Vector vortex mode generation method based on polarization-maintaining broadband long-period fiber grating

Abstract

The invention discloses a vector vortex mode generation method based on a polarization-maintaining broadband long-period fiber grating, and relates to the technical field of fiber vector vortex mode regulation and control. The method comprises the steps that based on a dispersion inflection point, a long-period fiber grating with broadband characteristics is inscribed on a polarization maintaining fiber to generate a stable and polarization-controllable broadband high-order mode, and the pulse walk-off effect can be avoided when the long-period fiber grating is applied to systems such as a mode-locked laser; by utilizing a mode superposition principle, a plurality of controllable vector vortex modes are generated by using a relatively simple device; the vector vortex mode comprises a column vector beam mode and a mode carrying orbital angular momentum. According to the invention, the vector mode with high stability, high reliability and high controllability can be generated through a simple device.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber vector vortex mode control, and in particular to a method for generating a vector vortex mode based on a polarization-maintaining broadband long-period optical fiber grating. Background Art

[0002] In the fiber vector mode generation system, the spectrum of the traditional mode conversion device presents narrowband characteristics, which has great limitations in application. For example, when used in mode-locked fiber lasers, the mode-locked spectrum is narrow and polarization cannot be controlled. When performing mode conversion of ultrashort pulses, the pulse walk-off effect is prone to occur, the conversion efficiency is low, the polarization is greatly affected, and it is difficult to self-start. In addition, conventional vector mode control technology usually uses devices such as polarization controllers (PCs) for control. Such methods are highly blind and cannot be converted into other physical quantities for quantitative control and characterization. Summary of the invention

[0003] The purpose of the present invention is to provide a method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating, which can generate a vector mode with high stability, high reliability and high controllability through a simple device.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] A method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating, comprising:

[0006] Based on the dispersion inflection point, a carbon dioxide fusion machine is used to write a long-period fiber grating on the polarization-maintaining fiber. Under the irradiation of carbon dioxide laser, a small periodic cone deformation is generated in the center of the fiber heating area, modulating the refractive index, and finally converting the LP 01 Mode conversion to LP 11bx Broadband high-order modes, to obtain polarization-maintaining broadband long-period fiber gratings;

[0007] The mode superposition principle and the polarization-maintaining broadband long-period fiber grating are used to perform mode synthesis, and a generating device is constructed. The generating device is used to generate a vector vortex mode according to the input linearly polarized light; the vector vortex mode includes a column vector beam mode and a mode carrying orbital angular momentum.

[0008] Optionally, the process of building the device for generating the column vector beam pattern is as follows:

[0009] Polarization-maintaining couplers and polarization-maintaining beam splitters are used for mode synthesis, and the generation device is built by adjusting the optical fiber length.

[0010] Optionally, the method of performing mode synthesis by using a polarization-maintaining coupler and a polarization-maintaining polarization beam splitter, and building a generation device by adjusting the length of an optical fiber, specifically includes:

[0011] First, the linearly polarized light is input into the polarization-maintaining broadband long-period fiber grating, and then the converted LP 11bx The broadband high-order mode is split into two paths by a polarization-maintaining beam splitter, one of which remains unchanged, and the other is converted to LP by welding at the first set angle. 11ay The broadband high-order mode is synthesized by using a polarization-maintaining coupler, and finally a fiber stretching device is placed at the synthesis end to adjust the fiber length, and finally the device for generating the column vector beam mode is completed.

[0012] Optionally, the first set angle is 90°.

[0013] Optionally, the process of constructing the generating device carrying the orbital angular momentum pattern is as follows:

[0014] The generating device is constructed by fusion-coating the optical fiber at the end of the grating and adjusting the wavelength of the optical fiber.

[0015] Optionally, the method of setting up a generating device by fusing an optical fiber at the end of the grating and adjusting the wavelength of the optical fiber specifically includes:

[0016] First, the linearly polarized light is input into the polarization-maintaining broadband long-period fiber grating, and a section of few-mode polarization-maintaining fiber is fused to the end of the grating by means of a second set angle fusion. By adjusting the wavelength of the tunable light source, the generation device carrying the orbital angular momentum mode is finally built.

