recorded by use of the lock-in amplifier 164.

[0580] As a result, the curves in both FIGS. 6B and 6C show that the observable photo-induced current which may be considered as the longitudinal sensor signal varied with a varying distance of the longitudinal optical sensor 114 from the object 112, thereby comprising a distinct minimum in an event in which the object 112 was focused on the longitudinal optical sensor 114. Thus, the optical detector 110 clearly exhibited the negative FiP effect, i.e. the observation of a minimum of the longitudinal sensor signal under a condition in which the organic photoconductive material 134 in the sensor region 130 is impinged by the light beam 132 with the smallest possible cross-section, which occurs in this setup when the sensor region 130 is located at the focal point 142 as effected by the refractive lens 122, i.e. at a distance of approximately 20 mm from the refractive lens 122. Further, by shifting the longitudinal optical sensor 114 up to 12.5 mm away from the focal point in both directions along the optical axis 116 the size of the light spot was filling most of the area of the sensor region 130 between the electrodes 176, 178.

[0581] The ratio which provides a quotient between the photo-induced current of the sensor region 130 being located at the focal point 142 to the sensor region 130 outside the focal point 142 assumes a value from 4 to 5 as indicated in FIG. 6B. The ratio could, however, be increased to a value more than 8 in a further experiment as depicted in FIG. 6C in which the same samples were used as for the experiment of FIG. 6B after they had been exposed to a halogen lamp in air, which is known to cause a doping of the organic photoconductive material P3HT:PC60BM. As can further be derived from both FIGS. 6B and 6C, generally, the ratio r assumes a high value, in particular since the photo-induced current nearly seem to vanish when the sensor region 130 becomes located near the focal point 142.

[0582] Further, FIG. 6D shows that the observable photo-induced current as the longitudinal sensor signal is a distinct function of the modulation frequency of the incident light beam. For this purpose, a single sample was used in which the layer 168 in the sensor region 130 of the longitudinal optical sensor 114 comprised the above-mentioned 80:20 wt % mixture of P3HT:PC60BM as the organic photoconductive material 134 and exhibited a thickness of d=430 m. Accordingly, FIG. 6D displays three different curves whereof two were recorded under different illumination conditions: [0583] with illumination by the light-emitting diode 158 emitting a wavelength of 530 nm; indicated as illuminated; and [0584] without illumination; indicated as dark; and

[0585] with the third curve indicated as difference provides the difference between the respective values for the illuminated curve minus the values for the dark curve. As can be derived from a comparison of the three different curves in FIG. 6D, the measured signal proved to be undistinguishable from a noise level of the setup at a frequency above approximately 1 kHz. On the other hand, at a frequency below approximately 50 Hz, a signal-to-noise-ratio of approximately 100 can be observed. It may be mentioned that the obtained peak at a frequency of 50 Hz can be attributed to the frequency of the mains supply. Thus, the longitudinal optical sensors 114 in which the layer 168 in the sensor region 130 comprises the above-mentioned mixture of P3HT: PC60BM as the organic photoconductive material 134 may, particularly, be used for a determination of the FiP effect at a frequency below 100 Hz, preferably below 50 Hz. In this frequency range the noise seems to be considerably low, in particular due to a virtually zero leakage current in this kind of materials.

[0586] FIGS. 6E to 6G illustrate further experimental examples in which the photoconductive material 134 within the sensor region 130 comprises a layer 168 of antimony trisulfide (Sb.sub.2S.sub.3). In the particular example as shown in FIGS. 6E and 6F, the layer 168 of the Sb.sub.2S.sub.3 exhibited a thickness of 400 nm and was sandwiched by a silver (Ag) electrode 176, 178 and a silver(I) selenide (Ag.sub.2Se) substrate 170. Herein, the longitudinal optical sensor 114 was operated under either a 5 V bias voltage across the longitudinal optical sensor 114 comprising this sample (see FIG. 6E, dashed line) or, alternatively, without an application of the bias voltage (see FIG. 6E, solid line; and FIG. 6F in amplified depiction). The FiP curves recorded without the application of a bias voltage in FIGS. 6F and 6G demonstrate that the longitudinal optical sensor 114 behaves here as a Schottky diode as, for example, described by J. P. Clifford et al., s. o. Accordingly, the incident light beam 132 may generate charge carriers, i.e. electrons and holes, within the layer 168 of the antimony trisulfide. Herein, the charge carriers may be collected at the boundaries towards both the silver(l)selenide substrate 170 and the silver electrode 176, 178. Thus, a depletion region may be formed within the layer 168 of the antimony trisulfide towards a Schottky barrier that may be located at an interface between the silver electrode 176, 178 and the layer 168 of the antimony trisulfide. Again, the light-emitting diode 158 as the illumination source 156 was modulated with the modulation frequency of 375 Hz by applying the modulation device 162 using 100 ms long current pulses with an amplitude of 1000 mA. Consequently, the longitudinal sensor signal was, again, measured by using the lock-in amplifier 164. In both cases, the result are the FiP curves as depicted in FIGS. 6E and 6F which, again, demonstrate the occurrence of the negative FiP effect under the mentioned conditions in this kind of material.

[0587] In contrast thereto, in the example as shown in FIG. 6G, the layer 168 of the antimony trisulfide exhibited a thickness of 1.3 m and was sandwiched by a silver (Ag) electrode 176, 178 and a transparent indium tin oxide (ITO) substrate 170. Probably due to a higher intensity of the illumination with respect to the sample which had been used for recording the curves in FIGS. 6E and 6F, a positive FIP effect could be monitored here without an application of a bias voltage across the longitudinal optical sensor 114 comprising this sample. Again, FIG. 6G demonstrates that the longitudinal optical sensor 114 comprising this embodiment of the layer 168 of the antimony trisulfide behaves here as a Schottky diode similar as in the example presented in FIG. 6F. Further, it may be mentioned that the increase in current as shown in FIG. 6G for short distances below approx. 13 mm as well as for large distances above approx. 24 mm may, similar to FIG. 5, originate from a geometrical effect that, by increasing the spot size at the sensor region 130, at some point the spot size exceeds the area of the sensor region 130.

