Wavelength self-matching writing system and method for cross-aligned fiber grating pairs

Abstract

The present invention provides a wavelength self-matching writing system and method for a cross-aligned fiber grating pair, which is used for simultaneously writing a high-reflection grating and a low-reflection grating with matching central wavelengths on a polarization-maintaining optical fiber to be written. The writing system includes a light source and a phase mask plate arranged in sequence along the light output direction. By arranging slow-axis matching regions and fast-axis matching regions of different periods on the phase mask plate, and matching the polarization-maintaining optical fiber to be written, which is composed of a cross-aligned first optical fiber segment and a second optical fiber segment, the first optical fiber segment is arranged corresponding to the slow-axis matching region, and the second optical fiber segment is arranged corresponding to the fast-axis matching region, the high-reflection grating and the low-reflection grating with matching central wavelengths can be simultaneously written on the polarization-maintaining optical fiber to be written, thereby eliminating the influence of uncertainty on the central wavelength of the grating, improving the yield rate, and reducing the difficulty of producing the fiber grating pair.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber gratings, and in particular to a wavelength self-matching writing system and method for a cross-aligned optical fiber grating pair. Background Art

[0002] In recent years, with the rapid development of fiber and laser technologies, high-power linearly polarized fiber lasers have found widespread application in fields such as coherent communications, sensing, nonlinear frequency conversion, gravitational wave detection, and industrial processing. Currently, achieving high-power linearly polarized laser output in fiber lasers often involves cross-aligning the high- and low-reflection gratings inscribed on the polarization-maintaining fiber within a fully polarization-maintaining linear cavity. This ensures that only laser light with a single polarization can oscillate within the cavity, thereby achieving linearly polarized laser output. This approach, which consists solely of the high- and low-reflection gratings and the gain fiber, without any other components, can achieve narrow-linewidth linearly polarized laser output up to kilowatts. However, this approach to achieving high-power, narrow-linewidth laser light places extremely high demands on the high- and low-reflection grating pair. To achieve optimal output efficiency, the wavelengths of the high- and low-reflection gratings must be as close as possible, and the 3dB bandwidth of the high-reflection grating's reflection spectrum must be smaller than the wavelength difference introduced by the refractive index difference between the fast and slow axes of the fiber to ensure that only laser light with a single polarization can oscillate.

[0003] During the actual grating writing process, the actual amount of hydrogen permeated into different sections of the fiber during hydrogen loading before writing will result in different initial wavelengths. The amount of ineffective UV light exposure caused by environmental vibrations during writing will also increase the wavelength by different amounts. The amount of wavelength contraction during high-temperature annealing after writing will also vary, resulting in uncertainty in the center wavelength of the completed grating. High-reflectivity gratings and low-reflectivity gratings are generally written separately. These wavelength offset differences greatly increase the difficulty of matching high- and low-reflectivity gratings, thereby reducing the yield rate and making grating production very difficult. Summary of the Invention

[0004] In response to the above technical problems, the present invention provides a wavelength self-matching writing system and method for a cross-aligned fiber grating pair, which can realize the simultaneous writing of high-reflection grating and low-reflection grating on the same section of optical fiber, thereby eliminating the influence of uncertainty on the grating center wavelength.

[0005] The present invention provides a wavelength self-matching writing system for a cross-aligned fiber grating pair, which is used to simultaneously write a high-reflection grating and a low-reflection grating with matching central wavelengths on a polarization-maintaining optical fiber to be written. The writing system includes a light source and a phase mask template arranged in sequence along the light output direction; the light source is used to provide a working laser along the light output direction; the phase mask template is used to diffract the laser to form ±1-order diffraction output and suppress 0-order diffraction, and the phase mask template includes a slow-axis matching region and a fast-axis matching region arranged in sequence along a first direction, the slow-axis matching region has a first period, the fast-axis matching region has a second period, the first period is different from the second period, and the first direction is vertical. perpendicular to the light emitting direction; the polarization-maintaining optical fiber to be inscribed extends along a first direction, and the polarization-maintaining optical fiber to be inscribed includes a first optical fiber segment and a second optical fiber segment, the fast and slow axes of the first optical fiber segment and the second optical fiber segment are cross-aligned, the first optical fiber segment is corresponding to the slow axis matching area, and the second optical fiber segment is corresponding to the fast axis matching area; wherein, the central wavelength of the inscribed high-reflection grating and the low-reflection grating is the target wavelength, the refractive index of the first optical fiber segment corresponding to the target wavelength is a first refractive index, the refractive index of the second optical fiber segment corresponding to the target wavelength is a second refractive index, and the product of the first refractive index and the first period, and the product of the second refractive index and the second period are both equal to the target wavelength.

