Self-selected mode self-injection feedback single-frequency laser

Abstract

The application discloses a self-selected mode self-injection feedback single-frequency laser, which comprises a pump source, a coupling system, an input coupling mirror, a laser crystal, an output coupling mirror, a full reflection cavity mirror set, a reflective temperature body holographic Bragg grating and a semiconductor refrigeration device. The inner cavity ring oscillator and the outer cavity reflective temperature body holographic Bragg grating jointly constitute a composite cavity oscillator. The reflective temperature body holographic Bragg grating performs mode self-selection on incident laser with constant resonant diffraction efficiency, and then injects the ring oscillator with constant laser intensity, realizes the stable one-way operation of the composite cavity ring oscillator, and solves the problem of unstable structure of the composite cavity laser. The life of the oscillation photons in the cavity is greatly increased, and the output laser has the characteristics of high efficiency, low noise and narrow line width.

Description

Technical Field

[0001] This invention relates to lasers and the field of laser technology, specifically to a self-selected mode self-injection feedback single-frequency laser. Background Technology

[0002] High-power, tunable, low-noise, and narrow-linewidth single-frequency lasers have important and wide-ranging applications in fundamental scientific research fields such as quantum information, cold atom physics, precision spectroscopy, and precision measurement, as well as in deep space exploration fields such as space laser communication and satellite navigation, and in national defense and security fields such as space lidar and laser remote sensing. Currently, a major method for fabricating high-power single-frequency lasers is to use a ring laser resonator. The ring resonator eliminates the spatial hole-burning effect of the laser, and a Faraday optics unidirectional device is inserted within the ring laser resonator to force the laser to operate in one direction. Combined with mode-selection elements such as etalons or nonlinear elements, single-frequency operation of the laser is achieved, ultimately realizing stable unidirectional, single-frequency operation of the ring laser resonator. However, the mode-selection elements introduced into the cavity of this type of single-frequency laser, such as etalons or nonlinear elements, introduce losses that affect the laser's output power. The damage threshold of the etalon is a factor limiting the laser's output power and is also one of the factors causing laser instability. When the intracavity power of a laser is high, the non-negligible thermal lensing effect of the magneto-optical medium constituting the laser unidirectional laser affects the stable operation characteristics of the laser. Simultaneously, the unidirectional laser device is also one of the factors contributing to the complexity of the laser structure and system instability. Another method to achieve a high-power single-frequency laser involves using a highly reflective mirror outside the ring laser resonator to reflect forward or backward propagating laser light back into the ring laser resonator. By creating a laser intensity difference between the two backward propagating laser beams, unidirectional laser operation is forced. Combined with the insertion of a mode selection element (such as an etalon) within the cavity, single-frequency operation of the laser is achieved, ultimately realizing unidirectional, single-frequency laser operation. The unidirectional operation of the laser relies on the intensity control of the laser light injected from the external cavity, while the single longitudinal mode operation mainly relies on the mode selection function of the internal cavity mode selection element. There is always intense mode competition between the external cavity oscillation mode and the internal cavity oscillation laser, which is the main factor causing mode instability in composite cavity lasers. Similarly, the introduction of a mode selection element within the ring resonator also increases the device instability of the laser. Furthermore, in order to form a stable laser intensity difference between two back-propagating laser beams in this type of laser, a combination of half-wave plate, prism, and quarter-wave plate needs to be introduced into the reflected laser beam path. The quarter-wave plate and prism combination is used to adjust the reflected laser to achieve a constant intensity, and the half-wave plate is used to calibrate the polarization direction of the back-injected laser. However, the introduction of quarter-wave plate, prism, and half-wave plate increases the complexity and instability of the laser, which is the main factor causing the structural instability of the composite cavity laser. Summary of the Invention

[0003] The technical problem this invention aims to solve is that the introduction of quarter-wave plates, prisms, and half-wave plates into the reflected laser beam path increases the complexity and instability of the laser, resulting in structural instability in the composite cavity laser. The goal is to provide a self-selected mode self-injection feedback single-frequency laser. This laser uses an internal ring oscillator and an external reflective temperature volume holographic Bragg grating to form the composite cavity oscillator. The reflective temperature volume holographic Bragg grating performs mode self-selection of the incident laser with a constant resonant diffraction efficiency before injecting it into the ring oscillator with a constant laser intensity, achieving stable unidirectional operation of the composite cavity ring oscillator and solving the problem of structural instability in composite cavity lasers.

