CN115808693A

CN115808693A - Laser radar

Info

Publication number: CN115808693A
Application number: CN202111079548.6A
Authority: CN
Inventors: 吴世祥; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2021-09-15
Filing date: 2021-09-15
Publication date: 2023-03-17
Also published as: WO2023040377A1

Abstract

The present invention provides a laser radar, including: a light emitting unit for emitting a probe light signal; a light receiving unit for receiving an echo light signal generated from the probe light signal; a main optical system disposed between the light emitting unit and the light receiving unit, for receiving the detection light signal and transmitting it to the outside; and for receiving the echo optical signal and transmitting it to the optical receiving unit; the beam expanding unit is arranged between the main optical system and the light receiving unit and used for receiving the echo light signals passing through the main optical system, expanding the beams and then transmitting the expanded signals to the light receiving unit; the equivalent focal length of the combination of the main optical system and the beam expanding unit is larger than that of the main optical system so as to compress the field angle of the light receiving unit. The laser radar of the invention enables the receiving end to extend the focal length through the optical system so as to compress the field angle of the receiving end, does not need devices such as a diaphragm and the like, and is matched with the coaxial receiving and transmitting optical system so as to enable the structure to be more compact.

Description

Laser radar

Technical Field

The invention relates to the field of optical ranging, in particular to a laser radar.

Background

The lidar is a detection device that calculates an object distance by emitting laser light and detecting an echo signal reflected after the laser light reaches the surface of the object. The ranging performance is an important technical index of the laser radar, and mainly depends on the signal-to-noise ratio level of a laser radar system, and the reduction of the ambient light is an important link in the design of an optical system of the laser radar because the ambient light is an important noise source influencing the signal-to-noise ratio level of the laser radar.

The current way of suppressing ambient light of the optical system of laser radar has two main aspects:

on the one hand, it is necessary to set the proper focal length of the optical system at the receiving end (i.e., the detector side). Particularly, the focal length of the optical system at the receiving end needs to be matched with the emitting focal length, the effective size of the laser and the effective size of the optical detector. In addition, the length of the focal length of the optical system has a great influence on the total volume of the laser radar. Therefore, most of the receiving end optical systems have focal lengths within 100mm at present, regardless of mechanical radars or solid-state radars.

For example, silicon photomultipliers (sipms) are susceptible to saturation under intense ambient light conditions. It is often desirable to limit the field of view of the SiPM to avoid receiving more ambient light. However, this creates a contradiction. For example, in a receiving end optical system, a large-size detector is used, and a long-focus optical system is required to be compressed to a small field angle; however, the use of long focal length optical systems is not conducive to compact, small lidar designs.

Referring to fig. 1, the height of the detector 101 shown in fig. 1 is L, f is the focal length of the receiving lens 102 (equivalently, a convex lens), and θ is the field angle. Here, the Field angle is an Instantaneous Field angle (IFOV), and refers to a light receiving angle or an observation Field of view of a single photodetector. The calculation formula for obtaining the angle of view is

As can be seen from the formula, if the detector 101 with a large photosensitive surface is used (for example, when SiPM is used), the height L is large, and in order to limit the field angle θ of the detector 101 to avoid saturation of the detector 101 due to receiving more ambient light, the focal length f of the receiving-end optical system needs to be increased.

To solve this problem, as shown in fig. 2, in the prior art, ambient light is suppressed by adding an aperture stop 203 to the receiving-end optical system. Specifically, as shown in the figure, by providing an aperture stop 203 between the receiving lens 202 and the detector 201, the aperture stop 203 is located at the focal position of the receiving lens 202, and the light passing through the aperture stop 203 is made to cover the entire effective area of the detector 201 (the coverage height L is taken as an example in the figure). As can be seen from the figure, the aperture stop 203 allows the light corresponding to the field angle θ 'to pass through, while the light of other field angles is blocked, so that the actual field angle of the detector 201 is compressed from θ to θ', and the aperture stop 203 allows the passing light to cover the whole effective area of the detector 201, so as to achieve the effect of the long-focus optical system.

However, for the laser radar, the aperture stop belongs to an optical component which needs to be additionally added, on one hand, the additional cost is increased, and on the other hand, the installation and debugging work is also increased.

On the other hand, there is a method of using a filter corresponding to the laser wavelength to filter ambient light other than the laser wavelength by compressing the filter bandwidth. However, the bandwidth of the filter is affected by factors such as the bandwidth of the laser, the temperature of the working environment and the like. For most of the laser radars which adopt a semiconductor laser as a light source, the space for further compressing the bandwidth of an optical filter is limited, and the ambient light cannot be controlled to an ideal level.

Disclosure of Invention

In view of the above disadvantages of the prior art, the present invention provides a laser radar, which suppresses the influence of ambient light on a detector, improves the dynamic range of the laser radar during detection, and improves the ranging capability of the laser radar.

To achieve the above and other related objects, a first aspect of the present invention provides a lidar comprising: a light emitting unit for emitting a probe light signal; a light receiving unit for receiving an echo light signal generated by the probe light signal; a main optical system, configured between the light emitting unit and the light receiving unit, for receiving the probe light signal and transmitting it outwards; and the optical receiving unit is used for receiving the echo optical signal and transmitting the echo optical signal to the optical receiving unit; the beam expanding unit is arranged between the main optical system and the light receiving unit and used for receiving an echo light signal passing through the main optical system, expanding the beam and then transmitting the expanded echo light signal to the light receiving unit; wherein the equivalent focal length of the combination of the main optical system and the beam expanding unit is larger than that of the main optical system so as to compress the field angle of the light receiving unit.

