A mask plate and an etching system thereof

Abstract

The application discloses a mask plate and an etching system, comprising a quartz glass substrate, a Bragg grating (FBG) mask unit and a Raman tilted fiber grating (TFBG) mask unit integrated on the quartz glass substrate, the composite mask plate integrates the Bragg grating (FBG) and the Raman tilted fiber grating (TFBG) mask unit on the same quartz glass substrate in a left-right layout, and no mask plate switching is needed during inscription, so that the operation process is simplified, the risk of product defects caused by human errors is reduced, the production stability and reliability are improved, the continuity of the two gratings is realized, the photosensitivity is prevented from being changed due to time difference, the stable photosensitivity of the fiber is ensured, the inscription quality and efficiency are improved, the production cycle is shortened, the stripe relative substrate plane angle θ of the TFBG mask unit is between 3° and 5°, the two gratings can be inscribed by using one set of etching system, the mask plate does not need to be rotated, the system structure is simplified, the equipment complexity and maintenance cost are reduced, the angle adjustment error is avoided, and the inscription precision and consistency are improved.

Description

Technical Field

[0001] This application belongs to the field of gratings, and in particular relates to a photomask and its etching system. Background Technology

[0002] In industrial processing and cutting, high-power fiber lasers typically require long-distance armored cables for laser transmission. However, these long cables can lead to the generation of Raman signals, and stimulated Raman scattering (SRS) causes power loss, beam quality degradation, and spectral broadening, severely impacting cutting performance. Using a Raman tilt grating can directly filter out non-signal wavelengths at the output, improving the cutting penetration of highly reflective materials (such as copper and aluminum), ensuring long-range cutting accuracy, and also enhancing the laser's lifespan and stability. Simultaneously, the high / low reflection grating (HR / LR FBG), as a core component of the resonant cavity, needs to achieve high stability and high reflectivity (HR > 99.5%, LR < 10%), replacing traditional dielectric mode mirrors to simplify the optical path structure.

[0003] However, the writing of Raman gratings and high / low reflection gratings faces numerous challenges in existing manufacturing processes. Firstly, writing these two types of gratings requires different phase masks. If a single grating system is used, the mask must be manually changed when writing different types of gratings. This process is not only time-consuming, but also requires readjusting parameters such as energy and focal length, as well as re-optimizing process parameters such as tilt angle control, significantly increasing the complexity of debugging. Improper calibration can lead to defects in the grating, affecting product quality.

[0004] Secondly, the traditional integrated low-reflection grating and Raman grating technology has significant drawbacks. This approach involves first writing the low-reflection grating, then switching the mask and using a Raman mask to continue writing the Raman grating on the fiber already inscribed with the low-reflection grating. However, due to the time lag after the mask switch, the fiber loses hydrogen, resulting in decreased photosensitivity and insufficient reflectivity of the grating, severely impacting the writing quality and even causing writing failure.

[0005] Furthermore, the lifespan of masking sheets is significantly reduced due to frequent disassembly and assembly. Masking sheets are expensive, typically costing hundreds of thousands of yuan, and frequent replacements undoubtedly increase production costs. If a dual-production-line parallel mode with two production lines is adopted, equipment investment will increase by 200%, further exacerbating the company's financial burden.

[0006] Furthermore, currently, both the Raman mask stripes and the high / low reflection mask stripes are vertically designed, requiring the Raman mask to be rotated by a certain angle (3°-5°) during use. If two masks are used side-by-side, not only is it necessary to adjust the angle of the Raman mask, but also to equip an additional adjustment bracket, making the system structure cumbersome. At the same time, the difference in the total length of the non-striped areas of the two masks will lead to poor continuity in the writing process, resulting in a time lag, which further affects the grating writing quality.

[0007] The aforementioned bottlenecks severely restrict the mass production efficiency of fiber Bragg gratings (FBGs) for high-power lasers, becoming a key factor hindering the industry's development. Therefore, existing technologies require further improvement and enhancement. Summary of the Invention

[0008] The present invention provides a mask template and an etching system thereof to at least solve or alleviate one or more technical problems in the prior art, or at least provide a beneficial alternative.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A mask template includes: a quartz glass substrate; a Bragg grating (FBG) mask unit and a Raman tilted fiber grating (TFBG) mask unit integrated on the quartz glass substrate, wherein the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are arranged in a left-right structural layout on the quartz glass substrate.

