Polarization maintaining fiber grating inscribing system and method thereof

Abstract

The invention provides a polarization-maintaining fiber bragg grating inscribing system and a polarization-maintaining fiber bragg grating inscribing method. The system comprises a detection device which is used for detecting the fast axis position and the slow axis position of the end face of the polarization maintaining optical fiber; the optical fiber clamping structure is used for rotating a detection end face according to the fast axis position and the slow axis position; and the grating inscribing device is used for focusing laser on the inscribing area of the rotated polarization maintaining optical fiber so as to form a grating pattern in the fiber core of the inscribing area. According to the polarization-maintaining fiber bragg grating inscribing system and the method thereof, a polarization-maintaining structure can be effectively visualized, it can be guaranteed that the corresponding refractive indexes of laser inscribing and emitting positions are basically consistent, the inscribing consistency of the polarization-maintaining fiber bragg grating is improved, the process is controllable, and large-scale production is easy to form.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber gratings, and in particular to a polarization-maintaining optical fiber grating writing system and method thereof. Background Art

[0002] High-power linearly polarized fiber lasers have broad application prospects in power spectrum synthesis, coherent detection, nonlinear frequency conversion, and gravitational wave measurement. As the core device of high-power linearly polarized fiber lasers, polarization-maintaining fiber gratings have very strict requirements on key indicators such as central wavelength, spectral width, and reflectivity.

[0003] Currently, polarization-maintaining fiber gratings are prepared using conventional non-polarization-maintaining fiber grating writing systems. The process window is very small, and the prepared polarization-maintaining gratings often cannot meet the requirements of high-power linearly polarized fiber lasers.

[0004] There is a big difference in the difficulty of making polarization-maintaining fiber gratings and non-polarization-maintaining fiber gratings, which is mainly affected by their characteristics. The refractive index distribution in non-polarization-maintaining fiber is uniform and the structure is simple. The fiber gratings prepared with it have high writing consistency and are easy to achieve quantitative production. However, the polarization-maintaining fiber has birefringence characteristics and uneven internal refractive index distribution. The fiber grating spectrum written by the non-polarization-maintaining fiber grating writing system is prone to distortion. Furthermore, the spectral distortion leads to a large range of central wavelength, spectral width, and reflectivity, poor repeatability, and a narrow process window, which makes it difficult to mass produce. When applied to linearly polarized fiber lasers, the laser has a low nonlinear threshold and it is difficult to achieve stable high-power output. Figure 2b As shown, when the prior art uses the same parameters to repeatedly write on different polarization-maintaining optical fibers, the wavelength deviation is large, and spectrum distortion is caused, resulting in poor writing repeatability. Summary of the invention

[0005] The present invention provides a polarization-maintaining fiber grating writing system and method. Through a detection device, the internal structure distribution of the polarization-maintaining fiber can be visually seen to determine the fast axis and slow axis positions corresponding to different refractive indices in the polarization-maintaining fiber, solving the problem of uncontrollable refractive index corresponding to the optical path writing position when the fiber is placed, ensuring that the refractive index at the writing position is basically consistent, reducing spectral distortion, and thus solving the problem of large variation ranges of the central wavelength, spectrum width, reflectivity, etc. of the written grating. Through the rotation adjustment structure designed in the writing device, the placement position can be further accurately adjusted to ensure the stable output of the grating writing spectrum.

[0006] In a first aspect, the present invention provides a polarization-maintaining fiber grating writing system, characterized in that the system comprises:

[0007] A detection device, which is used to detect the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber;

[0008] An optical fiber clamping structure, which is used to rotate the detection end face according to the fast axis position and the slow axis position;

[0009] A grating writing device is used for focusing laser light on a writing area of ​​a rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area.

[0010] In a second aspect, the present invention further provides a polarization-maintaining fiber grating writing method, characterized in that a polarization-maintaining fiber grating writing system is provided, including a detection device, a fiber clamping structure and a grating writing device; the method comprises:

[0011] The detection device detects the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber;

[0012] The optical fiber clamping structure rotates the detection end face according to the fast axis position and the slow axis position;

[0013] The grating writing device focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area.

[0014] The polarization-maintaining fiber grating writing system and method provided by the present invention:

[0015] First, the fast and slow axis positions can be accurately detected and adjusted. The fast and slow axis positions of the detection end face can be accurately identified through the microscopic imaging system or the internal stress detection device. The fast axis of the optical fiber is adjusted to be parallel to the laser direction in combination with the optical fiber clamping structure and the optical fiber fixing device to ensure the consistency of the refractive index distribution, reduce the spectral fluctuation range and distortion, improve the consistency of polarization-maintaining grating writing, and the repeated writing wavelength deviation is less than 0.03nm (such as Figure 2a As shown), it meets the high stability requirements and is suitable for mass production.

[0016] Second, efficient and automated adjustment. The system integrates a digital display module, an automated rotary adjustment device, and a tension monitor. It automatically marks the relative positions of the fast axis and the slow axis without visual observation. It achieves synchronous adjustment of the polarization-maintaining fiber through a stepper motor and a rotary encoder, which simplifies manual operation and avoids inconsistent adjustments between the writing area and the detection end face. It monitors the tension of the optical fiber in real time to ensure that the tension state is constant during the writing process, thereby stabilizing the grating parameters and improving the adjustment efficiency and accuracy.

[0017] Third, the coarse and fine adjustments of the optical fiber position are performed by using the optical fiber clamping structure to coarsely adjust the position of the polarization-maintaining optical fiber according to the fast-axis position and slow-axis position obtained by the detection device. Then, the optical fiber fixing device is used to further perform fine adjustments by observing whether the diffraction fringes are symmetrical through the plate to ensure the stable output of the grating writing spectrum. The detection device and the plate are used in combination, and the coarse and fine adjustments are completed in steps, which helps to quickly lock the general direction during the adjustment process and then optimize the details.

[0018] Fourth, the system adaptability is enhanced. The fiber clamping structure cooperates with the slide rail to support the adjustment of fiber pigtails of different lengths. It supports various writing light sources, 248nm and 213nm ultraviolet lasers, and femtosecond lasers. It is compatible with a variety of polarization-maintaining fiber structures (such as panda eyes, bow ties, ovals, etc.) and a variety of writing modes (such as point-by-point scanning and one-time exposure) to meet the grating writing needs of different types of polarization-maintaining fibers.

[0019] Fifth, high-precision repeatable grating engraving. By integrating an automated adjustment device, precise process parameter settings and a stable mechanical structure, the present invention realizes a high-precision and high-consistency grating writing process. The process parameters such as writing power, writing time and writing length can be quickly fixed according to the required grating parameters, and repetitive writing can be performed subsequently. Repetitive writing does not require readjustment of complex parameters, and the operation is simple, the efficiency is high, and it is easy to use in batches. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative labor.