[0588] Finally, FIG. 6H illustrates further experimental results for which a 15 mm15 mm doped crystalline silicon (Si) sample comprising a low dopant concentration and a low defect density was employed and furnished with contacts in a manner of a photoconductor in order to provide a silicon-based photoconductor which exhibited a high resistivity, a high charge-carrier lifetime, and a low surface recombination rate. As described above, the photoconductive material may here be contacted by an Ohmic contact, thus, providing an electrical junction which may exhibit a linear current-voltage ratio according to Ohm's law but does not comprise any photovoltaic properties. For this purpose, the silicon sample showing an electrical resistivity from 770 to 2020 .Math.cm was used. The experimental results as depicted in FIG. 6H were obtained by applying a bias voltage of 10 V across the longitudinal optical sensor 114 comprising this sample, thereby using two different wavelengths for the illumination, i.e. 530 nm (solid line) and 850 nm (dashed line), in order to investigate the behavior of this sample in the visual and the infrared spectral range, respectively. In both spectral ranges, the negative FIP effect could be observed.

[0589] As described above, the optical detector 110 may comprise a single longitudinal optical sensor 114 or, as e.g. disclosed in WO 2014/097181 A1, a stack of longitudinal optical sensors 114, particularly in combination with one or more transversal optical sensors 184. Hereby, using a layer of the organic photoconductive materials in the longitudinal optical sensors 114 may, particularly, by preferred, mainly due to the transparency, semitransparency or translucency of the organic photoconductive materials. As an example, one or more transversal optical sensors 184 may be located on a side of the stack of longitudinal optical sensors 114 facing towards the object. Alternatively or additionally, one or more transversal optical sensors 184 may be located on a side of the stack of longitudinal optical sensors 114 facing away from the object. Again, additionally or alternatively, one or more transversal optical sensors 184 may be interposed in between the longitudinal optical sensors 114 of the stack. However, embodiments which may only comprise a single longitudinal optical 114 sensor but no transversal optical sensor 184 may still be possible, such as in a case wherein only determining the depth, i.e. the z-coordinate, of the object may be desired.

[0590] Thus, in a case in which determining the x- and/or y-coordinate of the object in addition to the z-coordinate may be desired, it may be advantageous to employ, in addition to the at one longitudinal optical sensor 114 at least one transversal optical sensor 184 which may provide at least one transversal sensor signal. For potential embodiments of the transversal optical sensor, reference may be made to WO 2014/097181 A1. Accordingly, the transversal optical sensor 184 may be a photo detector having at least one first electrode, at least one second electrode and at least one photovoltaic material, wherein the photovoltaic material, preferably, one or more dye-sensitized organic solar cells, such as one or more solid dye-sensitized organic solar cells, may be embedded in between the first electrode and the second electrode.

[0591] In contrast to this known embodiment, FIG. 7A shows a side view of a preferred exemplary embodiment of the transversal optical sensor 184 pursuant to the present invention.

[0592] Accordingly, the transversal optical sensor 184 has a layer 168 of the photoconductive material 134 which, in particular comprises a chalcogenide 136, such as lead sulfide (PbS), lead selenide (PbSe), or another appropriate material. Herein, the layer 168 of the photoconductive material 134 may, preferably, be embedded in between two layers 186 of a transparent conducting oxide 188, preferably comprising indium tin oxide (ITO), fluorine doped tin oxide (FTO), or magnesium oxide (MgO). However, other material may be feasible, in particular according to the desired transparent spectral range.

[0593] Further, at least two electrodes 190, 192 may be present for recording the transversal optical signal. As schematically depicted in the side view of the of the transversal optical sensor 184 according to FIG. 7B, at least of the electrodes 190, 192 of the transversal optical sensor 184 may be a split electrode having at least two partial electrodes 194, 196, wherein the transversal optical 184 sensor may have a sensor area 198, wherein the at least one transversal sensor signal may indicate a x- and/or a y-position of the incident light beam 132 within the sensor area 198 in a similar manner as described for the transversal optical sensor 184 as disclosed in WO 2014/097181 A1. Accordingly, the transversal optical sensor 184 may comprise the sensor area 198, which, preferably, may be transparent to the light beam 132 travelling from the object 112 to the detector 110. The transversal optical sensor 184 may, therefore, be adapted to determine a transversal position of the light beam 132 in one or more transversal directions, such as in x- and/or in y-direction. For this purpose, the at least one transversal optical sensor 184 may further be adapted to generate at least one transversal sensor signal. Thus, the evaluation device 140 may be designed to generate at least one item of information on a transversal position of the object 112 by evaluating the transversal sensor signal of the longitudinal optical sensor 184.

[0594] As an example, FIG. 8 shows an exemplary embodiment of a detector system 200, comprising at least one optical detector 110, such as the optical detector 110 as disclosed in one or more of the embodiments shown in FIGS. 1 to 7 and 9 to 12. Herein, the optical detector 110 may be employed as a camera 202, specifically for 3D imaging, which may be made for acquiring images and/or image sequences, such as digital video clips. Further, FIG. 8 shows an exemplary embodiment of a human-machine interface 204, which comprises the at least one detector 110 and/or the at least one detector system 200, and, further, an exemplary embodiment of an entertainment device 206 comprising the human-machine interface 204. FIG. 8 further shows an embodiment of a tracking system 208 adapted for tracking a position of at least one object 112, which comprises the detector 110 and/or the detector system 200.

[0595] With regard to the optical detector 110 and to the detector system 200, reference may be made to the full disclosure of this application. Basically, all potential embodiments of the detector 110 may also be embodied in the embodiment shown in FIG. 8. The evaluation device 140 may be connected to each of the at least two longitudinal optical sensors 114, in particular, by the signal leads 138. As described above, a use of two or, preferably, three longitudinal optical sensors 114 may support the evaluation of the longitudinal sensor signals without any remaining ambiguity. The evaluation device 140 may further be connected to the at least one optional transversal optical sensor 184, in particular, by the signal leads 138. By way of example, the signal leads 138 may be provided and/or one or more interfaces, which may be wireless interfaces and/or wire-bound interfaces. Further, the signal leads 138 may comprise one or more drivers and/or one or more measurement devices for generating sensor signals and/or for modifying sensor signals. Further, again, the at least one transfer device 120 may be provided, in particular as the refractive lens 122 or convex mirror. The optical detector 110 may further comprise the at least one housing 118 which, as an example, may encase one or more of components 114, 184.

[0596] Further, the evaluation device 140 may fully or partially be integrated into the optical sensors 114, 184 and/or into other components of the optical detector 110. The evaluation device 140 may also be enclosed into housing 118 and/or into a separate housing. The evaluation device 140 may comprise one or more electronic devices and/or one or more software components, in order to evaluate the sensor signals, which are symbolically denoted by the longitudinal evaluation unit 148 (denoted by z) and a transversal evaluation unit 210 (denoted by xy) and. By combining results derived by these evolution units 154, 156, a position information 212, preferably a three-dimensional position information, may be generated (denoted by x, y, z). Similar to the embodiment according to FIG. 1, a bias voltage source 150 may be provided configured to provide a bias voltage above ground 152. Further, the longitudinal sensor signals as provided by the longitudinal optical sensors 114 may first be amplified by means of an amplifier 154 before supplying it to the longitudinal evaluation unit 148.

