Fiber grating and preparation method and application thereof

Abstract

The invention discloses a fiber grating and a preparation method and application thereof, and belongs to the field of gratings. The preparation method of the fiber grating comprises the following steps: providing an optical fiber, wherein the optical fiber comprises a fiber core, a cladding layer and a first coating layer which are sequentially arranged from inside to outside along the radial direction of the optical fiber; removing the first coating layer on the optical fiber; synchronously etching a high-low reflective grating and a Raman grating on the fiber core; the periphery of the cladding corresponding to the high-low reflection grating is coated with a second coating layer, and the periphery of the cladding corresponding to the Raman grating is sleeved with a glass tube. According to the method, the high-low reflective grating and the Raman grating can be synchronously etched on the fiber core, the functional requirements of different gratings are met through a differentiated packaging process, and the quality and stability of the fiber grating are improved.

Description

Technical Field

[0001] The present application relates to a fiber grating and a preparation method and application thereof, belonging to the field of gratings. Background Art

[0002] In the field of industrial processing and cutting, high-power fiber lasers generally need to transmit lasers through long-distance armored cables. However, long armored cables will cause the generation of Raman signals, and stimulated Raman scattering (SRS) will lead to power loss, beam quality degradation and spectral broadening, which seriously affects the cutting effect. The use of Raman tilted gratings can directly filter out non-signal wavelengths at the output end, improve the cutting penetration of highly reflective materials (such as copper and aluminum), ensure remote cutting accuracy, and also improve the life and stability of the laser. At the same time, as the core component of the resonant cavity, the high-low reflection grating (HR / LR FBG) needs to achieve high stability and high reflectivity (HR>99.5%, LR<10%), replacing the traditional dielectric mode mirror to simplify the optical path structure.

[0003] However, the existing production process, which integrates high- and low-reflectivity gratings with Raman gratings, has significant drawbacks. This approach first inscribes the high- and low-reflectivity gratings, then uses a Raman mask to continue inscribing the Raman grating on the fiber already inscribed with the high- and low-reflectivity gratings. However, the time lag between mask switching causes hydrogen loss in the fiber to be inscribed, reducing its photosensitivity. This, in turn, results in insufficient reflectivity for the inscribed grating, severely impacting inscription quality and even leading to inscription failure.

[0004] In addition, high and low reflectivity gratings will have their performance degraded due to external factors such as temperature and humidity changes, mechanical wear, and dust contamination, so they need to be coated and packaged. Since the function of the tilted Raman grating is to destroy the oscillation conditions of non-signal light in the optical fiber and leak the non-signal light through the cladding, the tilted Raman grating does not require coating.

[0005] Therefore, how to realize the integrated preparation of tilted Raman grating and high and low reflection grating on the same optical fiber and improve the quality and stability of multifunctional fiber Bragg grating has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In order to solve the above problems, a fiber Bragg grating and its preparation method and application are provided, which can simultaneously etch high- and low-reflection gratings and Raman gratings on the fiber core, and meet the functional requirements of different gratings through differentiated packaging processes, thereby improving the quality and stability of the fiber Bragg grating.

[0007] The present invention provides the following technical solutions:

[0008] According to one aspect of the present application, a method for preparing a fiber Bragg grating is provided, comprising: providing an optical fiber, wherein the optical fiber comprises a core, a cladding, and a first coating layer arranged in sequence from the inside to the outside along the radial direction of the optical fiber;

[0009] removing the first coating layer on the optical fiber;

[0010] Synchronously etching high and low reflection gratings and Raman gratings on the fiber core;

[0011] A second coating layer is coated on the periphery of the cladding corresponding to the high and low reflection gratings, and a glass tube is set on the periphery of the cladding corresponding to the Raman grating.

[0012] Optionally, the specific steps of etching high and low reflection gratings and Raman gratings on the fiber core include:

[0013] The mask plate and cylindrical mirror are fixed and the ultraviolet laser is scanned at different positions of the mask plate by moving the translation stage to achieve the writing of high and low reflection gratings and Raman gratings.