[0006] Preferably, the engraving system also includes a shaping template, which is arranged between the light source and the phase mask, and the shaping template includes a first shaping area and a second shaping area arranged in sequence along a first direction, the first shaping area is arranged corresponding to the slow axis matching area, and the second shaping area is arranged corresponding to the fast axis matching area, a first shaping hole is provided in the first shaping area, and a second shaping hole is provided in the second shaping area.

[0007] Furthermore, a height of the first shaping hole along a direction perpendicular to the first direction is equal to a height of the second shaping hole along a direction perpendicular to the first direction.

[0008] Furthermore, the maximum length of the first shaping hole along the first direction is not greater than the maximum length of the second shaping hole along the first direction.

[0009] Furthermore, the first shaping hole and the second shaping hole are both rectangular structures, Gaussian structures, super Gaussian structures, or SINC structures.

[0010] Furthermore, the writing system also includes a beam expander assembly for expanding the laser beam, and the beam expander assembly is arranged between the light source and the shaping template.

[0011] Furthermore, the beam expander assembly includes a first cylindrical lens and a second cylindrical lens. The light source, the first cylindrical lens, the second cylindrical lens, and the shaping template are arranged in sequence. The first cylindrical lens is used to receive the laser provided by the light source, focus the laser, and diverge after passing through the focus. The second cylindrical lens is used to refract the divergent laser into a parallel laser.

[0012] Furthermore, the writing system also includes a third cylindrical lens for focusing the shaped laser. The third cylindrical lens is arranged between the shaping template and the phase mask. The polarization-maintaining optical fiber to be written is located at the focus of the laser focused by the second cylindrical lens.

[0013] On the other hand, the present invention provides a wavelength self-matching writing method for a cross-aligned fiber grating pair, which is used to simultaneously write a high-reflection grating and a low-reflection grating on a polarization-maintaining optical fiber to be written. The writing method comprises the following steps:

[0014] S1. The first fiber segment and the second fiber segment are fused at 90 degrees to obtain a polarization-maintaining fiber to be written, wherein the polarization-maintaining fiber to be written extends along a first direction, and the fast and slow axes of the first fiber segment and the second fiber segment are cross-aligned;

[0015] S2 provides a working laser along the light direction, the light direction is perpendicular to the first direction;

[0016] S3. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a first-intensity spatially periodically modulated light spot is incident on the first fiber segment. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a second-intensity spatially periodically modulated light spot is incident on the second fiber segment. The period of the first-intensity spatially periodically modulated light spot is different from the period of the second-intensity spatially periodically modulated light spot.

[0017] Among them, the central wavelength of the engraved high-reflection grating and low-reflection grating is the target wavelength, the refractive index of the first optical fiber segment corresponding to the target wavelength is the first refractive index, the refractive index of the second optical fiber segment corresponding to the target wavelength is the second refractive index, and the product of the period of the first-intensity spatially periodically modulated light spot and the first refractive index and the product of the period of the second-intensity spatially periodically modulated light spot and the second refractive index are both equal to the target wavelength.

[0018] Preferably, step S3 includes the following steps:

[0019] S31. The laser is shaped into a first laser and a second laser;

[0020] S32. The first intensity spatially periodically modulated light spot of the first laser after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the first optical fiber segment, and the second intensity spatially periodically modulated light spot of the second laser after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the second optical fiber segment.

