CN113036582A

CN113036582A - Laser, laser radar including the same, and scanning method of the laser radar

Info

Publication number: CN113036582A
Application number: CN201911335202.0A
Authority: CN
Inventors: 付萌; 李大汕; 向少卿
Original assignee: Hesai Technology Co Ltd
Current assignee: Hesai Technology Co Ltd
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2021-06-25
Anticipated expiration: 2039-12-23
Also published as: CN113036582B

Abstract

The invention relates to a laser comprising: a first pump unit configured to generate a first pump light; the resonance unit is arranged at the downstream of the optical path of the first pumping unit and used for receiving the first pumping light and outputting first laser; and a filter unit configured to receive the first laser light output by the resonance unit and emit the first laser light after filtering, wherein the resonance unit is configured to receive seed light, and a wavelength of the first laser light output from the resonance unit is the same as a wavelength of the seed light.

Description

Laser, laser radar including the same, and scanning method of the laser radar

Technical Field

The present invention relates generally to the field of optoelectronics, and more particularly to a laser, a lidar including the laser, and a method of scanning using the lidar.

Background

Diode Pumped Solid State Laser (DPSSL), a new type of laser, has developed rapidly in recent years. Compared with the traditional lamp-pumped solid-state laser, the DPSSL replaces a flash lamp with a laser diode with a specific wavelength, and achieves higher light-light conversion efficiency, longer working time and small size. At present, many types of diode-pumped solid-state lasers are commercialized and widely used for laser ranging, industrial processing and the like.

Passive Q-switching is one way in which a solid-state laser generates pulsed laser light. The Q-value of the cavity is defined as the ratio of the total energy stored to the energy lost per unit time in the cavity. The Q value in the cavity is adjusted by changing the loss in the cavity, and a laser pulse is formed when the Q switch is opened.

Laser radar is a range finding sensor commonly used, has characteristics such as detection range is far away, resolution ratio is high, receive environmental disturbance little, and the wide application is in fields such as intelligent robot, unmanned aerial vehicle, unmanned driving. In recent years, the automatic driving technology has been rapidly developed, and the laser radar has become indispensable as a core sensor for distance sensing. For a short-distance and strong-reflection measured object, the tof (time of flight) laser radar needs to reduce the laser pulse energy, otherwise, the detector signal saturation occurs, and the detection effect is affected. The passive Q-switched solid-state laser is difficult to realize continuous adjustment of single pulse energy because the Q-switched solid-state laser generates laser by pumping a laser gain medium through a semiconductor diode. Once the pump power reaches the pump threshold power, the energy of the generated laser pulse changes little with increasing pump power. It is not possible to directly adjust the output power by changing the injection current, as in a semiconductor laser.

As far as the inventor knows, the main problem of using the polarizer to adjust the laser power at present is that the whole device is large in size, which is not beneficial to the packaging and integration of the solid laser and the miniaturization of the laser.

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

Disclosure of Invention

In view of at least one of the deficiencies of the prior art, the present invention provides a laser comprising:

a first pump unit configured to generate a first pump light;

the resonance unit is arranged at the downstream of the optical path of the first pumping unit and used for receiving the first pumping light and outputting first laser; and

a filter unit configured to receive the first laser light output from the resonance unit and emit the first laser light after filtering,

wherein the resonance unit is configured to receive seed light, and a wavelength of the first laser light output from the resonance unit is the same as a wavelength of the seed light.

According to an aspect of the invention, the resonance unit includes:

a first laser cavity including a first resonance portion into which the first pump light is transmitted and a second resonance portion from which the first laser light exits, wherein the first laser cavity is configured to receive seed light, and a mode having a wavelength closest to a wavelength of the seed light preferentially forms oscillation in the first laser cavity so that the wavelength of the first laser light output from the resonance unit is the same as the wavelength of the seed light;

a first gain unit;

a quality factor adjusting unit;

wherein the first gain unit and the quality factor adjustment unit are located between the first resonance section and the second resonance section.

According to an aspect of the invention, the laser further comprises a seed light generation unit comprising:

a second pump unit configured to generate second pump light;

a second gain unit located downstream of an optical path of the second pump unit and receiving the second pump light;

a light splitting unit configured to generate the seed light and a plurality of tuning lights of different wavelengths, the tuning lights of different wavelengths having different propagation directions;

the scanning unit is configured to receive the tuning lights with the different wavelengths and return at least one original optical path in the tuning lights with the different wavelengths to the light splitting unit;

and the reflecting unit is positioned between the second pumping unit and the second gain unit, the reflecting unit is configured to reflect the light beam from the second gain unit to the second gain unit, the reflecting unit, the light splitting unit and the scanning unit form a second laser resonant cavity, and the tuning light which is returned to the light splitting unit by the original path finally forms oscillation in the second laser resonant cavity.

