A MEASUREMENT HEAD FOR DETERMINING A POSITION OF AT LEAST ONE OBJECT

Abstract

Described herein is a measurement head for determining a position of at least one object including at least one transfer device, where the transfer device has at least one focal length in response to at least one incident light beam propagating from the object to the measurement head, and

at least two optical receiving fibers, where at least one of the optical receiving fibers and/or the transfer device has a ratio ε.sub.r/k≥0.362 (m.Math.K)/W, where k is the thermal conductivity and ε.sub.r is the relative permittivity.

Claims

1. A measurement head (110) for determining a position of at least one object (112) comprising: at least one transfer device (114), wherein the transfer device (114) has at least one focal length in response to the at least one incident light beam (122) propagating from the object (112) to the measurement head (110); and at least two optical receiving fibers (116), wherein at least one of the optical receiving fibers (116) and/or the transfer device (114) has a ratio ε.sub.r/k≥0.362 (m.Math.K)/W, wherein k is the thermal conductivity and ε.sub.r is the relative permittivity.

2. The measurement head (110) according to claim 1, wherein at least one of the optical receiving fibers (116) and/or the transfer device (114) has the ratio ε.sub.r/k≥0.743 (m.Math.K)/W.

3. The measurement head (110) according to claim 1, wherein the ratio ε.sub.r/k is in a range 0.362 (m.Math.K)/W≤ε.sub.r/k≤1854 (m.Math.K)/W.

4. The measurement head (110) according to claim 1, wherein the transfer device (114) has a ratio ν.sub.e/n.sub.D in a range 9.05≤ν.sub.e/n.sub.D≤77.3, wherein ν.sub.e is the Abbé-number and n.sub.D is the refractive index, wherein the Abbé-number ν.sub.e is given by wherein n.sub.D is the refractive index for different wavelengths, wherein n.sub.C is the refractive index for 656 nm, n.sub.D is the refractive index for 589 nm and n.sub.F is the refractive index for 486 nm.

5. The measurement head (110) according to claim 1, wherein a product αΔn is αΔn≤110 dB/km at at least one wavelength in a visual and near infrared wavelength range, wherein α is the attenuation coefficient and Δn is the refractive index contrast with Δn=(n12−n22)/(2n12), wherein n1 is the maximum core refractive index and n2 is the cladding refractive index.

6. The measurement head (110) according to claim 5, wherein the product α Δn is α Δn≤23 dB/km.

7. The measurement head (110) according to claim 1, wherein the transfer device (114) has an aperture area D.sub.1 and at least one of the optical receiving fibers (116) has a fiber core (166) with a cross-sectional area D.sub.2, wherein a ratio D.sub.1/D.sub.2 is in a range 0.54≤D.sub.1/D.sub.2≤5087.

8. The measurement head (110) according to claim 1, wherein the measurement head (110) comprises at least one spacer device (124), wherein the spacer device (124) is configured for connecting the at least one transfer device (114) and at least one of the optical receiving fibers (116).

9. The measurement head (110) according to claim 8, wherein the spacer device (124) comprises a solid volume V.sub.s and a hollow volume V.sub.h, wherein a ratio of solid volume and hollow volume V.sub.s/V.sub.h is in a range 0.013≤V.sub.s/V.sub.h≤547.

10. The measurement head (110) according to claim 1, wherein the measurement head (110) further comprises an illumination source (130) for illuminating the object (112), wherein the illumination source (130) has a geometrical extend G in a range 1.5.Math.10.sup.−7 mm.sup.2.Math.sr≤G≤314 mm.sup.2.

11. The measurement head (110) according to claim 1, wherein each optical receiving fiber (116) comprises the at least one fiber cladding (168) and the at least one core (166), wherein a ratio d.sub.1/BL is in a range 0.0011≤d.sub.1/BL≤513, where d.sub.1 is the diameter of the core (166) and BL is a baseline.

12. The measurement head (110) according to claim 1, wherein each optical receiving fiber (116) has at least one entrance face (118), wherein a geometric center of the respective entrance face (118) is aligned perpendicular with respect to an optical axis (120) of the transfer device (114).

13. The measurement head (110) according to claim 1, wherein at least one of the optical receiving fibers (116) is a structured fiber having a shaped and/or structured entrance (118) and/or exit face.

14. The measurement head (110) according to claim 1, wherein the measurement head (110) comprises at least one actuator (164) configured to move the measurement head (110) to scan a region of interest.

15. A kit (126) comprising at least one measurement head (110) according to claim 1 and a detector (128) for determining a position of at least one object (112), the detector (128) comprising: at least two optical sensors (140), wherein each optical sensor (140) has at least one light sensitive area (146), wherein each optical sensor (140) is designed to generate at least one sensor signal in response to an illumination of its respective light-sensitive area (146) by a light beam having passed through at least one of the optical receiving fibers (116) of the measurement head (110); and at least one evaluation device (148) being configured for determining at least one longitudinal coordinate z of the object (112) by evaluating a combined signal Q from the sensor signals.

16. The kit (126) according to claim 15, wherein the evaluation device (148) is configured for deriving the combined signal Q by one or more of dividing the sensor signals, dividing multiples of the sensor signals, or dividing linear combinations of the sensor signals.

17. The kit (126) according to claim 16, wherein the evaluation device (148) is configured for using at least one predetermined relationship between the combined signal Q and the longitudinal coordinate for determining the longitudinal coordinate.