[0021] Compared with the prior art, the wavelength self-matching writing system and method for the cross-aligned fiber Bragg grating pair of the present invention, by setting slow axis matching areas and fast axis matching areas of different periods on the phase mask, cooperates with the polarization-maintaining fiber to be written composed of a first fiber segment and a second fiber segment that are cross-aligned, the first fiber segment is set corresponding to the slow axis matching area, and the second fiber segment is set corresponding to the fast axis matching area, so as to achieve the simultaneous writing of a high-reflection grating and a low-reflection grating with matching central wavelengths on the polarization-maintaining fiber to be written, thereby eliminating the influence of uncertainty on the central wavelength of the grating, improving the yield rate, and reducing the production difficulty of the fiber Bragg grating pair. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Schematic diagram of the structure of a wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to an embodiment of the present invention.

[0024] Figure 2 FIG. 4 is a schematic structural diagram of a phase mask according to an embodiment of the present invention.

[0025] Figure 3 FIG. 1 is a schematic structural diagram of a wavelength self-matching writing system for cross-aligned fiber grating pairs according to another embodiment of the present invention.

[0026] Figure 4 This is a structural diagram of a shaping template according to an embodiment of the present invention.

[0027] Figure 5 This is a schematic structural diagram of a shaping template according to another embodiment of the present invention.

[0028] Figure 6 FIG. 1 is a schematic structural diagram of a wavelength self-matching writing system for cross-aligned fiber grating pairs according to another embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to provide a further understanding of the purpose, structure, features, and functions of the present invention, the present invention is described in detail below with reference to the embodiments.

[0030] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the present invention.

[0031] According to the Bragg condition, the wavelength reflected by the grating is determined by the period of refractive index modulation in the fiber core and the refractive index of the fiber. That is, when light that meets the Bragg condition passes through the grating, it will be distributedly reflected. The specific expression of the Bragg condition is:

[0032] ,

[0033] Where λ is the laser wavelength, is the effective refractive index of the optical fiber core, is the period of refractive index modulation in the fiber core.

[0034] The relationship between the fiber core refractive index modulation period and the spatial structure period on the phase mask is:

[0035] ,

[0036] in, is the phase mask period.

[0037] From the above, we can know that the central wavelength of the grating is equal to the phase mask period multiplied by the effective refractive index of the fiber core, that is,

[0038] .

[0039] See Figure 1 and Figure 2 The wavelength self-matching writing system for a cross-aligned fiber Bragg grating pair of the present invention is used to simultaneously write a high-reflection grating and a low-reflection grating with matching central wavelengths on a polarization-maintaining optical fiber 3 to be written. The writing system includes a light source 1 and a phase mask 2 arranged in sequence along the light output direction.

[0040] The light source 1 is used to provide working laser light along a light-emitting direction. In one embodiment, the light source 1 may be an ultraviolet laser for emitting ultraviolet laser light.

[0041] The phase mask 2 is used to diffract the laser to form ±1 order diffraction output and suppress 0 order diffraction. The phase mask 2 includes a slow axis matching area 21 and a fast axis matching area 22 arranged in sequence along a first direction. The slow axis matching area 21 has a first period t1, and the fast axis matching area 22 has a second period t2. The first period t1 is different from the second period t2, and the first direction is perpendicular to the light output direction.

[0042] The polarization-maintaining optical fiber 3 to be inscribed extends along a first direction and includes a first optical fiber segment 31 and a second optical fiber segment 32. The fast and slow axes of the first and second optical fiber segments 31, 32 are cross-aligned. The first optical fiber segment 31 is disposed correspondingly to the slow-axis matching region 21, and the second optical fiber segment 32 is disposed correspondingly to the fast-axis matching region 22. In one embodiment, the first and second optical fiber segments 31, 32 are two halves of the same polarization-maintaining optical fiber that are split in the middle. These two halves are fused together at 90 degrees, i.e., their fast and slow axes are cross-aligned, to obtain the polarization-maintaining optical fiber 3 to be inscribed.

[0043] The central wavelength of the inscribed high-reflection grating and low-reflection grating is the target wavelength λ, the refractive index of the first optical fiber segment 31 corresponding to the target wavelength λ is the first refractive index n1, and the refractive index of the second optical fiber segment 32 corresponding to the target wavelength λ is the second refractive index n2, and n1*t1=n2*t2=λ.