According to one aspect of the invention, the scanning unit changes the incident angles of the plurality of tuning lights in a swinging or rotating manner, and the tuning lights which are vertically incident to the scanning unit return according to an original optical path, pass through the light splitting unit, and are projected to the reflecting unit to form back-and-forth reflection of the tuning lights with corresponding wavelengths in the second laser resonant cavity.

According to an aspect of the present invention, the light splitting unit includes: a grating, the grating comprising: at least one of a reflective grating or a transmissive grating.

According to one aspect of the invention, the grating comprises: -a level 1 or +1 high diffraction efficiency grating;

the light splitting unit generates the emergent laser in the emergent direction of 0-order light of the-1-level high diffraction efficiency grating, and generates the tuning lights in the emergent direction of-1-level diffraction light of the-1-level high diffraction efficiency grating;

alternatively, the spectroscopic unit generates the emission laser light in the 0 th order light emission direction of the +1 st order diffraction efficiency grating, and generates the plurality of tuning lights in the +1 st order diffraction light emission direction of the +1 st order diffraction efficiency grating.

According to an aspect of the present invention, the filtering unit includes a narrow band filter whose transmittance continuously varies with a wavelength variation over a certain wavelength range.

According to an aspect of the invention, the laser further comprises a beam splitter configured to receive the seed light and reflect at least a portion of the seed light, and to receive the first laser light and transmit at least a portion of the first laser light, wherein the reflected at least a portion of the seed light is transmitted from the second resonator into the first laser resonator, and the transmitted at least a portion of the first laser light is incident on the filter unit.

According to an aspect of the present invention, the laser further includes an optical isolator that receives the seed light and allows only the seed light to pass in one direction, the seed light passing through the optical isolator being incident on the beam splitter.

According to one aspect of the invention, the first gain unit and/or the second gain unit comprises a gain medium, and the first gain unit and/or the second gain unit is a microchip type gain unit; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the first gain unit and the quality factor adjusting unit are mutually attached.

According to an aspect of the invention, the laser further comprises a control unit coupled to the scanning unit and controlling an angle of the scanning unit to control a wavelength of the tuning light oscillating within the second laser cavity.

The invention also relates to a lidar comprising:

a transmitting device comprising a laser as described above;

the receiving device is configured to receive an echo generated after the laser emitted by the laser is reflected on an obstacle; and

a signal processing device configured to obtain the distance and/or reflectivity of the obstacle currently scanned by the laser radar according to the echo.

According to one aspect of the invention, the lidar is configured to adjust the angle of the scanning unit of the laser in dependence on the obtained distance and/or reflectivity of the obstacle currently scanned by the lidar.

The invention also relates to a method for scanning using a lidar as described above, comprising:

emitting a detection laser beam to the outside of the laser radar;

receiving a radar echo;

obtaining the distance and/or reflectivity of the obstacle currently scanned by the laser radar;

and adjusting the transmitting power of the laser radar according to the distance and/or reflectivity of the obstacle.

According to one aspect of the invention, said adjusting the transmission power of the laser of the lidar comprises: and adjusting the wavelength of the seed light so as to adjust the transmitting power of a laser of the laser radar.

According to one aspect of the invention, the step of adjusting the transmission power of the laser of the lidar comprises: when the distance is smaller than a distance threshold and/or the reflectivity is higher than a reflectivity threshold, adjusting the angle of a scanning unit of the laser, and changing the wavelength of the tuning light oscillated in the laser resonant cavity to reduce the power of the laser emitted from the filter unit.

The invention mainly provides a passive Q-switched solid laser of a laser diode pump, and the output power of the passive Q-switched solid laser is continuously adjustable. For a pulsed laser, the single pulse energy/pulse width is the peak power, and hereinafter, unless otherwise specified, the power refers to the single pulse peak power, and the energy refers to the single pulse energy.

Compared with the mode of adjusting power by a polaroid, the embodiment of the invention does not need to use a rotary component, and realizes an all-solid-state structure. Meanwhile, the core part of the laser adopts a microchip type structure, which is beneficial to reducing the cost and realizing stable and reliable integral packaging.

Drawings

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

FIG. 1 shows a schematic diagram of a laser with adjustable output power according to an embodiment of the present invention;

FIG. 2 shows transmission lines of a narrow band filter according to one embodiment of the invention;

FIG. 3 shows a schematic view of a scanning unit according to an embodiment of the invention;

fig. 4 illustrates a method of scanning using a lidar in accordance with one embodiment of the present invention.