[0011] An intermediate non-striated region is provided between the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit, and the length l of the intermediate non-striated region satisfies 20mm≤l≤40mm;

[0012] The stripes of the Raman tilted fiber grating (TFBG) mask unit have an angle θ relative to the substrate plane, satisfying 3°≤θ≤5°.

[0013] This application's composite photomask integrates Bragg grating (FBG) and Raman tilted fiber grating (TFBG) mask units onto the same quartz glass substrate in a left-right arrangement. This eliminates the need to switch masks during etching, simplifying the operation process, reducing the risk of product defects due to human error, improving production stability and reliability, achieving continuous etching of the two gratings, preventing photosensitivity degradation due to time differences, ensuring stable photosensitivity of the fiber, improving etching quality and efficiency, shortening the production cycle, and enhancing the company's production capacity and competitiveness. The integrated design allows one mask to complete the etching of both gratings, reducing the number of masks used, extending their lifespan, lowering production costs, and eliminating the need for two production lines, thus reducing the economic burden on the company. The TFBG mask unit fringes at an angle θ relative to the substrate plane between 3° and 5° allow both gratings to be etched using a single etching system without rotating the mask, simplifying the system structure, reducing equipment complexity and maintenance costs, avoiding angle adjustment errors, and improving etching accuracy and consistency. The length l of the non-striped area in the middle is between 20mm and 40mm, which not only meets the process operation requirements of FBG coating and TFBG texturing sleeve, but also avoids resource waste, increased manufacturing costs, and excessively high standards for components such as displacement stage range and cylindrical mirror, which would increase procurement costs and maintenance difficulty, thus achieving optimal resource allocation.

[0014] In the preferred implementation, the center wavelength of the Bragg grating (FBG) mask unit is 1080 nm, the chirp rate is 0.7 nm / cm to 1.5 nm / cm, and the fringe length is 40 mm to 60 mm; the center wavelength of the Raman tilted fiber grating (TFBG) mask unit is 1135 nm, the chirp rate is 1.5 nm / cm to 2 nm / cm, and the fringe length is 80 mm to 100 mm.

[0015] In a preferred implementation, the Bragg grating (FBG) mask unit is ≤15mm away from one side of the substrate, and the Raman tilted fiber grating (TFBG) mask unit is ≤15mm away from the other side of the substrate.

[0016] In a preferred implementation, the width of the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit is 10 mm.

[0017] In a preferred embodiment, the quartz glass substrate is 200 mm long, 20 mm wide, and 6 mm thick, and the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are located at the center of the width of the quartz glass substrate.

[0018] The etching system used for the photomask includes:

[0019] Ultraviolet light source, used to provide the ultraviolet laser required for etching;

[0020] An aperture, placed in the optical path of an ultraviolet light source, is used to adjust the size and shape of the ultraviolet laser beam;

[0021] The ultraviolet reflector, together with the aperture, is fixed on the displacement stage to change the propagation direction of the ultraviolet laser, ensuring that the beam can be perpendicularly irradiated onto the mask during the movement of the displacement stage.

[0022] The displacement stage is used to support and move the ultraviolet reflector and aperture to adjust the irradiation position of the ultraviolet laser on the mask.

[0023] A cylindrical mirror, positioned below the displacement stage, is used to focus the ultraviolet laser, ensuring that the ultraviolet laser is focused into the core of the optical fiber.

[0024] The mask is placed below the cylindrical mirror to diffract the ultraviolet laser, where the nth order diffracted beam overlaps with the -nth order diffracted beam and produces interference fringes in the overlapping area.

[0025] The optical fiber is placed close to the mask template and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core;

[0026] During the writing process, the photomask and cylindrical mirror are fixed in place, and the ultraviolet laser is scanned at different positions of the photomask by moving the displacement stage to write high and low reflection gratings and Raman gratings.

[0027] The etching system and mask template greatly simplify the etching process, reduce the errors and operational complexity that may be caused by adjusting the fiber angle, improve etching efficiency and stability, and reduce production costs. At the same time, it is also conducive to realizing large-scale, standardized grating production, meeting the large demand for high-power fiber laser gratings in industrial processing and cutting fields.