[0044] The wavelength self-matching writing system for the cross-aligned fiber Bragg grating pair of this embodiment, by setting slow-axis matching regions 21 and fast-axis matching regions 22 of different periods on the phase mask 2, cooperates with the polarization-maintaining fiber 3 to be written, which is composed of a cross-aligned first fiber segment 31 and a second fiber segment 32. The first fiber segment 31 is set corresponding to the slow-axis matching region 21, and the second fiber segment 32 is set corresponding to the fast-axis matching region 22. This enables the simultaneous writing of a high-reflection grating and a low-reflection grating with matching central wavelengths on the polarization-maintaining fiber 3 to be written, thereby eliminating the influence of uncertainty on the central wavelength of the grating, improving the yield rate, and reducing the difficulty of producing the fiber Bragg grating pair.

[0045] In practical use, the present invention can be specifically embodied in the following embodiments:

[0046] The target wavelength λ is 1064 nm (nanometers). The polarization-maintaining fiber 3 to be inscribed is made by cross-aligning two sections of PM980 optical fibers. The birefringence coefficient of the commonly used PM980 optical fiber is about 2.72×10 -4 The refractive index of PM980 fiber at 1064 nm is approximately 1.452. According to the formula n1*t1=n2*t2=λ, the period of the slow-axis matching region 21 on the phase mask 2 is 732.65 nm, and the period of the fast-axis matching region 22 is 732.78 nm.

[0047] When writing a fiber Bragg grating pair, the phase mask 2 with appropriate periods of the slow-axis matching region 21 and the fast-axis matching region 22 is selected according to the target wavelength λ and the refractive index of the first fiber segment 31 and the second fiber segment 32 that constitute the polarization-maintaining fiber 3 to be written, so that the simultaneous writing of high-reflection grating and low-reflection grating can be achieved.

[0048] See Figure 3 , Figure 3 FIG1 is a schematic diagram of a wavelength self-matching writing system for a cross-aligned fiber grating pair according to another embodiment of the present invention. Figure 1 Compared to the embodiment in the previous embodiment, in this embodiment, the writing system further includes a shaping template 4, which is used to shape the spatial distribution of the laser light, dividing the laser light into two paths, respectively writing a high-reflection grating and a low-reflection grating. The shaping template 4 is arranged between the light source 1 and the phase mask 2. The shaping template 4 includes a first shaping area 41 and a second shaping area 42 arranged in sequence along a first direction. The first shaping area 41 is arranged corresponding to the slow-axis matching area 21, and the second shaping area 42 is arranged corresponding to the fast-axis matching area 22. Figure 4 or Figure 5 A first shaping hole 411 is provided in the first shaping area 41 , and a second shaping hole 421 is provided in the second shaping area 42 .

[0049] See Figure 4 , Figure 4 Schematic diagram of the structure of the shaping template 4 according to an embodiment of the present invention. In this figure, the first shaping hole 411 and the second shaping hole 421 are both rectangular structures.

[0050] To ensure that the power density of the laser hitting the first optical fiber segment 31 and the second optical fiber segment 32 is the same, the height H1 of the first shaping hole 411 perpendicular to the first direction is equal to the height Hh of the second shaping hole 421 perpendicular to the first direction.

[0051] When the first optical fiber segment 31 is used to write a low-reflection grating and the second optical fiber segment 32 is used to write a high-reflection grating, the laser light shaped by the first shaping hole 411 is used to write the low-reflection grating, and the laser light shaped by the second shaping hole 421 is used to write the high-reflection grating. The refractive index of the high-reflection grating is 99%. By adjusting the maximum length L1 of the first shaping hole 411 along the first direction to be no greater than the maximum length Lh of the second shaping hole 421 along the first direction, the reflectivity of the low-reflection grating can be varied between 1% and 99%.

[0052] Preferably, the slow-axis matching region 21 and the fast-axis matching region 22 are symmetrical about the center line of the phase mask 2 , so as to facilitate the manufacture of the phase mask 2 .

[0053] Because the first shaping region 41 of the shaping template 4 corresponds to the slow-axis matching region 21, and the second shaping region 42 corresponds to the fast-axis matching region 22, the first shaping region 41 and the second shaping region 42 are symmetrical about the centerline of the shaping template 4. Thus, when arranging the various components of the writing system, it is sufficient to arrange them along a common axis of symmetry.

