WO2022000419A1

WO2022000419A1 - Laser system

Info

Publication number: WO2022000419A1
Application number: PCT/CN2020/099919
Authority: WO
Inventors: 刘永俊; 黄启睿
Original assignee: 华为技术有限公司
Priority date: 2020-07-02
Filing date: 2020-07-02
Publication date: 2022-01-06
Also published as: CN114982077A

Abstract

A laser system (1), comprising: a pumping source (1.2), a reflection mirror assembly (1.1) and an output mirror assembly (2.1), the reflection mirror assembly (1.1) and the output mirror assembly (2.1) defining and forming a resonant cavity, and a gain medium (1.3) being arranged in the resonant cavity; the reflection mirror assembly (1.1) comprises a first reflection mirror (1.11) and a first focusing lens (1.12), a reflection surface of the first reflection mirror (1.11) being arranged facing the gain medium (1.3), the first focusing lens (1.12) being arranged between the first reflection mirror (1.11) and the gain medium (1.3), the first reflection mirror (1.11) being arranged on a plane perpendicular to a main optical axis of the first focusing lens (1.12); the output mirror assembly (2.1) comprises a second reflection mirror (2.11) and a second focusing lens (2.12), the reflection surface of the second reflection mirror (2.11) being arranged to face the gain medium (1.3), the second focusing lens (2.12) being arranged between the second reflection mirror (2.11) and the gain medium (1.3), and the second reflection mirror (2.11) being arranged on a plane perpendicular to the main optical axis of the second focusing lens (2.12). The laser system reduces the diffraction loss and improves the laser output power.

Description

a laser system

technical field

The present application relates to the field of laser technology, and in particular, to a laser system.

Background technique

The basic principle of laser is stimulated radiation, that is, electrons in excited state atoms, under the action of incident photons, when they transition from high energy level to low energy level, radiate photons with the same frequency, phase, polarization and propagation direction as the incident light. , forming a larger light intensity, and the enhanced light can carry out new stimulation, and after repeated action, a resonance is formed, resulting in a laser with high intensity, good monochromaticity and good directionality. As shown in Figure 1, the laser system mainly includes three parts: pump source, gain medium, and resonator. The pump source excites electrons at low energy levels to high energy levels to achieve population inversion; the gain medium is excited The material in which the electrons are located, the material properties determine the output wavelength; the resonator is usually a mirror with two parallel sides, one of which is totally reflective, and the other side (output mirror) has a partial transmission function, and the light goes back and forth between the two mirrors The reflection will be continuously amplified through the gain medium. When the gain is greater than the loss, a stable laser output can be formed.

Due to the good coherence and concentrated direction of the laser, there are safety problems in the application, and there are strict restrictions on the safe output power. Therefore, there will be challenges in applications such as laser charging, and it is necessary to meet the requirements of output power under the premise of safety constraints. External resonator laser is a relatively new type of laser system, as shown in Figure 2, in principle, part of the transmission mirror of the laser system is physically separated from the rest, separated by a certain distance, such as on the laser receiving terminal, In this way, once the space between sending and receiving is partially blocked, the resonance condition will be destroyed, and no laser output will be generated, thus ensuring the safety of laser transmission. But the problem with this system is that it is difficult to ensure the parallelism between the two mirrors.

As shown in Figure 3, in the existing external resonator laser, the mirrors on both sides of the transceiver use corner prisms, which avoids the problem of parallelism. Because the corner cube is composed of three mutually perpendicular plane mirrors, it is widely used in various optical systems, and the direction of the reflected light can be opposite to the direction of the incident light (as shown in Figure 4), which greatly reduces the transmission and reception costs. Relative angle requirements for endoscopes. However, it still has the problem of inconvenient device integration, especially the integration on the terminal side. At the same time, because the corner cube is a three-dimensional structure, the integration volume is large, which is easy to be damaged, and the cube has geometrical changes, light diffraction and processing. Accuracy will affect the reflection accuracy of light and reduce the problem of resonance power.

Application content

The embodiments of the present application provide a laser system, the mirror assembly and the output mirror assembly are small in size and easy to integrate; at the same time, because there is no geometrical change in the shape of the mirror assembly and the output mirror assembly, the diffraction loss is reduced, and the output of the laser is improved. power and output efficiency.

The present application provides a laser system, comprising: a gain medium, a pump source for exciting the gain medium to generate radiation light, a mirror assembly for total reflection of the radiation light, and an output mirror for partial reflection of the radiation light component; both the mirror component and the output mirror component are arranged on the incident path or the reflection path of the laser light; the mirror component and the output mirror component define a resonant cavity, and a gain medium is arranged in the resonant cavity; the mirror component includes: a first mirror and a The first focusing lens, the reflective surface of the first reflecting mirror is arranged towards the gain medium, the first focusing lens is arranged between the first reflecting mirror and the gain medium, and the first reflecting mirror is arranged perpendicular to the main optical axis of the first focusing lens. on a plane; the output mirror assembly includes: a second mirror and a second focusing lens, the reflective surface of the second mirror is arranged towards the gain medium, the second focusing lens is arranged between the second mirror and the gain medium, the second mirror It is arranged on a plane perpendicular to the main optical axis of the second focusing lens.