In an embodiment of the first aspect, a transmission path of the probe light signal is partially the same as a transmission path of the return light signal in the lidar.

In an embodiment of the first aspect, the primary optical system comprises: a positive lens unit and a light splitting unit; the positive lens unit is used for receiving the detection light signal from the light splitting unit and transmitting the detection light signal outwards; the optical splitter is used for receiving the echo optical signal and transmitting the echo optical signal to the optical splitting unit; the light splitting unit is used for receiving the detection light signal and transmitting the detection light signal to the positive lens unit; and a positive lens unit for receiving the echo optical signal from the positive lens unit and transmitting the echo optical signal to the light receiving unit.

In an embodiment of the first aspect, a distance between the beam expanding unit and the positive lens unit is smaller than a focal length of the positive lens unit.

In an embodiment of the first aspect, the light-sensing surface of the light-receiving unit is located at a focal plane of the combination of the main optical system and the beam expanding unit.

In an embodiment of the first aspect, the equivalent focal length is also larger than a distance between a principal plane of the principal optical system and a photosensitive surface of the light receiving unit.

In an embodiment of the first aspect, the light splitting unit comprises: a reflection unit including a reflection portion for reflecting one of the echo optical signal and the probe optical signal; the reflection unit further includes a transmission portion or an external gap fitted to the reflection unit for passing the other of the probe light signal and the echo light signal.

In an embodiment of the first aspect, the primary optical system further comprises: the polarization unit is arranged on one side, back to the light splitting unit, of the positive lens unit and is used for changing the polarization states of the detection optical signal and the echo optical signal so as to enable the output detection optical signal to be in a first polarization state and enable the output echo optical signal to be in a second polarization state, and the first polarization state is different from the second polarization state; the beam splitting unit is arranged between the positive lens unit and the beam expanding unit and is configured to allow the echo optical signals in the second polarization state to pass through.

In an embodiment of the first aspect, the lidar further includes: and the scanning unit can be rotationally arranged in one dimension or two dimensions, is used for rotating to a preset posture to enable the detection light signals to be outwards transmitted at a corresponding scanning angle, and is used for transmitting the echo light signals corresponding to the detection light signals to the main optical system.

In an embodiment of the first aspect, the light receiving unit includes: an array of photodetectors; the beam expanding unit comprises a sub beam expanding unit array, wherein each sub beam expanding unit is arranged corresponding to one or more light detectors.

In an embodiment of the first aspect, a light detector corresponding to each first sub beam expansion unit in the middle area of the sub beam expansion unit array corresponds to a central field angle of a field of view of the lidar, and each first sub beam expansion unit includes a non-eccentric lens; and the optical detector corresponding to each second sub beam expansion unit in the peripheral area except the middle area of the sub beam expansion unit array corresponds to the edge view field angle except the central view field angle of the laser radar, and each second sub beam expansion unit comprises an eccentric lens.

In an embodiment of the first aspect, the array of sub beam expanding units is a micro lens array for packaging the photodetector array.

In an embodiment of the first aspect, the photodetector array comprises: a circuit substrate having a first surface on which the photodetector array is disposed; and the optical carrier is provided with a second surface for arranging the micro-lens array, is packaged into a whole with the circuit substrate, and enables the second surface to be opposite to the first surface, so that each micro-lens is arranged corresponding to each light detector.

In an embodiment of the first aspect, the light receiving unit includes: the light receiving unit includes: the optical detector array is arranged in a linear array; the beam expanding unit comprises at least one cylindrical negative lens, the cylindrical negative lens is arranged corresponding to part or all of the light detector arrays in the light receiving unit, and the extending direction of the cylindrical negative lens is the length direction of the light detection arrays.

The laser radar in the embodiment of the invention has the following beneficial effects:

the long-focus optical system is realized by combining the main optical system and the beam expanding unit, and the long-focus optical system is applied to the laser radar and can realize the long focus of the light receiving unit in a compact volume.

On one hand, the long-focus optical system can greatly reduce the influence of ambient light on a detector (such as SiPM) under the condition of using the detector with larger photosensitive surface size, and can still keep the compact structure of the laser radar.

On the other hand, under the condition of the same angular resolution, a detector (such as SiPM) with a larger photosurface size is used, so that the detector can have more photosite units, and the dynamic range of the detection system is improved. Therefore, the optical system in the embodiment of the invention plays an important role in the ranging performance of the laser radar no matter the influence of the ambient light is reduced or the dynamic range is improved.

Drawings

Fig. 1 shows a schematic diagram of the relationship between the detector size, the field angle and the focal length in an example.

Fig. 2 shows a schematic diagram of an example lidar employing an aperture stop to suppress ambient light.

Fig. 3 is a schematic structural diagram of an optical system of a lidar in an embodiment of the invention.

Fig. 4 shows a schematic diagram of an optical system in an embodiment of the invention.

Fig. 5A and 5B respectively show structural schematic diagrams of an optical system of a two-dimensional scanning lidar based on a polarization beam splitting unit for achieving beam splitting in different embodiments of the present invention.

Fig. 6 and fig. 7 respectively show schematic structural diagrams of an optical system of a two-dimensional scanning lidar for realizing light splitting based on a reflection unit in different embodiments of the invention.

Fig. 8A shows a schematic structural diagram of a positive-negative lens combination implementation in yet another embodiment of the present invention.

FIG. 8B shows a perspective view of the positive-negative lens combination of FIG. 8A.

FIG. 9A is a schematic diagram of an arrangement of a photo-detector array according to an embodiment of the invention.

FIG. 9B is a schematic diagram of another arrangement of the photo-detector array in the embodiment of the invention.