[0017] Optionally, the second set angle is 45°.

[0018] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0019] The present invention discloses a method for generating vector vortex modes based on polarization-maintaining broadband long-period fiber gratings, the method comprising: based on the dispersion inflection point, writing a long-period fiber grating with broadband characteristics on a polarization-maintaining optical fiber to generate a stable, polarization-controllable broadband high-order mode, which can avoid the occurrence of pulse walk-off effect when used in systems such as mode-locked lasers; and then using the principle of mode superposition to generate a variety of controllable vector vortex modes with a relatively simple device; the vector vortex modes include a column vector beam mode and a mode carrying orbital angular momentum. The present invention can generate a vector mode with high stability, high reliability and high controllability through a simple device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments 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 The experimental spectra in this embodiment; wherein, part (a) is a schematic diagram of the phase matching curve of the long-period fiber grating based on the dispersion inflection point; part (b) is a broadband long-period fiber grating transmission spectrum; part (c) is the LP 11bx Schematic diagram of the mode spot and polarization direction; (d) shows the LP at different wavelengths 11 Intensity distribution diagram;

[0022] Figure 2 This is a diagram of a device for preparing a polarization-maintaining broadband long-period fiber grating by a carbon dioxide laser welding machine in this embodiment;

[0023] Figure 3 The diagram is a diagram of the CVBs generation principle and generation device in this embodiment; wherein, part (a) is a schematic diagram of the CVBs superposition generation principle; part (b) is a diagram of the full polarization-maintaining CVB superposition generation device;

[0024] Figure 4 Schematic diagram of the OAM mode generation principle and generation device in this embodiment; wherein, part (a) is a schematic diagram of the OAM mode superposition generation principle; part (b) is a diagram of the full polarization-maintaining OAM mode superposition generation device; part (c) is a schematic diagram of the evolution of different wavelength output modes and corresponding interference patterns;

[0025] Figure 5 It is a schematic flow chart of a method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating according to the present invention.

[0026] Reference numerals:

[0027] 1. Supercontinuum broadband light source; 2. First slow axis polarizer; 3. First fusion point; 4. Second fusion point; 5. Spectrometer; 6. Middle area to be processed of polarization-maintaining few-mode optical fiber; 71. First moving motor; 72. Second moving motor; 81. First mode stripping; 82. Second mode stripping; 9. First narrowband light source; 10. First slow axis polarizer; 11. First polarization-maintaining broadband long-period fiber grating; 12. Polarization-maintaining coupler; 13. First fusion method; 14. A polarization-maintaining polarization beam splitter; 151, a first stretching device; 152, a second stretching device; 16, a first focusing lens; 17, a first CCD; 18, an analyzer; 19, a second narrow-band light source; 20, a second slow-axis polarizer; 21, a second polarization-maintaining broadband long-period fiber grating; 22, a second fusion method; 23, a second focusing lens; 24, a second polarization-maintaining polarization beam splitter; 251, a first reflector; 252, a second reflector; 26, a second CCD. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The purpose of the present invention is to provide a method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating, which can generate a vector mode with high stability, high reliability and high controllability through a simple device.

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] like Figure 1-Figure 5 As shown, the present invention provides a method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating, comprising:

[0032] Step 100: Based on the dispersion inflection point, a carbon dioxide fusion splicer is used to write a long-period fiber grating on the polarization-maintaining fiber. Under the irradiation of carbon dioxide laser, a small periodic cone deformation is generated in the center of the fiber heating area, the refractive index is modulated, and finally the LP 01 Mode conversion to LP 11bx Broadband high-order modes, to obtain polarization-maintaining broadband long-period fiber gratings;

[0033] Step 200: Perform mode synthesis using the mode superposition principle and the polarization-maintaining broadband long-period fiber grating, and build a generating device, wherein the generating device is used to generate a vector vortex mode according to the input linearly polarized light; the vector vortex mode includes a column vector beam mode and a mode carrying orbital angular momentum.

[0034] Based on the above technical solution, the following embodiments are provided to explain each step in detail.