18. The kit (126) according to claim 15, wherein the optical sensors (140) are partial diodes of a bi-cell or quadrant diode and/or comprise at least one CMOS sensor.

19. A method for determining a position of at least one object (112), the method comprising the following steps: providing at least one measurement head (110), the measurement head (110) comprising: at least one transfer device (114), wherein the transfer device (114) has at least one focal length in response to the at least one incident light beam (122) propagating from the object (112) to the measurement head (110); at least two optical receiving fibers (116), wherein at least one of the optical receiving fibers (116) and/or the transfer device (114) has a ratio ε.sub.r/k≥0.362 (m.Math.K)/W, wherein k is the thermal conductivity and ε.sub.r is the relative permittivity; providing at least one detector (128), the detector (128) comprising at least two optical sensors (140), wherein each optical sensor (140) has at least one light-sensitive area (146), wherein each optical sensor (140) is designed to generate at least one sensor signal in response to an illumination of its respective light-sensitive area (146) by a light beam having passed through at least one of the optical receiving fibers (116) of the measurement head (110); illuminating each light-sensitive area (146) of at least two optical sensors (140) of the detector (128) with at least one light beam having passed through at least one of the optical receiving fibers (116), wherein, thereby, each of the light-sensitive areas (146) generates at least one sensor signal; and evaluating the sensor signals, thereby, determining at least one longitudinal coordinate z of the object (112), wherein the evaluating comprises deriving a combined signal Q of the sensor signals.

20. A method of using the measurement head (110) according to claim 1, the method comprising using the measurement head (110) for a purpose, selected from the group consisting of: a position measurement in traffic technology; an entertainment application; an optical data storage application; a security application; a surveillance application; a safety application; a human-machine interface application; a logistics application; an endoscopy application; a medical application; a tracking application; a photography application; a machine vision application; a robotics application; a quality control application; a 3D printing application; an augmented reality application; a manufacturing application; and a purpose in combination with optical data storage and readout.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0211] 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 in an isolated fashion or in combination with other features. 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.

[0212] Specifically, in the figures:

[0213] FIGS. 1A to C show embodiments of a measurement head according to the present invention;

[0214] FIG. 2 shows an embodiment of a kit according to the present invention;

[0215] FIG. 3 shows a cross section of a fiber arrangement of the measurement head;

[0216] FIGS. 4A to MM show in top view embodiments of measurement heads;

[0217] FIGS. 5A to MM show in top view embodiments of fiber and lens arrangement of measurement heads;

[0218] FIGS. 6 A to D show side views of embodiments of fiber and lens arrangement in the measurement head;

[0219] FIGS. 7 A to F show lens arrangement at fiber ends;

[0220] FIGS. 8A to E show further embodiments of the measurement head;

[0221] FIG. 9 shows a further embodiment of the measurement head;

[0222] FIG. 10 shows a further embodiment of the measurement head; and

[0223] FIG. 11 shows an embodiment of an optical receiving fiber.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0224] In FIGS. 1A to C, schematic views of exemplary embodiments of a measurement head 110 for determining a position of at least one object 112 are depicted. The measurement head 110 comprises at least one transfer device 114. The transfer device 114 has at least one focal length in response to the at least one incident light beam propagating from the object 112 to the measurement head 110. The measurement head 110 comprises at least two optical receiving fibers 116.

[0225] The optical receiving fibers 116 may have specific mechanical and optical properties to ensure stability of the distance measurement in a broad range of environments. The mechanical properties of the optical receiving fibers 116 may be identical or the mechanical properties of the optical receiving fibers 116 may differ. Without wishing to be bound by this theory, a light supporting function of optical receiving fibers 116 relies on relationships of refractive indices and certain energy transport properties. Further certain mechanical parameters may be prerequisite that all functions of the optical receiving fibers 116 are maintained in a stable way. Therefore, certain mechanical parameters may act as prerequisite to ensure a stable measurement itself. At least one of the optical receiving fibers and/or the transfer device has a ratio ε.sub.r/k≥0.362 (m.Math.K)/W. Preferably, at least one of the optical receiving fibers and/or the transfer device has the ratio ε.sub.r/k≥0.743 (m.Math.K)/W, preferably the ratio is ε.sub.r/k≥1.133 (m.Math.K)/W. At least one of the optical receiving fibers 116 and/or the transfer device 114 has the ratio ε.sub.r/k in the range 0.362 (m.Math.K)/W≤ε.sub.r/k≤1854 (m.Math.K)/W, wherein k is the thermal conductivity and ε.sub.r is the relative permittivity. The relative permittivity is also known as the dielectric constant. Preferably, the ratio ε.sub.r/k is in the range 0.743 (m.Math.K)/W≤ε.sub.r/k≤194 (m.Math.K)/W. More preferably, the ratio ε.sub.r/k is in the range 1.133 (m.Math.K)/W≤ε.sub.r/k≤88.7 (m.Math.K)/W. At least one of the optical receiving fibers 116 and/or the transfer device 114 may have a relative permittivity in the range 1.02≤ε.sub.r≤18.5, preferably in the range 1.02≤ε.sub.r≤14.5, more preferably in the range 1.02≤ε.sub.r≤8.7, wherein the relative permittivity is measured at 20° C. and 1 kHz. The optical receiving fibers 116 and/or the transfer device 114 may have a thermal conductivity of k≤24 (m.Math.K)/W, preferably k≤17 (m.Math.K)/W, more preferably k≤14 (m.Math.K)/W. The optical receiving fibers 116 and/or the transfer device 114 may have a thermal conductivity of k≥0.003 (m.Math.K)/W, preferably k≤0.007 (m.Math.K)/W, more preferably k≤0.014 (m.Math.K)/W. The thermal conductivity may be measured at 0° C. and <1% relative humidity. The transfer device 114 may have a ratio v.sub.e/n.sub.D in the range 9.05≤v.sub.e/n.sub.D≤77.3, wherein v.sub.e is the Abbé-number and n.sub.D is the refractive index. The Abbé-number v.sub.e is given by