[0597] Further, the optical detector 110 and/or to the detector system 200 may comprise an imaging device 214 which may be configured in various ways. Thus, as depicted in FIG. 8, the imaging device 214 can for example be part of the detector 110 within the detector housing 118. Herein, the imaging device signal may be transmitted by one or more imaging device signal leads 138 to the evaluation device 140 of the detector 110. Alternatively, the imaging device 214 may be separately located outside the detector housing 118. The imaging device 214 may be fully or partially transparent or intransparent. The imaging device 214 may be or may comprise an organic imaging device or an inorganic imaging device. Preferably, the imaging device 214 may comprise at least one matrix of pixels, wherein the matrix of pixels may particularly be selected from the group consisting of: an inorganic semiconductor sensor device such as a CCD chip and/or a CMOS chip; an organic semiconductor sensor device.

[0598] In the exemplary embodiment as shown in FIG. 8, the object 112 to be detected, as an example, may be designed as an article of sports equipment and/or may form a control element 216, the position and/or orientation of which may be manipulated by a user 218. Thus, generally, in the embodiment shown in FIG. 8 or in any other embodiment of the detector system 200, the human-machine interface 204, the entertainment device 206 or the tracking system 208, the object 112 itself may be part of the named devices and, specifically, may comprise the at least one control element 216, specifically, wherein the at least one control element 216 has one or more beacon devices 220, wherein a position and/or orientation of the control element 216 preferably may be manipulated by user 218. As an example, the object 112 may be or may comprise one or more of a bat, a racket, a club or any other article of sports equipment and/or fake sports equipment. Other types of objects 112 are possible. Further, the user 218 may be considered as the object 112, the position of which shall be detected. As an example, the user 218 may carry one or more of the beacon devices 220 attached directly or indirectly to his or her body.

[0599] The optical detector 110 may be adapted to determine at least one item on a longitudinal position of one or more of the beacon devices 220 and, optionally, at least one item of information regarding a transversal position thereof, and/or at least one other item of information regarding the longitudinal position of the object 112 and, optionally, at least one item of information regarding a transversal position of the object 112. Particularly, the optical detector 110 may be adapted for identifying colors and/or for imaging the object 112, such as different colors of the object 112, more particularly, the color of the beacon devices 220 which might comprise different colors. The opening 124 in the housing 118, which, preferably, may be located concentrically with regard to the optical axis 116 of the detector 110, may preferably define a direction of a view 126 of the optical detector 110.

[0600] The optical detector 110 may be adapted for determining the position of the at least one object 112. Additionally, the optical detector 110, specifically an embodiment including the camera 202, may be adapted for acquiring at least one image of the object 112, preferably a 3D-image. As outlined above, the determination of a position of the object 112 and/or a part thereof by using the optical detector 110 and/or the detector system 200 may be used for providing a human-machine interface 204, in order to provide at least one item of information to a machine 222. In the embodiments schematically depicted in FIG. 8, the machine 222 may be or may comprise at least one computer and/or a computer system comprising the data processing device 166. Other embodiments are feasible. The evaluation device 140 may be a computer and/or may comprise a computer and/or may fully or partially be embodied as a separate device and/or may fully or partially be integrated into the machine 222, particularly the computer. The same holds true for a track controller 224 of the tracking system 208, which may fully or partially form a part of the evaluation device 140 and/or the machine 222.

[0601] Similarly, as outlined above, the human-machine interface 204 may form part of the entertainment device 206. Thus, by means of the user 218 functioning as the object 112 and/or by means of the user 218 handling the object 112 and/or the control element 216 functioning as the object 112, the user 218 may input at least one item of information, such as at least one control command, into the machine 222, particularly the computer, thereby varying the entertainment function, such as controlling the course of a computer game.

[0602] FIG. 9 shows a simulation of a change in a resistance in percent of the longitudinal sensor signal in a detector which comprises an interconnected array of individual photoconductors as the longitudinal optical sensor 114. In FIG. 9, the resistance for an entire grid comprising the interconnected array is depicted for a number of focusing steps, starting from the fully illuminated array and, consecutively, increasing the focus of the light beam 132 step-by-step, thereby, however, maintaining the incident power of the illumination for each of the levels from 50 mW to 1000 mW as indicated. Hereby, the value of the resistance for the first step which corresponds to the fully illuminated array was used as a reference.

[0603] For this simulation, a resistor network software was initially compared with experimental results for photoconductors comprising PbS as the photoconductive material in the longitudinal optical sensor. After having achieved reasonable agreement between simulation and experiment, an interconnected array of individual photoconductors was employed for simulation. Herein, the array yielded an aggregate DC resistance which turned out to be non-linear with respect to the illumination density as long as not all of the individual photoconductors were illuminated equally. This feature could even be observed in a case in which the individual photoconductors exhibit a perfectly linear resistive response to the illumination density. Consequently, this feature could be employed to determine the cross-section of the light beam 132 on the array within the sensor region 130 and, hence, the distance between the detector 110 and the source of the light or IR radiation, even within the LWIR spectral range, i.e. from 5 m to 15 m. For the purposes of the simulation, a Gaussian profile was assumed for the light beam 132, which, at the first step, significantly overfilled the array until it was consecutively reduced in diameter in the following steps.

[0604] FIG. 10A shows a further exemplary embodiment of an arrangement of the longitudinal optical sensor 114. Herein, the longitudinal optical sensor 114 has a layer 226 of a material capable of sustaining an electrical current located between a first electrode 228 and a second electrode 230. Herein, the sensor region 130 comprises the material being capable of sustaining an electrical current, wherein the electrical current of the material, given the same total power of the illumination, is dependent on the beam cross-section of the light beam 132 in the sensor region 130. In particular for enabling the light beam 132 to reach the layer 226, the first electrode 228 being located within the beam path 232 of the incident light beam 132 is at least partially optically transparent. Preferably, the at least partially optically transparent first electrode 228 may, thus, comprise one or more transparent conductive oxides (TCO), in particular indium-doped tin oxide (ITO). The second electrode 230, also denominated as back electrode, was here selected to be optically intransparent, and may, thus, comprise a metal electrode. As schematically depicted in FIG. 10A, the second electrode 230 may, herein, comprise a uniform metal layer. Alternatively, the second electrode 230 may be a split electrode which might be arranged as a number of partial electrodes or in form of a metallic grid. In this embodiment, the layer 226 is exemplarily arranged in order to form a PIN diode 234. As shown in FIG. 10A, the PIN diode 234 comprises an i-type semiconductor layer 236 being located between an n-type semiconductor layer 238 and a p-type semiconductor layer 240. In particular, the i-type semiconductor layer 236 exhibits a thickness which exceeds the thickness of the n-type semiconductor layer 238 as well as of the p-type semiconductor layer 240.