[0035] The solution of this embodiment can be used to convert LP 01 Mode conversion to LP 11bx Broadband high-order modes: The generated high-order modes can be superimposed to generate multiple vector modes.

[0036] Step 1: Analyze the broadband resonance characteristics of long-period fiber Bragg grating and determine the grating period.

[0037] Using refractive index simulation software, combined with the long-period fiber grating phase matching formula:

[0038]

[0039] Where Λ is the grating period, λ is the resonant wavelength, and Respectively represent LP 01 Mode and LP 11 The effective refractive index of the mode is calculated by numerically calculating the mode parameters supported by the few-mode fiber at each wavelength, and the curve of the effective refractive index of the eigenmode supporting transmission changing with wavelength is obtained, which is the dispersion curve of the few-mode fiber. Figure 1 As shown in (a), the curve is a quadratic parabola, and the lowest point of the parabola is the dispersion inflection point. This means that one period will correspond to two different resonant wavelengths, and a double-peak resonance phenomenon will be shown in the transmission spectrum. The long-period fiber grating prepared at the dispersion inflection point has broadband characteristics, which means that mode conversion can be performed in a longer wavelength range. And the period corresponding to the dispersion inflection point is the period of the long-period fiber grating set during the preparation process.

[0040] Step 2: Prepare polarization-maintaining broadband long-period fiber grating.

[0041] The preparation method adopted by the present invention is a carbon dioxide laser point-by-point writing method. Figure 2The experimental device shown in the figure connects the broadband light source, slow axis polarizer, polarization-maintaining few-mode fiber, single-mode fiber, and spectrometer in sequence, and uses a rubber rod with a diameter of about 1 cm to wrap the two ends of the polarization-maintaining few-mode fiber 2-3 times for mode stripping, which is used to filter out the high-order modes that may be generated during the welding process. The second section of single-mode fiber is used to filter out the high-order modes generated by the grating, so as to obtain the transmission spectrum of the grating in real time on the spectrometer; the slow axis polarizer is used to observe the transmission spectrum of the grating when the input light is linearly polarized light on the slow axis.

[0042] Use wire strippers to remove about 4 cm of coating from the middle area of ​​the polarization-maintaining few-mode fiber to be processed, and wipe the part with a dust-free paper dipped in an appropriate amount of alcohol to clean the part with the coating removed. Straighten the two ends of the area where the coating is removed and fix them on the clamp of the fusion splicer motor. The grating period is obtained by the synchronous and unidirectional movement of the two motors, and the fiber can always be kept straight, and the transmission spectrum at this time is measured. The procedure for writing gratings includes the following steps: First: keep the motors stationary, that is, the fiber remains stationary, and the fiber is exposed by laser; second: after the exposure stops, the exposed area of ​​the fiber is in a molten state, the left motor moves a short distance, and the right motor is kept stationary, so that the fiber is in a straight state again; third: the left and right motors drive the polarization-maintaining few-mode fiber to move a distance of a grating period at the same time, and the writing of one period is completed; fourth: repeat the above steps to complete the writing of multiple grating periods. During the writing process, the transmission spectrum displayed by the spectrometer is observed in real time. The deeper the depression, the higher the efficiency of converting the LP01 mode to the LP11bx mode. When the depression reaches the deepest, the laser writing is stopped to obtain the prepared polarization-maintaining broadband long-period fiber grating. The transmission spectrum results are shown in Figure 2. Figure 1 As shown in (b), it can be seen that the spectrum is broadband, the conversion efficiency is as high as 98.7%, and the 3-dB bandwidth is about 180nm, that is, high-efficiency mode conversion can occur in the wavelength range of 990nm to 1170nm.

[0043] Finally, since the gate area is relatively fragile, it needs to be encapsulated with a customized U-shaped glass groove and heat shrink tube after preparation.

[0044] Step 3: Overlay to generate CVB.

