Device for preparing optical fiber grating and method for preparing optical fiber grating

Abstract

The present application discloses a device for preparing fiber gratings and a method for preparing fiber gratings. By presetting the temperature distribution on the photosensitive fiber, a phase template method is used on the photosensitive fiber with a preset and precisely controlled regional distribution lengthening to prepare a linear chirped grating. After the preparation is completed, the carbon dioxide laser is turned off, and the temperature of the photosensitive fiber is restored to uniformity. The temperature change process causes the fiber to shrink nonlinearly, thereby realizing the preparation of a nonlinear chirped grating. The device for preparing fiber gratings and the method for preparing fiber gratings proposed in the application can reduce the process difficulty of preparing gratings, and the operation is simple, the cost is low, and the compatibility is good.

Description

Technical Field

[0001] The present application relates to the field of optical information technology, and specifically to, but not limited to, a device for preparing a fiber grating and a method for preparing a fiber grating. Background Art

[0002] The emergence of chirped pulse amplification (CPA) system has led to a leap in laser focusing power density. Fiber Bragg gratings are important optical devices in chirped pulse amplification systems. There are many methods for preparing fiber Bragg gratings, among which the phase template method is one of the commonly used methods. However, in order to compensate for the third-order dispersion in the system, nonlinear chirp technology is usually required. At present, the gratings are mainly prepared by applying a predetermined stress / non-uniformly distributed temperature field or a nonlinear chirped phase template on the linear chirped grating. The former affects the process and reliability of the product, and it is difficult to accurately control it during long-term use; while the latter has a high production cost, and the same phase template can only produce gratings with a preset dispersion amount, and has poor compatibility. Summary of the invention

[0003] The main purpose of the embodiments of the present application is to propose a device for preparing a fiber grating and a method for preparing a fiber grating, aiming to use components such as photosensitive optical fibers and lasers to realize grating writing, thereby reducing the process difficulty of preparing the grating, and having simple operation, low cost and good compatibility.

[0004] In a first aspect, an embodiment of the present application provides a device for preparing a fiber grating, comprising: an ultraviolet laser, a beam shaping system, a reflector, a cylindrical lens, a phase template, a photosensitive optical fiber and a carbon dioxide laser; the ultraviolet laser forms an output beam; the output beam passes through the beam shaping system and is shaped into a collimated beam with a pure light spot; the collimated beam is reflected by the reflector and incident on the cylindrical lens; the focusing lens focuses the collimated beam and forms a focused light; after the focused light passes through the phase template, interference fringes are formed; the interference fringes are irradiated to the photosensitive optical fiber; the carbon dioxide laser outputs a laser beam, and the laser beam is irradiated to the photosensitive optical fiber.

[0005] In the second aspect, an embodiment of the present application provides a method for preparing a fiber grating, comprising: removing a coating layer from a photosensitive optical fiber in an area to be written; cleaning the surface of the photosensitive optical fiber; setting the photosensitive optical fiber to a phase template and making it 90° with the phase template lines; scanning the laser beam along the axis of the photosensitive optical fiber through a scanning galvanometer of a carbon dioxide laser; achieving grating toe-cutting by scanning back and forth with an ultraviolet laser and a reflector; and completing the grating preparation after the reflector performs one or more cycles of scanning.

[0006] The device and method for preparing fiber gratings proposed in this application preset the temperature distribution / lengthening amount on the photosensitive fiber, and use the phase template method to make a linear chirped grating on the photosensitive fiber with a preset precisely controlled regional distribution lengthening amount. After the production is completed, the carbon dioxide laser is turned off, and the temperature of the photosensitive fiber is restored to uniformity. The temperature change process causes the fiber to shrink nonlinearly, thereby realizing the preparation of a nonlinear chirped grating. The device and method for preparing fiber gratings proposed in the application can reduce the process difficulty of preparing gratings, and the operation is simple, the cost is low, and the compatibility is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a device for preparing a fiber Bragg grating in an embodiment of the present application;

[0008] Figure 2 is a flow chart of a method for preparing a fiber Bragg grating according to an embodiment of the present application;

[0009] Figure 3 This is a schematic diagram of the carbon dioxide laser of the present application and its operation;

[0010] Figure 4 is another schematic diagram of the carbon dioxide laser of the present application and its operation;

[0011] Figure 5 It is a schematic diagram of the axial scanning speed of the carbon dioxide laser scanning galvanometer of the present application.

