Raman filter, and apparatus and method for manufacturing same

Abstract

The present invention provides an apparatus for manufacturing a Raman filter. The apparatus comprises a light source, a mask plate, a timing and / or power controller and an optical fiber, wherein the light source is configured to output ultraviolet light; the mask plate is provided with at least one section of grating stripes located between the light source and the optical fiber and is configured to project a grating stripe pattern onto the optical fiber obliquely relative to an optical fiber axis by means of the ultraviolet light; and the timing and / or power controller controls the time and / or power of projecting the grating stripe pattern onto the optical fiber to form on the optical fiber multiple sections of a grating having different refractive index depths. The present invention further provides a method for manufacturing a Raman filter and a Raman filter manufactured by the method, so as to solve the problems of high temperature in a grating region when a high-power chirped and tilted grating transmits high-power signal light, and the occurrence of heating caused by SRS light concentrated at the initial end of a high-power tilted grating region after being filtered out by a high-refractive-index adhesive coating of the chirped and tilted grating, and to effectively suppress SRS and improve the performance of a laser.

Description

Raman filter and manufacturing device and method thereof Technical Field

[0001] The present invention relates to the field of fiber lasers, and in particular to a Raman filter of a fiber laser system and a manufacturing device and method thereof. Background Art

[0002] Due to a series of advantages such as high conversion efficiency, good beam quality, compact structure, low cost, good stability, and convenient thermal management, fiber lasers have important applications in industrial manufacturing and processing, optical communications, medical cosmetology, national defense, and scientific research, and their market share in the global laser industry has grown rapidly. With the increase in the output power requirements of fiber lasers, the stimulated Raman scattering effect (SRS) has become increasingly serious, that is, the generation of new wavelength components different from the laser's own wavelength, which reduces the laser's monochromatic performance. Furthermore, SRS is a nonlinear growth process, and the proportion of SRS wavelengths will increase rapidly with the increase of output power. When the proportion of SRS wavelength components reaches a certain proportion, the fiber will experience severe heating, leading to damage to the laser.

[0003] In order to suppress SRS and improve laser performance, large-core optical fiber is usually used, but this will lead to a decrease in beam quality. SRS can also be suppressed by optimizing different pumping methods, but the structure is relatively complex and is not conducive to the development of lightweight lasers.

[0004] In recent years, a Raman filter has emerged that uses chirped tilted fiber Bragg gratings to filter out SRS in high-power fiber laser systems. The tilted fiber Bragg grating can couple most of the SRS light into the cladding and filter it out, significantly increasing the maximum output power of the laser.

[0005] When used, a high-power chirped tilted grating is fused to the fiber laser's signal output. After the SRS light is coupled to the cladding, it propagates in the opposite direction of the signal. It is usually filtered out by the high-refractive-index glue coating of the high-power chirped tilted grating and dissipated through the metal housing, or filtered out by a preceding cladding light filter. This filter can suppress SRS, but it still has the following disadvantages:

[0006] First, due to the special structural characteristics and manufacturing process of the chirped tilted grating, the temperature of the grating area is very high when transmitting high-power signal light;

[0007] Second, due to the characteristics of the backward transmission of SRS light coupled into the cladding and the limited filtering ability of the high-refractive-index glue coating of the chirped tilted grating, the temperature rise at the starting end of the high-power tilted grating region (i.e., the signal light incident end) produces a superposition effect with the increase of the backward transmission filtering power, resulting in a higher temperature.

[0008] Third, since high-power tilted gratings generate more heat than conventional fiber gratings, and the thermal conductivity of high-refractive-index glue is very low, it is not enough to effectively transfer heat to the metal shell for heat dissipation.

[0009] Summary of the Invention

[0010] The present invention provides a Raman filter and a manufacturing device and method thereof, so as to solve the problem that when a high-power chirped tilted grating transmits high-power signal light, the grating region temperature is high, and the SRS light is concentrated at the starting end of the high-power tilted grating region and generates heat after being filtered by the high-refractive-index glue coating of the chirped tilted grating. The filter effectively suppresses SRS and improves laser performance.

[0011] In a first aspect, the present invention provides a device for manufacturing a Raman filter, characterized in that the device comprises a light source, a mask, a timing and / or power controller, and an optical fiber; wherein

[0012] The light source is used to output ultraviolet light;

[0013] The mask has at least one section of grating stripes, which is located between the light source and the optical fiber and is used to project the grating stripe pattern onto the optical fiber at an angle relative to the optical fiber axis through the ultraviolet light;

[0014] The timing and / or power controller controls the time and / or power of projecting the grating fringe pattern onto the optical fiber to form a plurality of gratings with different refractive index depths on the optical fiber, wherein the gratings are tilted relative to the optical fiber axis.

[0015] In a second aspect, the present invention also provides a method for manufacturing a Raman filter, characterized in that the method comprises the following steps:

[0016] Output ultraviolet light;

[0017] Projecting at least one section of the grating fringe pattern on the mask onto the optical fiber by means of the ultraviolet light;

[0018] The time and / or power of projecting the grating fringe pattern onto the optical fiber is controlled to form a plurality of gratings with different refractive index depths on the optical fiber, wherein the gratings are tilted relative to the optical fiber axis.

[0019] In a third aspect, the present invention further provides a method for manufacturing a Raman filter, characterized in that the method comprises the following steps:

[0020] Output a point source of ultraviolet light so that it irradiates the optical fiber through a mask;

[0021] The reflector moves to drive the UV point light source to scan and write along the axial direction of the optical fiber;

[0022] Rotate the mask to change the tilt angle of the UV point light source;

[0023] By adjusting the power or moving speed of the ultraviolet point light source, multiple sections of gratings with different refractive index modulation depths are formed on the optical fiber;

[0024] The moving speed of the ultraviolet light point light source of each grating section is gradually slowed down and / or the power is gradually increased from the starting end of the grating area, so as to modulate the refractive index depth of different grating sections. After the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing refractive index modulation depth of each section is formed.

[0025] In a fourth aspect, the present invention also provides a Raman filter manufactured by the above method and apparatus, the Raman filter comprising an optical fiber and a plurality of chirped tilted gratings having different refractive index depths and interval periods formed on the optical fiber, wherein:

[0026] The refractive index depth of the chirped tilted grating close to the laser incident end is lower than that of the chirped tilted grating far from the incident end;

[0027] The filtering wavelength of the chirped tilted grating close to the laser incident end is shorter than that of the chirped tilted grating far from the incident end.

