Method and system for manufacturing annular fiber bragg grating for high-order mode coupling fundamental mode

Abstract

The invention discloses an annular fiber grating manufacturing method and system for a high-order mode coupling fundamental mode, and the method comprises the steps: starting a femtosecond laser and corresponding equipment, and enabling the femtosecond laser and corresponding equipment to be in a standby state, so as to guarantee the stability of laser processing; a coating layer at the optical fiber processing position is stripped, the relative distance and height of the electric rotating clamps on the two sides are adjusted, so that the exposed part of the optical fiber is located between the electric rotating clamps on the two sides, and the horizontal and vertical positions of the electric displacement platform are adjusted; the grating period lambda, the rotating speed of the electric rotating clamp, the moving speed of the electric displacement platform, the interval time of opening and closing of the laser valve and the period number are preset on the computer; and executing a preset program, and forming annular fiber gratings periodically distributed along the fiber axis on the interface of the fiber core and the cladding. The annular fiber bragg grating inscribed by the method has circular symmetry performance, and the problem that mode coupling is influenced by random azimuth angles of a transverse mode field in a high-order mode influenced by non-uniform fiber refractive index distribution and external environment disturbance can be effectively avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of fiber grating preparation, and more specifically, relates to a method and system for preparing a ring-shaped fiber grating for high-order mode coupling fundamental mode. Background Art

[0002] Fiber Bragg grating is a diffraction-type passive device. It is widely used in fiber sensing, fiber communication, fiber laser and other fields due to its small size, simple structure, low insertion loss and easy matching with fiber systems. In fiber communication, the mode coupling characteristics of fiber Bragg grating can be used to achieve efficient coupling from the fundamental mode to the higher-order mode, thereby expanding the communication capacity; in fiber lasers, the mode coupling characteristics of fiber Bragg grating can be used to output lasers of different modes, thereby achieving the regulation of the output light field.

[0003] According to the size of the grating period, gratings can be divided into long-period gratings and Bragg gratings. Long-period fiber gratings are often used for mode coupling in optical fibers due to their advantages such as forward propagation, high mode coupling efficiency, and large mode conversion bandwidth.

[0004] There are many methods for making long-period fiber gratings, including chemical etching, arc discharge, mechanical extrusion, acoustic modulation, laser writing, etc. Among them, laser writing has the advantages of high repeatability, simple processing, and good grating effect, making it a more commonly used method.

[0005] The point-by-point method of a carbon dioxide laser is used to expose and write fiber gratings on a single side. Based on the high thermal absorption efficiency of the quartz material in the optical fiber for the 10.6-micron laser in the carbon dioxide band, the residual stress is released and the optical fiber geometric deformation is deformed. A periodic refractive index distribution is formed on the single-sided axis, which can break the orthogonality of the mode and achieve efficient coupling from the fundamental mode to the higher-order mode. The coupling from the fundamental mode to the fourth-order mode has been achieved. The line-by-line method of a femtosecond laser is used to write on a certain surface near the optical fiber core with high precision and asymmetry. Based on the multiphoton absorption effect, tunneling ionization, avalanche ionization and other effects, the grating structure can be formed with high repeatability to achieve coupling from the fundamental mode to the higher-order mode.

[0006] Whether it is mode demultiplexing in optical fiber communication or controlling beam quality in high-power lasers, there is a need to couple high-order modes into fundamental modes. Nowadays, spatial devices such as phase plates and spatial modulators are often used to couple high-order modes into fundamental modes. Because high-order modes in optical fibers are non-circularly symmetric and the azimuth angle of the transverse mode field is random, it is difficult to accurately align the grating modulation area of ​​the asymmetric structure to achieve coupling to the fundamental mode. Summary of the invention

[0007] In view of the above defects or improvement needs of the prior art, the present invention provides a method and system for manufacturing an annular fiber grating for coupling high-order modes to a fundamental mode. By using laser processing at the junction of the cladding and the core in the optical fiber, the refractive index of the optical fiber changes. The annular fiber grating has a refractive index change in 360 degrees in an angular direction, so that high-order modes at various azimuths can be coupled, the coupling efficiency is higher, the number of required grating periods is smaller, the grating length is shorter, and the area where the grating is designed is not located at the center of the core to reduce the loss. The annular fiber grating has circular symmetry and can effectively couple high-order modes at various azimuths on the cross section of the optical fiber into a fundamental mode, avoiding the problem that the lateral mode field azimuth angle is random due to uneven distribution of the refractive index of the optical fiber or high-order modes affected by external environmental disturbances, which affects the mode coupling. The annular grating is manufactured by adjusting the light emission time, duty cycle and rotation speed of the electric rotating clamp of the laser.