[0012] Reference numerals:

[0013] Ultraviolet laser-1; beam shaping system-2; reflector-3; cylindrical lens-4; phase template-5; photosensitive optical fiber-6; carbon dioxide laser-7; carbon dioxide laser body-71; scanning galvanometer-72. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solution and advantages of the present application clearer, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments described herein in a possible implementation are only used to explain the present application and are not intended to limit the present application. In the absence of conflict, the embodiments in the present application and the features in the embodiments can be combined arbitrarily with each other.

[0015] In the description of the embodiments of the present application, suffixes such as "module", "component" or "unit" used to represent elements are used only to facilitate the description of the present application and have no specific meaning. Therefore, "module", "component" or "unit" can be used in a mixed manner.

[0016] It should be noted that, although the functional modules are divided in the device schematic diagram and the logical order is shown in the flow chart, in some cases, the steps shown or described may be performed in a different order than the module division in the device or the order in the flow chart. The terms "first", "second", etc. in the specification, claims and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. In addition, unless otherwise clearly defined, terms such as setting, installing, and connecting should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the embodiments of this application in combination with the specific content of the technical solution.

[0017] See also Figure 1 , Figure 1 This is a device for preparing a fiber grating provided in one embodiment of the present application. Figure 1 As shown, the device for preparing the fiber grating at least includes: an ultraviolet laser 1, a beam shaping system 2, a reflector 3, a cylindrical lens 4, a phase template 5, a photosensitive optical fiber 6, and a carbon dioxide laser 7.

[0018] The ultraviolet laser is turned on to generate an output beam, and the output beam L1 is incident on the beam shaping system 2. The beam shaping system 2 shapes the output beam L1 and outputs a collimated beam L2. The collimated beam L2 is incident on the reflector 3, and after being reflected by the reflector 3, it is emitted to the cylindrical lens 4. The collimated beam L2 passes through the cylindrical lens 4 and forms a focused light beam L3. The focused light beam L3 is emitted to the phase template 5. After passing through the phase template 5, the ±1st order diffraction light forms interference fringes. The photosensitive optical fiber 6 is placed behind the phase template 5 and is set in the interference fringes area. The carbon dioxide laser 7 outputs a laser beam L4 and irradiates the photosensitive optical fiber 6 after passing through the scanning galvanometer.

[0019] The reflector 3 is fixed to the electrically controlled translation stage through a lens holder, so that the reflector 3 can be scanned at variable speed along the axial direction of the collimated light beam L2 according to preparation requirements, thereby realizing fiber grating apodization.

[0020] The scanning galvanometer is programmable. Through programmable control of the scanning galvanometer, the laser beam L4 is quickly scanned back and forth along the axial direction of the photosensitive optical fiber 6, thereby heating the photosensitive optical fiber 6. The scanning speed of the laser beam L4 at different positions is different, so that the photosensitive optical fiber 6 reaches a preset temperature distribution condition along the axial direction.

[0021] In a possible implementation, the ultraviolet laser 1 may be an excimer laser or a solid-state laser. The laser emission wavelength of the ultraviolet laser 1 may be any wavelength between 193 nm and 355 nm, preferably 193 nm, 213 nm, 248 nm, 266 nm, and 355 nm; the coherence length may be greater than 1.5 mm, and the beam quality M 2 Less than 1.6.

[0022] In a possible implementation, the beam shaping system 2 includes necessary optical elements such as lenses, apertures, slits, and pinholes to shape the output beam L1 of the ultraviolet laser 1 into a collimated beam L2 with a diameter of 0.5 mm to 6 mm and a pure spot.

[0023] In a possible implementation, the reflective surface of the reflector 3 forms an angle of 45° with the incident collimated light beam L2 , and the collimated light beam L2 is rotated 90° before being emitted to the cylindrical lens 4 .

[0024] In a possible implementation, the cylindrical lens 4 is an ultraviolet quartz cylindrical lens that is evaporated with an anti-reflection film of a corresponding wavelength or is uncoated, so as to focus the collimated light beam into a horizontal light.

[0025] In a possible implementation manner, the interference fringes formed after passing through the phase template 5 have a fringing period that is half of the period of the phase template, and are preferably chirped fringes.