[0028] The present invention provides a Raman filter and a manufacturing device and method thereof: first, a focuser is used to convert the divergent light beam into a more focused light beam with a certain tilt angle relative to the optical fiber axis at one time, so as to meet the requirements of manufacturing a tilted grating, and the tilt angle can be adjusted; second, different sections of mask plates are used to control the irradiation position and range of each grating section, so as to manufacture multiple gratings with different refractive index modulation depths; third, the scanning time of each grating section is gradually lengthened and / or the power is increased from the starting end of the grating area, so as to manufacture multiple gratings with different interval periods, so that the refractive index modulation depth and interval period of each grating section increase in a gradient manner. Fourth, the temperature of each grating segment gradually decreases from the starting end of the grating area due to the superposition effect caused by the backward transmission of the filtered light, while the temperature of each grating segment gradually increases due to the gradient change of the refractive index modulation depth. By manufacturing multiple gratings with different refractive index modulation depths and interval periods, these two different temperature changes are reasonably controlled so that the two temperature change trends of each grating segment offset each other, and the temperature of each grating segment tends to be uniform, thereby solving the problem of high grating area temperature when the high-power chirped tilted grating transmits high-power signal light, and SRS light concentrated at the starting end of the high-power tilted grating area after being filtered by the high-refractive index glue coating of the chirped tilted grating. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only 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.

[0030] FIG1 is a schematic diagram of a chirped tilted grating structure provided by an embodiment of the present invention;

[0031] FIG2A is a schematic diagram of the refractive index modulation result of a chirped tilted grating provided in an embodiment of the present invention;

[0032] FIG2B is a schematic diagram showing the Raman light rejection rate of a section of a chirped tilted grating for each wavelength band provided by an embodiment of the present invention;

[0033] FIG2C is a schematic diagram showing the Raman light rejection rates of three-segment chirped tilted gratings for each wavelength band provided by an embodiment of the present invention;

[0034] FIG2D is a schematic diagram showing the Raman light rejection rate of the multi-segment chirped tilted grating for each wavelength band provided by an embodiment of the present invention;

[0035] 2E and 2F are schematic diagrams showing that the temperature at the beginning of an optical fiber is higher after Raman scattering is filtered out by using multiple chirped tilted gratings with the same refractive index depth in the prior art;

[0036] 2G and 2H are schematic diagrams showing how the temperature of an optical fiber is uniformed overall after Raman scattering is filtered out by using multiple chirped tilted gratings with gradiently increased refractive index depth according to the present invention;

[0037] FIG3 is a schematic diagram of a manufacturing module for a chirped tilted grating according to an embodiment of the present invention;

[0038] FIG4 is a schematic diagram of a device for manufacturing a chirped tilted grating according to Example 1 of the present invention;

[0039] FIG5 is a schematic diagram of a device for manufacturing a chirped tilted grating according to Example 2 of the present invention;

[0040] FIG6 is a flow chart of a method for manufacturing a chirped tilted grating Raman filter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments.

[0042] SUMMARY OF THE INVENTION

[0043] As previously described, the present invention provides a device and method for manufacturing a Raman filter. This device utilizes a chirped tilted fiber Bragg grating (FBG) to filter out SRS light in a high-power fiber laser system. The refractive index modulation depth of each grating segment is controlled to ensure that the temperatures of each fiber Bragg grating segment are approximately equal, thereby increasing the heat dissipation efficiency of the Raman filter, effectively suppressing SRS light, and improving laser performance.

[0044] FIG1 is a schematic diagram of a chirped tilted grating structure provided by an embodiment of the present invention. As shown in FIG1 , a high-power chirped tilted grating 105 comprises a core 104 , a cladding 103 , an outer coating 102 , and a heat dissipation structure 101 .

[0045] Each chirped tilted grating 105 segment has a length of 4 cm to 10 cm, and the Raman spectrum width filtered is greater than 15 nm. The length of the grating 105 determines the size of the filtering bandwidth. A longer grating 105 length provides a wider filtering bandwidth, while a shorter grating 105 length results in a narrower filtering bandwidth.

[0046] The fiber core 104 is refractive index modulated according to a certain chirp rate within a certain length range to form a grating 105 structure. The Bragg wave vector of the grating 105 has a certain tilt angle with the axial direction of the optical fiber 100.

[0047] The "chirp rate" of grating 105 refers to the slope or rate of change of its refractive index as it changes with spatial coordinates. In grating 105, the refractive index typically varies periodically, and the chirp rate describes the rate of change. Specifically, the chirp rate of the chirped tilted grating 105 determines the rate of change in the wavelength and position of light. The larger the chirp rate, the faster the wavelength and position of light change. Therefore, the choice of chirp rate directly affects the range and characteristics of light wavelength rejection.

[0048] Refractive index modulation of the chirped tilted grating 105 refers to the process of adjusting the frequency or wavelength response of the grating 105 by changing the refractive index distribution within its structure. In the chirped grating 105, the refractive index varies with spatial periodicity. By adjusting the structural parameters of the grating 105, such as the period and chirp rate, the refractive index distribution can be changed. This refractive index modulation can be used to adjust the optical properties of the grating 105.

[0049] The refractive index modulation depth of the conventional chirped tilted grating 105 is typically modulated with a constant amplitude along the axial direction of the optical fiber 100 (see FIG2F ). Due to the limited filtering capability of the high-refractive-index glue coating of the chirped tilted grating 105, the temperature rise at the starting end of the grating region of the high-power tilted grating 105 (i.e., the signal light incident end) produces a superposition effect as the filtering power of the backward transmission increases. Without considering the heat generated by the high-power tilted grating 105 itself when transmitting signal light, the temperature variation of the tilted grating 105 follows the rule of T'1>T'2>T'3...>T'm (See Figure 2E).

[0050] To address the aforementioned issues of the prior art, the chirped tilted grating 105 provided by the present invention exhibits a refractive index modulation depth along the axial direction of the optical fiber 100, rather than the constant amplitude modulation typically employed in conventional high-power tilted gratings 105. Instead, it exhibits an increasing trend along the direction of incident signal light. Assuming the fiber core 104 is divided into m segments along the direction of incident signal light, where m ≥ 2, the refractive index modulation depth n varies as follows: n1 < n2 < n3 ... < nm (see FIG2H ). Because a deeper refractive index modulation depth increases the heat generated by the high-power tilted grating 105 when transmitting signal light, ignoring the heat generated by Raman filtering, when using a high-power tilted grating 105 with a gradient refractive index modulation depth, the temperature variation of the tilted grating 105 follows the pattern of T1 < T2 < T3 ... < Tm. Due to the limited filtering capacity of the high-refractive-index glue coating of the chirped tilted grating 105, the temperature rise at the starting end of the grating region of the high-power tilted grating 105 (i.e., the signal light incident end) produces a superposition effect with the increase of the filtering power transmitted backward. Without considering the heat generated by the high-power tilted grating 105 when transmitting signal light, the temperature variation of the tilted grating 105 is T'1>T'2>T'3...>T' m Reasonably control the refractive index modulation depth of each segment so that the T m +T' m They are approximately equal (see FIG. 2G ), thereby solving the problem of heat generation concentrated at the starting end of the grating region of the high-power tilted grating 105 when the high-power chirped tilted grating 105 transmits high-power signal light.

