OPTOELECTRONIC SENSOR AND METHOD OF DETECTING OBJECTS IN A MONITORED ZONE

Abstract

An optoelectronic sensor for detecting objects in a monitored zone that has a light receiver having a reception optics arranged in front of it for generating a received signal from received light that impinges the sensor in a direction of incidence of light from the monitored zone, wherein the reception optics comprises a flat light guide plate having a first main surface and a lateral edge bounding the first main surface at a side; wherein the first main surface of the light guide plate is arranged transversely to the direction of incidence of light and has a diffractive structure to deflect the incident received light to the lateral edge; and wherein a control and evaluation unit is provided to evaluate the received signal.

Claims

1. An optoelectronic sensor for detecting objects in a monitored zone, the optoelectronic sensor comprising a light receiver having a reception optics arranged in front of it for generating a received signal from received light that impinges the optoelectronic sensor in a direction of incidence of light from the monitored zone, wherein the reception optics comprises a flat light guide plate having a first main surface and a lateral edge bounding the first main surface at a side; wherein the first main surface of the light guide plate is arranged transversely to the direction of incidence of light and has a diffractive structure to deflect the incident received light to the lateral edge; and a control and evaluation unit to evaluate the received signal, wherein the light receiver is spatially resolving; and wherein the control and evaluation unit is configured to acquire a piece of distance information of a detected object from the point of impingement of the received light on the light receiver.

2. The optoelectronic sensor in accordance with claim 1, wherein the optoelectronic sensor is one of a light barrier and a light sensor.

3. The optoelectronic optoelectronic sensor in accordance with claim 1, that is configured as a background masking light sensor in which the light receiver has a near zone and a far zone and that has a switching outlet whose switching state depends on whether an object is detected in the near zone.

4. The optoelectronic optoelectronic sensor in accordance with claim 1, that is configured as a triangulation sensor in which the control and evaluation unit measures the distance of the detected object from the point of impingement of the received light on the light receiver.

5. The optoelectronic sensor in accordance with claim 1, that has a light transmitter in a triangulation arrangement with respect to the light guide plate.

6. The optoelectronic sensor in accordance with claim 1, wherein the diffractive structure has a grating structure.

7. The optoelectronic sensor in accordance with claim 6, wherein the grating structure is one of a blazed grating and an echelette grating.

8. The optoelectronic sensor in accordance with claim 1, wherein the reception optics has a plurality of flat light guide plates at whose lateral edges a respective light reception element of the light receiver is arranged.

9. The optoelectronic sensor in accordance with claim 8, wherein the light guide plates are arranged rotated with respect to one another with respect to a normal on their main surfaces.

10. The optoelectronic sensor in accordance with claim 9, wherein two light guide plates are arranged rotated with respect to one another by 180 with respect to a normal on their main surfaces.

11. The optoelectronic sensor in accordance with claim 10, wherein the control and evaluation unit is configured to determine the piece of distance information from a difference of the first received signal of the light reception element associated with the first light guide plate and of the second received signal of the light receiver element associated with the second light guide plate.

12. The optoelectronic sensor in accordance with claim 11, wherein the control and evaluation unit is configured to determine the piece of distance information from the quotient of the difference and sum of the first received signal and the second received signal.

13. The optoelectronic sensor in accordance with claim 8, wherein the diffractive structures of the light guide plates are configured to deflect respective received light having a direction of incidence of light of an acceptance angle range, with the acceptance angle ranges of the light guide plates being different.

14. The optoelectronic sensor in accordance with claim 1, wherein the light receiver is configured to determine the point of impingement of the received light at the lateral edge of a light guide plate.

15. The optoelectronic sensor in accordance with claim 14, wherein only one single light guide plate is provided.

16. The optoelectronic sensor in accordance with claim 14, wherein a diaphragm is arranged in front of the main surface.

17. The optoelectronic sensor in accordance with claim 14, wherein the light transmitter is arranged with respect to the light guide plate such that the direction of incidence of light varies with the distance of the detected object at an angle transversely to the direction of the lateral edge.

18. The optoelectronic sensor in accordance with claim 17, wherein the light transmitter is arranged with respect to the light guide plate such that the direction of incidence of light is in an acceptance angle range of the diffractive structure.

