A novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing

Abstract

The present invention discloses a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing, comprising the following steps: S1, initial processing of the multi-core optical fiber to be processed; S2, position adjustment of the multi-core optical fiber by a nano-positioning XYZ displacement platform and an optical fiber rotator; S3, observing the core distribution of the multi-core optical fiber; S4, writing Bragg gratings in multiple cores of the multi-core optical fiber using a femtosecond laser by a point-by-point method. The present invention adopts the above-mentioned novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing, and the optical fiber rotator can rotate the optical fiber at different angles (0° to 360°) to achieve high-quality optical fiber Bragg grating writing in different situations. This method can perform corresponding Bragg grating writing on different cores of the multi-core optical fiber according to user requirements, thereby improving the accuracy and efficiency of the writing process.

Description

Technical Field

[0001] The invention relates to the field of optical fiber device preparation and sensing technology, and in particular to a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing. Background Art

[0002] In recent years, as multi-core optical fiber has attracted more and more attention from all walks of life, people have begun to apply fiber Bragg gratings in multi-core optical fiber and designed multi-core fiber Bragg gratings of the same category. This type of device integrates the advantages of multi-core optical fiber and fiber Bragg grating, and has important practical value and wide application in the field of optical fiber communication and sensor technology.

[0003] The fiber Bragg grating (FBG) has a periodic refractive index structure and can reflect light waves at a specified resonant wavelength, which plays a very important role in the development of devices based on multi-core optical fibers. At the same time, based on multi-core optical fibers, the differential spectral response of FBGs in different cores to the optical fiber can be utilized, so that multi-core optical fibers can not only be studied in many sensing aspects in the case of longitudinally distributed grating arrays, but also the shape of the optical fiber cross section can be reconstructed in space.

[0004] Femtosecond laser direct writing technology is a very convenient and practical method for manufacturing fiber Bragg gratings, which has the advantages of flexible structural design, high writing accuracy, and short manufacturing time. The fiber Bragg gratings made by this technology are resistant to high temperatures, have a strong structure, and are not easy to damage. In addition, this method has no requirements for the photosensitivity of the optical fiber, which reduces the additional cost required for increasing photosensitivity operations. In addition, femtosecond laser direct writing technology can also produce gratings with other complex structures. Therefore, this technology has become a popular technology in the field of fiber Bragg grating manufacturing.

[0005] In recent years, multi-core fiber (MCF) has been gradually applied in multiplexing technology and has become a hot spot and focus of research by domestic and foreign researchers. Since the space occupied by information storage and interaction sites is limited, such as Internet nodes, data centers, etc., especially the places where information storage and interaction are realized in these sites, the space is even smaller and the space utilization rate is required to be higher. Therefore, it is necessary to increase the transmission capacity and speed of information. In addition, in terms of physics, it is not possible to increase the transmission capacity simply by using more optical fibers and their related communication systems. It is also necessary to increase the transmission capacity of a single optical fiber. Each core in a multi-core optical fiber, or the different modes of transmission in each core, can be used as an independent channel, which broadens the road of optical fiber communication transportation. And the spatial growth capacity of multi-core optical fiber can reach 2 to 3 orders of magnitude. Therefore, the development of multi-core optical fiber has far-reaching significance in terms of increasing the amount of information transmission and reducing the cost of optical cables. Summary of the invention

[0006] The purpose of the present invention is to provide a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing, which can perform corresponding Bragg grating writing on different cores of the multi-core optical fiber according to user requirements, thereby improving the accuracy and efficiency of the writing process.

[0007] To achieve the above object, the present invention provides a novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing, comprising the following steps:

[0008] S1. Performing initial processing on the multi-core optical fiber to be processed;

[0009] S2, adjusting the position of the multi-core optical fiber by using the nano-positioning XYZ displacement platform and the optical fiber rotator;

[0010] S3. Observe the core distribution of the multi-core optical fiber;

[0011] S4. Using a femtosecond laser, Bragg gratings are written in multiple cores of a multi-core optical fiber using a point-by-point method.