FIG. 10 shows a schematic layout of the negative lens array and the photo-detector array in the embodiment of the invention.

Fig. 11A and 11B respectively show structural diagrams of an optical system employing a negative lens array as a beam expanding unit according to different embodiments of the present invention.

Fig. 12A and fig. 12B respectively show structural diagrams of an arrangement of a negative lens array suitable for an optical detector array in different embodiments of the present invention.

FIG. 13 is a schematic diagram of a photodetector array and a microlens array package according to an embodiment of the invention.

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In order to clearly explain the present invention, components that are not related to the description are omitted, and the same reference numerals are given to the same or similar components throughout the specification.

Throughout the specification, when a device is referred to as being "connected" to another device, this includes not only the case of being "directly connected" but also the case of being "indirectly connected" with another element interposed therebetween. In addition, when a device "includes" a certain constituent element, unless otherwise specified, it means that the other constituent element is not excluded, but may be included.

When a device is said to be "on" another device, this may be directly on the other device, but may also be accompanied by other devices in between. When a device is said to be "directly on" another device, there are no other devices in between.

Although the terms first, second, etc. may be used herein to describe various elements in some instances, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first interface and a second interface, etc. are described. Also, as used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes" and/or "including," when used in this specification, specify the presence of stated features, steps, operations, elements, components, items, species, and/or groups, but do not preclude the presence, or addition of one or more other features, steps, operations, elements, components, species, and/or groups thereof. The terms "or" and/or "as used herein are to be construed as inclusive or meaning any one or any combination. Thus, "a, B or C" or "a, B and/or C" means "any of the following: a; b; c; a and B; a and C; b and C; A. b and C ". An exception to this definition will occur only when a combination of elements, functions, steps or operations are inherently mutually exclusive in some way.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" include plural forms as long as the words do not expressly indicate a contrary meaning. The term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and/or components.

Terms representing relative spatial terms such as "lower", "upper", and the like may be used to more readily describe one element's relationship to another element as illustrated in the figures. Such terms are intended to include not only the meanings indicated in the drawings, but also other meanings or operations of the device in use. For example, if the device in the figures is turned over, elements described as "below" other elements would then be oriented "above" the other elements. Thus, the exemplary terms "under" and "beneath" all include above and below. The device may be rotated 90 or other angles and the terminology representing relative space is to be interpreted accordingly.

Although not defined differently, including technical and scientific terms used herein, all have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms defined in commonly used dictionaries are to be interpreted as having meanings consistent with those of the related art documents and the present prompts, and must not be excessively interpreted as having ideal or very formulaic meanings unless defined otherwise.

The optical system of the laser radar has the problem of ambient light interference, and especially in the case of considering the distance measuring capability of the laser radar, a light detector (such as SiPM) with a larger size is selected, and the corresponding field angle is larger, which means that the angle capable of receiving the interfering ambient light is larger. For this reason, the foregoing two improvements of suppressing ambient light have been made in the present laser radar, but the laser radar product is limited in volume so that it is difficult to set an appropriate focal length, and an optical device such as an aperture stop needs to be added to achieve an extension of the focal length of the optical system. Another is to compress the angle of view of the photodetector by compressing the bandwidth of the filter, but there is a problem of being limited by the physical configuration parameters of the lidar.

In view of this, the embodiments of the present invention provide an improved structure of the lidar.

Fig. 3 is a schematic structural diagram of an optical system of a lidar in an embodiment of the present invention. The laser radar 300 includes: a light emitting unit 301, a light receiving unit 302, a main optical system 303, and a beam expanding unit 304.

The light emitting unit 301 is configured to emit a probe light signal, which may also be referred to as an emitting end. In some embodiments, the light emitting unit 301 may include a light emitter array including a plurality of light emitters arranged in a two-dimensional area array or a one-dimensional linear array. Each light emitter may be an Edge-Emitting semiconductor Laser (EEL) or a Vertical-Cavity Surface-Emitting Laser (VCSEL).

The light receiving unit 302 is configured to receive an echo light signal generated by the probe light signal, where the probe light signal may be irradiated on an obstacle surface and reflected to form the echo light signal; the light receiving unit 302 may also be referred to as a receiving end. In some embodiments, the light receiving unit 302 may include a photodetector array including a plurality of photodetectors arranged in a two-dimensional planar array or a one-dimensional linear array. Each photodetector may be a silicon photomultiplier tube (SiPM) or a Single Photon Avalanche Diode (SPAD), or the like.

The main optical system 303 is configured between the light emitting unit 301 and the light receiving unit 302, and is used for receiving the detection light signal and transmitting the detection light signal to the outside; and is configured to receive the echo optical signal and transmit the echo optical signal to the optical receiving unit 302.

In the illustration, the first transmission path J of the probe optical signal is partially the same as the second transmission path K of the echo optical signal, i.e., the main optical system 303 is a coaxial optical system for transmitting and receiving. The main optical system 303 includes a positive lens unit 331 and a light splitting unit 332. The light beam transmission path between the positive lens unit 331 and the light splitting unit 332 is common to a first transmission path J indicated by an arrow along a thin black solid line and a second transmission path K indicated by a thick hatched arrow.

