Laser line width compression device and debugging method thereof

Abstract

The present application provides a laser linewidth compression device and a debugging method thereof, which relates to the field of resonator technology, and includes: an FP resonant cavity, which is composed of a multi-layer parallel and reflective nano-film optical fiber body coated at both ends, wherein the optical fiber body is a nonlinear optical fiber with a birefringence effect, and the FP resonant cavity generates a first refracted light and a second refracted light in the cavity after receiving a pump laser, wherein the first refracted light and the second refracted light form two sets of longitudinal modes with perpendicular polarization directions in the FP resonant cavity, and a stress applying device, including a base. The present invention forms a Fabry-Perot resonant cavity structure by encapsulating and coating both ends of a section of optical fiber, and then forms a resonant longitudinal mode with two sets of polarizations by applying a birefringence effect caused by pressure to the FP resonant cavity, and finally outputs a stimulated Brillouin laser. The laser obtained in this way has a narrower linewidth, and can also effectively suppress the multi-longitudinal mode cascade problem of a general stimulated Brillouin laser.

Description

[0001] This application claims the priority of the Chinese patent application filed with the China Patent Office on March 2, 2022, with application number 202210199962.9 and invention name “A laser line width compression device and its debugging method”, the entire contents of which are incorporated by reference in this application. Technical Field

[0002] The present application relates to the field of resonator technology, and in particular to a laser line width compression device and a debugging method thereof. Background Art

[0003] The principle of laser is to use stimulated radiation to amplify or oscillate light in certain excited substances. Fiber lasers use optical fibers doped with rare earth ions or the nonlinear effects of the optical fibers themselves as their gain medium. Under the action of the pump laser, a high power density is formed in the fiber core, causing the number of particles in the energy level of the doped ions in the fiber to reverse, and then oscillate back and forth in the resonant cavity to form laser output. Compared with traditional lasers, narrow linewidth lasers are an important tool in both scientific research and industrial fields, and play an important role in fields such as precision frequency measurement, optical clocks, coherent optical communications, and lidar.

[0004] Stimulated Brillouin scattering (SBS) is a very important nonlinear effect in optical fiber. The existing narrow-linewidth laser based on the SBS effect is achieved by injecting the laser into a certain medium and using the nonlinear effect in the medium to generate an SBS gain zone of a specific frequency or photons of a specific frequency. When the gain of the photon propagating in the medium is greater than its loss, it will show a stimulated emission phenomenon like the injected laser. This new frequency laser is the stimulated Brillouin laser (SBL), and the linewidth of the SBL is narrower than the original laser.

[0005] In the prior art, optical fibers are processed to form optical fiber resonant cavities, so that light is reflected back and forth in the resonant cavity to enhance the SBS effect and generate SBL lasers. Figure 1 , is a schematic diagram of the principle of generating SBL using resonant cavity technology in the prior art. When light is continuously reflected in a medium, interference will occur between the light and the light. Only when the light meets certain conditions, the interference result will increase the total light intensity. The frequency that meets the constructive interference condition is called the longitudinal mode frequency of the cavity. Figure 1 The thin column in the middle represents the longitudinal mode frequency of the resonant cavity. When the frequency of the pump laser meets the longitudinal mode frequency of the resonant cavity, it can propagate back and forth in the cavity to enhance the interaction between the laser and the medium and generate Stokes photons with a specific frequency offset. Figure 1△f refers to the frequency interval (in Hz) between two adjacent longitudinal modes with different polarizations. When the photon frequency also meets the oscillation conditions of the resonant cavity, the oscillation can be enhanced in the cavity and finally output SBL laser. Therefore, whether the resonant frequency can be accurately controlled to allow the pump light and Stokes light to oscillate simultaneously in the cavity is the key to generating SBL. Whether the laser can propagate back and forth in the cavity can be judged by the following formula:

[0006] v = n × FSR;

[0007]

