A chirped tilted fiber bragg grating and a method for manufacturing the same

Abstract

The present application relates to the technical fields of fiber laser, and discloses a kind of chirped tilted fiber Bragg grating and preparation method thereof, comprising: optical fiber matrix, cladding, core, chirped tilted grating, core mode, cladding mode, backward core mode;Chirped tilted grating is engraved in core, and grating plane of chirped tilted grating is inclined to optical fiber axis arrangement.The chirped tilted fiber Bragg grating, by the cooperative configuration of inclination angle θ and chirp rate C, makes forward core mode coupled to backward core mode and cladding mode, and adjusts the mode coupling intensity and reflection spectrum distribution at different wavelengths in target waveband, so as to compensate the spectrum unevenness between long-wave side and short-wave side, improve the flatness of different wavelength reflection spectrum in target waveband, realize the uniform regulation of relevant waveband optical signal.The fiber grating of the application has the advantages of strong reflection spectrum regulation ability, good thermal stability, easy engineering implementation, etc., and has good application prospect in the field of fiber laser.

Description

Technical Field

[0001] This invention belongs to the field of fiber laser technology, specifically relating to a chirped tilted fiber Bragg grating and its fabrication method. Background Technology

[0002] High-power fiber lasers are the core light source for advanced laser manufacturing equipment, and gratings are key components of high-power continuous fiber lasers. Their main functions include: firstly, serving as the emitting cavity mirror of the laser resonator; and secondly, suppressing the nonlinear effects of the laser. With the development of fiber laser applications, the power of high-power fiber lasers is continuously increasing, thus placing higher demands on the power carrying capacity of gratings.

[0003] Although the laser carrying capacity of existing high-power fiber Bragg gratings has reached 3 kW to 5 kW, the poor flatness of the reflection spectrum between the long-wavelength and short-wavelength sides leads to uneven distribution of filtering loss and a significant local heat accumulation effect. This causes the grating temperature to rise too quickly, posing a risk of thermal runaway or even burnout. This severely limits the further improvement of laser power and the long-term thermal stability and reliability of the device.

[0004] Patent CN117220127A discloses a fiber laser for suppressing stimulated Raman scattering (SRS) and its parameter optimization method. This method splits the seed laser beam to a power transmission fiber and a chirped tilted fiber grating array via a coupler, and introduces a fiber Bragg grating feedback loop to stabilize the laser's time-domain characteristics, significantly improving the SRS threshold and supporting kilowatt output. However, this scheme employs a multi-grating array structure, which is complex to fabricate and package. Furthermore, the reflection spectrum of the chirped tilted grating array exhibits poor flatness between the long-wavelength and short-wavelength sides, leading to uneven insertion loss and severe heat accumulation effects. At high power, the grating temperature rises too rapidly, resulting in insufficient long-term reliability.

[0005] Patent CN115986535A discloses a bidirectional Raman-isolated fiber amplifier. By setting a bidirectional Raman isolation unit containing first and second Raman tilted gratings at the front end of the fiber amplification stage, bidirectional Raman optical isolation between the oscillation stage and the amplification stage is achieved, significantly improving the power carrying capacity. However, this bidirectional isolation unit has limited ability to adjust the flatness of the tilted grating reflection spectrum, and the spectral shape difference between the long-wavelength side and the short-wavelength side is significant. This easily leads to non-uniform filtering loss and local thermal load, resulting in significant heat accumulation effect during high-power long-term operation, posing risks of grating burnout and system stability.

[0006] Patent CN112886374A discloses a fiber laser and its manufacturing method for suppressing stimulated Raman scattering. By directly writing high-reflectance and low-reflectance grating pairs and tilted gratings onto the active fiber, the number of fusion splices is reduced, improving the laser's compactness and overall efficiency. However, the direct writing of the tilted grating results in a significant difference in flatness between the long-wavelength and short-wavelength sides of the reflection spectrum. This leads to increased local losses and concentrated heat accumulation at high power, causing rapid grating temperature rise and making it difficult to meet the requirements for long-term high-reliability operation.