[0008] In order to achieve the above object, according to one aspect of the present invention, a method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode is provided, comprising the following steps:

[0009] S100: Turn on the femtosecond laser and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing;

[0010] S200: stripping the coating layer at the position where the optical fiber needs to be processed, adjusting the relative distance and height of the electric rotating clamps on both sides so that the exposed part of the optical fiber is in the middle of the electric rotating clamps on both sides, and adjusting the horizontal and vertical positions of the electric displacement platform;

[0011] S300: Preset the grating period Λ, the rotation speed of the electric rotating fixture, the moving speed of the electric displacement platform, the interval time of the laser valve switch and the number of cycles on the computer;

[0012] S400: Wear protective glasses and execute the preset program. After the optical fiber is processed by laser, turn off the femtosecond laser, and finally form a ring-shaped fiber grating distributed periodically along the fiber axis at the interface between the fiber core and the cladding. By using laser processing at the junction of the cladding and the core in the optical fiber, the refractive index of the optical fiber changes. The ring-shaped fiber grating has a refractive index change in 360 degrees, which is used to couple high-order modes at various angles.

[0013] Furthermore, step S200 specifically includes the following steps:

[0014] S210: Strip the coating layer of the optical fiber where it needs to be processed, and wipe the exposed part of the optical fiber with optical fiber paper dipped in alcohol;

[0015] S220: Place the optical fiber horizontally and gently in the groove of the electric rotating fixture, adjust the relative distance and height of the electric rotating fixtures on both sides, so that the exposed part of the optical fiber is in the middle of the electric rotating fixtures on both sides, and ensure that the distance between the electric rotating fixtures on both sides is greater than the length of the exposed part of the optical fiber. During the placement process, keep the optical fiber from bending and not affected by the stress of the hand;

[0016] S230: adjusting the horizontal position of the electric displacement platform so that the distance between the light emitting position of the femtosecond laser and the right side of the left electric rotating fixture is greater than the radius of the focusing spot;

[0017] S240: Adjust the height of the electric displacement platform relative to the femtosecond laser to ensure that the center of the focused light spot can be focused on the junction of the optical fiber core and the cladding;

[0018] S250: Select appropriate focusing lens and aperture to filter out stray light while making the focused spot size meet the design requirements.

[0019] Furthermore, the diameter of the focused light spot formed by the femtosecond laser is 4 to 10 microns, that is, the radius difference between the inner and outer circles of the annular fiber grating is 4 to 10 microns.

[0020] Furthermore, a groove which can be adjusted according to the size of the optical fiber is provided on the top of the electric rotating fixture, and the electric rotating fixture is slidably connected to the electric displacement platform.

[0021] Furthermore, the rotation speed and rotation direction of the electric rotating clamps on both sides are consistent.

[0022] Furthermore, the laser valve, the electric rotating fixture, and the electric displacement platform are all controlled by a computer.

[0023] Furthermore, the position of the laser emitted by the femtosecond laser itself is fixed, and the processing of different positions of the optical fiber is achieved by driving the optical fiber with an electric rotating fixture and an electric displacement platform.

[0024] Furthermore, the laser valve controls the start and stop of the laser output, and its start time is the same as the stop time of the electric displacement platform.

[0025] Furthermore, the grating period Λ is related to the optical fiber parameters and the coupled mode.

[0026] According to another aspect of the present invention, there is provided a ring-shaped fiber Bragg grating manufacturing system for high-order mode coupling fundamental mode, comprising:

[0027] Control module: Turn on the femtosecond laser and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing;

[0028] Adjustment module: strip the coating layer at the position where the optical fiber needs to be processed, adjust the relative distance and height of the electric rotating clamps on both sides, make the exposed part of the optical fiber in the middle of the electric rotating clamps on both sides, and adjust the horizontal and vertical positions of the electric displacement platform;

[0029] Parameter preset module: preset the grating period Λ, the rotation speed of the electric rotating fixture, the moving speed of the electric displacement platform, the interval time of the laser valve switch and the number of cycles on the computer;

[0030] Execution module: Wear protective glasses, execute the preset program, and finally form a ring-shaped fiber grating periodically distributed along the fiber axis at the interface between the fiber core and the cladding.