[0004] This invention is achieved through the following technical solution:

[0005] A self-selected mode self-injection feedback single-frequency laser, comprising:

[0006] Pump source, coupling system, input coupling mirror, laser crystal, output coupling mirror, total reflection cavity mirror assembly, reflective temperature volume holographic Bragg grating and semiconductor cooling device;

[0007] The reflective temperature volume holographic Bragg grating is positioned behind the output coupling mirror and is on the same horizontal plane as the output coupling mirror;

[0008] The total reflection cavity mirror assembly, together with the input coupling mirror, the output coupling mirror, and the laser crystal, constitutes a closed ring oscillator;

[0009] The ring oscillator and the reflective temperature volume holographic Bragg grating together constitute a composite cavity ring oscillator;

[0010] The pump source emits laser light, which is injected into the inner cavity of the ring oscillator via a coupling system. The laser light in the horizontal output direction of the ring oscillator is mode-selected by a reflective temperature volume holographic Bragg grating with constant resonant diffraction efficiency, and then reflected into the inner cavity of the ring oscillator with constant laser intensity.

[0011] The temperature of the reflective temperature-controlled holographic Bragg grating is regulated using a semiconductor cooling device.

[0012] In the above technical solution, the reflective temperature volume holographic Bragg grating serves as both an external cavity reflective mirror and a mode selection element. After the output laser of the ring oscillator is mode-selected with constant resonant diffraction efficiency, it is injected into the ring oscillator with constant laser intensity, forming a constant laser intensity difference that forces the laser to operate unidirectionally, thereby pulling the laser oscillation frequency of the inner cavity of the ring oscillator and realizing the single longitudinal mode operation of the composite cavity ring oscillator.

[0013] A reflective temperature-body holographic Bragg grating is used as the external cavity mirror of the composite cavity ring oscillator. This grating simultaneously provides filtering, mode selection, and frequency tuning functions for vertically incident laser light, avoiding the impact of introducing mode selection and frequency adjustment elements into the ring oscillator on the laser's optical-to-optical conversion efficiency and output laser stability. The temperature of the reflective temperature-body holographic Bragg grating is controlled using a semiconductor cooling device; laser frequency tuning is achieved by adjusting the temperature of the reflective temperature-body holographic Bragg grating.

[0014] The composite cavity oscillator is constructed by combining an inner ring oscillator and an outer cavity reflective temperature volume holographic Bragg grating. The reflective temperature volume holographic Bragg grating performs mode self-selection on the incident laser with a constant resonant diffraction efficiency before injecting it into the ring oscillator with a constant laser intensity. Stable unidirectional operation of the composite cavity ring oscillator can be achieved without an additional laser intensity adjustment device, avoiding the structural instability introduced by using a laser intensity adjustment device.

[0015] In one alternative embodiment, the composite cavity length of the composite cavity ring oscillator is... The inner cavity length is twice that of the ring oscillator. The external cavity length of a holographic Bragg grating cavity with twice the size of a reflective temperature volume is... sum.

[0016] In one alternative embodiment, the amplification factor of the coupling system depends on the laser beam waist radius at the laser crystal, and the ratio of the laser beam waist radius at the pump source to the laser beam waist radius at the laser crystal is ~1.2.

[0017] In one alternative embodiment, the angle between the reflective temperature volume holographic Bragg grating and the incident laser depends on the laser intensity required for stable unidirectional operation of the laser; the diffraction efficiency of the reflective temperature volume holographic Bragg grating for perpendicularly incident laser is ~95%.

[0018] In one optional embodiment, the reflective temperature volume holographic Bragg grating is made of silicate glass crystal; the front end face of the reflective temperature volume holographic Bragg grating is coated with an oscillating laser high-transmittance film, and the rear end face is coated with an oscillating laser high-reflectance film.

