CN211655309U - Laser and laser radar including the same - Google Patents
Laser and laser radar including the same Download PDFInfo
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- CN211655309U CN211655309U CN201922377881.XU CN201922377881U CN211655309U CN 211655309 U CN211655309 U CN 211655309U CN 201922377881 U CN201922377881 U CN 201922377881U CN 211655309 U CN211655309 U CN 211655309U
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Abstract
The invention relates to a laser comprising: a pumping unit configured to generate pumping light; a gain unit located downstream of the optical path of the pumping unit and receiving the pumping light; a quality factor adjusting unit; a light splitting unit configured to generate an exit laser light and a plurality of tuning lights of different wavelengths, the tuning lights of different wavelengths differing in propagation direction; the scanning unit is configured to receive a plurality of tuning lights with different wavelengths and return at least one original light path in the tuning lights with different wavelengths to the light splitting unit; the laser device comprises a reflection unit, a light splitting unit and a scanning unit, wherein the reflection unit, the light splitting unit and the scanning unit form a laser resonant cavity, tuning light returned to the light splitting unit by a primary path finally forms oscillation in the laser resonant cavity, and a quality factor adjusting unit is configured to adjust a quality factor of the laser resonant cavity; and the filtering unit is configured to receive the emergent laser generated by the light splitting unit and emit the laser after filtering.
Description
Technical Field
The present invention generally relates to the field of optoelectronic technologies, and in particular, to a laser, a lidar including the laser, and a scanning method 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 performance 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 pulses remains substantially constant as the pump power increases. 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 pumping unit configured to generate pumping light;
a gain unit located downstream of the pump unit in an optical path and receiving the pump light;
a quality factor adjusting unit;
a light splitting unit configured to generate an outgoing laser light and a plurality of tuning lights of different wavelengths, the tuning lights of different wavelengths differing in propagation direction;
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;
the reflection unit, the light splitting unit and the scanning unit form a laser resonant cavity, and the tuning light returned to the light splitting unit by the original path finally forms oscillation in the laser resonant cavity, wherein the quality factor adjusting unit is configured to adjust the quality factor of the laser resonant cavity; and
and the filtering unit is configured to receive the emergent laser generated by the light splitting unit and emit the laser after filtering.
According to one aspect of the invention, the reflection unit is located between the pumping unit and the gain unit and configured to reflect the light beam from the gain unit toward the pumping unit back to the gain unit, the scanning unit changes the incident angles of the plurality of tuning lights in a swinging or rotating manner, and returns the tuning lights which are vertically incident according to the original optical path, and the tuning lights are projected to the reflection unit through the light splitting unit to form back and forth reflection of the tuning lights with corresponding wavelengths in the laser resonant cavity.
According to an aspect of the present invention, the light splitting unit generates the outgoing laser light based on the oscillation-forming tuned light.
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 configured to output laser light having different power according to a difference in transmittance of different wavelengths within a certain wavelength range.
According to an aspect of the present invention, the gain unit includes a gain medium, the gain medium being a microchip type gain medium; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the 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 laser cavity.
The present invention also provides a laser radar 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 provides a scanning method using the laser radar, which comprises the following steps:
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, 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, and the scanning mirror, the diffraction grating and the narrow-band filter all belong to optical components with mature technology, so that the cost is reduced, and stable and reliable integral packaging is realized.
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 a schematic view of a scanning unit according to an embodiment of the invention;
FIG. 3 shows a schematic diagram of a laser including a reflective beam splitting cell according to one embodiment of the present invention;
FIG. 4 shows transmission lines of a narrow band filter according to one embodiment of the invention; and
fig. 5 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.