In another possible implementation, the first reflecting mirror is disposed on the focal plane of the first focusing lens, and the second reflecting mirror is disposed on the focal plane of the second focusing lens.

In another possible implementation, the first reflecting mirror is disposed on the side of the focal plane of the first focusing lens close to the first focusing lens, and the second reflecting mirror is disposed on the focal plane of the second focusing lens away from the second focusing lens one side of the focusing lens;

Alternatively, the first reflection mirror is arranged on the side of the focal plane of the first focusing lens away from the first focusing lens; the second reflection mirror is arranged on the side of the focal plane of the second focusing lens close to the second focusing lens.

In another possible implementation, the focal lengths of the first focusing lens and the second focusing lens are both f, the distance between the first reflecting mirror and the focal plane of the first focusing lens, the distance between the second reflecting mirror and the The distances between the focal planes of the two focusing lenses are both d.

In another possible implementation, the d is less than or equal to f/10.

In another possible implementation, the first focusing lens and/or the second focusing lens are convex lenses.

In another possible implementation, the first focusing lens and/or the second focusing lens is a plano-convex lens, a side of the plano-convex lens close to the gain medium is a plane structure, and a side away from the gain medium is a convex structure.

In another possible implementation, the first focusing lens and/or the second focusing lens is a metasurface lens, and a metasurface structure is provided on one side of the metasurface lens close to the gain medium.

In another possible implementation, the first reflecting mirror is composed of multiple first reflecting mirror units located on the same plane, and the first focusing lens is composed of multiple first focusing lens units located on the same plane;

The second reflecting mirror is composed of a plurality of second reflecting mirror units located on the same plane, and the second focusing lens is composed of a plurality of second focusing lens units located on the same plane;

Alternatively, the first reflecting mirror, the first focusing lens, the second reflecting mirror and the second focusing lens are all integral structures.

In another possible implementation, the mirror assembly and the output mirror assembly are disposed opposite to each other at an interval, and a region between the mirror assembly and the output mirror assembly forms a resonant cavity.

In another possible implementation, the laser system further includes a second reflection mirror, and the second reflection mirror, the reflection mirror assembly and the output mirror assembly are all arranged on the reflection path or the incident path of the laser light;

The third reflector, the reflector assembly and the output mirror assembly define a resonant cavity, the reflector assembly and the output mirror assembly are disposed on the same side of the gain medium, and the third reflector is disposed on the side of the gain medium where the reflector assembly and the output mirror assembly are disposed On the opposite side of the third reflector, the reflective surface of the third mirror is disposed toward the gain medium.

In another possible implementation, the gain medium may be any one of a solid gain medium, a gas gain medium, a semiconductor gain medium, and a liquid gain medium.

Based on the laser system provided by the embodiment of the present application, the mirror assembly and the output mirror assembly are improved. The mirror assembly is composed of a first reflection mirror and a first focusing lens, and the reflection surface of the first reflection mirror is arranged toward the gain medium, so The first focusing lens is arranged between the first reflecting mirror and the gain medium, and the first reflecting mirror is arranged on a plane perpendicular to the main optical axis of the first focusing lens; the output mirror assembly is composed of a second reflecting mirror and a second reflecting mirror. It consists of a focusing lens, the reflective surface of the second reflecting mirror is set towards the gain medium, the second focusing lens is set between the second reflecting mirror and the gain medium, and the second reflecting mirror is set at a position close to the second focusing lens. on a plane perpendicular to the main optical axis. The mirror assembly and the output mirror assembly are small in size and easy to integrate; at the same time, since there is no geometric abrupt change in the shape of the mirror assembly and the output mirror assembly, the diffraction loss is reduced, and the output power and output efficiency of the laser are improved.

Description of drawings

The following briefly introduces the accompanying drawings required in the description of the embodiments or the prior art.

Figure 1 is the basic schematic diagram of the laser;

Figure 2 is a schematic diagram of an external resonator laser;

FIG. 3 is a schematic structural diagram of an external resonator laser using a cube mirror;

4 is a schematic diagram of the light path of the incident light and the reflected light of the cube mirror;

FIG. 5 is a system block diagram of a laser system according to an embodiment of the present application;

6 is a schematic structural diagram of a mirror assembly provided by an embodiment of the present application;

FIG. 7 is a schematic structural diagram of an output mirror assembly provided by an embodiment of the present application;

FIG. 8 is a schematic diagram 1 of the influence of a mirror moving close to a convex lens on reflected light according to an embodiment of the present application;

FIG. 9 is a schematic diagram 2 of the influence of the reflection mirror moving close to the convex lens on the reflected light provided by the embodiment of the present application;

