Method for manufacturing dispersion fiber grating with high flatness of hyperspectrum

Abstract

This invention discloses a method for fabricating highly spectrally flat dispersive fiber gratings (GFFFs). Addressing the issues of strong sidelobes on both sides of the resonance peak caused by abrupt refractive index changes at both ends during GFFF writing and short-wavelength loss during use, this invention proposes a method for fabricating highly spectrally flat GFFFs. First, ultraviolet laser beam expansion and shaping are used to homogenize the Gaussian spot, ultimately obtaining an ideal optical field and reducing the degree of refractive index abrupt changes at both ends of the GFFF. Second, by precisely controlling the scanning speed of the stepper motor to change the exposure time at different positions of the GFFF, the refractive index modulation depth at different positions of the fiber grating is controlled to eliminate abrupt refractive index changes at both ends and compensate for the problem of lower reflectivity at short wavelengths than at long wavelengths caused by short-wavelength loss. Ultimately, this significantly improves the spectral flatness of the GFFF. Compared with existing methods, the method proposed in this invention has advantages such as low cost, high flexibility, and high stability.

Description

Technical Field

[0001] This invention belongs to the field of ultrafast fiber lasers, specifically relating to a method for fabricating a high-spectral-flatness dispersive fiber grating. Background Technology

[0002] Dispersive fiber gratings (GFCGs) must possess high spectral flatness to ensure uniform reflection of laser light from ultrafast laser seed sources across all wavelengths into the amplification stage of a CPA system. However, two factors degrade spectral flatness during GFCG fabrication. First, the refractive index at both ends of the GFCG undergoes abrupt changes during fabrication, leading to strong sidelobes on either side of its resonance peak. This allows some non-active laser light to enter the amplification stage, degrading the output pulse quality. Second, because light enters the GFCG from the longer wavelength direction during use, the resulting short-wavelength loss causes a decrease in reflectivity at shorter wavelengths, further degrading the overall flatness of the reflection spectrum.

[0003] Currently, there is virtually no solution to address the spectral flatness degradation caused by the combined effects of side lobes on both sides of the resonant peak of a dispersive fiber grating and short-wavelength loss. Therefore, a convenient and stable method is needed to ensure the reflectance spectral flatness of the dispersive fiber grating. Summary of the Invention

[0004] The purpose of this invention is to provide a method for fabricating a high-spectral-flatness dispersive fiber grating, thereby improving the reflectance spectral flatness of the dispersive fiber grating. This method has advantages such as easy fabrication, high stability, and high reusability of the grating.

[0005] The technical solution to achieve the objective of this invention is: a method for fabricating a high-spectral-flatness dispersive fiber grating, comprising the following steps:

[0006] Step 1: Using homogenized ultraviolet light field control technology, the ultraviolet laser beam is expanded and shaped to disperse its originally dense Gaussian energy distribution, so as to achieve the purpose of homogenizing the Gaussian light spot and finally obtain the ideal writing light field; thereby reducing the degree of refractive index change at both ends of the fiber grating during the ultraviolet writing scanning process and improving the side mode suppression ratio of the dispersive fiber grating.

[0007] Step 2: Utilize high-edge suppression ratio apodization technology by controlling the scanning speed V of the stepper motor. a By changing the exposure time at different positions of the fiber grating, the refractive index modulation depth at different positions of the fiber grating can be controlled to eliminate the abrupt change in refractive index at both ends, resulting in an apodized dispersion fiber grating with a side-mode suppression ratio greater than or equal to 20dB.

[0008] Step 3: Utilize progressive scanning writing technology, superimposed with progressive scanning speed V bThe scanning speed of the ultraviolet laser at the short wavelength position is V. b1 The scanning speed of the ultraviolet laser at the long wavelength position is V. b2 V b1 ≤V b2 This method aims to improve the reflectivity of dispersive fiber gratings at short wavelengths and reduce their reflectivity at long wavelengths, thereby compensating for the problem that the reflectivity of dispersive fiber gratings at short wavelengths is lower than that at long wavelengths due to short-wavelength loss. Ultimately, it effectively suppresses short-wavelength loss and yields dispersive fiber gratings with spectral flatness less than or equal to 2% and side-mode suppression ratio greater than or equal to 20dB.

[0009] Compared with the prior art, the significant advantages of this invention are:

[0010] (1) Taking into account the deterioration of spectral flatness caused by the combined side lobes on both sides of the resonant peak of the dispersion fiber grating and the short-wavelength loss, we combine three key technologies: homogenized ultraviolet light field control, high side mode suppression ratio apodization, and progressive scanning writing, and finally realize the fabrication of a dispersion fiber grating with high spectral flatness and high side mode suppression ratio.

