CN110780283A

CN110780283A - Receiving system, laser radar comprising same and echo receiving method

Info

Publication number: CN110780283A
Application number: CN201911157917.1A
Authority: CN
Inventors: 吴世祥; 王瑞; 向少卿
Original assignee: Hesai Photonics Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2020-02-11
Anticipated expiration: 2039-11-22
Also published as: CN110780283B

Abstract

The invention relates to a receiving system for a laser radar, comprising: the receiving lens is configured to receive and converge the light beams reflected by the obstacles; an optical modulator having "on" and "off states, the optical modulator being disposed downstream of the optical path of the receiving lens and receiving the light beam converged by the receiving lens; a detector disposed downstream of the optical modulator, wherein the optical modulator is configured to allow the focused light beam to be incident on the detector when in an "on" state; when in the "off" state, the focused beam is not allowed to impinge on the detector.

Description

Receiving system, laser radar comprising same and echo receiving method

Technical Field

The present invention generally relates to the field of photoelectric technology, and more particularly, to a receiving system for a laser radar, a laser radar including the same, and a method for processing echo reception of a laser radar.

Background

LiDAR is a general name of laser active detection sensor equipment, and the working principle of the LiDAR is roughly as follows: the laser radar transmitter transmits a laser beam, the laser beam is reflected diffusely after encountering an object and returns to the laser receiver, and the radar module can calculate the distance between the transmitter and the object by multiplying the light speed by half of the time interval between the transmission and the reception of the signal. For the Lidar system to realize remote measurement performance, the signal-to-noise ratio needs to be improved. In many systems, such as those using SiPM or other detectors with single photon sensitivity, the shot noise caused by ambient light is a major noise source in the system, and therefore it becomes important to control the ambient light.

The emission end of the scanning type solid laser radar system can realize the scanning of the emitted light beam through scanning mechanisms such as an MEMS mirror, an OPA and the like; the receiving end can receive through a paraxial light path of the array detector or can receive through a coaxial light path of the scanning structure. Array detector reception usually requires a large-sized detector array, such as an APD or SiPM array, which is high in cost, currently difficult to obtain commercially, and high in cost; the scanning mechanism receives coaxially, the effective receiving aperture is limited by the receiving aperture that the scanning mechanism can provide, and the problems of receiving efficiency loss, internal stray light and the like are inevitably existed. Therefore, there is currently no good way to implement a solid-state radar system.

The statements in the background section are merely prior art as they are known to the inventors and do not, of course, represent prior art in the field.

Disclosure of Invention

The invention provides a receiving system for a laser radar, the laser radar comprising the receiving system and a method for receiving and processing echoes of the laser radar.

According to an aspect of the present invention, there is provided a receiving system usable with a laser radar, comprising:

the receiving lens is configured to receive and converge the light beams reflected by the obstacles;

an optical modulator having "on" and "off states, the optical modulator being disposed downstream of the optical path of the receiving lens and receiving the light beam converged by the receiving lens;

a detector disposed downstream of the optical modulator,

wherein the light modulator is configured to allow the converging light beam to be incident on the detector when in an "on" state; when in the "off" state, the focused beam is not allowed to impinge on the detector.

According to another aspect of the invention, the light modulator comprises a digital micromirror array comprising a plurality of micro-reflective cells, each of which is individually controllable and switchable between "on" and "off" states, when one of the micro-reflective cells is in the "on" state, it allows a light beam incident thereon to be reflected onto the detector; when it is in the "off" state, it stops reflecting the beam incident on it onto the detector.

In accordance with another aspect of the invention, the light modulator includes a light valve that, when in an "on" state, allows a light beam incident thereon to pass through and impinge on the detector; when in the "off" state, the light beam incident thereon is prevented from passing.

According to another aspect of the invention, the receiving system further comprises a delay lens disposed between the optical modulator and the detector and configured to converge the light beam from the optical modulator onto the detector.

