Test bench for exciting a photodetector

Abstract

The invention relates to a test bench for exciting a photodetector, comprising a light signal device, which comprises a surface structure of light-emitting devices that can be activated and deactivated independently of one another, and is designed to emit light emitted by any light-emitting device in at least approximately collimated light beams, a converging lens, which is designed and arranged to focus the light beams emitted from the light signal device at a point of accumulation, and a holding device for the photodetector arranged at the point of accumulation, by means of which the photodetector can be placed at the point of accumulation such that a first light beam generated in accordance with any first light-emitting device and a second light beam generated in accordance with any second light-emitting device reach the photodetector at different spatial angles with respect to the optical axis of the test bench.

Description

Background Technology

[0001] An environmental detection system is a sensor system configured to analyze and process sound waves or electromagnetic waves emitted by an object in order to detect the object. An active environmental detection system is configured to transmit a signal into the environment and analyze the reflection of the signal, for example, to locate the object based on the direction and round-trip time of the reflection, or to measure the object's velocity based on the frequency shift of the reflection. Otherwise, it is called a passive environmental detection system. According to current technology, active environmental detection systems are typically based on ultrasound, radio waves (radar), or shortwave light (LiDAR). Examples of passive systems are camera systems that analyze and process images, motion sensors, and passive radar.

[0002] Environmental monitoring systems are used in safety-critical systems, such as for controlled robots or automated vehicles, and therefore require particularly thorough evaluation before mass deployment to eliminate potential faults as much as possible. For this purpose, target simulators exist on the market. A test bench can be understood as being configured to record signals emitted by an active environmental monitoring system for detecting an object and to generate time-delayed echo signals, in order to simulate the reflection of signals on the object for the environmental monitoring system.

[0003] An example of a radar target simulator is the radar test bench from dSPACE LLC. The radar test bench includes multiple antennas arranged on a rotatable ring, which can be used to simulate radar echoes arriving from different directions to a radar system positioned as a test sample (product information "Radar Test Bench" can be accessed at https: / / www.dspace.com / shared / data / pdf / 2020 / dSPACE-Radar-Testbench_Product-Information_2020-03_E.pdf).

[0004] Meanwhile, schemes for lidar target simulators used in lidar systems are also known. An exemplary description can be found in the paper "LIDAR echo emulator (International Conference on SpaceOptics–ICSO 2018)" by PawelAdamiec et al. The target simulator described therein includes two laser diodes used to simulate two reflections of lidar signals, which are transmitted to the test sample via fiber optic cables. For some test cases, however, such a construction is too simplistic. As an example, a lidar system designed for driving autonomous or highly automated vehicles should be mentioned. Such lidar systems are configured to simultaneously locate multiple objects in the vehicle's environment. Accordingly, the target simulator suitable for testing such lidar systems should support multiple targets; that is, the target simulator should be designed to generate multiple simulated reflections that can reach the photodetectors of the environmental detection system, which is the test sample, from different spatial directions over a sufficiently large span. Summary of the Invention

[0005] Against this backdrop, a novel structure for a test bench based on a light-based environmental monitoring system is proposed. The environmental monitoring system can be understood as follows: its functional principle is based on detecting electromagnetic waves emitted by an object, particularly those from the visible, ultraviolet, or infrared spectrum, using a photodetector.

[0006] This invention relates to a test stand for stimulating a photodetector. The test stand includes an optical signaling device comprising a surface structure of light-emitting devices that can be independently activated and deactivated, and is designed to emit light emitted from any of the light-emitting devices in a beam that is at least approximately collimated, i.e., parallel oriented.

[0007] In other words, for the test stand according to the invention, it is important that each light-emitting device can be driven individually and independently of other light-emitting devices on the optical signaling device in order to emit light; and the optical signaling device is configured to emit light generated by each light-emitting device individually as at least approximately collimated beams, such that the activation of a certain number of light-emitting devices causes the same number of at least approximately collimated beams to be emitted from the optical signaling device, wherein each beam is emitted from exactly one activated light-emitting device.