[0014] Optionally, when writing the high-reflection grating, the laser power is 60-120 mW;

[0015] When writing the low-reflection grating, the laser power is 30-50 mW;

[0016] When writing the Raman grating, the laser power is 30-100 mW.

[0017] Optionally, the specific steps of coating a second coating layer on the periphery of the cladding corresponding to the high-low reflection grating include:

[0018] Coating a low-reflection adhesive on the outer periphery of the cladding corresponding to the high-low-reflection grating, and curing the low-reflection adhesive to form a second coating layer;

[0019] The specific steps of installing a glass tube on the periphery of the cladding corresponding to the Raman grating include:

[0020] The glass tube is placed on the periphery of the cladding corresponding to the Raman grating, and glue is applied on both sides to fix the glass tube.

[0021] Optionally, the specific steps of removing the first coating layer on the optical fiber include:

[0022] The first coating layer on the optical fiber is stripped by a stripping machine, so that the transition area between the stripped end and the cladding is smooth, burr-free and free of residual debris.

[0023] Optionally, after etching the high and low reflection gratings and the Raman grating on the fiber core, a heat treatment step is further included:

[0024] The fiber Bragg grating is treated in a high temperature environment of 400-500° C. for 1-2 minutes.

[0025] Optionally, the fiber core diameter is 20 μm, the cladding diameter is 400 μm, and the fiber core numerical aperture is 0.065.

[0026] Optionally, the etching system used includes:

[0027] An ultraviolet light source, used to provide ultraviolet laser required for etching;

[0028] The aperture is set in the light path of the ultraviolet light source and is used to adjust the size and shape of the ultraviolet laser beam;

[0029] The UV reflector, fixed together with the aperture on the translation stage, is used to change the propagation direction of the UV laser to ensure that the beam can be vertically irradiated onto the mask during the movement of the translation stage;

[0030] A translation stage is used to carry and move the UV reflector and the aperture to adjust the irradiation position of the UV laser on the mask;

[0031] The cylindrical mirror is arranged below the translation stage and is used to focus the ultraviolet laser so that the ultraviolet laser is focused in the core of the optical fiber;

[0032] The mask is arranged below the cylindrical mirror and is used to diffract the ultraviolet laser, wherein the n-th order diffracted beam and the -n-th order diffracted beam overlap and generate interference fringes in the overlapping area;

[0033] The optical fiber is placed close to the bottom of the mask and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core;

[0034] Wherein, the mask comprises:

[0035] a quartz glass substrate;

[0036] A Bragg grating (FBG) mask unit and a Raman tilted fiber Bragg grating (TFBG) mask unit integrated on a quartz glass substrate, wherein the Bragg grating (FBG) mask unit and the Raman tilted fiber Bragg grating (TFBG) mask unit are arranged in a left-right structure on the quartz glass substrate;

[0037] An intermediate non-fringe area is provided between the Bragg grating (FBG) mask unit and the Raman tilted fiber Bragg grating (TFBG) mask unit, and a length l of the intermediate non-fringe area satisfies 20 mm ≤ l ≤ 40 mm;

[0038] The stripes of the Raman tilted fiber Bragg grating (TFBG) mask unit have an angle θ relative to the substrate plane, which satisfies 3°≤θ≤5°.

[0039] According to another aspect of the present application, a fiber Bragg grating (FBG) is provided, which is prepared by any of the above-mentioned methods for preparing a fiber Bragg grating, and the fiber Bragg grating comprises:

[0040] The core and cladding are arranged in sequence from inside to outside along the radial direction of the fiber grating;

[0041] The fiber core is provided with high and low reflection gratings and Raman gratings. A second coating layer is provided on the periphery of the cladding corresponding to the high and low reflection gratings. A glass tube is provided on the periphery of the cladding corresponding to the Raman grating.

[0042] According to another aspect of the present application, there is provided an application of the fiber Bragg grating as described above in a laser.