19. A method of detecting objects in a monitored zone in which a light receiver having a reception optics arranged in front of it generates a received signal from received light incident with a direction of incidence of light, wherein the received light impinges transversely on a first main surface of a flat light guide plate of the reception optics and is deflected in the flat light guide plate by means of a diffractive structure to a lateral edge bounding the first main surface, wherein the light receiver is spatially resolving; and wherein a piece of distance information of a detected object is acquired from the received signal in accordance with the point of impingement of the received light on the light receiver.

Description

[0044] The invention will be explained in more detail in the following also with respect to further features and advantages by way of example with reference to embodiments and to the enclosed drawing. The Figures of the drawing show in:

[0045] FIG. 1 a schematic view of an optoelectronic sensor with a flat plate collector as a reception optics;

[0046] FIG. 2 a schematic view of a further embodiment of an optoelectronic sensor as a light sensor or as a reflection light barrier;

[0047] FIG. 3 a schematic plan view of a reception optics configured as a flat plate collector;

[0048] FIG. 4 a three-dimensional view of an exemplary beam extent in a reception optics in accordance with FIG. 3;

[0049] FIG. 5 a further representation of the beam extent in the reception optics to explain double impingements;

[0050] FIG. 6 a representation of which angles of incidence lead to a light reception at which lateral location X on the flat plate collector and which do not;

[0051] FIG. 7 a representation of the coupling efficiency of the flat plate collector in dependence on the angle of incidence ;

[0052] FIG. 8 a representation of an arrangement of two flat plate collectors rotated by 180 with respect to one another for a distance measurement;

[0053] FIG. 9 a schematic representation of the point of impingement of the received light on a light receiver migrating in accordance with the triangulation principle;

[0054] FIG. 10 a spatially resolved light receiver built up of a plurality of flat plate collectors for distance measurement in accordance with the triangulation principle;

[0055] FIGS. 11a-d various arrangements of flat plate collectors rotated with respect to one another for a distance measurement in accordance with the triangulation principle;

[0056] FIG. 12 a plan view of a flat plate collector to explain a distance measurement with only one flat plate collector with an arrangement of light transmitter to flat plate collector rotated by 90 to utilize a perpendicular angle component of the direction of incidence of the received light for a triangulation;

[0057] FIG. 13 a sketch for the explanation of the angle component ;

[0058] FIG. 14 a three-dimensional view similar to FIG. 4, but in a varied perspective and with a reception optics having an additional deflection element at the outlet side;

[0059] FIG. 15 a schematic plan view of a reception optics configured as a flat plate collector and with a non-linear grating structure;

[0060] FIG. 16 a schematic plan view of a reception optics configured as a flat plate collector with a plurality of segments; and

[0061] FIG. 17 a three-dimensional view of an exemplary beam extent in a reception optics in accordance with FIG. 16.

[0062] FIG. 1 shows a schematic block diagram of an optoelectronic sensor 10. Received light 12 from a monitored zone 14 is incident on a flat reception optics 16 having a large aperture with a direction of incidence of light corresponding to the arrows to collect as much received light 12 as possible. The reception optics 16 initially deflects the received light 12 laterally and then a further time back into the direction of incidence of light before it is incident on a light receiver 18, The second deflection is optional; otherwise the light receiver 18 is oriented perpendicularly.

[0063] The reception optics 16 and its light deflection will be explained in more detail below in different embodiments with reference to FIGS. 3 to 17. Only its rough geometrical design is provisionally of interest, namely that it is particularly flat.

[0064] The light receiver 18 generates an electronic received signal from the incident received light 12, said electronic received signal being supplied to a control and evaluation unit 20. In FIG. 1, the control and evaluation unit 20 is only shown symbolically as a circuit board on which the light receiver 18 is also arranged. They are generally any desired analog and/or digital evaluation modules such as one or more analog circuits, microprocessors, FPGAs, or ASICs, with or without an analog preprocessing.

[0065] The parallel alignment of the reception optics 16, the light receiver 18, and the circuit board with the control and evaluation unit 20, on which other electronics can also be accommodated, permits a total structure of the optoelectronic sensor in the shown flat construction with an extremely small construction depth of only a few millimeters.

