CN113625295A

CN113625295A - Optical system for laser radar and laser radar

Info

Publication number: CN113625295A
Application number: CN202110689841.8A
Authority: CN
Inventors: 王鹏; 谢会开; 杨文�
Original assignee: Wuxi Wio Technology Co ltd
Current assignee: Wuxi Weiwen Semiconductor Technology Co ltd
Priority date: 2021-06-22
Filing date: 2021-06-22
Publication date: 2021-11-09

Abstract

Disclosed are an optical system for a lidar and a lidar, the optical system comprising: a laser for emitting an outgoing beam; the spectroscope is used for transmitting the outgoing light beam and reflecting the echo light beam; the MEMS micro-mirror is used for changing the irradiation direction of the emergent light beam; the first lens is positioned on a light path of the emergent light beam reflected by the MEMS micro-mirror, collimates the reflected emergent light beam, transmits the collimated emergent light beam to an object to be detected, and receives an echo light beam reflected by the object to be detected; and the photoelectric detector receives the echo light beam reflected by the MEMS micro-mirror and reflected again by the spectroscope, wherein the light spot of the emergent light beam after passing through the first lens is larger than the light spot irradiated on the MEMS micro-mirror, and the light spot size of the echo light beam received by the first lens is larger than the light spot size of the MEMS micro-mirror, so that the light receiving capacity of the optical system is enhanced, and the signal-to-noise ratio is improved.

Description

Optical system for laser radar and laser radar

Technical Field

The invention relates to the technical field of laser radars, in particular to an optical system for a laser radar and the laser radar.

Background

The laser radar is an active distance detection device which takes a laser as a transmitting light source and adopts a photoelectric detection means, and has the advantages of small volume and high measurement precision, wherein, the MEMS (Micro-Electro-Mechanical System) laser radar can scan a specified range and obtain accurate distance information of a target by using a method for measuring the flight time of pulsed light, so the laser radar is widely applied to the fields of unmanned driving, automatic distance measurement, robots and the like.

At present, laser radar is divided into two structures of an off-axis light path and a coaxial light path according to the relative position of an optical axis of a transmitting end and an optical axis of a receiving end, the off-axis light path is that a laser emitting beam irradiates on an object through a first group of lenses, a detector receives a laser beam reflected by the object through a second group of lenses, and different lenses are adopted for emission and reception, so that multi-angle laser signals need to be collected, and large ambient light noise can be caused generally.

In the coaxial light path, the laser emission beam and the detector receiving beam adopt the same group of lenses, so that the ambient light noise can be greatly reduced. At present, a common method in the coaxial optical path of the MEMS laser radar is to deflect and receive an optical signal by using the same MEMS micro-mirror, but because the MEMS micro-mirror generally has a small mirror surface size, the energy for receiving the measured signal is low, resulting in a small signal-to-noise ratio and a relatively short distance measurement.

Disclosure of Invention

In view of this, the present invention provides an optical system and a lidar for a coaxial MEMS lidar, which improve the signal-to-noise ratio of a measured laser signal.

According to a first aspect of the present invention, there is provided an optical system for lidar comprising:

a laser for emitting an outgoing beam;

a beam splitter for transmitting the outgoing beam and reflecting the echo beam;

the MEMS micro-mirror is used for changing the irradiation direction of the emergent light beam;

the first lens is positioned on a light path of the MEMS micro-mirror for reflecting the emergent light beam, the emergent light beam which is reflected is collimated and then emitted to an object to be detected, the first lens receives the echo light beam which is reflected back from the object to be detected, and the echo light beam is reflected by the MEMS micro-mirror and is reflected again by the spectroscope;

a photodetector that receives the echo beam;

and the light spot of the emergent light beam after passing through the first lens is larger than the light spot irradiated on the MEMS micro-mirror.

Optionally, the first lens is configured to collimate the outgoing light beam in a first direction, and the optical system further includes:

and the second lens is positioned on a light path of the emergent light beam emitted by the laser, and is used for collimating the emergent light beam in a second direction and then emitting the emergent light beam to the spectroscope, wherein the first direction is perpendicular to the second direction.

the third lens is positioned on a light path of the outgoing light beam emitted by the laser, and is used for collimating the outgoing light beam in both the first direction and the second direction and then emitting the outgoing light beam to the spectroscope;

and the fourth lens is positioned on the emergent light path of the spectroscope and used for converging the emergent light beam in a first direction and irradiating the converged emergent light beam on the MEMS micromirror, wherein the first direction is perpendicular to the second direction.

Optionally, the optical system further comprises:

and the fifth lens is positioned on a light path of the photoelectric detector for receiving the echo light beam, is used as a receiving lens and is used for converging the echo light beam reflected by the spectroscope.