Detailed Description

As described above, the main problem of using a polarizer to adjust the output laser power is the large size of the whole device. The inventor finds that the laser power adjusting device using the polaroid needs to adopt a motor to drive a half-wave plate to rotate, so that the polarization direction of laser is changed, and the energy of the laser passing through a rear analyzer (polaroid) is changed. Thus, the adoption of an additional mechanical mechanism (motor) can lead to the large volume of the whole device, be not beneficial to the packaging and integration of the solid laser and be not beneficial to the miniaturization of the laser.

The inventor analyzes and researches the requirements of the laser radar and concludes that the solid laser has the following characteristics as the light source of the laser radar:

1) the power of a laser applied to the laser radar is expected to be continuously adjustable so as to avoid the situation that a detection signal of a detector is saturated when a short-distance and strong-reflection target is detected;

2) it is desirable for lidar to have high peak power and narrow pulse widths. The wavelength of a light source of the laser radar is out of the range of a visible light wave band of human eyes, and the high peak power and the narrow pulse width are favorable for improving the measurement distance and the signal-to-noise ratio;

3) the laser radar has variable working environment, the performance of the laser radar is easily influenced by natural conditions such as atmospheric environment, air temperature and the like, and requirements are provided for the reliability of a laser. If it can be packaged as a whole, high reliability and stability can be achieved;

4) it is desirable that the laser has a high degree of integration, a compact structure and a low cost.

On the basis of the above research, the inventor provides the laser in the embodiment of the invention, so that the output power of the laser is adjustable, and the laser has an all-solid-state compact structure, and the requirements of the laser radar on a light source are better met.

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

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

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

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

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

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

Fig. 1 shows a laser with adjustable output power according to one embodiment of the present invention, and preferably, the output power of the laser is continuously adjustable. Described in detail below with reference to fig. 1.

As shown in fig. 1, the laser 10 includes a laser generating unit 20 and a seed light generating unit 30, wherein the seed light generating unit 30 is configured to generate seed light Ls, the seed light Ls is coupled into the laser generating unit 20, and the laser generating unit 20 can generate outgoing laser light having the same wavelength as the seed light Ls by injection locking of the seed light Ls. As will be described in detail below.

The laser generating unit 20 includes a first pump unit 21, a first pump optical element 22, a resonant unit, and a filter unit 26, wherein the first pump unit 21 is, for example, a semiconductor laser diode, and is configured to generate a first pump light L1 and to be incident on the first pump optical element 22. The first pump optical element 22 comprises a lens or a lens group or a coupling mirror for suitable shaping modulation of the first pump light L1 and coupling into a resonant cell located in the optical path downstream of the first pump cell 21. The resonant unit is configured to receive the first pump light L1, and a light beam with a certain wavelength may oscillate in the resonant unit and output a first laser LO. The filtering unit 26 is configured to receive the first laser LO output by the resonance unit, and emit the first laser LO after filtering. According to an embodiment of the present invention, the resonance unit is configured to receive the seed light Ls output from the seed light generation unit 30 such that in the resonance unit, a mode having a wavelength closest to the wavelength of the seed light Ls preferentially forms an oscillation, and thus the wavelength of the first laser light LO output from the resonance unit is the same as the wavelength of the seed light Ls. The structure of the resonance unit is described in detail below.

As shown in fig. 1, the resonance unit includes: a first laser resonator (27,28), a first gain unit 23 and a quality factor adjustment unit 24. Wherein said first laser cavity comprises a first resonance section 27 and a second resonance section 28, the specifications of the first laser cavity being defined by said first resonance section 27 and said second resonance section 28. According to a preferred embodiment of the present invention, the first resonance part 27 is, for example, a reflection film plated on the incident surface of the first gain cell 23, and has high transmittance for light of the first pump light wavelength and high reflectance for light of the laser wavelength, so that in the optical path of fig. 1, the first resonance part 27 will allow the first pump light L1 from the first pump cell 21 to pass through, and reflect the light beam from the first gain cell 23 toward the first pump cell 21 back to the first gain cell 23. Alternatively, the first resonant portion 27 may be disposed between the first gain unit 23 and the first pump unit 21 (or the first pump optical element 22), as long as it allows the first pump light L1 from the first pump unit 11 to pass through while the light in the laser resonant cavity toward the first pump unit 21 is reflected back into the resonant cavity, which is not described herein again. According to one embodiment of the present invention, the second resonance section 28 includes, for example, a film highly reflective of the laser wavelength plated on the output face of the quality factor adjusting unit 24, which constitutes a first laser resonator with the first resonance section 27 on the incident face of the first gain medium 23. The second resonator portion 28 simultaneously allows the seed light Ls to pass through and enter the first laser cavity to form an oscillation of the light of a particular wavelength of the first laser cavity.

