WO2020207434A1

WO2020207434A1 - Laser and laser radar

Info

Publication number: WO2020207434A1
Application number: PCT/CN2020/083963
Authority: WO
Inventors: 李大汕; 向少卿
Original assignee: 上海禾赛光电科技有限公司
Priority date: 2019-04-10
Filing date: 2020-04-09
Publication date: 2020-10-15
Also published as: CN109950784A; CN109950784B

Abstract

A laser and a laser radar. The laser comprises: a pumping unit, a gain unit, a Q modulation unit, and a light splitting unit sequentially provided along an optical axis, wherein the pumping unit generates a pumping light; the gain unit comprises a gain medium; the Q modulation unit comprises a saturable absorber; the light splitting unit generates an emergence laser and a plurality of tuning lights having different wavelengths; and a tuning reflective surface and a scanning unit, wherein the tuning reflective surface is located between the gain unit and the pumping unit; the scanning unit is located on an optical path of the plurality of tuning lights; the scanning unit selects one from the plurality of tuning lights and returns the selected tuning light by an original optical path. The laser is a tunable laser which can achieve Q modulation, can obtain a higher peak power and a larger pulse energy, effectively shorten the cavity length of a resonant cavity, and reduce the volume of the resonant cavity, and facilitates achieving both high integration and high peak power.

Description

Laser and Lidar

Technical field

The invention relates to the field of laser detection, in particular to a laser and a laser radar.

Background technique

A tunable laser (Tunable Laser) refers to a laser that can continuously change the laser output wavelength within a certain range. This kind of laser has a wide range of uses, such as spectroscopy, photochemistry, medicine, biology, integrated optics, and optical communications. Current tunable solid-state lasers mainly use a separate structure and a birefringent filter or etalon as an intracavity tuning element to achieve wavelength tuning. For example, US5317447 uses a birefringent plate combined with active Q-switching to achieve a tunable pulsed laser. For example, US5623510 uses etalon as the tuning element.

Lidar is a commonly used ranging sensor, which has the characteristics of long detection distance, high resolution, and low environmental interference. It is widely used in intelligent robots, unmanned aerial vehicles, unmanned driving and other fields. In recent years, autonomous driving technology has developed rapidly, and lidar has become indispensable as its core sensor for distance perception.

In lidar applications, detection distance, measurement frequency, and scanning mirror design all put forward demands on lasers. However, the existing tunable solid-state lasers are difficult to meet the application requirements of lidar, and it is difficult to achieve both high integration and high peak power.

Summary of the invention

The problem solved by the present invention is to provide a laser and a laser radar to meet the requirements of the laser radar and realize the balance of high integration and high peak power.

To solve the above-mentioned problems, the present invention provides a laser, including:

The pump unit, the gain unit, the Q-switching unit, and the light splitting unit are arranged in sequence along the optical axis; the pumping unit generates pump light; the gain unit includes a gain medium; the Q-switching unit includes a saturable absorber; The light splitting unit generates outgoing laser light and multiple tuning lights of different wavelengths, and the tuning lights of different wavelengths have different propagation directions; a resonant reflective surface and a scanning unit, and the resonant reflective surface, the light splitting unit and the scanning unit are used in cooperation To form a laser resonant cavity, the resonant reflection surface is located between the gain unit and the pump unit, the scanning unit is located on the optical path of the plurality of tuning lights, and the scanning unit Select one of the lights and return the selected tuning light to the original optical path.

Optionally, the scanning unit changes the incident angle of the plurality of tuning lights by swinging or rotating, and causes the tuning lights that are vertically incident to return according to the original optical path, and are projected to the resonant reflection surface through the light splitting unit The resonance of the tuning light of the corresponding wavelength is formed in the laser cavity.

Optionally, when the intensity of the tuning light forming resonance in the laser cavity is higher than a preset output threshold, the light splitting unit generates the outgoing laser based on the tuning light forming the resonance.

Optionally, the light splitting unit includes: a grating.

Optionally, the grating includes at least one of a reflective grating or a transmissive grating.

Optionally, the grating includes: a -1 order high diffraction efficiency grating or a +1 order high diffraction efficiency grating; the beam splitting unit generates the outgoing laser light in the 0 order light emission direction of the -1 order high diffraction efficiency grating , Generating the plurality of tuning lights in the exit direction of the -1st order diffracted light of the -1st order high diffraction efficiency grating; or, the light splitting unit generates the plurality of tuning lights in the exit direction of the 0th order light of the +1st order high diffraction efficiency grating The outgoing laser light generates the plurality of tuning lights in an outgoing direction of the +1 order diffracted light of the +1 order high diffraction efficiency grating.

Optionally, the -1 order broadband diffraction efficiency of the -1 order high diffraction efficiency grating is greater than or equal to 95%, or the +1 order broadband diffraction efficiency of the +1 order high diffraction efficiency grating is greater than or equal to 95%.

Optionally, the grating includes: a deep etched binary phase grating.

Optionally, the scanning unit includes a galvanometer.

Optionally, the scanning unit includes a MEMS galvanometer.

Optionally, the gain medium is a microchip gain medium; the saturable absorber is a microchip saturable absorber.

Optionally, the gain medium and the saturable absorber are attached to each other.

Optionally, the gain medium includes: at least one of Cr:LiSAF, Nd:YAG, Nd:YVO4, and Er and Yb co-doped glasses and crystals.

Optionally, the material of the saturable absorber includes: at least one of Cr:YAG, carbon nanotubes or graphene.