[0021] Figure 1 Schematic diagram of a polarization-maintaining fiber Bragg grating writing system provided by an embodiment of the present invention;

[0022] Figure 2a is a wavelength curve diagram for maintaining consistency in repeated engraving provided by an embodiment of the present invention;

[0023] Figure 2b It is a wavelength curve diagram of spectral distortion caused by repeated writing in the prior art;

[0024] Figure 3 This is a schematic diagram of an embodiment of the present invention in which the fast axis direction is parallel to the laser direction;

[0025] Figure 4 It is a flow chart of a polarization-maintaining fiber grating writing method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. SUMMARY OF THE INVENTION

[0028] As mentioned above, the present invention provides a polarization-maintaining fiber grating writing system and method thereof, which solves the light source problems such as poor consistency and severe distortion in the preparation of traditional polarization-maintaining fiber gratings through precise fiber fast and slow axis identification, fiber position adjustment and multi-capacity writing system, and realizes efficient, high-precision and controllable production of polarization-maintaining fiber gratings, which has significant creativity and application value.

[0029] Exemplary Devices

[0030] Figure 1 Schematic diagram of a polarization-maintaining fiber Bragg grating writing system provided by an embodiment of the present invention. Figure 1 As shown, the system 100 provided in this embodiment includes: a detection device 1, a fiber clamping structure 2, a slide rail 3, a fiber support frame 4, a grating writing device 5 and a reference platform 6.

[0031] Specifically, the detection device 1 is used to detect the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber.

[0032] The polarization-maintaining structure of the polarization-maintaining optical fiber 7 includes but is not limited to a panda eye structure (such as Figure 3 As shown), a bow-tie structure, an elliptical structure, a tiger-eye structure, a side hole structure and / or a photonic crystal fiber structure.

[0033] like Figure 1 As shown, the detection device 1 is a first microscopic imaging system, which is used to detect the fast axis position and the slow axis position of the detection end surface through microscopic imaging.

[0034] The first microscopic imaging system further comprises a microscope, a one-dimensional adjustment frame, a plane reflector and a support structure, wherein the microscope is arranged on the one-dimensional adjustment frame, and the one-dimensional adjustment frame is arranged on the support structure;

[0035] The support structure is used to support the one-dimensional adjustment frame and the microscope;

[0036] The one-dimensional adjustment frame is used to adjust the focus position of the microscope along the light path direction;

[0037] The plane reflector is used to reflect the detection end surface image into the microscope;

[0038] The microscope is used to magnify the end surface image at a high magnification and display it clearly.

[0039] The fast axis and slow axis of the polarization-maintaining optical fiber 7 are related to the position of the stress rod. The stress rod is a high-stress material embedded in the optical fiber cladding, and its main function is to form polarization-maintaining performance by introducing birefringence. The stress rod is usually located on both sides of the optical fiber cross section and is symmetrically distributed with the optical fiber core. The connection direction of the two stress rods is defined as the slow axis direction of the optical fiber.

[0040] like Figure 3 The panda eye structure shown in the figure, if the cross section of the optical fiber is regarded as a "panda face", the fiber core is the "nose" at the center, the stress rods are the "eyes" distributed symmetrically on the left and right, the fast axis direction is perpendicular to the line connecting the two "eyes", and the slow axis direction is along the line connecting the two "eyes".

[0041] In addition to using microscopic imaging technology, the detection device 1 can also obtain the fast axis position and slow axis position of the detection end face by detecting the internal stress distribution of the detection end face. Specifically, the detection device 1 can use a Raman distribution optical fiber stress analyzer.

[0042] Among them, the Raman distribution fiber stress analyzer detects changes in the Raman scattering effect of the internal material of the optical fiber under stress. The Raman scattering effect is that when light passes through the optical fiber, some photons are inelastically scattered (Raman scattering) by the molecular vibrations in the optical fiber material, generating light of different wavelengths. In the polarization-maintaining optical fiber 7, due to the different mechanical stresses in the fast axis and slow axis directions, the characteristics of the Raman scattering spectrum, such as Raman frequency shift, intensity ratio, etc., will change. By scanning different positions of the optical fiber and recording the changes in the Raman scattered light signal, the stress distribution of the optical fiber can be calculated.

[0043] Specifically, monochromatic light (usually laser) is injected into one end of the polarization-maintaining optical fiber 7, and then the scattered light signal is collected along the length direction of the optical fiber using a Raman distribution optical fiber stress analyzer, and the intensity and frequency shift of the scattered light signal are analyzed to draw a stress distribution diagram of the optical fiber. The stress in the fast axis direction is small and the refractive index is low. The stress in the slow axis direction is large and the refractive index is high. According to the stress change trend in the stress distribution diagram, the fast and slow axis directions of the optical fiber are determined.

[0044] The advantage of using Raman distribution fiber stress analyzer is that it can measure the stress distribution of the optical fiber in a non-contact manner with high accuracy. It can provide detailed stress distribution diagrams of the fast and slow axes and is suitable for global detection.

[0045] The detection device 1 also includes a digital display module, which is used to accurately measure and automatically mark the laser direction and the relative position of the fast axis and the slow axis. For example, the fiber end face structure is magnified and projected onto a digital screen through a high-definition imaging module, and auxiliary graphics or color markings are used to guide the user to quickly locate the fast and slow axis positions.

[0046] The digital display module can eliminate the human judgment error of traditional visual observation, especially when the fast and slow axis angles are matched, it can position more accurately.

[0047] In addition, the digital display module can also be connected to the optical fiber clamping structure 2 to directly provide the adjustment parameters of the optical fiber clamping structure 2. All adjustment parameters are digitally recorded to facilitate the reproduction and verification of subsequent processes. The digital information can also be output through the network interface to facilitate remote monitoring of the system or integration into a larger automation system.

[0048] The system 100 may further include an optical compensation device, which is used to input arbitrary light, preferably polarized light, from the non-detection end face of the polarization-maintaining optical fiber 7 when performing end face detection, so as to enhance the image contrast and clarity of the end face detection process, optimize the imaging effect of the detection device 1, and ensure more accurate acquisition of the fast axis and slow axis positions of the detection end face.

[0049] The optical fiber clamping structure 2 is used to rotate the detection end face according to the fast axis position and the slow axis position, and clamp the polarization-maintaining optical fiber 7 close to the detection end face.

[0050] The optical fiber clamping structure 2 comprises:

[0051] The rotation module is used to rotate the coarse adjustment of the detection end face so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain the coarse adjustment position. Since the stress in the slow axis is greater and more uneven than that in the fast axis, the laser is easier to control and has better consistency when writing from the fast axis direction than when writing from the slow axis direction. Therefore, the laser is preferably incident on the writing area from the fast axis direction for writing.

[0052] A locking module is used to lock the detection end surface at the coarse adjustment position.

[0053] The bottom adjustment frame is used to adjust the detection end surface to the position of the plane reflector.

[0054] Preferably, the bottom adjustment frame is a three-dimensional adjustment frame, which is used to adjust the detection end surface in three directions: X, Y, and Z.