[0008] The test stage also includes a converging lens, which is designed and arranged to focus a beam of light emitted from the optical signaling device onto a focal point. If the optical signaling devices are designed to emit beams that are parallel to each other and parallel to the optical axis of the converging lens, then the focal point is located at the same position as the focal point of the converging lens.

[0009] A holding device for the photodetector is arranged at the accumulation point, and the photodetector can be placed at the accumulation point by means of the holding device, such that a first light beam generated by any first light-emitting device and a second light beam generated by any second light-emitting device reach the photodetector at different spatial angles relative to the optical axis of the test stage.

[0010] The test stand according to the invention supports multiple targets. Depending on the resolution of the optical signaling device, a substantially arbitrary number of beams can be generated simultaneously to simulate an arbitrary number of targets in different spatial directions for a photodetector or an environmental detection system including a photodetector. Simultaneously, the test stand is relatively cost-effective and low-maintenance because it can operate using a planar optical signaling device and does not include moving parts. To simulate multiple targets using the test stand, it is stipulated that a plurality of spatial angles are predetermined from a range of spatial angles, said range covering the field of view of the photodetector as a whole, wherein each of the predetermined spatial angles corresponds to the direction of a virtual (i.e., non-real) object simulated in the field of view of the photodetector. Then, a plurality of suitable beams corresponding to the number of spatial angles are emitted by means of the optical signaling device, said beams being focused by a lens to an accumulation point, such that each beam reaches the photodetector arranged at the accumulation point at exactly one of a plurality of spatial angles relative to the optical axis of the test stand.

[0011] For optical signaling devices, different implementation schemes are possible. Optical signaling devices do not necessarily have to be implemented as a uniform component, but can also include multiple spatially separated components.

[0012] In one embodiment, the optical signaling device includes a surface structure consisting of point light sources, such as photodiodes, that can be independently activated and deactivated. Generally, a point light source can be understood as a light source freely arranged in space that does not produce a collimated beam but rather produces a substantially spherical electromagnetic wavefront. To produce at least a nearly collimated beam, the optical signaling device further includes a transparent collimator surface disposed between the surface structure and a converging lens, the collimator surface being designed to absorb or reflect light incident at a sufficiently sharp angle onto the collimator surface.

[0013] Such collimator surfaces are commercially available, for example, as "Light-Control-Film" (LC-Film) or "Kollimatorfolie" by Falcon Illumination MV GmbH & Co. KG. The function of the collimator surface is to ensure that light emitted by each light-emitting device passes only through a portion that is at least approximately parallel to the optical axis of the test stage and oriented accordingly, so that each light-emitting device produces a beam of light that is at least approximately collimated and oriented parallel to the optical axis after the collimator surface.

[0014] The surface structure composed of point light sources can be designed as a surface structure of discrete and self-emissive light sources, such as a photodiode surface structure. In an alternative design, the surface structure includes a background illumination element and a screen arranged between the background illumination element and the collimator surface. The screen is divided into multiple controllable units, each of which can be switched to a transparent or opaque state by controlling a corresponding unit, thereby combining with the background illumination element, with each transparent unit serving as a point light source. The screen can be, for example, a liquid crystal display (LCD). It should be noted that the response time of an LCD may be too high for some applications of the test bench.

[0015] In other possible implementations, the collimator surface can be omitted. For this purpose, the optical signal device can be designed as a collimated light source surface structure, whereby each individual light source directly emits at least a nearly collimated beam when the corresponding light source is activated. For this purpose, the collimator surface can be designed, for example, as a semiconductor laser surface structure or a light-emitting device surface structure, where each light-emitting device is equipped with a collimating lens or a concave mirror.

[0016] Generating a well-collimated beam is technically costly. In particular, collimator surfaces typically only approximate collimation of the incident light. In most, and especially cost-effective, implementations of the test stand, it is desirable to emit a conical beam from the optical signaling device that is only approximately collimated. In an advantageous design, the focal length of the converging lens is chosen such that it compensates for the conical shape of the beam, that is, the conical beam is converted into an electromagnetic wave that is at least approximately planar upon refraction, so that from the perspective of the photodetector, the electromagnetic wave appears approximately as a point of light at infinity. The focal length of the converging lens can also be chosen such that it slightly converges or fans out the conical beam, that is, it also converts the beam into a conical beam, the conical beam having its cone circumference slightly reduced or increased along its path from the lens to the photodetector. From the perspective of the photodetector, this results in a certain degree of blurring of the perceived point of light, which is entirely a desirable technical effect. Unclearity can cause adjacent light spots to blend seamlessly together, which can be advantageous for reliable modeling of patterns (such as vehicle outlines) in automotive LiDAR systems, or for the typically large light spots used to simulate large objects.