The first gain unit 23 includes a laser gain medium therein. The laser gain medium is used for realizing population inversion to form optical amplification. The Q-factor adjustment unit 24 comprises a saturable absorber as a Q-switch for passive Q-switching for generating laser pulses.

The laser gain medium may be at least one of Nd: YAG, Nd: YVO4, and Er, Yb co-doped glass and crystal. The specific properties (center wavelength or wavelength range, etc.) of the gain medium and the specific selection of the gain medium can be set according to the application field of the laser or the wavelength of the laser light generated by the laser, and the invention is not limited thereto. In this embodiment, the laser gain medium is a microchip type gain medium.

In an embodiment of the present invention, the figure of merit adjustment unit 24 comprises, for example, a saturable absorber. In the present invention, the first gain unit 23 and the quality factor adjusting unit 24 are processed into a microchip, reducing the laser size. The whole structure can carry out air tightness packaging, and not only can ensure that the laser is small in size and compact in structure, but also can ensure low cost. The material of the saturable absorber within the quality factor adjustment unit 24 includes: at least one of YAG, carbon nanotube and graphene. Preferably, the material of the saturable absorber is at least one of carbon nanotubes or graphene. The carbon nano tube or the graphene has good heat conductivity, and can effectively improve the heat conduction and heat dissipation effects of components in the laser resonant cavity. According to a preferred embodiment of the present invention, as shown in fig. 1, the laser gain medium of the first gain unit 23 and the saturable absorber of the quality factor adjusting unit 24 are bonded to each other, that is, the surface of the gain medium in the first gain unit 23 facing the quality factor adjusting unit 24 and the surface of the saturable absorber in the quality factor adjusting unit 24 facing the first gain unit 23 are bonded to each other in contact. By processing the laser gain medium and the saturable absorber into a microchip type and attaching the microchip type and the saturable absorber together, the laser has a compact structure, can effectively control the size of a laser resonant cavity, and is beneficial to realizing high repetition frequency, narrow pulse width and high peak power.

Typically, the initiation of the Q-switching process in a laser is random and the time interval between pulses varies widely. In the invention, the Q-switched pulse is triggered by injecting the seed light Ls, and the period jitter of the seed light Ls is very small (which can be realized by modulated pump light), so the time jitter of the finally output laser pulse is improved by injection locking, and the consistency of the laser is better. In addition, the laser resonator in the embodiment of fig. 1 is shorter, and only the lengths of the first gain unit 23 and the quality factor adjusting unit 24 are included, so that higher single-pulse energy is easier to obtain. The laser gain medium and the saturable absorber are both processed into a microchip and are bonded together to form a whole. The whole laser has small size, short cavity length and compact structure, and can realize high repetition frequency, narrow pulse width and high peak power. In addition, the whole solid laser is installed on the radiating bottom plate and hermetically packaged into the metal shell, so that high reliability and high stability are achieved.

In fig. 1, the first pump light L1 is transmitted from the first resonator portion 27 into the first laser resonator. The first laser cavity may receive the seed light Ls, and thus a mode having a wavelength closest to the wavelength of the seed light Ls preferentially forms an oscillation in the first laser cavity, so that the wavelength of the first laser light LO output from the resonance unit is the same as the wavelength of the seed light Ls. The first gain unit 23 and the quality factor adjusting unit 24 are located between the first resonance section 27 and the second resonance section 28, and the first laser LO is emitted from the second resonance section 28. It should be noted that, in the first laser cavity, when the gain is equal to or greater than the loss, stable laser oscillation can be established in the cavity.

In addition, those skilled in the art will readily appreciate that the first pump optical element 22 is not required. The first pump optical element 22 may not be provided, for example, when the first pump light L1 generated by the first pump unit 21 satisfies the condition for coupling into the first gain unit 23. Alternatively, the first pump optical element 22 may be integrated with the first pump unit 21, so that pump light exiting the first pump unit 21 may be coupled directly into the first gain unit 23.

According to an embodiment of the present invention, the filtering unit 26 includes a narrow band filter, and the transmittance of the narrow band filter varies continuously with the wavelength within a certain wavelength range, and the laser with different powers is output according to the transmittance of different wavelengths, so as to adjust the power of the output laser. The narrow band filter of the present invention is, for example, an FP etalon, a narrow band filter, or other optical element having a narrow band transmission spectrum. The performance of the filter element 26 (e.g., FP etalon) varies with temperature, such as line slope, width, etc. Therefore, according to a preferred embodiment of the present invention, the laser generating unit 20 further comprises a semiconductor refrigerator 29, the semiconductor refrigerator 29 acts on the filtering unit 26, and the change of the transmission line, such as the slope, width, etc. of the line can be realized as required by controlling the temperature of the filtering unit 26.