[0051] The cladding 103 is the structure of the optical fiber itself and is not specially processed and is not limited here.

[0052] The outer coating 102 is used for heat conduction. It is made by mixing a high-refractive-index glue with a high-thermal-conductivity powder material. The powder material evenly scatters the SRS light coupled into the high-refractive-index glue. Because the powder material has a high thermal conductivity, it effectively conducts heat to the heat sink, thereby effectively reducing the temperature of the high-power tilted grating 105. A thin protective layer can also be added between the outer coating 102 and the cladding 103 to protect the fiber cladding 103 from contamination and damage from the powder material, thereby enhancing reliability.

[0053] The heat dissipation structure 101 is used to dissipate heat from the optical fiber 100 and protect the optical fiber 100 from heat damage. The heat dissipation structure 101 can be made of metal material, which has high strength, thermal conductivity and corrosion resistance.

[0054] Figure 2A is a schematic diagram of the refractive index modulation structure of the chirped tilted grating provided in an embodiment of the present invention. Figure 2B is a schematic diagram of the Raman light filtering rate of a certain section of the chirped tilted grating provided in an embodiment of the present invention for each band. Figure 2C is a schematic diagram of the Raman light filtering rate of three sections of the chirped tilted grating provided in an embodiment of the present invention for each band. Figure 2D is a schematic diagram of the Raman light filtering rate of the multi-section chirped tilted grating as a whole for each band provided in an embodiment of the present invention. Among them, since the refractive index change of the chirped tilted fiber Bragg grating 105 is linearly or nonlinearly related to its position, the spatial modulation of the refractive index can be achieved by gradually changing the period of the grating 105. Normally, the period of the grating 105 will gradually increase or decrease with the change of position, forming a linear or nonlinear gradient. As shown in Figure 2A, along the signal light transmission direction 106, the initial grating segment 105A has small line spacing and a short period, filtering out short wavelengths. Due to short UV exposure times or low power, the refractive index modulation depth is relatively small. Subsequent grating segments 105B-105C have gradually increasing period and refractive index modulation depth, filtering out medium and long wavelengths. The longer the UV exposure time or the higher the power, the deeper the refractive index modulation depth. The period of the engraved grating 105 determines the center wavelength λ1 of the filtered Raman light. The period and refractive index modulation depth of each grating segment 105 decrease or increase from the center segment to the sides, causing the grating 105's Raman light rejection rate to vary, with a lower rejection rate for short-wavelength Raman light and a higher rejection rate for the center wavelength and long wavelength Raman light.

[0055] The formula for calculating the wavelength of filtered light is: λ = 2*neff*Λ / con(θ), where neff is the effective refractive index of the fiber, Λ is the period of the grating perpendicular to the grating plane, and θ is the grating tilt angle. This formula, based on the principle of Bragg scattering, describes the reflection or transmission characteristics of the periodic structure of the grating with respect to light wavelengths and is applicable to one-dimensional chirped tilted gratings. The period of the grating varies with position, and the filtering effect can be adjusted by adjusting the chirp rate and the physical parameters of the grating. The choice of tilt angle θ affects the wavelength range and slope of the filtered light.

[0056] Example modules

[0057] 3 is a schematic diagram of a chirped tilted grating fabrication module according to an embodiment of the present invention. The fabrication module 300 includes a light source 301 , a light shield 302 , a mask 303 , a timing and / or power controller 304 , and an optical fiber 100 .

[0058] The light source 301 is used to provide ultraviolet light, and is usually a laser or a mercury lamp, etc., which is not limited here.

[0059] The light shield 302 is used to block the propagation of light or limit the irradiation time and range of light. The light shield 302 is generally made of a sheet or film-like device made of metal or other opaque materials, which is not limited here. The metal light shield 302 can be made by cutting, stamping or laser cutting, and the shape and size can be customized as needed. The light shield 302 can be used to control the propagation path of light and limit the irradiation range of light; it can be used to control the switch of the light source so that the light source only irradiates the optical fiber 100 during a specific time period. The switch operation of the light shield 302 can control the irradiation time and position of light, thereby accurately controlling the characteristics of each segment of the grating 105.

[0060] The mask 303 is used to position and align the optical fiber 100 and control the irradiation position and range of each segment of the grating 105. The mask 303 is generally made using photolithography technology. During the grating 105 production process, the light beam passes through the transparent and opaque areas on the mask 303, selectively irradiating the scanning optical fiber 100 to form the desired grating 105 structure. The mask 303 can be made in sections using a material with a longer structure, or multiple segments of the mask 303 can be made using multiple shorter materials, which is not limited here. Each segment of the mask 303 is made with the same size. The groove interval period of the initial segment of the mask 303 is smaller, and the groove interval period of each subsequent segment is larger. The intermediate interval period of the mask 303 determines the intermediate interval period of the grating, and thus determines the center wavelength of the Raman light to be filtered out. Since the Raman filter needs to filter out as much Raman light of the center wavelength as possible, this may sacrifice some short-wave filtering capability. The interval period of the middle section of mask 303 is designed based on the central wavelength of the Raman light. The interval period of each section of mask 303 decreases or increases from the middle section toward the ends. To compensate for the lack of short-wavelength filtering capability, a section with a smaller interval period is added at the end of mask 303 to perform a secondary filtering of short-wavelength Raman light not filtered by the previous section.

[0061] The timing and / or power controller 304 is used to time the grating scan time, accurately control and monitor the scanning time of each grating segment, and / or control the emission power of the light source. During the grating 100 fabrication process, the specific timing and / or power controller 304 used depends on the fabrication process, equipment requirements, and application needs.

[0062] The optical fiber 100 is used as a transmission medium for optical signals and is the target for fabricating the grating 105. The basic structure of the optical fiber 100 includes a core 104 and a cladding 103. The core 104 is composed of a material with a relatively high refractive index to ensure the transmission of the optical signal within the optical fiber. The cladding 103 is a layer of material surrounding the core 104 and is made of a material with a relatively low refractive index to form an optical interface for total internal reflection, thereby limiting the propagation of the optical signal within the core 104 and preventing optical signal loss. The optical fiber 100 utilizes the principle of total internal reflection to allow the optical signal to propagate along the fiber axis within the core 104. When an optical signal propagates from a medium with a higher refractive index to a medium with a lower refractive index, the difference in refractive index causes the optical signal to be completely reflected back into the core 104, thereby achieving optical signal transmission. Optical fiber 100 offers advantages such as high bandwidth, low loss, and anti-interference, and is widely used in optical communications, data transmission, medical equipment, sensor technology, industrial control, and other fields.

[0063] Among them, the optical fiber materials used to make Bragg gratings include: 1) Photonic crystal fiber: Photonic crystal fiber is a special optical fiber with a periodic microstructure. By controlling the microstructure of the photonic crystal fiber, the production of Bragg gratings can be achieved. Photonic crystal fiber usually has a higher refractive index modulation efficiency and a larger modulation range. 2) Rare earth-doped fiber: Rare earth-doped fiber is an optical fiber that is doped with rare earth elements (such as erbium, neodymium, terbium, etc.) to achieve specific optical functions. Bragg gratings can be made by introducing periodic refractive index changes in rare earth-doped optical fibers. This is not limited here.