[0028] During the inscription process, the grating can be freely inscribed according to the following situations: ① When only high-reflectivity or low-reflectivity gratings need to be inscribed, it is only necessary to control the displacement stage to scan and expose the FBG area with the ultraviolet laser source. If only Raman suppression gratings need to be inscribed, only the TFBG area needs to be exposed. ② If it is necessary to integrate the low-reflectivity grating and the Raman grating into a single fiber, the displacement stage can be controlled to scan and inscribe the entire mask area. Because it is a multiple scan, the order of inscription does not need to be standardized.

[0029] In a preferred implementation, the length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit, the Raman tilted fiber grating (TFBG) mask unit, and the intermediate non-fringe region in the mask template.

[0030] In a preferred implementation, the displacement stage moves a distance greater than the length of the mask template to cover the striped area of ​​the mask template.

[0031] In the preferred implementation, the displacement stage is a speed-adjustable DC servo linear displacement stage with a round-trip error accuracy of less than 1µm and a maximum speed of 100mm / s. The displacement stage moves faster in the corresponding non-striped area than it moves in the striped area.

[0032] In the preferred implementation, before writing the grating, the optical fiber undergoes a stripping coating process. After writing, the left low-reflection grating is coated with low-refractive adhesive, and the right Raman suppression grating is protected by a glass tube. Attached Figure Description

[0033] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain this application and do not constitute an undue limitation of the invention. In the drawings:

[0034] Figure 1 A schematic diagram illustrating one embodiment of the mask template of this application is shown.

[0035] Figure 2 A schematic dimensional diagram illustrating one embodiment of the mask template of this application is shown;

[0036] Figure 3 A schematic diagram illustrating one embodiment of the etching system of this application is shown.

[0037] Figure 4 A complete schematic diagram of the integrated low-reflection grating and Raman grating device of this application is shown;

[0038] Figure 5 A schematic diagram of the laser structure is shown;

[0039] Label Explanation:

[0040] 1. Ultraviolet light source; 2. Aperture a; 3. Ultraviolet mirror; 4. Displacement stage; 5. Aperture b; 6. Cylindrical mirror; 7. Mask; 8. Optical fiber; 9. Ordinary high and low reflection grating fringes; 10. Quartz glass substrate; 11. Tilted Raman fiber fringes; 12. Low reflection grating a; 13. Low refractive index adhesive; 14. Glass tube; 15. Non-signal light; 16. Raman grating a; 17. High reflection grating; 18. Low reflection grating b; 19. Fusion joint; 20. Raman grating b. Detailed Implementation

[0041] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit and scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0042] The present invention will now be described with reference to the accompanying drawings.

[0043] The specific solution adopted is as follows:

[0044] like Figure 1-2 As shown, the present invention provides a mask template, comprising: a quartz glass substrate; a Bragg grating (FBG) mask unit and a Raman tilted fiber grating (TFBG) mask unit integrated on the quartz glass substrate, wherein the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are arranged in a left-right structural layout on the quartz glass substrate.

[0045] An intermediate non-striated region is provided between the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit, and the length l of the intermediate non-striated region satisfies 20mm≤l≤40mm;

[0046] The stripes of the Raman tilted fiber grating (TFBG) mask unit have an angle θ relative to the substrate plane, satisfying 3°≤θ≤5°.

[0047] The composite mask of this application integrates a Bragg grating (FBG) mask unit and a Raman tilted fiber grating (TFBG) mask unit on the same quartz glass substrate, arranged in a left-right structure. During the etching process, there is no need to switch masks, greatly simplifying the operation process, reducing the possibility of product defects due to human error, and improving production stability and reliability. The elimination of mask switching ensures continuous etching of the two gratings, avoiding the problem of photosensitivity degradation due to time differences. The optical fiber remains in a stable photosensitivity state throughout the etching process, guaranteeing the quality of the grating. At the same time, etching efficiency is significantly improved, shortening the production cycle and enhancing the company's production capacity and market competitiveness.

[0048] Through integrated design, only one photomask is needed to write two types of gratings, reducing the number of photomasks used, extending their lifespan, and lowering production costs. At the same time, it eliminates the need to build two production lines, avoiding high equipment investment, effectively reducing the company's economic burden and improving its economic efficiency.