[00007]$v_e=\frac{\left(n_D-1\right)}{\left(n_F-n_C\right)},$

wherein n.sub.i is the refractive index for different wavelengths, wherein n.sub.C is the refractive index for 656 nm, n.sub.D is the refractive index for 589 nm and n.sub.F is the refractive index for 486 nm, measured at room temperature, see e.g. https://en.wikipedia.org/wiki/Abbe_number. Preferably, the ratio v.sub.e/n.sub.D is in the range of 13.9≤v.sub.e/n.sub.D≤44.7, more preferably in the range of 15.8≤v.sub.e/n.sub.D≤40.1.

[0226] Each of the optical receiving fibers 116 may comprise the at least one cladding 168 and the at least one core 166. A product αΔn may be in the range 0.0004 dB/km≤αΔn≤110 dB/km at at least one wavelength in a visual and near infrared wavelength range, preferably at at least one wavelength selected from 656 nm, 589 nm, or 486 nm, wherein a the attenuation coefficient and Δn is the refractive index contrast with Δn=(n.sub.1.sup.2−n.sub.2.sup.2)/(2n.sub.1.sup.2), wherein n.sub.1 is the maximum core refractive index and n.sub.2 is the cladding refractive index. Preferably, the product αΔn is in the range 0.002 dB/km≤αΔn≤23 dB/km, more preferably in the range 0.02 dB/km≤αΔn≤11.26 dB/km. The refractive index contrast Δn may be in the range 0.0015≤Δn≤0.285, preferably in the range 0.002≤Δn≤0.2750, more preferably in the range 0.003≤Δn≤0.25. The attenuation coefficient of the optical receiving fiber 116 may be in the range 0.2 dB/km≤α≤420 dB/km, preferably in the range 0.25 dB/km≤α≤320 dB/km. The transfer device 114 may have an aperture area D.sub.1 and at least one of the optical receiving fibers may have the fiber core 166 with a cross-sectional area D.sub.2, wherein a ratio D.sub.1/D.sub.2 is in the range 0.54≤D.sub.1/D.sub.2≤5087, preferably 1.27≤D.sub.1/D.sub.2≤413, more preferably 2.17≤D.sub.1/D.sub.2≤59.2. A diameter d.sub.core of the core 166 of at least one of the optical receiving fibers may be in the range 2.5 μm≤d.sub.core≤10000 μm, preferably in the range 7 μm≤d.sub.core≤3000 μm, more preferably in the range 10 μm≤d.sub.core≤500 μm.

[0227] The optical receiving fibers 116 and/or the transfer device 114 may have a Youngs modulus, also denoted elastic modulus, of less or equal 188 GPa, measured at room temperature, for example by using ultrasonic testing. Preferably the optical receiving fibers 116 and/or the transfer device 114 may have a Youngs modulus of less or equal 167 GPa, more preferably in the range from to 0.0001 GPa to 97 GPa. The optical receiving fibers 116 and/or the transfer device 114 may have a Youngs modulus of greater or equal 0.0001 GPa, preferably of greater or equal 0.007 GPa, more preferably of greater or equal 0.053 GPa.

[0228] Each of the optical receiving fibers 116 may have at least one entrance face 118. A geometric center of the respective entrance face 118 may be aligned perpendicular with respect to an optical axis 120 of the transfer device 114. At least one of the optical receiving fibers 116 may have an entrance face 118 which is oriented towards the object 112. The optical receiving fibers 116 may be arranged in a direction of propagation of an incident light beam 122 propagating from the object 112 to the measurement head 1120 behind the transfer device 114. The optical receiving fibers 116 and the transfer device 114 may be arranged such that the light beam 122 passes through the transfer device 114 before impinging on the optical receiving fibers 116.

[0229] As shown in FIGS. 1A and 1B, the measurement head 110 may comprise at least one spacer device 124. The spacer device 123 may be configured for connecting the at least one transfer device 114 and at least one of the optical receiving fibers 116. FIG. 1A shows an embodiment, wherein the measurement head 110 comprises one transfer device 114, such as a lens, and two optical receiving fibers 116. The spacer device may be configured to attach the transfer device 114 to both of the optical receiving fibers 116. FIG. 1B shows an embodiment, wherein the measurement head 110 comprises two transfer devices 114, such as two lenses, and two optical receiving fibers 116. The spacer device 124 may be configured for connecting each of the transfer devices 114 with one of the optical receiving fibers 116. The spacer device 124 may comprise a solid volume V.sub.s and a hollow volume V.sub.h. The solid volume may be defined by the volume of solid material of which the spacer device 124 consists of. The convex hull volume of the spacer device may be defined as the volume of the smallest convex hull of the solid volume of the spacer device. The hollow volume of the spacer device may be defined as the convex hull volume of the spacer device minus the solid volume of the spacer device. For example, the empty volume may be defined by inner edges of the solid material. A ratio of solid volume and hollow volume V.sub.s/V.sub.h may be in the range 0.013≤V.sub.s/V.sub.h≤547, preferably in the range 0.047≤V.sub.s/V.sub.h≤87.6, more preferably in the range 0.171≤V.sub.s/V.sub.h≤26.2.