[0064] Exemplary device 1

[0065] 4 is a schematic diagram of a chirped tilted grating fabrication apparatus according to Embodiment 1 of the present invention. The fabrication apparatus 400 comprises a reference platform 401 , a light source 301 , a beam diverging and focusing unit 402 , a mask 303 , a grating clamping unit 403 , and a timing and / or power controller 304 .

[0066] The reference platform 401 is used to fix the light source 301, the beam diverging and focusing unit 402, the mask 303, the grating clamping unit 403 and the timing and / or power controller 304. The material of the reference platform 401 is generally aluminum, stainless steel, marble, etc., which is not limited here.

[0067] The light source 301 is configured to output ultraviolet light to the beam diverging and focusing unit 402 .

[0068] The beam diverging and focusing unit 402 is used to expand the beam and adjust the irradiation angle of the light. The beam diverging and focusing unit 402 includes a beam shaper 4021 and a focuser 4022.

[0069] The beam shaper 4021 is used to transform the ultraviolet light into a divergent beam. After shaping, the light forms a divergent beam or spot. The beam shaper 4021 can be a general spherical lens or an aspherical lens, such as a spherical convex lens or a spherical concave lens, which is not limited here.

[0070] The focuser 4022 is used to convert the divergent light beam into a more focused light beam with a certain tilt angle relative to the axial direction of the optical fiber 100. The focuser 4022 can be a convex lens, a concave mirror that makes the light path more compact, or other optical elements with a converging function, which are not limited here.

[0071] The mask 303 is used to position and align the optical fiber 100 and control the illumination position and range of each grating 105 segment. During the grating 105 fabrication process, the mask 303 needs to be replaced to produce gratings 105 with different interval periods. The mask 303 is made of materials such as quartz, graphite, or glass, which are not limited here.

[0072] The grating clamping unit 403 is used to fix the grating 105 of the optical fiber 100 to be processed. As shown in Figure 4, the grating clamping unit 403 may include a linear scanner 4031, which is used to control the grating clamping unit 403 to adjust the longitudinal direction of the optical fiber 100 so that the light passes through the mask 303 and scans the grating 105 in different positions in sections.

[0073] The timing and / or power controller 304 is used to time the grating scan time, accurately controlling and monitoring the scanning time of each grating segment 105 and / or controlling the emission power of the light source. The timing and / or power controller 304 is placed on the grating clamping unit 403 and connected to the light source 301 to record and control the light exposure time and / or control the emission power of the light source.

[0074] For easier understanding, the following is further explained through Example 1.

[0075] The light source 301 outputs ultraviolet light to the beam diverging and focusing unit 402. The beam diverging and focusing unit 402 expands the ultraviolet light and adjusts the angle of illumination. The beam diverging and focusing unit 402 includes a beam shaper 4021 and a focuser 4022. The beam shaper 4021 is located in front of the light source and converts the light signal from the light source 301 into a diverging beam. The light is shaped into a diverging beam or spot. The focuser 4022 converts the diverging beam from the beam shaper 4021 into a more focused beam with a predetermined tilt angle relative to the axial direction of the optical fiber 100. The mask 303 is positioned and aligned with the optical fiber 100 to control the position and range of the tilted beam irradiating the optical fiber 100. The tilted beam from the focuser 4022 passes through the transparent and opaque areas of the mask 303, selectively irradiating the scanning optical fiber 100, causing the refractive index of the illuminated optical fiber 100 to change, thereby forming the desired grating 105 structure.

[0076] The grating clamping unit 403 fixes the grating 105 of the optical fiber 100 to be processed, wherein the grating clamping unit 403 also includes a linear scanner 4031; the linear scanner 4031 is turned on to control the grating clamping unit 403 to adjust the longitudinal direction of the optical fiber 100, as shown by the arrow below in Figure 4, so that the inclined light beam from the focuser 4022 passes through the mask plate 303 and scans in segments at different positions of the grating 105.

[0077] The timing and / or power controller 304 will time the time it takes for the tilted light beam to scan and illuminate each segment of the grating 105, accurately controlling and monitoring the scanning time of each segment of the grating 105 so that the scanning time of each segment of the grating 105 gradually increases from the starting end of the grating area of ​​the grating 105 onwards; and / or control the emission power of the light source 301 so that the scanning power of each segment of the grating 105 gradually increases from the starting end of the grating area of ​​the grating 105 onwards, modulating the refractive index depth of different segments of the grating 105, that is, after the optical fiber 100 is scanned by the light beam, a chirped tilted grating 105 is formed in which the refractive index modulation depth of each segment shows a gradient increase. The present invention has been verified through a large number of experimental tests. According to the temperature rise at the starting end of the grating area of ​​the chirped tilted grating 105 increases with the filtering power of the backward transmission, without considering the heat generated by the grating 105 itself when transmitting signal light, the temperature change law of the tilted grating 105 is T'1>T'2>T'3...>T' m Therefore, when manufacturing the chirped tilted grating 105, the refractive index modulation depth of the grating 105 is controlled by controlling its scanning time and / or power in segments, so that the refractive index modulation depth n of each segment of the grating 105 changes in the following order: n1<n2<n3...<n mThe deeper the refractive index modulation depth is, the more serious the heat generated by the grating 105 when transmitting the signal light. The temperature variation caused by the refractive index modulation depth is T1<T2<T3...<T m The two changing rules produce a superposition effect. By reasonably controlling the scanning time and / or power of each grating 105, the refractive index modulation depth thereof is controlled, and finally the T of each segment is m +T' m The values ​​of the grating area and the chirped grating area are approximately equal, thereby solving the problem of heat generation concentrated at the starting end of the high-power tilted grating region when the high-power chirped tilted grating 105 transmits high-power signal light.

[0078] The advantages of this embodiment are as follows: First, the beam shaper 4021 uses a general spherical lens or an aspherical lens, which can convert the optical signal into a divergent beam. After the light is shaped by the beam shaper, it becomes a divergent beam or a light spot. Second, the focuser 4022 is used to convert the divergent beam into a more focused beam with a certain tilt angle relative to the axial direction of the optical fiber 100, so as to meet the requirements of manufacturing the tilted grating 105. The tilt angle can be adjusted by the focuser 4022. Third, since different segments of the grating 105 are manufactured by moving the optical fiber, and the position of the mask 303 is fixed, each segment of the grating can be adjusted according to the grating manufacturing requirements. When the grating 105 is manufactured, the period of each grating segment 105 is different, so the mask plate 303 is replaced, and the irradiation position and range of each grating segment 105 are controlled by using different mask plates 303, so that gratings 105 with different interval periods can be manufactured; fourthly, the timing and / or power controller 304 is used to time and control the grating scanning time and / or power, so that the scanning time of each grating segment 105 is gradually lengthened or the power is increased from the starting end of the grating area 105 onward, so that the refractive index modulation depth of each grating segment 105 has a gradient growth feature, thereby realizing the control of the refractive index modulation depth change of each grating segment 105.