Optionally, the surface of the gain medium facing the pump unit is coated with an optical film layer to form the resonant reflection surface.

Correspondingly, the present invention also provides a laser radar, including:

A transmitting device, which includes the laser of the present invention.

Optionally, the lidar further includes: a light splitting device that generates scanning light with different propagation directions based on the wavelength of the light generated by the emitting device.

Optionally, the spectroscopic device includes: at least one of a grating or a prism.

Optionally, the lidar further includes: a detection unit that detects the moment when the laser oscillation is formed.

Optionally, the detection unit includes: a photodiode.

Compared with the prior art, the technical solution of the present invention has the following advantages:

In the technical solution of the present invention, a Q-switching unit including a saturable absorber is used as a Q-switching switch, and the resonant reflective surface cooperates with the scanning unit to form two reflective surfaces of the laser resonant cavity; Select one of the plurality of tuning lights and return the selected tuning light to the original optical path. The tuning light returned by the original optical path can form resonance in the laser cavity. The laser of the present invention is a tunable laser capable of Q-switching, so higher peak power and larger pulse energy can be obtained, and a saturable absorber is used to achieve Q-switching of the laser resonator, which can effectively shorten the length of the resonant cavity. , Reducing the volume of the resonant cavity is conducive to achieving both high integration and high peak power.

In an alternative solution of the present invention, the scanning unit changes the incident angle of the plurality of tuning lights by swinging or rotating, and causes the tuning lights that are vertically incident to return according to the original optical path to form a corresponding wavelength tuning in the laser cavity. Resonance of light. The selection of the tuning light is realized by the swing or rotation of the scanning unit, and the mechanical structure is simple, and the speed of the tuning light selection can be controlled by setting the swing or rotation frequency, which is beneficial to realize high-speed wavelength tuning flexibly.

In an alternative solution of the present invention, when the intensity of the tuning light forming resonance in the laser cavity is higher than the saturation absorption light intensity of the saturable absorber, the spectroscopic unit generates the outgoing laser based on the tuning light forming resonance . The loss of the laser resonator is related to the saturable absorption light intensity of the saturable absorber. The choice of the saturable absorber can affect the loss of the laser resonator, control the threshold of the laser resonator, and control the accumulation of upper-level particles In addition, under the same pump power, the laser repetition frequency can be increased, and the appropriate peak power and single pulse energy can be obtained, so as to achieve both detection distance and detection frequency.

In an alternative solution of the present invention, the light splitting unit may include a grating, in particular a -1 order or +1 order high diffraction efficiency grating, and the 0th order diffracted light of the -1 order or +1 order high diffraction efficiency grating is emitted The outgoing laser light is generated in the direction, and the plurality of tuning lights are generated in the emission direction of the −1 order diffracted light of the −1 order high diffraction efficiency grating or the +1 order diffracted light of the +1 order high diffraction efficiency grating . Since the grating is a -1 order or +1 order high diffraction efficiency grating, the 0th order diffracted light intensity of the grating is relatively small, which can effectively reduce the laser cavity loss and reduce the accumulation of upper energy level particles. Controlling the single pulse energy of the emitted laser is beneficial to obtaining high-repetition pulses.

Moreover, the selection of the saturable absorber and the selection of the spectroscopic device can control the loss of the laser resonator, which not only can effectively improve the flexibility of the laser re-frequency setting of the present invention, but also can effectively expand the saturable absorber and the spectroscopic device. Select the range.

In an optional solution of the present invention, the scanning unit may include a galvanometer. The galvanometer with high vibration frequency can quickly change the incident angles of the multiple tuning lights, thereby changing the tuning lights forming laser oscillations in the laser resonator at high speed, thereby realizing high-speed wavelength tuning. In addition, the galvanometer may also include a MEMS galvanometer, so that the volume of the scanning unit can be effectively reduced and the integration of the laser can be improved.

In an alternative solution of the present invention, the gain medium is a microchip type gain medium, the saturable absorber unit is a microchip saturable absorber, and the gain medium and the saturable absorber are attached to each other, so The surface of the gain medium facing the pump unit is a resonant reflection surface to form a resonant cavity. The gain medium and the saturable absorber are both processed into a microchip shape and bonded together, and the surface of the gain medium facing the pump unit is used as a cavity mirror to form a resonant cavity, so that the laser structure It is compact and can effectively control the size of the laser cavity, which is conducive to the realization of high repetition frequency, narrow pulse width and high peak power.

In an alternative solution of the present invention, the saturable absorber may be configured as at least one of carbon nanotubes or graphene. Carbon nanotubes or graphene have good thermal conductivity, which can effectively improve the heat conduction and heat dissipation effects of the components in the laser cavity.

In an optional solution of the present invention, the lidar further includes the light splitting device, and the light splitting device generates scanning light in different propagation directions based on the wavelength of the emitted laser light generated by the emitting device. Since the laser radar emitting device includes the laser of the present invention, the emitting device can realize the tuning of the emitted laser wavelength. Therefore, the laser radar can realize one-dimensional scanning without additional devices, thereby reducing the overall laser radar Design difficulty (for example, two-dimensional scanning can be achieved with only one-dimensional device), which helps reduce the manufacturing difficulty and cost of lidar.