The positive lens unit 331 is configured to receive the probe light signal from the light splitting unit 332 and transmit the probe light signal in a direction outside the laser radar 300, and is configured to receive the echo light signal and transmit the echo light signal to the light splitting unit 332. Specifically, the positive lens unit 331 may converge the received probe light signal to collimate the probe light signal and transmit the probe light signal to the outside, and specifically, as shown in the figure, the probe light signal may be output to the scanning unit 305 and transmitted to the outside of the laser radar 300 through the scanning unit 305; the positive lens unit 331 may also converge the echo optical signals and transmit them to the light receiving unit 302, specifically, as shown in the figure, receive the echo optical signals from the scanning unit 305. In some examples, the scanning unit 305 may be rotationally arranged in one or two dimensions, and configured to rotate to a predetermined posture so that the probe light signal is transmitted outward at a corresponding scanning angle, and configured to transmit the echo light signal corresponding to the probe light signal to the main optical system 303. Illustratively, the scanning unit 305 may include any one of a galvanometer, a MEMS mirror, and a turning mirror.

The light splitting unit 332 transmits the probe light signal and the echo light signal among the light emitting unit 301, the light receiving unit 302, and the positive lens unit 331. As shown in fig. 4, on one hand, the detection optical signal is transmitted along the first transmission path J indicated by the thin black solid arrow, and the optical splitting unit 332 receives the detection optical signal of the optical transmitting unit 301 and transmits the detection optical signal to the positive lens unit 331; and on the other hand, the echo optical signal is transmitted in the direction of the second transmission path K indicated by the arrow with thick hatching, and the light splitting unit 332 receives the echo optical signal from the positive lens unit 331 and transmits it to the light receiving unit 302. Illustratively, the light splitting unit 332 may split the probe light signal and the echo light signal by deflection or transmission. For example, in the example of fig. 4, the light splitting unit 332 transmits the echo light signal, and deflects (e.g., reflects) the probe light signal for transmission. In other embodiments, the optical system may also be configured such that the beam splitting unit 332 deflects the received echo optical signal and transmits the deflected echo optical signal to transmit the received probe optical signal.

The beam expanding unit 304 is disposed between the primary optical system 303 and the light receiving unit 302, and configured to receive the echo light signal passing through the primary optical system 303, expand the beam, and transmit the expanded beam to the light receiving unit 302. In a specific example, the beam expanding unit 304 corresponds to a negative lens unit in the embodiment of fig. 3, and may be implemented by a negative lens or a negative lens group. The focal length of the receiving-end optical system in laser radar 300 is lengthened by the combined action of positive lens unit 331 and the negative lens unit.

In some embodiments, the light splitting unit 332 may be an optical component that passes the optical signal of a specific polarization state, and the optical signal of the remaining polarization state does not pass through. In a specific example, the probe optical signal and the echo optical signal may have different polarization states, so that the echo optical signal in a specific polarization state is allowed to pass through by the light splitting unit 332, and the probe optical signal in the other polarization state is not allowed to pass through.

In order to make the probe optical signal and the echo optical signal in different polarization states, in a possible example, the main optical system 303 further includes a polarization unit, disposed on a side of the positive lens unit 331 opposite to the light splitting unit 332, for changing the polarization states of the probe optical signal and the echo optical signal so as to make the output probe optical signal in a first polarization state and make the output echo optical signal in a second polarization state, where the first polarization state is different from the second polarization state; accordingly, the beam splitting unit 332 is disposed between the positive lens unit 331 and the beam expanding unit 304, and configured to allow the echo optical signal in the second polarization state to pass through.

In still other embodiments, the light splitting unit 332 may also be implemented by a reflection unit, and the reflection unit may include a reflection portion for reflecting one of the echo light signal and the detection light signal, and the reflection unit further includes a transmission portion (refer to fig. 7 embodiment in particular) or the reflection unit is fitted with an external gap (refer to fig. 6 embodiment in particular) for passing, e.g. transmitting, the other of the detection light signal and the echo light signal.

The principle of the positive lens unit 303 and the beam expanding unit 304 cooperating to realize the long focal length optical system is described in detail below from the perspective of the optical path structure.

It should be noted that the viewing angles shown in the following embodiments of fig. 4, 5A, 5B, 6, and 7 are instantaneous viewing angles, i.e., the principle of the technical solution of the present invention is more clearly and intuitively explained through the light receiving angle or the observation field of the single photodetector.

Fig. 4 is a schematic structural diagram of an optical system according to an embodiment of the present invention. The optical system in fig. 4 can be applied to the receiving end of a laser radar. Specifically, the optical system includes a combination of a positive lens 401 and a negative lens 402. The positive lens 401 has a focal length f1, an angle of view α, and a focal point a. The negative lens 402 has an angle of view γ. The light passing through the positive lens 401 should be converged at the point a, but after the negative lens 402 is disposed between the principal plane of the positive lens 401 and the focal point a of the positive lens 401, the converging point of the light is moved away from the point a to the point B due to the expanding action of the negative lens 402 on the light, and the angle of view becomes γ, which is smaller than α. The positive lens 401 and the negative lens 402 in combination form an equivalent lens with a principal plane and a focal point B at a distance f, i.e. the focal length of the equivalent lens is f.

It was found that f was extended compared to f 1. At a certain distance between the positive lens 401 and the negative lens 402 (e.g., the distance between the principal planes of the two is smaller than the focal length of the positive lens 401), the focal length of the optical system can be increased by the combination of the positive lens 401 and the negative lens 402.

Moreover, if the light detector is arranged at the focal plane of point B, the distance L between the principal plane of the positive lens 401 and the focal plane of point B is the physical length of the optical system, and f is greater than L, which indicates that the equivalent focal length f of the equivalent lens exceeds the limit of the physical size of the optical system.

It should be noted that the positive lens 401 and the negative lens 402 in the drawings are only simplified representations, and may be equivalent representations of lens groups in practical applications, which are not limited to the drawings.

Obviously, the optical system can effectively prolong the focal length to obtain the focal length beyond the limit of physical size, and can keep the compact structure of the laser radar, thereby effectively solving the problems in the prior art and omitting an aperture diaphragm.