[0079] Exemplary Device 2

[0080] FIG5 is a schematic diagram of an apparatus for fabricating a chirped tilted grating according to Example 2 of the present invention. As shown in FIG5 , compared to Example 1, Example 2 includes an additional light shielding plate 302. The mask plate 303 is longer and fixed in position. The mask plates 303 for multiple grating segments 105 are fabricated on the same mask plate 303, eliminating the need to replace the mask plate 303 when fabricating different grating segments 105. The light shielding plate 302 is positioned above the mask plate 303 and is used to position and align the optical fiber material. The tilted light beam from the focuser 4022 passes through the light shielding plate 302 to control the position and range of the ultraviolet light irradiating the mask plate. The light beam that passes through the light shielding plate 302 then passes through the mask plate 303 to selectively illuminate the scanning optical fiber 100, modulating the refractive index depth to form the grating 105 structure. In which, the shading plate 302 can adjust the longitudinal direction of the optical fiber 100, as shown by the arrow in Figure 5, so that the inclined light beam from the focuser 4022 passes through the shading plate 302 and the mask plate 303 and is scanned in segments at different positions of the grating 105; the timing and / or power controller 304 is connected to the shading plate 302, used to time the grating scanning time and control the scanning time of each segment of the grating 105 and / or connected to the light source 301, used to control the scanning power of each segment of the grating 105.

[0081] The mask plate 303 of exemplary device 1 has a shorter structure, and a replaceable mask plate 303 is used to control the irradiation position and range of each segment of the grating 105. Different types of mask plates 303 can be replaced to produce gratings 105 with different interval periods. Compared with the two exemplary devices, the gratings 105 produced by exemplary device 1 are more diverse in types, but since the mask plate 303 needs to be replaced, the grating 105 production process will be interrupted; in exemplary device 2, the mask plate 303 has a longer structure and a fixed position, and the irradiation position and range of each segment of the grating 105 are controlled by moving the light shielding plate 302 in the longitudinal direction of the optical fiber 100, which can ensure that the production process of each segment of the grating 105 is continuous and has higher energy utilization.

[0082] Exemplary Methods

[0083] FIG6 is a flow chart illustrating a method 600 for fabricating a chirped tilted grating Raman filter according to an embodiment of the present invention. As described with reference to the above figures, the method 600 may be performed by any suitable device, module, or apparatus. In some embodiments, operations 601-603 of the method 600 are performed sequentially.

[0084] Starting at operation 601 , the light source 301 provides ultraviolet light and outputs the ultraviolet light to the beam diverging and focusing unit 402 . Then proceed to operation 602, the ultraviolet light output by the light source 301 reaches the beam diverging and focusing unit 402 for beam expansion and adjustment of its irradiation angle, so that the ultraviolet light has a certain tilt angle relative to the axial direction of the optical fiber 100; then proceed to operation 603, the tilted light beam passes through the light shielding plate 302, and the position and time of the ultraviolet light passing through the window area of ​​the light shielding plate 302 to irradiate the mask plate 303 are controlled by controlling the moving position and residence time of the light shielding plate 302; the timing and / or power controller 304 times the grating scanning time, accurately controls and monitors the scanning time of each grating segment 105, so that the scanning time of each grating segment from the starting end of the grating area 105 is gradually lengthened; and / or is connected to the light source 301, accurately controls and monitors the scanning power of each grating segment 105, so that the scanning power of each grating segment from the starting end of the grating area 105 is gradually lengthened. Finally, the process proceeds to operation 604 , where the ultraviolet light selectively illuminates the scanning optical fiber 100 through the transparent and opaque areas of the mask 303 , and scans the optical fiber 100 in sections, so that the refractive index of the illuminated optical fiber 100 changes, forming the desired grating 105 structure.

[0085] The present invention also provides a chirped tilted grating Raman filter fabricated using the above-described apparatus and method, wherein the optical fiber includes multiple chirped tilted grating segments, wherein the chirped tilted grating segments near the laser input end have a lower refractive index depth than the chirped tilted grating segments farther from the input end, and the chirped tilted grating segments near the laser input end have a shorter filtering wavelength than the chirped tilted grating segments farther from the input end. Preferably, the filtering wavelength of the chirped tilted grating segment farthest from the input end is the same as the filtering wavelength of the first chirped tilted grating segment, thereby compensating for the short-wavelength Raman scattering filtering deficiency caused by the shallow refractive index depth of the first chirped tilted grating segment.

[0086] It should be noted that while the detailed description above mentions a chirped tilted grating Raman filter manufacturing module, apparatus, and method, this division is merely exemplary and not mandatory. In practice, according to embodiments of the present invention, the features and functions of two or more modules described above may be embodied in a single module. Conversely, the features and functions of a single module described above may be further divided and embodied by multiple modules.

[0087] Other writing methods and devices can also be used, such as the point light source scanning writing method, in which the point light source is driven to scan and write along the axial direction of the optical fiber by moving the reflector, the tilt angle is achieved by rotating the mask, and the refractive index modulation depth of different segments is achieved by adjusting the power of the writing light source or the speed of the light source movement. This method can still achieve the same effect.

[0088] Furthermore, although the operations of the method for fabricating a Raman filter of the present invention are described in a particular order in the accompanying drawings, this does not require or imply that the operations must be performed in this particular order, or that all illustrated operations must be performed to achieve the desired results. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0089] Although the spirit and principles of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the specific embodiments disclosed, and the division into various aspects does not mean that the features of these aspects cannot be combined to benefit. Such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0090] The present invention also provides:

[0091] 1. A device for manufacturing a Raman filter, characterized in that the device comprises a light source, a mask, a timing and / or power controller, and an optical fiber; wherein

[0092] The light source is used to output ultraviolet light;

[0093] The mask has at least one section of grating stripes, which is located between the light source and the optical fiber and is used to project the grating stripe pattern onto the optical fiber at an angle relative to the optical fiber axis through the ultraviolet light;

[0094] The timing and / or power controller controls the time and / or power of projecting the grating fringe pattern onto the optical fiber to form a plurality of gratings with different refractive index depths on the optical fiber, wherein the gratings are tilted relative to the optical fiber axis.

[0095] 2. The device for manufacturing a Raman filter according to item 1, characterized in that the device further comprises: a reference platform, a beam diverging and focusing unit, and a grating clamping unit; wherein

[0096] The reference platform is used to fix the light source, the beam diverging and focusing unit and the mask, the grating clamping unit and the timing and / or power controller;

[0097] The light source outputs ultraviolet light to the beam diverging and focusing unit;

[0098] The beam diverging and focusing unit is used to expand the beam and adjust the irradiation angle of the light on the mask;

[0099] The grating clamping unit fixes the optical fiber to be processed for forming a grating.