[0055] The system 100 further includes: an optical fiber support frame 4, which is used to support the optical fiber area between the detection end face position and the writing area, to ensure that the entire pigtail is in a horizontal straight state, and to prevent the direction of the optical fiber from being affected by external forces. By supporting the optical fiber, the rotation force of the detection end face is transmitted to the writing area to the greatest extent, ensuring that the angle difference between the writing area and the detection end face is minimized.

[0056] Optical fiber is flexible and will deform to a certain extent due to its own elasticity when rotating. If the rotational force (torque) cannot be evenly distributed over the entire length of the fiber, the rotation angles of the front and rear sections of the fiber will not be completely consistent. When the fiber is long, the rotational force will be attenuated when it is transmitted from the detection end face to the end, especially when the middle part of the fiber is not fixed. The unfixed part will have elastic deformation or hysteresis, resulting in deviations in the actual rotation angle. If the force on the fiber is uneven, some areas may accumulate stress, resulting in bending or other deformations, which will affect the performance of the fiber and the stability of the polarization state.

[0057] Therefore, the optical fiber support frame 4 ensures that the optical fiber is in a straight line between the detection end face position and the writing area, reducing the angle error caused by local bending.

[0058] The length of the optical fiber support frame 4 is 10 to 50 centimeters.

[0059] The system 100 also includes a slide rail 3, which is installed in a direction of sliding along the axial direction of the optical fiber. The optical fiber clamping structure 2 and the detection device 1 are both installed on the slide rail 3, and the slide rail 3 is used to roughly adjust the positions of the optical fiber clamping structure 2 and the detection device 1 within a certain distance range along the axial direction of the optical fiber. After the rough adjustment, the three-dimensional adjustment frame of the optical fiber clamping structure 2 and the one-dimensional adjustment frame of the first microscopic imaging system are used to perform fine adjustment to focus on the detection end face. The use of the slide rail 3 allows the pigtails of optical fibers of different lengths to be adjusted to a suitable position.

[0060] The adjustment range of the slide rail 3 is 20 to 50 centimeters.

[0061] The grating writing device 5 is used to focus the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area.

[0062] Specifically, the grating writing device 5 further includes:

[0063] The laser 8 is used to output the laser, the laser includes ultraviolet laser and femtosecond laser, and the wavelength of the ultraviolet laser includes 248nm and 213nm.

[0064] A reflecting device 9, which is used to reflect the laser to the writing area;

[0065] The bottom of the reflection device 9 also includes a moving platform, which is used to select different writing modes. The writing modes include point-by-point scanning writing and / or one-time exposure writing at a specific position.

[0066] A laser focusing device 10, which is used to focus the laser on the writing area to form a grating pattern in the core of the writing area;

[0067] The signboard 11 is used to display the diffraction stripes formed on the signboard 11 by the laser light output by the laser 8 passing through the mask and the writing area.

[0068] The signboard 11 is a CCD and / or CMOS. The laser power should be moderate to avoid overexposure of the CCD and / or CMOS due to excessive light, or unclear stripes due to too weak light. The photosensitive elements of CCD and CMOS sensors are based on silicon, which inherently have a certain response to near-ultraviolet light (200-400nm), but the efficiency is low. Most commercial sensors have anti-reflective coatings or passivation layers on their surfaces. These coatings are usually optimized for the visible light range (400-700nm) and absorb ultraviolet light. In order to increase the sensitivity of CCD or CMOS to ultraviolet light output by the laser, the passivation layer on the surface of the CCD or CMOS sensor can be removed or replaced with an ultraviolet transparent material.

[0069] The grating writing device 5 further comprises: a second microscopic imaging system 12, a mask fixing device 13 and a mask.

[0070] The second microscopic imaging system 12 is used to detect the distance between the writing area and the mask.

[0071] The mask plate fixing device 13 is used to adjust and fix the position of the mask plate, has a lifting function, and adjusts the distance between the writing area and the mask plate. The smaller the distance, the lower the laser energy required for writing. Specifically, the distance between the writing area and the mask plate is 50 to 200 microns.

[0072] The mask is used to separate the laser into ±1st order diffraction lights, and form a grating pattern in the fiber core of the writing area through the interference of the ±1st order diffraction lights, wherein the grating pattern is a periodic refractive index modulation structure.

[0073] Specifically, the mask is usually a transparent glass sheet, including a transparent area and a ruled area. When the light beam passes through the ruled area, diffraction occurs, while the transparent area ensures direct passage of the laser. The ruled area usually has periodic ruled lines with a depth of micrometers or nanometers. These ruled lines are designed according to the period of the required fiber grating (the Bragg wavelength of the optical fiber) and are made by laser direct writing, electron beam etching or photolithography technology. Extremely high processing accuracy is required to meet the coherent interference requirements of the fiber grating. The period of the ruled lines determines the central wavelength of the fiber grating, and the ruled line spacing directly determines the spectral characteristics of the fiber grating. The mask also includes a transparent substrate, which is usually made of quartz glass or other transparent materials. The transparency of the substrate ensures that when the laser passes through the mask, the diffraction effect will not be absorbed or interfered by the material. Some high-precision mask templates will have an anti-reflection coating applied to the surface to reduce laser reflection loss and ensure higher transmission efficiency. The size of the ruled area of ​​the mask is determined by the size of the fiber writing area, which is usually in the millimeter level (such as 5mm×10mm).

[0074] When the laser is incident on the mask, the lines on the mask split the laser into multiple diffracted lights, among which the ±1st order diffracted lights are the key beams for forming the fiber grating. The ±1st order diffracted lights interfere in the fiber writing area to form periodic interference fringes. These interference fringes cause the refractive index in the fiber core to change periodically, thus forming a grating. By changing the mask's line period, the laser wavelength, or the refractive index modulation depth of the fiber, the central wavelength and reflection bandwidth of the grating can be adjusted. Common mask types include: fixed period masks, sampling masks, and phase masks.

[0075] The writing process using the mask plate can be to adjust the relative position of the optical fiber and the mask plate to ensure that the optical fiber core in the writing area is aligned with the marking lines of the mask plate; adjust the laser intensity and focal length to ensure that the laser is focused on the writing area behind the mask plate; the laser forms interference fringes through the mask plate and writes a grating pattern inside the optical fiber; the grating writing device 5 can also include a spectral detection device to monitor the central wavelength and reflection characteristics of the grating in real time through the spectral detection device.

[0076] It should be noted that not all grating writing systems require masks, such as systems that use femtosecond lasers to directly write optical fibers. Femtosecond lasers have extremely short pulse widths and can directly produce nonlinear effects in optical fiber materials, forming high-precision refractive index modulation. Femtosecond laser systems rely on high-resolution focusing and can directly write the required grating structure inside the optical fiber without the need for mask splitting.

[0077] The optical fiber fixing device 14 is used to apply tension to the writing area to fix the optical fiber so that the writing area is suspended.

[0078] The optical fiber fixing device 14 also includes a tension monitor, which is used to monitor the tension of the writing area to prevent grating distortion caused by tension changes.