[0007] In summary, excessively high spectral flatness between the long-wavelength and short-wavelength sides leads to increased loss and severe heat accumulation, resulting in rapid grating temperature rise or even burnout. Therefore, developing a chirped-tilted fiber Bragg grating that can achieve spectral flattening through coordinated configuration of structural parameters such as tilt angle and chirp rate, while possessing good thermal stability, is of great significance to meet the requirements of high-power fiber lasers. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a chirped tilted fiber Bragg grating and its fabrication method, thereby solving the problems in the prior art where fiber Bragg gratings exhibit spectral unevenness, uneven reflection spectrum distribution, and difficulty in coordinating mode coupling strength at different wavelengths between the long-wavelength and short-wavelength sides within the target wavelength band.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a chirped tilted fiber Bragg grating, comprising: an optical fiber matrix, a cladding, a fiber core, a chirped tilted grating, a core mode, a cladding mode, and a backward core mode;

[0010] The chirped tilted grating is inscribed within the fiber core, and the grating plane of the chirped tilted grating is tilted relative to the fiber axis, with the angle between the grating plane and the fiber axis being the tilt angle. i ; The local grating period of the chirped tilted grating varies continuously along the fiber axis to form a chirped structure, with a central reflection wavelength chirp rate of [missing information]. C ; The grating period along the x' direction is Λ g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate , ; L The length of the grating; the bandwidth of the i-th cladding mode. The range of reflectivity fluctuation within the target band Δ R satisfy: ; By tilt angle i With chirp rate CThe coordinated configuration enables the forward core mode to couple to the backward core mode and cladding mode, and adjusts the mode coupling intensity and reflection spectrum distribution at different wavelengths within the target band, thereby compensating for the spectral unevenness between the long-wavelength side and the short-wavelength side and improving the flatness of the reflection spectrum within the target band.

[0011] Preferably, the tilt angle i The value range is 0° to 8°, preferably 3° to 8°.

[0012] Preferably, the local grating period is composed of Continuous change to Chirp rate of the center reflection wavelength C The value range is 0.1nm / mm to 1nm / mm, preferably 0.2nm / cm to 0.7nm / cm.

[0013] Preferably, the reflectance spectrum flatness within the target band is within the reflectance fluctuation range Δ R Characterization, the Δ R It is the difference between the maximum and minimum reflectivity within the target band; The tilt angle i The chirp rate of the center reflection wavelength is used to adjust the cladding mode resonance position and mode coupling intensity distribution. C This is used to adjust the reflectance spectral bandwidth and the local reflectance distribution at different wavelengths. The two are matched and set to make the reflectance fluctuation range Δ within the target band... R Not greater than 2 dB.

[0014] Preferably, the tilt angle i With chirp rate C Matching settings: by adjusting the tilt angle i To position the cladding mode resonance center at 1100–1300 nm, the chirp rate was adjusted. C The reflectance spectrum is made to cover the target band with a 3 dB bandwidth, and the reflectance fluctuation range Δ within the target band is made to be within the target band. R Not greater than 2 dB; after being acted upon by the grating, the forward core mode is at least partially coupled into a backward core mode and a cladding mode; wherein, the backward core mode is used to form reflections within the target band, and the cladding mode is used to adjust the energy distribution at different wavelengths within the target band.

[0015] The tilt angle i With chirp rate C The matching settings ensure that the cladding mode resonance center is located within the target band, and that the reflection spectrum bandwidth covers the target band.

[0016] A method for fabricating a chirped tilted fiber Bragg grating includes the following steps: S1. A chirped tilted Bragg grating is inscribed in the core of the optical fiber using ultraviolet laser combined with phase mask method. The tilt angle is controlled by adjusting the relative angle between the phase mask and the optical fiber. i The chirp rate is controlled by adjusting the phase mask chirp parameters and the writing scan parameters. C ; S2. The chirped tilted Bragg grating is stabilized after writing to improve its thermal stability, thereby reducing the hydroxyl content in the grating and reducing residual thermal stress, thus improving the thermal stability and high-power operation stability of the chirped tilted fiber Bragg grating.

[0017] Preferably, in S1, the ultraviolet laser combined with phase mask method uses a continuous ultraviolet laser with a wavelength of 244nm and an output power of 100mW generated by an argon ion laser, which is then shaped by a cylindrical lens and irradiated onto the phase mask and the optical fiber region.

[0018] Preferably, the phase mask has a mask period of 394.5 nm, a chirp rate of 1.5 nm / cm, and a length of 10 mm.

[0019] Preferably, the spacing between the optical fiber and the phase mask is controlled to be approximately 20 μm.