A first aspect of the invention provides a passively Q-switched laser with adjustable output power, 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 pumping unit 11, a pumping optical element 12, a gain unit 13, a quality factor adjusting unit 14, a light splitting unit 15, a scanning unit 16, a reflecting unit 18, and a filtering unit 17. The pump unit 11 is, for example, a pump semiconductor laser diode, which can generate pump light and is incident on the pump optical element 12. The pump optical element 12 comprises a lens or a lens group or a coupling mirror for coupling pump light into the gain unit 13, the gain unit 13 comprising a laser gain medium which is located in the optical path downstream of said pump unit 11 and which receives said pump light. The laser gain medium in the gain unit 13 is used to realize population inversion to form optical amplification. The Q-factor adjustment unit 14 comprises a saturable absorber as a Q-switch for passive Q-switching for generating laser pulses. The light splitting unit 15 is configured to generate the outgoing laser light and a plurality of tuned lights of different wavelengths, which differ in the propagation direction. The scanning unit 16 is configured to receive the tuning lights with the plurality of different wavelengths and return at least one of the tuning lights with the different wavelengths to the light splitting unit 15. In the above optical path system, the reflection unit 18, the light splitting unit 15, and the scanning unit 16 together form a laser resonator, and the tuning light returned to the light splitting unit 15 by the original optical path finally forms oscillation in the laser resonator, wherein the quality factor adjustment unit 14 is configured to adjust the quality factor of the laser resonator. The filter unit 17 is configured to receive the outgoing laser beam generated by the beam splitter unit 15, filter the outgoing laser beam, and output the filtered outgoing laser beam to form the outgoing laser beam of the laser 10.
In addition, the skilled person will readily understand that the pump optical element 12 is not essential. For example, when the pump light generated by the pump unit 11 satisfies the condition for coupling into the gain unit 13, the pump optical element may not be provided. Alternatively, the pump optics 12 can be integrated with the pump unit 11, so that the pump light exiting from the pump unit 11 can be coupled directly into the gain unit 13.
According to a preferred embodiment of the present invention, the reflection unit 18 is, for example, a reflection film plated on the incident surface of the gain unit 13, and has high transmittance for light with a pump light wavelength and high reflectance for light with a laser wavelength, so that in the optical path of fig. 1, the reflection unit 18 allows the pump light from the pump unit 11 to pass through, and reflects the light beam from the gain unit 13 toward the pump unit 11 back to the gain unit. Alternatively, the reflection unit 18 may be disposed between the gain unit 13 and the pumping unit 11 (or the pumping optical element 12), as long as it allows the pump light from the pumping unit 11 to pass through while the light in the laser resonant cavity toward the pumping unit 11 is reflected back into the resonant cavity, which is not described herein again.
It should be noted that the laser gain medium in the gain unit 13 is related to the wavelength of the laser light generated by the laser. The laser gain medium can be at least one of Nd: YAG, Nd: YVO4, 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.
The light splitting unit 15 includes, for example, a diffraction grating, and outputs the 0 th order of the diffraction grating as laser light. The light passing through the gain unit 13 and the quality factor adjusting unit 14 is incident on the diffraction grating. The diffraction angles of 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 15 can generate a plurality of tuning lights with different wavelengths at the-1 level and emit laser lights with 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 15 can effectively ensure the light splitting effect of the generated emergent laser and the plurality of tuning lights, and the difference of the propagation directions 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 15 may be configured as other optical devices capable of splitting a plurality of tuning lights, such as a prism.
As shown in fig. 1, the light splitting unit 15 is a transmissive grating, such as a deep etched binary phase grating, in which laser light exits from the transmission 0 order, and a plurality of tuning lights with different wavelengths are transmitted in different directions after the transmission-1 order is divided. The implementation of light splitting by using a transmissive grating in the light splitting unit 15 is merely an example. In other embodiments of the present invention, the grating may also comprise a reflective grating. Fig. 3 shows an embodiment of a reflective grating, in which the laser light exits from the reflection 0 stage and a plurality of tuning lights with different wavelengths propagate in different directions after the reflection-1 stage is separated, which is not described herein.