[0066] Due to the deflection, the control and evaluation unit 20 receives a summary intensity signal that is suitable for evaluations in which the light spot geometry or a piece of angular information of the incident received light 12 is not required. An example is a threshold value comparison to determine the presence of objects. Time of flight measurements are also conceivable provided that the demands on accuracy are not too high since in the millimeter range different light paths mix in the reception optics 16. The result of the evaluation, for example a switching signal corresponding to the binary object determination signal or a measured distance can be output at an interface 22.

[0067] The sensor 10 shown in FIG. 1 is passive, that is it receives received light 12 of any desired source. Instead, however, received light 12 from an associated light transmitter can also be received. In the case of a through beam sensor, the light transmitter is located on the oppositely disposed side of the monitored zone 14 and the control and evaluation unit 20 can recognize objects in the beam path by an intensity drop because they cover the light transmitter.

[0068] FIG. 2 shows a further embodiment of an optoelectronic sensor 10 having its own light transmitter 24 together with an associated transmission optics 26. The received light 12 is in this case its own transmission light 28 after it has been reflected back in the monitored zone 14. This is the principle of a light sensor that recognizes an object 30 when the transmitted light 28 is incident thereon and is remitted. However, it is also the functional principle of a reflection light barrier to which a cooperative reflector 32 belongs to which the transmitted light 28 is aligned. The control and evaluation unit 20 in this case expects the received light 12 reflected back by the reflector 32. If an object 30 moves in front of the reflector 32, the received level drops and the object 30 can be recognized thereby; for example again by a threshold value comparison. To distinguish its own transmitted light 28 from extraneous light and thus to make the switching behavior substantially more robust, two polarization filters can be arranged in the transmission and reception path whose direction of polarization is crossed in accordance with a polarization rotation of the reflector 32.

[0069] FIG. 3 shows a schematic plan view of the reception optics 16. The received light 12 is shown symbolically by a plurality of arrows whose direction of incidence is substantially perpendicular to the plane of the paper which can only be perspectively indicated.

[0070] The reception optics 16 has a flat light guide plate 34 or a flat plate collector. In a plan view, only the upper main surface 36 or a flat side of the flat light guide plate 34 can be recognized. In the depth direction perpendicular to the plane of the paper, the light guide plate 34 is very thin; its thickness is smaller by factors than the lateral extent of the main surface 36. The light guide plate 34 collects received light 12 with a very large aperture with the main surface 36.

[0071] A diffractive structure 38 on the light guide plate 34 provides a deflection of the received light 12 toward a lateral edge 40. The diffractive structure 38 can be upwardly arranged at the first main surface 36 and/or downwardly at the oppositely disposed flat side. After the deflection, received light 12a propagates in a new direction, to the right in FIG. 3, within the light guide plate 34, and is guided in total reflection in so doing. The lateral edge 40 is not necessarily only a single straight part piece, but can also be straight in parts with edge segments at an angle close to 180 with respect to one another or can be curved.

[0072] The diffractive structure 38 can in particular be an echelette grating (blazed grating). Such an echelette grating diffracts incident received light 12 of a defined wavelength by a very large amount and almost only in one specific order of diffraction. The diffraction is therefore chromatically selective, which simultaneously provides the advantage of an optical bandpass effect that can be matched to its own light transmitter 24. The diffraction is additionally very direction-specific due to the high maximum in an order of diffraction. A new preferred direction of the bundle of beams toward the lateral edge 40 is thereby produced at such flat angles that the deflected received light 12a remains in the light guide plate 34 due to total reflection. No received light 12 is diffracted in the direction of the further edges of the light guide plate 34 so that nothing is lost there either. It would, however, also be possible to apply a mirror coating here.

[0073] At least one component of the received light 12 is incident on the plane of the paper on the reception optics 16 along the normal. The differences from the normal are described here and in the following using two angles and . Since they relate to said normal, both angles , are measured in a first and second plane perpendicular to the main surface of the reception optics 16 or in FIG. 3 the plane of the paper. The first plane of the angle additionally comprises the main direction of deflection of the deflected received light 12 toward the lateral edge 40 and is a horizontal plane perpendicular to the plane of the paper in FIG. 3. The second plane of the angle is perpendicular to the first plane and is a vertical plane perpendicular to the plane of the paper in FIG. 3.