[0012] Preferably, in step S1, the multi-core optical fiber to be processed is initially processed, which specifically includes the following steps:

[0013] S11, select a multi-core optical fiber fusion transmission spectrum structure of single mode-multimode-multicore-multimode-single mode;

[0014] S12, removing the optical fiber coating layer of the multi-core optical fiber at the part to be processed;

[0015] S13, cutting the end face of the multi-core optical fiber by using an optical fiber cutting knife;

[0016] S14, using an optical fiber fusion splicer to fusion-splice the multi-core optical fibers in the above step S13, to complete the initial processing of the optical fibers to be processed.

[0017] Preferably, before step S2, the method further includes building a femtosecond laser writing multi-core optical fiber experimental system, and the specific steps are as follows:

[0018] Step 1: Designing the structure of the optical fiber rotator fixture by using simulation software, wherein the optical fiber rotator fixture includes a bottom base and a fixing pin;

[0019] Step 2: Processing the designed optical fiber rotator fixture into shape using organic glass;

[0020] Step 3: A groove is formed on the upper end surface of the fixing pin along the axis, and a sliding connection between the optical fiber rotator and the fixing pin is achieved through the groove.

[0021] Preferably, the specific steps of adjusting the position of the multi-core optical fiber in step S2 are as follows:

[0022] S21, fixing the multi-core optical fiber initially processed in step S1 on a nanopositioning XYZ displacement platform;

[0023] S22, using a nanopositioning XYZ displacement platform to straighten the multi-core optical fiber so that the horizontal direction of the multi-core optical fiber is parallel to the moving Y axis of the nanopositioning XYZ displacement platform;

[0024] S23, rotating the multi-core optical fiber using an optical fiber rotator so that the multiple fiber cores are in the same plane;

[0025] S24, adjusting the Z axis of the nanopositioning XYZ displacement platform so that the laser is located at the center of the multi-core optical fiber for writing.

[0026] Preferably, in step S3, an end-face microscope is used to observe the core distribution of the multi-core optical fiber, and μFab software is used to display the core distribution result.

[0027] Preferably, step S4 is specifically:

[0028] S41, observing the laser focus position through a CCD camera, and moving the position to the center of the core of the multi-core optical fiber;

[0029] S42, inputting a pre-set processing program into the software, and controlling the nanopositioning XYZ displacement platform to write the Bragg grating;

[0030] S43. According to the set pulse energy, frequency and moving speed of the nanopositioning XYZ displacement platform, adjust the output energy, power output Power and laser emission intensity AOM Intensity of the software controlling the femtosecond laser.

[0031] Therefore, the present invention adopts the above-mentioned novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing, and the beneficial effects are as follows:

[0032] (1) The present invention uses SolidWorks software to design the bottom base part and the stabilizing pin part, and the structure is stable and simple, so as to realize the height adjustment of the optical fiber rotator.

[0033] (2) The optical fiber rotator used in the present invention can rotate the optical fiber with high precision, which can effectively improve the writing accuracy and efficiency during the optical fiber writing process, and can rotate at a large angle, so that the fiber core writing structure is controllable.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is an overall flow chart of an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0036] Figure 2 It is a schematic diagram of the bottom base of an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0037] Figure 3 It is a schematic diagram of a stabilizing pin of an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0038] Figure 4 It is a schematic diagram of the assembly of the bottom base part and the stabilizing pin part of an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0039] Figure 5 This is a physical picture of the end face of a multi-core optical fiber according to an embodiment of a novel multi-core optical fiber multiplexing grating writing method based on femtosecond laser direct writing of the present invention;

[0040] Figure 6 This is a multi-core optical fiber end face simulation diagram of an embodiment of a novel multi-core optical fiber multiplexing grating writing method based on femtosecond laser direct writing of the present invention;

[0041] Figure 7 It is a schematic diagram of multi-core optical fibers located in different planes in an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0042] Figure 8 It is a schematic diagram of multi-core optical fibers located in the same plane in an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention;

[0043] Fig. 9 It is a multi-core optical fiber FBG writing transmission spectrum of an embodiment of a novel multi-core optical fiber multiplexed grating writing method based on femtosecond laser direct writing of the present invention.