[0008] Where FSR is the free spectral range of the resonant cavity (in Hz), v is the laser frequency (in Hz), c is the speed of light, η is the refractive index of the medium, n is an arbitrary integer, and L is the length of the resonant cavity (m). In order to successfully inject the laser into the resonant cavity, its frequency must be an integer multiple of the resonant cavity FSR, and FSR is related to the length and refractive index of the cavity. Because most existing resonant cavities only use one polarization mode in the cavity, for the same polarization mode, the intervals between the resonant frequencies can be approximately equal within a certain range, so it is necessary to accurately control the length of the cavity to make the pump photon and the generated Stokes photon frequency meet the following conditions:

[0009]

[0010] In the formula, v1 is the pump photon frequency (unit Hz), v2 is the Stokes photon frequency (unit Hz), FSR1 is the longitudinal mode free spectral range of the second refracted light (unit Hz), FSR2 is the longitudinal mode free spectral range of the first refracted light (unit Hz), n and m are arbitrary integers. Because the two-frequency photons share the same set of FSR, the processing accuracy and difficulty of the resonant cavity are greatly improved; at the same time, when the SBL oscillates in the cavity, it will continue to generate photons of new frequencies. The new photon frequencies such as v3, v4... still meet the above conditions. Therefore, when the pump power is high, multiple lasers with equal frequency intervals will be generated (cascade problem), and high-power single-frequency lasers cannot be obtained. Summary of the invention

[0011] The present application provides a laser line width compression device and a debugging method thereof, so as to solve the cascade problem existing in the prior art that the resonant cavity manufacturing process has high requirements and exists under high power.

[0012] In a first aspect, the present application provides a laser linewidth compression device, comprising: an FP resonant cavity, which is composed of a multi-layer parallel and reflective nano-film optical fiber body coated at both ends, wherein the optical fiber body is a nonlinear optical fiber with a birefringence effect, and the FP resonant cavity generates a first refracted light and a second refracted light in the cavity after receiving a pump laser, wherein the first refracted light and the second refracted light form two sets of longitudinal modes with perpendicular polarization directions in the FP resonant cavity, and a stress applying device, comprising a base, wherein a groove for clamping the FP resonant cavity and a force applying mechanism for applying stress to the surface of the FP resonant cavity are provided on the base, wherein the force applying mechanism is detachably connected to the base, and the force applied by the force applying mechanism is adjusted by an adjustment component connected to the force applying mechanism.

[0013] Optionally, a mounting groove is provided on the base, a rotating block rotatable in a vertical plane is arranged in the mounting groove, a placement groove for placing part of the FP resonant cavity is provided on the rotating block, when the rotating block is in an initial state, the placement groove on the rotating block and the groove on the base are connected and are in the same horizontal plane, and a third force-applying member is detachably connected to the rotating block.

[0014] Optionally, the force-applying mechanism includes a first force member and a second force member, the first force member, the second force member are connected to the base via a second bolt, the third force member is connected to the rotating block via a second bolt, the adjustment assembly includes a handle fixedly connected to both ends of the rotating block and a second bolt for loosening or tightening the first force member, the second force member and the third force member, and when the rotating block rotates, the angle formed by the longitudinal axis of the rotating block and the plane where the base is located is in the range of 0° to 90°.

[0015] Optionally, a plurality of columns are detachably connected to the top of the base, a top plate is detachably connected to the top of the column, the force-applying mechanism comprises a pressure plate arranged parallel to the base, the pressure plate is located between the top plate and the base, the pressure plate is sleeved with the column, a stress block for applying stress to the FP resonant cavity is fixedly connected to the bottom of the pressure plate, the adjustment assembly comprises a first bolt threadedly connected to the top plate, a spring is fixedly connected to the bottom of the first bolt, a pressure block is fixedly connected to the bottom of the spring, a ball is rotatably connected to the bottom of the pressure block, a limiting groove for limiting the ball is provided on the top of the pressure plate, and the ball is located in the limiting groove.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the laser line width compression device can form two sets of longitudinal modes with mutually perpendicular polarization directions in one cavity through the FP resonant cavity formed by coating at both ends of a nonlinear optical fiber with a birefringence effect, and change the longitudinal mode resonant frequency of the first refracted light by applying stress to the FP resonant cavity using a stress applying device, so that the frequency of the pump photon and the frequency of the Stokes photon in the FP resonant cavity respectively meet the following conditions:

[0017]

[0018] The SBL is obtained by using two sets of longitudinal modes with orthogonal polarizations. Compared with the general FP resonant cavity using one set of longitudinal modes, the present invention uses two sets of longitudinal modes to respectively meet the resonance conditions of pump photons and Stokes photons. When the polarization directions of the original pump laser and the newly generated SBL are perpendicular to each other, the pump laser and the SBL can be effectively separated by a polarization beam splitter. In addition, the present invention can change the propagation speed of the extraordinary light in the optical fiber by adjusting the pressure applied to the FP resonant cavity, thereby changing the resonant frequency of a set of longitudinal modes, which greatly reduces the precision requirements for the processing of the FP resonant cavity. In addition, after using two sets of longitudinal modes to realize the SBL, the SBL will continue to generate Stokes photons of a new frequency, but the frequencies of the newly generated Stokes photons do not meet the resonance conditions of the two sets of cavity modes of the present invention. That is, v1-v2 is not an integer multiple of the free spectrum range (FSR1, FSR2, so another advantage of the present invention is that the cascade of the SBL can be effectively suppressed during high-power pumping, and only a narrow linewidth laser of a new frequency is generated.

[0019] On the other hand, the present application provides a laser line width compression device debugging system, comprising the laser line width compression device described in the present invention, and also comprising a spectrometer, an optical fiber laser, an input end polarization controller, an output end polarization controller and a polarization beam splitter, wherein the optical fiber laser, the input end polarization controller, the laser line width compression device, the output end polarization controller and the polarization beam splitter are connected in sequence, and the spectrometer is connected to the laser line width compression device to detect whether the laser line width compression device successfully generates SBL laser. After the laser emitted by the optical fiber laser is input into the input end polarization controller, the polarization direction is adjusted by the input end polarization controller and the laser line width compression device is input into the laser line width compression device for line width compression to obtain pump laser and SBL laser, and finally the pump laser and SBL laser output by the laser line width compression device are separated and output through the output end polarization controller and the polarization beam splitter.

[0020] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the laser linewidth compression device debugging system, by adopting the laser linewidth compression device described in the present invention, effectively suppresses the cascade of SBL during high-power pumping, and only generates a narrow-linewidth laser of a new frequency, and when the polarization directions of the original pump laser and the newly generated SBL are perpendicular to each other, the pump laser and the SBL can be effectively separated by a polarization beam splitter, and the propagation speed of the extraordinary light in the optical fiber can be changed by adjusting the pressure applied to the FP resonant cavity.

[0021] The present application also provides a debugging method for a laser line width compression device debugging system, the method comprising the following steps:

[0022] Utilizing a fiber laser to output laser light, an input end polarization controller adjusts the polarization direction of the laser light output by the fiber laser so that the polarization direction of the laser light output by the fiber laser is consistent with the polarization direction of the longitudinal mode of the FP resonant cavity;

[0023] Using a stress applying device to adjust the stress applied to the FP resonant cavity, so that two sets of longitudinal modes formed in the FP resonant cavity meet the oscillation conditions of the pump laser and the SBL laser respectively;

[0024] According to the resonance frequency of any longitudinal mode polarization mode, adjusting the wavelength of the fiber laser to be close to the resonance frequency of any longitudinal mode polarization mode, and observing whether the SBL laser is successfully generated by a spectrometer;

[0025] If SBL laser is not generated, the wavelength and output power of the fiber laser are further fine-tuned to meet the resonance conditions in the FP resonant cavity until SBL laser is generated;

[0026] The output end polarization controller and the polarization beam splitter are adjusted to separate and output the pump laser and SBL laser generated by the FP resonant cavity.

[0027] Optionally, when the fiber laser outputs laser, the fiber laser is in a wavelength scanning mode.

[0028] Optionally, the optical fiber laser, the input end polarization controller and the laser line width compression device are directly plugged in via a flange and a ceramic sleeve.