FIG. 10 is a schematic diagram 3 of the influence on reflected light by moving a mirror closer to a convex lens according to an embodiment of the application;

FIG. 11 is a schematic diagram of the influence of a mirror away from a convex lens on reflected light according to an embodiment of the application;

12 is a schematic diagram of the positional relationship when the focal planes of the reflecting mirror and the convex lens provided in the embodiment of the present application are arranged in parallel;

13 is a schematic structural diagram of a mirror assembly or an output mirror assembly after the metasurface lens replaces the convex lens;

14 is a schematic diagram of an optical path of a reflector assembly or an output mirror assembly using a convex lens provided by an embodiment of the present application;

15 is a top view of a micro-nano structure distribution of a hyper-planar lens provided by an embodiment of the present application;

16 is a diagram of the focusing effect of light by a hyperplane lens provided in an embodiment of the application;

17 is a schematic diagram of the principle of metasurface refraction;

FIG. 18 is a schematic structural diagram of forming a resonant cavity jointly defined by a third mirror, a mirror assembly, and an output mirror assembly according to an embodiment of the present application.

detailed description

The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings in the embodiments of the present application.

In the description of this application, the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", " The orientation or positional relationship indicated by "bottom", "inside", "outside", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations on this application.

In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , it may also be a conflicting connection or an integral connection; those of ordinary skill in the art can understand the specific meanings of the above terms in this application under specific circumstances.

The laser system of the present application includes at least a laser transmitter and a receiver. The laser transmitter includes a pump source, a gain medium and a total reflection cavity mirror, the receiver includes a partial reflection cavity mirror with a partial light transmission function, and the laser transmitter and the receiver together form a laser resonant cavity. The application scenarios of the present application include wireless optical communication and laser charging. If the above-mentioned laser system is used for wireless optical communication, the receiver is arranged on the communication terminal, and the receiver also includes a signal processing module, which is communicatively connected to the communication terminal to realize Wireless optical communication function. If the above laser system is used for laser charging, the receiver is arranged on the charging terminal, and the receiver further includes an energy receiving module, which is electrically connected to the power supply module of the charging terminal to realize the laser charging function.

As an embodiment of the present application, as shown in FIG. 5 , the laser transmitter 1 includes a gain medium 1.3, a pump source 1.2 and an emission mirror 1.1. The gain medium 1.3 may be a medium such as a solid, a gas, a semiconductor, or a liquid, and contains particles that can be activated. The pump source 1.2 can usually be a light source or a power supply, providing energy for the gain medium 1.3, and the excited substance is continuously in a high-energy state in order to achieve stimulated radiation luminescence, if it is a light source, it can irradiate light on the gain medium 1.3, if it is a power supply. , the current can be injected into the gain medium 1.3 through the electrode wire connection. The transmitting retro-reflective cavity mirror 1.1 has retro-reflection effect on the light of the output wavelength, that is, the reflected light is reflected in the opposite direction of the incident light. In the case of optical pumping, the wavelength of the pumping light may be inconsistent with the wavelength of the output light, so The transmitting retro-reflective cavity mirror 1.1 may reflect the output wavelength, but transmit the pump light wavelength, so that the pump light can be irradiated onto the gain medium through the transmitting retro-reflective cavity mirror 1.1 to realize end-pumping. If the pump source 1.2 and the gain medium 1.3 are on the same side of the emitting retro-reflecting cavity mirror 1.1, it is a side pumping method.

The receiver 2 includes a receiving retroreflective cavity mirror 2.1, and may further include a signal processing module or an energy receiving module 2.2 according to application scenarios. The receiving retro-cavity mirror 2.1 has a retro-reflection effect on the light of the output wavelength, that is, the reflected light is reflected in the opposite direction of the incident light, and at the same time, it has a certain transmittance for the light of the output wavelength, so that the transmitted light can be used for signal processing or energy reception.

In an actual laser system, one laser transmitter 1 may correspond to one receiver 2 or multiple receivers 2, or multiple laser transmitters 1 may correspond to one receiver 2, or multiple laser transmitters 1 may correspond to multiple receivers. device 2. The wavelength of the output light depends on the gain medium 1.3, so the wavelengths of the output light corresponding to different laser transmitters 1 may be different, and one receiver 2 may receive lasers of multiple wavelengths.

In one embodiment, the transmitting retroreflective cavity mirror 1.1 is composed of a mirror assembly, and the receiving retroreflective cavity mirror 2.1 is composed of an output mirror assembly. As shown in FIG. 6 , the mirror assembly includes a mirror 1.11 and a focusing lens 1.12 located on the reflection path or incident path of the laser light. The reflective surface of the mirror 1.11 is arranged toward the gain medium, and the mirror 1.11 is arranged between the gain medium and the gain medium. The focusing lens 1.12, the reflecting mirror 1.1 and the focal plane of the focusing lens 1.12 are arranged to coincide with each other. What needs to be explained here is that the reflecting mirror 1.11 is a plane mirror that fully reflects the light irradiated on its reflecting surface.