[0019] In one alternative embodiment, the effective gain bandwidth of the composite cavity ring oscillator is the spectral bandwidth. The selection range satisfies: 6GHz≤ ≤ ,in, The gain bandwidth of the laser crystal; the spectral bandwidth of the reflective temperature volume holographic Bragg grating. The selection range satisfies: 6GHz≤ ≤ Effectively narrowing the emission spectral width of the laser ,in This represents the total cavity loss of the composite cavity ring oscillator.

[0020] In one alternative embodiment, the laser crystal is any one of visible light, near-infrared, infrared, and mid-infrared laser crystals.

[0021] In one alternative embodiment, the total internal reflection cavity mirror assembly includes at least one plano-concave lens.

[0022] In one alternative embodiment, the temperature control accuracy of the semiconductor cooling device is 0.005°C.

[0023] In one alternative embodiment, the tuning frequency of the laser is: ,in, The laser resonance wavelength at room temperature (25℃) is the coefficient of thermal expansion of the grating. The thermo-optic coefficient of the grating. It is the absolute value of the difference between the actual temperature of the grating and the ambient temperature of 25°C.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. This invention uses a reflective temperature volume holographic Bragg grating as the external cavity reflector of the composite cavity ring oscillator, and at the same time has the functions of filtering, mode self-selection and frequency tuning for vertically incident lasers, thus avoiding the influence of introducing mode selection elements and frequency adjustment elements into the ring oscillator on the laser's optical-to-optical conversion efficiency and laser output stability.

[0026] 2. The present invention is based on a composite cavity oscillator composed of an inner cavity ring oscillator and an outer cavity reflective temperature volume holographic Bragg grating. The reflective temperature volume holographic Bragg grating performs mode self-selection of the incident laser with a constant resonant diffraction efficiency and then injects it into the ring oscillator with a constant laser intensity. Stable unidirectional operation of the composite cavity ring oscillator can be achieved without an additional laser intensity adjustment device, avoiding the structural instability introduced by using a laser intensity adjustment device.

[0027] 3. In this invention, the reflective temperature volume holographic Bragg grating is placed after the planar output coupling mirror and is in the same horizontal direction as the planar output coupling mirror. This structural design allows the laser transmitted in the external cavity optical path to have a large spot radius, reduces the laser intensity at the volume holographic Bragg grating, and is beneficial for the fabrication of long-life self-injection feedback single-frequency lasers.

[0028] 4. The composite cavity ring oscillator proposed in this invention, which consists of an inner cavity ring oscillator and an outer cavity reflective temperature volume holographic Bragg grating, greatly increases the lifetime of the oscillating photons in the cavity, enabling the output laser to have the characteristics of high efficiency, low noise, and narrow linewidth.

[0029] 5. This invention is applicable to the fabrication of both high-power single-frequency continuous lasers and pulsed lasers. The lasers have a wide wavelength range, covering the visible light to mid-infrared 500~2700nm. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0031] Figure 1 A schematic diagram of a self-selected membrane self-injection feedback single-frequency laser provided in an embodiment of this application;

[0032] Figure 2 A graph showing the variation trend of the effective gain bandwidth and emission spectral width of a laser as a function of the spectral bandwidth of a temperature-controlled volumetric holographic Bragg grating, according to an embodiment of this application.

[0033] Figure 3 The figure shows the result of numerical fitting of a ring oscillator and a compound cavity ring oscillator provided in an embodiment of this application.

[0034] The attached diagram shows the markings and corresponding component names:

[0035] 1-Pump source, 2-Coupled system, 3-Input coupling mirror, 4-Output coupling mirror, 5-First reflecting mirror, 6-Second reflecting mirror, 7-Laser crystal, 8-Reflective temperature volume holographic Bragg grating, 9-Semiconductor cooling device, 10-Measurement system. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0037] Example

[0038] This application provides a self-selected mode self-injection feedback single-frequency laser, such as... Figure 1As shown, it includes: a pump source 1, a coupling system 2, an input coupling mirror 3, a laser crystal 7, an output coupling mirror 4, a total reflection cavity mirror group, a reflective temperature volume holographic Bragg grating 8, and a semiconductor cooling device 9.