Description of the drawings

FIG. 1 is a schematic diagram of the optical path structure of an embodiment of the laser of the present invention;

FIG 2 is a tunable laser shown in FIG λ ₀ Example 1, the scanning unit time t ₀ of the plurality of tunable optical _{_{_{142λ 0, 142λ 1, 142λ 2}}} , ...... is selected from the wavelength of light and 142λ ₀ A schematic diagram of the optical path structure of the tuning light 142λ ₀ returning according to the original optical path;

Figure 3 is a laser embodiment, the scanning unit time t ₁ of the plurality of tunable optical tunable optical _{_{_{142λ 0, 142λ 1, 142λ 2}}} , ...... is selected from a wavelength λ ₁ and the 142λ _{1 1} A schematic diagram of the optical path structure of the tuning light 142λ ₁ returning according to the original optical path;

FIG 4 is a view of a laser embodiment shown embodiment, the scanning unit _{_{_{142λ 0, 142λ 1, 142λ 2}}} , ...... wavelength is selected at time t ₂ from the plurality of tuning the tunable optical λ ₂ and light 142λ ₂ A schematic diagram of the optical path structure of the tuning light 142λ ₂ according to the original optical path;

Fig. 5 is a schematic diagram of the optical path structure of another embodiment of the laser of the present invention.

detailed description

It can be known from the background technology that the tunable laser in the prior art has a problem that it is difficult to meet the needs of lidar.

Specifically, for example, in autonomous driving and unmanned driving, first of all, it is hoped that the detection range of lidar is far enough (for example, when the reflectivity is 10%, the detection range reaches 300m), the laser needs to have high peak power and large pulse Energy; secondly, if you want to obtain a denser point cloud to accurately identify pedestrians, vehicles, etc., you need a laser with high repetition frequency; after that, it is hoped to reduce the design difficulty of scanning mirrors (one-dimensional scanning mirrors are much less difficult to design than two-dimensional scanning mirrors ), if a one-dimensional scanning mirror is used instead of a two-dimensional scanning mirror, the laser needs to be able to be tuned quickly and combined with a beam splitter element to achieve high resolution in one-dimensional direction.

From the perspective of tuning methods, the current tunable solid-state lasers are large in size (with long cavity length) and slow in tuning speed, and cannot simultaneously achieve the characteristics of high repetition frequency, small size, narrow pulse width, and high-speed tuning. High-speed tunable semiconductor lasers usually cannot obtain high peak power and large pulse energy.

In order to solve the technical problem, the present invention provides a laser, including: a pump unit, a gain unit, a Q-switch unit, and a light splitting unit arranged in sequence along an optical axis; the pump unit generates pump light; the gain unit The Q-switching unit includes a gain medium; the Q-switching unit includes a saturable absorber; the beam splitting unit generates the emitted laser light and a plurality of tuning lights of different wavelengths, and the propagation directions of the tuning lights of different wavelengths are different; the resonant reflective surface and the scanning unit, the The resonant reflective surface, the beam splitting unit and the scanning unit cooperate to form a laser resonant cavity, the resonant reflective surface is located between the gain unit and the pump unit, and the scanning unit is located in the plurality of On the optical path of the tuning light, the scanning unit selects one of the plurality of tuning lights and returns the selected tuning light to the original optical path.

The laser of the present invention is a tunable laser capable of Q-switching, so higher peak power and larger pulse energy can be obtained, and a saturable absorber is used to achieve Q-switching of the laser resonator, which can effectively shorten the length of the resonant cavity. , Reducing the volume of the resonant cavity is conducive to achieving both high integration and high peak power.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Referring to Fig. 1, a schematic diagram of the optical path structure of an embodiment of the laser of the present invention is shown.

The laser includes: a pump unit 110, a gain unit 120, a Q-switch unit 130, and a light splitting unit 140 arranged in sequence along an optical axis; wherein the pump unit 110 generates pump light; the gain unit 120 includes a gain medium The Q-switching unit 130 includes a saturable absorber; the beam splitting unit 140 generates the emitted laser 141 and a plurality of tuning lights 142 of different wavelengths, and the propagation directions of the tuning lights 142 of different wavelengths are different; the resonant reflective surface 150 and the scanning unit 160. The resonant reflective surface 150, the beam splitting unit 140, and the scanning unit 160 cooperate to form a laser resonant cavity (not shown in the figure), and the resonant reflective surface 150 is located between the gain unit 120 and the Between the pumping units 110, the scanning unit 160 is located on the optical path of the plurality of tuning lights 142, and the scanning unit 160 selects one of the plurality of tuning lights 142 and makes the selected tuning light follow the original optical path return.

In the technical solution of the present invention, the Q-switching unit 130 including a saturable absorber is used as a Q-switching switch, and the resonant reflective surface 150 cooperates with the scanning unit 160 to form two reflective surfaces of the laser resonator; The unit 160 selects one of the plurality of tuning lights 142 and returns the selected tuning light 142 to the original optical path. The tuning light 142 returned in the original optical path can form resonance in the laser cavity. The laser of the present invention is a tunable laser capable of Q-switching, so higher peak power and larger pulse energy can be obtained, and a saturable absorber is used to achieve Q-switching of the laser resonator, which can effectively shorten the length of the resonant cavity. , Reducing the volume of the resonant cavity is conducive to achieving both high integration and high peak power.

The pump unit 110 is used as a pump source of the laser to provide pump light to pump the laser gain medium.

In this embodiment, the pump unit 110 may be a semiconductor laser, so as to achieve the purpose of low energy consumption and small size.

The gain medium in the gain unit 120 is used to achieve population inversion to form optical amplification.

Specifically, the gain medium in the gain unit 120 covers a wide wavelength range, which makes it possible to form tuning lights of different wavelengths and form a tunable laser. In this embodiment, the laser is applied to lidar, and the center wavelength of the gain medium is 850 nm, and the covered wavelength range is 750 nm to 950 nm. The gain medium may be Cr:LiSAF.