[0043] The beneficial effects of this application include but are not limited to:

[0044] 1. The fiber Bragg grating (FBG) of the present application, its preparation method, and application can simultaneously etch high- and low-reflection gratings and Raman gratings on the fiber core without switching masks during writing, thereby simplifying the operating process, reducing the risk of product defects caused by human errors, improving production stability and reliability, achieving continuity in writing of the two gratings, avoiding deterioration of photosensitivity due to time difference, ensuring a stable photosensitivity state of the optical fiber, improving writing quality and efficiency, shortening the production cycle, and enhancing the company's production capacity and competitiveness.

[0045] 2. The fiber Bragg grating (FBG) of the present application, its preparation method, and application, after being written, the tilted Raman grating is encapsulated by a glass tube, which not only ensures the efficient leakage of non-signal light, but also provides basic mechanical protection through the glass tube, avoiding the problem of fragility of bare optical fiber; the high and low reflective gratings are encapsulated by a coating layer, effectively isolating them from humidity, dust, and mechanical friction, significantly improving the environmental stability of the grating; through partitioned protection, the problem of limited Raman grating function or easy aging of high and low reflective gratings in traditional single coating processes is avoided, thereby improving the service life of the fiber Bragg grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0047] Figure 1 This is a schematic diagram of the complete low-reflection grating and Raman grating integrated device for this application.

[0048] Figure 2 This is a schematic structural diagram of an illustrative embodiment of the etching system of the present application.

[0049] Figure 3 This is a schematic structural diagram of an exemplary embodiment of the mask of this application.

[0050] Figure 4 This is a schematic diagram of the dimensions of a mask of the present application.

[0051] Figure 5 Schematic diagram of the laser structure.

[0052] Description of labels:

[0053] 1. UV light source; 2. Aperture a; 3. UV reflector; 4. Translation stage; 5. Aperture b; 6. Cylindrical mirror; 7. Mask; 8. Optical fiber; 9. Ordinary high- and low-reflection grating stripes; 10. Quartz glass substrate; 11. Tilted Raman fiber stripes; 12. Low-reflection grating a; 13. Low-fold adhesive; 14. Glass tube; 15. Non-signal light; 16. Raman grating a; 17. High-reflection grating; 18. Low-reflection grating b; 19. Fusion point; 20. Raman grating b. DETAILED DESCRIPTION

[0054] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0055] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or those recommended by the manufacturer. The raw materials or instruments used, if the manufacturers are not specified, are all conventional products that can be purchased commercially.

[0056] The embodiment of the present application provides a method for preparing a fiber Bragg grating, comprising: providing an optical fiber, wherein the optical fiber comprises a core, a cladding, and a first coating layer arranged in sequence from the inside to the outside along the radial direction of the optical fiber;

[0057] Specifically, light is transmitted in the fiber core, and the cladding provides a reflection surface for the transmission of light, and the cladding can also play a role in mechanical protection; the first coating layer is wrapped around the outside of the cladding to protect the fiber core and the cladding.

[0058] The fiber model provided in this embodiment is Nufern's LMA-GDF-20 / 400-HP double-clad fiber, with a core diameter of 20μm, a cladding diameter of 400μm, and a core numerical aperture (NA) of 0.065. The large mode area and low numerical aperture (NA) design effectively suppresses mode instability and nonlinear effects, outputting high-quality laser light, and resolving the conflict between power and beam quality.

[0059] removing the first coating layer on the optical fiber;

[0060] Specifically, the first coating layer on the optical fiber is stripped by a stripping machine, so that the transition area between the stripped end and the cladding is smooth and free of burrs and residual debris.

[0061] After removing the first coating layer on the optical fiber, the surface of the cladding is cleaned and dried to ensure that the moisture is completely evaporated.

[0062] Synchronously etching high and low reflection gratings and Raman gratings on the fiber core;

[0063] Specifically, the mask plate and the cylindrical mirror are fixed, and the ultraviolet laser is scanned at different positions of the mask plate by moving the translation stage to achieve the writing of high and low reflection gratings and Raman gratings.

[0064] When writing the high-reflection grating, the laser power is 60-120 mW;

[0065] When writing the low-reflection grating, the laser power is 30-50 mW;

[0066] When writing the Raman grating, the laser power is 30-100 mW.