Optionally, the beam splitter comprises:

a polarization beam splitter for transmitting the outgoing beam of a first polarization state and reflecting the echo beam of a second polarization state, the direction of the first polarization state being perpendicular to the direction of the second polarization state;

the quarter wave plate is used for converting the emergent light beam in the first polarization state into a light beam in a circular polarization state and converting the light beam in the circular polarization state into the echo light beam in the second polarization state, and an included angle between the quarter wave plate and the vertical direction of the propagation direction of the emergent light beam is-10 degrees to 10 degrees.

Optionally, the polarizing beamsplitter comprises a flat mirror and a cubic prism; the phase difference between the ordinary light and the extraordinary light propagated in the quarter-wave plate of the emergent light beam is 1/4, and the thickness of the quarter-wave plate and the angle of the included angle both have a corresponding relation with the wavelength of the emergent light beam.

Optionally, the laser comprises a solid state laser, a semiconductor laser, and a fiber laser; the emergent light beam emitted by the laser passes through the polarization beam splitter and then is emergent in the original direction, and the echo light beam passes through the polarization beam splitter and then is reflected to the photoelectric detector.

Optionally, the MEMS micro-mirror comprises a one-dimensional MEMS micro-mirror and a two-dimensional MEMS micro-mirror; and the MEMS micro-mirror comprises an electrostatic MEMS micro-mirror, an electromagnetic MEMS micro-mirror, a piezoelectric MEMS micro-mirror and an electrothermal MEMS micro-mirror, and the object to be detected is scanned by controlling the reflection micro-mirror inside the MEMS micro-mirror to turn over.

Optionally, the first to fifth lenses include a spherical lens, an aspherical lens, a spherical cylindrical lens, an aspherical lens having non-uniform curvatures in horizontal and vertical directions, a single lens or a lens group

Optionally, if the first polarization state is an S polarization state, the second polarization state is a P polarization state; and if the first polarization state is a P polarization state, the second polarization state is an S polarization state.

According to a second aspect of the present invention, there is provided a lidar comprising:

the optical system described above;

the main control board is connected with the optical system and controls the optical system to work; and

the photoelectric circuit board is provided with a photoelectric detector and is connected with the main control board and the optical system, the photoelectric circuit board receives an optical signal of the optical system and converts the optical signal into an electric signal, and then the electric signal is sent to the main control board.

The invention provides an optical system for a laser radar and the laser radar, wherein an emergent light beam is emitted by a laser, penetrates through a spectroscope and is reflected by an MEMS (micro-electromechanical system) micro-mirror, the emitting angle is changed, the emergent light beam is collimated by a collimating lens and then irradiates on an object to be detected, and an echo light beam diffusely reflected by the object to be detected sequentially passes through the collimating lens, the MEMS micro-mirror, the spectroscope and a receiving lens and is finally received by a photoelectric detector, so that the optical signal is received. The emergent light spot size on the collimating lens is larger than that of the MEMS micro-mirror, so that when an echo light beam is received, the received light spot size of the collimating lens is larger than that of the MEMS micro-mirror, the light receiving capacity is enhanced, the detectable distance is increased, and the signal-to-noise ratio is improved.

Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the embodiments of the present invention with reference to the accompanying drawings.

Fig. 1 shows a schematic block diagram of an optical system for lidar according to a first embodiment of the present invention.

Fig. 2a shows a schematic partial light path diagram of a conventional optical system for lidar.

Fig. 2b shows a schematic partial light path diagram of an optical system for a lidar according to a first embodiment of the invention.

Fig. 3 shows an optical path diagram of an optical system for a lidar according to a first embodiment of the present invention when the MEMS micro-mirror is flipped.

Fig. 4 shows a schematic block diagram of an optical system for lidar according to a second embodiment of the present invention.

Fig. 5 shows a schematic block diagram of an optical system for lidar according to a third embodiment of the present invention.

Fig. 6 shows a schematic block diagram of an optical system for lidar according to a fourth embodiment of the present invention.

Fig. 7a and 7b show optical path diagrams of an optical system for lidar according to a fourth embodiment of the present invention in the fast axis direction and the slow axis direction, respectively.

FIG. 8 shows a schematic block diagram of a lidar in accordance with an embodiment of the invention.

Detailed Description

The invention will be described in more detail below with reference to the accompanying drawings. Like elements in the various figures are denoted by like reference numerals. For purposes of clarity, the various features in the drawings are not necessarily drawn to scale. Moreover, certain well-known elements may not be shown in the figures.

The embodiment of the invention provides an optical system for a coaxial MEMS laser radar, which can effectively improve the signal-to-noise ratio of a detected laser signal. The following detailed description is made with reference to the accompanying drawings.