It should be noted that the gain medium is related to the wavelength of the laser light generated by the laser. Therefore, in this embodiment, the center wavelength, the wavelength range of the gain medium, and the specific selection of the gain medium are only an example. In other embodiments of the present invention, the gain medium may also be at least one of Nd:YAG, Nd:YVO ₄ , and Er and Yb co-doped glasses and crystals. The specific properties of the gain medium (center wavelength or wavelength range, etc.) 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 generated by the laser, which is not limited by the present invention .

It should also be noted that, in this embodiment, the laser further includes a pumping optical element 111, and the pumping optical element 111 is located on the optical path between the pumping unit 110 and the gain unit 120. The pump optical element 111 is used to couple the pump light generated by the pump unit 110 into the laser gain medium in the gain unit 110. Specifically, the pumping optical element 111 may include optical elements such as a collimator lens and a coupling mirror, which are not limited in the present invention.

The Q-switching unit 130 serves as a Q-switch of the laser to control the Q value of the laser cavity.

The Q value is called the quality factor, which is an index to evaluate the quality of the optical resonator in the laser. The Q value is defined as the ratio of the energy stored in the laser cavity to the energy lost per unit time in the cavity:

Among them, W is the total energy stored in the laser cavity; dW/dt is the loss rate of photon energy in the laser cavity, that is, the energy lost per unit time; ν ₀ is the center frequency of the generated laser.

Q-switching technology is to compress the laser energy generated by the laser into a very narrow pulse by adjusting the Q value of the laser cavity, thereby increasing the peak power of the generated laser by several orders of magnitude, and obtaining a narrow pulse width and peak Value of laser. Specifically, through the Q-switching technology, the peak power of the laser can reach megawatts (10 ⁶ W) or more, and the pulse width can be compressed to a nanosecond (10 ^-9 s) pulse.

Generally speaking, the Q value of the laser resonator is adjusted by changing the cavity loss. Specifically, at the beginning of pumping, the loss of the laser cavity is large, that is, the Q value of the laser cavity is reduced, so that the gain medium accumulates the number of inverted particles; after a certain period of pumping, the laser resonance is suddenly reduced Cavity loss, that is, increase the Q value of the laser resonant cavity, so that the accumulated inversion population can complete the stimulated radiation in a short time to form a narrow pulse width, high peak power optical pulse.

In Q-switching technology, the laser resonator is in a state of high loss and low Q during most of the pumping process. Therefore, the threshold of the resonant cavity is too high to start vibration. The gain medium is located at the upper energy level and realizes the inversion. The number of revolved particles continues to accumulate; when the accumulated number of reversal particles reaches a certain value, the loss of the resonant cavity suddenly drops, the Q value suddenly rises, and the threshold of laser oscillation decreases rapidly; then the laser resonant cavity begins to build up Laser oscillation; due to the large number of particles accumulated when the loss decreases and the Q value increases, the stimulated radiation increases very rapidly at this time, and the energy stored in the gain medium is released in a short time, thus forming a high peak and narrow Pulse width laser.

Specifically, the Q-switching unit 130 includes a saturable absorber. A saturable absorber is an optical device with a definite loss. When the incident light intensity exceeds the threshold of the saturable absorber, the optical loss becomes smaller, the transmittance increases, and the Q value of the laser cavity rises.

In this embodiment, the material of the saturable absorber in the Q-switching unit includes at least one of Cr:YAG, carbon nanotubes, or graphene. Preferably, the material of the saturable absorber is at least one of carbon nanotubes or graphene. Carbon nanotubes or graphene have good thermal conductivity and can effectively improve the thermal conductivity and heat dissipation effects of the components in the laser cavity.

In this embodiment, the gain medium is a microchip gain medium; the saturable absorber is a microchip saturable absorber, that is, in the light propagation direction, the gain medium and the saturable The size of the absorbent body is small, about the order of centimeters.

Moreover, as shown in FIG. 1, the gain medium and the saturable absorber are attached to each other, that is, the gain medium in the gain unit 120 faces the surface of the Q-switch unit 130 and the surface of the Q-switch unit 130 The surfaces of the saturable absorber facing the gain unit 120 are in contact with each other.

The method of processing both the gain medium and the saturable absorber into a microchip shape and bonding them together makes the laser compact and can effectively control the size of the laser cavity, which is beneficial to high repetition frequency, narrow pulse width, and high peak power The realization.

The light splitting unit 140 is used to generate the emitted laser 141 or multiple tuning lights 142 of different wavelengths. Wherein, the outgoing laser 141 is the output light of the laser; the tuning light 142 realizes resonance in a laser resonant cavity.

Specifically, the light emitted from the gain unit 120 and the Q-switching unit 130 is projected onto the light splitting unit 140, and the light splitting unit 140 generates a laser 141 or multiple tuning lights 142 of different wavelengths based on the light.

In this embodiment, the light splitting unit 140 includes: a grating. Using a grating as the spectroscopic device can effectively ensure the generation of the beam splitting effect of the emitted laser 141 or multiple tuning lights 142, and the selection of suitable gratings (such as having a smaller grating constant) enables the tuning of light 142 between different wavelengths. The propagation direction difference is large enough to reduce the difficulty of subsequent scanning unit selection. However, in other embodiments of the present invention, the light splitting unit may also be configured as another optical device capable of separating multiple tuning lights, such as a prism.