[0049] In this scheme, the fringes of the Raman tilted fiber grating (TFBG) mask unit have an angle θ relative to the substrate plane, satisfying 3°≤θ≤5°. This design allows two gratings to be etched using a single etching system without rotating the mask, simplifying the system structure and reducing equipment complexity and maintenance costs. Simultaneously, it avoids etching errors caused by improper angle adjustment, improving etching accuracy and consistency.

[0050] The length *l* of the non-striped area in the middle satisfies 20mm ≤ *l* ≤ 40mm. This spacing setting has two advantages: First, FBG requires coating, and the length should ideally cover the stripped area; TFBG requires texturing and sleeve treatment, with a certain amount of extra space at both ends. Too short a spacing is detrimental to subsequent processing operations and cannot meet the processing requirements of FBG and TFBG. Second, if the spacing of the non-striped area is too long, it will waste mask resources, increasing mask manufacturing costs. Furthermore, it will impose stricter standards on the displacement stage range and cylindrical mirrors at the front end of the etching system; the range and cylindrical mirror length must cover the entire striped area of ​​the mask, increasing equipment procurement costs and maintenance difficulty. The spacing setting in this solution effectively controls costs while meeting process requirements, achieving optimal resource allocation.

[0051] In a preferred embodiment of this application, the center wavelength of the Bragg grating (FBG) mask unit is 1080 nm, the chirp rate is 0.7 nm / cm to 1.5 nm / cm, and the fringe length is 40 mm to 60 mm; the center wavelength of the Raman tilted fiber grating (TFBG) mask unit is 1135 nm, the chirp rate is 1.5 nm / cm to 2 nm / cm, and the fringe length is 80 mm to 100 mm.

[0052] Currently, industrial fiber optic cleavers use lasers with a wavelength of 1080nm. A 1080nm FBG (Fiber Optic Generator) can amplify and oscillate the 1080nm light, resulting in stimulated emission. This ensures sufficient power for cutting even after long-distance transmission through armored cables. The choice of a 1135nm center wavelength is also strategic. In Raman scattering applications, this wavelength effectively suppresses 1135nm Raman signals and creates a difference from the FBG's center wavelength, facilitating direct filtering of non-signal wavelengths at the output. An appropriate chirp rate can also extend the FBG's spectral response range.

[0053] The relatively high chirp rate of TFBGs is determined by their unique Raman tilt structure. A chirp rate range of 1.5 nm / cm to 2 nm / cm allows TFBGs to produce richer spectral characteristics during Raman scattering, enhancing the filtering effect on non-signal wavelengths. However, excessively long fringe lengths in FBG mask units place higher demands on mask fabrication. For example, higher precision and more complex processes are required to ensure fringe uniformity and consistency, undoubtedly increasing manufacturing costs and difficulty. Furthermore, long fringe gratings also have longer sides, complicating subsequent coating processes. The coating material needs to uniformly cover the grating surface to protect it and improve its performance; however, coating long gratings is prone to uneven coating and bubbles, affecting the quality and stability of the grating. Conversely, excessively short fringe lengths result in a narrow bandwidth. A narrow bandwidth limits the interaction range between the laser and the material, reducing cutting efficiency and accuracy.

[0054] For TFBG mask units, excessively long fringe lengths also present several problems. Besides increasing the difficulty and cost of mask fabrication, longer fringe gratings lead to more complex subsequent glass tube protection processes. The glass tube needs to be precisely fitted onto the grating to ensure its safety and performance; however, deviations are prone to occur during the fitting of long gratings, resulting in uneven gaps between the glass tube and the grating, affecting heat dissipation and stability. Conversely, excessively short fringe lengths weaken the Raman scattering effect of the TFBG, limiting its ability to filter out non-signal wavelengths.

[0055] The parameters of the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit have been carefully designed, taking into full account the actual needs and application characteristics of industrial processing and cutting in terms of center wavelength, chirp rate and fringe length, providing a strong guarantee for achieving efficient, accurate and stable cutting.

[0056] In a preferred embodiment of this application, the Bragg grating (FBG) mask unit is ≤15mm away from one side of the substrate, and the Raman tilted fiber grating (TFBG) mask unit is ≤15mm away from the other side of the substrate.