The first embodiment is as follows:

As shown in fig. 1, the optical system 100 for lidar provided in the present embodiment is an optical system of a MEMS coaxial lidar, and includes a transmitting optical unit and a receiving optical unit. The transmitting optical unit includes a laser 110, a beam splitter 120, a MEMS micro-mirror 130, and a first lens 140, and the receiving optical unit includes the first lens 140, the MEMS micro-mirror 130, the beam splitter 120, and a photodetector 150.

The laser 110 is used for emitting an emergent beam, and on a subsequent optical path of the emergent beam emitted by the laser 110, sequentially arranged are: a beam splitter 120 and a MEMS micro-mirror 130. The beam splitter 120 is used to transmit the outgoing beam. The MEMS micro-mirror 130 is used to change the irradiation direction of the outgoing light beam, i.e. the light beam passing through the beam splitter 120 is reflected on the MEMS micro-mirror 130. The incident angle of the outgoing beam emitted from the laser 110 incident on the MEMS micro-mirror 130 is, for example, 45 °. In this embodiment, a first lens 140 is further disposed on the light path of the outgoing light beam reflected by the MEMS micro-mirror 130, and the outgoing light beam reflected by the MEMS micro-mirror 130 is collimated by the first lens 140 in a first direction, for example, a slow axis direction, and then emitted onto the object 101 to be measured. The MEMS micro-mirror 130 is further configured to receive an echo light beam, where the echo light beam is a light beam reflected by the object 201 to be measured, and the echo light beam is reflected by the MEMS micro-mirror 130 after passing through the first lens 140, and then is reflected again when passing through the beam splitter 120. The size of the MEMS micro-mirror 130 is typically small so the spot size of the received light beam is small, which is limited by the size of the MEMS micro-mirror 130 if a collimating lens is placed between the MEMS micro-mirror 130 and the laser 110, i.e., the received spot size is equal to the size of the MEMS micro-mirror 130. In this embodiment, the first lens 140 is disposed between the MEMS micro-mirror 130 and the object 101 to be measured, so that the light spot of the emergent light beam passing through the first lens 140 is larger than the light spot irradiated on the MEMS micro-mirror 130, the effective receiving light spot size of the echo light beam reflected from the object 101 to be measured is also larger than the size of the MEMS micro-mirror 130, and the light receiving capability of the optical system 100 is enhanced by the disposition position of the first lens 140, thereby improving the energy of the received light signal and increasing the signal-to-noise ratio.

Further, the photodetector 150 is disposed on the optical path of the echo beam reflected by the beam splitter 120, and receives the echo beam. Photodetector 150 is not limited to a single pixel photodiode, but may be a single pixel or array pixel optoelectronic device having the same function. The photodetector 150 includes, for example, an APD (Avalanche photodiode), an SPIM (Silicon photomultiplier), an APD array, an SPAD (Single Photon Avalanche Diode), and the like.

The laser 110 includes a solid laser, a semiconductor laser, and a fiber laser, for example, the fiber laser in this embodiment, the laser 110 emits an outgoing beam, the divergence angle is θ, and the outgoing beam passes through the beam splitter 120, wherein the beam splitter 120 is coated with a semi-transparent and semi-reflective film layer, so that most of the light can be transmitted or reflected, thereby maintaining a high light utilization rate. The outgoing light beam transmitted through the beam splitter 120 is reflected by the surface of the MEMS micromirror 130, and the reflected light beam is collimated by the first lens 140 (collimating lens) and then irradiated onto the object 101 to be measured, wherein the focal length of the collimating lens 140 is f, and the fiber laser 110 is exactly located at the focal point of the collimating lens 140.

Therefore, the irradiation spot size of the fiber laser 110 on the collimating lens 140 is D, where:

the distance of the MEMS micromirror 130 from the fiber laser 110 is L1, and since the MEMS micromirror 130 is located between the fiber laser 110 and the first lens 140, L1< f. Wherein the irradiation spot size of the fiber laser 110 on the MEMS micro-mirror 130 is D1, then:

so D > D1. That is, the spot of the emergent beam after passing through the collimating lens 140 is larger than the spot of the light irradiating on the MEMS micro-mirror 130.

The emergent light irradiates the surface of the object to be measured 101 to generate diffuse reflection, the diffusely reflected echo light beam passes through the collimating lens 140 for the second time, and the angle of the mirror surface of the MEMS micro-mirror 130 is the same as the angle of the emergent light beam, so the echo light beam is reflected by the mirror surface of the MEMS micro-mirror 130, irradiates the spectroscope 120 according to the original path, is reflected on the spectroscope 120, and is reflected to the photoelectric detector 150. In the same way, the light spot size of the echo light beam received by the collimating lens 140 is also larger than that of the MEMS micro-mirror 130, so that the light receiving capability of the optical system is enhanced and the signal-to-noise ratio is improved.