[0605] In the example as depicted in FIG. 10B, all three layers, i.e. the i-type, the n-type, and the p-type semiconductor layers 236, 238, 240, comprised optically transparent hydrogenated amorphous silicon (a-Si:H). Herein, the thickness of the i-type semiconducting layer was approx. 690 nm while the thickness of both the n-type and the p-type semiconductor layer was below 50 nm. The PIN diode 234 which comprises a-Si and/or a-Si:H in at least one of the semiconductor layers 236, 238, 240 may preferably be employed in the detector 110 in a case in which the incident beam 132 has a wavelength within the visual spectral range, especially from 380 nm to 700 nm.

[0606] As shown in FIG. 10B, the positive FiP effect could be observed in the longitudinal sensor 114 comprising the arrangement as schematically depicted in FIG. 10A. Herein, for a modulation frequency of 375 Hz, resulting FiP curves, i.e. ac photocurrents I in nA vs. a distance d of the longitudinal optical sensor 114 from the object 112, are presented for a number of different illumination intensities, which are given in control currents in mA as required for controlling an light-emitting diode 158 as the modulated illumination source 160. It is emphasized here that a control current of 1 mA for controlling the light-emitting diode 158 corresponds to a very weak 5 nA longitudinal sensor signal. Thus, FIG. 10B further demonstrates that a considerably high signal-to-noise ratio compared to other known FiP devices could be observed here.

[0607] Moreover, as can be derived from FIG. 10C, the ac current I as the longitudinal sensor signal exhibits a substantially frequency-independent behavior in a range of a modulation frequency f of the light beam of 0 Hz to 50 kHz. Herein, the solid lines represent the respective curves in an in-focus position while the dashed lines refer to a 2 cm out-of-focus position. The various curves relate to various settings of a bias current from 1 mA to 367 mA. The curves as presented here are all taken without room light.

[0608] Further, FIG. 10D illustrates a variation of the FIP curves as observed for different modulation frequencies of 27 Hz (solid line), 375 Hz (dashed line), and 2177 Hz (dotted line), whereby the modulation current of 69 mA and the illumination wavelength of 530 nm were kept constant. No bias voltage was applied here to the sample. Further, from FIG. 10E it can be derived that the amplitude of the optical transmission for the optically transparent a-Si:H depends over a wavelength range from 500 nm to 800 nm on the thickness of the i-type semiconducting layer. As illustrated in FIG. 10E, the transmission optical depends on the thickness of the optically transparent hydrogenated amorphous silicon (a-Si:H). Herein, i denotes a thickness of the optically transparent layer of 230 nm, whereas 2i refers to a thickness of 460 nm and 3i to a thickness of 690 nm.

[0609] In an alternative embodiment (not depicted here), at least one of the i-type semiconductor layer 236, the n-type semiconductor layer 238, and the p-type semiconductor layer 240 in the PIN diode 234 comprises an amorphous silicon carbon alloy (a-SiC), preferably a hydrogenated amorphous silicon carbon alloy (a-SiC:H). In this alternative embodiment, at least one of the p-type semiconductor layer 240 or the i-type semiconductor layer 236 may exhibit a thickness from 2 nm to 20 nm, preferably from 4 nm to 10 nm, in particular about 5 nm. This kind of alternative PIN diode 234 may preferably be used in the detector 110 according to the present invention for detecting a wavelength of the incident beam 132 within the UV wavelength range, in particular, completely over at least one of UVA wavelength range from 315 nm to 400 nm and the UVB wavelength range from 280 nm to 315 nm.

[0610] In a further alternative embodiment as illustrated in FIG. 10F, at least one of the three kinds of the layers, preferably all of the three kinds of the layers, i.e. the i-type semiconductor layer 236, the n-type semiconductor layer 238, and the p-type semiconductor layer 240 in the PIN diode 234, comprise a microcrystalline silicon (c-Si), preferably a hydrogenated microcrystalline silicon (c-Si:H). Alternatively (not depicted here), an amorphous alloy of germanium and silicon (a-GeSi), preferably a hydrogenated amorphous germanium silicon alloy (a-GeSi:H), can also be used. This further kind of alternative PIN diode 234 may preferably be suitable for detecting wavelengths within the NIR wavelength range from 760 nm to 1400 nm, in particular from 760 nm to 1000 nm. Therefore, the curve as shown in FIG. 10F has been recorded by using an illumination source with the wavelength of 850 nm and the modulation frequency of 375 Hz. The longitudinal optical sensor 114 equipped with this kind of alternative PIN diode 234 may, in particular, be employed for night vision or fog vision or in case animals or human being may be left undisturbed for any reason by using an NIR illumination source.

[0611] In order to enable the longitudinal optical sensor 114 also to be sensitive within at least a part of the ultraviolet (UV) spectral range, a further alternative embodiment, such as depicted in FIG. 10G where a gallium phosphide (GaP) photodiode has been used, may be employed. As known to the skilled person, the material GaP exhibits a non-negligible spectral response within the spectral range from about 140 nm to 580 nm and may, therefore, employed for this purpose. Accordingly, the curve as depicted in FIG. 10G has been recorded by using an illumination wavelength of 490 nm, wherein the light-emitting diode was driven with a current of 100 mA. However, further materials which may exhibit a different non-negligible spectral response within at least a part of the UV spectral range may also be feasible.

[0612] FIG. 11A illustrates a further preferred example of the optical detector 110 in a further arrangement in which the longitudinal optical sensor 114 exhibits a device structure of a typical thin-film solar cell 242, wherein the p-type semiconductor layer 240 comprises a p-type absorber material 244 as described above. Preferably, a I-III-VI.sub.2 compound, in particular copper indium sulfide (CulnS.sub.2; CIS) or copper indium gallium selenide (CIGS; see FIG. 11E), or a I.sub.2-II-IV-VI.sub.4 compound, in particular copper zinc tin sulfide (CZTS; see FIGS. 11F to 11H), copper zinc tin selenide (CZTSe), or a copper-zinc-tin sulfur-selenium chalcogenide (CZTSSe) and doped variants of all of them may be applied for this purpose. Alternatively, a halide perovskite compound, in particular an organic-inorganic halide perovskite, especially methylammonium lead iodide (CH.sub.3NH.sub.3Pbl.sub.3), may also be employed. However, further examples, wherein cadmium telluride (CdTe; see FIG. 11C) or zinc cadmium telluride (ZnCdTe; see FIG. 11D) have been used as the p-type absorber material 244, demonstrate that the concept as presented here is more general.