[0017] Preferably, the test stand includes a programmable control device configured to drive an optical signal device to activate selected light-emitting devices on the optical signal device according to a predetermined control program programmed on the control device, thereby generating a light pattern on the optical signal device. The light pattern may consist of multiple separately activated light-emitting devices, or it may include an aggregation of adjacent activated light-emitting devices. This is to simulate large light spots or extended objects for the photodetector. The light pattern can be designed to be static or dynamic, i.e., it can change over time. The control program can read information defining the light pattern design from data memory integrated into the test bench, particularly the control device. The control device may include an interface for providing information via an entity (Instanz) located outside the test bench. The control device may also include an interface for storing information in data memory via an entity located outside the test bench. This entity may, in particular, be a simulation computer that processes a simulation in which a virtual entity of the photodetector interacts with a virtual object in a virtual environment, wherein the control device is configured to read the relative position of the virtual object provided by the simulation computer, and drive an optical signaling device such that a beam of light emitted from the optical signaling device for the photodetector simulates light emitted by the virtual object.

[0018] Advantageously, the control program includes simulating the refractive behavior of a converging lens to account for refraction when generating light patterns. In particular, the control program can be designed to account for lens errors and perspective distortion when generating light patterns.

[0019] The test stand can be designed as a target simulator for active environmental detection systems, particularly lidar systems. In this design, the test stand includes a detector for detecting optical signals from an environmental detection system arranged in the test stand as a test sample. The control program is designed to determine the round-trip time and spatial direction of the optical signal reflection on a virtual object, and, by driving the optical signal device, to generate a light pattern for simulating reflection for the photodetector of the environmental detection system, which is positioned in a holding device, according to the predetermined spatial angle and round-trip time. Attached Figure Description

[0020] The invention is further illustrated below with reference to the accompanying drawings. The drawings and their description disclose exemplary embodiments of a test bench according to the invention, designed as a target simulator, and the optical path of the test bench. The drawings are schematic and do not allow for the deduction of the geometry and distances between the components shown. Detailed Implementation

[0021] Figure 1The accompanying drawings illustrate a lidar system 4, which is arranged as a test sample in a test stand 2. The lidar system includes: a laser device 10 for illuminating the environment of the lidar system 4 by means of a light signal in the form of laser pulses in the infrared spectrum; a photodetector 6 arranged in a holding device of the test stand 2 for detecting reflections of the laser pulses on objects in the environment of the lidar system 4; and a control mechanism 8 for driving the laser device 10 and for analyzing the reflections detected by means of the photodetector 6. The analysis may specifically include detecting the spatial angle and round-trip time of the reflection to locate objects in the environment based on the reflection. The analysis may also include image recognition to assign tags to the located objects and mark them, for example, as vehicles, pedestrians, road signs, trees, or buildings. Furthermore, the analysis may include measuring the velocity of the object by repeatedly locating it.

[0022] The test stage 2 includes a control device 12, an optical signal device 16 (arranged along the optical axis 14 of the test stage 2), a plano-convex converging lens 18, and a holding device (not shown) for the photodetector 6. The optical signal device 16 includes a surface structure of a light-emitting device designed as an infrared photodiode 22 arranged on a carrier plate 20, and a transparent collimator surface 24. The carrier plate 20 includes an interface through which each photodiode 22 can be individually activated and deactivated, i.e., turned on and off, independently of other photodiodes.

[0023] The control device 12 is connected to the carrier board 20 via a data line interface to generate a light pattern on the optical signal device 16 by activating or deactivating a selected photodiode 22. For this purpose, the control device 12 includes: a processor 26 on which a control program 28 is programmed; and a data memory 30 on which the relative positions of virtual objects can be stored. For example, two positions of the virtual object are stored in the data memory 30. Each position stored in the data memory 30 is stored in spherical coordinates, i.e., including spatial angles α and β and distances r1 and r2.