[0057] The FBG marking area has a 15mm margin at one end, plus a portion of the non-stripe area in the middle. This overall layout ensures sufficient clearance at both ends, which is crucial for the coating process. During coating, the coating equipment needs adequate space to apply the coating material evenly and ensure a tight bond between the coating layer and the fiber surface, preventing issues such as bubbles and uneven coating. The 15mm margin 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 FBG's performance and lifespan.

[0058] TFBG requires texturing and sleeve processing. The TFBG mask unit is 15mm away from the other side of the substrate. Combined with the length reservation of the non-striped area in the middle, there is enough space at both ends of the TFBG area to install the texturing sleeve and perform the adhesive application.

[0059] Furthermore, the width of the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit is 10mm. A width of 10mm is relatively moderate while ensuring grating performance. Mask units that are too wide would increase manufacturing difficulty and cost, requiring higher-precision processing equipment and more complex processes; while mask units that are too narrow would not meet the writing requirements. Therefore, the 10mm width design achieves a good balance between manufacturing difficulty and cost, which is beneficial for improving production efficiency and economic benefits.

[0060] The quartz glass substrate is 200mm long, 20mm wide, and 6mm thick. The Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are located in the center of the width of the quartz glass substrate. The central layout makes the FBG and TFBG mask units symmetrical on the quartz glass substrate, reducing the difference in grating performance caused by positional deviation. Its 10mm thickness design can provide sufficient mechanical strength for the quartz glass substrate, ensuring that the substrate will not be deformed or damaged during the writing process.

[0061] The holographic ion beam etching method used in the mask preparation method has the core technology of forming a tunable grating structure by using two-beam interference: when two coherent lasers generate spatial interference on the substrate surface, the photoresist layer records the distribution of alternating bright and dark stripes. By adjusting the beam angle and wavelength parameters, the grating period can be precisely controlled, thereby meeting the preparation requirements of devices with different wavelengths of 1080nm and 1135nm.

[0062] First, high-purity fused silica is selected as the substrate, ensuring its smoothness. After plasma cleaning, a chromium mask layer is deposited using magnetron sputtering as a hard mask. A layer of photoresist is uniformly coated onto the surface of the fused silica, with the thickness adjusted according to the mask period. The coated photoresist is then dried to ensure uniformity, absence of air bubbles, and good adhesion to the substrate. The coated substrate is placed in an interference optics system for holographic exposure. The photoresist records the interference fringes formed by the holographic exposure. A dual-beam interference system is used, with two coherent beams symmetrically incident. By precisely adjusting the interference angle θ, the fringe spacing Λ satisfies the grating equation: Λ=λ / (2sinθ), achieving spatial modulation of the target period. After exposure, the substrate is immersed in a developing solution for development. The development time is adjusted in real time based on the presence of residual adhesive at the bottom of the tank, and then dried and cured. This process yields a photoresist relief grating pattern.

[0063] A substrate with a photoresist relief grating pattern obtained through holographic lithography is etched using an ion beam. Reactive ion etching (RIE) with a mixed gas allows the mask pattern to be transferred to the surface of the substrate material. The ion beam contains a chemically reactive gas, and the specific gas used must be selected depending on the material being etched. RIE uses a mixed gas that primarily contains fluorine (F) and chlorine (Cl). Under certain conditions, these gases split into ions, which are highly reactive and readily react with atoms in the material to produce gaseous compounds.

[0064] To prevent the two wavelength gratings from interfering with each other during holographic lithography and reactive ion etching, a step-by-step exposure and etching method is adopted. The grating positions are protected with opaque materials (such as plastic) to ensure that the etching process of each grating is carried out independently.

