A method and apparatus for manufacturing a fiber grating

Abstract

The present disclosure relates to the technical field of fiber grating manufacturing, and particularly relates to a fiber grating preparation method and preparation device, the method comprising the following steps: step 1, according to a preset target light field, a corresponding holographic phase map is obtained through iterative algorithm inversion calculation; step 2, the holographic phase map is loaded to a spatial light modulator to modulate the phase of incident laser, and modulated laser is obtained; step 3, femtosecond laser direct writing is performed on a fiber sample using the modulated laser, and a fiber grating is obtained. The present disclosure simplifies the grating preparation process, reduces the preparation cost, and effectively improves the preparation efficiency and writing precision.

Description

Technical Field

[0001] This disclosure relates to the field of fiber Bragg grating manufacturing technology, and in particular to a method and apparatus for fabricating fiber Bragg gratings. Background Technology

[0002] Grating devices, with their ability to diffract incident beams, can be used for beam splitting, pulse broadening, and pulse compression, and are widely applied in fields such as spectral measurement, optical computing, optical information processing, and laser amplification systems. Currently, common grating fabrication methods include mechanical scribing, ultraviolet exposure, and femtosecond laser direct writing. Among these, femtosecond laser direct writing, as an innovative fabrication method, is gaining increasing popularity. This method utilizes the high peak power and extremely short pulse width of femtosecond pulsed lasers to generate nonlinear effects when interacting with transparent media, achieving a permanent change in the material's refractive index. Using femtosecond laser direct writing, grating structures can be directly written onto the fiber core through various transparent coatings. This fabrication method is characterized by high efficiency, flexibility, and precision, providing new pathways and potential for the fabrication and application of grating devices.

[0003] Existing techniques for fabricating fiber gratings include point-by-point fabrication, line-by-line fabrication, surface-by-surface fabrication, and core scanning. However, these methods are limited by the size of the light spot and the spatial alignment accuracy, resulting in gratings whose precision cannot meet more diverse requirements. These traditional grating fabrication methods rely heavily on the accuracy of the displacement stage and mask, leading to high costs and difficulties in dynamic control.

[0004] Furthermore, ultraviolet (UV) exposure is widely used for writing FBG (Fiber Bragg Grating) and LPG (Long Period Grating) gratings, but it typically requires a phase mask or amplitude mask to assist the writing process. This dependence limits the flexibility and versatility of grating writing, as the resonant wavelength of the grating is directly affected by the template period. In addition, hydrogen loading is often required to make the fiber photosensitized, which further increases the complexity and difficulty of the grating writing process. This dependence and complexity are particularly pronounced for writing large-core fiber gratings.

[0005] In summary, although fiber gratings have broad application prospects in the field of optics, existing fabrication processes still present some challenges. One major issue is the complexity of the fabrication process, which increases the complexity and cost of the fabrication. Another issue is the quality stability during fabrication; even minor errors or instabilities can cause the grating's performance to fall short of expectations, limiting its repeatability and consistency, and thus hindering large-scale production and commercial applications.

[0006] Therefore, existing technologies need further improvement. Summary of the Invention

[0007] The purpose of this invention is to reduce the fabrication cost of fiber Bragg gratings and improve their fabrication efficiency and marking accuracy.

[0008] To address the aforementioned technical problems, this disclosure provides a method for fabricating a fiber grating, comprising the following steps: Step 1, obtaining a corresponding holographic phase map by inversion calculation using an iterative algorithm based on a preset target light field; Step 2, loading the holographic phase map onto a spatial light modulator to perform phase modulation on the incident laser to obtain a modulated laser; Step 3, using the modulated laser to perform femtosecond laser direct writing on the fiber sample to obtain a fiber grating.

[0009] In some embodiments, in step 1, the iterative algorithm is the Gersberg-Saxton iterative algorithm.

[0010] In some embodiments, in step 2, the energy density of the incident light is lower than the damage threshold of the spatial light modulator.

[0011] In some embodiments, in step 3, the modulated laser is spatially filtered and zero-order diffraction is suppressed before femtosecond laser direct writing is performed on the fiber sample.

[0012] In addition, this disclosure also provides a fiber optic grating fabrication apparatus for implementing the above-described fabrication method. The fabrication apparatus includes a computing module, a femtosecond laser, and a spatial light modulator. The computing module is used to preset the target light field and run an iterative algorithm to generate the corresponding holographic phase map. The femtosecond laser is used to emit the incident laser. The spatial light modulator is used to receive the incident laser and the holographic phase map, and to perform phase modulation on the incident laser, outputting a modulated laser to perform femtosecond laser direct writing on the fiber sample.