[0054] See Figure 5 , Figure 5 This is a structural diagram of a shaping template 4 according to another embodiment of the present invention. In this figure, both the first shaping hole 411 and the second shaping hole 421 are Gaussian structures, so as to perform apodization during the grating writing process and make the reflection spectrum without sidebands.

[0055] In actual use, apodization is performed during grating writing, and the first shaping hole 411 and the second shaping hole 421 may also be a super-Gaussian structure or a SINC structure, and so on.

[0056] See Figure 6 , Figure 6 FIG1 is a structural diagram of a wavelength self-matching writing system for a cross-aligned grating pair according to another embodiment of the present invention. Figure 3 Compared with the embodiment in the preceding text, in this embodiment, the writing system also includes a beam expander assembly 5 for expanding the laser. The beam expander assembly 5 is arranged between the light source 1 and the shaping template 4. The laser expanded by the beam expander assembly 5 completely covers the first shaping hole 411 and the second shaping hole 421 to achieve simultaneous writing of high-reflection grating and low-reflection grating.

[0057] In a preferred embodiment, the beam expander assembly 5 includes a first cylindrical lens 51 and a second cylindrical lens 52. The light source 1, the first cylindrical lens 51, the second cylindrical lens 52, and the shaping template 4 are arranged in sequence. The first cylindrical lens 51 is used to receive the laser provided by the light source 1, and focus the laser, and diverge after passing through the focus. The second cylindrical lens 52 is used to refract the divergent laser into a parallel laser. The first cylindrical lens 51 and the second cylindrical lens 52 work together to expand the laser beam.

[0058] Preferably, the writing system also includes a third cylindrical lens 6 for focusing the shaped laser. The third cylindrical lens 6 is arranged between the shaping template 4 and the phase mask template 2. The polarization-maintaining optical fiber 3 to be written is located at the focus of the laser focused by the third cylindrical lens 6, so that the intensity of the laser after passing through the phase mask template 2 is spatially periodically modulated and incident on the optical fiber with the strongest power density.

[0059] The working process of the writing system is as follows: the working laser provided by the light source 1 is expanded in the first direction through the first cylindrical lens 51 and the second cylindrical lens 52, completely covering the first shaping hole 211 and the second shaping hole 221. Then, the laser is shaped by the shaping template 4 and divided into two paths. The two laser paths are focused by the third cylindrical lens 6 respectively. Since the polarization-maintaining optical fiber 3 to be written is located at the focus of the laser focusing by the third cylindrical lens 6, one of the laser paths passes through the first intensity spatial periodic modulation spot after the slow axis matching area 21 with the strongest power density and is incident on the first optical fiber segment 31 to achieve periodic modulation of the refractive index of the optical fiber core. The other laser path passes through the second intensity spatial periodic modulation spot after the fast axis matching area 22 with the strongest power density and is incident on the second optical fiber segment 32 to achieve periodic modulation of the refractive index of the optical fiber core, thereby achieving simultaneous writing of high-reflection grating and low-reflection grating.

[0060] The present invention also provides a wavelength self-matching writing method for a cross-aligned fiber grating pair, which is used to simultaneously write a high-reflection grating and a low-reflection grating on a polarization-maintaining optical fiber to be written. The writing method comprises the following steps:

[0061] S1. The first fiber segment and the second fiber segment are fused at 90 degrees to obtain the polarization-maintaining fiber to be written. The polarization-maintaining fiber to be written extends along a first direction, and the fast and slow axes of the first and second fiber segments are cross-aligned;

[0062] S2 provides a working laser along the light direction, the light direction is perpendicular to the first direction;

[0063] S3. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a first-intensity spatially periodically modulated light spot is incident on the first fiber segment. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a second-intensity spatially periodically modulated light spot is incident on the second fiber segment. The period of the first-intensity spatially periodically modulated light spot is different from the period of the second-intensity spatially periodically modulated light spot.