As shown in FIG. 7 , the output mirror assembly includes a mirror 2.11 and a focusing lens 2.12 located on the reflection path or incident path of the laser light. The reflection surface of the mirror 2.11 is arranged toward the gain medium, and the mirror 2.11 is arranged between the gain medium and the gain medium. The focusing lens 2.12 and the reflecting mirror 2.11 are arranged to coincide with the focal plane of the focusing lens 2.12. It should be explained here that the reflector 2.11 is a plane mirror that partially reflects and partially transmits the light irradiated on its reflecting surface.

According to the principle of geometric optics, the point on the focal plane is the focal point. The focal point refers to the point where the optical axis intersects the focal plane. The light emitted from the focal point is emitted in the same direction after passing through the focusing lens. The light incident through the focusing lens, after being reflected by the plane mirror and then passing through the focusing lens again, the reflected light is opposite to the direction of the original incident light. Therefore, this structure realizes the function of the retro-cavity mirror. In this way, the external resonator laser system has low requirements on the alignment of the terminal cavity mirror and is easy to emit light, and at the same time avoids the problems of large volume, difficult integration, and large diffraction loss caused by the existing cube mirror.

In one embodiment, both the focusing lens 1.12 and the focusing lens 2.12 are convex lenses. The convex lens can be selected from conventional convex lens or plano-convex lens. In this embodiment, the focusing lens 1.12 and the focusing lens 2.12 are both conventional convex lenses (ie, lenses with convex structures on both opposite sides). The conventional convex lens is arranged opposite to the mirror 1.11 to form a mirror assembly, or the conventional convex lens is arranged opposite to the mirror 2.11 to form an output mirror assembly. To use a conventional convex lens as focusing lens 1.12 and focusing lens 2.12, it only needs to satisfy that the conventional convex lens is arranged between the reflector 1.11 and the gain medium, or between the reflector 2.11 and the gain medium, and the focal plane of the reflector 1.11 or the reflector 2.11 coincides with the conventional convex lens That's it. There is no requirement on the front and back of the conventional convex lens when it is installed and installed, and it is easy to be installed to form a reflector assembly with the reflector 1.11 or an output mirror assembly with the reflector 2.11.

In another embodiment, the focusing lens 1.12 and the focusing lens 2.12 are both plano-convex lenses, one side of the plano-convex lens close to the gain medium is a plane structure, and one side far from the gain medium is a convex structure. That is, the side of the plano-convex lens facing the mirror 1.11 or the mirror 2.11 is a convex structure, and the side away from the mirror 1.11 or the mirror 2.11 is a plane structure. Between the plano-convex lens and the mirror 1.11, or between the plano-convex lens and the mirror 2.11, there may be a vacuum, or filled with air or other medium. In this way, both sides of the reflector assembly and the output mirror assembly are flat, and the integration on the terminal is relatively convenient, there is no problem of dust accumulation, and there is no problem of diffraction loss at the intersection of the three sides of the corner cube prism.

In another embodiment, the focusing lens 1.12 is a plano-convex lens, and the focusing lens 2.12 is a conventional convex lens (ie, a lens with a convex structure on both opposite sides). One side of the plano-convex lens close to the gain medium is a plane structure, and one side away from the gain medium is a convex structure. That is, the side of the plano-convex lens facing the mirror 1.11 is a convex structure and the side away from the mirror 1.11 is a plane structure. Between the plano-convex lens and the mirror 1.11, or between the conventional convex lens and the mirror 2.11, there can be a vacuum, or filled with air or other medium. In this way, both sides of the mirror assembly are flat, the integration on the terminal is relatively convenient, there is no problem of dust accumulation, and there is no problem of diffraction loss at the intersection of the three sides of the corner cube prism.

In another embodiment, the focusing lens 1.12 is a conventional convex lens (ie, a lens with a convex structure on both opposite sides), and the focusing lens 2.12 is a plano-convex lens. One side of the plano-convex lens close to the gain medium is a plane structure, and one side away from the gain medium is a convex structure. That is, the side of the plano-convex lens facing the mirror 2.11 is a convex structure, and the side away from the mirror 2.11 is a plane structure. The space between the plano-convex lens and the mirror 2.11 can be a vacuum, or filled with air or other medium. In this way, both sides of the reflector assembly and the output mirror assembly are flat, and the integration on the terminal is relatively convenient, there is no problem of dust accumulation, and there is no problem of diffraction loss at the intersection of the three sides of the corner cube prism.

The convex lens has a focusing function, and the power density of the laser is very high, which is easy to cause damage to the mirror. Therefore, it is necessary to use a material resistant to strong light to manufacture the mirror, which undoubtedly increases the cost. To reduce the effects of focusing, the position of the mirror can be changed to translate a small distance forward (closer to the focal plane) or backward (away from the focal plane) along the optical axis from the focal plane, which can greatly reduce the focused light intensity. However, when the position of the mirror is not in the focal plane, the retroreflection condition is not satisfied.