[0074] Optionally, a second light collecting or light concentrating function adjoins the coupling into the light guide plate 34 by the diffractive structure 38 and thus the deflection in the light guide plate 34 to the lateral edge 40. For this purpose, an optical funnel element 42 is preferably arranged at the lateral edge 40. The optical funnel element 42 is an element that tapers in the cross-section and that generates the received light 12b concentrated in a transverse direction of the funnel element 42 in parallel with the extent of the lateral edge 40.

[0075] The beam extent in the reception optics 16 becomes better understandable by a simulated example that is show in a three-dimensional view in FIG. 4. The two angles and are again also drawn here by which the respective direction of incidence can be described. The received roughly perpendicular incident light 12 with the differences in and is diffracted at the upper side or lower side by the diffractive structure 38 and is conducted as deflected received light 12a to the lateral edge 40. It becomes concentrated received light 12b in the optical funnel element 42 that is incident on the light receiver 18 arranged at a beam exit point of the funnel element 42.

[0076] The received light 12 is thus concentrated in both cross-sectional directions. The extent is limited in the vertical direction by the small thickness of the light guide plate 34 that continues in the optical funnel element 42 or that is even further reduced there. The focusing effect or concentration effect comes into force in the width direction, in parallel with the lateral edge, due to the cross-section reducing geometry of the optical funnel element 42. Both axes satisfy the condition of the waveguide-led total reflection. The light guide plate 34 and the optical funnel element 42 are manufactured from suitable transparent plastic such as PMMA or PC. Mirror coatings can be applied to support the total reflection.

[0077] The optical funnel element 42 is preferably equally of a flat design like the light guide plate 34 and thus directly adjoins the shape of the lateral edge 40. It is possible to configure both in one piece. To further optimize the beam shaping in the optical funnel element 42, the taper can also have a parabolic or a different tapering cross-sectional extent.

[0078] It has been explained that the light guide plate 34 and the optional funnel element collect the received light 12 and the light receiver accordingly only produces a common received signal. In accordance with the invention, however, a distance should be measured by a triangulation principle and a distinction should be made for this purpose between different angles of incidence. The light receiver 18 is therefore first configured as spatially resolving, i.e. from a plurality of discrete light receivers, for example photodiodes, as a PSD (position sensitive device) or as an integrated reception pixel arrangement, for instance in the form of a receiver array. This alone would, however, not yet lead to the objective since the received light 12b arriving at the light receiver 18 no longer includes the desired spatial information at all due to the light collecting properties of the reception optics 16. To understand the different embodiments with which a spatially resolved detection and thus a kind of triangulation is nevertheless achieved, the light guidance in the light guide plate 34 should first be described even more exactly with reference to FIGS. 5 to 7.

[0079] For this purpose, FIG. 5 first again shows a longitudinal sectional view of the coupling of received light 12 into the reception optics 16 and of the beam extents therein. The received light 12 is incident onto the diffractive structure 38, that has a length L, at the angle and is diffracted in the direction toward the light receiver 18. For this purpose, an order of diffraction different from zero is used, typically the first order of diffraction, with the diffractive structure 38 preferably being optimized such that practically all the received light 12 is diffracted in this order of diffraction. Practically no received light 12 reaches the light receiver 18 any more for angles that are too large outside the acceptance angle range. Depending on the point of impingement, the angle , the length L, and the configuration of the diffractive structure 38, it may occur that an incident light beam 12 impinges on the diffractive structure twice, a so-called double impingement. This is shown for the light beam 12 in FIG. 5.

[0080] Such light beams 12d are decoupled to a large extent and a substantial portion is lost for the detection since the portion reflected at the diffractive structure on a double impingement is considerably weakened.

[0081] FIG. 6 is a compact representation of the coupling and guidance properties of the light guide plate 36 without a funnel element 42. The angle of incidence is entered on the X axis, the lateral point of impingement X of the received light 12 on the light guide plate 34 on the Y axis, see also FIG. 5 again for the definition of and X. Black regions of the parameter space shown stand for no light guidance or for only a greatly weakened light guidance up to the light receiver 18; conversely, white regions stand for a high coupling onto the light receiver 18.

[0082] The two black strips to the left and right correspond to a non-adapted angle of incidence : either the condition for total reflection is no longer satisfied in the left region after the deflection so that the received light 12 is not guided in the light guide plate 34 or a diffraction only takes place grazingly or no longer at all in the right region. This acceptance region can be varied by properties of the diffractive structure 38, in particular its period, the wavelength of the received light 12, and the refractive index of the material of the light guide plate 34.