Fig. 2a shows a schematic partial light path diagram of a conventional optical system for lidar. Fig. 2b shows a schematic partial light path diagram of an optical system for a lidar according to a first embodiment of the invention. The light receiving capability of the optical system for a lidar of the present invention and the optical system for a lidar of the second embodiment of the present invention is compared below with fig. 1-2 b.

As shown in fig. 2a, in the conventional optical system for lidar, a laser 10, a lens 20 and a MEMS micro-mirror 30 are included in an outgoing light path, the lens 20 is disposed in front of the MEMS micro-mirror 30, an emitted light beam emitted from the laser 10 passes through the lens before reaching the MEMS micro-mirror 30, and a spot of the laser light beam reflected by the MEMS micro-mirror 30 is small (shown by a solid line). In fig. 2b, which is a part of the optical path of the optical system 100 for lidar according to the embodiment of the present invention, the outgoing light beam emitted by the laser 110 is transmitted by the beam splitter 120, reflected by the MEMS micro-mirror 130, and then collimated by the first lens 140, at this time, the light spot of the outgoing light beam becomes larger (shown by a dotted line in the figure), that is, the size of the outgoing light spot on the first lens 140 is larger than the size of the light spot on the MEMS micro-mirror 130, so that when the echo light beam is received, the size of the received light spot on the first lens 140 is also larger than the size of the light spot on the MEMS micro-mirror 130, and therefore, the optical system for lidar according to the present embodiment has a better light receiving capability compared with the conventional optical system for lidar.

According to the optical system 100 of the laser radar shown in fig. 1, when the MEMS micro-mirror 130 is turned, the angle of the reflected outgoing light beam changes, and the angle of the reflected outgoing light beam on the object 101 changes. As shown in fig. 3, when the MEMS micro-mirror 130 is flipped by an angle α, the fiber laser 110 may deviate from the focal plane position of the collimating lens 140 relative to the virtual image of the MEMS micro-mirror 130 (according to the optical principle, the light beam can be collimated normally only when the fiber laser 110 is located on the focal plane of the collimating lens 140), and the offset amount is Δ L. Then:

since the virtual image of the fiber laser 110 deviates from the focal plane of the collimator lens 140, the outgoing light rays passing through the collimator lens 140 will not be collimated beams but slightly divergent with a divergence angle β. The collimation of the outgoing beam is degraded when the MEMS flips 130.

In actual use, the fiber laser 110 is slightly deviated from the focus position of the collimating lens 140, when the MEMS micro-mirror 130 is not turned, the fiber laser 110 is negatively defocused with respect to the collimating lens 140 by an amount of- Δ L/2, and when the MEMS micro-mirror 130 is turned by an angle α, the fiber laser 110 is positively defocused with respect to the collimating lens 140 by an amount of Δ L/2. Therefore, the MEMS micro-mirror 130 is in the +/-alpha overturning range, the focal plane of the fiber laser 110 relative to the collimating lens 140 is always changed in the +/-delta L/2 range, and the maximum divergence angle of the emergent light beam is beta/2. In practice, the scanning angle and the beam collimation of the MEMS micro-mirror 130 need to be chosen to a balance value according to the actual use requirements.

Example two

As shown in fig. 4, the optical system 200 for lidar provided by the present embodiment includes a transmitting optical unit and a receiving optical unit. The transmitting optical unit includes a laser 210, a second lens 260, a beam splitter 220, a MEMS micro-mirror 230, and a first lens 240, and the receiving optical unit includes a first lens 240, a MEMS micro-mirror 230, a beam splitter 220, and a photodetector 250.

In this embodiment, only one second lens 260 is added compared to the first embodiment, and other optical elements are the same as those in the first embodiment, which are not described herein again. The second lens 260 is located on a subsequent optical path of the outgoing light beam emitted by the laser 210, on which are arranged in sequence: a second lens 260, a beam splitter 220, and a MEMS micro-mirror 230. The second lens 220 is used for collimating the outgoing light beam in a second direction, the collimated outgoing light beam passes through the beam splitter 220, the first direction is perpendicular to the second direction, and the second direction is a fast axis direction, so that the first lens 240 collimates a slow axis direction of the emerging light beam, and the second lens 260 collimates a fast axis direction of the emerging light beam.

Further, the first lens 240 is used for collimating the outgoing light beam in a first direction (slow axis direction), and the second lens 260 is used for collimating the outgoing light beam in a second direction (fast axis direction), wherein the first direction is perpendicular to the second direction. The light beam emitted from the laser 210 generally has different divergence angles in two mutually perpendicular planes, and then the second lens 260 collimates the light beam emitted from the laser 210 in the fast axis direction and passes through the beam splitter 220. And the first lens 240 collimates the slow axis direction beam emitted by the laser 210. The laser signals collimated in two directions are projected onto the object 101, wherein the fast axis direction and the slow axis direction of the laser 210 are 90 degrees. The collimated light can be received by the receiving optical unit, so that the light utilization rate can be improved, light signals can be enhanced, and the signal-to-noise ratio can be improved.