As shown in FIG. 1, the light splitting unit 140 is a transmissive grating. The method of implementing light splitting by using a transmissive grating in the light splitting unit 140 is only an example. In other embodiments of the present invention, the grating may include at least one of a reflective grating or a transmissive grating.

In addition, in this embodiment, the grating includes: a -1 order high diffraction efficiency grating or a +1 order high diffraction efficiency grating. When the grating is a -1st order high diffraction efficiency grating, the beam splitting unit 140 generates the outgoing laser 141 in the 0th order light exiting direction of the -1st order high diffraction efficiency grating, and is diffracted at the -1st order high diffraction efficiency. The output direction of the −1st order diffracted light of the efficiency grating generates the plurality of tuning lights 142; when the grating is a +1 order high diffraction efficiency grating, the beam splitting unit 140 is set at 0 of the −1 order high diffraction efficiency grating. The first-order light emission direction generates the emitted laser light, and the plurality of tuning lights 142 are generated based on the first-order diffracted light emission direction of the +1-order high diffraction efficiency grating.

In the light splitting unit 140, the -1 order high diffraction efficiency grating or the +1 order high diffraction efficiency grating is used to realize light splitting, which can effectively increase the energy of the plurality of tuning lights 142 generated by the light splitting unit 140 and reduce the light splitting. The energy of the output light of the unit 140 is equivalent to reducing the output transmittance of the laser resonator, which can effectively reduce the loss of the laser resonator, reduce the accumulation of upper-level particles, and can effectively control the pulse energy of the output light.

The relationship between laser repetition frequency (repetition frequency), pump power, single pulse energy, and laser cavity length:

Among them, L is the length of the laser cavity.

It can be seen that the shorter the laser cavity length, the higher the repetition frequency of the laser; under the same pump power, the single pulse energy is relatively lower, and higher repetition pulses can be output. Therefore, the -1 order high diffraction efficiency grating or the +1 order high diffraction efficiency grating is set in the spectroscopic device 140 to achieve light splitting, which can control the energy of the output light and is beneficial to obtaining high-repetition pulses.

In addition, since the Q-switching unit 130 includes a saturable absorber, the selection of the saturable absorber and the selection of the spectroscopic unit 140 can both control the loss of the laser resonator, which can not only effectively improve the present invention The flexibility of laser re-frequency setting is also conducive to expanding the selection range of saturable absorbers and spectroscopic devices.

Specifically, the grating can be a deep etched binary phase grating. When the grating is a -1st order high diffraction efficiency grating, the -1st order broadband diffraction efficiency of the -1st order high diffraction efficiency grating is greater than or equal to 95%; when the grating is a +1th order high diffraction efficiency grating, The +1 order broadband diffraction efficiency of the +1 order high diffraction efficiency grating is greater than or equal to 95%.

With continued reference to FIG. 1, the laser further includes a resonant reflection surface 150 between the gain unit 120 and the pump unit 110 and a scanning unit 160 located on the optical path of the plurality of tuning lights 142.

The resonant reflective surface 150 and the scanning unit 160 cooperate to form two reflective surfaces of the laser resonant cavity. Therefore, the gain unit 120, the Q-switching unit 130, and the light splitting unit 140 are located in the resonant reflective surface. The optical path between the surface 150 and the scanning unit 160, that is, the gain unit 120, the Q-switching unit 130, and the light splitting unit 140 are all located between the two reflective surfaces of the laser cavity.

It should be noted that, as shown in FIG. 1, in this embodiment, the resonant reflective surface 150 and the scanning unit 160 are used to form two reflective surfaces of a laser resonator, and the gain unit 120 and the Q switch The unit 130 and the light splitting unit 140 are located in the optical path in the laser cavity. But this approach is only an example. In other embodiments of the present invention, based on specific requirements, other optical components may be provided in the optical path in the laser resonant cavity to achieve optical path adjustment.

In this embodiment, in this embodiment, the surface of the gain medium facing the pump unit 110 is coated with an optical film 151 to form the resonant reflection surface 150, and on the surface of the gain medium facing the pump unit 110 The formation of the resonant reflection surface 150 can effectively control the size of the laser, reduce the length of the laser cavity, and has a compact structure. It is also conducive to the realization of high repetition frequency, narrow pulse width, and high peak power; and the optical coating 151 can be set to have A film layer that increases the transmittance of the pump light and improves the reflectivity of the resonant reflective surface 150, thereby achieving the purpose of improving the performance of the laser resonant cavity. However, in other embodiments of the present invention, the resonant reflective surface can also be flexibly adopted in other setting methods.

The scanning unit 160 is used to form a reflective surface of the laser resonant cavity, and is also used to select one of the multiple tuning lights 142 of different wavelengths, and return the selected tuning light 142 to the original optical path. To form resonance.

As shown in FIG. 1, in this embodiment, the scanning unit 160 changes the incident angle of the plurality of tuning lights 142 by swinging or rotating, and causes the tuning lights 142 that are vertically incident to return according to the original optical path. The beam splitting unit 140 is projected to the resonant reflection surface 150 to form a resonance corresponding to the wavelength-tuning light in the laser cavity. The selection of the tuning light 142 is realized by the swing or rotation of the scanning unit 160, the mechanical structure is simple, and the selection speed of the tuning light 142 can be controlled by setting the swing or rotation frequency, which is beneficial to realize high-speed wavelength tuning flexibly.