[0024] The control device 12 includes an interface (not shown) for storing positions on the data memory 30. The storage of positions can be designed to be arbitrarily complex. In the simplest case, positions are statically stored. These positions can be overwritten by new positions in a predetermined order. The positions can be changed incrementally in small steps to simulate moving objects. Position storage can also be implemented, in particular, by a simulation computer that processes simulations in which a virtual entity of the photodetector 6 interacts with other virtual objects in a virtual environment, wherein the positions stored in the data memory 30 by the simulation computer represent the relative positions of the virtual objects to the photodetector 6 within the field of view of the virtual entity of the photodetector 6. Alternatively, multiple positions can be used to represent a unique virtual object to simulate extended objects or complex geometric structures of objects through multiple spatial points.

[0025] The control device 12 further includes a detector 32 for detecting the optical signal from the laser device 10. The detector 32 is designed, for example, as a photodetector, but other designs are also possible. For example, the detector 32 could be configured to detect control signals transmitted from the control mechanism 8 to the laser device 10 to trigger the optical signal.

[0026] Control program 28 is configured to detect the light signal from laser device 10 using detector 32. Once control program 28 detects the light signal, it retrieves the location stored in data memory 30. Control program 28 calculates the round-trip time of the light signal for each location based on distances r1 and r2, and determines the photodiode 22 to be activated to simulate the reflection of the light signal based on spatial angles α and β. For example, it stores the two locations of two point-like virtual objects, the first object at location (α, r1) and the second object at location (β, r2). Control program 28 calculates the first round-trip time t1 of the light signal's reflection on the first object according to the following formula:

[0027] t1=2cr1

[0028] (c: speed of light). To determine the photodiode 22 to be activated for simulating reflection, control program 28 includes simulating the refractive behavior of converging lens 18, based on which control program 28 performs calculations of the light path along the opposite direction of light travel, as shown in the figures. Control program then takes a beam emitted from photodetector 6 at a spatial angle α relative to optical axis 14 as a starting point and simulates the path of the beam through converging lens 18 to calculate a first initial point of the beam on carrier plate 20. Control program 28 calculates the second round-trip time t2 and the second initial point of the second object in a similar manner.

[0029] To simulate the reflection of a light signal on a first object, the control device 12 activates the photodiode 22 closest to the first initial point or a cluster of photodiodes 22 arranged around the first initial point. To simulate the reflection of a light signal on a second object, the control device 12 activates the photodiode 22 closest to the second initial point or a cluster of photodiodes 22 arranged around the second initial point.

[0030] In the accompanying drawings, two photodiodes 22 are activated based on two reflections to be simulated. Each activated photodiode 22 generates electromagnetic elemental waves 34a, 34b propagating in all free space directions. The collimator surface 24 is an array of optical channels that absorbs all portions of the collimator surface 24 incident at sufficiently sharp angles from each elemental wave 34a, 34b, thereby generating a first conical beam 36a originating from a first initial point and a second conical beam 36b originating from a second initial point after the collimator surface 24.

[0031] Importantly for this invention is that the optical signaling device 16 emits at least approximately collimated light beams 36a and 36b, but collimation does not necessarily occur with the aid of collimator surface 24. Alternatively, the optical signaling device 16 can be designed as a collimated light source surface structure, with each individual light source designed to directly emit at least approximately collimated light beams. For this purpose, the light-emitting device 22 can be designed, for example, as a semiconductor laser or a light source respectively equipped with collimating lenses or concave mirrors.

[0032] The focal length of the converging lens 18 is selected such that it converts the conical beams 36a and 36b into electromagnetic waves 38a and 38b that are at least approximately planar, in other words, improving the collimation of the beams. According to the known law of beam reversibility, the first planar wave 38a generated by the first beam 36a reaches the photodetector 6 at a spatial angle α relative to the optical axis 14; and the second planar wave 38b generated by the second beam 36b reaches the photodetector 6 in a similar manner at a spatial angle β relative to the optical axis 14. The photodetector is then positioned at a point of accumulation where the first planar wave 38a and the second planar wave 38b meet, and in the illustrated case, this point of accumulation coincides with the focal point of the converging lens 18.