EXAMPLE III

As shown in fig. 5, the lidar optical system 300 of the present embodiment is an optimized structure of the lidar optical system 100 of fig. 1, and is substantially the same as the structure of the lidar optical system 100 shown in the first embodiment. The laser radar optical system 300 of the present embodiment includes a transmitting optical unit and a receiving optical unit. The emission optical unit includes: the laser 310, the third lens 370, the beam splitter 320, the fourth lens 380, the MEMS micro-mirror 330, and the first lens 340, and the receiving optical unit includes the first lens 340, the MEMS micro-mirror 330, the fourth lens 380, the beam splitter 320, and the photodetector 350. In this embodiment, the third lens 370 and the fourth lens 380 are added compared with the first embodiment, and the remaining optical elements are the same as those in the first embodiment and are not described again.

The optical system 200 of the second embodiment utilizes the second lens 260 to collimate the light beam in the fast axis direction, and the slow axis direction is still in a divergent state, so that the light beam has a certain energy loss and the energy utilization is incomplete when the light beam irradiates on the MEMS micro-mirror 230. Therefore, the present embodiment is further optimized to provide the third lens 370 and the fourth lens 380, and the third lens 370 and the fourth lens 380 are the same as the first lens to the second lens.

Specifically, the third lens 370 of the present embodiment is located on the optical path of the outgoing light beam emitted from the laser 310, and collimates both the fast axis and slow axis directions of the outgoing light beam, and then emits the collimated light beam to the beam splitter 320. The fourth lens 380 is disposed on the light path exiting from the beam splitter 320, and converges the light emitted from the laser 310 in the slow axis direction and irradiates the MEMS micro-mirror 330. The exiting beam is then re-collimated in the slow axis direction by the first lens 340, where the divergence angle in the slow axis direction is determined by the parameters of the laser 310.

Then in one example of this embodiment, laser light is first emitted from laser 310 (both the fast and slow axes are diverging beams), and then collimated in the fast and slow axes by third lens 370, and the emitted light is collimated in both the fast and slow axes. Then, the light passes through a beam splitter 320 (the light is collimated light in the fast axis direction and the slow axis direction), and then passes through a fourth lens 380, the light in the fast axis direction is unchanged, and the light in the slow axis direction is converged; finally, the slow axis direction is collimated again by the first lens 340. Therefore, light is greatly absorbed, the light utilization rate is improved, and the signal-to-noise ratio is improved.

Example four

Fig. 6 shows a schematic block diagram of an optical system for lidar according to a fourth embodiment of the present invention. Fig. 7a and 7b show optical path diagrams of an optical system for lidar according to a fourth embodiment of the present invention in the fast axis direction and the slow axis direction, respectively.

As shown in fig. 6, this embodiment is a further improvement of the optical system of the third embodiment, in this embodiment, the beam splitter includes a polarization beam splitter 421 and a quarter-wave plate 422, and a fifth lens 490 is added as a receiving lens, and a narrow-band filter 491 is also added. The laser radar optical system 400 of the present embodiment includes a transmitting optical unit and a receiving optical unit. The emission optical unit includes: the laser 410, the third lens 470, the polarization beam splitter 421, the quarter wave plate 422, the fourth lens 480, the MEMS micro-mirror 430 and the first lens 440, and the receiving optical unit includes the first lens 440, the MEMS micro-mirror 430, the fourth lens 480, the quarter wave plate 422, the polarization beam splitter 421, the fifth lens 490, the narrow band filter 491 and the photodetector 450. Compared with the third embodiment, this embodiment has more polarization beam splitter 421, quarter-wave plate 422, fifth lens 490 and narrow-band filter 491, and the rest of the optical elements are the same as those in the fourth embodiment and will not be described again.

The laser 410 is, for example, a semiconductor laser for emitting an outgoing beam of linearly polarized light, for example, emitting polarized light of only the S-polarization state or emitting polarized light of only the P-polarization state. On the subsequent optical path of the outgoing light beam emitted by the semiconductor laser 410 are sequentially arranged: a third lens 470, a polarization beam splitter 421, a quarter wave plate 422, a fourth lens 480, and MEMS micro-mirrors 430. The polarization beam splitter 421 is configured to transmit polarized light in a first polarization state and reflect polarized light in a second polarization state, where the first polarization state is perpendicular to the second polarization state, and the outgoing light beam is in the first polarization state, the echo light beam is in the second polarization state (the first polarization state is an S polarization state, the second polarization state is a P polarization state, and the first polarization state is a P polarization state, the second polarization state is an S polarization state).