[0065] Specifically, high-purity fused silica is selected as the substrate to ensure its smoothness; after plasma cleaning, a chromium mask layer is deposited using magnetron sputtering as a hard mask; a layer of photoresist is uniformly coated on the surface of the fused silica, with the thickness adjusted according to the mask cycle; the coated photoresist is dried to ensure that the photoresist layer is uniform, bubble-free, and adherent to the substrate; step-by-step holographic lithography is performed, and the first holographic exposure protects one side of the grating position: an opaque material (such as plastic) is used to cover one of the gratings (assuming it is the grating corresponding to wavelength λ1) to ensure that the photoresist in that area is not exposed; the substrate coated with photoresist is placed in an interference optical system, and a dual-beam interference system is used to perform holographic exposure on the uncovered side (the grating position corresponding to wavelength λ1). Two coherent beams are symmetrically incident. By precisely adjusting the interference angle θ, the fringe spacing Λ is made to satisfy the grating equation Λ=λ2 / (2sinθ), achieving spatial modulation of the target period. A second holographic exposure is performed to protect the exposed area. The substrate after the first exposure is removed, and the grating position corresponding to wavelength λ2 (where holography has already been completed) is covered with an opaque material. The substrate is then placed back into the interference optical system for holographic exposure of the grating position corresponding to wavelength λ1. Similarly, the interference angle θ is adjusted to ensure the fringe spacing Λ satisfies the grating equation Λ=λ1 / (2sinθ). The substrate after two holographic exposures is placed in a developing solution for development. After development, the substrate is removed, dried, and cured to make the photoresist relief grating pattern more robust. Step-by-step etching is then performed, using an opaque material (such as plastic) to cover one of the grating positions (the grating corresponding to wavelength λ1) to ensure that this area is not etched. The substrate is placed in a reactive ion etching apparatus; the substrate after the first etching is removed, and the grating position corresponding to wavelength λ1 (where etchography has already been completed) is covered with an opaque material. The substrate is placed in the reactive ion etching equipment again to etch the grating position corresponding to wavelength λ2. After the two etchings are completed, the opaque material is removed to obtain two independent wavelength grating structures.

[0066] The etching system used for the photomask includes:

[0067] Ultraviolet light source, used to provide the ultraviolet laser required for etching;

[0068] An aperture, placed in the optical path of an ultraviolet light source, is used to adjust the size and shape of the ultraviolet laser beam;

[0069] The ultraviolet reflector, together with the aperture, is fixed on the displacement stage to change the propagation direction of the ultraviolet laser, ensuring that the beam can be perpendicularly irradiated onto the mask during the movement of the displacement stage.

[0070] The displacement stage is used to support and move the ultraviolet reflector and aperture to adjust the irradiation position of the ultraviolet laser on the mask.

[0071] A cylindrical mirror, positioned below the displacement stage, is used to focus the ultraviolet laser, ensuring that the ultraviolet laser is focused into the core of the optical fiber.

[0072] The mask is placed below the cylindrical mirror to diffract the ultraviolet laser, where the nth order diffracted beam overlaps with the -nth order diffracted beam and produces interference fringes in the overlapping area.

[0073] The optical fiber is placed close to the mask template and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core;

[0074] During the writing process, the photomask and cylindrical mirror are fixed in place. By moving the displacement stage, the ultraviolet laser scans at different photomask positions to write high and low reflection gratings and Raman gratings. The writing of high and low reflection gratings and Raman gratings can be achieved without additional adjustment of the fiber angle.

[0075] Figure 3 The diagram shows a schematic of the etching system. Ultraviolet light source 1 is transmitted through aperture a2 to an ultraviolet reflector 3 placed at a certain angle. Reflector 3 and aperture a5 are fixed together on a displacement stage 4. The ultraviolet light is focused into the core of fiber 8 by cylindrical mirror 6. A photomask 7 is placed in the optical path to diffract the ultraviolet laser. The nth-order diffracted beam overlaps with the -n-order diffracted beam, generating interference fringes in the overlap region. A grating is placed close to the bottom of the photomask, placing the fiber in the interference field, forming an axially periodic refractive index modulation structure in the fiber core. From the grating equation, we know 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. B Follow the following quantitative relationship:

[0076]

[0077] Where n eff To determine the effective refractive index of the cladding mode, a first-order diffraction beam is typically used, given a pump wavelength λ. B In this case, the required mask cycle can be calculated.

[0078] Figure 4 This is a schematic diagram of the complete integrated device of low-reflection grating a12 and Raman grating a16. Before writing the gratings, the fiber needs to undergo a stripping coating process. After writing, since the function of the tilted Raman grating is to disrupt the oscillation conditions of non-signal light in the fiber and allow non-signal light 15 to leak out through the cladding, the tilted Raman grating does not require coating; only a sleeve treatment is needed. However, the low-reflection grating's performance can degrade due to external factors such as temperature and humidity changes, mechanical wear, and dust contamination, so it requires coating and encapsulation. Specifically, the low-reflection grating on the left is coated with low-refractive adhesive 13, and the Raman grating on the right is protected by a glass tube 14, with adhesive dots fixing the glass tubes on both sides.