[0044] Reference numerals

[0045] 1. Base; 2. Middle pin; 3. Rib structure; 4. Insert column; 5. Insert hole; 6. Groove. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0047] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0048] like Figure 1 As shown, a novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing comprises the following steps:

[0049] S1. Preliminary processing of the multi-core optical fiber to be processed, including the following steps:

[0050] S11. For the smooth progress of subsequent observation results, a multi-core optical fiber fusion transmission spectrum structure of single-mode-multi-mode-multi-core-multi-mode-single-mode is selected; that is, a three-core optical fiber, to ensure that the optical path can be smoothly coupled and passed;

[0051] S12, using an optical fiber stripper to remove the optical fiber coating layer of the multi-core optical fiber to be processed, and wiping the optical fiber with alcohol to remove impurities;

[0052] S13, cut the end face of the multi-core optical fiber using the Furukawa FITEL S325 optical fiber cutter to ensure the subsequent fusion quality;

[0053] S14: After the cutting is completed, the multi-core optical fiber in step S13 is fused using a fiber fusion splicer Furukawa FITEL S178 to obtain the required transmission spectrum structure, thus completing the initial processing of the optical fiber to be processed.

[0054] Build a femtosecond laser writing multi-core optical fiber experimental system. The specific steps are as follows:

[0055] Step 1. Select the high-precision fiber rotator model 466A-717. The 466A-717 high-precision fiber rotator is an economical fiber rotator designed for low-requirement rotational alignment. Its slotted design enables easy insertion and removal of multi-core optical fibers and overall 360° rotation. It has a high sensitivity of approximately 0.1° and fixes the optical fiber in a 250-micron V-groove with a single clamp arm. The V-block can be repositioned by the user.

[0056] like Figure 2 and Figure 3 As shown in the figure, the structure of the optical fiber rotator fixture is designed using the simulation software SolidWorks. The optical fiber rotator fixture includes a bottom base and a fixing pin, and then the bottom base part and the fixing pin are assembled as shown in the figure. Figure 4 shown.

[0057] Step 2: Use organic glass to process and shape the designed optical fiber rotator fixing device. The lower part is the bottom base part. Choose a 6mm base 1. At the same time, the middle pin 2 is stabilized by the rib structure 3 and the base 1 to ensure that the stabilizing pin remains stable when inserted and the bottom base remains stable. For the insertion column 4 of the stabilizing pin, two different methods can be selected to fix it on the bottom base: the first is to insert the insertion column 4 of the stabilizing pin into the insertion hole 5 of the middle pin 2, and then fix the overlapping part (connection area) of the base 1 and the insertion column 4 with screws and nuts; the second is to open holes in the two side areas of the middle pin 2, and fix them on the left and right sides respectively to ensure the stability of the stabilizing pin and there will be no deviation.

[0058] The upper part is the insertion part, i.e., the stabilizing pin. Later, the 466A-717 fiber rotator is placed on the stabilizing pin, and the above-mentioned pin method is selected for fixing to ensure the stability of the fiber placement.

[0059] Step 3: A long groove 6 is opened along the axis of the upper end surface of the stabilizing pin part, and the sliding connection between the optical fiber rotator and the stabilizing pin is realized through the groove 6. After the optical fiber rotator is fixed on the stabilizing pin, the position can be moved for adjustment. In addition, a rib structure 3 is also selected to reinforce the insertion column 4 of the lower part of the stabilizing pin and the plane where the optical fiber rotator is placed on the upper part. Secondly, holes of a certain depth are also punched on both sides, and a certain length of offset is performed up and down, so that fine adjustment can be performed in a small range. At the same time, the distance of the downward drilling must ensure that the screws can be drilled tightly to ensure the stability of the fixed connection between the upper and lower parts.