[0079] When the rotating module rotates to roughly adjust the detection end face, the optical fiber fixing device 14 does not fix the polarization-maintaining optical fiber 7 and keeps the optical fiber area between the rotating module and the writing area in a straight state, and the optical fiber can be freely rotated and adjusted without being restricted by fixation.

[0080] After the rotating module completes the coarse rotation adjustment, the optical fiber fixing device 14 fixes the polarization-maintaining optical fiber 7 for fine adjustment to ensure the position of laser incidence. When the rotating module completes the coarse adjustment and the angle and position of the optical fiber end face are roughly adjusted, the optical fiber fixing device will lock the position of the optical fiber, thereby ensuring that the optical fiber does not move during the fine adjustment process.

[0081] The optical fiber fixing device 14 also includes an X / Y / Z three-dimensional regulator, which is used to adjust the position of the writing area so that it is on the scanning path of the laser, ensure that the writing area is parallel to the mask, and can also adjust the distance between the two.

[0082] The optical fiber fixing device 14 also includes a rotating shaft, which is used to fine-tune the position of the writing area according to whether the diffraction stripes displayed on the billboard are symmetrically rotated along the optical fiber axis so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction.

[0083] When the fast axis is parallel to the laser direction, the diffraction fringes are symmetrical. If the fringes are asymmetrical, it means that the fast axis and slow axis of the optical fiber are not correctly aligned, and the rotation angle of the optical fiber needs to be further adjusted using the rotation axis so that the fast axis of the optical fiber gradually aligns with the laser. The tension of the optical fiber needs to be kept stable during rotation adjustment to avoid affecting the formation of diffraction fringes. During the fine-tuning process, the symmetry of the diffraction fringes serves as real-time feedback to help the adjuster complete the final adjustment more quickly and accurately.

[0084] Performing rough adjustment first and then fine adjustment can ensure that the alignment of the optical fiber axis and the laser direction has been roughly completed when fine adjustment is performed, avoiding wasting time and energy due to inadequate initial adjustment during the fine adjustment process.

[0085] The goal of the coarse adjustment stage is to roughly align the fiber with the grating writing area and the incident direction of the laser beam. In this stage, the fiber end face is quickly positioned by rotating the module so that the fast axis of the fiber is roughly aligned with the laser direction. Coarse adjustment can be accomplished through intuitive adjustments and fast feedback (such as microscopic imaging).

[0086] The goal of the fine-tuning stage is to further optimize the alignment between the fiber and the laser beam, ensuring that the fast axis is completely parallel to the laser beam direction and the slow axis is perpendicular to the laser beam. At this point, the rotation angle of the fiber needs to be precisely adjusted and the diffraction fringes will be more symmetrical.

[0087] If you skip the coarse adjustment and go directly to the fine adjustment, the axial direction of the optical fiber and the direction of the laser beam will be quite different at the beginning of the fine adjustment, and it will be difficult to find the right angle accurately during the fine adjustment, because the subtle adjustment will be limited by the large initial deviation. Fine adjustment depends on the careful observation of the diffraction fringes. If the coarse adjustment is not performed, the diffraction fringes will be very asymmetric, and there will be no feedback on the adjustment direction provided by the coarse adjustment. With direct fine adjustment, the symmetry of the diffraction fringes cannot provide a clear adjustment direction, especially when the fast axis of the optical fiber and the direction of the laser beam are very different, which will lead to uncertainty in the adjustment process, increase the complexity of the operation and the debugging time.

[0088] In short, the combined use of the detection device and the signboard makes the coarse and fine adjustment processes more intuitive and efficient. Coarse and fine adjustments are completed in steps, which helps to quickly lock the general direction during the adjustment process and then optimize the details. The diffraction stripes of the signboard serve as real-time feedback and provide a visual reference for adjustments. Through coarse adjustment, the optical fiber can be quickly adjusted to a near-ideal initial position, thereby reducing the time and adjustment range required for fine adjustment. After the coarse adjustment is completed, the fine adjustment can be concentrated in a smaller adjustment range, quickly locking the target position, ensuring the writing accuracy, avoiding complex adjustments caused by the optical fiber position being too far away, and ensuring that the adjustment process is more intuitive and efficient.

[0089] In addition to the above-mentioned coarse and fine adjustments completed in steps, if the adjustments of the writing area and the detection end face are inconsistent, the deviation can also be compensated by increasing the rotation angle of the detection end face, that is, the detection end face is over-deflected so that the laser incident direction of the writing area is parallel to the fast axis position, avoiding deviation or unevenness of the grating pattern during the writing process.

[0090] In addition, the problem of inconsistent adjustment between the writing area and the detection end face can be solved by synchronously rotating the optical fiber clamping structure 2 and the optical fiber fixing device 14.

[0091] The system 100 may further include an automated rotation adjustment device for synchronously rotating the fiber clamping structure 2 and the fiber fixing device 14 according to the fast axis position and the slow axis position obtained by the detection device 1 .

[0092] The automated rotation adjustment device includes a stepper motor and a rotary encoder. The stepper motor controls the execution of the rotation action, can achieve rotation adjustment of a small angle with extremely high resolution, and can provide stable and repeatable operation to ensure that the adjustment is in place every time. The rotary encoder monitors the rotation angle in real time, feedbacks the current adjustment status, ensures accurate adjustment, and can also provide angle data to support automated control to avoid excessive rotation or error accumulation. The optical fiber clamping structure 2 rotates synchronously with the optical fiber fixing device 14 to ensure that the rotation angle of the detection end face and the writing area are consistent, and the optical properties are consistent.

[0093] In summary, the automated rotation adjustment device provides a high-precision and high-efficiency rotation adjustment function through the combined action of the stepper motor and the rotary encoder, ensuring the precise alignment of the fast and slow axes of the polarization-maintaining optical fiber 7 and the consistency of the grating writing.

[0094] The reference platform 6 is used to place other devices in the system 100 on the same plane, and the material includes but is not limited to aluminum, stainless steel, marble, etc.

[0095] Exemplary Methods

[0096] Accordingly, the embodiment of the present invention also provides a polarization-maintaining fiber Bragg grating writing method. A polarization-maintaining fiber Bragg grating writing system 100 is provided, comprising: a detection device 1, a fiber clamping structure 2, and a grating writing device 5; Figure 4 : is a flow chart of a polarization-maintaining fiber grating writing method provided by an embodiment of the present invention, and the embodiment comprises the following steps:

[0097] S401: The detection device 1 detects the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber;

[0098] S402: The optical fiber clamping structure 2 rotates the detection end face according to the fast axis position and the slow axis position;

[0099] S403: The grating writing device 5 focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area.

[0100] The detection device 1 is a first microscopic imaging system;

[0101] The steps of the detection device 1 detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically as follows: the first microscopic imaging system detects the fast axis position and the slow axis position of the detection end face through microscopic imaging.