[0613] Herein, a glass of about of a thickness of 1 mm to 3 mm, such as a soda-lime glass, may here, as commonly, used as the transparent substrate 170, 180, in particular since a presence of sodium in the glass substrate allowing yielding a substantial open-circuit voltage increase, presumably through surface and/or grain boundary defects passivation. However, as in this example as depicted in FIG. 11A in which the beam path 232 of the incident light beam 132 may not traverse the substrate 170, which, therefore, may not require to be transparent, other kinds of substrates 170 may also be feasible, in particular lighter and more flexible substrates, such as polyimide sheets or metal foils.

[0614] A back-contact layer 246 which can serve as the back contact and, additionally, may reflect a considerable amount of unabsorbed light into the absorbing p-type semiconductor layer 240 may comprise a thin metal layer, such as a molybdenum (Mo) metal layer, which might be produced by depositing, such as by sputtering, the respective metal onto the substrate 170. Further, following molybdenum deposition, the p-type absorber material 244 may be grown on top of the back-contact layer 246 by one of several methods, such as, for example, described in W. Hermes et al., s. o. Accordingly, thin-films of can, generally, be prepared via a two-step process. During a first step, a thin film of the p-type absorber material 244 may be deposited by a vacuum-based or a solution-based method. For this purpose, elements or a precursor material can be coated sequentially or mixed, wherein high efficiency is obtained for elements already mixed in the film. As an alternative, nanoparticles comprising the p-type absorber material 244 can be deposited. In the second step, the layer may be annealed at temperatures from 500 C. and 600 C. which may result in the formation of the desired p-type absorber material 244 from the elements or a sintering of the nanoparticles. To alternatively fabricate the p-type absorber material 244 absorber material in a one-step approach, the elements may be simultaneously deposited at elevated temperatures, such via co-sputtering or co-evaporation onto heated substrates, thus, leading to a direct formation of the p-type absorber material 244 during deposition. However, other kinds of materials may be possible.

[0615] Further, particularly as a result of a direct contact between the molybdenum (Mo) metal present in the back-contact layer 246 and the adjacent p-type absorber material 244 comprising sulfur (S) atoms as in this example, a layer comprising molybdenum sulfide MoS.sub.2 may be obtained in-situ as a thin boundary layer 248 located between the back contact layer 246 and the p-type absorber material 244.

[0616] On top of the p-type absorber material 244, a thin n-type semiconductor layer 238 which may, preferably, work as a buffer layer 250 may be provided. As typically in the case of the thin-film solar devices 242, the buffer layer 250 can comprise a material such as cadmium sulfide (CdS) which might, for example, be deposited via chemical bath deposition. In addition, the buffer layer 250 may be overlaid with a thin protection layer 252 which may, further, be capped by a comparatively thicker charge-carrier collection layer 254. Generally, the protection layer 252 may comprise a layer of intrinsic zinc oxide (i-ZnO) which can, particularly, be used for protecting both the buffer layer 250 and the p-type absorber material 244 from sputtering damages which may otherwise occur during deposition of the charge-carrier collection layer 254. Herein, the charge-carrier collection layer 254 may, preferably, comprise an aluminum (Al) doped ZnO layer (ZnO:A1), usually denoted as ZnO:Al window layer, which may, as usually, produced by DC sputtering which is known as a rather damaging process. Other kinds of materials may also be feasible for being used within the respective layers, such as zinc sulfide (ZnS), zinc oxide (ZnO), or zinc hydroxide (ZnOH) within the buffer layer 250 in order to avoid toxic cadmium (Cd). The charge-carrier collection layer 254 can, preferably, serve as a transparent conducting oxide layer 256 for collecting and moving charge-carriers from the p-type absorber material 244 while absorbing incident light from the light beam 132 to the at least one first electrode 176 and the at least one second electrode 178 as arranged here on top of the charge-carrier collection layer 254. Accordingly, a photodiode 258 is, thus, formed at least by the n-type semiconductor layer 238 and the p-type semiconductor layer 240 and which may, as further illustrated in FIG. 11A, be supplemented by one or more other kinds of additional layers, such as the ones described here, i.e. the back-contact layer 246, the boundary layer 248, the protection layer 252 and the charge-carrier collection layer 254, or by one or more further layers, as well as by the at least one first electrode 176 and the at least one second electrode 178.

[0617] FIG. 11B presents a further preferred example of the optical detector 110 in an arrangement in which the longitudinal optical sensor 114 exhibits a device structure of a typical thin-film solar cell 242 as a photodiode 258 which deviates from the depiction in FIG. 11A in some way. In particular contrast to the setup of the device according to FIG. 11A, the thin-film solar cell 242 pursuant to FIG. 11B may be employed in a setup in which the beam path 232 of the incident light beam 132 may be capable of traversing the substrate 170 which is, therefore, transparent in this example. Accordingly, a transparent substrate 170, 180, preferably glass, quartz or a solid transparent polymer, is used as a basis on which a transparent conducting oxide layer 256 may serve as the first transparent electrode 228. Between the transparent electrode 228 and the second electrode 230, which can exhibit optically transparent or, preferably, intransparent properties, the photodiode 258 is, again, formed at least by the p-type semiconductor layer 240 and the n-type semiconductor layer 238, wherein here, additionally, the buffer layer 250 as described above in more detail is employed. Preferably, one of the above-mentioned p-type absorber materials 244, is used here as the p-type semiconductor layer 240. For further details concerning this type of arrangement, reference may be made to the description of FIG. 11A.

[0618] FIGS. 11C to 11H present experimental results which have been acquired by employing the optical detector 110 according to the present invention in which the longitudinal optical sensor 114 uses the a thin-film solar cell 242 as the photodiode 258, preferably according to one of the arrangements as depicted in FIG. 11A or 11B.