[0230] In the embodiment of FIG. 1C, the transfer device 114 may comprise at least one gradient index (GRIN) lens 114. The transfer device 114 and the optical receiving fibers 116 may be configured as one-piece. The optical receiving fibers 116 may be attached to the transfer device 114 such as by a polymer or glue or the like, to reduce reflections at interfaces with larger differences in refractive index.

[0231] The optical receiving fibers 116 may be arranged as such, that the light beam 122 impinges on the optical receiving fibers 116 between the transfer device 114 and the focal point of the transfer device 114. For example, a distance in a direction parallel to the optical axis 120 between the transfer device 114 and the position where the light beam 122 impinges on the optical receiving fibers 116 may be at least 20% of the focal length, more preferably at least 50% of the focal length, most preferably at least 80% of the focal length. For example, the distance in a direction parallel to the optical axis 120 between the entrance face 118 at least one of the optical receiving fibers 116 receiving the light beam 122 and the transfer device 114 may be at least 20% of the focal length, more preferably at least 50% of the focal length, most preferably at least 80% of the focal length.

[0232] In FIG. 2, a schematic view of an exemplary embodiment of a kit 126 comprising the measurement head 110 and a detector 128 for determining a position of at least one object 112 is depicted. In this embodiment, the measurement head 110 comprises the transfer device 114 and two optical receiving fibers 116. For further description of the measurement head 110 reference is made to the description of FIGS. 1A to C. In addition, the measurement head 110 may comprise at least one illumination source 130 for illuminating the object 112. As an example, the illumination source 130 may be configured for generating an illuminating light beam for illuminating the object 112. Specifically, the illumination source 130 may comprise at least one light source 132 such as at least one laser and/or laser source. Various types of lasers may be employed, such as semiconductor lasers. Additionally or alternatively, non-laser light sources may be used, such as LEDs and/or light bulbs. The illumination source 130 may comprise an artificial illumination source, in particular at least one laser source and/or at least one incandescent lamp and/or at least one semiconductor light source, for example, at least one light-emitting diode, in particular an organic and/or inorganic light-emitting diode. As an example, the light emitted by the illumination source 130 may have a wavelength of 300 to 1000 nm, especially 500 to 1000 nm. Additionally or alternatively, light in the infrared spectral range may be used, such as in the range of 780 nm to 3.0 μm. Specifically, the light in the part of the near infrared region where silicon photodiodes are applicable specifically in the range of 700 nm to 1000 nm may be used. Further, the illumination source 130 may be configured for emitting modulated or non-modulated light. In case a plurality of illumination sources 130 is used, the different illumination sources may have different modulation frequencies which, later on may be used for distinguishing the light beams. The illumination source 130 may comprise at least one optical illumination fiber 134 adapted to transmit a light beam 136 generated by the light source 132 such that it illuminates the object 112. The light beam 136 may leave the optical illumination fiber 134 at an exit face 138 of the optical illumination fiber 134.

[0233] In FIG. 2, the object 112 is depicted for two different object distances. The detector 128 comprises at least two optical sensors 140, for example a first optical sensor 142 and a second optical sensor 144, each having at least one light-sensitive area 146.

[0234] The first optical sensor 142, in response to the illumination by the light beam 122, may generate a first sensor signal s.sub.1, whereas the second optical sensor 144 may generate a second sensor signal s.sub.2. Preferably, the optical sensors 140 are linear optical sensors. The sensor signals s.sub.1 and s.sub.2 are provided to an evaluation device 148 of the detector 128. The evaluation device 148 is embodied to derive a combined signal Q from the sensor signal, specifically by evaluating a quotient signal. From the combined signal Q, derived by dividing the sensor signals s.sub.1 and s.sub.2 or multiples or linear combinations thereof, may be used for deriving at least one item of information on a longitudinal coordinate z of the object 112. The evaluation device 148 may have at least one divider 150 for forming the combined signal Q, and, as an example, at least one position evaluation device 152, for deriving the at least one longitudinal coordinate z from the combined signal Q. It shall be noted that the evaluation device 148 may fully or partially be embodied in hardware and/or software. Thus, as an example, one or more of components 150, 152 may be embodied by appropriate software components.

[0235] The illumination source 130 may have a geometrical extend G in the range 1.5.Math.10.sup.−7 mm.sup.2.Math.sr≤G≤314 mm.sup.2.Math.sr, preferable in the range 1.Math.10.sup.5 mm.sup.2.Math.sr≤G≤22 mm.sup.2.Math.sr, more preferable in the range 3.Math.10.sup.−4 mm.sup.2.Math.sr≤G≤3.3 mm.sup.2.Math.sr. The geometrical extent G of the illumination source 130 may be defined by

G=A.Math.Ω.Math.n.sup.2,

wherein A is the area of the surface, which can be an active emitting surface, a light valve, optical aperture or the area of the fiber core 166 with A=A.sub.OF=π.Math.r.sup.2.sub.OF, and f is the projected solid angle subtended by the light and n is the refractive index of the medium. For rotationally-symmetric optical systems with a half aperture angle θ, the geometrical extend is given by

G=π.Math.A.Math.sin.sup.2(θ)n.sup.2.

[0236] For optical receiving fibers a divergence angle is obtained by θ.sub.max=arcsin(NA/n), where NA is the maximum numerical aperture of the optical receiving fiber.