[0031] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0032] 1. The method for making an annular fiber grating of the present invention uses laser processing at the junction of the cladding and the core of the optical fiber to cause the refractive index of the optical fiber to change. The annular fiber grating has a refractive index change in 360 degrees, so it can couple high-order modes at various angles, and the coupling efficiency is higher. The engraved annular fiber grating has circular symmetry, which can effectively avoid the problem of random azimuth angle of the transverse mode field affecting mode coupling due to uneven distribution of the refractive index of the optical fiber or high-order modes affected by external environmental disturbances, and the polarization-related loss introduced by the asymmetric structure is relatively small.

[0033] 2. In the method for manufacturing annular fiber grating of the present invention, the engraved annular fiber grating deviates from the center of the fiber core, thereby reducing the loss of the core structure caused by laser processing.

[0034] 3. The ring-shaped fiber grating manufacturing method of the present invention has a refractive index change in 360 degrees of the angular direction, so it can couple high-order modes at all azimuth angles, with higher coupling efficiency, smaller number of required grating periods, and shorter grating length.

[0035] 4. The annular fiber grating manufacturing method of the present invention has the advantages of high precision and high repeatability through femtosecond laser processing, and can realize the coupling of high-order modes to fundamental modes for various fiber structures and mode orders. The combination of electric rotating clamps and electric displacement platforms can realize high-precision positioning and processing of optical fibers, ensure that the periodic structure of the grating is evenly distributed in the optical fiber, and improve production efficiency and processing quality. The actions of the laser, electric rotating clamp and electric displacement platform are controlled by a computer, which reduces the errors of human operation, improves the repeatability and stability of processing, and can adjust the laser focus, processing parameters and grating period according to specific needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The present invention is a flowchart of a method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to an embodiment of the present invention.

[0037] Figure 2 This is a flow chart of step S200 in a method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to an embodiment of the present invention;.

[0038] Figure 3 A schematic diagram of a ring-shaped fiber Bragg grating structure for high-order mode coupling fundamental mode according to an embodiment of the present invention;

[0039] Figure 4 The present invention is a schematic diagram of a ring-shaped fiber Bragg grating manufacturing device for high-order mode coupling fundamental mode according to an embodiment of the present invention.

[0040] In all the drawings, the same reference numerals represent the same technical features, specifically: 1-ring fiber Bragg grating, 2-cladding, 3-core, 4-coating, 5-femtosecond laser, 6-laser valve, 7-electric rotary clamp, 8-electric displacement platform, 9-computer. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0042] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0043] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] In this patent, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "includes..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0045] The invention provides a method and system for manufacturing an annular fiber grating for coupling a fundamental mode with a high-order mode. The method uses laser processing at the junction of the cladding and the core of the optical fiber to cause the refractive index of the optical fiber to change. The annular fiber grating has a refractive index change in 360 degrees of angular direction, so that high-order modes at various azimuth angles can be coupled, the coupling efficiency is higher, the number of required grating periods is smaller, the grating length is shorter, the area of ​​the designed grating is not located at the center of the fiber core to reduce the loss, the grating is designed to be an annular structure with circular symmetry, and the high-order modes at various azimuth angles on the plane can be effectively coupled into the fundamental mode, and the problem of random azimuth angle of the transverse mode field affecting the mode coupling due to uneven distribution of the refractive index of the optical fiber or high-order modes affected by external environmental disturbances is avoided. The manufacturing of the annular grating is completed by adjusting the light emission time and duty cycle of the laser and the rotation speed of an electric rotating clamp.