[0011] (2) Based on the existing ultraviolet mask writing technology, beam optimization is carried out by expanding and homogenizing the ultraviolet laser beam and directly applying it to the fabrication of dispersive fiber gratings. The beam homogenization and shaping gives the writing system the advantages of low complexity and high flexibility.

[0012] (3) For the two major technologies of progressive grating scanning and high edge mode suppression ratio apodization, it is only necessary to establish the intrinsic mapping relationship between the refractive index exposure time (i.e. stepper motor driven scanning function) and the reflectivity of the dispersive fiber grating in the writing process, so that the writing process can be modulated. It has the advantages of being easy to use, having a stable working state, and being able to be modulated in real time. Attached Figure Description

[0013] Figure 1 The optical path diagram for the beam homogenization module of the homogenization ultraviolet light field control technology described in this invention is designed.

[0014] Figure 2 This is a schematic diagram of a scanning and writing system and a real-time monitoring system for ultraviolet lithography phase masks.

[0015] Figure 3 The figures are schematic diagrams of the Gaussian apodization function distribution of exposure time and the Gaussian apodization function distribution of scanning speed at different positions of the dispersive fiber grating. Figure (a) shows the Gaussian apodization function distribution of exposure time, and Figure (b) shows the Gaussian apodization function distribution of scanning speed.

[0016] Figure 4The Gaussian apodization function distribution of exposure time and the Gaussian apodization function distribution of scanning speed at different positions of the dispersive fiber grating are shown in Figure (a) and Figure (b).

[0017] Figure 5 This is a schematic diagram of the reflection spectrum of the hyperspectral flatness dispersive fiber grating prepared in this invention.

[0018] Figure 6 This is a flowchart of a method for fabricating a high-spectral-flatness dispersive fiber grating according to the present invention. Detailed Implementation Plan

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments and methods described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the present invention.

[0020] Combination Figure 6 A method for fabricating a high-spectral-flatness dispersive fiber grating, comprising the following steps:

[0021] Step 1: Design and build the ultraviolet beam homogenization module 2-4. Use the homogenization ultraviolet light field control technology to expand and shape the ultraviolet laser beam, disperse the originally dense Gaussian energy distribution, so as to achieve the purpose of homogenizing the Gaussian light spot and finally obtain the ideal writing light field. In this way, the degree of refractive index change at both ends of the fiber grating is reduced during the ultraviolet writing scanning process, and the side mode suppression ratio of the dispersive fiber grating is improved.

[0022] Combination Figure 1The beam homogenization module 2-4 consists of three parts: a beam shaping structure, an optical path collimation structure, and a beam spot compression structure, all arranged sequentially along the optical axis. The beam shaping structure comprises a hemispherical lens 1-1 and an aperture 1-2, where the hemispherical lens 1-1 has a diameter of 5 mm and a convex radius of 2.5 mm. Since the beam diameter of the ultraviolet laser used for writing is on the micrometer scale, beam expansion requires changing the numerical aperture of the beam to disperse its originally dense, Gaussian-distributed energy. Furthermore, because the numerical aperture of the beam is directly proportional to the effective diameter of the lens and inversely proportional to the distance to the focal point, to increase the numerical aperture of the laser beam, a lens with a diameter approximately equal to the laser focal spot diameter and a very small focal length must be selected. After passing through the hemispherical lens 1-1, the laser energy distribution remains unchanged, still exhibiting a Gaussian distribution. However, because the hemispherical lens 1-1 expands the numerical aperture of the beam, the laser, after being focused, rapidly diverges from a single point, resulting in a large diverging spot, thus facilitating beam shaping. This system employs the simplest aperture method for beam shaping. By controlling the aperture size of aperture 1-2, the middle portion of the Gaussian beam is truncated, achieving a near-flat-top beam shaping effect. To simplify the system, plano-convex lenses 1-3 form the optical path collimation structure. Their parameters are: diameter 25.4 mm, radius of curvature 92 mm, focal length 200.7 mm, and center thickness 2.9 mm. Plano-convex lenses 1-3 are used to expand and collimate the shaped laser beam. For further system simplification, cylindrical mirrors 1-4 form the beam compression structure. Their parameters are: diameter 25.4 mm, radius of curvature 114.6 mm, focal length 238 mm, and center thickness 4 mm. Cylindrical mirrors 1-4 longitudinally compress the collimated beam obtained after beam expansion, forming a uniformly energetic linear beam spot that is directly used for grating writing.