[0102] The first microscopic imaging system further comprises a microscope, a one-dimensional adjustment frame, a plane reflector and a support structure, wherein the microscope is arranged on the one-dimensional adjustment frame, and the one-dimensional adjustment frame is arranged on the support structure;

[0103] The steps of the first microscopic imaging system detecting the fast axis position and the slow axis position of the detection end surface by microscopic imaging are specifically as follows:

[0104] The support structure supports the one-dimensional adjustment frame and the microscope;

[0105] The one-dimensional adjustment frame adjusts the focus position of the microscope along the optical path direction;

[0106] The plane reflector reflects the detection end surface image into the microscope;

[0107] The microscope magnifies the end surface image and displays it.

[0108] The steps of the detection device 1 detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically as follows:

[0109] The detection device 1 obtains the fast axis position and the slow axis position of the detection end surface by detecting the internal stress distribution of the detection end surface.

[0110] The detection device 1 includes a Raman distribution optical fiber stress analyzer.

[0111] The system 100 also includes a light compensation device;

[0112] The method also includes the optical compensation device inputting light from the non-detection end face of the polarization-maintaining optical fiber 7 .

[0113] The optical fiber clamping structure 2 comprises: a rotating module and a locking module;

[0114] The steps of rotating the optical fiber clamping structure 2 according to the fast axis position and the slow axis position to detect the end face are specifically as follows:

[0115] The rotating module rotates and roughly adjusts the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a rough adjustment position;

[0116] The locking module locks the detection end surface at the coarse adjustment position.

[0117] The optical fiber clamping structure 2 comprises: a bottom adjustment frame; the method further comprises the bottom adjustment frame adjusting the detection end surface to the position of the plane reflector.

[0118] The bottom adjustment frame is a three-dimensional adjustment frame;

[0119] The steps of adjusting the detection end surface to the position of the plane reflector by the bottom adjustment frame are specifically as follows:

[0120] The bottom adjustment frame adjusts the detection end surface in three directions: X, Y and Z.

[0121] The grating writing device 5 also includes: a laser 8, a reflecting device 9, a laser focusing device 10 and an optical fiber fixing device 14;

[0122] The grating writing device 5 focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area. Specifically, the steps are as follows:

[0123] The laser 8 outputs the laser;

[0124] The reflecting device 9 reflects the laser to the writing area;

[0125] The laser focusing device 10 focuses the laser on the writing area to form a grating pattern in the fiber core of the writing area;

[0126] The optical fiber fixing device 14 applies tension to the writing area.

[0127] The grating writing device 5 also includes a viewing plate 11;

[0128] The step of the grating writing device 5 focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area also includes:

[0129] The signboard 11 displays diffraction fringes formed when the laser light output by the laser 8 passes through the mask and the writing area and shines on the signboard 11 .

[0130] The display panel 11 is a CCD and / or a CMOS.

[0131] The grating writing device 5 further includes: a mask, a mask fixing device 13 and a second microscopic imaging system 12;

[0132] The step of the grating writing device 5 focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area also includes:

[0133] The second microscopic imaging system 12 detects the distance between the writing area and the mask;

[0134] The mask plate fixing device 13 adjusts and fixes the position of the mask plate;

[0135] The mask separates the laser into ±1st order diffraction lights, so as to form a grating pattern in the fiber core of the writing area, wherein the grating pattern is a periodic refractive index modulation structure.

[0136] The distance between the writing area and the mask plate is 50 to 200 microns.

[0137] The optical fiber fixing device 14 also includes an X / Y / Z three-dimensional adjuster;

[0138] The step of the grating writing device 5 focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area also includes:

[0139] The X / Y / Z three-dimensional regulator adjusts the position of the writing area so that it is on the scanning path of the laser.

[0140] The optical fiber fixing device 14 also includes a rotating shaft;

[0141] The step of the grating writing device 5 focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area also includes:

[0142] The rotation axis is rotated symmetrically along the optical fiber axis to fine-tune the position of the writing area so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction according to whether the diffraction stripes displayed on the billboard 11 are symmetrical.

[0143] The reflecting device 9 also includes a moving platform;

[0144] The step of the grating writing device 5 focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber 7 to form a grating pattern in the core of the writing area also includes:

[0145] The mobile platform selects different writing modes.

[0146] The writing mode includes point-by-point scanning writing and / or one-time exposure writing at a specific position.

[0147] The optical fiber fixing device 14 also includes a tension monitor;

[0148] The optical fiber fixing device 14 applies tension to the writing area further comprising:

[0149] The tension monitor monitors the tension of the writing area.

[0150] The detection device 1 also includes a digital display module;

[0151] The steps of the detection device 1 detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically as follows:

[0152] The digital display module is used to automatically mark the laser direction and the relative position of the fast axis and the slow axis.

[0153] The system 100 also includes an automated rotation adjustment device;

[0154] The method further comprises the automated rotation adjustment device synchronously rotating the optical fiber clamping structure 2 and the optical fiber fixing device 14 according to the fast axis position and the slow axis position obtained by the detection device 1 .

[0155] The automatic rotation adjustment device comprises a stepping motor and a rotary encoder.

[0156] The system 100 further includes: an optical fiber support frame 4;

[0157] The method also includes the optical fiber support frame 4 supporting the optical fiber area between the detection end surface position and the writing area.

[0158] The length of the optical fiber support frame 4 is 10 to 50 centimeters.

[0159] The system 100 further includes a slide rail 3, on which the optical fiber clamping structure 2 and the detection device 1 are both mounted;

[0160] The method further comprises the slide rail 3 adjusting the positions of the optical fiber clamping structure 2 and the detection device 1 along the axial direction of the optical fiber, and the adjustment range of the slide rail 3 is 20 to 50 centimeters.

[0161] The system 100 further includes a reference platform 6;

[0162] The method further includes placing other devices in the system 100 on the same plane using the reference platform 6 .

[0163] The polarization-maintaining structure of the polarization-maintaining optical fiber 7 includes a panda eye structure, a bow tie structure, an elliptical structure, a tiger eye structure, a side hole structure and / or a photonic crystal optical fiber structure.

[0164] The laser includes ultraviolet laser and femtosecond laser;

[0165] The ultraviolet laser wavelengths include 248nm and 213nm.

[0166] The rotating module rotates and roughly adjusts the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a rough adjustment position, and the locking module locks the detection end surface at the rough adjustment position in the specific steps of:

[0167] When the rotating module rotates to roughly adjust the detection end face, the optical fiber fixing device 14 does not fix the polarization-maintaining optical fiber 7 and keeps the optical fiber area between the rotating module and the writing area in a straight state;

[0168] After the rotating module completes the rough rotation adjustment, the optical fiber fixing device 14 fixes the polarization-maintaining optical fiber 7 for fine adjustment.