When the optical system is applied to the laser radar, the original optical system at the receiving end side of the laser radar is used for converging the echo light signalCorresponds to the positive lens 401 in fig. 4. Therefore, by only arranging the negative lens 402 or a lens group implementing the negative lens 402 between the lens group and the photodetector, the focal length of the receiving end can be greatly extended, so that when a larger-sized photodetector (e.g., siPM, the photosensitive surface of the SiPM is more than twice as large as that of APD), the optical lens system can be designed according to the requirements

f can be increased with increasing L to limit the field angle γ to suppress interference of ambient light and thus avoid saturation of the photodetector.

In some alternative embodiments, a structure for folding the optical path (such as adding a mirror) may be further provided on the basis of fig. 4, so that the system size L = f1, which may keep the structure compact and achieve a longer focal length f while keeping the physical size of the receiving-end optical system of the lidar unchanged.

In a possible example, as shown in fig. 5A and fig. 5B, schematic structural diagrams of an optical system of a two-dimensional scanning lidar based on polarization splitting unit for achieving beam splitting in different examples of the present invention are respectively shown.

The laser radar includes: a light emitter array 501, a light detector array 502, a positive lens 503 (equivalent representation, can be implemented by a lens set), a negative lens 504 (equivalent representation, can be implemented by a lens set), a polarization beam splitter, a quarter wave plate 506, a mirror 507, and a scanner 508. Fig. 5A and 5B illustrate a specific implementation on the basis of the embodiment of fig. 4, and the light emitter array 501 and the light detector array 502 correspond to the exemplary implementation of the light emitting unit and the light receiving unit in the embodiment of fig. 4, respectively. The positive lens 503 and the negative lens 504 correspond to example implementations of the positive lens 503 unit and the negative lens 504 unit in fig. 4, respectively, and are graphically represented in fig. 5A and 5B by simplified positive lens 503 and negative lens 504. The polarization splitting device corresponds to an example implementation of the splitting unit in the embodiment of fig. 4, the quarter-wave plate 506 corresponds to the polarization unit in the embodiment of fig. 4, and the quarter-wave plate 506 can be used for changing the polarization state of the passing optical signal. The scanner 508 corresponds to an example implementation of the scanning unit in fig. 4.

The difference between fig. 5A and fig. 5B is mainly that the polarization splitting device in fig. 5A is implemented as a polarization splitting prism 505A, and the polarization splitting device in fig. 5B is implemented as a polarization splitting sheet 505B.

Specifically, in the embodiment of fig. 5A and 5B, the light emitter array 501 emits laser beams, wherein a part of polarized light is reflected by the polarization beam splitter, collimated by the positive lens 503, changed into a first polarization state by the quarter-wave plate 506, reflected by the mirror 507, and scanned by the scanner 508 to irradiate a target in a corresponding field angle, and the target reflected laser beams form an echo light signal; the echo light signal returns to enter the laser radar, is reflected by the scanner 508 and the reflector 507, changes the polarization state of the laser beam to be the second polarization state again through the quarter wave plate 506, is converged through the positive lens 503, and then part of the polarization light is transmitted by the polarization beam splitter, and further realizes the extension of the focal length through the negative lens 504, and is correspondingly received by the detector array 502. The reflecting mirror 507 is used to fold the optical path, so that the overall optical path structure is more compact, but it is not a necessary device, for example, the reflecting mirror 507 may be omitted, and the light beam after passing through the quarter-wave plate 506 and having a polarization state changed is directly scanned by the scanner 508.

In a possible embodiment, the negative lens may be a single lens or a plurality of lenses arranged in tandem along the optical path to further extend the focal length.

In a specific embodiment, based on the optical path system shown in the above embodiments, the focal length of the receiving end of the optical system combined by the positive-negative lens can reach 100mm-300mm, for example. The transmitting end and the receiving end of the laser radar can share the positive lens, the polarization beam splitter is positioned between the positive lens and the negative lens, and the negative lens is independently positioned at the receiving end and is arranged corresponding to the light detector array, so that the receiving end optical system with the long focal length is realized.

In an optional example, the transmitting end can select an optical system for realizing a relatively short focal length, so that the laser can be effectively emitted; the receiving end can select an optical system for realizing a relatively long focal length; so that it can be received by a photodetector with a larger size photosensitive surface (e.g., siPM detector). Thus, for sipms, with smaller field angles, the corresponding ambient light can be received less. Meanwhile, under the condition of the same angular resolution, the laser radar has larger photosensitive surface size and can have more photosensitive units, so that the dynamic range of the laser radar is improved.

Lidar may alternatively employ an array of light emitters and an array of light detectors. The photodetector array may be arranged at a focal plane of the optical system, i.e. the photosensitive surface of the photodetector array is located at the focal plane of the combination of the main optical system and the beam expanding unit. The light emitter array and the light detector array can be a one-dimensional linear array or a two-dimensional area array, the two-dimensional area array can be arranged in a matrix form or a multi-column staggered form, one or more light emitters and one or more corresponding light detectors form a detection channel, and the light emitters and the light detectors in the same detection channel correspondingly transmit detection light signals and receive echo light signals generated by the light emitters and the light detectors.