[0013] In some embodiments, the fabrication apparatus further includes a shutter, a half-wave plate, and a polarizing beam splitter, wherein the incident laser emitted by the femtosecond laser passes through the shutter, the half-wave plate, and the polarizing beam splitter in sequence and is incident into the spatial light modulator.

[0014] In some embodiments, the fabrication apparatus further includes a transmission module, wherein the modulated laser emitted by the spatial light modulator is spatially filtered and zero-order diffraction is suppressed by the transmission module before being used to perform femtosecond laser direct writing on the fiber sample.

[0015] In some embodiments, the transmission module includes a first plano-convex lens, an aperture, a second plano-convex lens, and an objective lens. The modulated laser emitted by the spatial light modulator passes through the first plano-convex lens, the aperture, the second plano-convex lens, and the objective lens in sequence to perform femtosecond laser direct writing on the fiber optic sample.

[0016] In some embodiments, the preparation apparatus further includes an observation module, through which the reflected light from the fiber optic sample enters the observation module for imaging, thereby enabling the observation of the femtosecond laser direct writing process of the fiber optic sample.

[0017] In some embodiments, the observation module includes: a dichroic mirror, a white light source, an infrared filter, a lens, and a camera. The white light source emits illumination light, which is coupled into the objective lens through the dichroic mirror to illuminate the fiber optic sample. The reflected light generated by the fiber optic sample returns through the objective lens, is then split by the dichroic mirror, and passes sequentially through the infrared filter and the lens to be focused onto the camera.

[0018] By adopting the above technical solution, this disclosure has at least the following beneficial effects: By pre-setting the target light field and combining iterative algorithms to generate a holographic phase map, and relying on a spatial light modulator to complete laser phase modulation, the grating fabrication process is simplified and the fabrication cost is reduced without the need for a complex mechanical optical path adjustment structure. By precisely controlling the distribution of the incident laser light field through the holographic phase map, a modulated laser adapted for direct fiber writing is output, resulting in higher optical path control precision and effectively improving fabrication efficiency and writing accuracy. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart of a method for fabricating a fiber Bragg grating according to an embodiment of the present disclosure; Figure 2 This is a schematic diagram of a fiber Bragg grating fabrication apparatus according to an embodiment of the present disclosure; Figure 3 This is a holographic phase map according to an embodiment of the present disclosure; Figure 4 This is a schematic diagram of the structure of a fiber Bragg grating according to an embodiment of the present disclosure; Figure 5 This is an optical microscope image of a fiber Bragg grating according to an embodiment of the present disclosure.

[0021] Figure label: 1. Calculation module; 2. Femtosecond laser; 3. Shutter; 4. Half-wave plate; 5. First plane mirror; 6. Second plane mirror; 7. Spatial light modulator; 8. Polarizing beam splitter; 9. Third plane mirror; 10. Fourth plane mirror; 11. First plano-convex lens; 12. Aperture stop; 13. Second plano-convex lens; 14. First dichroic mirror; 15. Second dichroic mirror; 16. White light source; 17. Infrared filter; 18. Lens; 19. Camera; 20. Objective lens; 21. Sample stage; 22. Fiber optic sample. Detailed Implementation

[0022] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0023] These embodiments are provided to make the disclosure thorough and complete, and to fully express the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, material composition, numerical expressions, and values ​​set forth in these embodiments should be interpreted as exemplary only and not as limiting.

[0024] It should be noted that, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationship, are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0025] Furthermore, the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. "Vertical" is not strictly vertical, but within the permissible margin of error. "Parallel" is not strictly parallel, but within the permissible margin of error. Terms such as "including" or "contains" mean that the element preceding the word encompasses the element listed after the word, and do not exclude the possibility of encompassing other elements as well.

[0026] It should also be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure depending on the specific circumstances. When a particular device is described as being located between a first device and a second device, an intermediary device may or may not be present between the particular device and the first or second device.

[0027] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0028] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0029] As mentioned in the background section, although fiber gratings have broad application prospects in the optical field, existing fabrication processes still have some problems. One major problem is the complexity of the fabrication process, which increases the complexity and cost of the fabrication process; another problem is the quality stability during the fabrication process. Small errors or instabilities may cause the grating performance to fail to meet expectations, which limits the repeatability and consistency of the grating and restricts large-scale production and commercial applications. Based on the above, this disclosure provides a method and apparatus for fabricating fiber gratings. Through the method of this technical solution, the fabrication cost of fiber gratings is reduced, the fabrication efficiency of fiber gratings is improved, and the writing accuracy is increased, thus solving one or more problems in the prior art.