[0045] Experimental setup Figure 3 As shown in (b), the prepared polarization-maintaining broadband long-period fiber grating is connected to a narrow-band light source and a slow-axis polarizer, and a clear LP is observed at the output end using a CCD. 11bx Mode. Connect the slow axis polarizer to the grating prepared in step 1, and fuse a 50:50 polarization-maintaining few-mode polarization-maintaining coupler at the end of the grating to generate the LP 11bxSplit into two beams of equal intensity, and maintain the original mode polarization and intensity. And weld one of the output beams of the polarization-maintaining coupler to port 2 of the polarization-maintaining polarization beam splitter in a 90° welding manner to achieve LP 11bx Model to LP 11ay The two beams are then combined using a polarization-maintaining beam splitter.

[0046] According to the principle of mode superposition:

[0047] Δφ(L,λ)=LΔn eff (2π / λ)

[0048] By adjusting the wavelength or the length of the transmission fiber, when LP 11bx Mode and LP 11ay When the phase difference between the modes is exactly 2m (m = 0, 1, 2, ...), TE can be superimposed. 01 .

[0049] Use a stretching device to adjust the fiber length at the synthesis end of the polarization-maintaining polarization beam splitter, and use a CCD to observe the output mode at the end. When a donut-distributed image appears on the CCD, keep the fiber length unchanged and fix the output mode. 01 ,TM 01 , HE 21 even , HE 21 odd These four modes cannot be distinguished by the naked eye and can only be distinguished by their unique polarization states. Since the polarization direction of CVB is related to the azimuth angle, the four beams can be distinguished with the help of a polarizer.

[0050] Step 4: Superposition to generate OAM mode.

[0051] Experimental setup Figure 4As shown in (b), a tunable narrowband light source, a slow axis polarizer, and a polarization-maintaining broadband long-period fiber grating are connected in sequence, and a section of polarization-maintaining fiber is fused at the output end of the grating in a 45° alignment method. Finally, a self-interference system is built at the output end to interfere with the output beam to verify the generation of the vector mode. The self-interference system consists of two reflectors and a polarization-maintaining polarization beam splitter. The output annular beam enters the polarization-maintaining polarization beam splitter, and then exits from the polarization-maintaining polarization beam splitter to the reflectors on both sides. The reflectors on both sides are first roughly adjusted. When the two beams of light can appear on the mirror surface of the two reflectors at the same time, the positions and angles of the reflectors on both sides are fine-tuned to achieve the common path of the two beams of light. The separated two beams overlap at their intersection and interfere spatially, and the final interference pattern result is displayed on the CCD. According to the principle of mode superposition, the wavelength of the input light is adjusted to observe the change state of the output mode. When the mode is an annular beam and a fork-shaped interference fringe pattern appears, it means that the generated beam is an OAM mode.

[0052] According to the above test process, the following results can be obtained:

[0053] Figure 1 Middle (a): Schematic diagram of the phase matching curve of the long-period fiber grating based on the dispersion inflection point. The curve is in the shape of a quadratic parabola, which means that one period will correspond to two different resonant wavelengths, and a double-peak resonance phenomenon will be shown in the transmission spectrum. The lowest point of the parabola is the dispersion inflection point, and the long-period fiber grating prepared at the dispersion inflection point has broadband characteristics and can perform mode conversion in a longer wavelength range. And the period corresponding to the dispersion inflection point is the period of the broadband long-period fiber grating set during the preparation process.

[0054] Figure 1 Middle (b): Transmission spectrum of broadband long-period fiber grating. It can be seen that the spectrum is broadband, the conversion efficiency is as high as 98.7%, and the 3-dB bandwidth is about 180nm, that is, high-efficiency mode conversion can occur in the wavelength range of 990nm to 1170nm.

[0055] Figure 1 Middle (c): LP 11bx The mode spot intensity and the mode spot intensity after passing through the polarization analyzers in four directions. When the polarization direction of the input light is adjusted to the slow axis input, mode observation and polarization detection are performed at the output end. The results show that when the analyzer is rotated, only the mode intensity changes. When the analyzer is at 0° (the polarization direction is consistent with the polarization direction of the input light), its intensity is the strongest. When the analyzer is at 90° (the polarization direction is perpendicular to the polarization direction of the input light), the mode almost disappears. In short, the prepared polarization-maintaining broadband long-period fiber grating has high conversion efficiency and stability.

