CN114442104A

CN114442104A - Coherent laser radar

Info

Publication number: CN114442104A
Application number: CN202011194169.7A
Authority: CN
Inventors: 不公告发明人
Original assignee: Suzhou Leizhi Sensing Technology Co ltd
Current assignee: Suzhou Leizhi Sensing Technology Co ltd
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2022-05-06
Also published as: WO2022088334A1

Abstract

The invention discloses a coherent laser radar, comprising: the device comprises a laser, a local oscillation light path, a measuring light path, an echo light path, a scanning mechanism and a detection module; laser emitted by the laser forms measuring light after passing through a measuring light path; the measuring light is emitted to a target object after passing through the scanning mechanism, and an echo of the target object reaches the detection module along an echo light path after passing through the scanning mechanism; laser emitted by the laser passes through a local oscillator light optical path to form local oscillator light, and the local oscillator light reaches the detection module; the local oscillator light path or the echo light path comprises a compensation driving mechanism, and the compensation driving mechanism is used for driving a target optical device in the local oscillator light path or the echo light path to change the direction of the local oscillator light or the echo; the detection module is used for detecting interference signals of echo and local oscillator light. In the coherent laser radar, due to the effect of the compensation driving mechanism, the local oscillator light is parallel to the echo, so that effective interference signals are improved, and further, the performance of the coherent laser radar is improved.

Description

Coherent laser radar

Technical Field

The embodiment of the invention relates to the field of optics, in particular to a coherent laser radar.

Background

The Frequency Modulated Continuous Wave (FMCW) system is an important radar type. Compared with traditional radar systems such as pulse radar and phase radar, the system has the advantages of high precision, interference resistance, no distance blind area, capability of directly measuring speed, simple structure and the like, thereby having good application prospect in many fields. Because the method is based on the laser interferometry principle, the emitted measuring light can reach a target to scatter the echo and the local oscillator light, and the echo and the local oscillator light need to interfere to detect an effective signal. For an interference system using a free space optical element, the direction of an echo and the direction of local oscillation light are required to be strictly parallel to obtain a better interference signal.

Currently, for imaging coherent lidar, an optical scanning mechanism, such as a galvo galvanometer or a MEMS galvanometer, is required to scan the measurement light. Due to the high frame rate requirements, these scanning mechanisms are typically in continuous motion. And after passing through the continuously moving scanning mechanism, the echo interferes with the local oscillator light, and an interference signal of the echo and the local oscillator light is detected.

However, in the coherent laser radar, if the echo has a large delay, for example, the echo delay is 1us beyond 150 meters, the optical axis of the optical scanning mechanism has already been deflected, which may cause an angular deviation when the echo interferes with the local oscillator light, resulting in a significant degradation of the interference signal, and thus leading to a degradation of the performance of the coherent laser radar.

Disclosure of Invention

The invention provides a coherent laser radar, which aims to solve the technical problem that interference signals are reduced due to the fact that an included angle exists between an echo and local oscillator light in the conventional coherent laser radar.

An embodiment of the present invention provides a coherent laser radar, including: the device comprises a laser, a local oscillation light path, a measuring light path, an echo light path, a scanning mechanism and a detection module;

laser emitted by the laser passes through the measuring light path to form measuring light; the measuring light is emitted to a target object after passing through the scanning mechanism, and an echo of the target object reaches the detection module along an echo light path after passing through the scanning mechanism;

the laser emitted by the laser passes through the local oscillator light optical path to form local oscillator light, and the local oscillator light reaches the detection module;

the local oscillator optical path or the echo optical path comprises a compensation driving mechanism, and the compensation driving mechanism is used for driving a target optical device in the local oscillator optical path or the echo optical path to change the direction of the local oscillator light or the echo so as to reduce the angle deviation between the echo and the local oscillator light caused by echo delay and movement of a scanning mechanism;

the detection module is used for detecting the echo and the interference signal of the local oscillator light.

In the coherent laser radar as described above, the local oscillator optical path includes: the first polarization beam splitter, the first 1/4 wave plate, the partial reflector and the compensation driving mechanism;

the compensation driving mechanism is used for driving the partial reflector to rotate by a preset angle;

the laser emitted by the laser device is emitted from the first direction of the first polarization spectroscope and the first 1/4 wave plate, and then forms the local oscillation light after being reflected by the rotated partial reflector, and the local oscillation light passes through the first 1/4 wave plate and the first polarization spectroscope, is emitted from the second direction of the first polarization spectroscope, and then reaches the detection module.