[0020] Preferably, the stabilization treatment includes sequentially performing isothermal low-temperature annealing and variable-temperature high-temperature annealing; The constant temperature low-temperature annealing involves holding the temperature at 60°C to remove residual hydrogen molecules after writing. The variable-temperature high-temperature annealing involves gradually increasing the temperature from room temperature to 300°C at 50°C intervals, holding at 300°C for 15 minutes, and then gradually cooling down to room temperature. This process is used to reduce the hydroxyl content in the grating and decrease residual thermal stress, thereby improving the thermal stability and high-power operation stability of the chirped tilted fiber Bragg grating.

[0021] Compared with the prior art, the present invention provides a chirped tilted fiber Bragg grating and its fabrication method, which has the following beneficial effects: (1) This invention constructs a tilted chirped Bragg grating in the fiber core, and combines the tilt angle and chirp rate for coordinated control. This allows for simultaneous adjustment of the mode coupling state and reflection spectrum distribution at different wavelengths, thereby effectively compensating for the spectral unevenness between the long-wavelength side and the short-wavelength side in the target band and improving the flatness of the reflection spectrum.

[0022] (2) In this invention, the introduction of the tilt angle allows the forward core mode to be coupled into the cladding mode in addition to the backward core mode; the introduction of the chirped structure allows the local period of the grating to change continuously along the fiber axis, which is beneficial to change the local reflection distribution and reflection spectrum broadening characteristics at different wavelengths, thereby improving the spectral uniformity in the target band.

[0023] (3) The present invention uses the matching design of tilt angle and chirp rate to make the cladding mode resonance center located in the target band and make the reflection spectrum bandwidth cover the target band, thereby reducing the reflectivity difference between the long-wave side and the short-wave side and enhancing the device's ability to control the reflection spectrum in the target band.

[0024] (4) The preparation method of the present invention is simple and clear. The chirped tilted Bragg grating can be written by using the phase mask method, and the tilt angle can be controlled by adjusting the relative angle between the phase mask and the optical fiber, which is convenient for engineering implementation and device fabrication. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the chirped tilted fiber Bragg grating of the present invention.

[0026] In the figure: 1. Cladding; 2. Core; 3. Chirped tilt grating; 4. Core model; 5. Cladding model; 6. Backward core model. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] See attached document Figure 1 A chirped tilted fiber Bragg grating includes: an optical fiber matrix, a cladding 1, a fiber core 2, a chirped tilted grating 3, a core mode 4, a cladding mode 5, and a backward core mode 6. The chirped tilted grating 3 is inscribed inside the fiber core 2. The grating plane of the chirped tilted grating 3 is tilted relative to the fiber axis, and the angle between the grating plane and the fiber axis is the tilt angle. i ; The local grating period of the chirped tilted grating 3 varies continuously along the fiber axis to form a chirped structure, with a central reflection wavelength chirp rate of C ; The grating period along the x' direction is Λ g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate , ; L The length of the grating; the bandwidth of the i-th cladding mode. The range of reflectivity fluctuation within the target band Δ R satisfy: ; By tilt angle i With chirp rate C The coordinated configuration enables the forward core mode 4 to couple to the backward core mode 6 and the cladding mode 5, and adjusts the mode coupling strength and reflection spectrum distribution at different wavelengths within the target band, thereby compensating for the spectral unevenness between the long-wavelength side and the short-wavelength side and improving the flatness of the reflection spectrum within the target band.

[0029] The tilt angle i The value range is 0° to 8°, preferably 3° to 8°.

[0030] The local grating period is determined by Continuous change to Chirp rate of the center reflection wavelength C The value range is 0.1 nm / mm to 1 nm / mm, preferably 0.2 nm / cm to 0.7 nm / cm.

[0031] The reflectance spectrum flatness within the target band is expressed as a reflectance fluctuation range Δ R Characterization, the Δ R It is the difference between the maximum and minimum reflectivity within the target band; The tilt angle i The chirp rate of the center reflection wavelength is used to adjust the cladding mode resonance position and mode coupling intensity distribution. C This is used to adjust the reflectance spectral bandwidth and the local reflectance distribution at different wavelengths. The two are matched and set to make the reflectance fluctuation range Δ within the target band... R Not greater than 2 dB.