[0237] The half aperture angle θ and/or the divergence angle θ.sub.max may be small. In particular, the half aperture angle θ may be in the range 0.01°≤42°; preferably in the range of 0.1°≤θ≤21°; more preferably in the range of 0.15°≤θ≤13° and/or the divergence angle θ.sub.max be in the range 0.01°≤θ.sub.max≤42°; preferably in the range of 0.1°≤θ.sub.max≤21°; more preferably in the range of 0.15°≤θ.sub.max≤13° The area A may be small. In particular, the area A may be smaller than 10 mm.sup.2, preferably smaller than 3 mm.sup.2, more preferably smaller than 1 mm.sup.2.

[0238] The measurement head 110 may comprise a small baseline. Each optical receiving fiber 116 comprises the at least one fiber cladding 168 and the at least one core 166. A ratio d.sub.1/BL may be in the range 0.0011≤d.sub.1/BL≤513, where d.sub.1 is the diameter of the core 166 and BL is the baseline. Preferably, the ratio d.sub.1/BL is in the range 0.0129≤d.sub.1/BL≤28, more preferable in the range 0.185≤d.sub.1/BL≤ and 7.1. The baseline may have an extend greater than 0. The baseline may be in the range 10 μm≤BL≤127000 μm, preferably in the range 100 μm≤BL≤76200 μm, more preferably in the range 500 μm≤BL≤25400 μm.

[0239] The measurement head 110 may comprise at least two or more fibers. The optical receiving fibers 116 may be at least one multifurcated optical receiving fiber, in particular at least one bifurcated optical receiving fiber. In the cut through in FIG. 3, an exemplary embodiment is shown wherein the measurement head 110 may comprise four fibers. In particular the optical receiving fiber may comprise the optical illumination fiber 134 and two optical receiving fibers 116. As shown schematically in FIG. 3, the optical receiving fibers 116 may be arranged close to each other at an entrance end 154 of the measurement head 110 and may split into legs separated by a distance at an exit end 156 of the measurement head 110. The optical receiving fibers 116 may be designed as fibers having identical properties or may be fibers of different type. The measurement head 110 may comprise more than three fibers, for example four fibers as depicted in FIG. 3, wherein a fourth fiber 158 can be a further fiber 116.

[0240] FIGS. 4A to 4MM show in top view embodiments of measurement heads 110. The measurement head 110 may comprise at least one spacer device 124, for example at least one metal housing and/or plastic housing. Each of the measurement heads 110 may comprise a plurality of fibers, specifically a plurality of the at least one optical illumination fiber 134 and/or the at least one optical receiving fiber 116. In particular, FIGS. 4 A, B, F, G, H, L, R, M, N, R, S, X show embodiments of measurement heads 110 having one optical illumination fiber 134 and two optical receiving fibers 116, specifically a first optical receiving fiber 160 adapted to provide the light beam to the first optical sensor 142, and a second optical receiving fiber 162 adapted to provide the light beam 122 to the second optical sensor 144. The measurement head 110 may comprise at least one radially arranged or radially symmetric design. For example, at least two elements selected from the group consisting of: the first optical receiving fiber 160; the second optical receiving fiber 162; or the optical illumination fiber 134 may be arranged concentric and having and/or sharing a common central axis. For example, as shown in FIGS. 4 B, H and N, the first optical receiving fiber 160, the second optical receiving fiber 162 and the optical illumination fiber 134 may be arranged concentric and having and/or sharing a common central axis. Other embodiments of a radially arranged or radially symmetric design are possible. For example, as shown in FIGS. 4 GG, KK and LL a plurality of at least one element selected from the group consisting of: the first optical receiving fiber 160; the second optical receiving fiber 162; or the optical illumination fiber 134 may be arranged radially around at least one other element selected from the group consisting of: the first optical receiving fiber 160; the second optical receiving fiber 162; or the optical illumination fiber 134. The radially arranged or radially symmetric design may allow enhancing robustness of measurement values, in particular at strong black-and-white contrast in a measured point of the object or for measurements of concave or convex surfaces. FIGS. 4 C, D, E, I, J, K, O, P, Q, T, U, V, W, Y, Z and AA to MM show further possible arrangements of different numbers of optical illumination fibers 134, first optical receiving fibers 160 and second optical receiving fibers 162 within the measurement head 110. Other arrangements of the fibers within the measurement head 110 are thinkable.