In the coherent laser radar as described above, the measurement light path and the echo light path each include: the first polarizing beamsplitter, the first 1/4 wave plate, and the partial mirror;

the laser emitted by the laser device is emitted from the first direction of the first polarization beam splitter and the first 1/4 wave plate, and then forms the measuring light after being transmitted by the partial reflector;

and the echo passes through the scanning mechanism, the transmission of the partial reflector, the first 1/4 wave plate and the first polarization beam splitter, is emitted from the second direction of the first polarization beam splitter, and then reaches the detection module.

In the coherent laser radar as described above, the local oscillator optical path includes: the second polarization beam splitter, the second 1/4 wave plate, the first 1/2 wave plate, the first reflector and the compensation driving mechanism;

the compensation driving mechanism is used for driving the first reflector to rotate by a preset angle;

the laser emitted by the laser device is emitted from the first direction of the second polarization beam splitter and the second 1/4 wave plate, and then forms the local oscillation light after being reflected by the rotated first reflector, and the local oscillation light passes through the second 1/4 wave plate and the second polarization beam splitter, is emitted from the second direction of the second polarization beam splitter, and then reaches the detection module through the first 1/2 wave plate.

In the coherent lidar as described above, the measurement light path includes: the second polarization beam splitter and a third 1/4 wave plate;

and the laser emitted by the laser device is emitted from the third direction of the second polarization beam splitter and the third 1/4 wave plate to form the measuring light.

In the coherent lidar as shown above, the echo optical path includes: the second polarizing beamsplitter, the third 1/4 wave plate, and the first 1/2 wave plate;

and the echo passes through the scanning mechanism, the third 1/4 wave plate and the second polarization beam splitter, and then exits from the second direction of the second polarization beam splitter and the first 1/2 wave plate to reach the detection module.

In the coherent laser radar as described above, the local oscillator optical path includes: a beam splitting piece and a beam combining piece;

the laser emitted by the laser passes through the beam splitting sheet and then is emitted from the first direction of the beam splitting sheet to form the local oscillator light, and the local oscillator light passes through the beam combining sheet and then is emitted from the first direction of the beam combining sheet to reach the detection module.

In the coherent lidar as described above, the measurement light path includes: the beam splitter, the third polarization beam splitter and the fourth 1/4 wave plate;

the laser emitted by the laser device is emitted from the second direction of the beam splitter, the first direction of the third polarization beam splitter and the fourth 1/4 wave plate, and then the measuring light is formed.

In the coherent lidar as shown above, the echo optical path includes: the third polarizing beam splitter, the fourth 1/4 wave plate, a second 1/2 wave plate, a second reflecting mirror, the compensation driving mechanism, and the beam combining plate;

the compensation driving mechanism is used for driving the second reflecting mirror to rotate by a preset angle;

the echo passes through the scanning mechanism, the fourth 1/4 wave plate and the third polarization beam splitter, then exits from the second direction of the third polarization beam splitter and the second 1/2 wave plate, reaches the second reflecting mirror, and then exits from the first direction of the beam combining plate after being reflected by the second reflecting mirror and passing through the beam combining plate after rotating, and finally reaches the detection module.

In the coherent laser radar as described above, the compensation driving mechanism is configured to drive the target optical device in the local oscillator optical path or the echo optical path to rotate along a target direction, where the target direction is a moving direction of the scanning mechanism or a direction opposite to the moving direction of the scanning mechanism.

The embodiment of the invention provides a coherent laser radar, which comprises: the device comprises a laser, a local oscillation light path, a measuring light path, an echo light path, a scanning mechanism and a detection module; laser emitted by the laser forms measuring light after passing through a measuring light path; the measuring light is emitted to a target object after passing through the scanning mechanism, and an echo of the target object reaches the detection module along an echo light path after passing through the scanning mechanism; laser emitted by the laser passes through a local oscillator light optical path to form local oscillator light, and the local oscillator light reaches the detection module; the local oscillator light path or the echo light path comprises a compensation driving mechanism, and the compensation driving mechanism is used for driving a target optical device in the local oscillator light path or the echo light path to change the direction of the local oscillator light or the echo so as to reduce the angle deviation between the echo and the local oscillator light caused by echo delay and the movement of the scanning mechanism; the detection module is used for detecting interference signals of echo and local oscillator light. In this coherent laser radar, through set up compensation actuating mechanism in local oscillator light path or echo light path, after the laser that the laser instrument sent passes through local oscillator light path to and, the echo passes through the echo light path after, because compensation actuating mechanism's effect, local oscillator light is parallel with the echo, and detection module detects the interference signal of parallel echo and local oscillator light, has improved effective interference signal, and then, has improved coherent laser radar's performance.