[0100] 3. The device for manufacturing a Raman filter according to item 2 is characterized in that the device further comprises: a light shielding plate for blocking the propagation of light or limiting the position and range of the ultraviolet light irradiating the mask.

[0101] 4. The device for manufacturing a Raman filter according to item 2 or 3, wherein the beam diverging and focusing unit comprises a beam shaper and a focuser;

[0102] The beam shaper is used to transform the ultraviolet light into a divergent beam, and the light is shaped by the beam shaper to form a divergent beam or a light spot;

[0103] The focuser is used to convert the divergent light beam into a more focused light beam with a certain tilt angle relative to the axial direction of the optical fiber.

[0104] 5. The device for manufacturing a Raman filter according to item 4, wherein the beam shaper is a spherical lens or an aspherical lens;

[0105] The focuser adopts a convex lens.

[0106] 6. The manufacturing device of the Raman filter according to item 1, 2 or 3 is characterized in that the timing and / or power controller will time and / or power control the time of the tilted light beam scanning to irradiate each segment of the grating, so that the scanning time of each segment of the grating is gradually lengthened and / or the power is gradually increased from the starting end of the grating area, and the refractive index depth of different segments of the grating is modulated, that is, after the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing trend in the modulation depth of the refractive index of each segment is formed.

[0107] 7. The device for manufacturing a Raman filter according to item 1, 2 or 3, wherein the spatial modulation of the grating refractive index is achieved by gradually changing the interval period of the grating;

[0108] The interval period of the grating gradually increases or decreases with the change of position, forming a gradient. Along the transmission direction of the signal light, the interval of the lines of the initial section of the grating is small, and the interval period and refractive index modulation depth of each subsequent section of the grating gradually increase in a gradient.

[0109] 8. The device for manufacturing a Raman filter according to item 7, wherein the interval period between each segment of the grating determines the central wavelength (λ1) of the filtered Raman light;

[0110] The interval period and refractive index modulation depth of each grating segment decrease or increase from the middle segment to both sides.

[0111] 9. The device for manufacturing a Raman filter according to item 1 or 7, wherein the interval between the notches of the mask at the beginning is relatively small, and the interval between the notches of each subsequent section is relatively large.

[0112] The intermediate interval period of the mask determines the intermediate interval period of the grating, and further determines the central wavelength of the filtered Raman light;

[0113] The interval period of each segment of the mask plate becomes smaller or larger from the middle segment to both sides.

[0114] 10. The manufacturing device of the Raman filter according to item 7 is characterized in that a structure with a small interval period is added at the end of the mask plate to perform secondary filtering on the short-wave Raman light not filtered out in the previous section.

[0115] 11. The Raman filter manufacturing device according to item 1 is characterized in that, in the Raman filter grating manufacturing device, the mask plate is replaced as needed to manufacture gratings with different interval periods and refractive index modulation depths in segments.

[0116] 12. The manufacturing device of the Raman filter according to item 2 is characterized in that the grating clamping unit includes a linear scanner, which is used to control the grating clamping unit to adjust the longitudinal direction of the optical fiber so that the light passes through the mask plate and is scanned in segments at different positions of the grating.

[0117] 13. The Raman filter manufacturing device according to item 3 is characterized in that, in the Raman filter grating manufacturing device, the mask plates of multiple grating segments are manufactured on the same mask plate.

[0118] 14. The manufacturing device of the Raman filter according to item 3 is characterized in that the position of the shading plate is adjusted in the longitudinal direction of the optical fiber, so that the inclined light beam from the focuser passes through the shading plate and the mask plate and scans in segments at different positions of the grating.

[0119] 15. The device for manufacturing a Raman filter according to any one of items 1 to 14, wherein the length of each grating segment is 4 cm to 10 cm.

[0120] 16. The device for manufacturing a Raman filter according to any one of items 1 to 14, wherein the Raman spectrum width filtered by the Raman filter is greater than 15 nm.

[0121] 17. A method for manufacturing a Raman filter, characterized in that the method comprises the following steps:

[0122] Output ultraviolet light;

[0123] Projecting at least one section of the grating fringe pattern on the mask onto the optical fiber by means of the ultraviolet light;

[0124] The time and / or power of projecting the grating fringe pattern onto the optical fiber is controlled to form a plurality of gratings with different refractive index depths on the optical fiber, wherein the gratings are tilted relative to the optical fiber axis.

[0125] 18. The method for making a Raman filter according to item 17, wherein

[0126] Using a reference platform to fix the ultraviolet light source, the beam diverging and focusing unit, the mask, the grating clamping unit and the timing and / or power controller;

[0127] Outputting the ultraviolet light from the light source to the beam diverging and focusing unit;

[0128] Utilizing the beam diverging and focusing unit to expand the beam and adjust the irradiation angle of the light on the mask;

[0129] The optical fiber to be processed for forming a grating is fixed by the grating clamping unit.

[0130] 19. The method for manufacturing a Raman filter according to item 18 is characterized in that it also includes: using a light shield to block the propagation of light or limit the position and range of the ultraviolet light irradiating the mask.

[0131] 20. The method for manufacturing a Raman filter according to item 18, further comprising: using a beam shaper to transform the ultraviolet light into a divergent beam or a light spot;

[0132] A focuser is used to convert the divergent light beam into a more focused light beam with a certain tilt angle relative to the optical fiber axis.

[0133] 21. The method for manufacturing a Raman filter according to item 20, wherein the beam shaper is a spherical lens or an aspherical lens;

[0134] The focuser adopts a convex lens.

[0135] 22. The method for manufacturing a Raman filter according to item 17 is characterized in that the time for scanning the tilted light beam to illuminate each segment of the grating is timed and the power is controlled by using a timing and / or power controller, so that the scanning time of each segment of the grating is gradually lengthened and / or the power is gradually increased from the starting end of the grating area, and the refractive index depth of different segments of the grating is modulated. After the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing trend in the modulation depth of the refractive index of each segment is formed.

[0136] 23. The method for manufacturing a Raman filter according to item 17, wherein the spatial modulation of the grating refractive index is performed by gradually changing the interval period of the grating;

[0137] The interval period of the grating is set to gradually increase or decrease with the change of position to form a gradient, wherein along the transmission direction of the signal light, the interval of the lines of the initial section of the grating is small, and the interval period and refractive index modulation depth of each subsequent section of the grating gradually increase in a gradient.

[0138] 24. The method for manufacturing a Raman filter according to item 17, wherein the central wavelength (λ1) of the filtered Raman light is used to determine the intermediate interval period of each grating segment;

[0139] The interval period and refractive index modulation depth of each grating segment are set to become smaller or larger from the middle segment to both sides.