[0083] The circle-segment like double impingement region 46 is determined by the position of impingement and thus by the macroscopic geometry of the light guide plate 34 and of the arrangement in the sensor 10. This region in particular grows as the length L of the diffractive structure increases and vice versa. It is of particular interest that the double impingement region 46 is practically only at a negative . This produces asymmetry in the coupling efficiency at a of the same amount, but of a different sign that should be examined more exactly next.

[0084] For this purpose, the coupling efficiency is entered in FIG. 7 in dependence on for an exemplary light guide plate 34 having a diffractive structure 38 with a grating of the period 500 nm and a length L=5 mm as well as a funnel element 42 of 10 mm in length. The shown angle-dependent coupling function is only an example; it can be influenced by the design of the diffractive structure 38 and of the construction of the light guide plate 34.

[0085] In a simple model of an angle-selective diffractive structure 38 such as a blazed grating, a symmetrical arrangement would have to be expected here in which the coupling efficiency drops abruptly at both sides from a specific angle onward. In fact, however, a very shallow flank that starts at approximately 16 and even still reaches into the positive range at +1 is shown for negative angles . This can be utilized as a kind of working region of non-constant coupling efficiency to measure the angle of incidence and so to triangulate a distance.

[0086] FIG. 8 for this purpose shows as a possible embodiment a plan view of an arrangement of two partial reception optics 16a-b each having a light guide plate 34a-b and an optional funnel element 42a-b. They each collect the received light 12 on a light reception element 18a-b of their own. The two light reception elements 18a-b together form a spatially resolved light receiver 18 since the received signals of the light reception elements 18a-b are distinguished. Alternative arrangements of partial reception optics 16a-b and light reception elements 18a-b will be explained later with reference to FIGS. 11a-d.

[0087] As seen at FIG. 7, the coupling efficiency is asymmetrical with respect to the angle , with this asymmetry being a direct consequence of the double impingement or of the double impingement region 46. The two partial reception optics 16a-b therefore produce different received signals with light incident from a specific angle . A conclusion on the angle can therefore be drawn from a comparison of the two received signals S1 and S2 of the light reception elements 18a-b. The difference S1S2 is formed, for example, or for independence from the total level, preferably the signal contrast (S1S2)/(S1S2). The two received signals S1 and S2 can be called near signals and far signals because the angle depends on the distance of the detected object that reflects the received light 12.

[0088] Alternatively or additionally to the described utilization of the asymmetry of the coupling efficiency, it is also conceivable to use a plurality of diffractive structures 38 having different acceptance angles and thereby to sort the different possible angles of incidence through a plurality of partial reception optics to different light reception elements.

[0089] For this purpose, FIG. 9 first again sown how the angle of incidence differs with the object distance. The received light 12 therefore impinges at a different angle of incidence in dependence on the object distance and the received light spot migrates on the light guide plate 34.

[0090] FIG. 10 shows an arrangement of a plurality of partial reception optics 16a-d each having an associated light reception element 18a-d to evaluate the different reception angles . The light reception elements 18a-d can be discrete elements, but also regions of a pixel-resolved light receiver that together as a spatially resolved light receiver 18 produce four received signals.

[0091] The respective diffractive structures 38 of the light guide plates 34a-d are adapted to a specific and different angular range of their respective own. As can be recognized in FIG. 9, this corresponds to a respective distance region.

[0092] Each part structure 16a-d, 18a-d is accordingly responsible for a part interval of the distance region to be detected in total. The part intervals complement one another, preferably also with a certain overlap. The part structures 16a-d, 18a-d are thus near and distance zones or corresponding central zones.

[0093] The shown number of four part structures 16a-d, 18a-d is purely exemplary as is their arrangement next to one another. FIGS. 11a-d show a plurality of variations that are still by no means exclusive and that are suitable for embodiments with a utilization of the asymmetry of the coupling efficiency, as explained with respect to FIG. 8, and/or for distance dependent responsibilities of the respective diffractive structure 38, as just explained with respect to FIGS. 9 and 10. Although no different diffractive structure 38 is indicated by pattern fillings, as in FIG. 10, the part structures in FIGS. 11a-d can each be adapted to specific mutually complementing angular ranges .