In some embodiments, the lidar array and the photodetector array may be configured to emit light from each column of the respective detection channels. In one example, the light can be emitted between the columns in a row-by-row rotation manner, that is, the light emitter of each detection channel in the next row is emitted one by one when the light emission of one row is completed. Or, in another example, the respective column arrays may emit light simultaneously, that is, the first channel of each column array emits light simultaneously, and then the other detection channels of each column emit light simultaneously in sequence according to the arrangement order of the columns. Still alternatively, in another example, the corresponding detection channels of a plurality of linear arrays on the same column may emit light simultaneously, for example, the first detection channel of a plurality of linear arrays on the same column emits light simultaneously, then, similarly, other detection channels of a plurality of linear arrays emit light simultaneously in sequence according to the arrangement order of the columns, and after the plurality of linear arrays on the same column complete light emission, the light is emitted in turns row by row, that is, the plurality of linear arrays on one column complete light emission, and the plurality of linear arrays on the next column complete light emission in turn according to the above process. Each photodetector in the photodetector array also operates in conjunction with the light emitter of the same detection channel to receive the corresponding echo light signal as in any of the above.

It should be noted that, in other embodiments, the light emitting unit may also be implemented as a single laser, and the light receiving unit may also be implemented as a single photodetector, etc., which are not limited to the above.

In some other embodiments, in addition to the above-mentioned light splitting based on the polarization light splitting unit, the light splitting unit may be implemented by a reflection unit, the reflection unit has a reflection portion for reflecting one of the probe light signal and the echo light signal, and may have a transmission portion or be matched with an external gap to implement transmission of the other of the reflected probe light signal and the echo light signal, thereby implementing light splitting. Also, the above positive-negative lens combination can be applied to extend the focal length of the receiving end as well.

As shown in fig. 6 and fig. 7, schematic structural diagrams of optical systems of two-dimensional scanning lidar based on reflection unit for realizing beam splitting in different examples of the present invention are respectively shown.

As shown in fig. 6 and 7, the lidar includes: a light emitter array 601, a light detector array 602, a positive lens 603, a negative lens 604, a reflection unit, a mirror 606, and a scanner 607. Note that the positive lens 603 and the negative lens 604 are still equivalent representations.

The difference between the embodiments of fig. 6 and 7 is that there is a difference in the implementation of the reflection unit, and the positions of the transmitting end and the receiving end are changed accordingly.

The difference from fig. 5A and 5B is that the reflection unit in fig. 6 is implemented as a mirror 605A having a smaller size than the positive lens 603, and the reflection unit in fig. 7 is implemented as a pinhole mirror 605B.

In fig. 6, the detection light signal output by the light emitter array 601 is reflected to the positive lens 603 by the mirror 605A, collimated by the positive lens 603, reflected to the scanner 607 by the mirror 606, and reflected by the scanner 607 to emit the laser radar; the corresponding echo optical signal enters the laser radar, is reflected to the positive lens 603 by the scanner 607 and the reflecting mirror 606, and the positive lens 603 converges the echo optical signal, and the echo optical signal is transmitted to the negative lens 604 through the gap on the peripheral side of the reflecting mirror 605A, and enters the optical detector array 602 through the negative lens 604.

In fig. 7, the detection light signal output by the light emitter array 601 passes through a small hole in the middle of the small hole reflector 605B, and exits through the positive lens 603, the reflector 606, and the scanner 607; the corresponding echo optical signal enters the laser radar, passes through the scanner 607, the mirror 606, the positive lens 603, and the aperture mirror 605B, is reflected to the negative lens 604 through the aperture mirror 605B, and is transmitted to the photodetector array 602. It should be noted that, in the embodiment of fig. 7, the transmission part of the reflector is a small hole for allowing light to pass through; in other embodiments, the transmissive portion may have other shapes, not limited to a small hole; alternatively, the transmission part may be implemented in other forms, such as glass made of transparent material.

The implementation of the positive and negative lenses in the positive-negative lens combination can be selected.

In some embodiments, the positive lens may be implemented as a biconvex lens and the negative lens may be implemented as a biconcave lens.

In still other embodiments, the positive lens may be a biconvex lens and the type of negative lens may be a cylindrical negative lens. As shown in fig. 8A and 8B, the cylindrical negative lens combined with the positive lens 801 may be a plano-concave cylindrical lens 802, and fig. 8B is a perspective view of fig. 8A to facilitate understanding of the structure thereof. By employing a cylindrical negative lens, it is possible to make the positive-negative lens combination maintain a short focal length in one direction (e.g., as shown in the Y direction in fig. 8B, i.e., the direction in which the cylindrical negative lens extends) while achieving a long focal length in the other direction (e.g., the Z direction in fig. 8B, i.e., the long focal length is achieved by the concave surface that the cylindrical negative lens has in the Z direction). It should be noted that, in other embodiments, the cylindrical negative lens may also be a biconcave cylindrical negative lens, which is not limited to this embodiment.

Since the light receiving units, such as the light detector array, may be arranged in a non-centrosymmetric pattern, that is, the number, size, arrangement mode, etc. of the detectors arranged between different directions may be different, the cylindrical negative lens scheme described above may be applicable to a scene where the size of the light receiving unit is limited. When the size of the light sensing surface of the light receiving unit in a certain direction is limited, or a long focal length system is not suitable, the cylindrical negative lens scheme may be adopted. For example, in fig. 9A, a plurality of photodetectors 901 (e.g., sipms) are arranged at intervals in the longitudinal direction in the photodetector array.