As shown in Figure 8-11, the dotted line in the figure is the control optical path, and the solid line is the actual optical path. Let the incident angle θ of the convex lens 3 be the angle between the incident ray and the optical axis 3.2, the value range is (-π/2, π/2), when the light is incident from left to right, the incident angle θ<0, otherwise θ>0 , and take the focal point of the optical axis 3.2 and the focal plane 3.1 of the convex lens as the origin, and the x-axis direction is from right to left, according to the principle of geometric optics, if there is no reflector 1.11/2.11, the incident light is refracted by the convex lens 3 and the focal point of the convex lens The x-coordinate of the intersection of the planes 3.1 is f*tan θ, where f is the focal length of the convex lens 3 . If the mirror 1.11/2.11 is translated by a distance d from the focal plane 3.1 of the convex lens to the direction of the convex lens 3, when the x-coordinate of the intersection point of the incident light and the convex lens 3 is greater than f*tanθ, then the light refracted by the convex lens 3 after reflection is compared with the original, It will be deflected in the direction of the optical axis 3.2 (as shown in Figure 8). When the degree of deflection is relatively large, it will be deflected in the direction away from the optical axis 3.2 (as shown in Figure 9). When the x-coordinate of the intersection of the incident light and the convex lens 3 is less than f When *tanθ, the light refracted by the convex lens 3 after reflection will be deflected in the direction away from the optical axis 3.2 compared with the original (as shown in Figure 10).

And the mirror 1.11/2.11 moves from the focal plane 3.1 of the convex lens to the direction away from the convex lens 3, the light refracted by the convex lens 3 after reflection will be deflected toward the direction closer to the optical axis 3.2 than the original (as shown in Figure 11). The rest of the cases can be analyzed in the same way. In general, to investigate whether the incident angle increases, it is affected by three conditions. Condition 1 is whether the mirror translation direction is moving closer to the direction of the convex lens (F) or away from the direction of the convex lens (B). Condition 2 is that the direction of the incident light is in the direction of the convex lens. Is it forward on the x-axis, that is, from right to left (F) or reverse (B), and condition 3 is whether the intersection of the incident light and the optical axis is forward (F) or reverse (B) compared to the front focus on the y-axis , let the positive y-axis be perpendicular to the x-axis, from the mirror to the convex lens. When the three conditions are FBB, FFF, BBF or BFB, the next incident angle will become larger, and when the three conditions are FBF, FFB, BBB, and BFF, the next incident angle will become smaller. The above analysis is based on plane analysis. The actual object is three-dimensional, and the plane where the optical axis and the incident light are located is taken as the analysis plane.

In practical applications, the condition 2 is the same for the mirror assembly and the output mirror assembly, and the condition 3 is also the same when the resonance is stable, so only when the condition 1 of the mirror assembly and the output mirror assembly is different, it will appear once. When the incident angle increases, the primary incident angle decreases. Otherwise, the incident angle will always decrease or increase, causing the optical path to deviate from the resonator, thereby greatly reducing the output power or causing no light. Therefore, the mirror 1.11 can be translated a certain distance from the focal plane 1.121 to the direction away from the focusing lens 1.12, and the mirror 2.11 can be translated a certain distance from the focal plane 2.121 to the direction close to the focusing lens 2.12, or the mirror 1.11 can be translated from the focal plane 1.121 to the direction of the focusing lens 2.12. The direction close to the focusing lens 1.12 translates a certain distance, while the mirror 2.11 translates a certain distance from the focal plane 2.121 to the direction away from the focusing lens 2.12 (as shown in Figure 12), so that when the angle of one reflection is shifted, the next reflection will To get the correction, in order to control the deflection angle error, the translation distance is controlled within 0.1f. In this way, the possibility of damage to the mirror 1.11 or the mirror 2.11 by focusing is reduced, while maintaining the function of the resonator to a certain extent.

In another embodiment, the mirror 1.11 is arranged parallel to the focal plane 1.121. The mirror 2.11 is arranged parallel to the focal plane 2.121. In this way, the purpose of reducing the damage to the reflecting mirror 1.11 or the reflecting mirror 2.11 caused by focusing and increasing the service life of each component of the laser system is achieved.

Further, the reflector 1.11 is arranged on the side of the focal plane 1.121 close to the focusing lens 1.12, and the reflector 2.11 is arranged on the side of the focal plane 2.121 away from the focusing lens 2.12; or, the reflector 1.11 is arranged on the side of the focal plane 1.121 away from the focusing lens 2.12 One side of the focusing lens 1.12; the mirror 2.11 is arranged on the side of the focal plane 2.121 close to the focusing lens 2.12.