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 15 generates the laser light 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 15 generates the laser light in the 0-order light emission direction of the + 1-order high diffraction efficiency grating, and generates the plurality of tuning lights based on the + 1-order diffraction light emission direction of the + 1-order high diffraction efficiency grating.
The light splitting unit 15 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 15 can be effectively improved, and the output transmittance of the laser resonant cavity (namely the energy loss of the light to the outside when the light is 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 output laser.
The scanning unit 16 performs angle scanning within a certain range, a dielectric film with high reflectivity in the output wavelength range (or gain wavelength range of the gain medium) of the laser is coated on the surface of the scanning unit 16, and the scanning unit, the reflecting unit 18 and the light splitting unit 15 form a laser resonant cavity together. When the incident light from the light splitting unit 15 vertically enters the scanning unit 16, the incident light is reflected by the scanning unit 16 and returns to the original optical path, passes through the light splitting unit 15 and the quality factor adjusting unit 14, enters the gain unit 13 again, and is reflected by the reflecting unit 18, so that the incident light is reflected back and forth in the laser resonant cavity, and finally forms oscillation in the laser resonant cavity. Light incident on the scanning unit 16 at a non-normal angle is reflected by the scanning unit 16 to the outside of the laser resonator. As shown in fig. 2, at times t0, t1, and t2, light beams with wavelengths λ 0, λ 1, and λ 2 are respectively incident perpendicularly to the scanning unit 16, reflected by the scanning unit 16, return along the original optical path, and finally form laser oscillation in the laser resonator. The scanning unit 16 changes the incident angles of the tuning lights in a swinging or rotating manner, and makes the tuning lights which are vertically incident return according to the original light path, and the tuning lights pass through the light splitting unit, the quality factor adjusting unit and the gain unit and then are projected to the reflection unit 18 to form back-and-forth reflection of the tuning lights with corresponding wavelengths in the laser resonant cavity. 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 points t0, t1 and t2, the oscillation of the tuning light with the wavelengths λ 0, λ 1 and λ 2 starts to be formed in the laser cavity, i.e., the laser cavity can realize the oscillation of light with different wavelengths at different time points, so that the wavelength tuning of the laser is realized. While the laser 10 is shown in fig. 1 as including one scanning unit, 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 laser is related to the speed at which the scanning unit 16 selects light of different wavelengths. In this embodiment, the speed of the scanning unit 16 for selecting the tuning light with different wavelengths is related to the speed of the scanning unit 16 swinging or rotating. According to one embodiment of the present invention, the scanning unit 16 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 lights forming laser oscillation in the laser resonant cavity are changed at high speed, and high-speed wavelength tuning is realized. Moreover, the scanning unit 16 may include a MEMS galvanometer, so that the volume of the scanning unit 16 can be effectively reduced, which is beneficial to improve the integration level of the laser.
The Q value of the laser resonator can be adjusted by the quality factor adjusting unit 14, and the laser energy generated by the laser is compressed into a pulse with an extremely narrow width for emission, so that the peak power of the generated laser is increased by several orders of magnitude, and the laser with a narrow pulse width and a high peak value is obtained. In particular, the peak power of the laser can reach megawatt level (10) by the Q-switching technology6W) or more, pulse width compression to nanosecond (10)-9s) of the pulse.