[0046] Embodiment 1:

[0047] like Figure 1-4 As shown, an embodiment of the present invention provides a method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode, which specifically includes the following steps:

[0048] S100: Turn on the femtosecond laser 5 and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing;

[0049] Before turning on the femtosecond laser 5, a safety check of the equipment should be carried out, including power connection, cooling system, laser path, etc., to ensure that all equipment is in normal working condition; after turning on the femtosecond laser 5, it needs to be preheated and run stably for a period of time (such as 20 minutes to 30 minutes) so that the equipment gradually reaches the working temperature and reduces the thermal shock when the equipment is started; during operation, the system is calibrated to ensure that the output power, wavelength and other parameters of the femtosecond laser 5 meet the processing requirements; monitor the laboratory environment, including temperature, humidity, dust, etc., to ensure that the environmental conditions are suitable for high-precision laser processing; the operator should be familiar with the operating procedures during the standby period and wear personal protective equipment such as protective clothing and protective glasses.

[0050] S200: stripping the coating layer 4 at the position where the optical fiber needs to be processed, adjusting the relative distance and height of the electric rotating clamps 7 on both sides so that the exposed part of the optical fiber is in the middle of the electric rotating clamps 7 on both sides, and adjusting the horizontal and vertical positions of the electric displacement platform 8;

[0051] Use a special fiber stripping tool to carefully strip the fiber coating 4 to avoid damaging the fiber; after stripping the coating 4, use a dust-free cloth and alcohol to clean the fiber surface to ensure that there is no residue; adjust the relative distance and height of the electric rotating clamp 7 to ensure that the exposed part of the fiber is located in the middle of the clamp and the distance between the clamps on both sides is greater than the length of the exposed part of the fiber; gently place the fiber in the groove of the electric rotating clamp 7 to ensure that the fiber is not bent or stressed during placement; after the adjustment is completed, lock the electric rotating clamp 7 to ensure that the fiber position is stable during laser processing.

[0052] S300: Preset the grating period Λ, the rotation speed of the electric rotating fixture 7, the moving speed of the electric displacement platform 8, the interval time and the number of cycles of the laser valve 6 on and off on the computer 9;

[0053] Input parameters such as the grating period Λ, the rotation speed of the electric rotating fixture 7, and the moving speed of the electric displacement platform 8 on the computer 9 according to the application requirements; set the switching interval time and the number of cycles of the laser valve 6 to control the laser pulse sequence, and use the simulation software to preview the laser processing process to ensure that the parameter settings are reasonable. According to the simulation results, fine-tune the parameters to obtain the best grating formation effect, and back up the preset parameters so that they can be quickly restored when problems occur during the processing.

[0054] S400: Wear protective glasses and execute the preset program. After the optical fiber is processed by laser, turn off the femtosecond laser 5, and finally form a ring-shaped fiber grating 1 distributed periodically along the optical fiber axis at the interface between the optical fiber core and the cladding. By using laser processing at the junction of the cladding 2 and the core 3 in the optical fiber, the refractive index of the optical fiber changes. The ring-shaped fiber grating 1 has a refractive index change in 360 degrees, which is used to couple high-order modes at various angles.

[0055] Before executing the procedure, ensure that all operators have worn protective glasses to prevent laser radiation and other potential hazards, start the preset laser processing program, monitor the operating status of the femtosecond laser 5, and closely monitor the operating status of the equipment and the processing of the optical fiber during the laser processing, promptly detect and handle any abnormal situation to ensure the processing quality. When the program is completed, after the optical fiber is laser processed, a ring-shaped fiber grating 1 periodically distributed along the optical fiber axis will be formed at the interface between the core 3 and the cladding 2. At this time, the femtosecond laser 5 should be immediately turned off according to the operating procedures to avoid unnecessary energy consumption and potential risks. After the optical fiber is laser processed, check whether the periodic distribution of the fiber grating meets the design requirements. After confirming that the fiber grating processing is completed, the equipment should be maintained and cleaned daily.

[0056] like Figure 2 As shown, step S200 specifically includes the following steps:

[0057] S210: stripping the coating layer 4 at the position where the optical fiber needs to be processed, and wiping the exposed part of the optical fiber dry with optical fiber paper dipped in alcohol;

[0058] Use a dedicated fiber optic stripping pliers or chemical stripping solution to carefully strip the fiber coating 4, avoiding damage to the glass part of the fiber. Use fiber optic paper to dip an appropriate amount of alcohol and gently wipe the exposed part of the fiber to remove debris and residue that may be generated during the stripping process. After wiping, use clean fiber optic paper or dust-free cloth to gently dry the fiber to ensure that the surface of the fiber is completely dry and free of alcohol residue. After stripping and cleaning, check whether the fiber is damaged, such as scratches, cracks, etc., to ensure that the fiber is intact, and mark the position that needs to be processed on the fiber to ensure processing accuracy and position accuracy.