[0169] Specifically, the coating layer of the polarization-maintaining optical fiber 7 to be written is stripped off (the stripping length is determined according to the required grating length and the mask length), and the surface of the exposed writing area is cleaned; the writing area is aligned with and close to the mask grating area, and the optical fiber is fixed by the optical fiber fixing device 14; the optical fiber detection end face is processed with a suitable tool, usually cut with a cutting machine or a gem knife, to obtain a basically flat optical fiber end face, and then the detection end face is fixed to the optical fiber clamping structure 2 to expose the detection end face, the position of the slide rail 3 is adjusted, the position of the optical fiber clamping structure 2 is changed to straighten the optical fiber, the three-dimensional adjustment frame of the optical fiber clamping structure 2 and the one-dimensional adjustment frame of the first microscopic imaging system are adjusted, so that the optical fiber cross-sectional image is displayed on the screen; the optical fiber clamping structure 2 is rotated so that the fast axis of the polarization-maintaining optical fiber 7 is parallel to the direction of the ultraviolet writing laser, and the slow axis is perpendicular to the laser direction, and then the locking module is used to lock the position; the optical fiber fixing device 14 in the writing area is loosened to release the rotational torque, so that the polarization-maintaining optical fiber 7 is re-fixed on the optical fiber fixing structure 2 in a stress-free state. The laser 8 outputs a low-power laser, which passes through the mask and the writing area to form diffraction stripes on the billboard 11. By observing whether the diffraction stripes are symmetrical, it is judged whether the placement of the polarization-maintaining optical fiber 7 is normal; if not, the rotating structure of the optical fiber fixing device 14 is adjusted to further rotate and fine-tune the polarization-maintaining optical fiber 7; after determining that the fast axis position is parallel to the laser direction, the X / Y / Z three-dimensional adjuster of the optical fiber fixing device 14 is adjusted, and the spacing between the writing area and the mask is observed by the second microscopic imaging system 12. The mask fixing device 13 and the X / Y / Z three-dimensional adjuster are used to adjust the spacing, and then the X / Y / Z three-dimensional adjuster is continued to be adjusted to make the optical fiber parallel to the mask, and a certain tension is applied to the writing area by the optical fiber fixing device 14; the laser 8 is turned on to expose the writing area to form a grating pattern on the optical fiber core. The exposure method can be scanning and writing point by point by moving the moving platform of the reflecting device 9, or the fixed moving platform can realize writing by one exposure. The grating writing device 5 is usually equipped with a spectrum detection device, which monitors the central wavelength and reflection characteristics of the grating in real time, and monitors the writing process and results.

[0170] As an optional embodiment, the system 100 is used to write the 10-130 fiber Bragg grating of the panda eye polarization-maintaining structure, and a 213nm ultraviolet light source is used for point-by-point scanning writing. The length of the polarization-maintaining fiber is 1.2m, the length of the single-side pigtail is 0.6m, and the range of the slide rail 3 is 20cm.

[0171] Here are the steps:

[0172] First, after the polarization-maintaining 10-130 optical fiber is photosensitized under certain conditions, a 1.2-meter-long section of optical fiber is taken, the coating is stripped off 4 to 10 cm in the middle, and the bare fiber is properly cleaned;

[0173] Second, the fiber end face is cut with a cutting machine and fixed to the fiber clamping structure 2, with the end face exposed for 5 to 10 mm, and the focal plane position of the first microscopic imaging system is adjusted so that the fiber cross section is displayed on the screen;

[0174] Third, rotate the fiber clamping structure 2 so that the line connecting the two "eyes" is perpendicular to the laser direction, that is, the fast axis is parallel to the direction of the ultraviolet beam, and the slow axis is perpendicular to the direction of the laser, and use the locking module to lock this position;

[0175] Fourth, keep the current state of the optical fiber, place the optical fiber pigtail on the optical fiber support frame 4, keep it loose and without external force, align and fix the writing area near the mask plate, still keep the fast and slow axis direction, fix the optical fiber to the optical fiber fixing device 14, use the mask plate fixing device 13 and the X / Y / Z three-dimensional adjuster to adjust the spacing, and then continue to adjust the X / Y / Z three-dimensional adjuster to make the optical fiber parallel to the mask plate;

[0176] Fifth, turn on the ultraviolet laser, move the moving platform of the reflecting device, and write point by point on the optical fiber core to obtain a grating of a certain period.

[0177] The experimental results show that when the same parameters are repeatedly written on different polarization-maintaining optical fibers, the wavelength deviation is less than 0.03nm (e.g. Figure 2a ), indicating that the writing system has high repeatability.

[0178] As another optional embodiment, the laser light source adopts a writing system with a 248nm light source, and the rest remains unchanged, and the polarization-maintaining 10-130 optical fiber of the panda eye structure is written. By adjusting the position of the polarization-maintaining optical fiber so that the fast axis is parallel to the direction of the light source, the grating is written through a single exposure. The experimental results show that when the same parameters are used for repeated writing of different polarization-maintaining optical fibers, the wavelength deviation is less than 0.04nm, indicating that the writing system has high repeatability.

[0179] It should be noted that although several devices, units, or modules of the polarization-maintaining fiber grating writing system are mentioned in the above detailed description, this division is only exemplary and not mandatory. In fact, according to an embodiment of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided into multiple modules to be embodied.

[0180] In addition, although the operations of the polarization-maintaining fiber grating writing method of the present invention are described in a specific order in the accompanying drawings, this does not require or imply that these operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps can be omitted, multiple steps can be combined into one step, and / or one step can be decomposed into multiple steps.

[0181] Although the spirit and principle 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 disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims.