[0029] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the debugging method of the laser linewidth compression device debugging system applies stress to the FP resonant cavity having two sets of longitudinal modes, so that the two sets of longitudinal modes formed in the FP resonant cavity respectively meet the oscillation conditions of the pump laser and the SBL, and adjust the wavelength of the optical fiber laser according to the resonant frequency of any polarization mode so that the FP resonant cavity generates the SBL, and when the polarization directions of the original pump laser and the newly generated SBL are perpendicular to each other, the pump laser and the SBL can be effectively separated by a polarization beam splitter, thereby effectively improving the efficiency of generating the SBL. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solution of the present application, the drawings required for use in the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0031] Figure 1 It is a schematic diagram of the principle of generating SBL laser using resonant cavity technology in the prior art;

[0032] Figure 2A process flow chart of manufacturing the FP resonant cavity in the laser line width compression device provided in this application;

[0033] Figure 3 Schematic diagram of the laser line width compression device debugging system provided for this application;

[0034] Figure 4 A structural diagram of a stress applying device provided in this application;

[0035] Figure 5 A side view of another stress applying device provided by the present application;

[0036] Figure 6 for Figure 5 A top view of the stress applying device in an unassembled state;

[0037] Figure 7 Schematic diagram of the laser line width compression device provided in this application for generating SBL laser. DETAILED DESCRIPTION

[0038] To facilitate the technical solution of the application, some concepts involved in the application are first explained below.

[0039] The following briefly describes the principle of generating SBL using resonant cavity technology in the prior art, so as to more clearly illustrate the principle of the embodiments of the present application.

[0040] Embodiment 1

[0041] See also Figure 2 , which is a process flow chart of manufacturing the FP resonant cavity in the laser linewidth compression device provided in the embodiment of the present application. First, a nonlinear optical fiber of a certain length is selected, and the cladding at both ends of the optical fiber is stripped. By way of example, in order to improve the applicability of the embodiment of the present application, the FP resonant cavity provided in the embodiment of the present application is processed with commercial optical fiber as raw material, and commercial ceramic ferrules are inserted into both ends of the optical fiber and fixed with glue so that the interfaces at both ends are compatible with various commercial optical fiber devices. Because commercial ceramic ferrules of standard size are installed at both ends, and the optical fiber used also has a high concentricity, the FP resonant cavity provided in the embodiment of the present application can be directly plugged in and out with other optical fiber devices using a ceramic sleeve, and then mechanical grinding and polishing are performed together with the optical fiber end face and the ceramic ferrule to ensure the flatness of the optical fiber end face. Finally, both ends of the optical fiber are placed in a coating machine, and the coating parameters of the FP resonant cavity are determined according to the output wavelength range of the optical fiber laser to obtain the FP resonant cavity. For example, if the output wavelength of the laser is between 1550nm and 1560nm, the coating parameters of the embodiment of the present application can be selected within the wavelength range of 1545nm to 1565nm to achieve a reflectivity higher than 99%, thereby ensuring that the output laser can be continuously reflected in the FP resonant cavity. The coating materials are mainly titanium dioxide and silicon dioxide.

[0042] Embodiment 2

[0043] A laser line width compression device, comprising: Figure 2 The FP resonant cavity 2 shown is composed of a main body of a parallel and reflective nano-film optical fiber coated with multiple layers at both ends. Specifically, the main body of the optical fiber is a nonlinear optical fiber with a birefringence effect, and the optical fiber core is made of a uniaxial or biaxial crystal of silica or calcium fluoride. The nonlinear optical fiber core in this embodiment is made of a positive uniaxial crystal of silica. After receiving the pump laser, the FP resonant cavity 2 generates a first refracted light and a second refracted light in the cavity, wherein the first refracted light and the second refracted light form two sets of longitudinal modes with perpendicular polarization directions in the FP resonant cavity 2.