In one embodiment, the focal lengths of the focusing lens 1.12 and the focusing lens 2.12 are both f; the distance between the reflecting mirror 1.11 and the focal plane 1.121 and the distance between the reflecting mirror 2.11 and the focal plane 2.121 are both d. On the basis of reducing the damage to the mirror 1.11 or the mirror 2.11 caused by focusing, the problem that the position of the mirror is not on the focal plane and the reflected light is deflected out of the resonant cavity is solved.

In another embodiment, d is less than or equal to f/10. This reduces the possibility of damage to the mirror 1.11 or the mirror 2.11 caused by focusing, while maintaining the function of the resonator to a certain extent.

In one embodiment, as shown in FIG. 13 , the focusing lens 1.12 and/or the focusing lens 2.12 is a meta-surface lens 4, that is, the meta-surface lens 4 is used to realize the focusing function of the convex lens, and the meta-surface lens 4 is close to a part of the gain medium. A metasurface structure is arranged on the side surface, and the side away from the gain medium is a plane structure without a metasurface structure; or the metasurface lens 4 is provided with a metasurface structure on two opposite sides.

The focusing effect of a traditional convex lens is formed by one or two surfaces with a certain curvature, which is constrained by the "mirror making equation", that is, 1/f=(n/n _m -1)[1/R ₁ -1/R ₂ + (n-1)δ/(nR ₁ R ₂ )], where f is the focal length of the convex lens, n is the refractive index of the convex lens material, n _m is the refractive index of the material surrounding the convex lens, and R ₁ and R ₂ are the convex lens close to the light source and the The radius of curvature of the surface away from the light source, δ is the thickness of the convex lens (the distance between the two faces of the convex lens in the direction of the main optical axis). In general, the convex lens is surrounded by air, and it can be considered that n _m = 1. For the above-mentioned convex lens with a flat surface, the convex lens plane is closer to the light source, so R ₁ =∞, so the equation can be simplified to f=-R ₂ /(n-1 ), that is, the focal length is limited by the curvature of the convex lens and the refractive index of the material, for common materials, n<2, so |f|>R ₂ . Although materials with refractive indices greater than 2 exist, they are generally more expensive and have limited reductions in f. The general convex lens material is made of glass, the refractive index is about 1.5, so f=2*R ₂ , and the radius of curvature is limited by the size of the convex lens. For a spherical convex lens, the radius of curvature is not less than the radius of the convex lens, so the focal length is not less than the diameter of the convex lens. . Taking the plane mirror located on the focal plane of the convex lens as an example, the thickness of the mirror assembly or the output mirror assembly is larger than the focal length, and usually larger than the diameter of the traditional convex lens, which results in a difference between the thickness of the mirror assembly or the output mirror assembly and the size. The contradiction of the mirror assembly or the output mirror assembly is too small, which will affect the laser resonance and reduce the laser efficiency and light output power. If a certain size is to be guaranteed, the reflector assembly or the output mirror assembly will be too thick.

Therefore, there is a problem with the use of convex lens 3 (plano-convex lens or conventional convex lens) for focusing lens 1.12 or focusing lens 2.12. As shown in Figure 14, although the reflected light and the incident light are parallel, there is a certain distance D. According to the principle of geometric optics D=2(L*cosθ+f*sinθ) can be obtained, where L is the distance between the incident point and the center of the convex lens 3, θ is the angle between the incident direction and the optical axis 3.2, that is, the incident angle, and f is the focal length of the lens. Since the focal length f is difficult to make small, even if L=0, there is D=2f*sinθ. When the incident angle is large, the translation distance between the reflected light and the incident light will be relatively large. Since the population inversion area in the gain medium is limited, that is, the area with a large number of high-level electrons affected by the pump source, if D is too large, the reflected light will be deflected outside the inversion area, and the effect of stimulated amplification will not be achieved. , this will greatly reduce the light output power, and will lead to resonance failure. In addition, the distance between the reflected light and the incident light on the surface of the convex lens 3 is K=2(L+f*tanθ). When f and θ are larger, the larger K will cause the reflected light to be deflected out of the lens, resulting in no reflection. As a result, the effective area and effective angle of incidence of the mirror assembly and the output mirror assembly are substantially limited.

Metasurface technology is an emerging technology that can change and control electromagnetic waves, sound waves, heat, etc. through certain structures. Optically, subwavelength particles can change the propagation phase of light, manifesting as a change in the direction of light propagation. Since the wavelength of light is usually in the order of hundreds of nanometers to hundreds of micrometers, as shown in Figure 15, by processing the micro-nano particles on the flat surface, the incident light at different positions passes through the micro-nano particles and appends different phases to generate different phases. Deflection, to achieve the same convergence function as a convex lens (as shown in Figure 16). The size of micro-nano particles has a certain relationship with the wavelength of light, usually in the range of 1/10 to 1/2 of the wavelength of light. There can be many shapes of micro-nano particles, such as regular circle, square, rectangle, triangle, or more complex "U" shape, bow tie shape, etc. For a specific shape, the additional phase can pass through different sizes, different Place the angle to achieve. Different sizes refer to the differences in the size of the micro-nano particles within the above-mentioned certain range, for example, the additional phase of a circular particle with a radius of a is A, and the additional phase of a circular particle with a radius of b is B. Different placement angles refer to the included angles relative to the reference direction. For example, the x-axis is a direction axis on the metasurface plane, and _{when the positive angle with the x-axis is θ 1} , the additional phase is φ ₁ , and the included angle is θ ₂ When , add the phase φ ₂ .