[0030] This disclosure provides a method for fabricating fiber Bragg gratings, such as... Figure 1 As shown, the process includes the following steps: Step 1: Based on the preset target light field, the corresponding holographic phase map is obtained by inversion calculation using an iterative algorithm; Step 2: The holographic phase map is loaded onto the spatial light modulator 7 to modulate the phase of the incident laser, obtaining a modulated laser; Step 3: The modulated laser is used to perform femtosecond laser direct writing on the fiber sample 22 to obtain a fiber grating. The fabricated fiber grating is shown in the figure. Figure 4 and Figure 5 As shown.

[0031] Specifically, the method disclosed herein first relies on a preset target light field and uses an iterative algorithm to solve in reverse to obtain a holographic phase map that matches the light field requirements. Then, a spatial light modulator 7 is used to load the phase map to complete laser phase modulation. Finally, the modulated femtosecond laser is used to directly write the fiber sample 22. Relying on the nonlinear refractive index modulation effect of the laser, a fiber grating is finally formed, realizing laser light field writing without mechanical movement.

[0032] Compared with existing technologies, this disclosure proposes a method for fabricating fiber gratings. By pre-setting a target light field and combining iterative algorithms to generate a holographic phase map, laser phase modulation is completed using a spatial light modulator 7. This eliminates the need for complex mechanical optical path adjustment structures, simplifying the grating fabrication process and reducing fabrication costs. Furthermore, by precisely controlling the incident laser light field distribution through the holographic phase map, a modulated laser adapted for direct fiber writing is output, resulting in higher optical path control precision and effectively improving fabrication efficiency and writing accuracy.

[0033] In the above preparation method, in step 1, the iterative algorithm is the Gersberg-Saxton iterative algorithm. Specifically, the calculation process using the Gersberg-Saxton iterative algorithm is as follows: Intensity distribution information of the target light field is obtained from the target image; the phase mode of the spatial light modulator 7 is initialized; through iterative calculation, the phase mode is updated on the plane of the spatial light modulator 7 to gradually approximate the phase information of the target image; in each iteration, the updated phase mode is transmitted to the spatial light modulator 7, and the light field distribution of the coherent light is observed; based on the observed light field distribution, the phase mode is adjusted to further approximate the phase information of the target image; the above process is repeated until the phase mode converges to the phase information of the target image. A high-precision holographic phase map is obtained through the Gersberg-Saxton iterative algorithm, ensuring the accuracy of laser light field control. The holographic phase map is shown below. Figure 3 As shown.

[0034] In the above preparation method, in step 2, the energy density of the incident light is lower than the damage threshold of the spatial light modulator 7. Specifically, by controlling the energy density of the incident light, laser damage to the spatial light modulator 7 is avoided, thus protecting the core optical components.

[0035] In the above preparation method, in step 3, the modulated laser is spatially filtered and zero-order diffraction light is suppressed before femtosecond laser direct writing is performed on the fiber sample 22. Specifically, by spatially filtering the modulated laser and suppressing the zero-order diffraction stray light in the optical path, the interference of unwanted stray light on the writing spot is eliminated, thereby improving the uniformity of fiber grating writing and the quality of the finished product.

[0036] On the other hand, some embodiments of this disclosure also provide an apparatus for fabricating fiber Bragg gratings, such as... Figure 2As shown, it includes: a calculation module 1, a femtosecond laser 2, and a spatial light modulator 7. The calculation module 1 is used to preset the target light field and run an iterative algorithm to generate the corresponding holographic phase map. The femtosecond laser 2 is used to emit the incident laser. The spatial light modulator 7 is used to receive the incident laser and the holographic phase map, and to perform phase modulation on the incident laser and output modulated laser to perform femtosecond laser direct writing on the fiber sample 22.

[0037] Specifically, the computation module 1 performs optical field pre-setting and holographic phase diagram solving, the femtosecond laser 2 provides the processing light source, and the spatial light modulator 7 performs laser phase modulation. These three components work together to achieve fully automated optical field control and direct writing of the fiber optic grating. Preferably, the output from the femtosecond laser 2 is an ultrashort pulse laser with a center wavelength of 800 nm, a pulse width of approximately 50 fs, and a repetition frequency of 1000 Hz. The spatial light modulator 7 can be a liquid crystal type.