[0044] For details, see Figure 3 , which is a schematic diagram of the SBL generation of the laser linewidth compression device provided in the embodiment of the present application. When a beam of light is incident on the crystal (except for special directions), the light wave can be decomposed into two beams of first refracted light and second refracted light with mutually perpendicular vibration directions, different propagation speeds and refractive indices, namely, extraordinary light and ordinary light. Therefore, two sets of longitudinal modes with mutually perpendicular polarization directions can be formed in one cavity. The free spectral ranges of the two longitudinal modes are respectively:

[0045]

[0046] Where η o , η e are the refractive indices of ordinary light and extraordinary light, c is the speed of light (3×10^8m / s), FSR1 and FSR2 are the free spectral ranges of the ordinary and extraordinary longitudinal modes (in Hz), respectively. The propagation speed of ordinary light is independent of direction, while the propagation speed of extraordinary light is related to the propagation direction. When the pump laser meets a certain set of longitudinal mode resonant frequencies, Stokes photons are generated at a specific frequency away from the pump.

[0047] Stress applying device, see Figure 4-6 , both include a base 1, on which is provided a groove 101 for clamping the FP resonant cavity 2 and a force-applying mechanism 4 for applying stress to the surface of the FP resonant cavity 2, the force-applying mechanism 4 being detachably connected to the base 1, the force-applying surface of the force-applying mechanism 4 being parallel to the groove 101, and the force applied by the force-applying mechanism 4 being adjusted by an adjusting component 3 connected to the force-applying mechanism 4.

[0048] The pressure applied to the FP resonant cavity 2 is adjusted by adjusting the adjustment component 3, so as to change the refractive index of the extraordinary light, change the propagation speed of the extraordinary light in the optical fiber, and then change the resonant frequency of the extraordinary light longitudinal mode, so that the frequencies of the pump laser and the generated Stokes photons respectively meet the following conditions:

[0049]

[0050] Wherein, v1 is the pump photon frequency (unit Hz), v2 is the Stokes photon frequency (unit Hz), FSR1 is the longitudinal mode free spectral range of the second refracted light (unit Hz), FSR2 is the longitudinal mode free spectral range of the first refracted light (unit Hz), and n and m are arbitrary integers.

[0051] The propagation speed of the extraordinary light in the optical fiber is changed by adjusting the pressure applied to the FP resonant cavity 2, thereby changing the resonant frequency of a set of longitudinal modes, so that the two sets of longitudinal modes are used to meet the resonant conditions of the pump photons and the Stokes photons respectively, which greatly reduces the precision requirements for the processing of the FP resonant cavity 2. In addition, after the two sets of longitudinal modes are used to realize the SBL, the SBL will continue to generate Stokes photons of a new frequency, but the frequencies of the newly generated Stokes photons do not meet the resonant conditions of the two sets of cavity modes of the present invention, that is, v1-v2 is not an integer multiple of the free spectral range (FSR1, FSR2), so the cascade problem of the SBL can be effectively suppressed during high-power pumping, and only a narrow linewidth laser of a new frequency is generated.

[0052] Embodiment 3

[0053] like Figure 4 As shown, the stress applying device also includes the following structure:

[0054] The top of the base 1 is detachably connected to a plurality of columns 6, and the top of the columns 6 is detachably connected to a top plate 5. Specifically, the columns 6 are connected to the base 1 by threads, and the top plate 5 is fixed by threading nuts on the columns 6. The force-applying mechanism 4 includes a pressing plate 401 arranged parallel to the base 1, the pressing plate 401 is located between the top plate 5 and the base 1, the pressing plate 401 is sleeved with the columns 6, and a stress block 402 for applying stress to the FP resonant cavity 2 is fixedly connected to the bottom of the pressing plate 401.

[0055] The adjustment assembly 3 includes a first bolt 301 threadedly connected to the top plate, a spring 302 is fixedly connected to the bottom of the first bolt 301, a pressure block 303 is fixedly connected to the bottom of the spring 302, a ball 304 is rotatably connected to the bottom of the pressure block 303, and a limiting groove for limiting the ball 304 is provided on the top of the pressure plate 401, and the ball 304 is located in the limiting groove. Through the provided ball 304, when the pressure block 303 applies pressure to the pressure plate 401, the pressure can be balanced through the ball 304, thereby making the stress change as stable as possible. In this embodiment, retractable support plates are provided at both ends of the base 1, and the retractable support plates can be stretched toward both ends along the extension direction of the groove 101 to place FP resonant cavities 2 of different lengths.