[0079] Figure 5 The diagram shows the structure of a laser, in which a high-reflection grating 17 and a low-reflection grating b18 form the resonant cavity of the laser. 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. Using the composite mask template of this invention, the low-reflection grating b18 and the Raman grating b20 can be integrated. Compared with the traditional Raman grating, this integrated device eliminates the fusion point 19, which significantly improves the stability of the laser.

[0080] In a preferred embodiment of this application, the length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit, the Raman tilted fiber grating (TFBG) mask unit, and the intermediate non-fringe region in the mask template.

[0081] In the etching system, the cylindrical mirror and the mask remain fixed, while the light source moves along the path. The length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit, the Raman tilted fiber grating (TFBG) mask unit, and the intermediate non-fringe region. This is to ensure that the ultraviolet laser can always be effectively focused by the cylindrical mirror during the movement of the light source. If the length of the cylindrical mirror is insufficient, when the light source moves to certain positions, the laser beam cannot completely cover the effective working area of ​​the cylindrical mirror, resulting in poor focusing, or even failure to focus on the fiber core. This affects the quality and success rate of grating etching. A properly designed cylindrical mirror length ensures that during a single etching process, there is no need to interrupt etching, adjust the equipment, or reposition the light source due to insufficient coverage by the cylindrical mirror. This reduces downtime and operation time during production, improving production efficiency. At the same time, a stable etching process also helps reduce the scrap rate, further improving production efficiency.

[0082] Furthermore, the angle of the reflector is adjustable, for example, set to 45°, but it must be ensured that the beam can perpendicularly illuminate the mask during the movement of the stage, guaranteeing the stability and consistency of the beam movement. If the beam is not perpendicular to the mask, it will result in inconsistent exposure intensity of the beam to the fiber core, leading to insufficient reflectivity of the grating.

[0083] Furthermore, the displacement stage moves a distance greater than the length of the mask template to cover the striped area of ​​the mask template.

[0084] In the etching system, a displacement stage carries and moves the ultraviolet reflector and aperture, thereby adjusting the irradiation position of the ultraviolet laser on the photomask. The fringe area of ​​the photomask is the core region for forming the grating structure, containing the key patterns used to generate interference fringes for diffraction. The displacement stage moves a distance greater than the length of the photomask, ensuring that the ultraviolet laser can completely sweep across the fringe area of ​​the photomask throughout the etching process. If the displacement stage moves too little, some fringe areas of the photomask will not be irradiated by the laser, preventing these areas from participating in the grating etching process. The resulting grating structure will be incomplete and fail to meet design requirements. In a single etching process, the displacement stage can cover the fringe area of ​​the photomask in one go, reducing the time wasted due to multiple adjustments to the displacement stage position or repeated etching. This significantly improves production efficiency, especially in large-scale production, significantly shortening the production cycle and reducing production costs. Simultaneously, a stable etching process also helps reduce the scrap rate, further improving production efficiency.

[0085] The displacement stage is a speed-adjustable DC servo linear displacement stage with a round-trip error accuracy of less than 1µm and a maximum speed of 100mm / s. The displacement stage moves faster in the corresponding non-striped area than in the striped area.

[0086] Speed-adjustable DC servo linear stage can flexibly adjust its movement speed according to the specific requirements of the writing task. When writing Bragg gratings (FBGs) and Raman tilted fiber 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 the quality and performance of the gratings.

[0087] High-precision round-trip error control ensures that the stage accurately returns to its starting or designated position during movement, guaranteeing accurate irradiation of the ultraviolet laser on the photomask. This is crucial for writing gratings with high precision requirements, as even minute positional deviations can significantly degrade grating performance. Low round-trip error helps ensure repeatability and consistency in each writing process, resulting in multiple written gratings with similar performance parameters. This is of great significance for ensuring consistent product quality in mass production.

[0088] In the non-striped area, the ultraviolet laser does not require writing, thus allowing for a faster stage movement to reduce the time difference between writing two grating stripes. This improves the efficiency of the entire writing process and shortens the production cycle.

