CN110780284B - Receiving system, laser radar including the same, and method of echo reception processing - Google Patents
Receiving system, laser radar including the same, and method of echo reception processing Download PDFInfo
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- CN110780284B CN110780284B CN201911159309.4A CN201911159309A CN110780284B CN 110780284 B CN110780284 B CN 110780284B CN 201911159309 A CN201911159309 A CN 201911159309A CN 110780284 B CN110780284 B CN 110780284B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/487—Extracting wanted echo signals, e.g. pulse detection
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/491—Details of non-pulse systems
- G01S7/4912—Receivers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/491—Details of non-pulse systems
- G01S7/493—Extracting wanted echo signals
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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; a detector array disposed downstream of the receive lens, the detector array comprising a plurality of detectors configured to convert optical signals incident thereon into electrical signals; and a liquid crystal shutter array disposed between the receive lens and the detector array and comprising a plurality of independently controllable liquid crystal shutters, wherein when the liquid crystal shutters are open, light beams from the receive lens and incident on the open liquid crystal shutters are allowed to pass through and impinge on one or more detectors of the detector array.
Description
Technical Field
The present invention generally relates to the field of optoelectronic technologies, and in particular, to a receiving system for a laser radar, a laser radar including the receiving system, and a method for performing echo receiving processing by using the receiving system.
Background
LiDAR is a general name of laser active detection sensor equipment, and the working principle of the LiDAR is roughly as follows: laser radar's transmitter launches a bundle of laser, and after laser beam met the object, through diffuse reflection, returned to laser receiver, radar module multiplies the velocity of light according to the time interval of sending and received signal, divides by 2 again, can calculate the distance of transmitter and object. Depending on the number of laser beams, there are generally, for example, a single line laser radar, a 4-line laser radar, an 8/16/32/64-line laser radar, and the like. One or more laser beams are emitted along different angles in the vertical direction and scanned in the horizontal direction to realize the detection of the three-dimensional profile of the target area. The multiple measurement channels (lines) correspond to the scan planes at multiple tilt angles, so that the more laser beams in the vertical field, the higher the angular resolution in the vertical direction, and the greater the density of the laser point cloud.
In many systems, such as large-receiving-surface APD detectors or SiPM single-photon detectors, shot noise caused by ambient light becomes a main noise source in the system, so that it becomes especially important to control ambient light. In the case of system parameter determination, the reduction of ambient light is mainly achieved by reducing the area of detector gating. The current common methods mainly comprise two types, one is to adopt a detector array or an addressable detector, but when the detection surface of the required detector is large, the method is expensive or very complicated; the other is by using Spatial Light Modulation (SLM) technology to selectively deflect the received optical signal, such as digital micromirror array (DMD), Grating Light Valve (GLV), and liquid crystal phased array. The surface grating light valve has the highest speed, can reach hundreds of ns magnitude in expectation of the fastest speed, but has low light efficiency under a large deflection angle due to the adoption of a diffraction light deflection principle; the DMD is adopted to predict the speed to be in the order of tens of us, but the effective deflection caliber is generally about 10 mm; the response speed of the conventional liquid crystal phased array is generally in the order of ms, so that the speed is low, and the problem of light efficiency reduction when the deflection angle is large exists. In addition, these main methods are basically based on reflective deflection, and the spatial layout of each part using the reflective deflection system is complicated due to factors such as the aperture and the divergence angle of the received light. A transmissive, optically efficient technique for providing high-speed gating capability to the receiving unit would be advantageous.
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
In view of at least one of the deficiencies of the prior art, the present invention provides a receiving system usable with a lidar comprising:
the receiving lens is configured to receive and converge the light beams reflected by the obstacles;
a detector array disposed downstream of the receive lens, the detector array comprising a plurality of detectors configured to convert optical signals incident thereon into electrical signals; and
a liquid crystal shutter array disposed between the receive lens and the detector array and comprising a plurality of independently controllable liquid crystal shutters, wherein when the liquid crystal shutters are open, light beams from the receive lens and incident on the open liquid crystal shutters are allowed to pass through and impinge on one or more detectors of the detector array.