The light emitted from the gain unit 120 and the Q-switching unit 130 is projected onto the light splitting unit 140, and the light splitting unit 140 generates multiple tuning lights 142 of different wavelengths based on the light. Wherein, the propagation directions of the tuning lights 142 of different wavelengths are different.

Since the propagation directions of the tuning lights 142 of different wavelengths are different, as the scanning unit 160 swings or rotates, the incident angles of the tuning lights 142 with different propagation directions on the scanning unit 160 will change accordingly. At time _ti , when a certain tuning light is vertically incident on the scanning unit 160, the vertically incident tuning light is reflected by the scanning unit 160 and returns according to the original optical path; since the vertically incident tuning light is The light path returns. Therefore, after the above-mentioned tuning light is projected to the beam splitting unit 140, it will be projected again to the Q-switching unit 130 and the gain unit 120, and finally projected onto the resonant reflecting surface 150, thereby reflecting at resonance. The light path between the surface 150 and the scanning unit 160 reflects back and forth, that is, a resonance is formed in the laser cavity.

With reference to FIGS. 2 to 4, it is shown that in the laser embodiment shown in FIG. 1, the scanning unit 160 selects one of the plurality of tuning lights 142λ ₀ , 142λ ₁ , 142λ ₂ , ... and makes the selected Schematic diagram of the optical path structure of the tuning light returned by the original optical path.

As shown in Fig. 2 to Fig. 4, at t ₀ , t ₁ , t ₂ ,..., the tuning lights 142λ ₀ , 142λ ₁ , 142λ ₂ , ... with wavelengths λ ₀ , λ ₁ , λ ₂ , ..., respectively It is incident perpendicularly to the scanning unit 160, and is returned by the scanning unit 160 according to the original optical path until it is projected onto the resonant reflecting surface 150 to form resonance. Therefore, at t ₀ , t ₁ , t ₂ ,..., the laser resonant cavity respectively forms tuning lights 142λ ₀ , 142λ ₁ , 142λ ₂ , λ ₀ , λ ₁ , λ ₂ , ... The resonance of ..., that is, the laser resonant cavity can realize the resonance of light of different wavelengths at different times, thereby realizing the wavelength tuning of the laser.

It can be seen that the speed of the wavelength tuning of the laser is related to the speed at which the scanning unit 160 selects different wavelength tuning lights 142λ ₀ , 142λ ₁ , 142λ ₂ ,... In this embodiment, the selection speed of the scanning unit 160 for different wavelength tuning lights 142λ ₀ , 142λ ₁ , 142λ ₂ ,... Is related to the speed at which the scanning unit 160 swings or rotates.

Therefore, the scanning unit 160 includes a galvanometer. Galvanometer high vibration frequency, to quickly change the plurality of tunable optical _{_{_{142λ 0, 142λ 1, 142λ 2}}} , ...... incident angle, the plurality of tunable optical _{_{_{142λ 0, 142λ 1, 142λ 2}}} , ...... in High-speed selection is realized, thereby changing the tuning light of the laser oscillation formed in the laser resonator at high speed, thereby realizing high-speed wavelength tuning. Moreover, the scanning unit 160 may include a MEMS galvanometer, so that the volume of the scanning unit 160 can be effectively reduced, and the integration of the laser can be improved.

It should be noted that in this embodiment, the laser further includes the gain unit 120 and the Q-switching unit 130, and the gain unit 120 and the Q-switching unit 130 are located in the laser resonant cavity of the tuning light. The optical path formed by resonance. Therefore, when the intensity of the tuning light forming resonance in the laser cavity is higher than the preset output threshold, the spectroscopic unit 140 generates the outgoing laser based on the tuning light forming the resonance. Wherein, the preset output threshold is several times or even ten times of the saturated absorption light intensity of the saturable absorber.

The loss of the laser resonator is related to the saturable absorption light intensity of the saturable absorber. The choice of the saturable absorber can affect the loss of the laser resonator, control the threshold of the laser resonator, and control the accumulation of upper-level particles In addition, under the same pump power, the laser repetition frequency can be increased, and the appropriate peak power and single pulse energy can be obtained, so as to achieve both detection distance and detection frequency.

Specifically, on the one hand, the selected tuning light is reflected back and forth in the optical path between the resonant reflection surface 150 and the scanning unit 160 to form a resonance in the laser cavity; and the gain unit 120 is located in the laser In the optical path of the resonant cavity, and with the input of the pump light, the particles in the gain medium are continuously excited to a high-energy state, and the particles that achieve inversion continue to accumulate and increase; therefore, on the resonant reflecting surface 150 and the scanning unit 160 The intensity of the light reflected back and forth gradually increases.

On the other hand, the Q-switching unit 130 has a saturable absorber. As mentioned earlier, the saturable absorber is a nonlinear absorption medium, and its absorption coefficient is not constant. Under the action of a stronger laser, the absorption coefficient of the saturable absorber will decrease with the increase of light intensity until it is saturated, showing the characteristic of being transparent to light.

Further, the relationship between the absorption coefficient of the saturable absorber and the light intensity:

Where α ₀ is the absorption coefficient when the light intensity is very small (when the light intensity I approaches 0); I _s is the saturated absorption light intensity of the saturable absorber, which is related to the material of the saturable absorber; I is The intensity of light projected onto the saturable absorber.

It can be seen that when the intensity of light projected on the saturable absorber can be compared with the intensity of saturated absorption light, the absorption coefficient gradually decreases and the transmittance gradually increases; When the light intensity on the body reaches a certain value, the absorption of the light intensity by the saturable absorber reaches the saturation (minimum absorption) value, the absorption coefficient of the saturable absorber decreases sharply, and the transmittance increases sharply. The saturable absorber is suddenly "bleached" and becomes transparent.