According to another aspect of the invention, the light modulator is arranged at a focal plane of the receiving lens, the receiving system further comprising a lens array arranged between the receiving lens and the light modulator.

According to another aspect of the invention, the receiving system comprises N light modulators and N detectors, N being greater than 1, wherein each light modulator has a respective field of view, the fields of view of any two light modulators not being completely coincident.

An aspect of the present invention also provides a laser radar including:

a transmitting system configured to transmit a probe beam to an outside of the lidar; and

a receiving system, comprising:

the receiving lens is configured to receive and converge light beams from the outside of the laser radar;

an optical modulator including "on" and "off states, the optical modulator being disposed downstream of the optical path of the receiving lens and receiving the light beam converged by the receiving lens;

a detector disposed downstream of the optical modulator,

According to another aspect of the invention, the receiving system further comprises a delay lens disposed between the optical modulator and the detector, configured to converge the light beam from the optical modulator onto the detector,

the light modulator is disposed at a focal plane of the receive lens, the receive system further comprising a lens array disposed between the receive lens and the light modulator.

Another aspect of the present invention also provides a method for performing echo receiving processing by using the laser radar as described above, including:

controlling the light modulator to switch between an 'on' state and an 'off' state in a preset mode;

receiving and amplifying the electrical signal generated by the detector;

and generating a point cloud of the laser radar according to the amplified electric signal.

The scheme of the solid-state laser radar receiving optical system based on the optical modulator can well inhibit ambient light noise. The light modulator may include a digital micromirror array (reflective), a liquid crystal (transmissive), a light valve (shutter), etc., and its main function is a device having an on and off function for light. The approach of the embodiments of the present invention places the light modulator near the receiving lens focal plane so that each microcell can independently gate a single field of view of interest. In an embodiment of the present invention, a detector (e.g., SiPM, or APD) is placed at the aperture stop of the system, which can receive the beam at all angles of view of interest. Instantaneous field control is realized through the optical modulator, and the SiPM realizes light energy detection, so that a single SiPM can realize detection of a wide-range field angle. Since the DMD cell is very small (about 5.4-13.6 um), the instantaneous field angle is controllable, i.e. the ambient light is controllable. The fact that the ambient light is controllable mainly means that the light modulator is very small in size, and the size of the light modulator is much smaller than that of a detector such as APD or SiPM which can achieve the same field of view, and the received ambient light is very little; in the system, SiPM can select large photosensitive size, the number of units is increased, and therefore, the detection dynamic range is also increased. In addition, the number of SiPM detectors used by the system can be greatly reduced, and the cost is reduced.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 shows a schematic diagram of a receiving system that may be used in a lidar in accordance with one embodiment of the invention;

FIG. 2 illustrates one embodiment of a single channel detection small field of view;

FIG. 3 illustrates one embodiment of a multi-channel detection large field of view;

FIG. 4 shows a schematic diagram of a receiving system that may be used in a lidar in accordance with a preferred embodiment of the present invention;

FIG. 5 shows a schematic diagram of a lidar in accordance with an embodiment of the invention; and

fig. 6 illustrates a method for echo receive processing using a lidar in accordance with one embodiment of the present invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

Fig. 1 shows a schematic diagram of a receiving system 10 that may be used in lidar according to one embodiment of the present invention, described in detail below with reference to fig. 1.