[0094] FIG. 11a shows an arrangement of four part structures 16a-d, 18a-d arranged in star shape. In this respect, in particular two respective part structures 16a, c; b, d are, as in FIG. 8, rotated by 180 with respect to one another. FIG. 11b shows a further arrangement of four part structures 16a-d, 18a-d in a more compact arrangement and a pairwise rotation by 90. In FIG. 11c, three part structures 16a-c, 18a-c are arranged behind one another instead of next to one another as in FIG. 10. In FIG. 11d, three part structures 16a-c, 18a-c are in turn arranged next to one another, but due to a corresponding shape of the funnel elements 42a-c, the distance between the light reception elements 18a-c varies, which can facilitate the real design of the light receiver 18.

[0095] In the previous embodiments, the distinguishing of the angles of incidence was achieved in that a plurality of light guide plates 34 each having a simple light reception element were used that were each responsible for specific angles of incidence. It is, however, also possible to distinguish angles of incidence with only one light guide plate 34 and its diffractive structure.

[0096] FIG. 12 shows a plan view of a light guide plate 34 or of its diffractive structure 34. The spatially resolving light receiver 18 is arranged at the lateral edge 40. So that a localizable received light spot is produced at all, a diaphragm 48 is arranged on the main surface 36 of the light guide plate 34.

[0097] In contrast to the previous embodiments, the total light deflected by the light guide plate 34 is not deflected by only one light reception element and converted into a summary received signal. A distinction is rather made by the spatially resolving light receiver 18 where received light 12 is incident on the lateral edge 40. A plurality of discrete or pixel-like light reception elements 18a are associated with the same light guide plate 34 or with the diffractive structure 38. A PSD can alternatively be used. The optional funnel element 42 is dispensed with.

[0098] The angle was previously used for the distance measurement. Here it is now the angle perpendicular thereto. Both angles , were already introduced with respect to FIGS. 3 and 4 and are drawn again in FIG. 12. The previous implicit assumption was that the decoupling at is symmetrical and the angle was therefore neglected. The diffractive structure 38, however, is not only effective in the direction of the angle where an almost complete deflection takes place when the narrow acceptance angle range is maintained. The diffractive structure 34 acts almost as a mirror in the direction of the angle . Received light 12 is therefore deflected in the direction of the lateral edge 40 and there impinges on a specific point in dependence on the angle . The angular range for in which this works with a good coupling efficiency is particularly large when includes the ideal acceptance angle.

[0099] In the shown arrangement of the light transmitter 24, the received light 12 impinges at a different angle in dependence on the detected object. The point of impingement migrates due to the effective effect of the diffractive structure 38 on this angular component similar to a mirror in the representation in a vertical direction.

[0100] This is shown again from a different perspective in FIG. 13. The representation of FIG. 12 is rotated counterclockwise by 90 and is then again rotated by 90 to the rear into the plane of the paper. The light receiver 18 can thereby not be recognized; it is behind the light guide plate 34. The point of impingement migrates from left to right in accordance with the varying angle .

[0101] In order therefore to be able to measure using the angle , the light transmitter 24 is, as shown, to be offset in the direction corresponding to with respect to the light guide plate 34. The light transmitter 24 therefore has is triangulation offset in the direction of the lateral edge 40. The additional lateral offset serves the purpose that the different angle corresponds to the optimum acceptance angle. The angle does not vary here, however, but is rather fixed by the design, and indeed preferably to the ideal acceptance angle =0 so that a large angular range having good coupling efficiency is achieved for the angle .

[0102] With a suitable arrangement of the light transmitter 24, the angle varying with the distance is converted into an angle after the deflection. This in turn leads to a specific point of impingement on the spatially resolving light receiver 18. As can be seen, the offset on the spatially resolving light receiver 18 additionally relates linearly to the distance L, that is to the lateral extent of the light guide plate 34 if it is assumed that the aperture of the diaphragm 48 is respectively arranged at the outer margin. The sensitivity of the sensor 10 can thus be defined by this length L in a similar manner to the focal length of the lens with a conventional triangulation. With a larger L, a specific leads to a larger offset on the light receiver 18; the distance measurement therefore becomes more sensitive, and vice versa.

[0103] A distance measurement can take place with only one single light guide plate 34 or diffractive structure 38 using this embodiment. It is nevertheless also conceivable to combine this with the other embodiments and thereby, for example, to divide the total range to be covered in part portions, with now distances not only being able to be associated in a class-like manner, but also being able to be measured in each part portion with the embodiment in accordance with FIGS. 12 and 13.