[0064] Among them, the target wavelength of the engraved high-reflection grating and low-reflection grating is the central wavelength, the refractive index of the first optical fiber corresponding to the target wavelength is the first refractive index, the refractive index of the second optical fiber segment corresponding to the target wavelength is the second refractive index, and the product of the period of the first-intensity spatially periodically modulated light spot and the first refractive index and the product of the period of the second-intensity spatially periodically modulated light spot and the second refractive index are both equal to the target wavelength.

[0065] Preferably, step S3 includes the following steps:

[0066] S31. The laser is shaped into a first laser and a second laser;

[0067] S32. The first intensity spatially periodically modulated light spot of the first laser after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the first optical fiber segment, and the second intensity spatially periodically modulated light spot of the second laser after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the second optical fiber segment.

[0068] Furthermore, before step S31, the following steps are also included:

[0069] S20. Expand the laser beam in the first direction and adjust the spot to a rectangular shape;

[0070] The following steps are also included between step S31 and step S32:

[0071] S23. Focus the first laser and the second laser in the light-emitting direction.

[0072] In a preferred embodiment, step S3 is specifically as follows: after the laser passes through the phase mask, the 0th order diffraction is suppressed, and the ±1st order diffraction is output and incident on the first optical fiber segment and the second optical fiber segment, the phase mask includes a slow axis matching area and a fast axis matching area arranged in sequence along the first direction, the slow axis matching area has a first period, the fast axis matching area has a second period, the first period is different from the second period, the first optical fiber segment is arranged corresponding to the slow axis matching area, and the second optical fiber segment is arranged corresponding to the fast axis matching area, the product of the first refractive index and the first period, and the product of the second refractive index and the second period are both equal to the target wavelength, the first intensity spatially periodically modulated light spot of the laser after passing through the slow axis matching area is incident on the first optical fiber segment, and the second intensity spatially periodically modulated light spot of the laser after passing through the fast axis matching area is incident on the second optical fiber segment.

[0073] Correspondingly, step S32 specifically includes: passing the first laser beam through the slow axis matching region and then incident on the first optical fiber segment, and passing the second laser beam through the fast axis matching region and then incident on the second optical fiber segment.

[0074] The wavelength self-matching writing system and method for a cross-aligned fiber Bragg grating pair of the present invention achieves simultaneous writing of a high-reflection grating and a low-reflection grating with matching central wavelengths on the polarization-maintaining optical fiber to be written by arranging slow-axis matching regions and fast-axis matching regions of different periods on a phase mask template, and cooperating with a polarization-maintaining optical fiber to be written consisting of a first fiber segment and a second fiber segment that are cross-aligned. The first fiber segment is arranged correspondingly to the slow-axis matching region, and the second fiber segment is arranged correspondingly to the fast-axis matching region, thereby eliminating the influence of uncertainty on the central wavelength of the grating, improving the yield rate, and reducing the difficulty of producing the fiber Bragg grating pair.

[0075] The present invention has been described using the above-described embodiments. However, these embodiments are merely exemplary embodiments of the present invention. Furthermore, the technical features described above in the various embodiments of the present invention may be combined as long as they do not conflict with each other. It should be noted that the disclosed embodiments do not limit the scope of the present invention. On the contrary, modifications and enhancements made without departing from the spirit and scope of the present invention are within the scope of patent protection.

Claims

1. A wavelength self-matching writing system for a cross-aligned fiber Bragg grating pair, used for simultaneously writing a high-reflection grating and a low-reflection grating with matching center wavelengths on a polarization-maintaining optical fiber to be written, characterized in that: The writing system includes a light source and a phase mask plate arranged in sequence along the light output direction; The light source is used to provide working laser light along the light emitting direction; The phase mask is used to diffract the laser to form ±1-order diffraction outputs and suppress 0-order diffraction. The phase mask includes a slow-axis matching region and a fast-axis matching region sequentially arranged along a first direction. The slow-axis matching region has a first period, and the fast-axis matching region has a second period. The first period is different from the second period. The first direction is perpendicular to the light output direction. The polarization-maintaining optical fiber to be inscribed extends along a first direction, and includes a first optical fiber segment and a second optical fiber segment. The fast and slow axes of the first optical fiber segment and the second optical fiber segment are cross-aligned. The first optical fiber segment is arranged corresponding to the slow axis matching region, and the second optical fiber segment is arranged corresponding to the fast axis matching region. The central wavelength of the engraved high-reflection grating and the low-reflection grating is the target wavelength, the refractive index of the first optical fiber segment corresponding to the target wavelength is a first refractive index, the refractive index of the second optical fiber segment corresponding to the target wavelength is a second refractive index, and the product of the first refractive index and the first period and the product of the second refractive index and the second period are both equal to the target wavelength.

2. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 1, characterized in that: The invention also includes a shaping template, which is arranged between the light source and the phase mask. The shaping template includes a first shaping area and a second shaping area arranged in sequence along a first direction. The first shaping area is arranged corresponding to the slow axis matching area, and the second shaping area is arranged corresponding to the fast axis matching area. A first shaping hole is provided in the first shaping area, and a second shaping hole is provided in the second shaping area.

3. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 2, characterized in that: A height of the first shaping hole along a direction perpendicular to the first direction is equal to a height of the second shaping hole along the direction perpendicular to the first direction.

4. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 3, characterized in that: A maximum length of the first shaping hole along the first direction is not greater than a maximum length of the second shaping hole along the first direction.

5. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 2, characterized in that: The first shaping hole and the second shaping hole are both rectangular structures, Gaussian structures, super Gaussian structures, or SINC structures.

6. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 2, characterized in that: It also includes a beam expander assembly for expanding the laser beam, and the beam expander assembly is arranged between the light source and the shaping template.

7. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 6, characterized in that: The beam expander assembly includes a first cylindrical lens and a second cylindrical lens. The light source, the first cylindrical lens, the second cylindrical lens, and the shaping template are arranged in sequence. The first cylindrical lens is used to receive the laser provided by the light source, focus the laser, and diverge after passing through the focus. The second cylindrical lens is used to refract the divergent laser into a parallel laser.

8. The wavelength self-matching writing system for cross-aligned fiber Bragg grating pairs according to claim 2, characterized in that: It also includes a third cylindrical lens for focusing the shaped laser. The third cylindrical lens is arranged between the shaping template and the phase mask. The polarization-maintaining optical fiber to be written is located at the focus of the third cylindrical lens focusing the laser.

9. A wavelength self-matching writing method for a cross-aligned fiber Bragg grating pair, used for simultaneously writing a high-reflection grating and a low-reflection grating on a polarization-maintaining optical fiber to be written, characterized in that: The method comprises the following steps: S1. The first fiber segment and the second fiber segment are fused at 90 degrees to obtain the polarization-maintaining fiber to be inscribed, wherein the polarization-maintaining fiber to be inscribed extends along a first direction, and the fast and slow axes of the first fiber segment and the second fiber segment are cross-aligned; S2 provides a working laser along the light direction, the light direction is perpendicular to the first direction; S3. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a first-intensity spatially periodically modulated light spot is incident on the first optical fiber segment. After the laser is diffracted through 0th-order suppression and ±1st-order diffraction, a second-intensity spatially periodically modulated light spot is incident on the second optical fiber segment. The period of the first-intensity spatially periodically modulated light spot is different from the period of the second-intensity spatially periodically modulated light spot. The central wavelength of the engraved high-reflection grating and low-reflection grating is the target wavelength, the refractive index of the first optical fiber segment corresponding to the target wavelength is a first refractive index, the refractive index of the second optical fiber segment corresponding to the target wavelength is a second refractive index, and the product of the period of the first-intensity spatially periodically modulated light spot and the first refractive index and the product of the period of the second-intensity spatially periodically modulated light spot and the second refractive index are both equal to the target wavelength.

10. The wavelength self-matching writing method for a cross-aligned fiber Bragg grating pair according to claim 9, characterized in that: Step S3 includes the following steps: S31. The laser is shaped into a first laser and a second laser; S32. The first intensity spatially periodically modulated spot of the first laser beam after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the first optical fiber segment, and the second intensity spatially periodically modulated spot of the second laser beam after being suppressed by the 0th order diffraction and output by the ±1st order diffraction is incident on the second optical fiber segment.

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