[0033] Assuming the planar waves 38a and 38b are perfectly collimated, i.e., representing ideal planar waves, then photodetector 6 perceives the waves as point-like virtual images positioned at infinity with spatial angles α and β within the photodetector's field of view. Under real-world conditions, it is impossible to construct a converging lens 18 that converts each arbitrary beam 36a and 36b into an ideal planar wave. If the planar waves 38a and 38b are at least slightly fanned out or focused, then assuming photodetector 6 focuses at infinity, photodetector 6 perceives the planar waves as indistinct points. As mentioned above, this can be entirely advantageous because the simulation of the extended object is achieved by activating multiple adjacent photodiodes 22, allowing photodetector 6 to perceive the object as uniformly and continuously illuminated. Of course, the focal length of the converging lens 18 can also be intentionally chosen so that it produces slightly focused or fan-shaped planar waves 38a and 38b.

[0034] The activation times of the two photodiodes are selected such that the time elapsed between the light signal emitted by the laser device 10 and the arrival of the planar waves 38a and 38b at the photodiode 6 is equal to the round-trip time, which the control device 12 has calculated for simulating the reflection of the corresponding planar waves 38a and 38b. Specifically, the control device 12 drives the optical signal device 16 such that the wave 38a of the first planar wave arrives at the photodiode 6 exactly after a time interval t1 following the emission of the light signal, and the wave 38b of the second planar wave arrives at the photodiode 6 exactly after a time interval t2. Therefore, the simulation of the refraction behavior of the converging lens 18 implemented in the control program 28 also considers the travel time of the beams 36a and 36b from the carrier plate 20 to the photodiode 6, as well as the signal travel time from the detector 32 to the control device 12, the signal travel time from the control device 12 to the optical signal device 16, and the response time of the photodiode 22.

[0035] In the test scenarios shown in the accompanying drawings and previously described, the focus is on testing the control mechanism 8. Thus, even in extreme cases where readjustment cannot be performed safely in the field or at the test site, the control mechanism 8 can be tested safely and in a reproducible manner in a virtual environment as much as possible. Of course, the test bench 2 can also be used for other testing purposes. For example, the photodetector 6 can be arranged as the sample to be tested independently, without the need for the control mechanism 8 and the laser device 10, and the control device 12 can be programmed to sequentially activate all the light-emitting devices 22 to check the correct functioning of the photodetector 6. Similarly, the test bench 6 can be used for end-of-line testing of the photodetector 6 or the entire lidar system 4.

Claims

1. A test stand (2) for exciting the photodetector (6), wherein, The test bench includes: Optical signal device (16), the optical signal device comprising a surface structure consisting of light-emitting devices (22) that can be activated and deactivated independently of each other, and designed to emit light emitted from any of the light-emitting devices (22) in a beam (36a, 36b) that is at least approximately collimated; Converging lens (18), the converging lens being designed and arranged to focus a beam of light (36a, 36b) emitted from the optical signal device (16) at a point of accumulation; and A holding device for the photodetector (6) is arranged at the accumulation point, by means of which the photodetector (6) can be placed at the accumulation point such that a first light beam (36a) generated by any first light-emitting device and a second light beam (36b) generated by any second light-emitting device reach the photodetector (6) at different spatial angles (α, β) relative to the optical axis (14) of the test stage (2). Among them, a plurality of spatial angles (α, β) are predetermined from the range of spatial angles, the range covering the field of view of the photodetector (6) in its entirety, wherein each of the plurality of spatial angles (α, β) corresponds to the orientation of a virtual object simulated in the field of view of the photodetector (6); In this process, multiple beams (36a, 36b) corresponding to the number of spatial angles (α, β) are emitted by means of an optical signal device (16), and the beams are focused to the accumulation point by a converging lens (18) such that each beam (36a, 36b) reaches the photodetector (6) at exactly one of the multiple spatial angles (α, β) relative to the optical axis (14). The control program (28) of the test bench includes simulating the refraction behavior of the converging lens (18) so as to take the refraction behavior into account when generating light patterns.