[0104] All the embodiments described can be supplemented by further optical elements. For example, further angle filters and frequency filters can be affixed in front of the diffractive structure 38. Further variations will now be explained.

[0105] FIG. 14 again shows a three-dimensional view of an exemplary beam extent in a reception optics 16. Unlike FIG. 4, the light receiver 18 itself is not already located at the beam exit side of the funnel element 42, but a further deflection element 44 is rather first arranged therebetween for the light coupling into the light receiver 18. The exiting received light 12c thereby practically again returns to the original direction of incidence of light, only laterally offset and widened by the extent of the reception optics 16, which does not, however, play any role in the proximity of the light receiver 18. Due to the direction of incidence of light, the light receiver 18 can be aligned in parallel with the main surface 36 and this enables the particularly flat arrangement shown in FIG. 1 having a circuit board of the control and evaluation unit 20 in parallel with the reception optics 16.

[0106] The deflection element 44 is designed as a deflection prism in FIG. 14. The prism can have planar surfaces or can additionally have a light focusing shape, for instance with spherically or aspherically curved surfaces or with a free-form surface. The prism, like the optical funnel element 42, can be at least partly mirror coated to reduce decoupling losses, in particular at the end of the optical funnel element. Alternatively to a separate deflection element 44, it is also conceivable to configure the optical funnel element 42 with a kind of downwardly directed continuation, preferably with a mirror coating that satisfies this function. The light guide plate 34, the funnel element 42 and/or the deflection element 44 can be formed in one piece.

[0107] FIG. 15 shows a plan view of a further embodiment of the reception optics 16. in the previous embodiment, for instance in accordance with FIG. 3, the diffractive structure 38 is configured as a linear grating arrangement. A pure deflection and a concentration only in the depth direction of the light guide plate 34 accordingly take place. The concentration in the second lateral axis only takes place in the optical funnel element 42 there.

[0108] In the embodiment in accordance with FIG. 15, a non-linear grating arrangement is instead provided as the diffractive structure. The received light 12 is thereby already immediately concentrated in both axes. The funnel element 42 can accordingly be shorter or even be completely omitted.

[0109] FIG. 16 shows a plan view of a further embodiment of the reception optics 16. The light guide plate 34 is here divided into at least two segments 34a-c that are approximately of cross-strip type and divide the lateral edge 40 accordingly. The number of segments is initially not limited. The segments 34a, c are slightly inwardly tilted, with the exception of the central segment 34b. Strictly speaking, this is only relevant to the linear grating arrangement 38a, c thereon.

[0110] A certain concentration also already takes place in a lateral direction due to the segmented arrangement of linear grating arrangements 38a-c. The segmentation is therefore an alternative to a non-linear grating arrangement in accordance with FIG. 15 to manage with a shorter funnel element 42 or even completely without the funnel element 42. A segmentation in accordance with

[0111] FIG. 16 can, however, also be combined with non-linear grating structures in accordance with FIG. 15.

[0112] FIG. 17 illustrates an exemplary optical path in a reception optics 16 having a segmented light guide plate 34a-c as in FIG. 16 in a three-dimensional view. An angle of 9 was here selected as the setting angle of the outer segments 34a, c. The surface at the inlet, that is in the main surface 36, amounts to 4 mm*4.2 mm; at the outlet in front of the light receiver 18, the surface amounts to 1.2 mm*1.2 mm. A coupling efficiency of the total reception optics 16 of 56% can thus be achieved overall with a partially mirror-coated deflection prism 44.

[0113] A reception aperture of 25 mm.sup.2 and more is, for example, achieved with a diffractive flat plate collector in accordance with the invention with a construction depth of only 1 mm. Larger reception apertures of, for example, 6 mm*8 mm are also possible. The signal gain thus increases by an order of magnitude; the range of the sensor can be increased by factors of two, three, and more. There are in this respect extremely small construction depths of, for example, only 3.5 mm that would only permit a conventional aperture of 1.5 mm. In accordance with the invention, these 1.5 mm are available for the thickness of the flat reception optics 16 that, however, provides an immeasurably larger surface with edge lengths that exceed the thickness by a factor of two, three, and more in both directions.