According to one aspect of the invention, the detector comprises one or more of SiPM, APD, SPAD, the detector is in one-to-one correspondence with the liquid crystal shutter, and the liquid crystal shutter is a normally closed shutter.
According to an aspect of the present invention, the receiving system further includes a control unit that controls the plurality of liquid crystal shutters in the liquid crystal shutter array to open and close in sequence according to a preset sequence.
According to an aspect of the invention, the preset sequence corresponds to a transmission sequence of a plurality of lasers of a transmission system of the lidar.
According to one aspect of the invention, the receiving system further comprises a temperature control unit configured to monitor and control the temperature of the liquid crystal shutter array.
According to one aspect of the invention, the temperature control unit is configured to control the temperature of the liquid crystal shutter array about 20 degrees below a clearing temperature of liquid crystal material of the liquid crystal shutter array.
According to an aspect of the invention, the liquid crystal shutter array includes blue phase liquid crystal.
According to an aspect of the invention, the receiving system further comprises a wovenson prism and an 1/2 wave plate disposed in the optical path upstream of the liquid crystal shutter array, wherein the wovenson prism is configured to split the incident light into a first light beam having a first polarization state and a second light beam having a second polarization state, the first light beam is modulated into the second polarization state by the 1/2 wave plate, and the first light beam and the second light beam are incident on the liquid crystal shutter array together.
According to an aspect of the invention, the receiving system further comprises a converging lens, the converging lens is disposed between the 1/2 wave plate and the liquid crystal shutter array, and the second light beam and the first light beam after passing through the 1/2 wave plate are converged onto the liquid crystal shutter array by the converging lens.
According to one aspect of the invention, the detector array is integrated with the liquid crystal shutter array.
The invention also relates to a lidar comprising a receiving system as described above.
According to one aspect of the invention, the laser radar further comprises a transmitting system, the transmitting system comprises a plurality of lasers, the lasers correspond to the detectors in the detector array of the receiving system in a one-to-one mode, and the transmission of one laser triggers one or more liquid crystal shutters in the liquid crystal shutter array of the receiving system to be opened, so that the reflected light beams irradiate the detector corresponding to the laser.
According to an aspect of the present invention, the lidar further comprises a scanner and a controller, the scanner is disposed downstream of the optical path of the transmitting system and upstream of the optical path of the receiving lens, configured to reflect the light beam transmitted by the transmitting system to a three-dimensional space, and configured to receive and reflect an echo light beam reflected by a target to be measured in the three-dimensional space to the receiving lens; the controller is configured to predict the position of the echo light beam incident to the detector according to the movement speed of the scanner, and control one or more liquid crystal shutters corresponding to the predicted detector position to open.
The invention also relates to a method for processing echo reception by using the receiving system, which comprises the following steps:
controlling each liquid crystal shutter in the liquid crystal shutter array 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.
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 illustrates a receiving system according to one embodiment of the present invention;
FIG. 2 shows the liquid crystal switch array and detector array viewed from the front;
FIG. 3 shows a block diagram of a temperature control scheme in accordance with a preferred embodiment of the present invention;
FIG. 4 illustrates a solution to eliminate or mitigate energy loss due to polarization selectivity of liquid crystals;
FIG. 5 shows a schematic diagram of a paraxial lidar scheme in accordance with a preferred embodiment of the present invention;
FIG. 6 shows a schematic diagram of a coaxial lidar scheme in accordance with a preferred embodiment of the present invention;
FIG. 7 shows a liquid crystal switch array and detector array with static spots corresponding to spots while drifting;
fig. 8 shows a method for echo reception processing by the receiving system according to an 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 receiving system 10 according to an embodiment of the invention, which may be used, for example, in lidar to receive a reflected beam (or radar echo) from an external obstacle. Described in detail below with reference to fig. 1.