[0060] S2. Use the nanopositioning XYZ displacement platform and the fiber rotator to adjust the position of the multi-core optical fiber. The specific steps are as follows:

[0061] S21, placing the multi-core optical fiber initially processed in step S1 on a glass slide, and dripping corresponding matching oil on it, so that the core of the optical fiber can be observed during the observation process, and then covering it with a glass sheet, and fixing the multi-core optical fiber on a nanopositioning XYZ displacement platform;

[0062] First, fix one end of the optical fiber with a fiber clamp, and then straighten the optical fiber and close the fiber clamp at the other end so that the optical fiber can be tightened between the two clamps. During this process, the optical fiber needs to be straightened to improve the efficiency of the subsequent straightening and writing processes.

[0063] S22, using a nanopositioning XYZ displacement platform to straighten the multi-core optical fiber, and adjusting the position of the multi-core optical fiber by adjusting a micrometer so that the horizontal direction of the multi-core optical fiber is completely parallel to the moving Y axis of the nanopositioning XYZ displacement platform;

[0064] S23, using an optical fiber rotator to rotate the multi-core optical fiber so that the multiple cores are on the same plane, so as to facilitate subsequent writing and adjustment of clarity for corresponding comparison;

[0065] S24, adjusting the Z axis of the nanopositioning XYZ displacement platform so that the laser is located at the center of the multi-core optical fiber for writing.

[0066] S3, observe the core distribution of the multi-core optical fiber; in order to be able to adjust to the writing plane more quickly during writing, the present invention uses an end-face microscope to observe the specific distribution of the cores of the multi-core (three-core) optical fiber, such as Figure 5 and Figure 6 It shows that the three observed fiber cores are on the same straight line (note that the fiber cores of other types of three-core optical fibers may appear triangular, and the method provided by the present invention is also applicable), and the distance between the three fiber cores is 31.25 μm, which is evenly distributed.

[0067] At this time, use the μFab software to see Figure 7 The areas shown are three fiber cores at different focal lengths. Then, the multi-core (three-core) fiber is rotated using a fiber rotator to place the three cores in the same plane, which is parallel to the X-axis, to facilitate subsequent writing and adjustment of clarity for corresponding comparison. Figure 8 The area shown is the result of adjusting the three fiber cores to the same plane. At the same time, in order to achieve the best quality and efficiency of engraving, a multi-core optical fiber with a centrally symmetrical structure can achieve a clearer effect. The three-core optical fiber we selected has this feature.

[0068] S4. Using a femtosecond laser to write Bragg gratings in multiple cores of a multi-core optical fiber using a point-by-point method, specifically:

[0069] S41, observing the laser focus position through a CCD camera, and moving the position to the center of the core of the multi-core optical fiber;

[0070] S42. Input the pre-set processing program into the software to control the nanopositioning XYZ displacement platform to write the Bragg grating. The size of the written structure can be controlled by adjusting a series of parameters, such as writing length, writing interval and various laser parameters, such as laser intensity, laser frequency, etc.

[0071] S43. According to the set pulse energy, frequency and moving speed of the nanopositioning XYZ displacement platform, the output energy of the software controlling the femtosecond laser is adjusted to 7%, the Power to 20%, and the AOM Intensity to 8%, wherein the moving speed of the relevant displacement platform is adjusted accordingly according to the central wavelength Bragg grating to be written.

[0072] At the same time, whether the core of the multi-core optical fiber can be accurately positioned determines whether the corresponding fiber grating can be engraved on the corresponding core. Therefore, by adjusting the light spot to the middle of the first core, the preparation of the first FBG is completed. Adjust the nanopositioning XYZ displacement platform, and then repeat the above process to complete the preparation of the three-core FBG. In the writing process of multi-core optical fiber, compared with single-mode optical fiber, the biggest difficulty is the need to adjust and position the core of the multi-core optical fiber. This is because the increase in the number of cores and the irregularity of the geometric structure will lead to a corresponding increase in the difficulty of writing.

[0073] like Fig. 9 The dotted lines in the figure are the transmission spectra of the three fiber cores with different central wavelengths written by the present invention, and the central wavelengths are 1535nm, 1540nm and 1565nm respectively. The experimental results show that the fiber rotator can rotate the multi-core optical fiber at different angles (0° to 360°) to achieve high-quality fiber Bragg grating writing in different situations.