However, if the light detector array is arranged as shown in fig. 9B, the light detectors 901 are arranged in an elongated linear array, and the longitudinal direction (i.e., the transverse direction in the figure) of the light detector array can refer to the Y direction in fig. 8B, or can also refer to the row direction in fig. 10, 12A, and 12B. The echo light spot (which can be regarded as a circle) of the laser radar needs to cover the whole long strip-shaped linear array detector as much as possible. The photodetector array may comprise: a plurality of the long-shaped optical detector linear arrays are arranged in the width direction (refer to the Z direction in fig. 8B) perpendicular to the length direction, and the arrangement of the optical detector 901 may refer to the optical detectors 1001 in a plurality of rows in fig. 10. It is to be understood that, in fig. 9B, since the spacing between adjacent photodetectors 901 in the length direction may be small, if the focal length is increased in the length direction, crosstalk between the photodetectors 901 in the bars may easily occur, and thus it is not appropriate to adopt a long focal length system for the length direction, whereas the spacing between a plurality of bars may be large for the width direction, and even if the focal length is extended, crosstalk is relatively unlikely to occur. Therefore, for example, the cylindrical negative lens scheme in fig. 8A and 8B can be adopted, the focal length in the length direction is maintained, the long focal length is realized in the width direction, the ambient light is suppressed, and the signal-to-noise ratio is improved.

Fig. 10 is a schematic diagram showing an arrangement structure between the negative lens array and the photodetector array according to the embodiment of the present invention. The photodetectors 1001 are shown as squares, with each negative lens 1002 in the negative lens array being disposed corresponding to one photodetector 1001, and the circle covering each photodetector 1001 in the figure is a simplified representation of the spot 1003 of the return optical signal. The negative lens 1002 may be implemented as a concave microlens. The concave micro lens may be an aspherical lens, specifically, a cylindrical negative lens or a general concave lens, or a plano-concave lens or a biconcave lens. As shown, for example, each negative lens may be disposed corresponding to each photo detector (e.g., siPM), and each negative lens 1002 may be disposed separately from each other, for example, as indicated by the dashed box; alternatively, the plurality of negative lenses 1002 may be integrally molded, that is, all (or part) of the negative lenses in the negative lens array are connected to form one optical device, and as shown in block 1004, the integrated optical device of the negative lens array can realize a large field angle (e.g., 10 ° to 20 °).

In some embodiments, by setting the type of each concave microlens in the negative lens array, aberrations of different field angles can be corrected. Specifically, for example, since the peripheral field aberration is larger than the central field aberration, it is possible to set each concave microlens of the central region (corresponding to the central field angle of the lidar) of the negative lens array as a non-eccentric lens, and set each concave microlens of the peripheral region (corresponding to the peripheral field angle of the lidar) outside the central region as an eccentric lens. In particular, the eccentric lens may deflect the beam even at the edge positions toward the central region. Thus, this structure helps to reduce the spacing and size between the photodetectors.

In some embodiments, for each photodetector in the array of photodetectors, the beam expanding unit may comprise an array of sub beam expanding units, wherein each sub beam expanding unit corresponds to one or more photodetector arrangements. For example, the beam expanding unit may be a negative lens array, wherein each sub beam expanding unit is a negative lens.

As shown in fig. 11A and 11B, schematic structural diagrams of optical systems using a negative lens array 1102 as a beam expanding unit in different examples of the present invention are shown. The Z-axis and X-axis directions in fig. 11A and 11B may be the same as those in fig. 8B.

As shown in fig. 11A, an optical system suitable for a mechanical lidar, i.e., a lidar with a rotating structure that rotates during operation, is shown. The optical system includes a positive lens 1101, a negative lens array 1102. Each negative lens 1121 may correspond to one or more photodetectors 1131 to transmit the echo optical signals of the corresponding detection channel, corresponding to the photodetector array 1103.

Referring again to fig. 11B, an optical system suitable for use in a scanning lidar is shown. The optical system includes: a positive lens 1101, a negative lens array 1102, a scanner 1104, the negative lens array 1102 being arranged corresponding to the photodetector array 1103; the scanner 1104 may be rotated in one or two dimensions to select the optical signal transmission of the corresponding detection channel. The optical system of this embodiment can be applied to the embodiments of fig. 5A, 5B, 6 and 7, for example.

As can be seen from the embodiments in fig. 11A and 11B, the optical system with a positive-negative lens combination in the embodiment of the present invention can be flexibly applied to different types of laser radars to extend the focal length of the receiving end to compress the field angle, thereby suppressing ambient light interference. Therefore, through the optical system, the anti-interference performance of the laser radar products of different types can be improved, and the purpose of improving the ranging performance of different laser radar products of different types is achieved.

In some embodiments, the arrangement of the negative lens array may also be adapted to the photodetector array. For example, fig. 12A illustrates a structure of a negative lens array in an embodiment, where the negative lens array 1200A may be a continuous arrangement along a specific direction, and adaptively includes a plurality of strip-shaped concave microlenses 1201A (e.g., cylindrical concave lenses), each concave microlens 1201A may correspondingly cover a row of photodetectors, a photodetector array formed by a plurality of photodetectors, or a row of photodetectors formed by arranging photodetectors and the photodetector array at intervals, where the photodetector array is, for example, shown as the photodetector array in fig. 9B, and each photodetector, each photodetector array, or an interval between each photodetector and the photodetector array in each row may be as small as possible. Alternatively, as shown in fig. 12B, showing the structure of a negative lens array in yet another embodiment, the negative lens array 1200B includes a plurality of concave microlenses 1201B arranged at intervals, and each concave microlens 1201B can correspondingly cover one photodetector or a photodetector array formed by a plurality of photodetectors, for example, the photodetector array in fig. 9B. The structure of the negative lens array of fig. 12A and 12B may be selectively used according to the interval of the photo-detectors.

In some embodiments, the negative lens array is also readily packaged with a photodetector array to align with the individual photodetectors. Because the precision reaches millimeter level, the effect of lengthening the focal length is not easily influenced.

Fig. 13 is a schematic structural diagram of a package of a photodetector array and a microlens array (i.e., an array of a plurality of concave microlenses) according to an embodiment of the present invention.