[0056] When in use, the user first places the FP resonant cavity into the groove 101, and then rotates the first bolt 301 to drive the pressure block 303 to apply pressure to the pressure plate 401, so that the stress block 402 approaches the FP resonant cavity 2 and finally contacts the FP resonant cavity 2. The user changes the pressure applied by the pressure block 303 to the lifting plate 2 by rotating the first bolt 301, so as to change the stress applied to the optical fiber FP resonant cavity 2 placed in the groove 101 by using the stress block 402.

[0057] Embodiment 4

[0058] like Figure 5 , Figure 6 As shown, the stress applying device also includes the following structure:

[0059] The base 1 is provided with a mounting groove, in which a rotating block 7 rotatable in a vertical plane is arranged. Specifically, a fixing frame 8 is fixedly connected to the base 1, and the steering block 7 is rotatably connected to the fixing frame 8. A placement groove 701 for placing part of the FP resonant cavity 2 is provided on the rotating block 7. When the rotating block 7 is in an initial state, the placement groove 701 on the rotating block 7 and the groove 101 on the base 1 are connected and are in the same horizontal plane. The rotating block 7 is detachably connected with a third force-applying member 413.

[0060] The force applying mechanism includes a first force applying member 411 and a second force applying member 412 . The first force applying member 411 , the second force applying member 412 and the base 1 are connected via a second bolt 9 . The third force applying member 413 and the rotating block 7 are connected via a second bolt 9 .

[0061] The adjustment assembly 3 includes a handle 702 fixedly connected to both ends of the rotating block 7 and a second bolt 8 for loosening or tightening the first force member 411, the second force member 412 and the third force member 413. When the rotating block 7 rotates, the angle formed by the longitudinal axis of the rotating block 7 and the plane where the base 1 is located ranges from 0° to 90°.

[0062] When in use, the user first places the FP resonance cavity 2 into the groove 101, and then connects the first force member 411 and the second force member 412 to the base 1 through the second bolt 9, and connects the third force member 413 to the steering block 7 through the second bolt 9. The user can provide vertical stress to the FP resonance cavity by twisting the second bolts 9 on the first force member 411, the second force member 412 and the third force member 413; and can provide horizontal stress to the FP resonance cavity 2 by rotating the steering block 7.

[0063] Embodiment 5

[0064] like Figure 7As shown, this embodiment provides a laser line width compression device debugging system, comprising an optical fiber laser, an input end polarization controller, a laser line width compression device, an output end polarization controller and a polarization beam splitter connected in sequence; the input end polarization controller is used to adjust the laser polarization output by the optical fiber laser; an amplifier and an isolator connected in sequence are also arranged between the input end polarization controller and the laser line width compression device; the light intensity of the input laser is amplified by the arranged amplifier, and the arranged isolator can prevent the laser from returning to the amplifier along the original path after hitting the front end surface of the laser line width compression device, and the output end polarization controller and the polarization beam splitter are used to separate the pump laser output by the laser line width compression device from the SBL laser for output.

[0065] After the laser emitted by the optical fiber laser is input into the input end polarization controller, the polarization direction is adjusted by the input end polarization controller and input into the laser line width compression device for line width compression to obtain pump laser and SBL laser. Finally, the pump laser and SBL laser output by the laser line width compression device are separated and output through the output end polarization controller and the polarization beam splitter.

[0066] The laser linewidth compression device debugging system adopts the laser linewidth compression device of the present invention, effectively suppresses the cascade of SBL during high-power pumping, and only generates a narrow-linewidth laser with a new frequency. When the polarization directions of the original pump laser and the newly generated SBL are perpendicular to each other, the pump laser and the SBL can be effectively separated by a polarization beam splitter, and the propagation speed of the extraordinary light in the optical fiber can be changed by adjusting the pressure applied to the FP resonant cavity.