[0032] The tilt angle i With chirp rate C Matching settings: by adjusting the tilt angle i To position the cladding mode resonance center at 1100–1300 nm, the chirp rate was adjusted. C The reflectance spectrum is made to cover the target band with a 3 dB bandwidth, and the reflectance fluctuation range Δ within the target band is made to be within the target band. R Not greater than 2 dB; after being acted upon by the grating, the forward core mode is at least partially coupled into a backward core mode and a cladding mode; wherein, the backward core mode is used to form reflections within the target band, and the cladding mode is used to adjust the energy distribution at different wavelengths within the target band.

[0033] The tilt angle i With chirp rate C The matching settings ensure that the cladding mode resonance center is located within the target band, and that the reflection spectrum bandwidth covers the target band.

[0034] A method for fabricating a chirped tilted fiber Bragg grating includes the following steps: S1. A chirped tilted Bragg grating is inscribed in the core of the optical fiber using ultraviolet laser combined with phase mask method. The tilt angle is controlled by adjusting the relative angle between the phase mask and the optical fiber. i The chirp rate is controlled by adjusting the phase mask chirp parameters and the writing scan parameters. C ; The ultraviolet laser combined with phase mask method in S1 uses a continuous ultraviolet laser with a wavelength of 244nm and an output power of 100mW generated by an argon ion laser, which is then shaped by a cylindrical lens and irradiated onto the phase mask and the fiber area.

[0035] The phase mask has a mask period of 394.5 nm, a chirp rate of 1.5 nm / cm, and a length of 10 mm.

[0036] The spacing between the optical fiber and the phase mask is preferably controlled to be approximately 20 μm.

[0037] S2. The chirped tilted Bragg grating is stabilized after writing to improve its thermal stability, thereby reducing the hydroxyl content in the grating and reducing residual thermal stress, thus improving the thermal stability and high-power operation stability of the chirped tilted fiber Bragg grating.

[0038] The stabilization process includes sequential isothermal low-temperature annealing and variable-temperature high-temperature annealing. The isothermal low-temperature annealing involves holding the temperature at 60°C to remove residual hydrogen molecules after writing. The variable-temperature high-temperature annealing involves gradually increasing the temperature from room temperature to 300°C at 50°C intervals, holding at 300°C for 15 minutes, and then gradually cooling back to room temperature. This process reduces the hydroxyl content in the grating and decreases residual thermal stress, thereby improving the thermal stability and high-power operation stability of the chirped tilted fiber Bragg grating.

[0039] Example 1 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 7.807 nm, and its tilt angle is... i The angle is 3.2°, and the grating length is... L It is 10 mm. According to the formula , by local grating period Continuous change to The calculated local periodicity change rate C is 0.27 nm / mm.

[0040] The grating fabrication method includes: writing using ultraviolet laser combined with phase masking; followed by stabilization treatment. This treatment includes low-temperature annealing at 60°C, and variable-temperature high-temperature annealing, where the temperature is increased to 300°C at 50°C intervals from room temperature and held for 15 minutes, to trigger the hydroxyl dehydration reaction and eliminate residual stress. Under the parameter configuration of this embodiment, the reflectivity fluctuation range Δ within the target wavelength band is controlled by functions to adjust the chirp rate and tilt rate. R It is no greater than 2 dB, thus ensuring a flat spectrum.

[0041] Example 2 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 11.142 nm, and its tilt angle is... i It is 4.0°. L It is 10 mm. (By) Change to Chirping rate C The reflectance is 0.385 nm / cm. The range of reflectance fluctuation within the target band is controlled by adjusting the chirp rate and tilt rate using functions. R It is no greater than 2 dB, thus ensuring a flat spectrum.

[0042] The grating fabrication method includes: etching a chirped tilted Bragg grating within the core of the high-power grating carrier fiber using an ultraviolet laser combined with a phase mask method; irradiating the phase mask and fiber region with a continuous ultraviolet laser of 244 nm wavelength and 100 mW output power generated by an argon-ion laser after being shaped by a cylindrical lens; preferably controlling the spacing between the fiber and the phase mask to be approximately 20 μm; and controlling the tilt angle by adjusting the relative angle between the phase mask and the fiber. i The chirp rate is controlled by adjusting the phase mask chirp parameters and the writing scan parameters. C .

[0043] Example 3 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 15.065 nm, where the tilt angle is... i It is 4.8°. C It is 0.52nm / mm. L It is 10mm. (By...) Change to Based on the mapping relationship of the function, the coordinated setting of the medium parameters further adjusts the coupling distribution of the forward core mode to the backward core mode and the cladding mode.