[0140] 25. The method for manufacturing a Raman filter according to item 17, wherein the interval period of the notches in the initial section of the mask is smaller, and the interval period of the notches in each subsequent section is larger;

[0141] Determining the intermediate interval period of the mask using the intermediate interval period of the grating, and further determining the central wavelength of the Raman light to be filtered out;

[0142] The interval period of each section of the mask plate is set to become smaller or larger from the middle section to both sides.

[0143] 26. The method for manufacturing a Raman filter according to item 17 is characterized in that a second filtering is performed on the short-wave Raman light that was not filtered out in the previous section by adding a structure with a small interval period at the end of the mask.

[0144] 27. The method for manufacturing a Raman filter according to item 17 is characterized in that the gratings with different interval periods and refractive index modulation depths are manufactured in sections by replacing the mask according to the manufacturing needs.

[0145] 28. The method for manufacturing a Raman filter according to item 17 is characterized in that a linear scanner is used to control the grating clamping unit to adjust the longitudinal direction of the optical fiber, so that the light passes through the mask plate and is scanned in segments at different positions of the grating.

[0146] 29. The method for manufacturing a Raman filter according to item 19 is characterized in that the mask plates of multiple sections of the grating are manufactured on the same mask plate.

[0147] 30. The method for manufacturing a Raman filter according to item 17 is characterized in that the position of the shading plate can be adjusted in the longitudinal direction of the optical fiber, so that the inclined light beam from the focuser passes through the shading plate and the mask plate and is scanned in segments at different positions of the grating.

[0148] 31. The method for manufacturing a Raman filter according to any one of items 17 to 30, characterized in that the length of each grating segment is set to 4 cm to 10 cm.

[0149] 32. The method for manufacturing a Raman filter according to any one of items 17 to 30, characterized in that the Raman spectrum width filtered by the Raman filter is set to be greater than 15 nm.

[0150] 33. A method for manufacturing a Raman filter, characterized in that the method comprises the following steps:

[0151] Output a point source of ultraviolet light so that it irradiates the optical fiber through a mask;

[0152] The reflector moves to drive the UV point light source to scan and write along the axial direction of the optical fiber;

[0153] Rotate the mask to change the tilt angle of the UV point light source;

[0154] By adjusting the power or moving speed of the ultraviolet point light source, multiple sections of gratings with different refractive index modulation depths are formed on the optical fiber;

[0155] The moving speed of the ultraviolet light point light source of each grating section is gradually slowed down and / or the power is gradually increased from the starting end of the grating area, so as to modulate the refractive index depth of different grating sections. After the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing refractive index modulation depth of each section is formed.

[0156] 34. A Raman filter comprising an optical fiber and a plurality of chirped tilted gratings having different refractive index depths and interval periods formed on the optical fiber, wherein:

[0157] The refractive index depth of the chirped tilted grating close to the laser incident end is lower than that of the chirped tilted grating far from the incident end;

[0158] The filtering wavelength of the chirped tilted grating close to the laser incident end is shorter than that of the chirped tilted grating far from the incident end.

[0159] 35. The Raman filter according to item 34, wherein the filtering wavelength of the chirped tilted grating section farthest from the incident end is the same as the filtering wavelength of the first chirped tilted grating section.

Claims

1. A device for manufacturing a Raman filter, characterized in that: The device comprises a light source, a mask, a timing and / or power controller, and an optical fiber; wherein The light source is used to output ultraviolet light; The mask has at least one section of grating stripes, which is located between the light source and the optical fiber and is used to project the grating stripe pattern onto the optical fiber at an angle relative to the optical fiber axis through the ultraviolet light; The timing and / or power controller controls the time and / or power of projecting the grating fringe pattern onto the optical fiber to form a multi-segment grating with different refractive index depths on the optical fiber, wherein the grating is tilted relative to the optical fiber axis.

2. The manufacturing device of the Raman filter according to claim 1, characterized in that: The device also includes: a reference platform, a beam divergence and focusing unit, and a grating clamping unit; wherein The reference platform is used to fix the light source, the beam divergence and focusing unit and the mask, the grating clamping unit and the timing and / or power controller; The light source outputs ultraviolet light to the light beam diverging and focusing unit; The beam divergence and focusing unit is used for beam expansion and adjusting the irradiation angle of the light on the mask; The grating clamping unit fixes the optical fiber to be processed for forming a grating.

3. The manufacturing device of the Raman filter according to claim 2, characterized in that: The device also includes a light shielding plate, which is used to block the propagation of light or limit the position and range of the ultraviolet light irradiating the mask.

4. The manufacturing device of the Raman filter according to claim 2 or 3, characterized in that: The beam divergence and focusing unit includes a beam shaper and a focuser; wherein The beam shaper is used to transform the ultraviolet light into a divergent beam. Forming a divergent beam or spot; The focusing device is used to transform the divergent light beam into a more focused light beam having a certain tilt angle relative to the axial direction of the optical fiber.

5. The manufacturing device of the Raman filter according to claim 4, characterized in that: The beam shaper adopts a spherical lens or an aspherical lens; The focuser adopts a convex lens.

6. The manufacturing device of the Raman filter according to claim 1, 2 or 3, characterized in that: The timing and / or power controller will time and / or control the power of the tilted light beam scanning and irradiating each segment of the grating, so that the scanning time of each segment of the grating is gradually lengthened and / or the power is gradually increased from the starting end of the grating area, and the refractive index depth of different segments of the grating is modulated, that is, after the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing trend in the modulation depth of the refractive index of each segment is formed.

7. The manufacturing device of the Raman filter according to claim 1, 2 or 3, characterized in that: The spatial modulation of the refractive index of the grating is achieved by gradually changing the interval period of the grating; The interval period of the grating gradually increases or decreases with the change of position, forming a gradient, wherein along the transmission direction of the signal light, the interval of the lines in the initial section of the grating is small, and the interval period and refractive index modulation depth of each subsequent section of the grating gradually increase in a gradient.

8. The manufacturing device of the Raman filter according to claim 7, characterized in that: The intermediate interval period of each segment of the grating determines the central wavelength (λ1) of the Raman light filtered out; The interval period and refractive index modulation depth of each grating segment decreases or increases from the middle segment to both sides.

9. The manufacturing device of the Raman filter according to claim 1 or 7, characterized in that: The interval period of the notches in the initial section of the mask is relatively small, and the interval period of the notches in each subsequent section is relatively large; The intermediate interval period of the mask determines the intermediate interval period of the grating, and thus determines The central wavelength of the Raman light to be filtered out is determined; The interval period of each segment of the mask plate becomes smaller or larger from the middle segment to both sides.

10. The manufacturing device of the Raman filter according to claim 7, characterized in that: A structure with a small interval period is added at the end of the mask plate to perform secondary filtering on the short-wave Raman light that is not filtered out in the previous section.

11. The manufacturing device of the Raman filter according to claim 1, characterized in that: In the Raman filter grating manufacturing device, the mask is replaced as needed to manufacture gratings with different interval periods and refractive index modulation depths in sections.