[0067] Embodiment 6

[0068] This embodiment provides a debugging method for a laser line width compression device debugging system, the method comprising the following steps:

[0069] The optical fiber laser is used to output laser light, and the input end polarization controller adjusts the polarization direction of the laser light output by the optical fiber laser so that the polarization direction of the laser light output by the optical fiber laser is consistent with the polarization direction of the longitudinal mode of the FP resonant cavity.

[0070] The stress applied to the FP resonant cavity is adjusted by using a stress applying device so that two sets of longitudinal modes formed in the FP resonant cavity meet the oscillation conditions of the pump laser and the SBL laser respectively.

[0071] According to the resonance frequency of any longitudinal mode polarization mode, the wavelength of the optical fiber laser is adjusted to be close to the resonance frequency of any longitudinal mode polarization mode, and a spectrometer is used to observe whether SBL laser is successfully generated.

[0072] If SBL laser is not generated, the wavelength and output power of the fiber laser are further fine-tuned to meet the resonance conditions in the FP resonant cavity until SBL laser is generated.

[0073] The output end polarization controller and the polarization beam splitter are adjusted to separate and output the pump laser and SBL laser generated by the FP resonant cavity.

[0074] When the fiber laser outputs laser light, the fiber laser is in wavelength scanning mode. The purpose of putting the fiber laser in wavelength scanning mode is to adjust the polarization of the laser light. When the directions of the two sets of longitudinal mode polarization regions are different, it is necessary to ensure that the polarization direction of the laser light is consistent with one of them, so as to maximize the utilization of the laser energy.

[0075] The fiber laser, the input polarization controller and the laser line width compression device are directly plugged in through flanges and ceramic sleeves. Specifically, the embodiment of the present application is processed with commercial optical fiber as raw material, and the interfaces at both ends are compatible with various commercial optical fiber devices and can be directly plugged in and out, which improves the applicability of the present application.

[0076] The debugging method of the laser line width compression device debugging system applies stress to the FP resonant cavity with two sets of longitudinal modes, so that the two sets of longitudinal modes formed in the FP resonant cavity meet the oscillation conditions of the pump laser and the SBL respectively, and adjusts the wavelength of the fiber laser according to the resonance frequency of any polarization mode, so that the FP resonant cavity generates the SBL. When the polarization directions of the original pump laser and the newly generated SBL are perpendicular to each other, the pump laser and the SBL can be effectively separated by a polarization beam splitter, thereby effectively improving the efficiency of generating the SBL.

[0077] The above specific implementation methods further illustrate the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above are only specific implementation methods of the present application and are not used to limit the protection scope of the present application. Any modifications, equivalent substitutions, improvements, etc. made on the basis of the technical solutions of the present application should be included in the protection scope of the present application.

Claims

1. A laser line width compression device, characterized in that: include: The FP resonant cavity (2) is composed of a main body of a parallel and reflective nano-film optical fiber coated at both ends, wherein the main body of the optical fiber is a nonlinear optical fiber with a birefringence effect, and the FP resonant cavity (2) generates a first refracted light and a second refracted light in the cavity after receiving a pump laser, wherein the first refracted light and the second refracted light form two sets of longitudinal modes with perpendicular polarization directions in the FP resonant cavity (2); A stress applying device comprises a base (1), the base (1) being provided with a groove (101) for clamping an FP resonant cavity (2) and a force applying mechanism (4) for applying stress to the surface of the FP resonant cavity (2), the force applying mechanism (4) being detachably connected to the base (1), and the force applied by the force applying mechanism (4) being adjusted by an adjusting component (3) connected to the force applying mechanism (4); The base (1) is provided with a mounting groove, a rotating block (7) rotatable on a vertical plane is arranged in the mounting groove, the rotating block (7) is provided with a placement groove (701) for placing part of the FP resonant cavity (2), when the rotating block (7) is in an initial state, the placement groove (701) on the rotating block (7) and the groove (101) on the base (1) are connected and are located on the same horizontal plane, and a third force applying member (413) is detachably connected to the rotating block (7).