[0039] The total internal reflection cavity mirror assembly, together with the input coupling mirror 3, the output coupling mirror 4, and the laser crystal 7, constitutes a closed ring oscillator. The ring oscillator can be a three-mirror ring cavity, a four-mirror ring cavity, a six-mirror ring cavity, or a multi-mirror ring cavity. In this embodiment, a four-mirror ring cavity is used, and the total internal reflection cavity mirror assembly includes a first reflecting mirror 5 and a second reflecting mirror 6. The four-mirror ring cavity is composed of the input coupling mirror 3, the output coupling mirror 4, the first reflecting mirror 5, and the second reflecting mirror 6. Figure 1 As shown, the input coupling mirror 3 and the output coupling mirror 4 are located on the same horizontal plane, and the first reflecting mirror 5 and the second reflecting mirror 6 are also located on the same horizontal plane. A laser crystal 7 is disposed between the input coupling mirror 3 and the output coupling mirror 4.

[0040] A reflective temperature-body holographic Bragg grating 8 is disposed after the output coupling mirror 4, and the reflective temperature-body holographic Bragg grating 8 and the output coupling mirror 4 are located on the same horizontal plane. The reflective temperature-body holographic Bragg grating 8 and the ring oscillator together constitute a composite cavity ring oscillator, with the ring oscillator being the inner cavity and the reflective temperature-body holographic Bragg grating 8 located in the outer cavity. The reflective temperature-body holographic Bragg grating 8 achieves laser frequency adjustment by adjusting its temperature. In this embodiment, a semiconductor cooling device 9 is used to regulate its temperature.

[0041] Pump source 1, coupling system 2, input coupling mirror 3, laser crystal 7, output coupling mirror 4, and reflective temperature volume holographic Bragg grating 8 are located on the same horizontal plane. Pump source 1 emits pump laser light, which is shaped by coupling system 2 and then injected into the inner cavity of the ring oscillator. The pump laser light is focused at the center of laser crystal 7, oscillated by laser crystal 7, and then propagates through output coupling mirror 4. The laser light in the horizontal output direction of output coupling mirror 4 propagates to reflective temperature volume holographic Bragg grating 8 in the outer cavity. Reflective temperature volume holographic Bragg grating 8 simultaneously serves as an outer cavity reflecting mirror and a mode selection element, performing mode selection on the output laser light of the ring oscillator with constant resonant diffraction efficiency. The temperature of the reflective temperature-controlled holographic Bragg grating 8 in the external cavity is precisely controlled by a semiconductor cooling device 9. By adjusting the temperature, the external cavity laser frequency is first tuned. After the mode of the reflective temperature-controlled holographic Bragg grating 8 is selected, the laser is injected into the inner cavity of the ring oscillator with a constant intensity. After being reflected by the input coupling mirror 3, the output coupling mirror 4, the first reflecting mirror 5, and the second reflecting mirror 6, the laser exits through the output coupling mirror 4. At this point, the output characteristics of the laser are measured using a measurement system 10.

[0042] Furthermore, the input coupling mirror 3 is a concave-convex mirror, the output coupling mirror 4 is a plane mirror, and the first reflecting mirror 5 and the second reflecting mirror 6 are both plano-concave lenses.

[0043] Furthermore, the input coupling mirror 3 is coated with a high-transmittance film for the pump light and a high-reflectance film for the oscillating laser, while the output coupling mirror 4 is coated with a film system that has a certain transmittance for the fundamental frequency oscillating laser. The first reflecting mirror 5 and the second reflecting mirror 6 are coated with a high-reflectance film for the oscillating laser.

[0044] In one alternative embodiment, the tuning frequency of the composite cavity laser is: , The laser resonance wavelength at room temperature (25℃) is the coefficient of thermal expansion of the grating. The thermo-optic coefficient of the grating. It is the absolute value of the difference between the actual temperature of the grating and the ambient temperature of 25°C.