[0619] FIG. 11C shows three different HP curves in which the longitudinal optical sensor 114 uses a thin-film solar cell 242 as the photodiode 258 in the setup according to FIG. 11B, wherein the p-type semiconductor layer 240 comprising cadmium telluride (CdTe), the n-type semiconductor layer 238 comprising cadmium sulfide (CdS), and the additional buffer layer 250 comprising tin oxide (SnO.sub.2) are arranged between a layer of transparent indium tin oxide (ITO) as the first electrode 228 located on a glass substrate 170, 180 and a metal layer as the second electrode 230. Herein, the three FiP curves which demonstrate the occurrence of the negative FiP effect within this arrangement are recorded without the application of a bias voltage at an illumination wavelength of 850 nm, i.e. in the NIR spectral range, provided by a light-emitting diode 158 which was driven with a current of 100 mA (solid line), 500 mA (dashed line) or 1000 mA (dotted line), respectively.

[0620] A similar example is presented in FIG. 11D. Herein, the p-type semiconductor layer 240 which comprises a layer of zinc cadmium telluride (ZnCdTe) with a thickness of 2.5 m and the n-type semiconductor layer 238 which comprises a layer of zinc selenide (ZnSe) with a thickness of 220 nm are arranged between a layer of transparent indium tin oxide (ITO) as the first electrode 228 and a metallic silver (Ag) layer as the second electrode 230. Again, the negative FiP effect may be derived from the FiP curve as depicted in FIG. 11D which has been recorded without the application of a bias voltage, wherein the illumination source 156 was modulated with the modulation frequency of 375 Hz using 100 ms long current pulses exhibiting an amplitude of 1000 mA.

[0621] FIGS. 11E to 11H present experimental results in which the longitudinal optical sensor 114 uses the thin-film solar cell 242 as the photodiode 258, wherein the p-type semiconductor layer 240 comprises one of the p-type absorber materials 244 as described above, i.e. the I-III-VI.sub.2 compound copper indium gallium selenide (GIGS; see FIG. 11E) or the I.sub.2-II-IV-VI.sub.4 compound copper zinc tin sulfide (CZTS; see FIGS. 11F to 11H). Alternatively, a halide perovskite compound, in particular an organic-inorganic halide perovskite, especially methylammonium lead iodide (CH.sub.3NH.sub.3Pbl.sub.3), may also be employed for this purpose. Without any loss of generality, the compounds CIGS and CZTS are, however, used as paradigmatic examples in the following description although the examples from FIGS. 11C and 11D have illustrated that the concept of using the thin-film solar cell 242 as the photodiode 258 may be applied more generally.

[0622] Thus, FIG. 11E presents an experimental result in which the p-type semiconductor layer 240 comprises the I-III-VI.sub.2 compound copper indium gallium selenide (CIGS) as the p-type absorber material 244. Herein, the FiP curve as shown here which has been recorded without application of a bias voltage at an illumination wavelength of 850 nm, i.e. in the NIR spectral range, provided by a light-emitting diode 158 being driven with a comparatively high current of 500 mA clearly demonstrates the occurrence of the positive FiP effect in this kind of arrangement.

[0623] Further, FIGS. 11E to 11H present experimental results in which the p-type semiconductor layer 240 comprises the I.sub.2-II-IV-VI.sub.4 compound copper zinc tin sulfide (CZTS) as the p-type absorber material 244. As can be derived from a comparison from FIGS. 11F and 11H, on one hand, and FIG. 11G, on the other hand, it could be demonstrated here that, in case the photodiode 258 is driven in the photoconductive mode, a sign of the FiP effect may depend on an intensity of the incident light beam 132 impinging on the p-type absorber material 244 CZTS exhibiting a size of 3 mm3 mm. Thus, by using two suitably different values for the intensity of the incident light beam 132, it may be feasible to, again, acquire two individual measurement curves which may, particularly, be used as a reference base for resolving the above-mentioned ambiguities with respect to the longitudinal sensor signal by comparing the two individual measurement curves.

[0624] As illustrated in FIG. 11F, for a comparatively high intensity in which the illumination source 156 comprised the green light-emitting diode (LED) 158 emitting a wavelength of 530 nm and driven by a comparatively high current of 600 mA, the negative FiP effect could be observed. As a further example for comparatively high intensity in the same optical detector 110, the NIR light-emitting diode (LED) 158 emitting a wavelength of 850 nm and driven by an even higher current of 1000 mA was employed for obtaining the measurement curve as illustrated in FIG. 11H which also exhibits the negative FiP effect.

[0625] In contrast to these findings, the positive FiP effect could, although having a comparatively smaller amplitude, as illustrated in FIG. 11G, be observed in the same optical detector 110 by illuminating the p-type absorber material 244 CZTS within the longitudinal optical sensor 114 by a comparatively low intensity. For this purpose, the illumination source 156 comprised the green light-emitting diode (LED) 158 emitting a wavelength of 530 nm which was driven in the experiment here by a rather low current of only 8 mA, thus, providing the incident light beam 132 only with a comparatively low intensity.

[0626] This kind of behavior with respect to the sign of the FiP effect depending on the intensity of the incident light beam 132 may, in particular, be explained by an assumption that in case in which the incident light beam 132 has, given the same total power of the illumination, a small beam cross-section 174 and, thus, causes a high intensity within the area of the beam cross-section 174, recombination of a great number of generated charge-carriers may occur within the p-type absorber material 244 CZTS. In the opposing situation in which the incident light beam 132 has, given the same total power of the illumination, a large beam cross-section 174 and, therefore, may only lead to a low intensity within the area of the beam cross-section 174, virtually no recombination can occur within the p-type absorber material 244 CZTS, moreover, since this kind of material may, in particular, have a large number of defects.

[0627] Consequently, by switching between the at least two operational modes of the longitudinal optical sensor 114, it may, thus, be feasible to acquire two individual measurement curves, wherein one of the individual curves may, in particular, be used for reference purposes. Since the photodiode 258 may, generally, not exhibit the FIR effect in the photovoltaic mode while the same photodiode 258 may actually exhibit the FiP effect in the photoconductive mode, it may, accordingly, be possible to use the measurement curve acquired in the photovoltaic mode as a reference base for resolving the above-mentioned ambiguities with respect to the longitudinal sensor signal by comparing the two individual measurement curves.

[0628] Compared to the detector 110 in which the sensor region 130 of the longitudinal optical sensor 114 comprises the chalcogenide 136 lead sulfide (PbS) or lead selenide (PbSe) as the photoconductive material 134, the detectors 110 of this the kind as illustrated in FIGS. 11A to 11H exhibit a number of advantages, in particular, a homogeneous film formation, a low observable voltage, a lack of a dark current resulting in a higher signal-to noise ratio, a zero offset, a higher current at the same total power of the illumination, and a capability that the longitudinal optical sensor 114 may be transparent or translucent.