[0067] By selecting appropriate laser power, local heat accumulation in the optical fiber can be avoided to exceed the melting point of the optical fiber, which may lead to ablation, microcracks or even breakage of the core or cladding surface.

[0068] Coating a second coating layer on the periphery of the cladding corresponding to the high and low reflection gratings, and inserting a glass tube on the periphery of the cladding corresponding to the Raman gratings;

[0069] Specifically, a low-reflection glue is coated on the periphery of the cladding corresponding to the high-low reflection grating, and the low-reflection glue is cured to form a second coating layer; a glass tube is sleeved on the periphery of the cladding corresponding to the Raman grating, and the glass tube is fixed by glue on both sides to provide better protection for the cladding.

[0070] The glues mentioned above are all low-refractive index glues, namely DF-0016 from FOCENTER of the United States. This low-refractive index glue has an ultra-low refractive index (1.37) and high transparency, forming a better optical match with the optical fiber core, which can significantly reduce the scattering loss of the optical signal at the coating interface and improve the laser transmission efficiency.

[0071] The curing methods mentioned above are thermal curing or UV curing, both of which are conventional process. The curing parameters can be selected according to actual needs and will not be described in detail here.

[0072] After etching the high and low reflection gratings and the Raman grating on the fiber core, a heat treatment step is also included:

[0073] The fiber Bragg grating is treated in a high temperature environment of 400-500° C. for 1-2 minutes.

[0074] Ultraviolet writing will cause micro-stress in the fiber core. Annealing releases the stress by locally heating the grating area at high temperature to rearrange the atoms, making the refractive index modulation more stable, the grating performance more stable, and the life longer.

[0075] After writing, unstable chemical structures such as Ge-OH and Ge-H bonds in the fiber core can cause refractive index drift, interfering with the Bragg wavelength stability of the grating, leading to problems such as short lifetime and severe grating heat generation. Therefore, before grating writing, the fiber needs to be hydrogenated. The fiber is placed in a high-pressure hydrogen environment of 10-20MPa to allow hydrogen molecules to penetrate the fiber core and combine with germanium (Ge) defects to form photosensitive centers, thereby improving the refractive index modulation efficiency of UV writing. The dehydrogenation temperature is 100-200°C and the time is 7-15 days.

[0076] Figure 1 This is a schematic diagram of a complete integrated device consisting of a low-reflection grating a12 and a Raman grating a16. Before writing the grating, the optical fiber needs to be stripped of its coating. After writing, the tilted Raman grating does not require coating and only requires casing, as the tilted Raman grating's function is to destroy the oscillation conditions of non-signal light in the optical fiber and leak the non-signal light 15 out through the cladding. However, the low-reflection grating will experience degradation in grating performance due to external factors such as temperature and humidity changes, mechanical wear, and dust contamination, so it requires coating and packaging. That is, the low-reflection grating on the left is coated with low-refractive glue 13, and the Raman grating on the right is protected by a glass tube 14, with glue applied to both sides to secure the glass tube.

[0077] See also Figure 2 The embodiment of the present application further provides an etching system, through which the above-mentioned fiber Bragg grating is prepared, and the etching system includes:

[0078] An ultraviolet light source, used to provide ultraviolet laser required for etching;

[0079] The aperture is set in the light path of the ultraviolet light source and is used to adjust the size and shape of the ultraviolet laser beam;

[0080] The UV reflector, fixed together with the aperture on the translation stage, is used to change the propagation direction of the UV laser to ensure that the beam can be vertically irradiated onto the mask during the movement of the translation stage;

[0081] A translation stage is used to carry and move the UV reflector and the aperture to adjust the irradiation position of the UV laser on the mask;

[0082] The cylindrical mirror is arranged below the translation stage and is used to focus the ultraviolet laser so that the ultraviolet laser is focused in the core of the optical fiber;

[0083] The mask is arranged below the cylindrical mirror and is used to diffract the ultraviolet laser, wherein the n-th order diffracted beam and the -n-th order diffracted beam overlap and generate interference fringes in the overlapping area;

[0084] The optical fiber is placed close to the bottom of the mask and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core.