[0044] Example 4 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 17.405 nm. In this embodiment, the tilt angle... i It is 5.6°. C It is 0.6 nm / cm. L It is 10 mm. (By) Change to Ultraviolet laser writing combined with a 300℃ stepped annealing process was employed. Through matching of medium-high tilt angles and chirp rate, the function Δ... R This further expands the local reflection distribution at different wavelengths, effectively compensating for the spectral unevenness in the Raman scattering band.

[0045] Example 5 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 18.012 nm. In the embodiment, the tilt angle... i It is 6.4°. C It is 1.8 nm / cm. L It is 35 mm. (By...) Change to The local periodic rate of change was calculated. CThe value is 0.62 nm / cm. Under this configuration, the cladding mode resonance position and the reflectance spectral bandwidth change significantly, causing the reflectance fluctuation range within the target band to vary between long and short wave reflectance Δ. R The difference is only 0.3dB, achieving a balanced distribution of the reflection spectrum.

[0046] Example 6 This embodiment provides a chirped tilted fiber Bragg grating, in which a non-uniformly periodic grating region with a tilt angle is etched within the fiber core. The grating period along the x' direction is Λ. g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate Inclination i The bandwidth of the i-th cladding mode is 17.332 nm. In the embodiment, the tilt angle... i It is 7.2°. C The value is 0.63 nm / cm, and L is 30 mm. (From...) Change to By matching the high tilt angle and high chirp rate, the cladding mode resonance center is positioned within the target band. Although the flatness of the reflection spectrum slightly improves Δ R =1.1dB, but still meets the design requirement of ≤2dB.

[0047] Table 1. Main performance indicators of chirped tilted gratings in Examples 1-6

[0048] Table 2 Test parameters of chirped tilted gratings in Examples 1-6

[0049] Referring to Table 2, it can be seen that the chirped tilted fiber Bragg grating prepared by this invention exhibits high reflectivity levels in different embodiments. The long-wavelength side reflectivity gradually increases from 17.4 dB to 19.9 dB, indicating that each embodiment can form strong reflection within the target wavelength band. Meanwhile, with the tilt angle... i With chirp rate C Through coordinated adjustment, the flatness of the reflection spectrum within the target band is significantly improved: from Example 1 to Example 5, the shortwave side reflectivity gradually decreases from 20.9 dB to 20.2 dB, and the reflectivity fluctuation range Δ RAs the reflectance gradually decreased from 4.9 dB to 1.1 dB, the difference between the average reflectance on the long-wavelength side and the average reflectance on the short-wavelength side also decreased from 2.5 dB to 0.3 dB. These results indicate that by appropriately matching the tilt angle θ and the chirp rate C, the unevenness of the reflection spectrum between the long-wavelength and short-wavelength sides within the target band can be effectively compensated, resulting in a more uniform reflection distribution at different wavelengths and thus significantly improving the flatness of the reflection spectrum within the target band.

[0050] Furthermore, the grating obtained in Example 5 exhibits the best overall performance, with a maximum reflectivity of 19.9 dB, a minimum reflectivity of 20.3 dB, and a reflectivity fluctuation range Δ. R At only 0.3 dB, this embodiment demonstrates that while maintaining high reflectivity, it achieves a better balance in the distribution of the long-wavelength and short-wavelength reflection spectra. In contrast, although Embodiment 6 maintains a high maximum reflectivity, its minimum reflectivity decreases to 20.0 dB, with a reflectivity fluctuation range Δ R The difference between long-wave and short-wave reflectivity increases to 1.1 dB, indicating that when the tilt angle θ and chirp rate C continue to increase, the distribution of mode coupling intensity at different wavelengths within the target band may exhibit new imbalances, thereby causing a slight decrease in the flatness of the reflection spectrum.