12. The manufacturing device of the Raman filter according to claim 2, characterized in that: The grating clamping unit comprises a linear scanner, which is used to control the grating clamping unit to adjust the longitudinal direction of the optical fiber, so that the light passes through the mask plate and is scanned in sections at different positions of the grating.

13. The manufacturing device of the Raman filter according to claim 3, characterized in that: In the Raman filter grating manufacturing device, a mask plate of multiple sections of gratings is manufactured on the same mask plate.

14. The manufacturing device of the Raman filter according to claim 3, characterized in that: The position of the shading plate is adjusted in the longitudinal direction of the optical fiber, so that the inclined light beam from the focuser is scanned in sections at different positions of the grating through the shading plate and the mask.

15. The manufacturing device of the Raman filter according to any one of claims 1 to 14, characterized in that: The length of each grating segment is 4 cm to 10 cm.

16. The manufacturing device of the Raman filter according to any one of claims 1 to 14, characterized in that: The Raman spectrum width filtered out by the Raman filter is greater than 15 nm.

17. A method for manufacturing a Raman filter, characterized in that: The method comprises the following steps; wherein Output ultraviolet light; Projecting at least one section of the grating stripe pattern on the mask onto the optical fiber by means of the ultraviolet light; The time and / or power of projecting the grating fringe pattern onto the optical fiber is controlled to form a multi-segment grating with different refractive index depths on the optical fiber, wherein the grating is tilted relative to the optical fiber axis.

18. The method for manufacturing a Raman filter according to claim 17, characterized in that: in Using a reference platform to fix the ultraviolet light source, the beam divergence and focusing unit, the mask, the grating clamping unit and the timing and / or power controller; Outputting the ultraviolet light of the light source to the light beam diverging and focusing unit; Utilizing the beam divergence and focusing unit to expand the beam and adjust the irradiation angle of the light on the mask; The optical fiber to be processed for forming a grating is fixed by the grating clamping unit.

19. The method for manufacturing a Raman filter according to claim 18, characterized in that: Also includes: The shading plate is used to block the propagation of light or limit the position and range of the ultraviolet light irradiating the mask.

20. The method for manufacturing a Raman filter according to claim 18, characterized in that: The method further comprises: using a beam shaper to transform the ultraviolet light into a divergent beam or a light spot; A focusing device is used to convert the divergent light beam into a more focused light beam having a certain tilt angle relative to the axial direction of the optical fiber.

21. The method for manufacturing a Raman filter according to claim 20, characterized in that: The beam shaper adopts a spherical lens or an aspherical lens; The focuser adopts a convex lens.

22. The method for manufacturing a Raman filter according to claim 17, characterized in that: The time for scanning and irradiating each section of the grating with an inclined light beam is timed and the power is controlled by using a timing and / or power controller, so that the scanning time of each section of the grating is gradually lengthened and / or the power is gradually increased from the starting end of the grating area, and the refractive index depth of different sections of the grating is modulated. After the optical fiber is scanned by the light beam, a chirped inclined grating with a gradient increasing refractive index modulation depth of each section is formed.

23. The method for manufacturing a Raman filter according to claim 17, characterized in that: The spatial modulation of the refractive index of the grating is performed by gradually changing the interval period of the grating; The interval period of the grating is set to gradually increase or decrease with the change of position to form a gradient, wherein along the transmission direction of the signal light, the interval of the lines of the starting section of the grating is small, and the interval period and refractive index modulation depth of each subsequent section of the grating gradually increase in a gradient.

24. The method for manufacturing a Raman filter according to claim 17, characterized in that: Determining the intermediate interval period of each segment of the grating by using the central wavelength (λ1) of the filtered Raman light; The interval period and refractive index modulation depth of each grating segment are set to become smaller or larger from the middle segment to both sides.

25. The method for manufacturing a Raman filter according to claim 17, characterized in that: Setting the notch interval period of the mask template at the beginning to be smaller and the notch interval period of each subsequent section to be larger; Determine the intermediate interval period of the mask by using the intermediate interval period of the grating, and further determine the central wavelength of the Raman light to be filtered out; The interval period of each section of the mask template is set to become smaller or larger from the middle section to both sides.

26. The method for manufacturing a Raman filter according to claim 17, characterized in that: By adding a structure with a small interval period at the end of the mask, the short-wave Raman light not filtered out in the front section is filtered out for a second time.

27. The method for manufacturing a Raman filter according to claim 17, characterized in that: Gratings with different interval periods and refractive index modulation depths are manufactured in sections by replacing the mask according to the manufacturing needs.

28. The method for manufacturing a Raman filter according to claim 17, characterized in that: The grating clamping unit is controlled by a linear scanner to adjust the longitudinal direction of the optical fiber, so that the light passes through the mask plate and is scanned in sections at different positions of the grating.

29. The method for manufacturing a Raman filter according to claim 19, characterized in that: The mask plates of multiple sections of the grating are made on the same mask plate.

30. The method for manufacturing a Raman filter according to claim 17, characterized in that: The position of the shading plate can be adjusted in the longitudinal direction of the optical fiber, so that the inclined light beam from the focuser can be scanned in sections at different positions of the grating through the shading plate and the mask.

31. The method for manufacturing a Raman filter according to any one of claims 17 to 30, characterized in that: The length of each grating segment is set to 4 cm to 10 cm.

32. The method for manufacturing a Raman filter according to any one of claims 17 to 30, characterized in that: The Raman spectrum width filtered out by the Raman filter is set to be greater than 15 nm.

33. A method for manufacturing a Raman filter, characterized in that: The method comprises the following steps; wherein Outputting a point source of ultraviolet light so that it irradiates the optical fiber through a mask; The reflector moves to drive the ultraviolet point light source to scan and write along the axial direction of the optical fiber; Rotate the mask to change the tilt angle of the UV point light source; By adjusting the power or moving speed of the ultraviolet light point light source, a plurality of gratings with different refractive index modulation depths are formed on the optical fiber; The moving speed of the ultraviolet light point light source of each grating section is gradually slowed down and / or the power is gradually increased from the starting end of the grating area, so as to modulate the refractive index depth of different grating sections. After the optical fiber is scanned by the light beam, a chirped tilted grating with a gradient increasing trend in the modulation depth of the refractive index of each section is formed.

34. A Raman filter, comprising an optical fiber and a plurality of chirped tilted gratings with different refractive index depths and interval periods formed on the optical fiber, wherein: The refractive index depth of the chirped tilted grating close to the laser incident end is lower than the refractive index depth of the chirped tilted grating far from the incident end; The filtering wavelength of the chirped tilted grating close to the laser incident end is shorter than the filtering wavelength of the chirped tilted grating far from the incident end.

35. The Raman filter of claim 34, wherein the filtering wavelength of the chirped tilted grating section farthest from the incident end is the same as the filtering wavelength of the first chirped tilted grating section.

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