[0056] Figure 1Middle (d): LP at different wavelengths of broadband long-period fiber grating 11 Mode spot intensity. As can be seen from the figure, after the grating performs mode conversion on the input light, due to its broadband characteristics, a clear LP can be obtained at its output end in a longer wavelength range. 11 model.

[0057] Figure 2 :The device diagram of preparing polarization-maintaining broadband long-period fiber grating by CO2 laser welding machine. A supercontinuum broadband light source with a spectral range of 400-2400nm 1 will LP 01 The output is from the single-mode fiber, and then connected to the slow-axis polarizer 2 to convert the input light into linearly polarized light on the slow axis, and then fused with the few-mode fiber used to prepare the polarization-maintaining broadband long-period fiber grating at the first fusion point 3, and a section of single-mode fiber is fused at the second fusion point 4 at the end of the few-mode fiber to filter out the LP excited by the grating. 11 mode, and connect the spectrometer 5 at the end of the single-mode optical fiber to monitor the transmission spectrum of the grating in real time. Use wire strippers to strip about 4 cm of the coating layer from the middle area 6 of the polarization-maintaining few-mode optical fiber to be processed, and wipe the part where the coating layer is removed with a dust-free paper dipped in an appropriate amount of alcohol. Straighten the two ends of the area where the coating layer is removed and fix them on the two high-precision moving motors of the fusion splicer (including the first moving motor 71 and the second moving motor 72), and the cycle is obtained by the synchronous and unidirectional movement of the two motors. Perform mode stripping (including the first mode stripping 81 and the second mode stripping 82) on the few-mode optical fiber near the fusion point, that is, wrap the polarization-maintaining few-mode optical fiber 2-3 times with a rubber rod with a diameter of about 1 cm to filter out the high-order modes that may be excited by the fusion. Finally, use a carbon dioxide fusion splicer to process the middle area 6 of the polarization-maintaining few-mode optical fiber in a point-by-point writing manner.

[0058] Figure 3 Middle (a): Schematic diagram of the principle of CVBs superposition generation. In few-mode polarization-maintaining fiber, four types of LP 11 Mode (including LP 11ax LP 11ay LP 11bx and LP 11by The effective refractive index of the two modes is very different, which ensures their stable transmission, and CVB can be generated by the linear superposition of these modes.

[0059] Figure 3 Middle (b): Full polarization-maintaining CVB superposition generation device diagram. The first narrowband light source 9, the first slow axis polarizer 10 and the first polarization-maintaining broadband long-period fiber grating 11 are connected, and a 50:50 polarization-maintaining few-mode polarization-maintaining coupler 12 is fused at the end of the grating to generate the LP 11bxThe output beam of one of the polarization-maintaining couplers is welded to the port 2 of the polarization-maintaining polarization beam splitter 14 by the first welding method 13 of 90° to realize LP 11bx Model to LP 11ay Then the two beams are synthesized by using the polarization-maintaining polarization beam splitter 14, and the phase difference is changed by adjusting the optical fiber length using two stretching devices (including the first stretching device 151 and the second stretching device 152), and then the light beam is focused by the first focusing lens 16, and the mode is observed on the first CCD 17 and checked by the analyzer 18. If it is not the ideal mode, the optical fiber length is adjusted.

[0060] Figure 4 Middle (a): Schematic diagram of the principle of OAM mode superposition generation. In few-mode polarization-maintaining fiber, OAM ±1 The mode can be determined by LP 11a and LP 11b When the phase difference between the two modes is an integer multiple of p / 2, superposition can be achieved.