[0038] In some embodiments, such as Figure 2 As shown, the fabrication apparatus also includes a shutter 3, a half-wave plate 4, and a polarizing beam splitter 8. The incident laser emitted from the femtosecond laser 2 passes sequentially through the shutter 3, the half-wave plate 4, and the polarizing beam splitter 8 before entering the spatial light modulator 7. Specifically, the shutter 3 controls the number of incident laser pulses, and the half-wave plate 4 and the polarizing beam splitter 8 allow for precise adjustment of the laser energy, preventing the incident light energy density from exceeding the damage threshold of the spatial light modulator 7 and thus damaging it. Furthermore, multiple plane mirrors can be placed in the optical path between the femtosecond laser 2 and the spatial light modulator 7 to change the direction of the incident light, ensuring that the incident light is more precisely incident on the center of each component. Preferably, there are four plane mirrors, namely a first plane mirror 5, a second plane mirror 6, a third plane mirror 9, and a fourth plane mirror 10. Specifically, the first plane mirror 5 and the second plane mirror 6 are arranged in the optical path between the waveplate and the polarizing beam splitter 8, and the third plane mirror 9 and the fourth plane mirror 10 are arranged in the optical path between the polarizing beam splitter 8 and the spatial light modulator 7.

[0039] In some embodiments, the fabrication apparatus further includes a transmission module. The modulated laser emitted by the spatial light modulator 7 is spatially filtered and zero-order diffraction light is suppressed by the transmission module before being used for femtosecond laser direct writing on the fiber sample 22. Specifically, the transmission module achieves filtering and suppression of zero-order diffraction light, filters out stray light in the optical path, suppresses zero-order diffraction light, optimizes the laser spot quality, and avoids the impact of diffraction stray light on the fiber writing accuracy.

[0040] In some embodiments, such as Figure 2As shown, the transmission module includes a first plano-convex lens 11, an aperture 12, a second plano-convex lens 13, and an objective lens 20. The modulated laser emitted from the spatial light modulator 7 passes sequentially through the first plano-convex lens 11, the aperture 12, the second plano-convex lens 13, and the objective lens 20 to perform femtosecond laser direct writing on the fiber sample 22. Specifically, after the modulated laser undergoes a Fourier transform by the first plano-convex lens 11, it undergoes an inverse Fourier transform by the second plano-convex lens 13 to obtain a light field identical to the original field. This achieves the conversion of the modulated laser from the plane of the liquid crystal spatial light modulator 7 to the image plane of the objective lens 20, thereby realizing spatial filtering of the modulated laser. The aperture 12 is positioned in the optical path between the first plano-convex lens 11 and the second plano-convex lens 13 to suppress the zero-order diffraction light generated by the spatial light modulator 7. Specifically, a blazed grating phase is superimposed on the spatial light modulator 7 to offset the modulated laser from the zero point, and then the aperture 12 is used to block the zero-order diffraction light. Preferably, the aperture 12 is located at the image-side focal point of the first plano-convex lens 11.

[0041] In some embodiments, the fabrication apparatus further includes an observation module. The reflected light from the fiber optic sample 22 enters the observation module through the objective lens 20 for imaging, thereby enabling the observation of the femtosecond laser direct writing process on the fiber optic sample 22. The observation module allows for full monitoring of the femtosecond laser direct writing process, ensuring the quality of the fiber grating.

[0042] In some embodiments, such as Figure 2 As shown, the observation module includes a dichroic mirror, a white light source 16, an infrared filter 17, a lens 18, and a camera 19. The white light source 16 emits illumination light, which is coupled through the dichroic mirror into the objective lens 20, illuminating the fiber optic sample 22. The reflected light generated by the fiber optic sample 22 returns through the objective lens 20, is then split by the dichroic mirror, and passes sequentially through the infrared filter 17 and the lens 18 before being focused onto the camera 19. The above equipment enables the observation function of the observation module. Further, there can be two dichroic mirrors, namely a first dichroic mirror 14 and a second dichroic mirror 15. Specifically, the white light source 16 can be a white LED, whose emitted white light is coupled through the second dichroic mirror 15 and the first dichroic mirror 14 to a modulated laser, entering the objective lens 20 and radiating onto the fiber optic sample 22 placed on the processing sample stage 21. The diffuse reflected light from the fiber optic sample 22 is focused onto the camera 19 through the infrared filter 17 and the lens, forming a coaxial processing observation system.