[0085] The ultraviolet light source 1 is transmitted through the aperture a2 to the ultraviolet reflector 3 placed at a certain angle. The reflector 3 and the aperture a5 are fixed together on the translation stage 4. The ultraviolet light is focused into the core of the optical fiber 8 through the cylindrical mirror 6. The mask 7 is placed in the optical path to diffract the ultraviolet laser light. The n-order diffracted beam overlaps with the -n-order diffracted beam, and interference fringes are generated in the overlapping area. The grating is placed close to the bottom of the mask, and the optical fiber is in the interference field, forming an axial periodic refractive index modulation structure in the core. From the grating equation, it can be seen that the period Λ of the phase mask 7, the order n of the diffracted beam, and the Bragg wavelength λ of the grating are related to each other. B The following quantitative relationship follows:

[0086]

[0087] where n eff is the effective refractive index of the cladding mode, usually using the first-order diffracted beam, given the pump wavelength λ B In this case, the required mask period can be calculated.

[0088] See also Figure 3 and Figure 4 , the mask of the embodiment of the present application includes:

[0089] a quartz glass substrate;

[0090] A Bragg grating (FBG) mask unit and a Raman-tilted fiber Bragg grating (TFBG) mask unit are integrated on a quartz glass substrate. These FBG and TFBG mask units are arranged in a left-right configuration on the quartz glass substrate. During the writing process, there is no need to switch masks, which greatly simplifies the operation process, reduces the possibility of product defects due to human error, and improves production stability and reliability. Without switching masks, the continuity of the two grating writing is achieved, avoiding the problem of photosensitivity degradation due to time difference.

[0091] An intermediate non-stripe area is provided between the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit. The length l of the intermediate non-stripe area satisfies the requirement of 20mm≤l≤40mm. On the one hand, the FBG requires coating treatment, and the length is recommended to cover the stripping edge. The TFBG requires roughening sleeve treatment, and each end has a certain size. Too short a spacing is not conducive to subsequent process operations and cannot meet the process requirements of FBG and TFBG. If the spacing of the non-stripe area is too long, it will not only cause a waste of mask resources and increase the production cost of the mask, but also impose more stringent standards on components such as the translation stage range and cylindrical mirror at the front end of the etching system, increasing the procurement cost and maintenance difficulty of the equipment. The spacing setting of this solution effectively controls costs while meeting process requirements and achieves optimal resource allocation.

[0092] The fringes of the Raman-tilted fiber Bragg grating (TFBG) mask unit have an angle θ relative to the substrate plane that satisfies 3°≤θ≤5°. This allows two gratings to be written using a single etching system without the need to rotate the mask, simplifying the system structure and reducing equipment complexity and maintenance costs. Furthermore, this avoids writing errors caused by improper angle adjustment, improving writing accuracy and consistency.

[0093] Specifically, the central wavelength of the Bragg grating (FBG) mask unit is 1080nm, the chirp rate is 0.7nm / cm-1.5nm / cm, and the stripe length is 40mm-60mm; the central wavelength of the Raman tilted fiber grating (TFBG) mask unit is 1135nm, the chirp rate is 1.5nm / cm-2nm / cm, and the stripe length is 80mm-100mm.

[0094] In industrial cutting applications, the 1080nm center wavelength falls within the commonly used wavelength range for fiber optic communications and laser processing. Lasers at this wavelength exhibit low transmission loss when transmitted through optical fibers, ensuring sufficient power for cutting after long-distance armored cable transmission. The 1135nm center wavelength is also a targeted choice. In Raman scattering applications, this wavelength effectively excites Raman signals and creates a certain difference from the center wavelength of the fiber optic beam generator (FBG), facilitating direct filtering of non-signal wavelengths at the output. A suitable chirp rate can also extend the FBG's spectral response range.

[0095] The TFBG's relatively high chirp rate is due to its unique Raman tilt structure. A chirp rate range of 1.5nm / cm-2nm / cm enables the TFBG to produce richer spectral characteristics during Raman scattering, enhancing its ability to filter out non-signal wavelengths.