[0074] Therefore, the present invention adopts the above-mentioned novel multi-core fiber multiplexed grating writing method based on femtosecond laser direct writing, which is a highly adjustable and rotatable fiber Bragg grating writing method. The writing device is divided into three parts for combination, namely, a fiber rotator, a bottom base part, and a latch stabilizing part. Among them, the bottom base part and the latch stabilizing part are designed using SolidWorks, and the fiber Bragg grating is written after the multi-core fiber is rotated by the fiber rotator. This method can perform corresponding Bragg grating writing on different cores of the multi-core fiber according to user requirements, thereby improving the accuracy and efficiency of the writing process.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing, It is characterized in that The following steps are involved: S1. Performing initial processing on the multi-core optical fiber to be processed; S2, adjusting the position of the multi-core optical fiber by using the nano-positioning XYZ displacement platform and the optical fiber rotator; S3. Observe the core distribution of the multi-core optical fiber; S4, writing Bragg gratings in multiple cores of a multi-core optical fiber using a femtosecond laser using a point-by-point method; Before step S2, the process also includes building a femtosecond laser writing multi-core optical fiber experimental system. The specific steps are as follows: Step 1: Designing the structure of the optical fiber rotator fixture by using simulation software, wherein the optical fiber rotator fixture includes a bottom base and a fixing pin; Step 2: Processing the designed optical fiber rotator fixture into shape using organic glass; The lower part of the optical fiber rotator fixing device is a bottom base, on which a middle latch is arranged, and the middle latch is stabilized by a rib structure and the bottom base; The upper part of the optical fiber rotator fixing device is an insertion part, i.e., a stabilizing pin. The stabilizing pin includes an insertion column and an upper end surface. The insertion column of the stabilizing pin is inserted into the insertion hole of the middle pin, and then the overlapped part of the base and the insertion column is fixed by the cooperation of screws and nuts. Step 3: A groove is formed on the upper end surface of the fixing pin along the axis, and a sliding connection between the optical fiber rotator and the fixing pin is achieved through the groove.

2. According to claim 1, a novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing, It is characterized in that In step S1, the multi-core optical fiber to be processed is initially processed, which specifically includes the following steps: S11, select a multi-core optical fiber fusion transmission spectrum structure of single mode-multimode-multicore-multimode-single mode; S12, removing the optical fiber coating layer of the multi-core optical fiber at the part to be processed; S13, cutting the end face of the multi-core optical fiber by using an optical fiber cutting knife; S14, using an optical fiber fusion splicer to fusion-splice the multi-core optical fibers in the above step S13, to complete the initial processing of the optical fibers to be processed.

3. According to the novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing as described in claim 1, It is characterized in that The specific steps of adjusting the position of the multi-core optical fiber in step S2 are as follows: S21, fixing the multi-core optical fiber initially processed in step S1 on a nanopositioning XYZ displacement platform; S22, using a nanopositioning XYZ displacement platform to straighten the multi-core optical fiber so that the horizontal direction of the multi-core optical fiber is parallel to the moving Y axis of the nanopositioning XYZ displacement platform; S23, rotating the multi-core optical fiber using an optical fiber rotator so that the multiple fiber cores are in the same plane; S24, adjusting the Z axis of the nanopositioning XYZ displacement platform so that the laser is located at the center of the multi-core optical fiber for writing.

4. According to claim 1, a novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing, Features: In step S3, an end-face microscope is used to observe the core distribution of the multi-core optical fiber, and μFab software is used to display the core distribution result.

5. According to claim 1, a novel multi-core fiber multiplexing grating writing method based on femtosecond laser direct writing, It is characterized in that Step S4 is specifically as follows: S41, observing the laser focus position through a CCD camera, and moving the position to the center of the core of the multi-core optical fiber; S42, inputting a pre-set processing program into the software, and controlling the nanopositioning XYZ displacement platform to write the Bragg grating; S43, adjusting the output energy, power output and laser emission intensity of the software controlling the femtosecond laser according to the set pulse energy, frequency and moving speed of the nanopositioning XYZ displacement platform.

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