It can be seen that the selected tuning light is reflected back and forth between the scanning unit 160 and the resonant reflection surface 150:

At the beginning of the reflection back and forth, the autofluorescence in the laser cavity is very weak, the absorption coefficient of the saturable absorber is very large, so that the light transmittance is very low, and the laser cavity is in a state of high loss and low Q value. Although resonance can be formed in the laser cavity, the loss is too high, and the loss is greater than the gain, so laser oscillation cannot be formed. A large number of excited particles in the gain medium can only be maintained in a high-energy state, that is, the inverted particles are in the gain medium. To save

With the continuous input of pump light, more and more particles are excited, and the number of inverted particles in the gain medium further increases, and the autofluorescence in the laser cavity increases accordingly;

When the above-mentioned light intensity increases to be comparable to the saturated absorption light intensity I _{s of} the saturable absorber, the absorption coefficient of the saturable absorber becomes smaller, the transmittance gradually increases, and the loss of the laser cavity Decrease, Q value increase;

When the light intensity increases to a certain value, which is much higher than the saturated absorption light intensity of the saturable absorber, the absorption coefficient of the saturable absorber tends to zero, and the transmittance tends to 1, that is, the saturable absorber The absorber becomes transparent, the loss of the laser resonant cavity sharply decreases, the Q value increases sharply, and the gain of the laser resonant cavity is greater than the loss, so that laser oscillation is formed in the laser resonant cavity.

During the formation of laser oscillation, a large number of inverted particles in a high energy state accumulated in the gain medium transition to a low energy state in a short time, thereby forming an output laser; the output laser is projected to the spectroscopic unit 140, and the spectroscopic unit 140 The emitted laser light 141 is generated based on the output laser light.

It should be noted that when the gain in the laser resonant cavity is greater than the loss, the laser oscillation can be formed in the laser resonator to form the output laser, and then the outgoing laser 141 can be formed; and only when the laser resonant cavity is When the intensity of the tuning light forming the resonance is much higher than the saturation absorption light intensity of the saturable absorber, the saturable absorber can become transparent, and the gain in the laser cavity is greater than the loss, forming laser oscillation . Wherein, the intensity of the tuning light reflected back and forth when the saturable absorber becomes transparent and forms laser oscillation is related to the specific design of the laser cavity.

In this embodiment, the output threshold is ten times the saturation absorption light intensity of the saturable absorber, that is, the intensity of the tuning light that forms resonance in the laser cavity and the saturation absorption light intensity of the saturable absorber When the difference is at least an order of magnitude, the intensity of the tuning light forming resonance in the laser cavity is more than 10 times the intensity of the saturated absorption light, the saturable absorber becomes transparent, and the laser is formed in the laser cavity Oscillate to generate emission laser light 141.

It should be noted that the specific structure of the laser shown in FIG. 1 is only an example. In other embodiments of the present invention, the laser can also include other elements such as circuits and optical path adjustment elements, which are not limited by the present invention.

Referring to FIG. 5, a schematic diagram of the optical path structure of another embodiment of the laser of the present invention is shown.

This embodiment is the same as the previous embodiment, and the present invention will not be repeated here. The difference between this embodiment and the previous embodiment is that in this embodiment, the beam splitting device 240 is a reflective grating.

The pump light generated by the pump unit 210 is adjusted by the optical path of the pump optical element 211, and then is transmitted to the gain unit 220 and the Q-adjustment unit 230 after being transmitted through the resonant reflection surface 250; from the gain unit 220 and the Q-adjustment unit 230 The light emitted by 230 is reflected by the light splitting unit 240 to form a plurality of tuning lights 242 projected to the scanning unit 260; the scanning unit 260 changes the incident angle of the plurality of tuning lights 242 by swinging or rotating, and makes vertical incidence The tuning light 242 returns according to the original optical path, so that resonance is formed in the laser resonant cavity where the resonant reflective surface 250 and the scanning unit 260 are two reflective surfaces; the intensity of the tuning light when the resonance is formed in the laser resonant cavity When increasing to a certain value, laser oscillation is formed in the laser resonant cavity to form an output laser; the beam splitting unit 240 generates an output laser 241 based on the output laser.

Correspondingly, the present invention also provides a laser radar, including: a transmitting device, and the transmitting device includes the laser of the present invention.

Referring to FIG. 1, a schematic diagram of the optical path structure of an embodiment of the laser radar of the present invention is shown.

As shown in Fig. 1, the lidar includes a transmitting device, and the transmitting device includes the laser of the present invention. For specific technical solutions of the laser, refer to the foregoing laser embodiment, and the present invention will not be repeated here.

Since the emitting device includes the laser of the present invention, which is a tunable laser capable of Q-switching, the emitting device can generate light with higher peak power and larger pulse energy for detection, which is beneficial to laser The control of the energy consumption of the radar and the expansion of the detection range; and the use of the Q-switching technology of the saturable absorber is conducive to the acquisition of high repetition frequency and the realization of high integration of the lidar; in addition, the transmitting device can also achieve wavelength tuning, The lidar can realize one-dimensional scanning without an additional device, thereby reducing the overall design difficulty of the lidar (for example, two-dimensional scanning can be realized with only a one-dimensional device), which is beneficial to reducing the manufacturing difficulty and manufacturing cost of the lidar .