[0043] Compared to existing technologies, the fiber grating fabrication method and apparatus disclosed in this disclosure simplify the fabrication process, reduce fiber grating writing costs, and improve writing accuracy and efficiency. Simultaneously, it overcomes the limitations of existing technologies in terms of photomasks and high-precision displacement stages, and can fabricate fiber gratings with adjustable periods, breaking through the limitation of a single fixed writing period. Furthermore, the method of this disclosure eliminates the step of removing the coating layer required in the fiber grating fabrication process of existing technologies, improving fabrication efficiency and reliability.

[0044] The embodiments of this disclosure have now been described in detail. To avoid obscuring the concept of this disclosure, some details known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed herein based on the above description.

[0045] While specific embodiments of this disclosure have been described in detail by way of examples, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments or equivalent substitutions can be made to some technical features without departing from the scope and spirit of this disclosure. In particular, as long as there is no structural conflict, the technical features mentioned in the various embodiments can be combined in any manner.

Claims

1. A method for fabricating a fiber Bragg grating, characterized in that, Includes the following steps: Step 1: Based on the preset target light field, the corresponding holographic phase map is obtained by inversion calculation through an iterative algorithm; Step 2: Load the holographic phase map into a spatial light modulator to modulate the phase of the incident laser, thereby obtaining modulated laser; Step 3: Use the modulated laser to perform femtosecond laser direct writing on the fiber sample to obtain a fiber grating.

2. The method for fabricating a fiber Bragg grating according to claim 1, characterized in that, In step 1, the iterative algorithm is the Gersberg-Saxton iterative algorithm.

3. The method for fabricating a fiber Bragg grating according to claim 1, characterized in that, In step 2, the energy density of the incident light is lower than the damage threshold of the spatial light modulator.

4. The method for fabricating a fiber Bragg grating according to claim 1, characterized in that, In step 3, the modulated laser is spatially filtered and zero-order diffraction is suppressed before being used to perform femtosecond laser direct writing on the fiber sample.

5. An apparatus for fabricating fiber Bragg gratings, characterized in that, The fabrication apparatus for implementing the fabrication method according to any one of claims 1-4 includes: a computing module, a femtosecond laser, and a spatial light modulator. The computing module is used to preset the target light field and run an iterative algorithm to generate a corresponding holographic phase map. The femtosecond laser is used to emit an incident laser. The spatial light modulator is used to receive the incident laser and the holographic phase map, and to perform phase modulation on the incident laser, and output modulated laser to perform femtosecond laser direct writing on the fiber sample.

6. The apparatus for fabricating fiber Bragg gratings according to claim 5, characterized in that, The fabrication apparatus further includes a shutter, a half-wave plate, and a polarizing beam splitter. The incident laser emitted by the femtosecond laser passes sequentially through the shutter, the half-wave plate, and the polarizing beam splitter into the spatial light modulator.

7. The apparatus for fabricating fiber Bragg gratings according to claim 5, characterized in that, The fabrication apparatus further includes a transmission module, through which the modulated laser emitted by the spatial light modulator undergoes spatial filtering and zero-order diffraction suppression before being used to perform femtosecond laser direct writing on the fiber sample.

8. The apparatus for fabricating fiber Bragg gratings according to claim 7, characterized in that, The transmission module includes a first plano-convex lens, an aperture, a second plano-convex lens, and an objective lens. The modulated laser emitted by the spatial light modulator passes sequentially through the first plano-convex lens, the aperture, the second plano-convex lens, and the objective lens to perform femtosecond laser direct writing on the fiber optic sample.

9. The fabrication apparatus for fiber Bragg gratings according to claim 8, characterized in that, The preparation device also includes an observation module, through which the reflected light from the optical fiber sample enters the observation module for imaging, thereby enabling the observation of the femtosecond laser direct writing process of the optical fiber sample.

10. The apparatus for fabricating fiber Bragg gratings according to claim 9, characterized in that, The observation module includes a dichroic mirror, a white light source, an infrared filter, a lens, and a camera. The white light source emits illumination light, which is coupled into the objective lens through the dichroic mirror to illuminate the optical fiber sample. The reflected light generated by the optical fiber sample returns through the objective lens, is then split by the dichroic mirror, and passes sequentially through the infrared filter and the lens to be focused onto the camera.

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