2. A laser line width compression device according to claim 1, characterized in that: The force applying mechanism comprises a first force applying member (411) and a second force applying member (412); the first force applying member (411), the second force applying member (412) and the base (1) are connected via a second bolt (9); and the third force applying member (413) and the rotating block (7) are connected via a second bolt (9); The adjustment assembly (3) comprises a handle (702) fixedly connected to both ends of the rotating block (7) and a second bolt (9) for loosening or tightening the first force applying member (411), the second force applying member (412) and the third force applying member (413). When the rotating block (7) rotates, the angle formed by the longitudinal axis of the rotating block (7) and the plane where the base (1) is located is in the range of 0° to 90°.

3. The laser line width compression device according to claim 1, characterized in that: The top of the base (1) is detachably connected to a plurality of columns (6), and the top of the columns (6) is detachably connected to a top plate (5); The force-applying mechanism (4) comprises a pressure plate (401) arranged parallel to the base (1), the pressure plate (401) being located between the top plate (5) and the base (1), the pressure plate (401) being sleeved with the column (6), and a stress block (402) for applying stress to the FP resonant cavity (2) being fixedly connected to the bottom of the pressure plate (401); The adjustment assembly (3) comprises a first bolt (301) threadedly connected to the top plate, the bottom of the first bolt (301) is fixedly connected to a spring (302), the bottom of the spring (302) is fixedly connected to a pressure block (303), the bottom of the pressure block (303) is rotatably connected to a ball (304), and a limiting groove for limiting the ball (304) is provided on the top of the pressure plate (401), and the ball (304) is located in the limiting groove.

4. The laser line width compression device according to claim 1, characterized in that: The force applying surface of the force applying mechanism (4) is parallel to the groove (101).

5. A laser line width compression device debugging system, characterized in that: A laser line width compression device comprising any one of claims 1 to 4, further comprising a spectrometer, a fiber laser, an input end polarization controller, an output end polarization controller and a polarization beam splitter, wherein the fiber laser, the input end polarization controller, the laser line width compression device, the output end polarization controller and the polarization beam splitter are connected in sequence, and the spectrometer is connected to the laser line width compression device to detect whether the laser line width compression device successfully generates SBL laser; After the laser emitted by the optical fiber laser is input into the input end polarization controller, the polarization direction is adjusted by the input end polarization controller and input into the laser line width compression device for line width compression to obtain pump laser and SBL laser. Finally, the pump laser and SBL laser output by the laser line width compression device are separated and output through the output end polarization controller and the polarization beam splitter.

6. A laser line width compression device debugging system according to claim 5, characterized in that: An amplifier and an isolator are arranged between the input end polarization controller and the laser line width compression device.

7. A debugging method for a laser line width compression device debugging system, characterized in that: The method comprises the laser line width compression device debugging system as claimed in claim 5, wherein the method comprises the following steps: Utilizing a fiber laser to output laser light, an input end polarization controller adjusts the polarization direction of the laser light output by the fiber laser so that the polarization direction of the laser light output by the fiber laser is consistent with the polarization direction of the longitudinal mode of the FP resonant cavity; Using a stress applying device to adjust the stress applied to the FP resonant cavity, so that two sets of longitudinal modes formed in the FP resonant cavity meet the oscillation conditions of the pump laser and the SBL laser respectively; According to the resonance frequency of any longitudinal mode polarization mode, adjusting the wavelength of the fiber laser to be close to the resonance frequency of any longitudinal mode polarization mode, and observing whether the SBL laser is successfully generated by a spectrometer; If SBL laser is not generated, the wavelength and output power of the fiber laser are further fine-tuned to meet the resonance conditions in the FP resonant cavity until SBL laser is generated; The output end polarization controller and the polarization beam splitter are adjusted to separate and output the pump laser and SBL laser generated by the FP resonant cavity.

8. The debugging method of a laser line width compression device debugging system according to claim 7, characterized in that: When the optical fiber laser outputs laser light, the optical fiber laser is in a wavelength scanning mode.

9. The debugging method of a laser line width compression device debugging system according to claim 7, characterized in that: The optical fiber laser, the input end polarization controller and the laser line width compression device are directly plugged in through a flange and a ceramic sleeve.

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