Using the metasurface lens 4 to realize the focusing function of the convex lens 3, the focal length can be determined first, the parallel incident light will be focused on the focal point, and the angular deflection of the micro-nano particles at a certain position from the center can be calculated according to the optical path, so as to obtain the additional phase, and Design micro-nano particles of corresponding shape and size. Note that the same additional phase may correspond to an infinite variety of shapes and sizes, which can be selected according to other requirements, such as loss. Usually the calculation is more complicated, but it can be simulated by optical simulation software. Select better micro-nano particle parameters. As shown in FIG. 17 , when the incident light passes through the meta-surface lens 4, since the micro-nano particles on the meta-surface lens 4 have different additional phases at different positions, a phase gradient is formed and the light is refracted. According to the generalized Snell's law n _o sinθ _o -n _i sinθ _i =λ/(2π)*dφ/dx, where n _i and n _o are the refractive indices of the medium on the incident light side and the refracted light side of the metasurface lens 4, respectively , θ _i and θ _o are the incident angle and the refraction angle, respectively, the phase gradient change at the incident point is dφ/dx, and the light wavelength is λ. Therefore, if the incident angle and the refraction angle are determined, the corresponding phase gradient change can be calculated, that is, in the x-axis direction, a phase β is added to the additional phase α of the adjacent micro-nano particles, so that β/L=dφ/dx , where L is the distance from the adjacent micro-nano particles in the x-axis direction.

In order to achieve the focusing effect of the convex lens, the deflection of the vertically incident light can usually be analyzed first, the focal length f can be determined, and a reference phase can be determined at the center of the lens. Since the incident angle θ _i = 0 and the refraction angle θo = arctan (L/f), it can be calculated according to the above method, so starting from the center position, the additional phase above each position can be calculated along one direction, Therefore, the additional phase of the micro-nano particles at a distance D from the central position can be obtained. One possible phase is

Among them, the center position of the lens is the origin of the coordinate system, (x, y) is the coordinate of a certain position on the lens, f is the focal length,

is the phase, and λ is the wavelength of the incident light.

The above analysis only considers the vertical incidence of light. When the light is incident obliquely, if the incident angle is not large, it can be approximately focused on the sub-focus. If the incident angle is large, there is a large deviation, and the vertical incidence and For one or more incident angles of oblique incidence, select suitable micro-nano particles so that their shape and size can meet the conditions of multiple incident angles at the same time, so as to cope with the application of large field of view.

The use of metasurface lenses can achieve very short focal lengths. At present, focal lengths as short as 10 times the wavelength have been achieved. For example, for infrared light with a wavelength of 1 micron, the focal length can be only 10 microns, which is much smaller than the focal length of traditional convex lenses.

Therefore, since the metasurface lens 4 itself can be made very thin and the focal length can be made very short, a very thin retro-reflecting cavity mirror can be realized, and a certain size can be maintained, thereby solving the contradiction between size and thickness. When L>>f, the distance between the reflected light and the incident light is about 2L*cosθ (where L is the distance from the incident point to the center of the metasurface lens, f is the focal length of the metasurface lens, and θ is the incident light The angle of incidence), the translation distance between the incident light and the reflected light is significantly smaller than the case of using a traditional lens, and the distance K between the reflected light and the incident light on the surface of the lens is about 2L, which solves the problem that the reflected light may deflect out of the lens. Therefore, this retro-cavity mirror can achieve higher light output power.

In one embodiment, the reflecting mirror 1.11 is composed of a plurality of reflecting mirror 1.11 units located on the same plane, and the focusing lens 1.12 is composed of a plurality of focusing lens 1.12 units located on the same plane;

The reflecting mirror 2.11 is composed of a plurality of reflecting mirror 2.11 units located on the same plane, and the focusing lens 2.12 is composed of a plurality of focusing lens 2.12 units located on the same plane.

In another embodiment, the reflecting mirror 1.11, the focusing lens 1.12, the reflecting mirror 2.11 and the focusing lens 2.12 are all integral structures.

In one embodiment, the mirror assembly and the output mirror assembly are disposed opposite to each other at intervals, the region between the mirror assembly and the output mirror assembly forms a resonant cavity, and a gain medium is arranged in the resonant cavity. The pump source excites the gain medium to generate radiation light, which is oscillated and amplified in the resonant cavity (the radiation light is reflected and enhanced multiple times between the mirror assembly and the output mirror assembly), and the output mirror assembly has good coherence and concentrated direction. of the laser.