Drawings

FIG. 1 is a schematic structural diagram of a current coherent lidar;

FIG. 2 is a schematic diagram of a Gaussian optical coupling efficiency droop curve with angular deflection;

fig. 3 is a schematic structural diagram of a coherent lidar according to an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a coherent lidar according to another embodiment of the present invention;

FIG. 5 is a schematic structural diagram of a coherent lidar according to yet another embodiment of the present invention;

FIG. 6 is a schematic structural diagram of a coherent lidar in accordance with yet another embodiment of the present invention;

FIG. 7 is a schematic structural diagram of a coherent lidar according to another embodiment of the present invention;

fig. 8 is a schematic structural diagram of a detection module of a coherent lidar according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not limiting of the invention. It should be further noted that, for the convenience of description, only some structures related to the present invention are shown in the drawings, not all of them.

Fig. 1 is a schematic structural diagram of a conventional coherent lidar. As shown in fig. 1, the current coherent lidar includes: laser 11, beam splitter 12, circulator 13, scanning mechanism 14, coupler 15, balanced photodiode 16, amplifier 17, and processor 18. Laser light emitted by the laser 11 is split into local oscillation light and measurement light by the beam splitter 12. The measuring light is emitted through the circulator 13 and is spatially scanned by the scanning mechanism 14. After passing through the scanning mechanism 14 and the circulator 13, the target scattered echo is combined with the local oscillation light by the coupler 15 to interfere with the local oscillation light. The interference signal is detected by the balanced photodiode 16. The processor 18 performs sampling calculations on the signals detected by the balanced photodiode 16. However, for some coherent lidar, such as imaging coherent lidar, the scanning mechanism 14 is in continuous motion due to the high frame rate requirements. If the echo has a large delay, the optical axis of the scanning mechanism 14 has already deflected, which causes the direction of the echo to change, and further causes an angle deviation when the echo interferes with the local oscillator light, which causes a significant decrease in interference signal, thereby causing a decrease in performance of the coherent laser radar.

FIG. 2 is a graph illustrating a decrease in Gaussian optical coupling efficiency with angular deflection. The right graph in fig. 2 is a graph for calculating the decrease of the interference coupling efficiency of two gaussian beams of the same size with the increase of the included angle. It can be seen that the coupling efficiency decreases as the angle between the two gaussian beams increases. For example, assume a Gaussian beam radius w in the optical path₀Equal to 2.5mm and having a wavelength of 1550 nm. The 1550 nm optical diffraction divergence angle half-angle θ is 0.2 milliradians (mrad). The scanning angle of the scanning mechanism is 1 radian (rad), the scanning frequency is 250Hz, the one-way scanning time is 2ms, and the angular speed is 1rad/2ms on average to be 500 rad/s. For a 150 meter target, the round trip time is 1 us. During this round trip time, the angle change of the scanning mechanism was 0.5 mrad. That is, the angle between the two Gaussian beams is 0.5 mrad. The deviation of the angle normalized by the half-diffraction angle is:

although the abscissa of the right diagram in fig. 2 is at most 2, it can be estimated that when the deviation of the angle normalized by the half-diffraction angle is 2.5, the coupling efficiency is greatly reduced to less than 1% of the ideal value, and the signal is lost more than 20 dB. Scattered echoes decay inversely with distance squared and far-range echoes are already weak, with an unacceptable loss of 20dB of interference due to angular misalignment.

The embodiment of the invention provides a coherent laser radar which can compensate the angle deviation between an echo and local oscillator light so as to improve effective interference signals and improve the performance of the coherent laser radar.

Fig. 3 is a schematic structural diagram of a coherent lidar according to an embodiment of the present invention. As shown in fig. 3, the coherent lidar provided in this embodiment includes: the device comprises a laser 31, a local oscillator optical path 33, a measuring optical path 32, an echo optical path 34, a scanning mechanism 36 and a detection module 35.