In this embodiment, the semiconductor laser 410 emits a P-polarized emission beam (or P-polarized light), for example, the polarization beam splitter 421 transmits the P-polarized light and reflects the S-polarized light (almost all of the P-polarized light can transmit through the polarization beam splitter 421, and almost all of the S-polarized light is reflected by the polarization beam splitter 421), so that 100% of the light energy of the emission beam collimated by the third lens 470 horizontally transmits through the polarization beam splitter 421, and the emission beam passing through the polarization beam splitter 421 is still P-polarized light and exits in the original direction. The polarizing beam splitter 421 can be a flat mirror or a cubic prism.

The quarter waveplate 422 is used to convert the outgoing beam of the first polarization state into a beam of the circular polarization state and also to convert the beam of the circular polarization state into an echo beam of the second polarization state. Because the quarter-wave plate 422 is vertically disposed, a small amount of light may be reflected when the light beam passes through the quarter-wave plate 422, and the light beam is easily received by the photodetector 450 through the receiving optical path, so that noise interference is introduced, in this embodiment, the quarter-wave plate 422 is not limited to be vertically disposed, and the included angle θ (or the included angle with the optical axis) between the surface of the quarter-wave plate and the vertical direction of the propagation direction of the outgoing light beam is between-10 ° and 10 °. Further, the placement angle of the quarter-wave plate 422 may determine the thickness of the quarter-wave plate 422, and both the thickness and the included angle of the quarter-wave plate 422 have a corresponding relationship with the wavelength of the outgoing light beam, in this embodiment, the thickness of the quarter-wave plate 422 is determined by the used wavelength and the placement angle, and finally, when the outgoing light beam propagates therein, the phase difference between the ordinary light (o light) and the extraordinary light (e light) is 1/4 wavelengths. The combination of the quarter-wave plate 422 and the polarization beam splitter 421 is an existing optical isolator, and the outgoing beam transmission and the echo beam reflection of the present embodiment are realized by using this principle. The polarization beam splitter 421 and the quarter-wave plate 422 have the highest transmittance and the lowest polarization state change when ideally parallel light is incident. In this embodiment, the semiconductor laser 210 emits linearly polarized light, and then the linearly polarized light passes through the polarization beam splitter 421 and the quarter-wave plate 422, and the emitted light almost passes through the quarter-wave plate 422 and becomes circularly polarized light, so that the optical loss of the optical system 400 for the laser radar is reduced, the energy receiving efficiency is improved, and a longer detection distance is realized.

The MEMS micro-mirror 430 is further disposed behind the quarter-wave plate 422, and the MEMS micro-mirror 430 is small in size, facilitating miniaturization of the optical system 400. The MEMS micro-mirror 430 is used to change the irradiation direction of the circularly polarized light. The MEMS micro-mirror 430 of the present embodiment includes an electrostatic MEMS micro-mirror, an electromagnetic MEMS micro-mirror, a piezoelectric MEMS micro-mirror, and an electrothermal MEMS micro-mirror. The MEMS micro-mirror 430 is composed of a substrate, an actuating arm, and a reflective micro-mirror, and the reflective micro-mirror is driven by the actuating arm to translate or rotate, so that the MEMS micro-mirror 430 can deflect or deflect, and light irradiated on its surface can be emitted at different angles. Therefore, the MEMS micro-mirror 430 is further configured to change an angle at which the circularly polarized light irradiates on the object 101 by controlling the internal reflective micro-mirror to turn over, and scan the object 101, so as to obtain depth information of different positions of the object 101. The optical scanning angle achieved by the MEMS micro-mirror 430 depends on the angular amplitude of the sweep of the MEMS micro-mirror 430. And the MEMS micro-mirror 430 of the present embodiment includes a one-dimensional MEMS micro-mirror and a two-dimensional MEMS micro-mirror.

The MEMS micromirror 430 reflects the outgoing light beam and then passes through the first lens 440, and the first lens 440 collimates the reflected circularly polarized light in the slow axis direction and then transmits the collimated light to the object 101, and receives the echo light beam. The echo light beam is converged by the first lens 440, reflected by the MEMS micro-mirror 430 and converted into linearly polarized light of the second polarization state by the quarter-wave plate 422 again, at this time, the polarization state of the echo light beam is different from that of the outgoing light beam, for example, the outgoing light beam is in the P polarization state, and the echo light beam is in the S polarization state; the emergent beam is in S polarization state, and the echo beam is in P polarization state. At this time, after passing through the quarter-wave plate 422, the echo beam is totally reflected by the polarization beam splitter 421. Therefore, in this embodiment, the outgoing light beam emitted by the laser 410 passes through the polarization beam splitter 421 and then exits in the original direction, and the echo light beam passes through the polarization beam splitter 422 and then is reflected to the photodetector 450.