[0059] S220: Place the optical fiber horizontally and gently in the groove of the electric rotating clamp 7, adjust the relative distance and height of the electric rotating clamps 7 on both sides, so that the exposed part of the optical fiber is in the middle of the electric rotating clamps 7 on both sides, ensure that the distance between the electric rotating clamps 7 on both sides is greater than the length of the exposed part of the optical fiber, and keep the optical fiber from bending during the placement process and not affected by the stress of the hand;

[0060] Place the optical fiber horizontally and gently in the grooves of the electric rotating clamps 7 on both sides, ensuring that the optical fiber is in good contact with the electric rotating clamps 7 without sliding, adjust the relative distance and height of the electric rotating clamps 7 on both sides, so that the exposed part of the optical fiber is in the middle of the electric rotating clamps 7 on both sides, and ensure that the distance between the electric rotating clamps 7 on both sides is greater than the length of the exposed part of the optical fiber. During the adjustment process, avoid applying excessive force to the optical fiber to avoid bending or damage to the optical fiber. After the adjustment is completed, use the fixing device on the electric rotating clamp 7 to ensure that the optical fiber will not move or rotate during the processing. After fixing, check the optical fiber position again to ensure that it is accurate, and record the adjustment parameters for subsequent repeated operations.

[0061] S230: adjusting the horizontal position of the electric displacement platform 8 so that the distance between the light emitting position of the femtosecond laser 5 and the right side of the left electric rotating fixture 7 is greater than the radius of the focused light spot;

[0062] According to the requirements of laser processing, plan the laser path to ensure that the laser can accurately irradiate the optical fiber processing position, adjust the horizontal position of the electric displacement platform 8, make the distance between the light output position of the femtosecond laser and the right side of the left electric rotating fixture larger than the radius of the focused spot, and after adjustment, perform a spot test to ensure that the position and size of the focused spot meet the processing requirements. According to the test results, make fine adjustments to optimize the laser path to ensure the accuracy and efficiency of laser processing, and record the adjusted position parameters of the electric displacement platform 8 so that they can be quickly restored during subsequent repeated operations.

[0063] S240: adjusting the height of the electric displacement platform 8 relative to the femtosecond laser 5 to ensure that the center of the focused light spot can be focused on the junction of the optical fiber core 3 and the cladding 2;

[0064] Adjust the height of the electric displacement platform 8 relative to the femtosecond laser 5 to ensure that the center of the focused light spot can be accurately focused on the junction of the optical fiber core 3 and the cladding 2, and ensure that the focused light spot is accurately focused on the desired position, and then lock the height setting of the electric displacement platform 8 to ensure that it will not change during the processing.

[0065] S250: Select appropriate focusing lens and aperture to filter out stray light while making the focused spot size meet the design requirements.

[0066] According to the wavelength of the laser and the parameters of the optical fiber, select the appropriate focusing lens to obtain the best focusing effect, select the appropriate aperture to filter out stray light, and control the size of the focused spot to meet the design requirements. Adjust the position of the focusing lens and aperture until the size and shape of the focused spot fully meet the processing requirements. Integrate the focusing lens and aperture into the laser processing system to ensure the stability and repeatability of the system.