In fig. 2, a curve I shows an example of the transmission line of the narrow band filter, and a curve II shows the line of the laser beam emitted from the second resonator 28. The central wavelength of the laser line is determined by the seed light Ls, and the lasers with different central wavelengths correspond to different transmittances on the transmission line (as the arrow in the figure indicates the transmittance corresponding to the current laser line). By controlling the wavelength of the seed light Ls, wavelength tuning (shift of the center wavelength of the laser line) can be realized, and different transmittances can be obtained in the narrow band filter. When the wavelength of the seed light Ls is continuously changed, the laser power transmitted through the narrow-band filter is continuously changed, so that the laser power can be continuously adjusted.

The seed light generation unit 30 according to a preferred embodiment of the present invention is described in detail below.

As shown in fig. 1, the seed light generation unit 30 includes a second pumping unit 31, a second pumping optical element 32, a second gain unit 33, a light splitting unit 34, and a scanning unit 35. Wherein the second pump unit 31 is, for example, a semiconductor laser diode, and is configured to generate the second pump light L2 and to be incident on the second pump optical element 32. The second gain unit 33 is located downstream of the optical path of the second pump unit 31 and receives the second pump light L2. The light splitting unit 34 is configured to generate the seed light Ls and a plurality of tuning lights of different wavelengths, which differ in propagation direction. The scanning unit 35 is configured to receive the tuning lights with the different wavelengths and return at least one of the tuning lights with the different wavelengths to the light splitting unit 34. Similar to the first gain cell 23, the second gain cell 33 also comprises a gain medium, and the second gain cell 33 may be a microchip type gain cell.

The seed light generating unit 30 further includes a reflection unit 38 located between the second pumping unit 31 and the second gain unit 33, in fig. 1, the reflection unit 38 is a reflection film plated on an incident surface of the second gain unit 33, and has high transmittance for light of a pumping light wavelength and high reflectance for light of a laser wavelength, so that in the light path of fig. 1, the reflection unit 38 will allow the second pumping light from the second pumping unit 31 to pass through, and reflect the light beam from the second gain unit 33 toward the second pumping unit 31 back to the second gain unit 33, so that the reflection unit 38, the light splitting unit 34, and the scanning unit 35 constitute a second laser resonator, and the tuning light returned to the light splitting unit 34 by the original light path of the scanning unit 35 finally oscillates in the second laser resonator, and finally, the seed light Ls is emitted and formed. Alternatively, the reflection unit 38 may be disposed between the second gain unit 33 and the second pump unit 31 (or the second pump optical element 32), as long as it allows the second pump light from the second pump unit 31 to pass through while the light in the laser resonator toward the second pump unit 31 is reflected back to the resonator, and will not be described herein again.

The light splitting unit 34 includes, for example, a diffraction grating, and 0 th order of the diffraction grating is used as an output of the seed light Ls. The light passing through the second gain unit 33 is incident on the diffraction grating, and the diffraction angles of the light with different wavelengths are different in the same order (not 0 order) according to the grating equation. The diffraction grating in the present invention is, for example, a-1 order high diffraction efficiency grating, and-1 order broadband diffraction efficiency can be achieved to be more than 95%. Therefore, the light splitting unit 34 can generate a plurality of tuning lights of different wavelengths at the-1 level and emit the seed light Ls of different wavelengths at the 0 level based on the oscillation of part of the tuning lights in the laser resonator. In this embodiment, the grating of the light splitting unit 34 can effectively ensure the light splitting effect of the generated seed light Ls and the plurality of tuning lights, and the propagation direction difference of the tuning lights between different wavelengths can be made large enough to reduce the difficulty in selecting the subsequent scanning unit through the selection of a suitable grating (e.g., with a smaller grating constant). However, in other embodiments of the present invention, the light splitting unit 34 may be configured as other optical devices capable of splitting a plurality of tuning lights, such as a prism, which is within the protection scope of the present invention.

As shown in fig. 1, the light splitting unit 34 is a transmissive grating, such as a deep etched binary phase grating, the seed light exits from the transmission 0 level, and the tuning lights with different wavelengths propagate in different directions after the transmission-1 level is separated. The implementation of light splitting by using a transmissive grating in the light splitting unit 34 is merely an example. In other embodiments of the present invention, the grating may also include a reflective grating, which is not described herein again.