[0045] Among them, at a normal temperature of 25℃, the diffraction efficiency of the reflective temperature volume holographic Bragg grating 8 for perpendicularly incident laser is required to reach 95%. Combined with the angle between the adjustable volume grating and the incident laser, the intensity of the self-injected feedback laser is controlled, so as to realize the stable unidirectional and single-frequency operation of the laser.

[0046] In one alternative embodiment, the composite cavity length of the composite cavity ring oscillator is... The inner cavity length is twice that of the ring oscillator. The external cavity length of a holographic Bragg grating cavity with twice the size of a reflective temperature volume is... The sum of these can achieve low-noise, narrow-linewidth laser output.

[0047] According to the formula for photon lifetime in laser cavity It can be calculated that the intracavity photon lifetime of the composite cavity ring oscillator is more than twice that of the ring oscillator, thus extending the photon lifetime.

[0048] Furthermore, based on the full quantum noise function, the composite cavity ring oscillator exhibits a higher photon lifetime compared to the ring oscillator. This will reduce the output laser intensity noise of the composite cavity ring oscillator over a wide frequency range, including reducing the relaxation oscillation frequency, relaxation oscillation amplitude, and the frequency at which the intensity noise spectrum reaches the quantum noise limit, which is beneficial for the fabrication of low-noise lasers.

[0049] According to the Schalow-Townes linewidth limit formula: ,in , Using photon energy, the laser outputs laser light. ,in The number of photons inside the cavity.

[0050] As can be seen from the above equation, when the power is equal in the case of bidirectional laser output from the composite cavity ring oscillator and the ring oscillator, the photon lifetime within the cavity of the composite cavity ring oscillator is... The increase leads to a higher number of photons within the composite cavity ring cavity. Increase.

[0051] The Schalow-Townes linewidth limit formula for lasers can also be expressed as: .

[0052] From the above equation, we can see the number of photons in the composite cavity ring cavity. Increasing the laser linewidth reduces the laser linewidth. The laser linewidth of a composite cavity ring oscillator is smaller than that of a ring oscillator cavity. Therefore, lasers using composite cavity ring oscillators are more advantageous for fabricating narrow-linewidth lasers.

[0053] In one alternative embodiment, since the total cavity length of the four-mirror ring oscillator, the radii of curvature of the two plano-concave mirrors, and the distance between the two plano-concave mirrors play a crucial role in the size of the laser beam waist radius at the laser crystal 7, the amplification factor of the coupling system 2 depends on the size of the oscillating laser beam waist radius at the laser crystal 7. Therefore, in this embodiment, the ring oscillator calculates the relationship between the cavity length of the four-mirror ring oscillator and the oscillating laser beam waist radius at the laser crystal 7 based on the radii of curvature of the input coupling mirror 3, the output coupling mirror 4, the first reflecting mirror 5, and the second reflecting mirror 6, combined with the ABCD matrix, thus obtaining a ratio of ~1.2 between the pump laser beam waist radius and the oscillating laser beam waist radius at the laser crystal 7 under the required pump power.

[0054] In one alternative embodiment, the angle between the reflective temperature volume holographic Bragg grating 8 and the incident laser depends on the laser intensity required for stable unidirectional operation of the laser; the reflective temperature volume holographic Bragg grating 8 has a diffraction efficiency of ~95% for vertically incident laser.

[0055] In one alternative embodiment, the reflective temperature volume holographic Bragg grating 8 is made of silicate glass crystal (photosensitive glass PTR). The reflective temperature volume holographic Bragg grating 8 using silicate glass crystal has a laser damage threshold of up to 5 J / cm2 and can withstand temperatures up to 400°C, thereby reducing laser loss.

[0056] The reflective temperature volume holographic Bragg grating 8 is placed on the same horizontal plane as the output coupling mirror 4 in the four-mirror ring oscillator of the inner cavity, and is perpendicular to the laser output horizontally from the output coupling mirror 4, and offset from the output laser on the output inclined arm of the output coupling mirror 4.

[0057] Furthermore, the front end of the reflective temperature volume holographic Bragg grating 8 is coated with an oscillating laser high-transmittance film, and the rear end is coated with an oscillating laser high-reflectance film. The specific coating bandwidth is selected according to the laser frequency tuning bandwidth and laser linewidth requirements, and this embodiment does not impose further limitations.