[0241] The measurement head 110 comprises one or more transfer devices 114, in particular collimating lenses. FIG. 5 A to MM show in top view embodiments of lens arrangements in measurement heads 110. The arrangement of fibers in the measurement heads 110 of FIGS. 5 A to MM correspond to the arrangement shown in FIGS. 4 A to MM, wherein in FIG. 5 A and A1, C1 and C2 two embodiments for the fiber arrangement of FIGS. 4 A and C, respectively, are shown. For clarity reference numbers of respective fibers were omitted such that reference is made to FIGS. 4 A to MM. The measurement heads 110 shown in FIGS. 5 A, AA, BB, C2, E, EE, H, HH, JJ, K, M, MM, O, R, V, Y, Z comprise one transfer device 114 arranged in front of all fibers. FIGS. 5 A1, C1, DD, F, FF, G, I, KK, L, P, U, X show measurement heads 110 comprising two or more transfer devices 114 in front of the fibers. FIGS. 5 B, D, CC, GG, II, J, N, LL, S, T, W, Q show measurement heads 110 comprising at least one separate lens 114 for fibers having the same function. For example, in FIGS. 5 B, CC, D, II, J, LL, T and Q, the measurement head 110 comprises transfer device 114 covering all fibers and a separated lens 114 covering optical illumination fibers 134 only in addition. For example, in FIG. 5 GG, the measurement head 110 comprises two transfer devices 114. A first transfer device 114 may cover a optical illumination fiber 134 and a plurality of first optical receiving fibers 160, which are arranged radially around the first optical illumination fiber 134, and a second transfer device 114 may cover an optical illumination fiber 134 and a plurality of second optical receiving fibers 162, which are arranged radially around one second optical illumination fiber 134. Furthermore, in FIG. 5 GG two separated transfer devices 114 are shown which cover the illumination fibers 134 only and in addition. For example, FIG. 5 N shows an embodiment, wherein a first transfer device 114 may cover all optical fibers, a second separate transfer device 114 may cover the first optical receiving fiber 160 and the second optical receiving fiber 162 and a third separate transfer device 114 may cover the first optical receiving fiber 160 only. For example, FIG. 5 S shows an embodiment having three transfer devices 114: a first transfer device 114 covering only the second optical receiving fiber 162, a second transfer device 114 covering both of the first optical receiving fiber 160 and the optical illumination fiber 134 and a third transfer device 114 covering the first optical receiving fiber 160 only. For example, FIG. 5 W shows a measurement head 110 comprising two transfer devices 114; a first transfer device 114 covering all fibers and at least one separate lens 114 covering the first optical receiving fiber 160 and the second optical receiving fiber 162. The optical paths of the first measurement fiber and/or the second measurement fiber and/or the illumination fiber and/or the optical pathways of two or more transfer devices may be fully or partially optically separated by mechanical means such as parts of the spacer device and/or a fully or partially intransparent mechanical wall or cladding or the like to avoid internal reflections.

[0242] FIGS. 6 a to D show a side view of embodiments of fiber and lens arrangement in the measurement head 110. FIG. 6A corresponds to the fiber and lens arrangement depicted in FIGS. 4 FF and 5 FF. The measurement head 110 may comprise separate transfer devices for optical illumination fiber 134 and optical receiving fibers 116, i.e. the at least one first optical receiving fiber 160 and the at least one second optical receiving fiber 162. The measurement head 110 may comprise one optical illumination fiber 134. The measurement head 110 may comprise, in particular displaced from the optical illumination fiber 134, one second optical receiving fiber 162 which is surrounded by six first optical receiving fibers 160 which are arranged radial around the second optical receiving fiber 162. The measurement head 110 may comprise a first transfer device 114, which may be arranged in front of the optical illumination fiber 134, and a second transfer device 114 which may cover the first optical receiving fiber 160 and the second optical receiving fiber 162.

[0243] FIG. 6 B to D show embodiments of the measurement head 110 comprising one optical illumination fiber 134, six first optical receiving fiber 160 and six second optical receiving fibers 162. In FIG. 6 B an arrangement is shown wherein the optical illumination fiber 134 is arranged in a center which is radially surrounded by the six first optical receiving fibers 160. The first optical receiving fibers 160 may be surrounded radially by the six second optical receiving fibers 162. The measurement head 110 may comprise one transfer device 114 for the optical illumination fiber 134 and the receiving fibers. Internal reflections may be generated at the transfer device which may generate a signal offset to the receiving fibers. FIG. 6 B shows an embodiment of a radial arrangement without a baseline. In FIG. 6 C, a similar fiber arrangement is shown, but the measurement head 110 may comprise separate transfer devices 114 for the optical illumination fiber 134 and the receiving fibers. In this embodiment, the optical illumination fiber 134 may be guided up to the transfer device 114 such that internal reflections can be prevented. This embodiment shows a radial arrangement without a baseline. FIG. 6 D shows a fiber arrangement wherein the optical illumination fiber 134 is arranged displaced from the center of the arrangement. In this embodiment, the optical illumination fiber 134 may be guided up to the transfer device 114 such that internal reflections can be prevented.

[0244] FIGS. 7 A to F show different lens arrangements at the fiber ends. As described above, at least one transfer device 114 may be arranged at an end of the optical fibers. The transfer device 114 may be attached directly to one optical fiber or may be attached to a bundle of optical fibers. Alternatively, the transfer device 114 may be attached to the optical fiber or bundle of optical fibers using at least one spacer device 124. FIG. 7 A shows an optical fiber or a bundle of optical fibers. FIG. 7 B shows the optical fiber or bundle of optical fibers having attached at least one concave lens. FIG. 7 C shows the optical fiber or bundle of optical fibers having attached at least one convex lens. FIG. 7 D shows the optical fiber or bundle of optical fibers having attached at least one spherical lens. FIG. 7 E shows the optical fiber or bundle of optical fibers having attached at least one conical lens or at least one tip-shaped lens. FIG. 7 F shows the optical fiber or bundle of optical fibers having attached at least one prism shaped lens, in particular a non-rotationally symmetric lens.