In general, the adjustment of the Q value of the laser resonant cavity is realized by changing the loss in the cavity. Specifically, when the pumping starts, the loss of the laser resonant cavity is large, that is, the Q value of the laser resonant cavity is reduced, so that the gain medium accumulates the population of the inversion; after pumping for a certain time, the loss of the laser resonant cavity is suddenly reduced, namely the Q value of the laser resonant cavity is increased, so that the accumulated inversion population completes stimulated radiation in a short time to form optical pulses with narrow pulse width and high peak power. In the Q-switched technology, the laser resonant cavity is in a state of high loss and low Q value in most of the pumping process, so that the resonant cavity has a very high threshold value and cannot start oscillation, and the number of particles in the gain medium at the upper energy level to realize inversion is accumulated continuously, so that the light intensity of light rays reflected back and forth between the reflection unit 18 and the scanning unit 16 is gradually increased; when the number of the accumulated particles for realizing the inversion reaches a certain value, the loss of the resonant cavity suddenly drops, the Q value suddenly rises, and the threshold value of the laser oscillation is rapidly reduced; then laser oscillation begins to be established in the laser resonant cavity; because the number of particles accumulated during the loss reduction and Q value increase is large, the stimulated radiation is enhanced very quickly at the moment, and the energy stored in the gain medium is released in a short time, so that high-peak narrow-pulse-width laser is formed.
In particular, the figure of merit adjustment unit 14 comprises a saturable absorber. The saturable absorber is an optical device with definite loss, when the incident light intensity exceeds the threshold value of the saturable absorber, the optical loss becomes small, the transmittance is increased, and the Q value of the laser resonant cavity is increased.
In this embodiment, the material of the saturable absorber in the quality factor adjustment unit 14 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 gain unit 13 and the saturable absorber of the quality factor adjusting unit 14 are bonded to each other, that is, the surface of the gain medium in the gain unit 13 facing the quality factor adjusting unit 14 and the surface of the saturable absorber in the quality factor adjusting unit 14 facing the gain unit 13 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.
When the intensity of the tuning light forming the oscillation in the laser resonator is higher than the output threshold, the light splitting unit 15 generates the outgoing laser light based on the tuning light forming the oscillation. Wherein the output threshold is several times or even ten times of the saturation absorption light intensity of the saturable absorber.
According to an embodiment of the present invention, the filtering unit 17 includes a narrow band filter configured to output laser light having different power according to a difference in transmittance of different wavelengths within a certain wavelength range. A narrow-band filter is arranged at the downstream of the optical path of the light splitting unit 15, and the light transmittance of different wavelengths is different, so that the adjustment of the output laser power is realized. 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.
In fig. 4, curve I is an example of the transmission line of the narrow band filter, and curve II is the laser line. The central wavelength of the laser line is selected and determined by the scanning unit 16, 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). Wavelength tuning (shifting of the center wavelength of the laser line) can be achieved by the scanning unit and the light splitting unit, resulting in different transmittances in the narrow band filter. When the angle of the scanning unit is continuously changed, the laser power penetrating through the narrow-band filter is continuously changed along with the angle, so that the laser power can be continuously adjusted.
In the invention, the scanning unit is a micro-scanning mirror based on a silicon process or a non-silicon process of an MEMS (micro electro mechanical systems) processing technology, and the micro-scanning mirror can swing by applying alternating current to an electrode connected with 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. In the invention, the Q-switched crystal is a saturable absorber, for example, the saturable absorber is arranged in the resonant cavity, the transmittance of light is changed by utilizing the modulation of the light intensity on the absorption coefficient of the saturable absorber, and the Q-switched laser pulse is output by laser oscillation when the saturable absorber is saturated. 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 (cavity length is short), compact structure, and can realize high repetition frequency, narrow pulse width and high peak power. The whole solid laser is arranged on the radiating bottom plate and is packaged into the metal shell in an airtight mode, so that high reliability and high stability are achieved.
According to an embodiment of the invention, the laser 10 further comprises a control unit (not shown) coupled to the scanning unit and controlling the angle of the scanning unit to control the wavelength of the tuning light oscillating within the laser cavity.
According to an embodiment of the invention, the laser 10 further comprises a detection unit which can detect the moment at which the laser oscillation forms the output laser light. The detection unit may include a photodiode. The detection unit detects the partial light generated by the light splitting unit 15 to obtain the time when the laser oscillation forms the output laser.
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, and the scanning mirror, the diffraction grating and the narrow-band filter all belong to optical components with mature technology, so that the cost is reduced, and stable and reliable integral packaging is realized.