[0058] The temperature of the reflective temperature-body holographic Bragg grating 8 is controlled by a semiconductor cooling device 9. The laser frequency is tuned by adjusting the temperature of the reflective temperature-body holographic Bragg grating 8. The diffraction efficiency of the reflective temperature-body holographic Bragg grating 8 for perpendicularly incident laser light is about 95%. The angle between the reflective temperature-body holographic Bragg grating 8 and the incident laser light depends on the laser intensity required for stable unidirectional operation of the laser.

[0059] Furthermore, the semiconductor cooling device 9 adopts a Peltier thermoelectric semiconductor cooling device, with a temperature control accuracy of 0.005℃.

[0060] In one alternative embodiment, the front end of the laser crystal 7 is covered with an undoped matrix to reduce the thermal effect at the crystal end face, and the rear end of the laser crystal 7 is cut at a small angle of 1.5°. The polarization stability of the oscillating laser is ensured by reducing the thermal effect at the crystal end face by the undoped matrix on the front end of the laser crystal 7 and by cutting at a small angle of 1.5° at the rear end.

[0061] Furthermore, the front end of the laser crystal 7 is coated with a high-transmittance film for both the pump laser and the oscillating laser; the rear end of the laser crystal 7 is coated with a high-reflectance film for the pump laser and a high-transmittance film for the oscillating laser. These features can increase the absorption efficiency of the pump laser and thus reduce the transmission loss of the oscillating laser.

[0062] Furthermore, the laser crystal 7 can be any one of visible light, infrared light, infrared, and mid-infrared laser crystals. In practical applications, the laser crystal 7 is a laser crystal generated by visible light, infrared light, infrared, or mid-infrared lasers.

[0063] In one alternative embodiment, the pump source 1 can be either fiber-coupled output or free-space output; the pump source 1 can be a laser diode, a fiber laser, or an all-solid-state laser.

[0064] In one alternative embodiment, the pumping method of the ring oscillator is not limited to end-face pumping, but can also be side-pumping.

[0065] In one alternative embodiment, the ring oscillator can be a square structure or a butterfly structure.

[0066] In one optional embodiment, the laser crystal in the ring oscillator is Nd:YVO4, the absorption and divergence loss of the temperature volume holographic grating is 2%, the first-order diffraction efficiency of the temperature volume holographic grating is 95%, and the total loss of the composite cavity ring oscillator is... Laser crystal gain bandwidth The effective gain bandwidth and emission spectral width of the laser Spectral bandwidth of volumetric holographic Bragg grating (8) with temperature The trend of change is as follows Figure 2 As shown. From Figure 2 It can be seen that the composite ring oscillator designed in this application can narrow the laser gain spectral bandwidth by at least 3.5 times, which is beneficial for the preparation of low-noise, narrow-linewidth lasers and for realizing narrow-linewidth lasers.

[0067] In one alternative embodiment, the composite cavity length of the composite cavity ring oscillator is... The inner cavity length is twice that of the ring oscillator. The external cavity length of a holographic Bragg grating cavity with twice the size of a reflective temperature volume is... The sum. According to the laser cavity photon lifetime formula. It can be calculated that the intracavity photon lifetime of the composite cavity ring oscillator is more than twice that of the ring oscillator, thus extending the photon lifetime. According to the full quantum noise function: , among them These are related to the vacuum noise introduced by the output coupling mirror. Noise caused by intracavity loss Pump source noise Spontaneous radiated noise Dipole ripple noise The coefficients of the intensity noise spectrum. relaxation oscillation frequency and the rate of relaxation oscillation damping ,in , and These represent the photon attenuation rates caused by output loss and intracavity loss, respectively. This represents the transmission coefficient of the output coupling lens. Indicates intracavity linear loss, It represents the speed of light. Indicates the normalized pump rate. This represents the rate of spontaneous emission of an atom from a higher energy level to a lower energy level. This represents the normalized number of photons within the cavity. Among them, the stimulated emission rate... Represented as: , For stimulated emission rate, Let l be the stimulated emission cross section and l be the length of the laser crystal. Let be the atomic number density, be the refractive index of the laser crystal, and be the cavity length of the resonant cavity. For a ring oscillator: , , , , , , , , For compound cavity ring oscillators: , , , , , , , , The numerical fitting results are as follows: Figure 3 As shown, the dashed line represents the relative intensity noise spectrum of the ring oscillator, and the solid line represents the relative intensity noise spectrum of the composite cavity ring oscillator. Compared to the ring oscillator, the composite cavity ring oscillator has a higher photon lifetime within the cavity. It will reduce the output laser intensity noise of the oscillator over a wide frequency range, including reducing the relaxation oscillation frequency, relaxation oscillation amplitude, and the frequency at which the intensity noise spectrum reaches the quantum noise limit, which is beneficial for the fabrication of low-noise lasers.