[0245] FIGS. 8A to E show further embodiments of the measurement head 110. The lens and fiber arrangement in FIG. 8A corresponds to the lens and fiber arrangement as shown in FIG. 6 A. In FIG. 8A, in addition the measurement head 110 comprises the spacer device 124 which is adapted to attach the transfer devices 114 to the optical receiving fibers 116. The optical paths of the first measurement fiber 160 and/or the second measurement fiber 162 and/or the illumination fiber 134 and/or the optical pathways of two or more transfer devices 114 may be fully or partially optically separated by mechanical means such as a fully or partially intransparent mechanical wall or cladding or the like to avoid internal reflections. This optical separation by mechanical means may be part of the spacer device 124. In FIG. 8B an arrangement comprising three fibers is shown. The illumination fiber 134 may be arranged separately and parallel to the optical receiving fibers 116. The optical receiving fibers 116 may be arranged in one combined receiving fiber entrance end. A first transfer device 114 may be arranged in front of the combined receiving fiber entrance end of the optical receiving fibers 116 and a second transfer device 114 may be arranged in front of the exit end of the illumination fiber 134. The combined receiving fiber entrance end may be split up into the first measurement fiber 160 and the second measurement fiber 162. For example, in a cross sectional view the first measurement fiber 160 and the second measurement fiber may be arranged within the combined receiving fiber entrance end as half circles separated by a horizontal border. FIG. 8C shows a similar arrangement but in the embodiment of FIG. 8C, the first measurement fiber 160 and the second measurement fiber may be arranged within the combined receiving fiber entrance end as half circles separated by a vertical border. FIG. 8D shows an arrangement wherein the first measurement fiber 160 and the second measurement fiber 162 and the illumination fiber 134 each are designed as separated fibers. A first transfer device 114 may be arranged in front of the entrance end of the first measurement fiber 160 and a second transfer device 114 may be arranged in front of the entrance end of the second measurement fiber 162 and a third transfer device 114 may be arranged in front of the exit end of the illumination fiber 134. The entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134 may be arranged in the same plane such as plane-parallel. The transfer devices 114 may be arranged plane-parallel but in a different plane compared to the plane of the entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134 such spaced apart from the plane of the entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134. The plane of the entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134 and the plane of the transfer devices 114 may be parallel planes. The centers of the exit end of the illumination fiber 134 and the entrance ends of the optical receiving fibers 116 may be at the intersection of a first plane which is the plane of the entrance faces of the optical receiving fibers 116 and the exit end of the illumination fiber 134 with a second plane that is orthogonal to the first plane and contains the line connecting the centers of the exit end of the illumination fiber 134 and the entrance ends of the optical receiving fibers 116. In FIG. 8E, as in FIG. 8D, the first measurement fiber 160 and the second measurement fiber 162 and the illumination fiber 134 are designed as separated fibers. In this embodiment, a first transfer device 114 may be arranged in front of the entrance end of the optical receiving fibers 116 and a second transfer device 114 may be arranged in front of the exit end of the illumination fiber 134. As in FIG. 8D, the entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134 may be arranged in the same plane. The first transfer device 114 and/or the second transfer device 114 may be arranged non-parallel such as under an angle with respect to the plane of the plane of the entrance ends of the optical receiving fibers 116 and the exit end of the illumination fiber 134.

[0246] FIG. 9 shows a further embodiment of the measurement head 110 for determining a depth profile of a scenery. In FIG. 9 an embodiment is shown, wherein the measurement head 110 comprises one second optical receiving fiber 162 and six first optical receiving fibers 160 which are arranged around the second optical receiving fiber 162. Specifically, each of the optical receiving fibers 116 may have at least two ends, a distal end, also denoted as exit-end, and at least one proximal end, also denoted as receiving end. The proximal end may be arranged within and/or attached to the measurement head 110. The respective proximal end may be adapted to couple the light beam 122 into the respective optical receiving fiber 116. The distal end may be arranged closer to the optical sensors 140 and may be arranged such that the light beam travelling from the proximal end to the distal end through the optical receiving fibers 116 leaves the optical receiving fibers 116 at the distal end and illuminates the respective optical sensor 140.

[0247] The measurement head 110 further may comprise the at least one transfer device 114. The transfer device 114 may be arranged in front of the optical receiving fibers 116. The transfer device 114 may be adapted to focus the light beam 122 on the proximal end. For example, the transfer device 114 may comprise at least one element selected from the group consisting of: at least one concave lens; at least one convex lens; at least one spherical lens; at least one tip-shaped lens; at least one prism shaped lens, in particular a non-rotationally symmetric lens. In addition, the measurement head 110 may comprise at least one spacer device 124 which is adapted to attach the transfer devices 114 to the optical receiving fibers 116. Optical paths of the first measurement fiber 160 and the second measurement fiber 162 may be fully or partially optically separated by mechanical means such as a fully or partially intransparent mechanical wall or cladding or the like to avoid internal reflections. This optical separation by mechanical means may be part of the spacer device 124.

[0248] The measurement head 110 may comprise the at least one optical illumination fiber 134. The optical illumination fiber 134 may comprise at least one first end adapted to receive the at least one light beam and at least one second end from where the at least one light beam leaves the optical illumination fiber 134 for illumination of the object 112. At least the second end of the optical illumination fiber 134 may be arranged within and/or may be attached to the measurement head 110. The optical illumination fiber 134 may be arranged parallel to the direction of expansion of the optical receiving fibers 116, for example, in a bundle with the optical receiving fibers 116. The detector may comprise the at least one further transfer device 110 which may be arranged in front of the optical illumination fibers 134.