[0629] Further, as illustrated in FIG. 11J, the photocurrent through the longitudinal optical sensor 114 as presented here may, accordingly, be determined by using the detector 110, wherein, for this purpose, the bias voltage source 150 configured to provide a bias voltage, in particular, above ground 152 may, preferably, be used to drive the photodiode 258 in a photoconductive mode. For this purpose, the photodiode 258 is employed in a reverse biased mode, in which the n-type semiconductor layer 238 of the photodiode 258 is driven with a positive voltage with respect to the p-type semiconductor layer 240. This is in contrast to the so-called photovoltaic mode, in which a zero bias is used between the n-type semiconductor layer 238 and the p-type semiconductor layer 240 of the photodiode 258. Applying the photoconductive mode to the photodiode 258 may, generally, lead to the observation of the FIR effect in the photodiode 258, i.e. that, given the same total power of the illumination, the photocurrent as generated by the photodiode 258 may be found to be dependent on the beam cross-section of the light beam in the sensor region 130. Consequently, since the longitudinal sensor signal is dependent on the electrical conductivity within the sensor region 130, recording the at least one longitudinal sensor signal, thus, allows determining the beam cross-section of the light beam in the sensor region 130 and, thus, generating at least one item of information on the longitudinal position of the object 112. For further details in FIG. 11J, reference may be made to the description of FIGS. 11A or 11B.

[0630] In a preferred embodiment as further illustrated in FIG. 11J, a switching device 260 may, additionally, be employed, wherein the switching device 260 may, in particular, be adapted to exert an influence on the bias voltage source 150 in order to set the bias voltage to at least two individual values which may be different with respect to each other. Thus, the bias voltage source 150 may be configured to apply at least two different bias voltages to the photo-diode 258 in a manner that it may be possible to switch between at least two operational modes of the longitudinal optical sensor 114. As a result, the electrical conductivity within the sensor region 130 of the longitudinal optical sensor 114 may be adjustable by applying different bias voltages. In this embodiment, in a first operational mode, a non-zero bias voltage may be applied to the photodiode 258, in particular, in a reverse biased mode, in which the n-type semiconductor layer 238 of the photodiode 258 may, as described above, be driven with a positive voltage with respect to the p-type semiconductor layer 240. Thus, in the first operational mode, a first longitudinal sensor signal may be acquired. Further, in a second operational mode, a zero bias may be applied to the photodiode 258 which may result in an observation that the photodiode 258 may be unbiased and, thus, adopt the photovoltaic mode as also described above. Thus, in the second operational mode, a second longitudinal sensor signal may, similarly, be acquired which, generally, differs from the first longitudinal sensor signal.

[0631] FIGS. 12A, 12B, and 12D illustrate three further preferred examples of the longitudinal optical sensor 114 in which the photoconductive material 134 is provided in form of a colloidal film 262 which comprises quantum dots 264. Further, FIG. 12B shows experimental results which demonstrate the occurrence of the negative FiP effect in the longitudinal optical sensor 114 according to FIG. 12A, wherein the photoconductive material selected for the quantum dots 264 has been lead sulfide (PbS).

[0632] In a first embodiment as illustrated in FIG. 12A, the longitudinal optical sensor 114 behaves as a Schottky diode 266 as, for example, described by J. P. Clifford et al., s. o., wherein, the film 262 of the colloidal PbS quantum dots 264 (PbS CQD film) which acts as the photoconductive material 134 is sandwiched between a first electrode 268 and a second electrode 270. Herein, the first electrode 268 which is impinged by the incident light beam 132, preferably, comprises a layer of an electrically conducting and at least partially optically transparent electrode 272, more preferred at least one transparent conductive oxide (TCO), in particular an indium-doped tin oxide (ITO) electrode 274. However, other kinds of electrically conducting and optically transparent materials 272 may also be suitable as material for the first electrode 268, in particular one or more of fluorine-doped tin oxide (FTO), magnesium oxide (MgO), aluminum-doped zinc oxide (AZO), or, alternatively, metal nanowires, such as Ag or Cu nanowires. In contrast hereto, the second electrode 270 may be at least one optically intransparent electrode and may, thus, preferably comprise a metal electrode 276, in particular an aluminum (Al) electrode 278. In this particular example, the second electrode 270 may, preferably, comprise a uniform metal layer. As a result of this setup, a Schottky barrier 280 may form at an interface between the PbS CQD film 262 and the aluminum electrode 278. The incident light beam 132 through the ITO electrode 274 may generate electrons and holes in the CQD film 262 which can be collected at the boundaries towards the ITO electrode 274 and the aluminum electrode 278, respectively. Consequently, a depletion region may form in the CQD film 262 at the Schottky barrier 280 which is located at the metal-CQD interface, whereas the remaining volume of the CQD film 262 may be considered as a p-type semiconductor layer 240.

[0633] In this particular example, the PbS CQD film 262 which comprises PbS quantum dots 264 having diameters above 5 nm still exhibits a good absorption above 1000 nm. In order to achieve this result, a 100 mg/ml solution of PbS quantum dots 264 in an unpolar organic solvent, preferably octane, have been provided, from which two subsequent layers have been formed on the ITO electrode 274 by application of a deposition method, preferably by a spin-coating method with a rotation frequency from 1000 rpm to 6000 rpm, such as 4000 rpm. Each of the two layers has individually been treated with ethanedithiol during a treatment time, preferably from 10 s to 10 min, more preferred from 10 s to 1 min, such as 30 s, before a drying step was performed for a drying time, preferably from 1 min to 2 h, more preferred from 10 min to 1 h, such as 30 min, at a drying temperature from 50 C. to 250 C., preferred from 100 C. to 200 C. This kind of procedure turned out to be particularly advantageous with respect to obtaining a setup for the longitudinal optical sensor 114 with as little short circuits through the COD film 262 as possible. Finally, a 100 nm thick layer of aluminum was deposited through evaporation onto the colloidal film 262 as the metal electrode 276. Experimental results which demonstrate the occurrence of the negative FiP effect in this kind of specimen are shown in FIG. 12B for drying temperatures from 100 C. to 180 C. in 20 C. intervals. Similar as above, the NIR light-emitting diode (LED) 158 emitting a wavelength of 850 nm and driven by a comparatively high current of 1000 mA was employed for illuminating the longitudinal optical sensor 114 pursuant to FIG. 12A which behaves as a Schottky diode 266.