The laser light emitted from the laser 31 passes through the measuring light path 32 to form measuring light. The measurement light is emitted to the target object after passing through the scanning mechanism 36. The echo of the target object passes through the scanning mechanism 36 and then reaches the detection module 35 along the echo optical path 34.

The laser light emitted from the laser 31 passes through the local oscillation optical path 33 to form local oscillation light, and the local oscillation light reaches the detection module 35.

The local oscillation optical path 33 or the echo optical path 34 includes a compensation driving mechanism (not shown in the figure). The compensation driving mechanism is used for driving the target optical device in the local oscillator light path 33 or the echo light path 34 to change the direction of the local oscillator light or the echo, so as to reduce the angular deviation between the echo and the local oscillator light caused by the echo delay and the movement of the scanning mechanism.

The detection module 35 is configured to detect an interference signal of an echo and local oscillation light.

Specifically, in the coherent lidar of the present embodiment, the laser light emitted by the laser 31 may be a chirped laser light. The laser light emitted by the laser 31 passes through the measuring light path 32 to form measuring light; the laser light emitted from the laser 31 passes through the local oscillation optical path 33 to form local oscillation light.

The measuring light passes through the scanning mechanism 36 and then exits to the target object. The scanning mechanism 36 here may be galvo, MEMS galvanometer, or phased array. The target object in this embodiment refers to an object whose information needs to be measured, where the object may be a building, an obstacle, etc., and the information is parameters such as size, distance, and shape of the object.

The echo of the target object passes through the scanning mechanism 36 and then reaches the detection module 35 along the echo optical path 34.

In the current coherent laser radar, due to the echo delay and the movement of the scanning mechanism 36, the local oscillation light and the echo are not strictly parallel, and have an angle deviation. The angular deviation refers to an angle between the local oscillator light and the echo.

In the coherent laser radar of the present embodiment, the local oscillation optical path 33 or the echo optical path 34 includes a compensation driving mechanism. The compensation driving mechanism is used to drive the target optical device in the local oscillator light path 33 or the echo light path 34 to change the direction of the local oscillator light or the echo, so as to reduce the angular deviation between the echo and the local oscillator light caused by the echo delay and the movement of the scanning mechanism 36. More specifically, the compensation driving mechanism may make the echo parallel to the local oscillation light. After the laser passes through the local oscillator light path 33 in this embodiment, and the echo passes through the echo light path 34, the local oscillator light is parallel to the echo due to the effect of the compensation driving mechanism, and the detection module 35 detects an interference signal of the echo and the local oscillator light. Because the local oscillator light is parallel to the echo, the effective interference signal is improved, and further, the performance of the coherent laser radar is improved.

More specifically, the compensation driving mechanism in the present embodiment is a mechanism capable of controlling the movement of the target optical device. The compensation drive mechanism may control the target optics to move while the scanning mechanism is moving. Alternatively, the compensation driving mechanism may control the movement of the target optical device at any time point before receiving the laser light emitted by the laser or receiving the echo, as long as the purpose of reducing the angular deviation between the echo and the local oscillation light can be achieved. The present embodiment is not limited thereto. Which devices the target optical device may specifically be will be described in detail below.

Optionally, the compensation driving mechanism is configured to drive the target optical device in the local oscillation optical path or the echo optical path to rotate along the target direction. Wherein, the target direction is the motion direction of the scanning mechanism or the opposite direction of the motion direction of the scanning mechanism. Illustratively, assuming that the scanning mechanism rotates counterclockwise, the compensation driving mechanism is used to drive the target optical device in the local oscillator optical path or the echo optical path to rotate counterclockwise or clockwise.

In one possible implementation, the compensation driving mechanism is configured to drive the target optical device in the local oscillation optical path or the echo optical path to rotate by 0.5mrad along the target direction.