As shown in fig. 1, the receiving system 10 mainly includes a receiving lens 11, a detector array 12, and a liquid crystal shutter array 13. The receiving lens 11 is configured to receive an incident light beam, such as a light beam reflected from an obstacle, and condense or otherwise modulate the incident light beam so as to be incident on the detector array 13. The detector array 13 is arranged downstream of the optical path of the receiving lens 11 and comprises a plurality of detectors, as shown in fig. 1, comprising n detectors 13-1, 13-2, …, 13-n. When light is incident on the detector, the illuminated detector converts the light signal incident thereon into an electrical signal. The detector may be, for example, SiPM, APD, SPAD. The photoelectric conversion mechanism is not described in detail here. The n detectors may be arranged in a one-dimensional array, or may be arranged in a two-dimensional array, or may be arranged in a three-dimensional array, which are all within the scope of the present invention. The invention can also use a single large-area detector instead of an array with independent channels, and can also work normally, thereby solving the technical problem of the invention.
A liquid crystal shutter array 12 is disposed between the receiving lens 11 and the detector array 13, for example, overlying the detector array 13. The liquid crystal shutter array 12 includes a plurality of independently controllable liquid crystal shutters, which are shown in FIG. 1 as including m independently controllable liquid crystal shutters 12-1, 12-2, …, 12-m. In the invention, the liquid crystal shutter plays the role of a switch or a diaphragm, namely when the liquid crystal shutter is opened, the light beam which is from the receiving lens and is incident on the opened liquid crystal shutter is allowed to pass through and irradiate one or more detectors of the detector array. The liquid crystal shutter may be a normally closed shutter, i.e., a shutter in a closed state in a normal state, not allowing a light beam incident thereon to pass therethrough. Therefore, the ambient light is greatly blocked from being incident on the detector array 13, noise in the electrical signal generated by the detector is reduced, and the detection range of the laser radar can be significantly increased.
According to a preferred embodiment of the present invention, the number n of the detectors is equal to the number m of the liquid crystal shutters in a one-to-one correspondence relationship.
According to a preferred embodiment of the present invention, as shown in fig. 1, the receiving system 10 further comprises a control unit 14. The control unit 14 is coupled to the liquid crystal shutter array 12 so that the opening or closing of each of the liquid crystal shutters 12-1, 12-2, …, 12-m can be independently controlled. The control unit 14 may have a preset sequence logic built therein, for example, for sequentially controlling the plurality of liquid crystal shutters in the liquid crystal shutter array to open and close according to the sequence. In fig. 1, the liquid crystal shutter of dark color (labeled "ON") represents the liquid crystal shutter in an open state; the light color liquid crystal shutter (labeled "OFF") represents a liquid crystal shutter in a closed state.
When used in a lidar, the transmitting end of the lidar includes a plurality of lasers. For example, for mechanical radars, the number of lasers is the number of lines of the laser radar, and for 64-line laser radars, there are 64 lasers for emitting laser beams in a certain sequence, and the laser beams are reflected and modulated to emit probe beams from the laser radar. The same number of detectors, i.e. n equals the number of lines of the lidar, may be included in the detector array 13 of the receiving system 10 of the lidar, each detector corresponding to a laser at the transmitting end. In this case, the control unit 14 may control the opening and closing of the liquid crystal shutters in the liquid crystal shutter array 12 according to the emitting sequence of the laser at the emitting end, so that the liquid crystal shutter corresponding to one laser is opened after the probe beam emitted by the one laser is subjected to the diffuse reflection by the external obstacle of the laser radar, and the returned radar echo can pass through the opened liquid crystal shutter and irradiate on one detector corresponding to the laser.