[0023] Step 2: Utilizing high-edge suppression ratio apodization technology, the scanning speed V of the stepper motor is controlled. a By changing the exposure time at different positions of the fiber grating, the refractive index modulation depth at different positions of the fiber grating can be controlled to eliminate the abrupt change in refractive index at both ends, resulting in an apodized dispersion fiber grating with a side-mode suppression ratio greater than or equal to 20dB.

[0024] Combination Figure 2First, a high-spectral-flatness dispersive fiber grating ultraviolet (UV) writing system and a real-time monitoring system were constructed. The UV writing system consists of a UV laser (2-1), a stepper motor (2-2), a UV mirror (2-3), a beam homogenization module (2-4), a phase mask (2-5), an fiber support (2-6), and a six-dimensional adjustment frame (2-7). During writing the dispersive fiber grating, the UV laser is folded 90° by the UV mirror (2-3), homogenized by the beam homogenization module (2-4), and its energy is longitudinally compressed to increase power density. Then, it exposes the fiber to the phase mask (2-5). During the writing process, the stepper motor (2-2) drives the UV mirror (2-3) and the beam homogenization module (2-4) to move simultaneously along the grating area of ​​the phase mask (2-5), achieving scanning of the grating area and thus completing the writing of the dispersive fiber grating. The real-time monitoring system mainly includes a broadband light source (2-8), a circulator (2-9), a spectrometer (2-10), and a high-reflectivity Bragg fiber grating (2-11). The high-reflectivity Bragg fiber grating 2-11 uses PM980 fiber with a reflectivity of 99.9% and a center wavelength of 1070 nm. During measurement, port 1 of the circulator 2-9 is connected to the broadband light source 2-8, and port 2 is connected to the high-reflectivity Bragg fiber grating 2-11. The long-period end of the dispersive fiber grating is fused to the high-reflectivity Bragg fiber grating 2-11. Connecting port 3 to the spectrometer 2-10 allows simultaneous measurement of the reflection spectral intensity P1 of the dispersive fiber grating with a center wavelength around 1030 nm and the reflection spectral intensity P2 of the high-reflectivity Bragg fiber grating 2-11 with a center wavelength of 1070 nm. The reflectivity R of the dispersive fiber grating then satisfies the following formula:

[0025]

[0026] Combination Figure 3 Apodized dispersion fiber gratings with an edge mode suppression ratio (EMR) ≥ 20 dB were fabricated using a high-spectral-flatness ultraviolet writing system and a real-time monitoring system. The fiber type was PM980, the scanning length was 100 mm, the writing laser power was 30 mW, and the phase mask chirp rate was 3 nm / cm. A high EMR apodization technique was employed, achieved by controlling the scanning speed V of the stepper motor 2-2 during the writing process. a This allows us to change the exposure time at different positions of the dispersive fiber grating to achieve a Gaussian apodization effect. The Gaussian apodization function of the exposure time with respect to position is:

[0027]

[0028] Where L is the grating length, set to 100mm; k Gaussian The apodization factor is set to 0.7; T is the exposure time before apodization; and z is the real-time exposure position. Figure 3 (a) in the diagram is a schematic diagram of the Gaussian apodization function distribution of the exposure time at various positions of the dispersive fiber grating. Figure 3(b) shows a schematic diagram of the Gaussian apodization function distribution of the scanning speed. The scanning speed is inversely proportional to the exposure time. Considering the movement accuracy of stepper motor 2-2, the entire speed change process is divided into 50 segments. At the grating position corresponding to the Gaussian apodization function of 1, stepper motor 2-2 has the minimum scanning speed. The scanning speed of stepper motor 2-2 is set to 0.009 mm / s at this time, and the fiber grating is written with a Gaussian apodization scanning speed distribution.

[0029] Step 3: Utilize progressive scanning and writing technology, superimposed with progressive scanning speed V b The scanning speed of the ultraviolet laser at the short wavelength position is Make the scanning speed of the ultraviolet laser at the long wavelength position as To improve the reflectivity of dispersive fiber gratings at short wavelengths and reduce their reflectivity at long wavelengths, thereby compensating for the problem of lower reflectivity at short wavelengths than at long wavelengths caused by short-wavelength loss, the short-wavelength loss phenomenon is effectively suppressed, resulting in dispersive fiber gratings with spectral flatness less than or equal to 2% and side-mode suppression ratio greater than or equal to 20dB.