[0026] In a possible implementation, the refractive index of the photosensitive optical fiber 6 is modulated to meet writing requirements.

[0027] In a possible implementation manner, the carbon dioxide laser 7 preferably outputs a laser wave of the laser beam L4 of 10.6 um.

[0028] See also Figure 2 , Figure 2 FIG. 1 is a flow chart of a method for preparing a fiber Bragg grating provided in another embodiment of the present application. Figure 2 As shown, the preparation method comprises:

[0029] 210: Take a photosensitive optical fiber 6 of suitable size and remove the coating layer of the area where the grating is to be written;

[0030] 220: Clean the optical fiber surface;

[0031] 230: placing the photosensitive optical fiber 6 behind the phase template 5, and making the area to be written form an angle of 90° with the phase template lines;

[0032] 240: Using the scanning galvanometer of the carbon dioxide laser 7 to scan the laser beam L4 along the axis of the photosensitive optical fiber 6;

[0033] 250: using the ultraviolet laser 1 and the reflector 3 to scan back and forth to achieve the toe-cutting of the grating;

[0034] 260: After the reflector performs a scanning cycle, the grating preparation is completed.

[0035] In a possible implementation, the coating layer is removed by chemical etching or mechanical stripping.

[0036] In a possible implementation manner, the distance between the area to be written and the phase template is 50 um to 100 um.

[0037] In a possible implementation, the laser beam L4 scans along the axis of the photosensitive optical fiber 6, and the length of the scanning area covers the writing length; further, the scanning speed changes in a parabolic linear manner, with the fastest speed at the center, preferably about 300 mm / s, and the speeds on both sides gradually decreasing. Therefore, the temperature at the center is the lowest, and the elongation of different areas of the optical fiber is different, forming nonlinear elongation.

[0038] In a possible implementation, the ultraviolet laser 1 and the reflector 3 scan back and forth to achieve the apodization of the grating, and the scanning mode can be set according to the needs of the raised cosine apodization. Preferably, the central area is scanned at a uniform speed of 1 mm / min to 5 mm / min; the scanning speed at both ends of the writing area is faster, and the speed change satisfies the raised cosine function.

[0039] In order to further describe in detail the device and method for preparing optical fiber Bragg gratings of the present application, an example of a specific implementation of the device or method of preparing the present application is given below.

[0040] See also Figure 3 , 4 , Figure 3 , 4 This is a schematic diagram of a carbon dioxide laser and its operation provided in an embodiment of the present application. Figure 3 , 4 Components such as the carbon dioxide laser body 71, the scanning galvanometer 72, the laser beam L4, and the photosensitive optical fiber 6 are shown.

[0041] In this specific embodiment, the carbon dioxide laser body 71 emits a collimated laser beam L4 with a wavelength of 10.6um and a spot diameter of about 0.5mm to 1mm. The collimated laser beam L4 is adjusted in the transmission direction by the scanning galvanometer 72. Among them, the laser beam L4 can be irradiated to any position of the photosensitive optical fiber 6. In this specific embodiment, the laser beam L4 quickly scans back and forth along the area to be written of the photosensitive optical fiber 6. The precise photosensitive optical fiber 6 makes the photosensitive optical fiber 6 have no contact with the phase template 5 to avoid heating or damaging the phase template 5. Since quartz has a high absorption efficiency for carbon dioxide laser 7, under the irradiation of the laser beam L4, the photosensitive optical fiber 6 absorbs the laser beam L4 and heats up. The irradiation time of the photosensitive optical fiber 6 at different positions is controlled by the scanning galvanometer 72, so that the photosensitive optical fiber 6 absorbs different heat at different positions, thereby achieving the purpose of accurately controlling the temperature distribution of the photosensitive optical fiber 6. Through the thermal expansion coefficient of the quartz optical fiber 5.5×10-7 / ℃, the lengthening amount of each area of ​​the photosensitive optical fiber 6 at this time can be calculated. On the contrary, after the preset lengthening amount is calculated according to the dispersion compensation requirements, the lengthening amount can be precisely controlled by the irradiation amount of the laser beam L4.

[0042] In order to further describe in detail the device for preparing a fiber Bragg grating and the method for preparing a fiber Bragg grating of the present application, another specific implementation manner of the device or method for preparing the present application is exemplified below.