According to a preferred embodiment of the present invention, the liquid crystal shutters in liquid crystal shutter array 12 may open with a delay compared to the firing of the laser of the lidar and the corresponding time of the liquid crystal shutters is time-of-flight dependent. For example, if a target detection distance of 300 meters is considered, i.e., the minimum time interval between adjacent points in the point cloud is equal to about 2us of flight time, the response time of the liquid crystal shutter needs to be about 10us considering that a certain delay tolerance can be allowed for the addressing of the receiving end.
Fig. 2 shows the liquid crystal shutter array 12 and the detector array 13 viewed from the front, which are superimposed in the front view. As shown in fig. 2, most of the liquid crystal switches are in the OFF state, while only the liquid crystal switches in the area illuminated by the laser spot are in the ON state, allowing the laser to pass through and illuminate the underlying detector array. In the lidar, the position and the size of a receiving spot are predictable (as mentioned above, the transmitting and receiving of the multi-line lidar have a definite corresponding relationship, for example, the lasers at the transmitting end of the multi-line lidar are arranged from top to bottom in the vertical direction, the detectors at the receiving end are arranged from top to bottom in the vertical direction, and the laser at the uppermost end corresponds to the detector at the uppermost end), so that the liquid crystal shutter can be controlled dynamically to open only the position of the spot, thereby isolating the ambient light to the maximum extent; the effect of dynamic addressing can be achieved even if the detector array does not have addressing work. Fig. 2 shows that the laser spot is positioned to cover a plurality of detectors and to turn on a plurality of liquid crystal switches, but the present invention is not limited thereto, and only one of the liquid crystal switches, for example, the liquid crystal switch corresponding to the center position of the laser spot, may be turned on.
In addition, the properties of the liquid crystal are related to its temperature. For example, when the temperature is lower than the clear temperature of the liquid crystal, the response speed of the liquid crystal is higher, and the response speed can reach about 30-50ns at most. In order to ensure that the liquid crystal shutter operates at a high response speed, the liquid crystal shutter may be set at a high constant operating temperature, but the operation of the liquid crystal shutter is not limited to a constant temperature. According to a preferred embodiment of the present invention, the receiving system 10 further comprises a temperature control unit, for example, comprising a temperature sensor and a heat sink, wherein the temperature sensor can monitor the temperature of the liquid crystal shutter array 12. When the liquid crystal temperature is too low, the switch response speed is reduced; when the liquid crystal temperature is too high, the transmittance of light decreases. Therefore, when the temperature of the liquid crystal exceeds a certain range, the speed and sensitivity of signal reception and processing of the reception system 10 may be reduced. In the embodiment of the present invention, the temperature of the liquid crystal shutter array 12 may be detected, and when the temperature of the liquid crystal shutter array 12 exceeds a certain threshold, the heat sink is activated for lowering the temperature of the liquid crystal shutter array 12. Preferably, the temperature control unit is configured to control the temperature of the liquid crystal shutter array to be about 20 degrees below the clear temperature of the liquid crystal material of the liquid crystal shutter array to ensure a higher switching speed of the liquid crystal shutter array 12.
FIG. 3 shows a block diagram of a temperature control scheme according to one embodiment of the invention. As shown, a semiconductor cooler TEC is employed for temperature control. The temperature of the liquid crystal shutter array 12 is obtained through the temperature sensor, the temperature is fed back, the difference between the temperature and the target temperature is obtained, the difference value is input into the PID controller, and the PID controller is coupled with the semiconductor refrigerator to control the operation of the semiconductor refrigerator TEC, so that the liquid crystal shutter array 12 is maintained at a certain temperature or within a certain temperature range. The semiconductor cooler TEC can heat and radiate heat, and the controlled object is ensured to work at the target temperature by controlling the semiconductor cooler TEC. According to an alternative embodiment of the present invention, the heating wire may be used for heating, and then the semiconductor cooler TEC starts to operate only when the temperature of the liquid crystal shutter array is higher than a preset temperature.