[0030] Combination Figure 4 A progressive scanning inscription technique is employed. When short-wavelength light passes through a long-period grating structure, some of the light will satisfy the mode coupling condition with higher-order modes, leading to short-wavelength loss in the reflection spectrum of the dispersive fiber grating. This short-wavelength loss reduces the spectral flatness of the dispersive fiber grating, degrades the spectral effect of the broadened pulse, and reduces the output performance of the ultrafast laser. Progressive scanning inscription is introduced into the fabrication process of the dispersive fiber grating. The scanning speed of the stepper motor at the short-wavelength position is set 2-2. Stepper motor scanning speed at long wavelength positions (2-2) Ultimately, this increases reflectivity in the short-wavelength region, thereby compensating for short-wavelength loss and improving the spectral flatness of the dispersive fiber grating. This is achieved by further introducing a linear function:

[0031]

[0032] Where k Compensation T is the compensation factor, expressed in seconds per centimeter (s / cm), representing the change in exposure time per unit length of the grating. Gaussian Set k as the initial value for the exposure time distribution. Compensation = -0.005s / cm to compensate for shortwave loss. This is achieved through a compensation coefficient factor k. Compensation This allows for progressive scanning and writing during the preparation of CFBG, thereby increasing the reflectivity of the short-wavelength region relative to the long-wavelength region to improve the flatness of the CFBG spectrum, while compensating for short-wavelength loss.

[0033] Combination Figure 5 To ensure the successful fabrication of the dispersive fiber grating, its spectral flatness must be effectively tested. The specific process is as follows:

[0034] 1) Measure the reflection spectrum within ±6 nm of the center wavelength of the dispersive fiber grating using a spectrometer with a resolution of 0.02 nm, and measure the highest peak power P of five reflection spectra within this range. P1 To P P5 The lowest valley value P of the five reflectance spectral powers V1 To P V5 ;

[0035] 2) Calculate the spectral flatness η of the dispersive fiber grating according to the following formula;

[0036]

[0037] 3) Repeat the measurement ten times and record the results. Calculate the average value of the ten measurements as the calibration result for spectral flatness.

[0038] In summary, this invention provides a method for fabricating a dispersive fiber grating with high spectral flatness. By combining homogenized ultraviolet light field control technology, high edge mode suppression ratio apodization technology, and progressive scanning writing technology, a dispersive fiber grating with spectral flatness less than or equal to 2% and edge mode suppression ratio greater than or equal to 20dB is finally fabricated.

Claims

1. A method for fabricating a high-spectral-flatness dispersive fiber grating, characterized in that, The steps are as follows: Step 1: Use the homogenization ultraviolet light field control technology to expand and shape the ultraviolet laser beam, disperse its originally dense Gaussian energy distribution, so as to achieve the purpose of homogenizing the Gaussian light spot and finally obtain the ideal writing light field; thereby reducing the degree of refractive index change at both ends of the fiber grating during the ultraviolet writing scanning process and improving the side mode suppression ratio of the dispersive fiber grating. Step 2: Utilize high-edge suppression ratio apodization technology by controlling the scanning speed V of the stepper motor. a By changing the exposure time at different positions of the fiber grating, the refractive index modulation depth at different positions of the fiber grating can be controlled to eliminate the abrupt change in refractive index at both ends, resulting in an apodized dispersion fiber grating with a side mode suppression ratio greater than or equal to 20dB. Step 3: Utilize progressive scanning and writing technology, superimposed with progressive scanning speed V. b The scanning speed of the ultraviolet laser at the short wavelength position is [value missing]. Make the scanning speed of the ultraviolet laser at the long wavelength position as To improve the reflectivity of dispersive fiber gratings at short wavelengths and reduce their reflectivity at long wavelengths, thereby compensating for the problem of lower reflectivity at short wavelengths than at long wavelengths caused by short-wavelength loss, the short-wavelength loss phenomenon is effectively suppressed, resulting in dispersive fiber gratings with spectral flatness less than or equal to 2% and side-mode suppression ratio greater than or equal to 20dB.

2. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 1, characterized in that, In step 1, the ultraviolet laser is expanded and shaped using homogenized ultraviolet light field control technology to disperse its originally dense Gaussian energy distribution, thereby achieving the purpose of homogenizing the Gaussian light spot and ultimately obtaining the ideal writing light field. The specific implementation is as follows: S1-1, Design of beam homogenization module (2-4): The beam homogenization module (2-4) includes a beam shaping structure, an optical path collimation structure, and a beam spot compression structure arranged sequentially along the optical axis; The beam shaping structure includes a hemispherical lens (1-1) and an aperture (1-2); the optical path collimation structure includes a plano-convex lens (1-3); and the beam compression structure includes a cylindrical mirror (1-4). The hemispherical lens (1-1), aperture (1-2), plano-convex lens (1-3), and cylindrical lens (1-4) are arranged along the same optical axis in sequence; S1-2. Use the beam homogenization module (2-4) to homogenize the ultraviolet light field: 1-2-1) The writing laser first passes through a beam shaping structure. After passing through a hemispherical lens (1-1), the laser energy distribution remains unchanged and is still Gaussian. However, since the hemispherical lens (1-1) expands the numerical aperture of the beam, the laser beam diverges rapidly from a single point after being focused. The diverged spot facilitates beam shaping. Then, it passes through an aperture (1-2). By controlling the aperture size of the aperture (1-2), the middle part of the Gaussian beam is intercepted to achieve a flat-top beam shaping effect, thus obtaining the shaped writing laser. 1-2-2) The shaped writing laser is expanded and collimated using a plano-convex lens (1-3) to obtain a collimated laser; 1-2-3) The collimated laser passes through a cylindrical mirror (1-4) and is longitudinally compressed to form a linear spot with uniform energy, which is then used to write the grating.

3. The method for fabricating a high spectral flatness dispersive fiber grating according to claim 2, characterized in that, In step 2, the high-edge mode suppression ratio apodization technique is used to control the scanning speed V of the stepper motor. a By changing the exposure time at different positions of the fiber grating, the refractive index modulation depth at different positions of the fiber grating can be controlled to eliminate the abrupt change in refractive index at both ends, resulting in an apodized dispersion fiber grating with an edge mode suppression ratio greater than or equal to 20 dB, as detailed below: S2-1. Construct a high-spectral-flatness dispersive fiber grating ultraviolet writing system: 2-1-1) The ultraviolet writing system for high spectral flatness dispersive fiber gratings includes an ultraviolet laser (2-1), a stepper motor (2-2), an ultraviolet mirror (2-3), a beam homogenization module (2-4), a phase mask (2-5), an optical fiber support (2-6), and a six-dimensional adjustment frame (2-7); the ultraviolet mirror (2-3) and the beam homogenization module (2-4) are mounted on the stepper motor (2-2), the phase mask (2-5) and the optical fiber support (2-6) are mounted on the six-dimensional adjustment frame (2-7), and the optical fiber is fixed on the optical fiber support (2-6); An ultraviolet laser (2-1), a stepper motor (2-2), an ultraviolet mirror (2-3), a beam homogenization module (2-4), a phase mask (2-5), and a dispersive fiber grating are arranged sequentially along the optical path. 2-1-2) When writing a high-spectral-flatness dispersive fiber grating, the ultraviolet laser emitted from the ultraviolet laser (2-1) is folded 90° by the ultraviolet mirror (2-3) and homogenized by the beam homogenization module (2-4) to increase the power density by longitudinally compressing the energy. The laser then passes through the phase mask (2-5) to expose the fiber on the fiber support (2-6). During the writing process, the stepper motor (2-2) drives the ultraviolet mirror (2-3) and the beam homogenization module (2-4) to move simultaneously along the grating area of ​​the phase mask (2-5) to scan the grating area of ​​the phase mask (2-5), thereby achieving the purpose of writing the dispersive fiber grating. S2-2. Construct a real-time monitoring system for high spectral flatness dispersive fiber gratings: 2-2-1) The real-time monitoring system for high spectral flatness dispersive fiber Bragg gratings includes a broadband light source (2-8), a circulator (2-9), a spectrometer (2-10), and a high-reflection Bragg fiber Bragg grating (2-11); 2-2-2) During real-time monitoring of the center wavelength, reflectivity, and bandwidth of the dispersive fiber grating during the writing process, the high-reflectivity Bragg fiber grating (2-11) uses PM980 fiber with a reflectivity of 99.9% and a center wavelength of 1070nm. One port of the circulator (2-9) is connected to a broadband light source (2-8), and port 2 is connected to one end of the high-reflectivity Bragg fiber grating (2-11). One end of the fiber on the fiber support (2-6) is fused to the other end of the high-reflectivity Bragg fiber grating (2-11). Port 3 of the circulator (2-9) is connected to a spectrometer (2-10) to simultaneously measure the reflection spectral intensity P1 of the dispersive fiber grating with a center wavelength near 1030nm and the reflection spectral intensity P2 of the high-reflectivity Bragg fiber grating (2-11) with a center wavelength of 1070nm. The reflectivity R of the dispersive fiber grating then satisfies the following formula: S2-3. Fabrication of adoped dispersion fiber gratings with an edge mode suppression ratio greater than or equal to 20 dB using adoped technology with high edge mode suppression ratio: 2-3-1) Fabrication of apodized dispersion fiber gratings with a side-mode suppression ratio greater than or equal to 20dB based on an ultraviolet writing system and a real-time monitoring system; the fiber type is PM980, the scanning length is 100mm, the writing laser power is 30mW, and the phase mask chirp rate is 3nm / cm; the scanning speed V of the stepper motor (2-2) is adjusted during the writing process. a This allows for the alteration of exposure time at different positions within the dispersive fiber grating, achieving a Gaussian apodization effect. 2-3-2) At the grating position corresponding to the Gaussian apodization function of 1, the stepper motor (2-2) is at its minimum scanning speed. The scanning speed of the stepper motor (2-2) is set to 0.009 mm / s, and the fiber grating is started to be written at the scanning speed of Gaussian apodization.