[0096] For FBG mask units, if the stripe length is too long, higher requirements will be placed on the preparation of the mask. For example, during the mask production process, higher precision and more complex processes are required to ensure the uniformity and consistency of the stripes, which will undoubtedly increase the production cost and difficulty. Moreover, the grating length engraved with long stripes will also be long, making the subsequent coating process complicated. The coating material needs to be evenly covered on the grating surface to protect the grating and improve its performance, but the coating of long gratings is prone to problems such as uneven coating and bubbles, affecting the quality and stability of the grating. A stripe length that is too short will result in the bandwidth of the grating being engraved being too small. A narrow bandwidth will limit the range of interaction between the laser and the material, reducing cutting efficiency and accuracy.

[0097] For TFBG mask elements, excessively long stripes also present numerous challenges. Besides increasing the difficulty and cost of mask preparation, the increased length of the grating inscribed with long stripes complicates the subsequent protective glass tube sheathing process. The glass tube must be precisely sheathed over the grating to ensure its safety and performance, but sheathing long gratings is prone to deviation, resulting in uneven gaps between the glass tube and the grating, impacting the grating's heat dissipation and stability. Excessively short stripes weaken the TFBG's Raman scattering effect, limiting its ability to filter out non-signal wavelengths.

[0098] Specifically, the distance between the fiber Bragg grating (FBG) mask unit and one side of the substrate is 15 mm, and the distance between the fiber Raman tilted grating (TFBG) mask unit and the other side of the substrate is 85 mm.

[0099] The overall layout of the FBG inscribed area, consisting of 15mm at one end and a portion of the non-striped area in the middle, ensures that there is a reserve distance at both ends. This reserved distance is crucial for the coating process. During the coating process, the coating equipment requires a certain amount of space to evenly apply the coating material and ensure that the coating layer adheres tightly to the fiber surface to avoid problems such as bubbles and uneven coating. The reserved 15mm distance provides sufficient operating space for the coating equipment, allowing the coating material to smoothly cover the FBG area and ensuring the quality and thickness uniformity of the coating layer, thereby improving the performance and life of the FBG.

[0100] TFBG requires a roughened sleeve treatment. The TFBG mask unit is 85 mm away from the other side of the substrate. Combined with the reserved length of the middle non-striped area, there is enough space at both ends of the TFBG area to install the roughened sleeve and perform the glue coating operation.

[0101] Furthermore, the width of the fiber Bragg grating (FBG) and Raman-tilted fiber Bragg grating (TFBG) mask units is 10 mm. While ensuring grating performance, a 10 mm width is relatively moderate. Mask units that are too wide increase manufacturing difficulty and cost, requiring higher-precision processing equipment and a more complex process flow; on the other hand, mask units that are too narrow cannot meet the requirements for writing. Therefore, the 10 mm width design strikes a good balance between manufacturing difficulty and cost, contributing to improved production efficiency and economic benefits.

[0102] The quartz glass substrate is 200 mm long, 20 mm wide, and 10 mm thick. The Fiber Bragg Grating (FBG) mask unit and the Raman-tilted Fiber Bragg Grating (TFBG) mask unit are located in the center of the quartz glass substrate width. This centered layout places the FBG and TFBG mask units in symmetrical positions on the quartz glass substrate, reducing grating performance variations caused by positional deviations. The 100 mm thickness design provides sufficient mechanical strength for the quartz glass substrate, ensuring that the substrate will not deform or be damaged during the writing process.

[0103] In the embodiment of the present application, the length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit and the Raman tilted fiber Bragg grating (TFBG) mask unit in the mask plate and the middle non-stripe area.

[0104] In the etching system, the cylindrical mirror and mask remain fixed while the light source moves along the route. The length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit, the Raman-tilted fiber Bragg grating (TFBG) mask unit, and the intermediate non-stripe area. This is to ensure that the UV laser can always be effectively focused by the cylindrical mirror during the movement of the light source. If the cylindrical mirror is not long enough, when the light source moves to certain positions, the laser beam will not be able to completely cover the effective working area of ​​the cylindrical mirror, resulting in poor focusing effect, or even failure to focus into the fiber core, thus affecting the quality and success rate of grating writing. The reasonable design of the cylindrical mirror length can ensure that during a single writing process, there is no need to interrupt the writing, adjust the equipment, or reposition the light source due to insufficient cylindrical mirror coverage. This can reduce pauses and operation time in the production process and improve production efficiency. At the same time, a stable writing process also helps to reduce the scrap rate and further improve production efficiency.