Different from the previous embodiment, as shown in FIG. 18 , the laser system further includes a reflector 5. The reflector 5, the reflector assembly 1.10 and the output mirror assembly 2.10 are all arranged on the reflection path or incident path of the laser light. 5. The limited area of the mirror assembly 1.10 and the output mirror assembly 2.10 forms a resonant cavity, and the gain medium is arranged in the resonant cavity; the mirror assembly 1.10 and the output mirror assembly 2.10 are arranged on the same side of the gain medium, and the mirror 5 is arranged on the gain medium to set the reflection Opposite side of one side of mirror assembly 1.10 and output mirror assembly 2.10. The reflection surface of the mirror 5 is disposed toward the gain medium. In this way, the arrangement positions of the mirror assembly and the output mirror assembly can be more flexible.

The above are only specific embodiments of the present application, but the protection scope of the present application is not limited to this. should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

A laser system comprising:

gain medium;

a pump source for exciting the gain medium to generate radiant light;

A reflector assembly for total reflection of incident radiation;

an output mirror assembly for partially reflecting the incident radiation;

a resonant cavity, at least defined and formed by a mirror assembly and an output mirror assembly, in which the gain medium is arranged;

It is characterized in that,

The reflecting mirror assembly includes: a first reflecting mirror and a first focusing lens, the reflecting surface of the first reflecting mirror is disposed towards the gain medium, and the first focusing lens is disposed between the first reflecting mirror and the gain medium, so The first reflecting mirror is arranged on a plane perpendicular to the main optical axis of the first focusing lens;

The output mirror assembly includes: a second reflecting mirror and a second focusing lens, the reflecting surface of the second reflecting mirror is disposed toward the gain medium, and the second focusing lens is disposed between the second reflecting mirror and the gain medium, so The second reflecting mirror is arranged on a plane perpendicular to the main optical axis of the second focusing lens.
The laser system according to claim 1, wherein the first reflecting mirror is disposed on the focal plane of the first focusing lens, and the second reflecting mirror is disposed on the focal plane of the second focusing lens.
The laser system according to claim 1, wherein the first reflecting mirror is disposed on a side of the focal plane of the first focusing lens close to the first focusing lens, and the second reflecting mirror is disposed on the second focusing lens The focal plane is far from the side of the second focusing lens;

Alternatively, the first reflection mirror is arranged on the side of the focal plane of the first focusing lens away from the first focusing lens; the second reflection mirror is arranged on the side of the focal plane of the second focusing lens close to the second focusing lens.
The laser system according to claim 3, wherein the focal lengths of the first focusing lens and the second focusing lens are both f, the distance between the first reflecting mirror and the focal plane of the first focusing lens, the The distances between the second reflecting mirror and the focal plane of the second focusing lens are both d.
The laser system according to claim 4, wherein the d is less than or equal to f/10.
The laser system according to any one of claims 1-5, wherein the first focusing lens and/or the second focusing lens are convex lenses.
The laser system according to claim 6, wherein the first focusing lens and/or the second focusing lens is a plano-convex lens, a side surface of the plano-convex lens close to the gain medium is a plane structure, and a side away from the gain medium is a plane structure. The sides are convex structures.
The laser system according to any one of claims 1-5, wherein the first focusing lens and/or the second focusing lens is a meta-surface lens, and the meta-surface lens is arranged on a side surface close to the gain medium metasurface structure.
The laser system according to any one of claims 1-8, wherein the first reflecting mirror is composed of a plurality of first reflecting mirror units located on the same plane, and the first focusing lens is a plurality of first focusing lenses located on the same plane The first focusing lens unit is composed;

The second reflecting mirror is composed of a plurality of second reflecting mirror units located on the same plane, and the second focusing lens is composed of a plurality of second focusing lens units located on the same plane;

Alternatively, the first reflecting mirror, the first focusing lens, the second reflecting mirror and the second focusing lens are all integral structures.
The laser system according to any one of claims 1-9, wherein the mirror assembly and the output mirror assembly are disposed opposite to each other at intervals, and a region between the mirror assembly and the output mirror assembly forms a resonant cavity.
The laser system according to any one of claims 1-9, characterized in that, the laser system further comprises a third reflection mirror, and the third reflection mirror, the reflection mirror assembly and the output mirror assembly are all arranged on the reflection path or the output mirror assembly of the laser light. on the incident path;

The third reflector, the reflector assembly and the output mirror assembly define a resonant cavity, the reflector assembly and the output mirror assembly are disposed on the same side of the gain medium, and the third reflector is disposed on the side of the gain medium where the reflector assembly and the output mirror assembly are disposed On the opposite side of the third mirror, the reflective surface of the third mirror is disposed toward the gain medium.
The laser system according to any one of claims 1-11, wherein the gain medium can be any one of a solid gain medium, a gas gain medium, a semiconductor gain medium, and a liquid gain medium.