Laser emitted from the laser radar is generally polarized light, but a reflected light beam received by the laser radar generally has no polarization, and has different degrees of depolarization according to different reflectors; since most liquid crystal arrays are polarization selective, 50% of the received energy is expected to be lost after passing through the liquid crystal shutter array in the most severe cases (i.e., when the received light is fully depolarized), causing a reduction in the optical signal detected at the detector. To address this problem, according to a preferred embodiment of the present invention, the liquid crystal shutter array 12 employs blue phase liquid crystal. Since the blue phase liquid crystal has no polarization selectivity, almost all incident light can pass through the blue phase liquid crystal, and energy loss of light when the light passes through the blue phase liquid crystal is avoided or reduced.
Fig. 4 shows a preferred embodiment, which can be used to eliminate or reduce the above-mentioned problem of energy loss, wherein the received light without polarization characteristics can be first converted into polarized light, and the specific operation includes approximately lossless decomposing the general light into two polarized lights, changing the polarization state of one of the two polarized lights through a wave plate, and combining and converging the two polarized lights with the same polarization state, and then receiving the combined light by the detection end.
As shown in fig. 4, the receiving system 10 further includes a wovenson prism 15 and an 1/2 wave plate 16 disposed in the optical path upstream of the liquid crystal shutter array 12, wherein the wovenson prism is configured to split the incident light into a first light beam O in a first polarization state and a second light beam e in a second polarization state, and the first light beam is modulated into the second polarization state by the 1/2 wave plate, and then the first light beam and the second light beam are incident on the liquid crystal shutter array together. In this way, the problem of light energy loss through the liquid crystal shutter array is avoided or mitigated. In addition, preferably, the receiving system 10 further includes a converging lens 17, the converging lens 17 is disposed between the 1/2 wave plate and the liquid crystal shutter array, and the second light beam and the first light beam passing through the 1/2 wave plate are converged onto the liquid crystal shutter array by the converging lens. The above wovenson prisms 15 and 1/2 wave plate 16 and the converging lens 17 are disposed on the receiving lens 11 and the liquid crystal shutter array 12 of fig. 1, for example, so that the light beam received by the receiving lens 11 is first split into two polarization states, i.e., a first light beam and a second light beam, and the polarization state of one of the two light beams is changed by the 1/2 wave plate, and then the first light beam and the second light beam are incident on the liquid crystal shutter array 12 through the converging lens 17, and both the first light beam and the second light beam can pass through the opened liquid crystal shutter in the liquid crystal shutter array 12 and irradiate on the detector array 13, because the polarization states of the first light beam and the second light beam selectively coincide with the polarization of the liquid crystal shutter array 12. One of the main purposes of the condenser lens 17 is to make the received light incident as perpendicular as possible to the liquid crystal shutter array 12 to improve the light transmittance. Those skilled in the art will readily appreciate that the position of the converging lens 17 may be determined based on the actual spot and the system layout. Although the condenser lens 17 is shown in fig. 4 as being located between the 1/2 wave plate and the liquid crystal shutter array 12, the condenser lens 17 may be disposed upstream of the wovenson prism, i.e., the light beam is preliminarily condensed before being incident on the wovenson prism.
According to a preferred embodiment of the present invention, the detector array 13 and the liquid crystal shutter array 12 can be integrally manufactured by using a microelectronic process, the interface layer can be reduced by using an integrated manufacturing process to improve the optical efficiency, and the transmittance of visible light and near infrared light bands can reach about 90%.
The invention also relates to a lidar comprising a receiving system as described above.
As described above, the lidar further comprises a transmitting system comprising a plurality of lasers, the lasers corresponding to the detectors in the detector array of the receiving system one to one, and wherein the transmission of one laser triggers the opening of one or more liquid crystal shutters in the liquid crystal shutter array of the receiving system, so that the reflected light beam impinges on the one detector corresponding to the one laser.