[0105] Furthermore, the reflector angle can be adjusted, for example, to 45°. However, the beam must be perpendicular to the mask during the stage's movement to ensure consistent beam movement. If the beam is not perpendicular to the mask, the intensity of the beam exposure to the fiber core will vary, resulting in suboptimal grating reflectivity.

[0106] Furthermore, the moving distance of the translation stage is greater than the length of the mask so as to cover the stripe area of ​​the mask.

[0107] In the etching system, a translation stage carries and moves the UV reflector and aperture, thereby adjusting the UV laser's irradiation position on the mask. The mask's stripe area is the core region that forms the grating structure and contains the key pattern used for diffraction to produce interference fringes. The translation stage's movement distance is greater than the mask's length, ensuring that the UV laser can completely scan the mask's stripe area throughout the entire writing process. If the translation stage's movement distance is insufficient, parts of the mask's stripe area will not be illuminated by the laser, resulting in these areas being unable to participate in the grating writing process. The resulting grating structure is incomplete and fails to meet the design requirements. During a single writing process, the translation stage can cover the mask's stripe area in one go, reducing time wasted due to multiple adjustments to the stage's position or repeated writing. This greatly improves production efficiency, especially in large-scale production, significantly shortening production cycles and reducing production costs. Furthermore, a stable writing process helps reduce scrap rates and further improves production efficiency.

[0108] The translation stage is a speed-adjustable DC servo linear translation stage with a round-trip error accuracy of less than 1 μm and a maximum speed of 100 mm / s. The movement speed of the translation stage in the corresponding non-stripe area is greater than that in the stripe area.

[0109] The speed-adjustable DC servo linear stage allows for flexible adjustment of movement speed to meet the specific requirements of the writing task. When writing fiber Bragg gratings (FBGs) and Raman-tilted fiber Bragg gratings (TFBGs), different grating parameters (such as period and length) require different writing speeds. By adjusting the stage speed, the writing process can be optimized, ensuring that each grating is written under optimal conditions, thereby improving grating quality and performance.

[0110] High-precision round-trip error control ensures that the stage accurately returns to its starting or desired position during movement, ensuring that the UV laser illuminates the mask accurately. This is crucial for inscribing high-precision gratings, as even slight positional deviations can significantly degrade grating performance. Low round-trip error helps ensure repeatability and consistency in each inscription process, ensuring that multiple gratings have similar performance parameters. This is crucial for ensuring consistent product quality in large-scale production.

[0111] In the non-fringe areas, the UV laser does not need to perform a writing operation, so the translation stage can be moved faster to reduce the time difference between the writing of two grating stripes. This can improve the efficiency of the entire writing process and shorten the production cycle.

[0112] Figure 5Figure 3 is a schematic diagram of the laser structure, in which the high-reflection grating 17 and the low-reflection grating b18 constitute the laser's resonant cavity. The high-reflection grating 17 is fused to the signal end of the forward beam combiner, and the pump end is fused to multiple high-power pump sources. Similarly, the low-reflection grating b18 is fused to the signal end of the reverse beam combiner. The composite mask of the present invention can realize the integration of the low-reflection grating b18 and the Raman grating b20. Compared with the traditional Raman grating, this integrated device omits the fusion point 19, which significantly improves the stability of the laser.

[0113] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, various modifications and variations can be made to the present application. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for preparing a fiber Bragg grating, characterized in that: include: Providing an optical fiber, the optical fiber comprising a core, a cladding, and a first coating layer arranged in sequence from inside to outside along the radial direction of the optical fiber; removing the first coating layer on the optical fiber; Synchronously etching high and low reflection gratings and Raman gratings on the fiber core; A second coating layer is coated on the periphery of the cladding corresponding to the high and low reflection gratings, and a glass tube is set on the periphery of the cladding corresponding to the Raman grating.