The coherent laser radar provided by the embodiment comprises: the device comprises a laser, a local oscillation light path, a measuring light path, an echo light path, a scanning mechanism and a detection module; laser emitted by the laser forms measuring light after passing through a measuring light path; the measuring light is emitted to a target object after passing through the scanning mechanism, and an echo of the target object reaches the detection module along an echo light path after passing through the scanning mechanism; laser emitted by the laser passes through a local oscillator light optical path to form local oscillator light, and the local oscillator light reaches the detection module; the local oscillator light path or the echo light path comprises a compensation driving mechanism, and the compensation driving mechanism is used for driving a target optical device in the local oscillator light path or the echo light path to change the direction of the local oscillator light or the echo so as to reduce the angle deviation between the echo and the local oscillator light caused by echo delay and the movement of the scanning mechanism; the detection module is used for detecting interference signals of echo and local oscillator light. In this coherent laser radar, through set up compensation actuating mechanism in local oscillator light path or echo light path, after the laser that the laser instrument sent passes through local oscillator light path to and, the echo passes through the echo light path after, because compensation actuating mechanism's effect, local oscillator light is parallel with the echo, and detection module detects the interference signal of parallel echo and local oscillator light, has improved effective interference signal, and then, has improved coherent laser radar's performance.

The following describes a specific structure of the coherent laser radar provided in this embodiment based on different implementation manners of the local oscillation optical path, the measurement optical path, and the echo optical path.

Fig. 4 is a schematic structural diagram of a coherent lidar according to another embodiment of the present invention. As shown in fig. 4, in the coherent laser radar provided in this embodiment, the local oscillation optical path includes: a first polarization beam splitter 42, a first 1/4 wave plate 43, a partial mirror 44, and a compensation driving mechanism 49.

The compensation driving mechanism 49 is used to drive the partial reflecting mirror 44 to rotate by a preset angle.

The laser light emitted by the laser 41 is emitted from the first polarization beam splitter 42 in the first direction and the first 1/4 wave plate 43, and then reflected by the rotated partial reflecting mirror 44 to form the local oscillation light 47, and the local oscillation light 47 passes through the first 1/4 wave plate 43 and the first polarization beam splitter 42, and then is emitted from the first polarization beam splitter 42 in the second direction, and then reaches the detection module 46.

Optionally, the measurement light path and the echo light path in this embodiment each include: a first polarizing beamsplitter 42, a first 1/4 waveplate 43, and a partial mirror 44.

The laser light emitted from the laser 41 exits from the first polarizing beam splitter 42 in the first direction and the first 1/4 wave plate 43, and is transmitted by the partial mirror 44 to form measurement light.

The echo 48 passes through the scanning mechanism 45, the transmission of the partial reflecting mirror 44, the first 1/4 wave plate 43 and the first pbs 42, and then exits from the first pbs 42 in the second direction, and then reaches the detection module 46.

In this embodiment, a compensation driving mechanism 49 is disposed in the optical path of the local oscillation light for driving the partial mirror 44 to rotate by a preset angle. The preset angle here may be a value determined empirically or experimentally.

In this embodiment, the echo and the local oscillator light are polarized and rotated by 90 degrees by the first 1/4 wave plate 43, and then reflected by the first polarization beam splitter 42 to interfere in the detection module 46 to generate a difference frequency signal. By synchronously applying the preset angular deflection to the partially reflecting mirror 44, the angular offset of the far-range echo signal due to the deflection of the scanning mechanism can be compensated.

Illustratively, in the coherent lidar shown in fig. 4, the scanning mechanism 45 is rotated counterclockwise, and the compensation driving mechanism 49 is used to drive the target optics in the local oscillator light path, i.e., the partially reflecting mirror 44, to rotate in the counterclockwise direction.

The coherent laser radar that this embodiment provided, through set up compensation actuating mechanism in local oscillator light optical path, after the laser that the laser instrument sent passes through local oscillator light optical path to and, the echo passes through the echo optical path after, because compensation actuating mechanism's effect, local oscillator light is parallel with the echo, and detection module detects the interference signal of parallel echo and local oscillator light, has improved effective interference signal, and then, has improved coherent laser radar's performance.

Fig. 5 is a schematic structural diagram of a coherent lidar according to yet another embodiment of the present invention. As shown in fig. 5, in the coherent laser radar provided in this embodiment, the local oscillation optical path includes: a second polarization beam splitter 52, a second 1/4 wave plate 57, a first 1/2 wave plate 511, a first mirror 55, and a compensation driving mechanism 56.

The compensation driving mechanism 56 is used to drive the first reflecting mirror 55 to rotate by a predetermined angle.

The laser light emitted by the laser 51 is emitted from the first direction of the second pbs 52 and the second 1/4 wave plate 57, and then reflected by the rotated first reflecting mirror 55 to form the local oscillation light 510, and the local oscillation light 510 passes through the second 1/4 wave plate 57 and the second pbs 52, is emitted from the second direction of the second pbs 52, and then passes through the first 1/2 wave plate 511 to reach the detection module 58.