[0068] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-selected mode self-injection feedback single-frequency laser, characterized in that, include: Pump source (1), coupling system (2), input coupling mirror (3), laser crystal (7), output coupling mirror (4), total reflection cavity mirror group, reflective temperature volume holographic Bragg grating (8), and semiconductor cooling device (9); The reflective temperature volume holographic Bragg grating (8) is placed behind the output coupling mirror (4) and is on the same horizontal plane as the output coupling mirror (4); The total reflection cavity mirror group, together with the input coupling mirror (3), the output coupling mirror (4), and the laser crystal (7), constitutes a closed ring oscillator; The ring oscillator and the reflective temperature volume holographic Bragg grating (8) together constitute a composite cavity ring oscillator; Wherein, the pump source (1) emits laser and injects it into the inner cavity of the ring oscillator through the coupling system (2). The laser in the horizontal output direction of the ring oscillator is subjected to mode selection by the reflective temperature volume holographic Bragg grating (8) with constant resonant diffraction efficiency and then reflected into the inner cavity of the ring oscillator with constant laser intensity. The temperature of the reflective temperature-controlled holographic Bragg grating (8) is regulated by a semiconductor cooling device (9); Effective gain bandwidth and spectral bandwidth of compound cavity ring oscillators The selection range satisfies: 6GHz≤ ≤ ,in, This refers to the gain bandwidth of the laser crystal. The spectral bandwidth of the reflective temperature volume holographic Bragg grating (8) The selection range satisfies: 6GHz≤ ≤ Effectively narrowing the emission spectral width of the laser ,in This represents the total cavity loss of the composite cavity ring oscillator.

2. The self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The composite cavity length of the composite cavity ring oscillator The inner cavity length is twice that of the ring oscillator. The external cavity length of the twice-reflective temperature volume holographic Bragg grating (8) sum.

3. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The amplification factor of the coupling system (2) depends on the size of the laser beam waist radius at the laser crystal (7), and the ratio of the laser beam waist radius at the pump source (1) to the laser beam waist radius at the laser crystal (7) is ~1.

2.

4. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The angle between the reflective temperature body holographic Bragg grating (8) and the incident laser depends on the laser intensity required for the laser to operate stably in one direction; the diffraction efficiency of the reflective temperature body holographic Bragg grating (8) for vertically incident laser is ~95%.

5. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The material of the reflective temperature volume holographic Bragg grating (8) is silicate glass crystal; the front end of the reflective temperature volume holographic Bragg grating (8) is coated with an oscillating laser high-transmittance film, and the rear end is coated with an oscillating laser high-reflectance film.

6. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The laser crystal (7) is any one of visible light, near-infrared, infrared, and mid-infrared laser crystals.

7. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The total internal reflection cavity mirror assembly includes at least one plano-concave lens.

8. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The temperature control accuracy of the semiconductor cooling device (9) is 0.005℃.

9. A self-selected mode self-injection feedback single-frequency laser according to claim 1, characterized in that, The tuning frequency of the laser is ,in, The laser resonance wavelength at room temperature (25℃) is the coefficient of thermal expansion of the grating. The thermo-optic coefficient of the grating. It is the absolute value of the difference between the actual temperature of the grating and the ambient temperature of 25°C.

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