[0067] Furthermore, the diameter of the focused light spot formed by the femtosecond laser 5 is 4 to 10 microns, that is, the difference in radius between the inner and outer circles of the annular fiber grating 1 is 4 to 10 microns. The diameter of the focused light spot directly affects the difference in radius between the inner and outer circles of the annular fiber grating, that is, the grating period Λ. According to the Bragg condition of the fiber grating, the grating period is related to the laser wavelength, the fiber refractive index and the grating reflection wavelength. It is necessary to accurately control the beam quality of the femtosecond laser 5, including the mode and coherence of the beam. By adjusting the focusing lens and the aperture, the spot size can be optimized to meet the design requirements and stray light can be filtered out. The top of the electric rotating fixture 7 is provided with a groove that can be adjusted according to the size of the optical fiber. The groove design of the electric rotating fixture 7 needs to take into account the adaptation of optical fibers of different diameters. Through mechanical structure or fine adjustment The mechanism realizes the versatility of the electric rotary clamp 7. After adjustment, the electric rotary clamp 7 needs to ensure the stability of the optical fiber during the rotation process to avoid processing errors caused by sliding or shifting of the optical fiber, thereby increasing the versatility and flexibility of the electric rotary clamp 7 and reducing the need to customize clamps for different optical fiber diameters; the electric rotary clamp 7 is slidably connected to the electric displacement platform 8, allowing the electric rotary clamp 7 to be quickly adjusted on the electric displacement platform 8 so that it can adapt to different optical fiber lengths required for processing; the sliding connection design between the electric rotary clamp 7 and the electric displacement platform 8 needs to ensure rapid adjustment and precise positioning to meet the processing requirements of optical fibers of different lengths, and the connection mechanism needs to have sufficient structural strength and rigidity to maintain stability and precision during high-speed rotation or movement.

[0068] Furthermore, the rotation speed and rotation direction of the electric rotating clamps 7 on both sides are consistent, requiring precise synchronous control technology to ensure that the optical fiber is evenly stressed during processing, and an error compensation mechanism is designed to address the problem of uneven rotation speed caused by machining errors or material differences.

[0069] Furthermore, the laser valve 6, the electric rotating fixture 7, and the electric displacement platform 8 are all controlled by a computer 9. The computer 9 can control the laser valve, the electric rotating fixture, and the electric displacement platform to achieve accurate grating period Λ and structure production, improve the consistency and repeatability of the fiber grating, and the entire production process is controlled by a computer, which reduces manual operation, improves production efficiency and processing accuracy, and develops automated programming software to simplify the operating process and improve production efficiency and processing accuracy.

[0070] Furthermore, the position of the laser emitted by the femtosecond laser 5 itself is fixed, and the processing of different positions of the optical fiber is achieved by the electric rotating fixture 7 and the electric displacement platform 8 driving the optical fiber, ensuring that the position of the laser emitted by the femtosecond laser 5 is fixed, and the stability and repeatability of the femtosecond laser 5 are extremely high, so as to ensure the processing quality of different positions of the optical fiber, optimize the laser path, reduce the optical elements in the optical path, and improve the laser transmission efficiency and processing accuracy. The laser valve 6 controls the opening and stopping of the laser output, and its opening time is the same as the stopping time of the electric displacement platform 8; the opening time of the laser valve 6 needs to be precisely synchronized with the stopping time of the electric displacement platform 8 to ensure the accuracy of the grating period Λ, and establish a feedback control system to adjust the opening and closing of the laser valve in real time to cope with any deviations in the processing process.

[0071] Furthermore, the grating period Λ is related to the fiber parameters and the coupled mode. The grating period is one of the important parameters of the grating structure, which directly determines the characteristics of the grating such as the reflection wavelength and bandwidth. By accurately controlling the grating period, the coupling efficiency between the high-order mode and the fundamental mode can be optimized. At the same time, the selection of the grating period also needs to consider the fiber parameters and the coupling mode requirements to ensure that the performance of the grating meets the design requirements.

[0072] Embodiment 2:

[0073] Based on Example 1, the present invention provides a ring-shaped fiber Bragg grating manufacturing system for high-order mode coupling fundamental mode, comprising:

[0074] Control module: turn on the femtosecond laser 5 and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing;

[0075] Adjustment module: strip the coating layer 4 at the position where the optical fiber needs to be processed, adjust the relative distance and height of the electric rotating clamps 7 on both sides, so that the exposed part of the optical fiber is in the middle of the electric rotating clamps 7 on both sides, and adjust the horizontal and vertical positions of the electric displacement platform 8;

[0076] Parameter preset module: preset the grating period Λ, the rotation speed of the electric rotating fixture 7, the moving speed of the electric displacement platform 8, the interval time and the number of cycles of the laser valve 6 on and off on the computer 9;

[0077] Execution module: Wear protective glasses and execute the preset program. Finally, a ring-shaped fiber grating 1 periodically distributed along the fiber axis is formed at the interface between the fiber core and the cladding. Laser processing is used at the junction of the cladding 2 and the core 3 in the fiber to cause the refractive index of the fiber to change. The ring-shaped fiber grating 1 has a refractive index change in 360 degrees, which is used to couple high-order modes at various angles.

