LiDAR system with increased reliability

Abstract

The present application relates to a LIDAR receiving system with APD detectors or an APD detector. By means of an additional circuit and the evaluation of the optical input signal with a fast additional detector, the bias voltage at the APD detector is reduced in the case of large input signals before this optical input signal reaches the APD. The proposed new LIDAR receiving system comprises at least - One or more additional very fast detectors; - an evaluation electronics unit that controls the power supply of the APD detector; - an optical delay path with delay time delta t.

Description

[0001] The present application relates to a LIDAR receiving system.

[0002] LIDAR systems typically emit laser beams and receive reflected signals from the surrounding area. When a focused laser beam hits a point on the objects in the system's vicinity, the incident light is typically reflected back into the hemisphere. The reflected photons returning from this point to the LIDAR system's receiver are therefore often much weaker in intensity than the emitted laser beam. In order to reliably calculate the distance from the time difference between the transmission of the pulse and the arrival of the reflected signals at the receiver, very strong signal amplification is often required.

[0003] In modern systems this is often done in the detector via avalanche multiplication.

[0004] Avalanche detectors (APD, avalanche photo detector) usually require higher voltages and these operating point voltages usually also have to be adjusted with the ambient temperature, since the avalanche effect, which defines the gain, is strongly dependent on the ambient temperature.

[0005] At high ambient temperatures, the bias voltages on the detector must also be significantly larger to provide sufficient space for signal amplification.

[0006] In such situations, spontaneous discharges can sometimes occur in the detector system. This is particularly the case when not only weak optical input signals reach the detector, but also when significantly higher radiation intensities occur in the input signal. In practice, this can be caused by direct sunlight irradiating the detector system, for example, by direct laser irradiation from an oncoming vehicle with a very powerful LIDAR laser in the same wavelength range, or even by the direct reflection of the detector's own laser pulse from highly reflective surfaces.

[0007] In all of these cases, sufficiently well-stabilized, very high supply voltages at the detector can lead to an arc discharge and thus to the destruction of the APD sensor itself. Particularly if such stressful situations occur frequently at high temperatures and high bias voltages on the detector, it can also slowly lead to degradation in the detector, ultimately resulting in a sudden failure of the detector. While such an event is rare to very rare, since LIDAR systems are usually used in safety-critical areas, such an event should be suppressed as completely as possible through technical measures.

[0008] The object of the present invention is to eliminate or at least mitigate at least some of the aforementioned disadvantages of the prior art. In particular, it may be an object to significantly increase the reliability of a LIDAR system.

[0009] This object is achieved by arranging one or more additional very fast detectors and associated evaluation electronics, all located in close proximity to the APD detector, as well as by adding an optical delay line according to one of the independent claims. Advantageous or exemplary developments of the invention are set forth in the dependent claims and illustrated in the figures.

[0010] The proposed new LIDAR receiving system includes at least - One or more additional very fast detectors; - an evaluation electronics that controls the power supply of the APD detector; - an optical delay line with the delay time delta t.

[0011] In this case, the additional very fast detector can be a single detector. MIS detectors are preferably used here. The evaluation electronics ideally consists of a fast comparator circuit that monitors whether a specified threshold value of the optical input signal is present at the additional detector.

[0012] If a set threshold is exceeded, it can be assumed that the optical input signal is too high, and the evaluation electronics should then significantly and quickly reduce the bias voltage on the APD detector. After the time delta t, the input signal has passed through the optical delay line and reached the APD detector. This time should be sufficient to reliably reduce any excessive bias voltage on the APD detector after the time delta t.

[0013] If the excessively high optical input signal now reaches the APD detector, damage caused by arcing is no longer possible with the significantly lower operating point voltage at the APD detector. This also significantly reduces gradual degradation.

[0014] If the threshold value measured at the individual detector again signals permissible optical input signals, the evaluation electronics can increase the bias voltage at the APD detector again until safe operation of the LIDAR system is possible again.

[0015] In one embodiment, the optical delay line can be realized via a mirror system, Fig. 1. To maximize the time delta t, the mirror system can be filled with other transparent materials with a higher refractive index than the ambient air.

[0016] In an alternative embodiment, the optical delay line can be made with optical fibers, Fig. 2.

[0017] Advantageous further developments of the invention are explained by way of example in the following description of the figures.