Optionally, in this embodiment, the measurement light path includes: a second polarization beam splitter 52 and a third 1/4 waveplate 53.

The laser light emitted from the laser 51 is emitted from the third direction of the second pbs 52 and the third 1/4 wave plate 53, and then forms the measuring light.

Optionally, in this embodiment, the echo optical path includes: a second polarization beam splitter 52, a third 1/4 waveplate 53, and a first 1/2 waveplate 511.

The echo 59 passes through the scanning mechanism 54, the third 1/4 wave plate 53 and the second pbs 52, and then exits from the second direction of the second pbs 52 and the first 1/2 wave plate 511 to reach the detection module 58.

In this embodiment, the compensation driving mechanism 56 is disposed in the optical path of the local oscillator, and is used for driving the first reflecting mirror 55 to rotate by a preset angle. The preset angle here may be a value determined empirically or experimentally. In this embodiment, the angle of the echo due to the deflection of the scanning mechanism can be compensated for by simultaneously applying a preset angular deflection to the first mirror 55.

Illustratively, in the coherent lidar shown in fig. 5, the scanning mechanism 54 is rotated counterclockwise, and the compensation driving mechanism 56 is used to drive the target optics in the local oscillator optical path, i.e., the first mirror 55, in a clockwise direction.

Fig. 6 is a schematic structural diagram of a coherent lidar according to yet another embodiment of the present invention. As shown in fig. 6, in the coherent laser radar provided in this embodiment, the local oscillation optical path includes: a beam splitter 62 and a beam combiner 67.

The laser light emitted by the laser 61 passes through the beam splitter 62 and then exits from the first direction of the beam splitter 62 to form the local oscillation light 611, and the local oscillation light 611 passes through the beam combining sheet 67 and then exits from the first direction of the beam combining sheet 67 to reach the detection module 610.

Alternatively, the splitting sheet 67 may be a 50:50 reflective transmissive splitting sheet.

Further, the detection module 610 is also disposed in a second direction (i.e., another exit direction different from the first direction) of the beam combining sheet 67. The two detection modules 610 of the first direction and the second direction of the beam combining sheet 67 can form a balanced detection.

In a scenario where two detection modules 610 are provided, laser light emitted by the laser 61 passes through the beam splitter 62 and then exits from the first direction of the beam splitter 62 to form local oscillation light 611, and the local oscillation light 611 passes through the beam combiner 67 and then exits from the second direction of the beam combiner 67 to reach the detection modules 610.

Optionally, in this embodiment, the measurement light path includes: a beam splitter 62, a third polarization beam splitter 63, and a fourth 1/4 wave plate 64.

The laser beam emitted from the laser 61 exits from the second direction of the beam splitter 62, the first direction of the third polarization beam splitter 63, and the fourth 1/4 wave plate 64 to form the measurement light.

Optionally, in this embodiment, the echo optical path includes: a third PBS 63, a fourth 1/4 wave plate 64, a second 1/2 wave plate 66, a second reflecting mirror 69, a compensation driving mechanism 68, and a beam combining plate 67.

The compensation driving mechanism 68 is used for driving the second reflecting mirror 69 to rotate by a preset angle.

The echo 612 passes through the scanning mechanism 65, the fourth 1/4 wave plate 64, and the third pbs 63, then exits from the second direction of the third pbs 63 and the second 1/2 wave plate 66, reaches the second reflecting mirror 69, is reflected by the rotated second reflecting mirror 69, passes through the beam combining plate 67, exits from the first direction of the beam combining plate 67, and reaches the detection module 610. In a scenario where two detection modules 610 are provided, the echo passes through the scanning mechanism 65, the fourth 1/4 wave plate 64 and the third pbs 63, then exits from the second direction of the third pbs 63 and the second 1/2 wave plate 66, then reaches the second reflecting mirror 69, and then exits from the second direction of the beam combining plate 67 after being reflected by the second reflecting mirror 69 and passing through the beam combining plate 67, and then reaches the detection module 610.

In this embodiment, a compensation driving mechanism 68 is disposed in the echo optical path for driving the second mirror 69 to rotate by a preset angle.