As shown in fig. 1, the receiving system 10 includes a receiving lens group 11, a light modulator 12, and a detector 13. Wherein the receiving lens group 11 is configured to receive a light beam (e.g. a reflected light beam from an external obstacle of the lidar) and focus the light beam so that it is incident on the optical modulator 12 downstream of the optical path. The light modulator 12 includes an "on" state and an "off state and is switchable between the" on "state and the" off state. The detector 13 is arranged downstream of the light modulator 12. Wherein when said light modulator 12 is in the "on" state, it allows said converging light beam to be incident on said detector 13; when in the "off" state, the focused beam is not allowed to impinge on the detector. The light modulator 12 shown in fig. 1 may be, for example, a digital micromirror array (DMD). The digital micromirror array comprises a plurality of micro-reflective cells, each of which is individually controllable and switchable between "on" and "off" states, when one of the micro-reflective cells is in the "on" state, it allows a light beam incident thereon to be reflected onto the detector; when it is in the "off" state, it absorbs or reflects the light beam incident thereon onto the light absorbing portion, thereby avoiding reflection of the light beam incident thereon onto the detector 13. The detector 13 is, for example, a photodetector such as a photodiode, an avalanche photodiode, or SiPM or SPAD, which receives an incident light beam and generates and outputs an electrical signal according to the intensity of the incident light beam or the number of photons.

Or alternatively, the light modulator 12 comprises a liquid crystal shutter or light valve which, when in an "on" state, allows a light beam incident thereon to pass through and impinge on the detector; when in the "off" state, the light beam incident thereon is prevented from passing. Thus, light modulator 12 may be a reflective optical element, such as a digital micromirror array, or a transmissive optical element, such as a liquid crystal shutter or light valve.

Taking a digital micromirror array as an example, the surface of the digital micromirror array comprises thousands of micromirror surface units, each of which has two states of "on" and "off", respectively corresponding to two different reflection angles, and each of which can individually control its state. The micro-reflection units are positioned on the focal plane of the receiving lens, which means that each micro-reflection unit corresponds to a specific field angle, and when the unit is started, the light beams of the field angle can be selectively received, while the light beams of other field angles are not received, so that the digital micromirror array simultaneously plays the roles of field selection and field stop, and the digital micromirror array, the detector and the delay lens group are combined together to realize the function similar to an array detector, and have the function of field control, so that the ambient light can be controlled.

FIG. 1 shows that light modulator 12 includes an array of digital micromirrors, and two of the micromirrors are schematically illustrated: micromirror 12-1 and micromirror 12-2. Wherein the micromirror 12-1 corresponds to the first incident beam L1, the first incident beam L1 is converged on the micromirror 12-1 through the receiving lens 11; the micromirror 12-2 corresponds to a second set of incident beams L2, and the second set of incident beams L2 is converged on the micromirror 12-2 through the receiving lens 11. When micromirror 12-1 is in the "on" state, it further reflects the first set of incident beams L1 incident thereon onto detector 13; when micromirror 12-2 is in the "on" state, it further reflects a second set of incident light beams L2 incident thereon onto detector 13. Preferably, the states of the micromirror 12-1 and the micromirror 12-2 are mutually exclusive, i.e., only one of them is in the "on" state at the same time. Alternatively, multiple micromirrors may be simultaneously "on" at the same time.

The first set of incident light beams L1 corresponds to, for example, a first field of view and the second set of incident light beams L2 corresponds to a second field of view. Thus, by controlling the opening and closing of the micromirrors 12-1 and 12-2, the field of view detected by the detector 13, i.e., the detection field of view of the receiving system 10, can be controlled.

In the existing laser radar, the number of detectors at the receiving end is generally the same as the number of lasers at the transmitting end. For example, a 64-line laser radar generally has 64 lasers and 64 APDs, the lasers and the APDs are in a one-to-one correspondence relationship, and a detection beam emitted by one laser is received by a corresponding APD after a radar echo reflected by an obstacle. According to the solution shown in fig. 1, a plurality of light beams (corresponding to different lasers) emitted from the light modulator 12 can be made to be incident on the same detector. Therefore, the photosensitive detection and receiving of the multi-line laser radar can be realized by using a small number of detectors, a scanning mechanism is not needed for receiving, and the ambient light can be controlled.

According to one embodiment of the present invention, the receiving system 10 further includes a delay lens 14, for example, for performing the second spot focusing. The delay lens 14 is disposed between the light modulator 12 and the detector 13, and is configured to converge the light beam from the light modulator 12 onto the detector 13.