[0018] They show: Fig. 1 A schematic representation of a LIDAR receiving system with reflectors as delay elements.

[0019] The light incident on the LIDAR receiver at input 5 partially falls on the additional, very fast detector 3 and is fed, along with other parts, into the delay line 4. The evaluation circuit 2 determines whether the intensity of the input signal 5 exceeds a threshold and controls the operating point voltage at the APD detector 1 or the APD detector array accordingly. If a predefined threshold is exceeded, the operating point voltage at the APD detector 1 or the APD detector array is reduced very quickly.

[0020] After the delay time delta t, the optical input signal at the output of the delay line 6 falls on the APD detector 1 or the APD detector array. Fig. 2 a schematic representation of a LIDAR receiving system with optical fibers as delay elements.

[0021] The required delay time delta t is realized here via optical fibers.

[0022] In these embodiments, only a single additional detector 3 is shown for monitoring the optical input signal. In practical applications, however, two or more of these additional detectors can be arranged to monitor the optical input signal as completely as possible. Fig. 3 a schematic representation of a LIDAR receiving system with a partially transparent mirror in the area of ​​the input signal.

[0023] The embodiment in Fig.Figure 3 shows the use of additional optical elements in the input area of ​​the receiver system. In the simplest case, this is a plane-parallel glass 7 or a corresponding partially transparent mirror.

[0024] Common to all embodiments is the close spatial proximity of the three elements 1, 2 and 3. This is necessary in practice because optical signals move at almost the speed of light and the evaluation circuit 2 needs sufficient time to safely reduce the bias voltage at the APD detector before the optical input signal detected as being too large hits the APD detector after delta t.

[0025] Since safe operation of the LIDAR system is generally not possible if the optical input signals are too large, the evaluation circuit 2 should additionally be provided with an electrical output for the connected software, which then reports a LIDAR mode as out of operation.

[0026] As soon as the optical input signal has returned to smaller values, this signal can be reset. List of reference symbols 1 APD detector 1 or APD detector array 2 Evaluation circuit 3 additional very fast detector 4 Delay line for the optical signal 5 Input of the optical signal 6 Output of the delay line 7 additional optical elements in the input area of ​​the receiver

[0027] Defining terms (glossary): LIDAR - light detection and ranging, distance determination using light APD - English avalanche photo diode Comparator - comparison circuit that detects a threshold value

[0028] 1.) Research and References Terms: LIDAR receiver DE102013100696B3_1 DE102019130647A1 US000011280888B2 US020180188359A1 US020190041498A1 US020200142066A1 US020210116550A1 US020210132229A1 US020220357451A1 US020230098843A1 US020230109123A1 QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 102013100696B3

[0028] DE 102019130647A1

[0028] US 000011280888B2

[0028] US 020180188359A1

[0028] US 020190041498A1

[0028] US 020200142066A1

[0028] US 020210116550A1

[0028] US 020210132229A1

[0028] US 020220357451A1

[0028] US 020230098843A1

[0028] US 020230109123A1

[0028]

Claims

[1] LIDAR receiving system with avalanche receivers, in which one or more fast optical detectors and an associated evaluation circuit are arranged in close proximity to the avalanche detector system and in which the optical input signal passes through an optical delay line before hitting the avalanche detector. [2] LIDAR receiving system with avalanche receivers according to claim 1, wherein the optical delay line is realized with a mirror system. [3] LIDAR receiving system with avalanche receivers according to claim 1, wherein the optical delay line is implemented with an optical fiber system. [4] LIDAR receiving system with avalanche receivers according to claim 2, wherein the interior of the mirror system is not filled with atmospheric air. [5] LIDAR receiving system with avalanche receivers according to claim 1, wherein the delay time of the optical delay line is greater than the total delay time of the evaluation circuit until the operating point voltage at the avalanche detector is reduced. [6] LIDAR receiving system with avalanche receivers according to claim 1, wherein a semi-transparent detector is used to control the value of the optical input signal. [7] LIDAR receiving system with avalanche receivers according to claim 1, wherein additional optical elements are used to decouple the control signal from the optical input signal for the additional fast detector. [8] LIDAR receiving system with avalanche receivers according to claim 1, wherein the evaluation circuit additionally provides an electrical signal which reports to a connected software or processing circuit whether the LIDAR is currently operational or not.

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