[0043] In this specific embodiment, the ultraviolet laser 1 is a solid laser with an operating wavelength of 266 nm. After passing through the beam shaping system 2, the collimated beam L2 is obtained with a diameter of 3 mm and a beam quality M 2 is 1.5. The reflector 3 is moved by an electrically controlled platform. In the process of making the grating, the reflector 3 scans back and forth to achieve the raised cosine apodization. The phase template 5 has a central period of 709nm, a linear chirp of 5.5nm / cm, and a ±1-level principle. The photosensitive fiber 6 is a highly photosensitivity PM980 fiber that has been loaded with high-pressure hydrogen. The carbon dioxide laser scanning galvanometer 72 has an axial scanning speed of 0.0407 W / m. Figure 5 The scanning speed is the fastest when the center of the photosensitive fiber 6 is scanned, and the scanning speed on both sides is slower, so that the temperature at the center of the photosensitive fiber 6 is the lowest, and the temperature on both sides gradually increases, completing the production of the nonlinear chirped fiber Bragg grating, and its dispersion parameter is 12.3ps / nm, and the third-order dispersion value is 0.6ps 3 .

[0044] Those skilled in the art will appreciate that all or some of the steps in the methods disclosed above, and the functional modules / units in the systems and devices may be implemented as software, firmware, hardware, or a suitable combination thereof.

[0045] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but the scope of the present application is not limited thereby. Any modification, equivalent substitution and improvement made by a person skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.

Claims

1. A device for preparing a fiber Bragg grating, characterized in that: The device comprises: an ultraviolet laser, a beam shaping system, a reflector, a cylindrical lens, a phase template, a photosensitive optical fiber and a carbon dioxide laser; The ultraviolet laser outputs a light beam; The beam shaping system receives the output beam and shapes the output collimated beam; The reflector reflects the collimated light beam; The cylindrical lens focuses the reflected collimated light beam to form a focused light beam; After the focused light passes through the phase template, interference fringes are formed; The photosensitive optical fiber is arranged in the region where the interference fringes are formed, and the interference fringes are irradiated to the photosensitive optical fiber; The carbon dioxide laser outputs a laser beam, and the laser beam irradiates the photosensitive optical fiber; The carbon dioxide laser comprises: A scanning galvanometer, wherein the scanning galvanometer is programmable and controllable; The laser beam passes through the scanning galvanometer and then irradiates the photosensitive optical fiber; By controlling the scanning galvanometer, the laser beam is scanned along the axis of the photosensitive optical fiber.

2. The device according to claim 1, characterized in that The device also includes: Electric translation stage; The reflector is fixed to the electrically controlled translation stage; The reflector can scan along the axial direction of the collimated light beam at a variable speed.

3. The device according to claim 1, characterized in that: The reflecting surface of the reflector is at 45° to the collimated light beam before incidence; The collimated light beam reflected by the reflector forms an angle of 90° with the collimated light beam before incident.

4. The device according to claim 1, characterized in that: The phase template is a linear chirp phase template; The fringe period of the interference fringes is half of the phase template period.

5. The device according to claim 1, characterized in that: The output light beam wavelength is 193nm-355nm.

6. The device according to claim 1, characterized in that: The collimated light beam has a diameter of 0.5 mm to 6 mm.

7. A method for preparing a fiber Bragg grating, characterized in that: include: Removing the coating of photosensitive optical fibers; Cleaning the surface of the photosensitive optical fiber; The photosensitive optical fiber is arranged behind the phase template and is 90° with the phase template scribed line; The laser beam is scanned along the axis of the photosensitive optical fiber by a scanning galvanometer of a carbon dioxide laser; The grating is apodized by scanning back and forth with a UV laser and a reflector; After the reflector performs one or more cycles of scanning, the grating preparation is completed; The scanning galvanometer is programmable and controllable; By controlling the scanning galvanometer, the laser beam is scanned along the axis of the photosensitive optical fiber.

8. The method according to claim 7, characterized in that The step of removing the coating layer of the photosensitive optical fiber comprises: The coating layer of the photosensitive optical fiber to be written is removed by chemical etching or mechanical stripping.

9. The method according to claim 8, characterized in that The distance between the area to be written and the phase template is 50um to 100um.

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