According to a preferred embodiment of the present invention, the light modulator 12 is disposed at the focal plane of the receiving lens 11, so that the receiving lens 11 can converge the incident parallel light beam onto the light modulator.

As shown in fig. 4, according to a preferred embodiment of the present invention, the receiving system further includes a lens array 15 disposed between the receiving lens 11 and the light modulator 12 for performing light beam convergence. In fig. 4, at the back end of the focal plane of the receiving lens 11, the field of view stitching is realized by a group of lens arrays 15, the receiving module composed of the digital micromirror array, the delay lens and the detector is located at the back end of the lens array, and the lens array mainly provides the receiving module, especially provides the spatial arrangement for the digital micromirror array.

Fig. 2 shows an embodiment of single channel detection of a small field of view. As shown in fig. 2, the receiving system 10 includes an optical modulator 12 and a detector 13.

According to a preferred embodiment of the invention, the receiving system 10 comprises N light modulators 12 and N detectors 13, N being greater than 1, wherein each light modulator has a respective field of view, the fields of view of any two light modulators not being completely coincident. As shown in fig. 3, the receiving system is shown to include three optical modulators and three detectors. Wherein each light modulator and detector respectively corresponds to a certain field of view, and a plurality of fields of view are superposed to form a larger detection field of view. For example, a plurality of digital micromirror arrays are placed at the focal plane of the receiving lens, each digital micromirror array and the subsequent delay lens 14 and detector 13 are responsible for detecting a relatively small field of view, and the detection of a large field of view can be realized by splicing a plurality of receiving modules in the optical path.

As shown in fig. 5, the invention also relates to a lidar 100 comprising a transmitting system 20 and a receiving system 10 as described above. Wherein the transmitting system 20 is configured to transmit the probe beam externally of the lidar. As shown in fig. 5, the emission system 20 includes, for example, a laser 21, an emission lens 22, and a scanner 23. The laser 21 emits a laser beam, which is shaped by the emission lens 22 and then enters the scanner 23, and the scanner 23 scans and emits a probe beam. The receiving system 10 includes: a receiving lens 11, a light modulator 12, and a detector 13. Wherein the receiving system 10 shown in fig. 5 corresponds to the receiving system shown in fig. 3. Those skilled in the art will readily appreciate that the receiving system 10 of fig. 5 may also be the receiving system of fig. 1, 2, or 4, all of which are within the scope of the present invention.

According to one embodiment of the present invention, light modulator 12 comprises a digital micromirror array comprising a plurality of micro-reflective cells, each of which is individually controllable and switchable between "on" and "off" states, when one of the micro-reflective cells is in the "on" state, it allows a light beam incident thereon to be reflected onto the detector; when it is in the "off" state, it stops reflecting the beam incident on it onto the detector.

According to one embodiment of the invention, the light modulator 12 comprises a liquid crystal shutter or light valve which, when in an "on" state, allows a light beam incident thereon to pass through and be incident on the detector; when in the "off" state, the light beam incident thereon is prevented from passing.

According to an embodiment of the invention, the receiving system further comprises a delay lens disposed between the light modulator and the detector, configured to converge the light beam from the light modulator onto the detector, the light modulator being disposed at a focal plane of the receiving lens, the receiving system further comprising a lens array disposed between the receiving lens and the light modulator.

According to one embodiment of the invention, the receiving system 10 includes N light modulators and N detectors, N being greater than 1, wherein each light modulator has a corresponding field of view and the fields of view of any two light modulators do not completely coincide.

The invention also relates to a method 200 of echo reception processing with a lidar, which method 200 is implemented, for example, by a lidar 100 as described above, as shown in fig. 6. Described in detail below with reference to fig. 6.

In step S201, the optical modulator is controlled to switch between "on" and "off" states in a preset mode.

In step S202, the electrical signal generated by the detector is received and amplified.