According to the setting of this embodiment, emergent ray almost all changes the echo light beam, and receives the facula grow, and light utilization ratio further promotes, and the SNR promotes.

A fifth lens 490, a narrow-band filter 491 and a photodetector 450 are disposed on the optical path of the echo beam reflected by the polarization beam splitter 421. The fifth lens 490 is located on the optical path of the photodetector 450 for receiving the echo beam, and serves as a receiving lens for converging the echo beam reflected by the beam splitter. The optical axis of the receiving lens (fifth lens 490) and the optical axis of the outgoing light beam emitted by the semiconductor laser 410 are perpendicular to each other. The first lens to the fifth lens include a spherical lens, an aspherical lens, a spherical cylindrical lens, an aspherical lens having non-uniform curvatures in horizontal and vertical directions, a single lens, or a lens group. The first lens 440 to the fifth lens 490 are not limited to a single lens, but also include lens groups, and the positions are not limited to the positions illustrated in the drawings, and all fall within the scope of protection as long as the same or similar functions can be achieved.

The narrow-band filter 491 is used to filter the echo light beam and filter the unwanted light wave, thereby further improving the signal-to-noise ratio. And the position of the narrow-band filter 491 is not limited to the position between the fifth lens 490 and the photodetector 450, but may be positioned between the polarization beam splitter 421 and the fifth lens 490.

The photodetector 450 is disposed behind the fifth lens 490, and receives the echo beam reflected by the polarization beam splitter 421. Further, the surfaces of the quarter wave plate 422 and the first lens 440 may be provided with coatings to adjust the transmittance of light.

In summary, an example of the optical system 400 provided by the present embodiment is as follows:

the 905nm outgoing beam emitted by the semiconductor laser LD is linearly polarized light (defined as P light), the outgoing beam is firstly collimated in the directions of the fast axis and the slow axis by the third lens 470, then the linearly polarized light passes through the polarization beam splitter 421, the laser transmits the polarization beam splitter 421 by 100%, and the polarization state of the laser is still P light; then, the linearly polarized light is changed into circularly polarized light by the quarter wave plate 422; then, after being focused by the fourth lens 480, the light is reflected by the mirror surface of the MEMS micro-mirror 430; the reflected light is collimated in the slow axis direction through the first lens 440, the size of a collimated light spot is larger than that of an MEMS (micro-electromechanical system) micromirror, the first lens 440 is an aspheric cylindrical mirror, the slow axis direction of the laser beam has focal power, and the fast axis direction has no focal power; when the MEMS micro-mirror 430 is turned over along an axis parallel to the fast axis direction, the scanning of the emergent light beam in the one-dimensional direction can be realized, and the optical scanning angle is 2 times of the MEMS mechanical scanning angle; when the MEMS micromirror 430 has any effective scanning angle, the reflected emission beam irradiates the surface of the object 101 to be measured, and is diffusely reflected, and the diffusely reflected light spot is received by the first lens 440 again (receiving area > size of the MEMS micromirror); because the sweep angle of the MEMS micromirror 430 is not changed, the reflected light direction and the emergent light direction return coaxially and in the same way, the diffusely reflected light is circularly polarized light, and the polarization state thereof is changed from circularly polarized light to linearly polarized light in the S polarization state by passing through the quarter-wave plate 422 for the second time; the S polarized light is reflected by the polarization beam splitter 42; the reflected light is converged by the fifth lens 490 and focused on the photodetector 45, the first lens 440 and the fifth lens 490 combine to produce a receiving end optical path system, the effective field of view of which matches the effective spot size of the emitting end, avoiding receiving stray light outside the detection field of view; the narrow-band filter 491 is placed in front of the photodetector 450, so that stray light in other bands except the wavelength of the semiconductor laser LD can be filtered out, and a higher signal-to-noise ratio can be realized.

The present embodiment is illustrated by the following formula:

the light beam reflected by the MEMS micro-mirror 430 is diffusely reflected on the surface of the object 101 and received by the first lens 440. Since the deflection angle of the MEMS micro-mirror 430 is unchanged, only energy in the same direction as the emitted light in the received light can be received by the system. The received energy can be expressed by the following formula

Wherein P is_returnAnd P_laserEnergy received by the photodetector 450 and energy emitted by the semiconductor laser 410, A_apertureFor the receiving aperture, d is the distance between the object 101 and the semiconductor laser 410, and η is the light transmittance after propagation loss in the system and air.

For the optical system of the conventional coaxial lidar, the collimating lens is arranged in front of the MEMS micro-mirror, a_apertureDepending on the size of the MEMS micromirror, in the present embodiment, since the collimating lens 440 is disposed behind the MEMS micromirror 430, A_apertureDepending on the effective light-passing area of the first lens 440 (collimator lens), the effective light-passing area is larger than the size of the MEMS micromirror 430, and thus the energy of the received signal can be increased.