4. The method for fabricating a high spectral flatness dispersive fiber grating according to claim 3, characterized in that, Exposure time as a function of the Gaussian apodization function of position T Gaussian for: Where L is the grating length, k Gaussian denoted by the apodization factor, T is the exposure time before apodization, and z is the real-time exposure position.

5. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 4, characterized in that, L is set to 100mm, k Gaussian Set to 0.7, the scanning speed is inversely proportional to the exposure time. Considering the movement accuracy of the stepper motor (2-2), the entire speed change process is divided into 50 segments.

6. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 4, characterized in that, In step 3, progressive scanning writing technology is used, with progressive scanning speed V superimposed. b The scanning speed of the ultraviolet laser at the short wavelength position is [value missing]. Make the scanning speed of the ultraviolet laser at the long wavelength position as To improve the reflectivity of dispersive fiber gratings at short wavelengths and reduce their reflectivity at long wavelengths, thereby compensating for the problem of lower reflectivity at short wavelengths compared to long wavelengths due to short-wavelength loss, the short-wavelength loss phenomenon is effectively suppressed, resulting in a dispersive fiber grating with spectral flatness less than or equal to 2% and side-mode suppression ratio greater than or equal to 20dB, as detailed below: S3-1. Fabrication of dispersive fiber gratings with spectral flatness less than or equal to 2% and side-mode suppression ratio greater than or equal to 20dB using progressive scanning inscription technique: Set the scanning speed of the stepper motor (2-2) at the short wavelength position to [value missing]. The scanning speed of the stepper motor (2-2) at the long wavelength position is Ultimately, this improves the reflectivity in the short-wavelength region, thereby compensating for short-wavelength loss and enhancing the spectral flatness of the dispersive fiber grating. Further introduce linear function T Compensation This compensates for short-wavelength loss, thereby improving the spectral flatness of the dispersive fiber grating. S3-2. Measurement of spectral flatness of dispersive fiber gratings, the specific process is as follows: 3-2-1) The reflection spectrum within the range of ±6 nm from the center wavelength of the dispersive fiber grating was measured using a spectrometer with a resolution of 0.02 nm (2-10), and the highest peak power P of five reflection spectra was measured within this range. P1 To P P5 The lowest valley value P of the five reflectance spectral powers V1 To P V5 ; 3-2-2) Calculate the spectral flatness η of the dispersive fiber grating; 3-2-3) Repeat the measurement ten times and record the results. Calculate the average value of the ten measurements as the calibration result of the spectral flatness.

7. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 6, characterized in that, 8. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 6, characterized in that, In S3-1, the linear function T Compensation as follows: Where k Compensation The compensation coefficient, in units of s / cm, represents the change in exposure time per unit length of the grating. T Gaussian denoted as the initial value of the exposure time distribution, T as the exposure time before apodization, z as the real-time exposure position, and L as the grating length.

9. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 8, characterized in that, Set k Compensation = -0.005s / cm.

10. The method for fabricating a high-spectral-flatness dispersive fiber grating according to claim 6, characterized in that, In 3-2-2), calculate the spectral flatness η of the dispersive fiber grating; Among them, P P1 To P P5 P represents the highest peak value of the five reflectance spectral powers. V1 To P V5 This represents the lowest valley value of the power of the 5 reflection spectra.

Images