Illustratively, in the coherent lidar shown in fig. 6, the scanning mechanism 65 is rotated counterclockwise, and the compensation driving mechanism 68 is used to drive the target optics in the return optical path, i.e., the second mirror 69, in a clockwise direction.

The echo normally needs to return along the original path of the measuring light, the direction of the echo is adjusted through the second reflecting mirror 69 inside the coherent laser radar, and the echo and the local oscillator light have completely consistent directions after passing through the beam combining sheet 67, so that an effective interference signal can be generated in the detection module 610. However, in practical use, since the scanning mechanism 65 usually rotates at a high speed in a certain fast axis direction, when a long-distance echo returns, the scanning mechanism 65 has already rotated by a certain angle, so that the echo inside the coherent laser radar deviates from the optimal interference light direction, and a coherent electrical signal is greatly lost when interfering with local oscillation light.

In the coherent laser radar of this embodiment, a second reflecting mirror is disposed in the echo optical path. The second mirror may be a MEMS mirror or a mirror driven using piezoelectric ceramics (PZT). Synchronously, the second mirror is deflected by a predetermined angle relative to the static position while the scanning mechanism scans to compensate for angular deviations of the set range echo due to deflection of the scanning mirror. For a 2.5mm radius of Gaussian light, the preset angle is 0.2 mrad. So set up, can make the coupling efficiency of 150 meters echo light close to ideal value. Of course, a short range echo will deviate from the ideal by an angle of 0.2mrad, but the echo for a short range, e.g., 15 meter target, is 100 times more intense than 150 meters, or 20dB, so that even with a 20dB coupling loss, the total signal intensity is ideally similar to the 150 meter echo. Thus, another benefit of the coherent lidar is that the target echo interference signal strength from near to far is artificially lost to increase with distance without significant attenuation.

The coherent laser radar that this embodiment provided, through set up compensation actuating mechanism in the echo light path, after the laser that the laser instrument sent passes through local oscillator light path to and, the echo passes through the echo light path after, because compensation actuating mechanism's effect, local oscillator light is parallel with the echo, and detection module detects the interference signal of parallel echo and local oscillator light, has improved effective interference signal, and then, has improved coherent laser radar's performance.

Fig. 7 is a schematic structural diagram of a coherent lidar according to another embodiment of the present invention. As shown in fig. 7, the coherent lidar provided in this embodiment includes: a laser 71, a beam splitter 72, a circulator 73, an optical waveguide 74, a converging lens 75, a scanning mechanism 76, a coupler 78, and a detector 79.

Laser emitted by the laser 71 passes through the beam splitter 72 and is divided into two paths, one path is local oscillation light, and the other path is measurement light. The local oscillator light reaches the coupler 78. The measuring light passes through the circulator 73, then passes through the optical waveguide device 74, is collimated by the converging lens 75, and then reaches the scanning mechanism 76. After passing through the scanning mechanism 76 and the focusing lens 75, the echo 77 is required to be focused on the optical waveguide device 74. The echoes 77 are collected in the optical waveguide device 74 and coupled with the local oscillator light in the coupler 78 by the circulator 73. However, in the current scheme, due to the deflection of the scanning mechanism 76, after the echo passes through the converging lens 75, the converging point is deviated from the optical waveguide device 74.

In the coherent laser radar provided in this embodiment, a compensation driving mechanism is provided to control the positional shift of the optical waveguide device 74, or to control the shift of the focusing lens 75, so that the focusing point of the echo can be matched with the optical waveguide device 74, and the coupling loss of the optical waveguide device is reduced.

Specifically, when the compensation driving mechanism controls the position shift of the optical waveguide device 74, the shift amount may be d ═ β × f, where β denotes a preset angle and f is the focal length of the converging lens 75. Thus, the displacement of the focal point of the 150 m echo focus in the focal plane of the focusing lens 75 due to the deflection of the scanning mechanism is just compensated. The optical waveguide device 74 in this embodiment may be an optical fiber.

The coherent laser radar provided by the embodiment can control the position deviation of the optical waveguide device, or control the deviation of the converging lens, so that the converging point of the echo can be matched with the optical waveguide device, and the coupling loss of the optical waveguide device is reduced.

The structure of the coherent lidar detection module provided by this embodiment is described in detail below.

In an implementation manner, fig. 8 is a schematic structural diagram of a detection module of a coherent lidar according to an embodiment of the present invention. As shown in fig. 8, the detection module of the coherent lidar provided in this embodiment may include: a fourth polarizing beamsplitter 811, a photodetector 812, and a processor 813.