In step S203, a point cloud of the laser radar is generated according to the amplified electric signal.

Embodiments of the present invention provide a solid state receive optical system solution (the transmit end may be mechanical, scanning, or flash). As shown in fig. 1, the lidar receives reflected light from a target obstacle, converges the reflected light onto an optical modulator (e.g., a reflective mirror of a digital micromirror array) through the receiving lens group, and converges the reflected light onto a detector through the delay lens group, where the detector is conjugate to the receiving lens group, and thus, light beams with different view field angles can be received by the detector.

In embodiments of the invention, field selection may be achieved by the optical modulator, the ambient light is controlled, the cell detector achieves reception and may increase the dynamic range (e.g., for SPAD, when the photosensitive size is small, the number of photosensitive cells is small, and when the signal light or the ambient light is strong, all cells may be saturated). The expensive cost of replacing an array detector. For example, a plurality of detectors are required to form a linear array or an area array before, and the invention can be realized by a single detector.

In addition, the laser radar receiving system realizes a solid-state receiving scheme through the DMD, has no mechanical moving part and is high in reliability. Meanwhile, each reflector unit of the DMD is controllable, can correspond to a very small view field of a radar system, and is controllable in ambient light, so that high signal-to-noise ratio can be realized; the detector can use a larger-sized photosensitive surface, so that the SiPM and other single-photon detectors can provide a large dynamic range.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A receiving system usable with a lidar comprising:

a detector disposed downstream of the optical modulator,

2. The receiving system of claim 1, the light modulator comprising a digital micromirror array comprising a plurality of micro-reflective cells, each micro-reflective cell being individually controllable and switchable between an "on" and an "off" state, one of the micro-reflective cells allowing a light beam incident thereon to be reflected onto the detector when in the "on" state; when it is in the "off" state, a light beam incident thereon is absorbed or reflected onto the light absorbing portion.

3. The receiving system of claim 1, the optical modulator comprising a light valve that, when in an "on" state, allows a light beam incident thereon to pass through and impinge on the detector; when in the "off" state, the light beam incident thereon is prevented from passing.

4. The receiving system according to any one of claims 1 to 3, further comprising a delay lens disposed between the light modulator and the detector, configured to converge the light beam from the light modulator onto the detector.

5. The receiving system according to any one of claims 1-3, wherein the light modulator is arranged at a focal plane of the receiving lens,

the receive system also includes a lens array disposed between the receive lens and the light modulator.

6. A receiving system according to any of claims 1-3, wherein the receiving system comprises N light modulators and N detectors, N being larger than 1, wherein each light modulator has a respective field of view, the fields of view of any two light modulators being at least partially non-coincident.

7. A lidar comprising:

a receiving system, comprising:

a detector disposed downstream of the optical modulator,

8. The lidar of claim 7, wherein the light modulator comprises a digital micro-mirror array comprising a plurality of micro-reflective units, each micro-reflective unit being individually controllable and switchable between an "on" and an "off" state, when one of the micro-reflective units is in the "on" state, it allows a light beam incident thereon to be reflected onto the detector; when it is in the "off" state, it stops reflecting the beam incident on it onto the detector.

9. The lidar of claim 7, wherein the optical modulator comprises a light valve that, when in an "on" state, allows a beam of light incident thereon to pass through and impinge on the detector; when in the "off" state, the light beam incident thereon is prevented from passing.

10. The lidar according to any of claims 7-9, wherein the receiving system further comprises a delay lens arranged between the optical modulator and the detector, configured to converge the light beam from the optical modulator onto the detector,

11. Lidar according to any of claims 7-9, wherein the receiving system comprises N light modulators and N detectors, N being larger than 1, wherein each light modulator has a respective field of view, the fields of view of any two light modulators not completely coinciding.

12. A method of echo reception processing using a lidar according to any of claims 7 to 11, comprising:

receiving and amplifying the electrical signal generated by the detector;