Further, the grating may include a +1 order high diffraction efficiency grating in addition to a-1 order high diffraction efficiency grating. When the grating is a-1 st order high diffraction efficiency grating, the light splitting unit 34 generates the seed light Ls in the exit direction of 0 th order light of the-1 st order high diffraction efficiency grating, and generates the tuning lights in the exit direction of-1 st order diffraction light of the-1 st order high diffraction efficiency grating; when the grating is a + 1-order high diffraction efficiency grating, the light splitting unit 34 generates the seed light Ls in the 0-order light exit direction of the + 1-order high diffraction efficiency grating, and generates the plurality of tuning lights based on the + 1-order diffraction light exit direction of the + 1-order high diffraction efficiency grating.

The light splitting unit 34 adopts a-1 level high diffraction efficiency grating or a +1 level high diffraction efficiency grating to realize light splitting, so that the energy of the tuning lights generated by the light splitting unit 34 can be effectively improved, and the output transmittance of the second laser resonant cavity (i.e., the energy loss to the outside when the lights are reflected back and forth in the laser resonant cavity) is reduced, thereby effectively reducing the loss of the laser resonant cavity, reducing the energy waste of the pump light, and effectively controlling the pulse energy of the seed light.

The scanning unit 35 performs angle scanning within a certain range, a dielectric film with high reflectivity for the seed light wavelength range (or the second gain unit gain wavelength range) is coated on the surface of the scanning unit 35, and the scanning unit 35, the reflection unit 38 and the light splitting unit 34 together form a second laser resonant cavity. The scanning unit 35 changes the incident angles of the tuning lights in a swinging or rotating manner, and the tuning lights vertically incident to the scanning unit 35 return according to the original light path, and are projected to the reflection unit 38 after passing through the light splitting unit 34 and the second gain unit 33 to form back-and-forth reflection of the tuning lights with corresponding wavelengths in the second laser resonant cavity. Light incident non-perpendicularly to the scanning element 35 is reflected out of the laser cavity. As shown in fig. 3, at times t0, t1, and t2, tuning light with wavelengths λ 0, λ 1, and λ 2 are respectively vertically incident on the scanning unit 35, reflected by the scanning unit 35 along the original optical path, and finally form laser oscillation in the laser resonator. In the laser resonator, when the gain is equal to or greater than the loss, stable laser oscillation is established in the resonator. Therefore, at the time t0, t1, and t2, the laser cavity starts to oscillate the tuning lights with the wavelengths λ 0, λ 1, and λ 2, respectively, that is, the laser cavity can realize the oscillation of the lights with different wavelengths at different times, so as to realize the wavelength tuning of the seed light Ls. The seed light generating unit 30 shown in fig. 1 includes one scanning unit 35, but the present invention is not limited thereto and may include a plurality of scanning units.

It can be seen that the speed of wavelength tuning of the seed light generation unit 30 is related to the speed of selection of different wavelength tuning lights by the scanning unit 35. In this embodiment, the speed of the scanning unit 35 for selecting the tuning light with different wavelengths is related to the speed of the scanning unit 35 swinging or rotating. According to one embodiment of the present invention, the scanning unit 35 includes a galvanometer. The incident angles of the tuning lights can be quickly changed through the high vibration frequency of the vibrating mirror, and high-speed selection is realized in the tuning lights, so that the tuning light for forming laser oscillation in the second laser resonant cavity is changed at high speed, and high-speed wavelength tuning is realized. Moreover, the scanning unit 35 may include a MEMS galvanometer, so that the volume of the scanning unit 35 can be effectively reduced, which is beneficial to improve the integration level of the laser. In the present invention, the scanning unit 35 is, for example, a micro-scanning mirror of a silicon process or a non-silicon process based on the MEMS processing technology, and the micro-scanning mirror can be oscillated by applying an alternating current to an electrode connected to a coil of the MEMS scanning mirror. The micro-scanning mirror is, for example, of a resonant type and a millimeter-scale size, and is advantageous for miniaturization of the laser.

According to an embodiment of the present invention, no quality factor adjusting unit is provided in the seed light generating unit 30, and thus the generated seed light energy is low. The light splitting unit 34 and the scanning unit 35 can select light with a specific wavelength at different times, and generate the seed light Ls from the 0 th order of the diffraction grating as an output.

In order to couple the seed light Ls into the first laser cavity of the laser, the laser generating unit 20 of the laser 10 further comprises a beam splitter 25, such as a half mirror, the beam splitter 2 is configured to receive the seed light Ls and reflect at least a portion of the seed light Ls onto the second resonance part 28 and transmit through the second resonance part 28 into the first laser cavity, and the beam splitter 25 is configured to receive the first laser LO and transmit at least a portion of the first laser LO, and at least a portion of the transmitted first laser LO is incident on the filtering unit 26.