It should be noted that the specific structure of the transmitting device shown in FIG. 1 is only an example. In other embodiments of the present invention, the emitting device can also include other elements such as circuits and optical path adjustment elements, which are not limited by the present invention.

As shown in FIG. 1, the lidar further includes: a light splitting device 370 configured to generate scanning light 371 in different propagation directions based on the wavelength of the light generated by the emitting device.

The spectroscopic device 370 is used to form a plurality of scanning lights 370 in different propagation directions. Since the emitting device includes the laser of the present invention, that is, the emitting device includes a tunable laser, the emitting device can continuously change the laser output wavelength within a certain range. The spectroscopic device 370 generates scanning light 371 based on the wavelength of the light generated by the emitting device.

In this embodiment, the spectroscopic device 370 is a grating. According to the change of the wavelength of the light generated by the emitting device, a suitable grating can be selected, so that the emission direction of the different scanning light 371 can be suitable to obtain a suitable field of view and angular resolution. However, in other embodiments of the present invention, the spectroscopic device may also be at least one of a grating or a prism, which is not limited in the present invention.

It should be noted that, in this embodiment, the lidar is a lidar that detects based on time of flight, and the acquisition of the time of flight is related to the actual time when the emitting device generates light, and is further related to the formation of laser oscillation in the laser. The moment of laser output is related. Therefore, the lidar further includes a detection unit 380 that detects the moment when the laser oscillation is formed to generate output laser light.

In this embodiment, the detection unit 380 may include a photodiode. The detection unit 380 detects a part of the diffracted light generated by the spectroscopic unit 140 in the laser in the emitting device to obtain the time when the laser oscillation generates the output laser.

Although the present invention is disclosed as above, the present invention is not limited to this. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be subject to the scope defined by the claims.

Claims

A laser, which is characterized by comprising: a pump unit, a gain unit, a Q-switch unit and a light splitting unit arranged in sequence along an optical axis;

The pump unit generates pump light;

The gain unit includes a gain medium;

The Q-switching unit includes a saturable absorber;

The beam splitting unit generates outgoing laser light and multiple tuning lights of different wavelengths, and the tuning lights of different wavelengths have different propagation directions;

A resonant reflective surface and a scanning unit, the resonant reflective surface, the beam splitting unit and the scanning unit cooperate to form a laser resonant cavity, and the resonant reflective surface is located between the gain unit and the pump unit, The scanning unit is located on the optical path of the plurality of tuning lights, and the scanning unit selects one of the plurality of tuning lights and returns the selected tuning light to the original optical path.
The laser according to claim 1, wherein the scanning unit changes the incident angle of the plurality of tuning lights by swinging or rotating, and causes the tuning lights that are vertically incident to return according to the original optical path and pass through the splitting light. The unit is projected to the resonant reflection surface to form a resonance of the tuning light of the corresponding wavelength in the laser cavity.
The laser according to claim 1, wherein when the intensity of the tuning light forming resonance in the laser cavity is higher than a preset output threshold, the spectroscopic unit generates the outgoing laser based on the tuning light forming the resonance .
The laser according to claim 1, wherein the light splitting unit comprises: a grating.
The laser according to claim 4, wherein the grating comprises at least one of a reflective grating or a transmissive grating.
The laser according to claim 4, wherein the grating comprises: a -1 order high diffraction efficiency grating or a +1 order high diffraction efficiency grating;

The beam splitting unit generates the emitted laser light in the emission direction of the 0-order light of the -1 order high diffraction efficiency grating, and generates the plurality of tunings in the emission direction of the -1 order diffracted light of the -1 order high diffraction efficiency grating Light;

Alternatively, the beam splitting unit generates the emission laser light in the emission direction of the 0-order light of the +1-order high diffraction efficiency grating, and generates the multiple laser light in the emission direction of the +1-order diffracted light of the +1-order high diffraction efficiency grating. A tuning light.
7. The laser according to claim 6, wherein the -1st order broadband diffraction efficiency of the -1st order high diffraction efficiency grating is greater than or equal to 95%;

Alternatively, the +1 order broadband diffraction efficiency of the +1 order high diffraction efficiency grating is greater than or equal to 95%.
7. The laser according to any one of claims 4 to 7, wherein the grating comprises: a deep etched binary phase grating.
The laser according to claim 1, wherein the scanning unit comprises a galvanometer.
The laser according to claim 1, wherein the scanning unit comprises a MEMS galvanometer.
The laser according to claim 1, wherein the gain medium is a microchip gain medium; and the saturable absorber is a microchip saturable absorber.
The laser of claim 1, wherein the gain medium and the saturable absorber are attached to each other.
The laser as claimed in claim 1, wherein said gain medium comprises: Cr: LiSAF, Nd: YAG , Nd: YVO 4, and Er, Yb-doped glass and at least one co-crystal.
The laser according to claim 1, wherein the material of the saturable absorber comprises at least one of Cr:YAG, carbon nanotubes or graphene.
The laser according to claim 1, wherein the surface of the gain medium facing the pump unit is plated with an optical film layer to form the resonant reflection surface.
A laser radar is characterized in that it comprises:

A transmitting device, which comprises the laser according to any one of claims 1 to 15.
The laser radar according to claim 16, further comprising:

The spectroscopic device generates scanning light in different propagation directions based on the wavelength of the light generated by the emitting device.
The lidar according to claim 17, wherein the light splitting device comprises at least one of a grating or a prism.
The laser radar according to claim 16, further comprising:

The detection unit detects the moment when the laser oscillation is formed.
The lidar of claim 19, wherein the detection unit comprises a photodiode.