[0078] Embodiment 3:

[0079] like Figure 1-4 As shown, this embodiment of the present invention provides a method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode, and the specific steps include:

[0080] S100: Turn on the femtosecond laser 5 and corresponding equipment, and wait for 20 minutes to ensure the stability of subsequent laser processing;

[0081] S210: Strip the coating layer 4 at the position to be processed within 50 mm of the optical fiber, and wipe the exposed part of the optical fiber with optical fiber paper dipped in alcohol;

[0082] S220: Place the optical fiber horizontally and gently in the groove of the electric rotating clamp 7, adjust the relative distance and height of the electric rotating clamps 7 on both sides, so that the exposed part of the optical fiber is in the middle of the electric rotating clamps 7 on both sides, ensure that the distance between the electric rotating clamps 7 on both sides is greater than the length of the exposed part of the optical fiber, and keep the optical fiber from bending during the placement process and not affected by the stress of the hand;

[0083] S230: Adjust the horizontal position of the electric displacement platform 8 so that the distance between the light emitting position of the femtosecond laser 5 and the right side of the left electric rotating fixture 7 is 10 mm;

[0084] S240: adjusting the height of the electric displacement platform 8 relative to the femtosecond laser 5 to ensure that the center of the focused light spot can be focused on the junction of the optical fiber core 3 and the cladding 2;

[0085] S250: Select the appropriate focusing lens and aperture to filter out stray light while making the focused spot size 4 microns.

[0086] S300: On the computer, set the grating period Λ to 1mm, the electric rotating clamps 7 on both sides rotate in the clockwise direction, and the rotation speed is 2 radians per second. It takes π seconds for the electric rotating clamp 7 to rotate 360 ​​degrees. The initial speed of the electric displacement platform 8 is set to 0. After π seconds, the electric displacement platform 8 is set to move to the left at a speed of 200 microns per second to the next position to be engraved. The laser valve 2 is initially in the open state, the switch interval is set to 5 seconds, and the number of cycles is set to 30.

[0087] S400: Wear protective glasses and execute the preset program. After 30 cycles of laser processing, turn off laser 1, and finally form a ring-shaped fiber grating with a width of 4 microns and periodically distributed along the fiber axis at the interface between the fiber core and the cladding. The grating period is 1000 microns and the number of periods is 30.

[0088] The invention discloses a method for manufacturing an annular fiber grating for coupling a fundamental mode with a high-order mode. By precisely controlling the laser processing process, the effective coupling of the high-order mode with the fundamental mode is achieved, and the coupling efficiency of the grating is improved. The method can reduce the influence of uneven distribution of the optical fiber refractive index or external environmental disturbance on the high-order mode, and enhance the stability and reliability of the grating. By controlling the laser, the electric rotating fixture and the electric displacement platform by a computer, the accurate grating period and structure manufacturing is achieved, and the consistency and repeatability of the grating are improved. The entire manufacturing process is controlled by a computer, which reduces manual operation and improves production efficiency and processing accuracy. The grating with an annular structure has better structural stability and anti-interference ability than the traditional linear grating. By adjusting the laser processing parameters, such as the spot size, the rotation speed, the moving distance, etc., the gratings with different parameters can be flexibly manufactured to meet different application requirements. The automated and precise processing process reduces material waste and production costs, and improves economic benefits. The annular fiber grating can be applied to a variety of optical fiber communications, sensing and laser technology fields, and has broad market application prospects.

[0089] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode, characterized in that: The steps include: S100: Turn on the femtosecond laser (5) and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing; S200: stripping off the coating layer (4) at the position where the optical fiber needs to be processed, adjusting the relative distance and height of the electric rotating clamps (7) on both sides so that the exposed part of the optical fiber is located between the electric rotating clamps (7) on both sides, and adjusting the horizontal and vertical positions of the electric displacement platform (8); S300: Preset the grating period Λ, the rotation speed of the electric rotating fixture (7), the moving speed of the electric displacement platform (8), the interval time of the laser valve (6) switch and the number of cycles on the computer (9); S400: Wear protective glasses and execute the preset program. After the optical fiber is processed by laser, turn off the femtosecond laser (5), and finally form a ring-shaped fiber grating (1) distributed periodically along the optical fiber axis at the interface between the optical fiber core and the cladding. By using laser processing at the junction of the cladding (2) and the core (3) in the optical fiber, the refractive index of the optical fiber changes. The ring-shaped fiber grating (1) has a refractive index change in 360 degrees, which is used to couple high-order modes at various angles.