In conjunction with the above description, as shown in fig. 7a, the light in the fast axis direction enters the polarization beam splitter 421 after being collimated by the third lens 470, and then always irradiates on the MEMS micro-mirror 430 in the collimated direction, and the subsequent collimated direction is not changed. As shown in fig. 7b, the slow axis light is collimated by the third lens 470, enters the polarization beam splitter 421, is converged by the fourth lens 480, changes its direction, is reflected by the MEMS micro-mirror 430, and is collimated again by the first lens 440.

Therefore, in this embodiment, the scheme of collimating, converging, and collimating the slow axis direction first and then re-collimating is adopted, so that the energy attenuation and the polarization state change are minimum when the light passes through the polarization beam splitter 421 and the quarter-wave plate 422, so as to ensure a higher energy utilization rate. Meanwhile, the divergence angle of the slow axis can be reconfigured by the embodiment, so that the divergence angle of the slow axis is increased, and thus, when the first lens 440 is closer to the MEMS micromirror 430, the received light spot can be large, and the signal-to-noise ratio is improved.

As shown in fig. 8, a laser radar 500 according to an embodiment of the present invention includes the above-mentioned optical systems 100 to 400 for laser radar, a main control board 501, and a photoelectric circuit board 503, wherein the

photoelectric detector

150 and 450 in the optical system are disposed on the photoelectric circuit board 503. The main control board 501 is electrically connected to the optoelectronic circuit board 503 and the

optical system

100 and 400, and the optoelectronic circuit board 503 is also connected to the

optical system

100 and 400.

When the laser radar 500 works, the main control board 501 controls the

semiconductor laser

110 and 410 of the

optical system

100 and 400 to emit an outgoing beam through the circuit, the

optical system

100 and 400 works, when the

photoelectric detector

150 and 450 receives the echo beam, the optical signal is converted into an electrical signal and sent to the main control board 501 through the photoelectric circuit board 503, and the main control board 501 calculates to obtain distance data. Further, the photoelectric circuit board 503 is further provided with a delay unit for delaying the reception of the echo light beam by the photodetector, so as to avoid the influence of stray light.

In summary, in the optical system and the laser radar for the coaxial laser radar of the embodiment, the first lens is disposed on the light path of the outgoing light beam reflected by the MEMS micromirror, that is, the first lens is located behind the MEMS micromirror, and the size of the outgoing light beam in the collimation direction of the first lens is larger than the size of the spot on the MEMS micromirror, so that the size of the received light beam of the first lens is also larger than the size of the spot on the MEMS micromirror, which can achieve a larger light receiving capability, so that the optical system and the laser radar can receive more reflected signals, and the farther the corresponding detectable distance is, the higher the signal-to-noise ratio is.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

While embodiments in accordance with the invention have been described above, these embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments described. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An optical system for a lidar comprising:

a laser for emitting an outgoing beam;

a photodetector that receives the echo beam;

2. The optical system of claim 1, wherein the first lens is to collimate the exit beam in a first direction, the optical system further comprising:

3. The optical system of claim 1, wherein the first lens is to collimate the exit beam in a first direction, the optical system further comprising:

4. The optical system of any of claims 1-3, further comprising:

5. The optical system according to any one of claims 1-3, wherein the beam splitter comprises:

6. The optical system of claim 5, wherein the polarizing beamsplitter comprises a flat mirror and a cube prism; the phase difference between the ordinary light and the extraordinary light propagated in the quarter-wave plate of the emergent light beam is 1/4, and the thickness of the quarter-wave plate and the angle of the included angle both have a corresponding relation with the wavelength of the emergent light beam.

7. The optical system of claim 5, wherein the laser comprises a solid state laser, a semiconductor laser, and a fiber laser; the emergent light beam emitted by the laser passes through the polarization beam splitter and then is emergent in the original direction, and the echo light beam passes through the polarization beam splitter and then is reflected to the photoelectric detector.

8. The optical system according to any one of claims 1-3, wherein the MEMS micro-mirror comprises a one-dimensional MEMS micro-mirror and a two-dimensional MEMS micro-mirror; and the MEMS micro-mirror comprises an electrostatic MEMS micro-mirror, an electromagnetic MEMS micro-mirror, a piezoelectric MEMS micro-mirror and an electrothermal MEMS micro-mirror, and the object to be detected is scanned by controlling the reflection micro-mirror inside the MEMS micro-mirror to turn over.

9. The optical system according to claim 4, wherein the first to fifth lenses comprise a spherical lens, an aspherical lens, a spherical cylindrical lens, an aspherical lens having non-uniform curvatures in horizontal and vertical directions, a single lens, or a lens group.

10. A lidar, comprising:

the optical system according to any one of claims 1-9;