[0182] The present invention provides: 1. A polarization-maintaining fiber grating writing system, characterized in that the system comprises: A detection device, which is used to detect the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber; An optical fiber clamping structure, which is used to rotate the detection end face according to the fast axis position and the slow axis position; A grating writing device is used for focusing laser light on a writing area of ​​a rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area. 2. The system according to item 1 is characterized in that the detection device is a first microscopic imaging system, which is used to detect the fast axis position and the slow axis position of the detection end surface through microscopic imaging. 3. The system according to item 2 is characterized in that the first microscopic imaging system further comprises a microscope, a one-dimensional adjustment frame, a plane reflector and a support structure, the microscope is arranged on the one-dimensional adjustment frame, and the one-dimensional adjustment frame is arranged on the support structure; wherein The support structure is used to support the one-dimensional adjustment frame and the microscope; The one-dimensional adjustment frame is used to adjust the focus position of the microscope along the light path direction; The plane reflector is used to reflect the detection end surface image into the microscope; The microscope is used to magnify the end surface image and display it. 4. The system according to item 1 is characterized in that the detection device is used to obtain the fast axis position and the slow axis position of the detection end face by detecting the internal stress distribution of the detection end face. 5. The system according to item 4 is characterized in that the detection device includes a Raman distributed optical fiber stress analyzer. 6. The system according to any one of items 1 to 5 is characterized in that the system also includes an optical compensation device, which is used to input light from the non-detection end face of the polarization-maintaining optical fiber. 7. The system according to any one of items 1 to 5, wherein the optical fiber clamping structure comprises: A rotation module, which is used to rotate and roughly adjust the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a rough adjustment position; A locking module is used to lock the detection end surface at the coarse adjustment position. 8. The system according to item 7 is characterized in that the optical fiber clamping structure includes: a bottom adjustment frame, which is used to adjust the detection end face to the position of the plane reflector. 9. The system according to item 8 is characterized in that the bottom adjustment frame is a three-dimensional adjustment frame, which is used to adjust the detection end surface in three directions: X, Y, and Z. 10. According to the system of item 7, the grating writing device further comprises: A laser, which is used to output the laser light; A reflecting device, used for reflecting the laser to the writing area; A laser focusing device, which is used to focus the laser on the writing area to form a grating pattern in the core of the writing area; An optical fiber fixing device is used to apply tension to the writing area. 11. The system according to item 10 is characterized in that the grating writing device also includes a signboard for displaying diffraction stripes formed on the signboard when the laser output by the laser passes through the mask and the writing area. 12. The system according to item 11 is characterized in that the display panel is CCD and / or CMOS. 13. The system according to item 10, characterized in that the grating writing device further comprises: a mask, a mask fixing device and a second microscopic imaging system; The second microscopic imaging system is used to detect the distance between the writing area and the mask; The mask plate fixing device is used to adjust and fix the position of the mask plate; The mask is used to separate the laser into ±1st order diffraction lights, so as to form a grating pattern in the fiber core of the writing area, and the grating pattern is a periodic refractive index modulation structure. 14. The system according to item 13 is characterized in that the distance between the writing area and the mask is 50 to 200 microns. 15. The system according to item 10 is characterized in that the optical fiber fixing device also includes an X / Y / Z three-dimensional regulator, which is used to adjust the position of the writing area so that it is on the scanning path of the laser. 16. The system according to item 11 is characterized in that the optical fiber fixing device also includes a rotating axis, which is used to fine-tune the position of the writing area according to whether the diffraction stripes displayed on the billboard are symmetrically rotated along the optical fiber axis so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction. 17. The system according to item 10 is characterized in that the reflection device also includes a movable platform for selecting different writing modes. 18. The system according to item 17 is characterized in that the writing mode includes point-by-point scanning writing and / or one-time exposure writing at a specific position. 19. The system according to item 10 is characterized in that the optical fiber fixing device also includes a tension monitor, which is used to monitor the tension of the writing area. 20. According to the system of any one of items 1 to 5, the detection device also includes a digital display module, which is used to automatically mark the laser direction and the relative position of the fast axis and the slow axis. 21. According to the system of item 10, the system further comprises an automated rotation adjustment device for synchronously rotating the optical fiber clamping structure and the optical fiber fixing device according to the fast axis position and the slow axis position obtained by the detection device. 22. The system according to item 21 is characterized in that the automated rotation adjustment device comprises a stepper motor and a rotary encoder. 23. According to any one of items 1 to 5, the system further comprises: an optical fiber support frame for supporting the optical fiber area between the detection end face position and the writing area. 24. The system according to item 23 is characterized in that the length of the optical fiber support frame is 10 to 50 centimeters. 25. The system according to item 24 is characterized in that the system also includes a slide rail, and the optical fiber clamping structure and the detection device are both installed on the slide rail. The slide rail is used to adjust the position of the optical fiber clamping structure and the detection device along the axial direction of the optical fiber, and the adjustment range of the slide rail is 20 to 50 centimeters. 26. The system according to any one of items 1 to 5 is characterized in that the system also includes a reference platform, which is used to place other devices in the system on the same plane. 27. A system according to any one of items 1 to 5, characterized in that the polarization-maintaining structure of the polarization-maintaining optical fiber comprises a panda eye structure, a bow tie structure, an elliptical structure, a tiger eye structure, a side hole structure and / or a photonic crystal fiber structure. 28. The system according to any one of items 1 to 5, characterized in that the laser comprises an ultraviolet laser and a femtosecond laser; The ultraviolet laser wavelengths include 248nm and 213nm. 29. The system according to item 10, characterized in that when the rotating module rotates to roughly adjust the detection end face, the optical fiber fixing device does not fix the polarization-maintaining optical fiber and keeps the optical fiber area between the rotating module and the writing area in a straight state; After the rotating module completes the coarse rotation adjustment, the optical fiber fixing device fixes the polarization-maintaining optical fiber for fine adjustment. 30. A polarization-maintaining fiber grating writing method, characterized in that a polarization-maintaining fiber grating writing system is provided, including a detection device, a fiber clamping structure and a grating writing device; the method comprises: The detection device detects the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber; The optical fiber clamping structure rotates the detection end face according to the fast axis position and the slow axis position; The grating writing device focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area. 31. The method according to item 30, characterized in that the detection device is a first microscopic imaging system; The steps of the detection device detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically as follows: the first microscopic imaging system detects the fast axis position and the slow axis position of the detection end face through microscopic imaging. 32. The method according to item 31, characterized in that the first microscopic imaging system further comprises a microscope, a one-dimensional adjustment frame, a plane reflector and a support structure, the microscope is arranged on the one-dimensional adjustment frame, and the one-dimensional adjustment frame is arranged on the support structure; The steps of the first microscopic imaging system detecting the fast axis position and the slow axis position of the detection end surface by microscopic imaging are specifically as follows: The support structure supports the one-dimensional adjustment frame and the microscope; The one-dimensional adjustment frame adjusts the focus position of the microscope along the optical path direction; The plane reflector reflects the detection end surface image into the microscope; The microscope magnifies the end surface image and displays it. 33. The method according to item 30 is characterized in that the steps of the detection device detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically: The detection device obtains the fast axis position and the slow axis position of the detection end surface by detecting the internal stress distribution of the detection end surface. 34. The method according to item 33 is characterized in that the detection device includes a Raman distribution optical fiber stress analyzer. 35. The method according to any one of items 30 to 34, characterized in that the system further comprises an optical compensation device; The method also includes the optical compensation device inputting light from a non-detection end face of the polarization-maintaining optical fiber. 36. The method according to any one of items 30 to 34, characterized in that the optical fiber clamping structure comprises: a rotating module and a locking module; The steps of rotating the optical fiber clamping structure to detect the end face according to the fast axis position and the slow axis position are specifically as follows: The rotating module rotates and roughly adjusts the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a rough adjustment position; The locking module locks the detection end surface at the coarse adjustment position. 37. The method according to item 36 is characterized in that the optical fiber clamping structure includes: a bottom adjustment frame; the method also includes the bottom adjustment frame adjusting the detection end face to the position of the plane reflector. 38. The method according to item 37, characterized in that the bottom adjustment frame is a three-dimensional adjustment frame; The steps of adjusting the detection end surface to the position of the plane reflector by the bottom adjustment frame are specifically as follows: The bottom adjustment frame adjusts the detection end surface in three directions: X, Y and Z. 39. According to the method of item 36, the grating writing device further comprises: a laser, a reflection device, a laser focusing device and an optical fiber fixing device; The grating writing device focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area, specifically: The laser outputs the laser; The reflecting device reflects the laser to the writing area; The laser focusing device focuses the laser on the writing area to form a grating pattern in the fiber core of the writing area; The optical fiber fixing device applies tension to the writing area. 40. The method according to item 39, characterized in that the grating writing device further comprises a signboard; The step of the grating writing device focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area also includes: The signboard displays diffraction fringes formed when the laser light output by the laser passes through the mask and the writing area and shines on the signboard. 41. The method according to item 40 is characterized in that the display panel is CCD and / or CMOS. 42. The method according to item 39, characterized in that the grating writing device further comprises: a mask, a mask fixing device and a second microscopic imaging system; The step of the grating writing device focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area also includes: The second microscopic imaging system detects the distance between the writing area and the mask; The mask plate fixing device adjusts and fixes the position of the mask plate; The mask separates the laser into ±1st order diffraction lights, so as to form a grating pattern in the fiber core of the writing area, wherein the grating pattern is a periodic refractive index modulation structure. 43. The method according to item 42 is characterized in that the distance between the writing area and the mask is 50 to 200 microns. 44. The method according to item 39, characterized in that the optical fiber fixing device further comprises an X / Y / Z three-dimensional adjuster; The step of the grating writing device focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area also includes: The X / Y / Z three-dimensional regulator adjusts the position of the writing area so that it is on the scanning path of the laser. 45. The method according to item 40, characterized in that the optical fiber fixing device further comprises a rotating shaft; The step of the grating writing device focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area also includes: The rotation axis is rotated symmetrically along the optical fiber axis to fine-tune the position of the writing area so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction according to whether the diffraction stripes displayed on the billboard are symmetrical. 46. ​​The method according to item 39, characterized in that the reflection device further comprises a moving platform; The step of the grating writing device focusing the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the core of the writing area also includes: The mobile platform selects different writing modes. 47. The method according to item 46 is characterized in that the writing mode includes point-by-point scanning writing and / or one-time exposure writing at a specific position. 48. The method according to item 39, characterized in that the optical fiber fixing device further comprises a tension monitor; The optical fiber fixing device applying tension to the writing area also includes: The tension monitor monitors the tension of the writing area. 49. According to the method of any one of items 30 to 34, the detection device further comprises a digital display module; The steps of the detection device detecting the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber are specifically as follows: The digital display module is used to automatically mark the laser direction and the relative position of the fast axis and the slow axis. 50. The method according to item 39, wherein the system further comprises an automated rotation adjustment device; The method further includes the automated rotation adjustment device synchronously rotating the optical fiber clamping structure and the optical fiber fixing device according to the fast axis position and the slow axis position obtained by the detection device. 51. The method according to item 50 is characterized in that the automated rotation adjustment device comprises a stepper motor and a rotary encoder. 52. The method according to any one of items 30-34, wherein the system further comprises: an optical fiber support frame; The method also includes the optical fiber support frame supporting the optical fiber area between the detection end surface position and the writing area. 53. The method according to item 52 is characterized in that the length of the optical fiber support frame is 10 to 50 centimeters. 54. The method according to item 53, characterized in that the system further comprises a slide rail, and the optical fiber clamping structure and the detection device are both mounted on the slide rail; The method further comprises the slide rail adjusting the positions of the optical fiber clamping structure and the detection device along the axial direction of the optical fiber, and the adjustment range of the slide rail is 20 to 50 centimeters. 55. The method according to any one of items 30-34, characterized in that the system further comprises a reference platform; The method also includes the reference platform placing other devices in the system on the same plane. 56. The method according to any one of items 30 to 34 is characterized in that the polarization-maintaining structure of the polarization-maintaining optical fiber includes a panda eye structure, a bow tie structure, an elliptical structure, a tiger eye structure, a side hole structure and / or a photonic crystal fiber structure. 57. The method according to any one of items 30 to 34, characterized in that the laser comprises an ultraviolet laser and a femtosecond laser; The ultraviolet laser wavelengths include 248nm and 213nm. 58. The method according to item 39 is characterized in that the rotation module rotates the detection end surface to coarsely adjust the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a coarse adjustment position, and the locking module locks the detection end surface at the coarse adjustment position in the following steps: When the rotating module rotates to roughly adjust the detection end face, the optical fiber fixing device does not fix the polarization-maintaining optical fiber and keeps the optical fiber area between the rotating module and the writing area in a straight state; After the rotating module completes the coarse rotation adjustment, the optical fiber fixing device fixes the polarization-maintaining optical fiber for fine adjustment.