[0634] In an alternative embodiment as illustrated in FIG. 12C, a blocking layer 282 which, preferably, comprises a titanium dioxide (TiO.sub.2) blocking layer 284, was deposited onto the layer of the first electrode 268 which, preferably, comprises a layer of the electrically conducting and at least partially optically transparent electrode 272, more preferred the at least one transparent conductive oxide (TCO), in particular a fluorine-doped tin oxide (SnO.sub.2:F, FTO) electrode 286, before the CQD film 262 was deposited on top of the blocking layer 282 as the photoconductive material 134 similar to FIG. 12A. In the example as illustrated in FIG. 12C, an electrically conducting polymer 288, preferably a poly(3,4-ethylenedioxythiophene) (PEDOT) layer 290, was deposited onto the CQD film 262. In order to achieve a good electrical contact to outside electrical means, a split electrode 292 comprising at last two evaporated 200 nm silver (Ag) electrodes 294 have been deposited onto the PEDOT layer 290. Alternatively, the split electrode 292 may be selected from the group comprising a platinum (Pt) electrode and a gold (Au) electrode. Herein, the split electrode 292 may, preferably be arranged as a number of partial electrodes or in form of a metallic grid. Alternatively, as illustrated in FIG. 12C, a mesoporous titanium oxide (TiO.sub.2) layer 296 can, additionally, be deposited between the titanium dioxide (TiO.sub.2) blocking layer 284 and the CQD film 262, wherein the mesoporous titanium oxide (TiO.sub.2) layer 296 may be considered here as the n-type semiconductor layer 238 while the CQD film 262 may be attributed as the p-type semiconductor layer 240 also in this particular embodiment.

[0635] In a further embodiment as illustrated in FIG. 12D, the blocking layer 282 which, preferably, comprises the titanium dioxide (TiO.sub.2) blocking layer 284, was deposited onto the layer of the first electrode 268 which, preferably, comprises the layer of the electrically conducting and at least partially optically transparent electrode 272, more preferred the at least one transparent conductive oxide (TCO), in particular the fluorine-doped tin oxide (SnO.sub.2:F, FTO) electrode 286, before the CQD film 262 was deposited on top of the blocking layer 282 as the photoconductive material 134 similar to FIG. 12C. However, in contrast to FIG. 12C, the metal electrode 276 comprising the single evaporated 200 nm silver (Ag) electrode 294 is used in this embodiment as the second electrode 270. Alternatively, the mesoporous titanium oxide (TiO.sub.2) layer 296 may, additionally, be deposited between the titanium dioxide (TiO.sub.2) blocking layer 284 and the CQD film 262 in a similar manner as described in the embodiment as depicted in FIG. 12C. However, leaving out the additional mesoporous titanium oxide (TiO.sub.2) layer 296 as shown in FIG. 12D may result in more homogeneous layers.

[0636] As outlined above, the detector 110 may have a straight beam path or a tilted beam path, an angulated beam path, a branched beam path, a deflected or split beam path or other types of beam paths. Further, the light beam 132 may propagate along each beam path or partial beam path once or repeatedly, unidirectionally or bidirectionally. Thereby, the components listed above or the optional further components listed in further detail below may fully or partially be located in front of the longitudinal optical sensors 114 and/or behind the longitudinal optical sensors 114.

LIST OF REFERENCE NUMBERS

[0637] 110 detector

[0638] 112 object

[0639] 114 longitudinal optical sensor

[0640] 116 optical axis

[0641] 118 housing

[0642] 120 transfer device

[0643] 122 refractive lens

[0644] 124 opening

[0645] 126 direction of view

[0646] 128 coordinate system

[0647] 130 sensor region

[0648] 132 light beam

[0649] 134 photoconductive material

[0650] 136 chalcogenide

[0651] 138 signal leads

[0652] 140 evaluation device

[0653] 142 focal point

[0654] 144 actuator

[0655] 146 actuator control unit

[0656] 148 longitudinal evaluation unit

[0657] 150 bias voltage source

[0658] 152 ground

[0659] 154 amplifier

[0660] 156 illumination source

[0661] 158 light-emitting diode

[0662] 160 modulated illumination source

[0663] 162 modulation device

[0664] 164 lock-in amplifier

[0665] 166 data processing device

[0666] 168 layer of photoconductive material

[0667] 170 substrate

[0668] 172 ceramic substrate

[0669] 174 beam cross-section

[0670] 176 first electrode

[0671] 178 second electrode

[0672] 180 transparent substrate

[0673] 182 translucent substrate

[0674] 184 transversal optical sensor

[0675] 186 layer of transparent conducting oxide

[0676] 188 transparent conducting oxide

[0677] 190 first electrode

[0678] 192 second electrode

[0679] 194 first split electrode

[0680] 196 second split electrode

[0681] 198 sensor area

[0682] 200 detector system

[0683] 202 camera

[0684] 204 human-machine interface

[0685] 206 entertainment device

[0686] 208 tracking system

[0687] 210 transversal evaluation unit

[0688] 212 position information

[0689] 214 imaging device

[0690] 216 control element

[0691] 218 user

[0692] 220 beacon device

[0693] 222 machine

[0694] 224 track controller

[0695] 226 layer of material capable of sustaining an electrical current

[0696] 228 first electrode

[0697] 230 second electrode

[0698] 232 beam path

[0699] 234 PIN diode

[0700] 236 i-type semiconductor layer

[0701] 238 n-type semiconductor layer

[0702] 240 p-type semiconductor layer

[0703] 242 thin-film solar cell

[0704] 244 p-type absorber material

[0705] 246 back-contact layer

[0706] 248 boundary layer

[0707] 250 buffer layer

[0708] 252 protection layer

[0709] 254 charge-carrier collection layer

[0710] 256 transparent conducting oxide layer

[0711] 258 photodiode

[0712] 260 switching device

[0713] 262 colloidal film

[0714] 264 quantum dots

[0715] 266 Schottky diode

[0716] 268 first electrode

[0717] 270 second electrode

[0718] 272 optically transparent electrode

[0719] 274 indium-doped tin oxide (ITO) electrode

[0720] 276 metal electrode

[0721] 278 aluminum (Al) electrode

[0722] 280 Schottky barrier

[0723] 282 blocking layer

[0724] 284 titanium dioxide (TiO.sub.2) layer

[0725] 286 fluorine-doped tin oxide (SnO.sub.2:F, FTO) electrode

[0726] 288 electrically conducting polymer

[0727] 290 PEDOT layer

[0728] 292 split electrode

[0729] 294 silver (Ag) electrode

[0730] 296 mesoporous titanium oxide (TiO.sub.2) layer