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 one embodiment of the invention, the lidar may adjust the angle of the scanning unit of the laser according to the obtained distance and/or reflectivity of the obstacle currently scanned by the lidar. 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 laser radar is configured to control the laser to adjust the angle of the scanning unit of the laser so that the center wavelength of the laser light oscillated and emitted in the laser resonator is further deviated from the center wavelength of the pass band of the narrow band filter in the filter unit, thereby reducing the 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 such that the laser is controllable to adjust an angle of a scanning unit of the laser such that a center wavelength of laser light oscillated and emitted in the laser resonator is further close to a center wavelength of a pass band of a narrow-band filter in the filter unit, thereby increasing an energy of the emitted laser light pulse.
The invention also relates to a method 20 for scanning using a lidar as described above, as shown in fig. 5, and described in detail below with reference to fig. 5.
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 a distance threshold and/or the reflectivity is higher than a reflectivity threshold, the angle of the scanning unit of the laser is adjusted to change the wavelength of the tuning light oscillated in the laser cavity, so that the central wavelength of the laser light oscillated and emitted in the laser cavity is further deviated from the central wavelength of the passband of the narrow-band filter in the filtering unit, thereby reducing the power of the laser light emitted from the filtering unit. 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 laser is controllable to adjust an angle of a scanning unit of the laser such that a center wavelength of laser light oscillated and emitted in the laser resonator is further close to a center wavelength of a pass band of a narrow-band filter in the filter unit, thereby increasing an energy of the emitted laser light 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. 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 various changes may be made and equivalents may be substituted for elements thereof. 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 (10)
1. A laser, characterized in that the laser comprises:
a pumping unit configured to generate pumping light;
a gain unit located downstream of the pump unit in an optical path and receiving the pump light;
a quality factor adjusting unit;
a light splitting unit configured to generate an outgoing laser light and a plurality of tuning lights of different wavelengths, the tuning lights of different wavelengths differing in propagation direction;
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;
the reflection unit, the light splitting unit and the scanning unit form a laser resonant cavity, and the tuning light returned to the light splitting unit by the original path finally forms oscillation in the laser resonant cavity, wherein the quality factor adjusting unit is configured to adjust the quality factor of the laser resonant cavity; and
and the filtering unit is configured to receive the emergent laser generated by the light splitting unit and emit the laser after filtering.
2. The laser of claim 1, wherein the reflection unit is located between the pumping unit and the gain unit and configured to reflect the light beam from the gain unit toward the pumping unit back to the gain unit, the scanning unit changes the incident angles of the tuning lights in a swinging or rotating manner and returns the tuning light incident vertically to the original optical path, and the light beam is projected to the reflection unit through the light splitting unit to form back and forth reflection of the tuning light with corresponding wavelength in the laser resonator.
3. The laser according to claim 1 or 2, wherein the light splitting unit generates the outgoing laser light based on the oscillation-forming tuned light.
4. The laser according to claim 1 or 2, wherein the light splitting unit includes: a grating, the grating comprising: at least one of a reflective grating or a transmissive grating.
5. The laser of claim 4, wherein 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.
6. The laser according to claim 1 or 2, wherein the filter unit includes a narrow band filter configured to output laser light of different powers according to a difference in transmittance of different wavelengths in a certain wavelength range.
7. The laser of claim 1 or 2, wherein the gain cell comprises a gain medium, the gain medium being a microchip-type gain medium; the quality factor adjusting unit comprises a saturable absorber, the saturable absorber is a microchip type saturable absorber, and the gain unit and the quality factor adjusting unit are mutually attached.
8. The laser of claim 1 or 2, further comprising 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 laser resonator.
9. A lidar, characterized in that the lidar comprises:
a transmitting device comprising a laser as claimed in any one of claims 1 to 8;
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.
10. Lidar according to claim 9, 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.
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