In addition, according to a preferred embodiment of the present invention, as shown in fig. 1, the laser 10 further includes a mirror 36 and an optical isolator 37, the mirror 36 receives the seed light Ls and changes its direction by reflection so that the seed light Ls is incident on the optical isolator 37, the optical isolator 37 receives the seed light Ls and allows only the seed light Ls to pass through in one direction, the seed light Ls passing through the optical isolator is incident on the beam splitter 25 and at least partially enters the first laser cavity, so that a weak signal is injected during the Q-tuning start process, such that in the first laser cavity, a mode having a frequency closest to the frequency of the injected signal preferentially oscillates, and other modes are suppressed, such that the wavelength of the first laser LO output by the laser is the same as the wavelength of the seed light Ls. Therefore, the laser pulse wavelength, namely the wavelength of the locked seed laser, is emitted through the first laser resonant cavity. It is understood that the mirror 36 is not necessary, the seed light Ls can be directly incident into the optical isolator 37, and the use of the mirror 36 can further turn the light beam, making the structure more compact. The first laser LO is incident on a filtering unit 26 (for example, a narrow-band filter) through a beam splitter 25, and is output after power adjustment through filtering. The narrow band filter in this patent application may be an FP etalon, a narrow band filter or other optical element with a narrow band transmission spectrum.

Therefore, in the embodiment of the invention, the output power of the passive Q-switched solid-state laser can be adjusted by adopting a mode of combining seed light injection locking and laser tuning with a narrow-band filter.

In fig. 1 it is shown that the laser 10 comprises a seed light generation unit 30. It is readily understood by a person skilled in the art that the present invention is not limited thereto, and the laser 10 may not comprise a seed light generating unit, but may be directly coupled in seed light, which are within the scope of the present invention.

According to a preferred embodiment of the present invention, the laser 10 further comprises a control unit coupled to the scanning unit 35 and controlling the angle of the scanning unit 35 to control the wavelength of the tuning light oscillating in the second laser cavity to control the wavelength of the seed light and the wavelength of the first laser LO.

According to an embodiment of the present invention, the laser 10 further comprises a detection unit, which can detect a moment when the laser oscillation in the first laser cavity generates the output laser light. The detection unit may include a photodiode. The detection unit detects the output beam of the beam splitter 25 to obtain the time when the laser oscillation forms the output laser.

The invention also relates to a lidar comprising: a transmitting device, a receiving device, and a signal processing device. Wherein the emitting means comprises one or more lasers 10 as described above, thereby emitting a detection laser beam. The detection laser beam is diffusely reflected at the obstacle, and part of the reflected beam is returned to the laser radar as a radar echo to be received by the receiving means. The signal processing device is configured to obtain the distance and/or reflectivity of the obstacle currently scanned by the laser radar according to the radar echo and generate point cloud data.

According to an embodiment of the present invention, the lidar may adjust the wavelength of the seed light Ls (e.g., adjust the wavelength of the seed light Ls by adjusting the angle of the scanning unit 35) according to the obtained distance and/or reflectivity of the obstacle currently scanned by the lidar, so as to adjust the light emitting power of the laser. For example, the lidar may determine whether the distance is less than a preset distance threshold and the reflectivity is higher than a preset reflectivity threshold according to the distance and/or the reflectivity of the currently detected obstacle. When the distance of the obstacle is judged to be smaller than the preset distance threshold value and/or the reflectivity is higher than the preset reflectivity threshold value, the energy of the laser pulse of the laser preferably needs to be reduced when the transmitting device of the laser radar transmits the next detection beam, otherwise, the detector signal of the receiving device is saturated, and the detection performance is influenced. For this purpose, the lidar is configured such that the controllable laser adjusts an angle of a scanning unit of the laser such that a wavelength of the seed light (and thus a wavelength of the first laser light) oscillated and emitted in the second laser cavity is further deviated from a center wavelength of a pass band of the narrow band filter in the filter unit, thereby reducing an energy of the laser pulse. Additionally or alternatively, when it is determined that the distance of the obstacle is greater than the preset distance threshold and/or the reflectivity is less than the preset reflectivity threshold, the transmitting device of the laser radar preferably needs to increase the energy of the laser pulse of the laser to improve the detection performance when transmitting the next detection beam. For this purpose, the lidar is configured to control the laser to adjust the angle of the scanning unit of the laser such that the wavelength of the seed light (and thus the wavelength of the first laser light) oscillating and exiting in the laser resonator is brought further close to the central wavelength of the pass band of the narrow-band filter in said filter unit, thereby increasing the energy of the exiting laser pulse.

The invention also relates to a method 200 of scanning using a lidar as described above, comprising:

in step S201, a detection laser beam is emitted to the outside of the laser radar.