In fig. 8, the local oscillator light is indicated by a thick solid line with an arrow, and the echo is indicated by a broken line with an arrow.

The photodetector 812 may be specifically a photodiode. The number of photodetectors 812 may be two to filter out the dc component.

The local oscillation light and the echo that are parallel to each other are emitted from the first direction and the second direction of the fourth polarization beam splitter 811, respectively, after reaching the fourth polarization beam splitter 811. The photodetector 812 disposed at the first direction of the fourth polarization beam splitter 811 detects the interference signal of the local oscillator light and the echo. The photodetector 812 disposed at the second direction of the fourth polarization beam splitter 811 detects the interference signal of the local oscillator light and the echo. Processor 813 can determine the relevant information from the interference signal detected by photodetector 812.

It should be noted that the detection module shown in fig. 8 can be applied to the coherent lidar shown in fig. 5. With continued reference to fig. 5, the local oscillator light and the echo light are polarized relatively vertically. In fig. 5, the first 1/2 wave plate 511 rotates the polarization of the transmitted local oscillator light and the reflected echo light by 45 degrees after passing through the second pbs 52. Thus, the fourth PBS 811 of FIG. 8 can reflect and transmit half of the local oscillator light and echo light, respectively, to each of the photodetectors 812.

In another implementation manner, for the coherent lidar shown in fig. 4 and fig. 6, the detection module may include: a photodetector, and a processor. The photoelectric detector detects the interference signals of the local oscillator light and the echo which are parallel to each other. Processor 813 can determine the relevant information from the interference signal detected by photodetector 812.

It should be noted that, in the detection module provided in this embodiment, the converging lenses may be disposed in front of and behind the photodetector, so as to further improve the effective interference signal.

It is to be noted that the foregoing description is only exemplary of the invention and that the principles of the technology may be employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A coherent lidar comprising: the device comprises a laser, a local oscillation light path, a measuring light path, an echo light path, a scanning mechanism and a detection module;

laser emitted by the laser device forms measuring light after passing through the measuring light path; the measuring light is emitted to a target object after passing through the scanning mechanism, and an echo of the target object reaches the detection module along an echo light path after passing through the scanning mechanism;

2. The coherent lidar of claim 1, wherein the local oscillator optical path comprises: the first polarization beam splitter, the first 1/4 wave plate, the partial reflector and the compensation driving mechanism;

3. The coherent lidar of claim 2, wherein the measurement light path and the echo light path each comprise: the first polarizing beamsplitter, the first 1/4 wave plate, and the partial mirror;

4. The coherent lidar of claim 1, wherein the local oscillator optical path comprises: the second polarization beam splitter, the second 1/4 wave plate, the first 1/2 wave plate, the first reflector and the compensation driving mechanism;

the laser emitted by the laser device is emitted from the first direction of the second polarization spectroscope and the second 1/4 wave plate and then forms the local oscillator light after being reflected by the rotated first reflector, and the local oscillator light passes through the second 1/4 wave plate and the second polarization spectroscope, is emitted from the second direction of the second polarization spectroscope and then reaches the detection module through the first 1/2 wave plate.

5. The coherent lidar of claim 4, wherein the measurement light path comprises: the second polarization beam splitter and a third 1/4 wave plate;

6. The coherent lidar of claim 5, wherein the echo optical path comprises: the second polarizing beamsplitter, the third 1/4 wave plate, and the first 1/2 wave plate;

7. The coherent lidar of claim 1, wherein the local oscillator optical path comprises: a beam splitting piece and a beam combining piece;

8. The coherent lidar of claim 7, wherein the measurement light path comprises: the beam splitter, the third polarization beam splitter and the fourth 1/4 wave plate;

9. The coherent lidar of claim 8, wherein the return optical path comprises: the third polarizing beam splitter, the fourth 1/4 wave plate, a second 1/2 wave plate, a second reflecting mirror, the compensation driving mechanism, and the beam combining plate;

10. The coherent lidar of any of claims 1 to 9, wherein the compensation driving mechanism is configured to drive the target optics in the local oscillator optical path or the echo optical path to rotate along a target direction, wherein the target direction is a motion direction of the scanning mechanism or a direction opposite to the motion direction of the scanning mechanism.