A circuit substrate 1301 and an optical carrier 1302 are shown.

The circuit substrate 1301, such as a Printed Circuit Board (PCB), has a first surface on which the photodetector array is disposed. Two columns or rows of photodetectors 1303 in the photodetector array are exemplarily illustrated, but the number is not limited thereto. The Z, X directions in fig. 13 can be referred to in comparison with the X, Y, Z directions in fig. 8, 11A, 11B.

The optical carrier 1302 has a second surface on which the microlens array is disposed. The optical carrier is integrally packaged with the circuit substrate and the second surface is opposite to the first surface, so that each of the micro lenses 1305 (i.e. micro concave lenses) is disposed corresponding to each of the light detectors 1303, for example, in the corresponding relationship of positions in fig. 11, 12A, and 12B.

In this embodiment, the circuit substrate may include a sidewall 1306 protruding from the circuit substrate 1301 and disposed around the photodetector array, and the optical carrier 1302 is connected to the sidewall 1306 to form a cavity for accommodating the photodetector array. The circuit board 1301 and the side wall 1306 may be integrally formed, or may be independent components.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Those skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A lidar characterized by comprising:

a light emitting unit for emitting a probe light signal;

a light receiving unit for receiving an echo light signal generated from the probe light signal;

a main optical system arranged between the light emitting unit and the light receiving unit for receiving the detection light signal and transmitting the detection light signal to the outside; and a receiver for receiving the echo optical signal and transmitting the echo optical signal to the optical receiving unit;

the beam expanding unit is arranged between the main optical system and the light receiving unit and used for receiving an echo light signal passing through the main optical system, expanding the beam and then transmitting the expanded echo light signal to the light receiving unit;

the equivalent focal length of the combination of the main optical system and the beam expanding unit is larger than that of the main optical system so as to compress the field angle of the light receiving unit.

2. Lidar according to claim 1, wherein a transmission path of the probe light signal is partially identical to a transmission path of the return light signal in the lidar.

3. The lidar of claim 1, wherein the primary optical system comprises: a positive lens unit and a light splitting unit;

the positive lens unit is used for receiving the detection light signal from the light splitting unit and transmitting the detection light signal outwards; the optical splitting unit is used for receiving the echo optical signal and transmitting the echo optical signal to the optical splitting unit;

the light splitting unit is used for receiving the detection light signal and transmitting the detection light signal to the positive lens unit; and a positive lens unit for receiving the echo optical signal from the positive lens unit and transmitting the echo optical signal to the light receiving unit.

4. The lidar of claim 3, wherein a distance between the beam expanding unit and the positive lens unit is less than a focal length of the positive lens unit.

5. The lidar of claim 1, wherein the photosurface of the light receiving unit is located at a focal plane of the combination of the primary optical system and the beam expanding unit.

6. The lidar of claim 5, wherein the equivalent focal length is further greater than a distance between a principal plane of the principal optical system and a photosensitive surface of the light receiving unit.

7. The lidar of claim 3, wherein the light splitting unit comprises: a reflection unit including a reflection portion for reflecting one of the echo optical signal and the probe optical signal;

the reflection unit further includes a transmission portion or an external gap fitted to the reflection unit for passing the other of the probe light signal and the echo light signal.

8. The lidar of claim 3, wherein the primary optical system further comprises: the polarization unit is arranged on one side, back to the light splitting unit, of the positive lens unit and is used for changing the polarization states of the detection optical signal and the echo optical signal so as to enable the output detection optical signal to be in a first polarization state and enable the output echo optical signal to be in a second polarization state, and the first polarization state is different from the second polarization state;

the light splitting unit is arranged between the positive lens unit and the beam expanding unit and is configured to allow the echo light signals in the second polarization state to pass through.

9. The lidar of claim 1, further comprising: and the scanning unit can be rotationally arranged in one dimension or two dimensions, is used for rotating to a preset posture to enable the detection light signal to be transmitted outwards at a corresponding scanning angle, and is used for transmitting the echo light signal corresponding to the detection light signal to the main optical system.

10. The lidar of claim 1, wherein the light receiving unit comprises: an array of photodetectors; the beam expanding unit comprises an array of sub beam expanding units, wherein each sub beam expanding unit is arranged corresponding to one or more photodetectors.

11. The lidar of claim 10, wherein the photodetector corresponding to each first sub-beam expansion unit in the middle region of the array of sub-beam expansion units corresponds to a central field angle of the lidar field of view, and each first sub-beam expansion unit comprises a non-eccentric lens; and the light detectors corresponding to the second sub beam expansion units in the peripheral area except the middle area of the sub beam expansion unit array correspond to the edge field angle except the central field angle of the laser radar, and each second sub beam expansion unit comprises an eccentric lens.

12. The lidar of claim 10, wherein the array of sub-beam expanding units comprises a microlens array for encapsulating an array of photodetectors.

13. The lidar of claim 12, wherein the light receiving unit comprises:

a circuit substrate having a first surface on which the photodetector array is disposed;

and the optical carrier is provided with a second surface for arranging the micro-lens array, is packaged into a whole with the circuit substrate, and enables the second surface to be opposite to the first surface, so that each micro-lens is arranged corresponding to each light detector.

14. The lidar of claim 1, wherein the light receiving unit comprises: a plurality of photodetector arrays, each of the photodetector arrays arranged in a linear array; the beam expanding unit comprises at least one cylindrical negative lens, the cylindrical negative lens is arranged corresponding to part or all of the light detector array in the light receiving unit, and the extending direction of the cylindrical negative lens is the length direction of the light detection array.