2. The test bench (2) according to claim 1, wherein, The optical signal device (16) of the test stand includes a surface structure composed of point light sources that can be activated and deactivated independently of each other; The optical signal device (16) of the test stage includes a transparent collimator surface (24) arranged between the surface structure and the converging lens (18), the collimator surface being designed to absorb or reflect light incident on the collimator surface at a sufficiently sharp angle.

3. The test bench (2) according to claim 2, wherein, The surface structure of the test platform, composed of point light sources, is designed as a surface structure of discrete and self-emissive light sources.

4. The test bench (2) according to claim 2, wherein, The surface structure of the test platform, composed of point light sources, includes a background lighting element. Furthermore, it includes a screen arranged between the background lighting element and the collimator surface (24), the screen being divided into multiple controllable units, each of which can be switched to a transparent or opaque state by controlling the corresponding unit.

5. The test bench (2) according to claim 1, wherein, The optical signal device (16) of the test stand is designed as a collimated light source surface structure, a light-emitting device equipped with a collimating lens or a light-emitting device equipped with a concave mirror. Each individual light source in the light source directly emits at least a nearly collimated beam (36a, 36b) after activating the corresponding light source.

6. The test stand (2) according to any one of claims 1 to 5, wherein, The optical signal device (16) of the test stand is designed to emit light emitted by any light-emitting device in a cone-shaped beam (36a, 36b) that is only approximately collimated; Furthermore, the converging lens (18) of the test stage is designed with respect to its focal length to convert the conical beam (36a, 36b) into at least a planar wave (38a, 38b) during its refraction.

7. The test stand (2) according to any one of claims 1 to 5, wherein, The test stand includes a programmable control device (12) configured to drive an optical signal device (16) to activate or deactivate a light-emitting device (22) selected on the optical signal device (16) according to a predetermined control program (28) programmed on the control device (12) so as to generate static or dynamic light patterns on the optical signal device (16).

8. The test bench (2) according to claim 7, wherein, The test bench is used to simulate the active environmental detection system (4): The environmental detection system includes a detector (32) for detecting light signals emitted through the environmental detection system (4); The control program (28) of the environmental detection system is designed to determine the round-trip time and spatial angle (α, β) of the light signal reflected on the virtual object; and By using the drive light signal device (16), the photodetector (6) of the environmental detection system (4) arranged in the holding device generates a light pattern for simulating reflection according to the predetermined spatial angle (α, β) and round-trip time.

9. The test bench (2) according to claim 3, wherein, The light source is a photodiode.

10. The test bench (2) according to claim 5, wherein, The light source is a semiconductor laser.

11. The test bench (2) according to claim 8, wherein, The environmental monitoring system is a lidar system.

12. A method for stimulating a photodetector (6) in an environmental detection system (4) to detect the environmental detection system (4), wherein, The method includes the following steps: An optical signaling device (16) is arranged, the optical signaling device comprising a surface structure composed of light-emitting devices (22) that can be independently activated and deactivated, and the optical signaling device is designed to emit light emitted by any of the light-emitting devices (22) in a beam (36a, 36b) that is at least approximately collimated; and A converging lens (18) is arranged such that the converging lens (18) focuses the light beam (36a, 36b) emitted from the optical signal device (16) onto the accumulation point; A photodetector (6) is placed at the accumulation point; A plurality of spatial angles (α, β) are predetermined from a range of spatial angles, the range covering the field of view of the photodetector (6) in its entirety, wherein each of the plurality of spatial angles (α, β) corresponds to the orientation of a virtual object simulated in the field of view of the photodetector (6); Multiple beams (36a, 36b) corresponding to the number of spatial angles (α, β) are emitted by means of an optical signal device (16), and the beams are focused to the accumulation point by a converging lens (18) such that each beam (36a, 36b) reaches the photodetector (6) at exactly one of the multiple spatial angles (α, β) relative to the optical axis (14). The method includes simulating the refractive behavior of a converging lens (18) to take refractive behavior into account when generating light patterns.

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