Fig. 5 shows a schematic diagram of a paraxial lidar scheme according to a preferred embodiment of the present invention, wherein at the transmitting end (left side in fig. 5), the lidar comprises a light source, a transmitting lens and a scanner, wherein the light source emits a laser beam through the transmitting lens and onto the scanner, and the scanner is a micromirror or a galvanometer, for example, which oscillates back and forth within a certain range, so as to reflect the incident light beam to different directions and cover a certain range of exit angles. At the receiving end (right side in fig. 5) the lidar includes a receive lens, a liquid crystal shutter array, and a detector (e.g., a single APD or SiPM). The receiving lens is used for converging radar echoes from the outside of the laser radar, the converged radar echoes are incident on the liquid crystal shutter array, and a controller (not shown) of the laser radar controls one or more liquid crystal shutters in the liquid crystal shutter array to be opened, so that light beams incident on the liquid crystal shutters are allowed to pass through and irradiate on the detector, and photoelectric signals are converted.
Fig. 6 shows a schematic diagram of an on-axis lidar solution according to another preferred embodiment of the present invention, wherein, for a transmitting end (left side in fig. 6), the lidar comprises a light source, a transmitting lens (labeled as a lens in fig. 6), a scanner and a controller (not shown), wherein, a laser beam emitted by the light source passes through the transmitting lens and then irradiates the scanner, and the scanner, such as a micromirror or a galvanometer, swings back and forth within a certain range, so as to reflect the light beam incident thereon to different directions, covering a certain exit angle range. To the receiving end (lower left side in fig. 6), the lidar includes a receiving lens (denoted as lens in fig. 6, i.e. in this embodiment the same lens is used for both transmission and reception), an array of liquid crystal shutters, and a detector (e.g. a single APD or SiPM). The scanner also receives and reflects the echo light beam reflected by the target to be detected in the three-dimensional space to the receiving lens, the receiving lens is used for converging the radar echo from the outside of the laser radar, and the converged radar echo is incident on the liquid crystal shutter array. Theoretically, the detector is a stationary light spot, but the receiving end passes through the scanner first, and since the transmitting and receiving light path in fig. 6 uses the same scanner, there is a situation that the scanner is at position a during transmission and the light transmission takes a certain time during reception, if the scanner is at a faster scanning speed and the scanner is already at position B during reception, the receiving position will slightly change, and in order to compensate for this situation or to accommodate the spot enlargement or drift caused by optical system aberration, etc., the controller of the laser radar can predict the position where the echo light beam enters the detector according to the movement speed of the scanner and control one or more liquid crystal shutters corresponding to the predicted detector position to open (for example, refer to fig. 7), so that the light beam entering the detector is allowed to pass through, irradiating the detector to convert photoelectric signals. Due to the spot drift caused by the scanner, in this embodiment, the gating mainly acts to correct this spot drift, and the spot drift is larger as the angular velocity of the scanner is larger.
In other words, by predicting the light spot drift or deformation and adjusting the corresponding opening of the liquid crystal shutter accordingly, the light spot drift can be overcome when a high-speed scanner such as a galvanometer is adopted, so that the receiving energy is not wasted because of few opening windows, and a large amount of ambient light is not received because of gating too many channels. And, because the light spot drift amount is related to the scanning angular velocity of the galvanometer, the drift amount of the light spot position is predictable, so that different gating control can be performed for different displacements.
As shown in fig. 8, the present invention also relates to a method 100 for echo reception processing by using the receiving system as described above, including:
in step S101, each liquid crystal shutter in the liquid crystal shutter array is controlled to switch between an "on" state and an "off" state in a preset mode.
The preset pattern may for example correspond to the firing order of the laser at the transmitting end of the lidar. When one or more of the liquid crystal shutters is opened, a light beam incident on the opened liquid crystal shutter is allowed to pass therethrough to be irradiated onto the detector.