[0051] In summary, the present invention utilizes an inclined angle i With chirp rate C Coordinated configuration, It can effectively reduce the range of reflectivity fluctuations within the target band and the difference in reflectivity between the long and short wave sides while ensuring high reflectivity, thereby achieving reflectivity spectrum flattening control.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A chirped tilted fiber Bragg grating, characterized in that, include: Fiber matrix, cladding (1), fiber core (2), chirped tilt grating (3), core mode (4), cladding mode (5), backward core mode (6); The chirped tilt grating (3) is inscribed inside the fiber core (2). The grating plane of the chirped tilt grating (3) is tilted relative to the fiber axis, and the angle between the grating plane and the fiber axis is the tilt angle. θ ; The local grating period of the chirped tilted grating (3) varies continuously along the fiber axis to form a chirped structure, with a central reflection wavelength chirp rate of C ; The grating period along the x' direction is Λ g The grating period along the x-direction is Λ, and the core refractive index is... cladding refractive index Chirping rate , ; L The length of the grating; the bandwidth of the i-th cladding mode. The range of reflectivity fluctuation within the target band Δ R satisfy: ； By tilt angle θ With chirp rate C The coordinated configuration enables the forward core mode (4) to couple to the backward core mode (6) and the cladding mode (5), and adjusts the mode coupling intensity and reflection spectrum distribution at different wavelengths in the target band, thereby compensating for the spectral unevenness between the long-wave side and the short-wave side.

2. The chirped tilted fiber Bragg grating according to claim 1, characterized in that, The tilt angle θ The value range is 0° to 8°.

3. The chirped tilted fiber Bragg grating according to claim 1, characterized in that, The local grating period is determined by Continuous change to Chirp rate of the center reflection wavelength C The value range is 0.1nm / mm to 1nm / mm.

4. The chirped tilted fiber Bragg grating according to claim 1, characterized in that, The reflectance spectrum flatness within the target band is expressed as a reflectance fluctuation range Δ R Characterization, the Δ R It is the difference between the maximum and minimum reflectivity within the target band; The tilt angle θ The chirp rate of the center reflection wavelength is used to adjust the cladding mode resonance position and mode coupling intensity distribution. C This is used to adjust the reflectance spectral bandwidth and the local reflectance distribution at different wavelengths. The two are matched and set to make the reflectance fluctuation range Δ within the target band... R Not greater than 2 dB.

5. The chirped tilted fiber Bragg grating according to claim 1, characterized in that, The tilt angle θ With chirp rate C Matching settings: by adjusting the tilt angle θ To position the cladding mode resonance center at 1100–1300 nm, the chirp rate was adjusted. C The reflectance spectrum is made to cover the target band with a 3 dB bandwidth, and the reflectance fluctuation range Δ within the target band is made to be within the target band. R Not greater than 2 dB; after being acted upon by the grating, the forward core mode is at least partially coupled into a backward core mode and a cladding mode; wherein, the backward core mode is used to form reflections within the target band, and the cladding mode is used to adjust the energy distribution at different wavelengths within the target band. The tilt angle θ With chirp rate C The matching settings ensure that the cladding mode resonance center is located within the target band, and that the reflection spectrum bandwidth covers the target band.

6. A method for fabricating a chirped tilted fiber Bragg grating as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. A chirped tilted Bragg grating is inscribed in the core of the optical fiber using ultraviolet laser combined with phase mask method. The tilt angle is controlled by adjusting the relative angle between the phase mask and the optical fiber. θ The chirp rate is controlled by adjusting the phase mask chirp parameters and the writing scan parameters. C ; S2. Stabilize the chirped tilted Bragg grating after it has been written to improve its thermal stability, thereby reducing the hydroxyl content in the grating and reducing residual thermal stress.

7. The chirped tilted fiber Bragg grating and its fabrication method according to claim 6, characterized in that, The ultraviolet laser combined with phase mask method in S1 uses a continuous ultraviolet laser with a wavelength of 244nm and an output power of 100mW generated by an argon ion laser, which is then shaped by a cylindrical lens and irradiated onto the phase mask and the fiber area.

8. The chirped tilted fiber Bragg grating and its fabrication method according to claim 7, characterized in that, The phase mask has a mask period of 394.5 nm, a chirp rate of 1.5 nm / cm, and a length of 10 mm.

9. The chirped tilted fiber Bragg grating and its fabrication method according to claim 6, characterized in that, The spacing between the optical fiber and the phase mask is 20 μm.

10. The chirped tilted fiber Bragg grating and its fabrication method according to claim 6, characterized in that, The stabilization process includes sequentially performing isothermal low-temperature annealing and variable-temperature high-temperature annealing. The constant temperature low-temperature annealing involves holding the temperature at 60°C to remove residual hydrogen molecules after writing. The variable-temperature high-temperature annealing process involves gradually increasing the temperature from room temperature to 300°C in 50°C increments, holding at 300°C for 15 minutes, and then gradually decreasing the temperature back to room temperature.

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