Claims

1. A polarization-maintaining fiber grating writing system, characterized in that: The system comprises: A detection device, which is used to detect the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber; An optical fiber clamping structure, which is used to rotate the detection end face according to the fast axis position and the slow axis position; A grating writing device is used for focusing laser light on a writing area of ​​a rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area.

2. The system according to claim 1, characterized in that The detection device is a first microscopic imaging system, which is used to detect the fast axis position and the slow axis position of the detection end surface through microscopic imaging.

3. The system according to claim 2, characterized in that The first microscopic imaging system further comprises a microscope, a one-dimensional adjustment frame, a plane reflector and a support structure, wherein the microscope is arranged on the one-dimensional adjustment frame, and the one-dimensional adjustment frame is arranged on the support structure; in The support structure is used to support the one-dimensional adjustment frame and the microscope; The one-dimensional adjustment frame is used to adjust the focus position of the microscope along the light path direction; The plane reflector is used to reflect the detection end surface image into the microscope; The microscope is used to magnify the end surface image and display it.

4. The system according to claim 1, characterized in that The detection device is used to obtain the fast axis position and the slow axis position of the detection end surface by detecting the internal stress distribution of the detection end surface.

5. The system according to claim 4, characterized in that The detection device includes a Raman distribution optical fiber stress analyzer.

6. The system according to any one of claims 1 to 5, characterized in that: The system further comprises an optical compensation device for inputting light from a non-detection end face of the polarization-maintaining optical fiber.

7. The system according to any one of claims 1 to 5, characterized in that: The optical fiber clamping structure comprises: A rotation module, which is used to rotate and roughly adjust the detection end surface so that its fast axis is parallel to the laser direction and its slow axis is perpendicular to the laser direction to obtain a rough adjustment position; A locking module is used to lock the detection end surface at the coarse adjustment position.

8. The system according to claim 7, characterized in that The optical fiber clamping structure comprises: a bottom adjustment frame, which is used to adjust the detection end surface to the position of the plane reflector.

9. The system according to claim 8, characterized in that The bottom adjustment frame is a three-dimensional adjustment frame, which is used to adjust the detection end surface in three directions: X, Y, and Z.

10. A method for writing polarization-maintaining fiber gratings, characterized in that: A polarization-maintaining fiber grating writing system is provided, comprising a detection device, a fiber clamping structure and a grating writing device; the method comprises: The detection device detects the fast axis position and the slow axis position of the end face of the polarization-maintaining optical fiber; The optical fiber clamping structure rotates the detection end face according to the fast axis position and the slow axis position; The grating writing device focuses the laser on the writing area of ​​the rotated polarization-maintaining optical fiber to form a grating pattern in the fiber core of the writing area.

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