[0061] Figure 4 Middle (b): Full polarization-maintaining OAM mode superposition generation device diagram. The second narrowband light source 19, the second slow axis polarizer 20 are connected to the second polarization-maintaining broadband long-period fiber grating 21, and a specific length of polarization-maintaining fiber is fused at the output end of the grating by the second fusion method 22 with a panda eye 45° alignment, and a second focusing lens 23 is added thereafter for mode focusing. Finally, a self-interference optical path is built at the output to interfere with the output light beam to verify the generation of the vector mode. It consists of a second polarization-maintaining polarization beam splitter 24 and two reflectors (including a first reflector 251 and a second reflector 252). The annular light beam output from port 2 enters the second polarization-maintaining polarization beam splitter 24, and then is emitted from the second polarization-maintaining polarization beam splitter 24 to the reflectors on both sides. The two beams of light are made to co-path by adjusting the positions and angles of the reflectors on both sides. The separated two light beams overlap at their intersection and interfere spatially, and the final interference pattern result is displayed on the second CCD 26. The phase difference is changed by adjusting the wavelength of the input light until the interference pattern is the correct fork-shaped stripes.

[0062] Figure 4 (c): The evolution of the output modes and the corresponding interference patterns at different wavelengths. As the wavelength increases, the modes can be represented by OAM. +1 Become LP 11 , and then becomes OAM -1 , the entire conversion period is 4nm. It can be concluded that under the condition that the propagation fiber length is fixed, OAM can be flexibly generated by adjusting the wavelength of the input light. ±1 model.

[0063] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0064] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating, characterized in that: include: Based on the dispersion inflection point, a carbon dioxide fusion machine is used to write a long-period fiber grating on the polarization-maintaining fiber. Under the irradiation of carbon dioxide laser, a small periodic cone deformation is generated in the center of the fiber heating area, modulating the refractive index, and finally converting the LP 01 Mode conversion to LP 11bx Broadband high-order modes, to obtain polarization-maintaining broadband long-period fiber gratings; The mode superposition principle and the polarization-maintaining broadband long-period fiber grating are used to perform mode synthesis, and a generating device is constructed. The generating device is used to generate a vector vortex mode according to the input linearly polarized light; the vector vortex mode includes a column vector beam mode and a mode carrying orbital angular momentum.

2. The method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating according to claim 1, characterized in that: The process of building the device for generating the cylindrical vector beam pattern is as follows: Polarization-maintaining couplers and polarization-maintaining beam splitters are used for mode synthesis, and the generation device is built by adjusting the optical fiber length.

3. The method for generating a vector vortex mode based on a polarization-maintaining broadband long-period fiber grating according to claim 2, characterized in that: The method of using a polarization-maintaining coupler and a polarization-maintaining polarization beam splitter to perform mode synthesis and building a generation device by adjusting the length of the optical fiber specifically includes: First, the linearly polarized light is input into the polarization-maintaining broadband long-period fiber grating, and then the converted LP 11bx The broadband high-order mode is split into two paths by a polarization-maintaining beam splitter, one of which remains unchanged, and the other is converted to LP by welding at the first set angle. 11ay The broadband high-order mode is synthesized by using a polarization-maintaining coupler, and finally a fiber stretching device is placed at the synthesis end to adjust the fiber length, and finally the device for generating the column vector beam mode is completed.

4. The method for generating a vector vortex mode based on polarization-maintaining broadband long-period fiber grating according to claim 3, characterized in that: The first setting angle is 90°.

5. The method for generating a vector vortex mode based on polarization-maintaining broadband long-period fiber grating according to claim 1, characterized in that: The process of constructing the generating device carrying the orbital angular momentum mode is as follows: The generating device is constructed by fusion-coating the optical fiber at the end of the grating and adjusting the wavelength of the optical fiber.

6. The method for generating vector vortex mode based on polarization-maintaining broadband long-period fiber grating according to claim 5, characterized in that: The method of setting the optical fiber by fusing at the end of the grating and building a generating device by adjusting the wavelength of the optical fiber specifically includes: First, the linearly polarized light is input into the polarization-maintaining broadband long-period fiber grating, and a section of few-mode polarization-maintaining fiber is fused to the end of the grating by means of a second set angle fusion. By adjusting the wavelength of the tunable light source, the generation device carrying the orbital angular momentum mode is finally built.

7. The method for generating a vector vortex mode based on polarization-maintaining broadband long-period fiber grating according to claim 5, characterized in that: The second setting angle is 45°.

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