In step S102, the electrical signal generated by the detector is received and amplified.
The detector generates an electrical signal based on the light beam impinging thereon. The signal processing circuit receives the electrical signal. Generally, the electrical signal is weak, and therefore, amplification is required to perform subsequent operations such as data sampling, analog-to-digital conversion, and filtering.
In step S103, a point cloud of the laser radar is generated according to the amplified electrical signal.
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 (13)
1. A receiving system usable with a lidar comprising:
the receiving lens is configured to receive and converge the light beams reflected by the obstacles;
a detector array disposed downstream of the receive lens, the detector array comprising a plurality of detectors configured to convert optical signals incident thereon into electrical signals; and
a liquid crystal shutter array which is arranged between the receiving lens and the detector array and comprises a plurality of liquid crystal shutters which can be independently controlled, wherein when the liquid crystal shutters are opened, light beams from the receiving lens and incident on the opened liquid crystal shutters are allowed to pass through and irradiate one or more detectors of the detector array, wherein the opening or closing of the liquid crystal shutters is controlled to be related to the emergent angle of the emergent light beam of the laser radar;
the lidar further comprises a scanner and a controller, wherein:
the scanner is arranged on the downstream of the light path of the emission system and the upstream of the light path of the receiving lens, is configured to reflect the light beam emitted by the emission system to a three-dimensional space, and is configured to receive and reflect the echo light beam reflected by the target to be detected in the three-dimensional space to the receiving lens;
the controller is configured to predict the position of the echo light beam incident to the detector according to the movement speed of the scanner, and control one or more liquid crystal shutters corresponding to the predicted detector position to open.
2. The receiving system of claim 1, wherein the detector comprises one or more of SiPM, APD, SPAD, the detector being in a one-to-one correspondence with the liquid crystal shutter, the liquid crystal shutter being a normally closed shutter.
3. The receiving system according to claim 1, further comprising a control unit that controls a plurality of liquid crystal shutters in the liquid crystal shutter array to open and close in sequence according to a preset sequence.
4. The receiving system of claim 3, the preset order corresponding to a transmission order of a plurality of lasers of a transmission system of the lidar.
5. The receiving system of any of claims 1-3, further comprising a temperature control unit configured to monitor and control a temperature of the liquid crystal shutter array.
6. The receiving system of claim 5, wherein the temperature control unit is configured to control the temperature of the liquid crystal shutter array about 20 degrees below a clearing temperature of liquid crystal material of the liquid crystal shutter array.
7. The receiving system of any of claims 1-3, wherein the array of liquid crystal shutters comprises blue phase liquid crystal.
8. The receiving system of any of claims 1-3, further comprising a Wolff prism and 1/2 wave plate disposed optically upstream of the liquid crystal shutter array, wherein the Wolff prism is configured to split incident light into a first beam of a first polarization state and a second beam of a second polarization state, the first beam being modulated to the second polarization state by the 1/2 wave plate, the first beam and the second beam being co-incident on the liquid crystal shutter array.
9. The receiving system of claim 8, further comprising a converging lens disposed between the 1/2 wave plate and the liquid crystal shutter array, the second light beam and the first light beam after passing through the 1/2 wave plate being converged by the converging lens onto the liquid crystal shutter array.
10. The receiving system of any of claims 1-3, wherein the detector array is integrated with the liquid crystal shutter array.
11. A lidar comprising a receiving system as claimed in any of claims 1-10.
12. The lidar of claim 11, further comprising a transmit system comprising a plurality of lasers in one-to-one correspondence with detectors in the detector array of the receive system, and wherein transmission of one laser triggers opening of one or more liquid crystal shutters in the liquid crystal shutter array of the receive system such that the reflected beam impinges on the one detector corresponding to the one laser.
13. A method of echo reception processing using the receiving system of any of claims 1-10, comprising:
controlling each liquid crystal shutter in the liquid crystal shutter array 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.
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