[0249] The measurement head 110 may comprise at least one actuator 164 configured to move the measurement head 110 to scan a region of interest. Specifically, the actuator 164 may be attached and/or coupled and/or connected to the optical receiving fibers 116 and/or the optical illumination fiber 134 and may be adapted to generate a force causing the optical receiving fibers 116 and/or the optical illumination fibers 134 to move, in particular to oscillate. Thus, by driving the optical receiving fiber 116 and/or the optical illumination fiber 134 the measurement head 110 moves. The actuator 164 may be adapted to generate a force corresponding to a harmonic of a natural resonant frequency of the optical receiving fibers 116 and/or the optical illumination fiber 134. The actuator 164 may comprise at least one electromechanical actuator and/or at least one piezo actuator. The piezo actuator may comprise at least one actuator selected from the group consisting of: at least one piezoceramic actuator; at least one piezoelectric actuator. The actuator 164 may be configured to cause the measurement head 110, specifically the optical illumination fiber 134 and/or the optical receiving fibers 116 to oscillate. The actuator 164 may be adapted to move the measurement head 110 in a linear scan and/or a radial scan and/or a spiral scan. In FIG. 9, an exemplary movement of the measurement head 110 is shown. For example, the actuator 164 may be adapted to generate a force on the optical receiving fibers 116 such that the measurement head 110 moves upwards and downwards. For example, the actuator 164 may be configured to generate a force on the optical receiving fibers 116 such that the measurement head 110 moves in an orbit with a predefined radius. The radius may be adjustable. For example, the actuator 164 may be adapted to generate a force such that the measurement head 110 moves in a spiral such as with a radius which alternately decreases or increases.

[0250] FIG. 10 shows a further embodiment of the measurement head 110. FIG. 10 shows a front view of the measurement head 110. In this embodiment, the measurement head 110 may comprise a plurality of first measurement fibers 160 and a plurality of second measurement fibers 162 radially arranged around the optical illumination fiber 134. The optical illumination fiber 134 may be movable by the actuator 164. The optical illumination fiber 134 may be adapted to perform a spiral movement and/or a circular movement relative to the first measurement fibers 160 and the second measurement fibers 162 and thus, allow for a spiral or circular scan. The evaluation device 158 may be adapted to calibrate the position of the optical illumination fiber 134 and to evaluate a distance from the combined signal Q depending on the position of the optical illumination fiber 134. The measurement head 110 may comprise the at least one further transfer device 114 which may be arranged in front of the optical receiving fibers 116.

[0251] FIG. 11 shows a highly schematic view of an embodiment of an optical receiving fiber 116. Each of the optical receiving fibers 116 may comprise the at least one fiber core 166 which is surrounded by the at least one fiber cladding 168. The fiber cladding 168 may have a lower index of refraction as the fiber core 166. The fiber cladding 168 may also be a double or multiple cladding. The fiber cladding 168 may be surrounded by a buffer 170 and an outer jacket 172. The fiber cladding 168 may be coated by the buffer 170 which is adapted to protect the optical receiving fiber 116 from damages and moisture. The buffer 170 may comprise at least one UV-cured urethane acrylate composite and/or at least one polyimide material.

[0252] In order to assess the measurement stability of the measurement head 110, in an experimental setup, 20 mm spark gaps with each 25 kV were placed on each side of the measurement head 110 in a distance of 20 mm to the measurement head 110. Sparks were fired alternatingly on each side of the measurement head 110. In a length of 200 mm of the optical receiving fibers 116 including the measurement head 110 and the spark gaps were placed in a climate chamber and heated in steps of 20K to a maximum temperature T.sub.max. A target with 50% reflectivity was placed at 50 mm distance. The experiment was performed for optical fibers and transfer devices of different materials. For example, silica, acrylic and sapphire fibers were tested. The lens material of the transfer device was diamond, sapphire, float glass CaF.sub.2, Teflon, Acryl or silica. The measurement error Δz was determined as the standard deviation for 10.000 measurements.

[0253] The results in the following table clearly show a lower measurement error Δz for ε.sub.r/k≥0.362 (m.Math.K)/W compared to lower ratios.

TABLE-US-00001 Fiber material Lens material T.sub.max in ° C. Δz in mm ε.sub.r/k in (m .Math. K)/W Silica Diamond 180 3.3 0.006 (Lens) Silica Sapphire 180 2.9  0.25 (Lens) Silica Float Glass 180 0.8    4 (Lens) Silica CaF.sub.2 180 3.7  0.15 (Lens) Silica Teflon 180 1.3  8.4 (Lens) Silica Acrylic 180 1.2  13.5 (Lens) Acrylic Acrylic 180 1.4  13.5 (Both) Sapphire Sapphire 180 3.0  0.25 (Fiber) Sapphire Silica 180 2.5  0.25 (Fiber)

LIST OF REFERENCE NUMBERS

[0254] 110 Measurement head [0255] 112 Object [0256] 114 Transfer device [0257] 116 Optical receiving fiber [0258] 118 Entrance face [0259] 120 Optical axis [0260] 122 Light beam [0261] 124 Spacer device [0262] 126 kit [0263] 128 detector [0264] 130 Illumination source [0265] 132 Light source [0266] 134 Optical illumination fiber [0267] 136 Light beam [0268] 138 Exit face [0269] 140 optical sensor [0270] 142 First optical sensor [0271] 144 Second optical sensor [0272] 146 Light-sensitive area [0273] 148 Evaluation device [0274] 150 divider [0275] 152 position evaluation device [0276] 154 Entrance end [0277] 156 Exit end [0278] 158 Fourth fiber [0279] 160 first optical receiving fiber [0280] 162 Second optical receiving fiber [0281] 164 actuator [0282] 166 core [0283] 168 cladding [0284] 170 buffer [0285] 172 Outer jacket