2. The method for preparing a fiber Bragg grating according to claim 1, wherein: The specific steps of etching high and low reflection gratings and Raman gratings on the fiber core include: The mask plate and cylindrical mirror are fixed and the ultraviolet laser is scanned at different positions of the mask plate by moving the translation stage to achieve the writing of high and low reflection gratings and Raman gratings.

3. The method for preparing a fiber Bragg grating according to claim 2, wherein: When writing the high-reflection grating, the laser power is 60-120 mW; When writing the low-reflection grating, the laser power is 30-50 mW; When writing the Raman grating, the laser power is 30-100 mW.

4. The method for preparing a fiber Bragg grating according to claim 1, wherein: The specific steps of coating the second coating layer on the periphery of the cladding corresponding to the high and low reflection grating include: Coating a low-reflection adhesive on the outer periphery of the cladding corresponding to the high-low-reflection grating, and curing the low-reflection adhesive to form a second coating layer; The specific steps of installing a glass tube on the periphery of the cladding corresponding to the Raman grating include: The glass tube is placed on the periphery of the cladding corresponding to the Raman grating, and glue is applied on both sides to fix the glass tube.

5. The method for preparing a fiber Bragg grating according to claim 1, wherein: The specific steps of removing the first coating layer on the optical fiber include: The first coating layer on the optical fiber is stripped by a stripping machine, so that the transition area between the stripped end and the cladding is smooth, burr-free and free of residual debris.

6. The method for preparing a fiber Bragg grating according to claim 1, wherein: After etching the high and low reflection gratings and the Raman grating on the fiber core, a heat treatment step is also included: The fiber Bragg grating is treated in a high temperature environment of 400-500° C. for 1-2 minutes.

7. The method for preparing a fiber Bragg grating according to claim 1, wherein: The fiber core diameter is 20 μm, the cladding diameter is 400 μm, and the fiber core numerical aperture is 0.

065.

8. The method for preparing a fiber Bragg grating according to claim 2, wherein: The etching systems used include: An ultraviolet light source, used to provide ultraviolet laser required for etching; The aperture is set in the light path of the ultraviolet light source and is used to adjust the size and shape of the ultraviolet laser beam; The UV reflector, fixed together with the aperture on the translation stage, is used to change the propagation direction of the UV laser to ensure that the beam can be vertically irradiated onto the mask during the movement of the translation stage; A translation stage is used to carry and move the UV reflector and the aperture to adjust the irradiation position of the UV laser on the mask; The cylindrical mirror is arranged below the translation stage and is used to focus the ultraviolet laser so that the ultraviolet laser is focused in the core of the optical fiber; The mask is arranged below the cylindrical mirror and is used to diffract the ultraviolet laser, wherein the n-th order diffracted beam and the -n-th order diffracted beam overlap and generate interference fringes in the overlapping area; The optical fiber is placed close to the bottom of the mask and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core; Wherein, the mask comprises: a quartz glass substrate; A Bragg grating mask unit and a Raman tilted fiber Bragg grating mask unit integrated on a quartz glass substrate, wherein the Bragg grating mask unit and the Raman tilted fiber Bragg grating mask unit are arranged in a left-right structure on the quartz glass substrate; An intermediate non-fringe area is provided between the Bragg grating mask unit and the Raman tilted fiber Bragg grating mask unit, and a length l of the intermediate non-fringe area satisfies 20 mm ≤ l ≤ 40 mm; The stripes of the Raman tilted fiber grating mask unit have an angle θ relative to the substrate plane, which satisfies 3°≤θ≤5°.

9. A fiber Bragg grating, characterized in that: Prepared by the method for preparing a fiber Bragg grating according to any one of claims 1 to 8, the fiber Bragg grating comprises: The core and cladding are arranged in sequence from inside to outside along the radial direction of the fiber grating; The fiber core is provided with high and low reflection gratings and Raman gratings. A second coating layer is provided on the periphery of the cladding corresponding to the high and low reflection gratings. A glass tube is provided on the periphery of the cladding corresponding to the Raman grating.

10. Use of the fiber Bragg grating as claimed in claim 9 in a laser.

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