In step S202, a radar echo is received. The radar echo may be received, for example, by a photodetector in a lidar receiving device and the echo signal converted to an electrical signal.

In step S203, the distance and/or reflectivity of the obstacle currently scanned by the laser radar is obtained. Parameters such as the distance and/or reflectivity of the currently scanned obstacle may be obtained by processing the electrical signal, including but not limited to amplification, filtering, analog-to-digital conversion, etc.

In step S204, the transmitting power of the laser of the lidar is adjusted according to the distance and/or reflectivity of the obstacle. According to a preferred embodiment, when the distance is smaller than the distance threshold and/or the reflectivity is higher than the reflectivity threshold, the angle of the scanning unit of the laser is adjusted, and the wavelength of the tuning light oscillated in the second laser resonator is changed, so that the wavelength of the seed light (and thus the wavelength of the first laser light) oscillated and emitted in the second laser resonator is further away from the central wavelength of the passband of the narrow-band filter in the filtering unit, and the energy of the emitted laser pulse is reduced. Additionally or alternatively, when it is determined that the distance of the obstacle is greater than the preset distance threshold and/or the reflectivity is less than the preset reflectivity threshold, the transmitting device of the laser radar preferably needs to increase the energy of the laser pulse of the laser to improve the detection performance when transmitting the next detection beam. For this purpose, the lidar is configured such that the controllable laser adjusts an angle of a scanning unit of the laser such that a wavelength of the seed light (and thus a wavelength of the first laser light) oscillated and emitted in the second laser cavity is further close to a center wavelength of a pass band of the narrow-band filter in the filter unit, thereby increasing an energy of the emitted laser pulse.

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

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

Claims

1. A laser, comprising:

a first pump unit configured to generate a first pump light;

2. The laser of claim 1, wherein the resonating unit comprises:

a first gain unit;

a quality factor adjusting unit;

3. The laser of claim 1 or 2, further comprising a seed light generation unit comprising:

a second pump unit configured to generate second pump light;

4. The laser device as claimed in claim 3, wherein the scanning unit changes the incident angles of the tuning lights in a swinging or rotating manner, and the tuning light vertically incident to the scanning unit returns along the original optical path, passes through the light splitting unit, and is projected to the reflection unit to form back-and-forth reflection of the tuning light with corresponding wavelength in the second laser resonator.

5. The laser of claim 3, wherein the beam splitting unit comprises: a grating, the grating comprising: at least one of a reflective grating or a transmissive grating.

6. The laser of claim 5, wherein the grating comprises: -a level 1 or +1 high diffraction efficiency grating;

7. The laser of claim 1 or 2, wherein the filtering unit comprises a narrow band filter whose transmittance varies continuously with wavelength over a range of wavelengths.

8. The laser of claim 1 or 2, further comprising a beam splitter configured to receive the seed light and reflect at least a portion of the seed light, and to receive the first laser light and transmit at least a portion of the first laser light, wherein the reflected at least a portion of the seed light is transmitted from the second resonator into the first laser resonator and the transmitted at least a portion of the first laser light is incident on the filtering unit.

9. The laser of claim 8, further comprising an optical isolator that receives the seed light and allows only one-way passage of the seed light, the seed light passing through the optical isolator being incident on the beam splitter.

10. The laser of claim 3, wherein the first and/or second gain cells comprise a gain medium, the first and/or second gain cells being microchip-type gain cells; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the first gain unit and the quality factor adjusting unit are mutually attached.

11. The laser of claim 3, wherein the laser further comprises a control unit coupled to the scanning unit and controlling an angle of the scanning unit to control a wavelength of the tuning light oscillating within the second laser cavity.

12. A lidar comprising:

a transmitting device comprising a laser as claimed in any one of claims 1 to 11;

13. The lidar of claim 12, wherein the lidar is configured to adjust an angle of a scanning unit of the laser in dependence on an obtained distance and/or reflectivity of an obstacle currently scanned by the lidar.

14. A method of scanning using a lidar according to any of claims 12 to 13, comprising:

emitting a detection laser beam to the outside of the laser radar;

receiving a radar echo;

15. The method of claim 14, wherein the adjusting the transmit power of the laser of the lidar comprises: and adjusting the wavelength of the seed light so as to adjust the transmitting power of a laser of the laser radar.

16. The method of claim 14 or 15, wherein the step of adjusting the transmit power of the laser of the lidar comprises: when the distance is smaller than a distance threshold and/or the reflectivity is higher than a reflectivity threshold, adjusting the angle of a scanning unit of the laser, and changing the wavelength of the tuning light oscillated in the laser resonant cavity to reduce the power of the laser emitted from the filter unit.