2. The method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to claim 1, characterized in that: Step S200 specifically includes the following steps: S210: stripping off the coating layer (4) at the position where the optical fiber needs to be processed, and wiping the exposed part of the optical fiber dry with optical fiber paper dipped in alcohol; S220: Place the optical fiber horizontally and gently in the groove of the electric rotating clamp (7), adjust the relative distance and height of the electric rotating clamps (7) on both sides, so that the exposed part of the optical fiber is located between the electric rotating clamps (7) on both sides, ensure that the distance between the electric rotating clamps (7) on both sides is greater than the length of the exposed part of the optical fiber, and keep the optical fiber from bending during the placement process and not being affected by the stress of the hand; S230: adjusting the horizontal position of the electric displacement platform (8) so that the distance between the light output position of the femtosecond laser (5) and the right side of the left electric rotating fixture (7) is greater than the radius of the focused light spot; S240: adjusting the height of the electric displacement platform (8) relative to the femtosecond laser (5) to ensure that the center of the focused light spot can be focused on the junction of the optical fiber core (3) and the cladding (2); S250: Select appropriate focusing lens and aperture to filter out stray light while making the focused spot size meet the design requirements.

3. The method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to claim 2, characterized in that: The diameter of the focused light spot formed by the femtosecond laser (5) is 4 to 10 microns, that is, the difference in radius between the inner and outer circles of the annular fiber grating (1) is 4 to 10 microns.

4. The method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to claim 2, characterized in that: The top of the electric rotating clamp (7) is provided with a groove that can be adjusted according to the size of the optical fiber, and the electric rotating clamp (7) is slidably connected to the electric displacement platform (8).

5. The method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to claim 4, characterized in that: The rotation speed and rotation direction of the electric rotating clamps (7) on both sides are consistent.

6. A method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to any one of claims 1 to 5, characterized in that: The laser valve (6), the electric rotating fixture (7) and the electric displacement platform (8) are all controlled by a computer (9).

7. A method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to any one of claims 1 to 5, characterized in that: The position of the laser light emitted by the femtosecond laser (5) itself remains fixed, and the processing of different positions of the optical fiber is achieved by driving the optical fiber with the electric rotating fixture (7) and the electric displacement platform (8).

8. A method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to any one of claims 1 to 5, characterized in that: The laser valve (6) controls the start and stop of laser output, and its start time is the same as the stop time of the electric displacement platform (8).

9. A method for manufacturing a ring-shaped fiber Bragg grating for high-order mode coupling fundamental mode according to any one of claims 1 to 5, characterized in that: The grating period Λ is related to the fiber parameters and the coupled mode.

10. A ring-shaped fiber Bragg grating manufacturing system for high-order mode coupling fundamental mode, characterized in that: The application implements a method for manufacturing a ring-shaped fiber Bragg grating for a high-order mode coupling fundamental mode as described in any one of claims 1 to 9, comprising: Control module: Turn on the femtosecond laser (5) and corresponding equipment, and wait for a certain period of time to ensure the stability of subsequent laser processing; Adjustment module: stripping the coating layer (4) at the position where the optical fiber needs to be processed, adjusting the relative distance and height of the electric rotating clamps (7) on both sides so that the exposed part of the optical fiber is located between the electric rotating clamps (7) on both sides, and adjusting the horizontal and vertical positions of the electric displacement platform (8); Parameter preset module: preset the grating period Λ, the rotation speed of the electric rotating fixture, the moving speed of the electric displacement platform, the interval time of the laser valve switch and the number of cycles on the computer (9); Execution module: Wear protective glasses and execute the preset program, and finally form a ring-shaped fiber grating (1) distributed periodically along the fiber axis at the interface between the fiber core and the cladding. By using laser processing at the junction of the cladding (2) and the core (3) in the fiber, the refractive index of the fiber changes. The ring-shaped fiber grating (1) has a refractive index change in 360 degrees, which is used to couple high-order modes at various angles.

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