[0089] During the inscription process, the grating can be freely inscribed according to the following situations: ① When only high-reflectivity or low-reflectivity gratings need to be inscribed, it is only necessary to control the displacement stage to scan and expose the FBG area with the ultraviolet laser source. If only Raman suppression gratings need to be inscribed, only the TFBG area needs to be exposed. ② If it is necessary to integrate the low-reflectivity grating and the Raman grating into a single fiber, the displacement stage can be controlled to scan and inscribe the entire mask area. Because it is a multiple scan, the order of inscription does not need to be standardized.

[0090] For any parts not mentioned in this invention, existing technologies can be used or referenced.

[0091] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A photomask, characterized in that, include: A quartz glass substrate; A Bragg grating (FBG) mask unit and a Raman tilted fiber grating (TFBG) mask unit are integrated on a quartz glass substrate, and the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are arranged in a left-right structure on the quartz glass substrate. An intermediate non-striated region is provided between the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit, and the length l of the intermediate non-striated region satisfies 20mm≤l≤40mm; The stripes of the Raman tilted fiber grating (TFBG) mask unit have an angle θ relative to the substrate plane, satisfying 3°≤θ≤5°.

2. The mask template according to claim 1, characterized in that, The center wavelength of the Bragg grating (FBG) mask unit is 1080nm, the chirp rate is 0.7nm / cm~1.5nm / cm, and the fringe length is 40mm~60mm; the center wavelength of the Raman tilted fiber grating (TFBG) mask unit is 1135nm, the chirp rate is 1.5nm / cm~2nm / cm, and the fringe length is 80mm~100mm.

3. The mask template according to claim 1, characterized in that, The distance between the Bragg grating (FBG) mask unit and one side of the substrate is ≤15mm, and the distance between the Raman tilted fiber grating (TFBG) mask unit and the other side of the substrate is ≤15mm.

4. The mask template according to claim 1, characterized in that, The width of the Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit is 10 mm.

5. The mask template according to claim 1, characterized in that, The quartz glass substrate is 200mm long, 20mm wide and 6mm thick. The Bragg grating (FBG) mask unit and the Raman tilted fiber grating (TFBG) mask unit are located in the middle of the width of the quartz glass substrate.

6. The etching system for the photomask according to any one of claims 1-5, characterized in that, include: Ultraviolet light source, used to provide the ultraviolet laser required for etching; An aperture, placed in the optical path of an ultraviolet light source, is used to adjust the size and shape of the ultraviolet laser beam; The ultraviolet reflector, together with the aperture, is fixed on the displacement stage to change the propagation direction of the ultraviolet laser, ensuring that the beam can be perpendicularly irradiated onto the mask during the movement of the displacement stage. The displacement stage is used to support and move the ultraviolet reflector and aperture to adjust the irradiation position of the ultraviolet laser on the mask. A cylindrical mirror, positioned below the displacement stage, is used to focus the ultraviolet laser, ensuring that the ultraviolet laser is focused into the core of the optical fiber. The mask is placed below the cylindrical mirror to diffract the ultraviolet laser, where the nth order diffracted beam overlaps with the -nth order diffracted beam and produces interference fringes in the overlapping area. The optical fiber is placed close to the mask template and is in the interference field, forming an axial periodic refractive index modulation structure in the fiber core; During the writing process, the photomask and cylindrical mirror are fixed in place, and the ultraviolet laser is scanned at different photomask positions by moving the displacement stage to write Bragg gratings (FBG) and Raman tilted fiber gratings (TFBG).

7. The etching system according to claim 6, characterized in that, The length of the cylindrical mirror is greater than the total length of the Bragg grating (FBG) mask unit, the Raman tilted fiber grating (TFBG) mask unit, and the intermediate non-fringe region in the mask template.

8. The etching system according to claim 6, characterized in that, The displacement stage moves a distance greater than the length of the mask template to cover the striped area of ​​the mask template.

9. The etching system according to claim 6, characterized in that, The displacement stage is a speed-adjustable DC servo linear displacement stage with a round-trip error accuracy of less than 1µm and a maximum speed of 100mm / s. The displacement stage moves faster in the corresponding non-striped area than in the striped area.

10. The etching system according to claim 6, characterized in that, Before writing the gratings, the optical fiber undergoes a stripping coating process. After writing, the left Bragg grating (FBG) is coated with low-refractive adhesive, and the right Raman tilted fiber grating (TFBG) is protected with a glass tube.

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