A self-focusing fiber grating scattering device and processing method

Abstract

The present invention relates to a self-focusing fiber grating scattering device and a processing method. A radiation mode is emitted from the device, and the light emitted from the radiation mode is respectively gathered into points or lines at the focal plane according to its own wavelength. The design of the grating scattering device is based on the grating diffraction principle, and the optimal processing parameters of the grating are dynamically found through a point-by-point iterative calculation method. The present invention constructs a set of novel algorithms to solve the parameters of any focal plane grating, realize the optimization of grating scattering, reduce the interference of other orders of diffracted light, and increase the signal-to-noise ratio.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber grating technology, and in particular to a self-focusing optical fiber grating scattering device and a processing method thereof. Background Art

[0002] The propagation modes in optical fiber are divided into core mode, cladding mode and radiation mode.

[0003] The radiation mode refers to the mode of radiating light from the fiber core to space. The emission behavior of the fiber Bragg grating radiation mode can be controlled by the period of the grating points. The effect of the designed grating is similar to the effect of adding a lens behind the radiation mode, which can achieve self-focusing and diffusion of the radiation mode. This lens-like effect has played a huge role in promoting the miniaturization and low cost of optical fiber devices.

[0004] For example, in order to demodulate the spectrum of grating scattered light, it was necessary to place an optical lens on the fiber radiation mode path to achieve a focusing effect. However, the grating period modulation technology can eliminate the lens and only use the fiber grating itself to achieve the focusing effect.

[0005] To solve the problem of device miniaturization, most applications currently use chirped gratings as scattering elements to focus light. In this design, the focal plane is parallel to the radial direction of the optical fiber. However, there are many orders of diffraction in the radiation mode. If a parallel focal plane is used, light of different orders is prone to interference, reducing the signal-to-noise ratio.

[0006] The current traditional solution is to process chirped fiber gratings in optical fibers to achieve regulation of radiated light. Chirped fiber gratings are gratings whose period changes linearly with position, and their main function is to perform a focusing and defocusing function similar to a lens.

[0007] However, due to the diffraction characteristics of the grating, the radiated light has more than one diffraction order. Multiple output orders will be emitted in different directions at the same time, so there will be multiple diffraction orders.

[0008] When the focal plane of the device is parallel to the axis of the optical fiber, the diffracted light of different orders overlaps with each other, and the sensor on the focal plane is easily interfered by other orders, reducing the signal-to-noise ratio. Summary of the invention

[0009] The purpose of the present invention is to provide a self-focusing fiber grating scattering device and a processing method, aiming to solve the problem that the probability of overlapping of different diffraction orders of light in the focal plane is high and the sensor of the focal plane is easily disturbed by other orders.

[0010] To achieve the above-mentioned purpose, the present invention provides a self-focusing fiber grating scattering device, wherein the grating scattering device has a radiation mode emitted from the device, and the light emitted from the radiation mode is respectively converged into points or lines at the focal plane according to its own wavelength. The design of the grating scattering device is based on the grating diffraction formula, and the optimal processing parameters of the grating are dynamically found through a point-by-point iterative calculation method.

[0011] Furthermore, the grating diffraction formula is as follows: Where β is the diffracted light exit angle, α is the incident angle, λ is the incident wavelength, and d is the laser processing period.

[0012] Furthermore, the optimal processing parameter flow for designing the grating scattering device is:

[0013] Select the total number of processing points N required for the grating and calculate the first grating cycle;

[0014] After calculating the period, the total size of the diffusion circle formed by the current fiber Bragg grating in the focal plane is evaluated and minimized by adjusting the period of the current point;

[0015] After reaching the minimum value, the next cycle of cyclic calculation is performed;

[0016] When the grating period number reaches N, the calculation stops and the period value of each point of the grating is obtained;

[0017] At this point, the design of the grating device period is completed.

[0018] Furthermore, the focal plane is perpendicular to the fiber grating, or is inclined or parallel to the fiber grating.

[0019] Furthermore, the focal plane is a plane or a curved surface, and the curved surface is spherical.

[0020] Another aspect of the present invention provides a method for processing a self-focusing fiber grating scattering device. The designed grating scattering device is processed by ultraviolet exposure or femtosecond direct writing. The processing steps of the femtosecond direct writing method include:

[0021] Step 1: Place the optical fiber on the processing platform of femtosecond direct writing;

[0022] Step 2: Adjust the tension at both ends of the optical fiber to keep the tension at a set value, wherein the set value is 0.01 N to 20 N;

[0023] Step 3: Detect the shape of the processed optical fiber, determine the position of the optical fiber core, and the beginning and end processing positions;

[0024] Step 4: Determine the moving speed pattern of the translation stage through the data in step 3;

[0025] Step 5: Start processing, the translation stage moves according to the set method, and the laser shutter is opened synchronously to start processing;

[0026] Step 6: When the required length is reached, the processing process ends.

[0027] Furthermore, in the moving speed pattern of the translation stage in step 4, for a chirped grating, the translation stage is in uniformly accelerated motion; if it is not a chirped grating, the moving pattern of the translation stage is calculated by interpolation method.

[0028] The beneficial technical effect of the present invention is that the present invention constructs a set of novel algorithms to solve the parameters of any focal plane grating, thereby realizing the optimization of grating scattering; reducing the interference of other orders of diffracted light and increasing the signal-to-noise ratio.

[0029] Compared with traditional devices, the focal plane of the self-focusing device is placed in a vertical, inclined or parallel direction to increase the signal-to-noise ratio; secondly, the new algorithm is used to minimize the circle of confusion and improve the accuracy of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the realization result of a self-focusing fiber Bragg grating scattering device.

[0031] Figure 2 This is a structural diagram of a grating scattering device.

[0032] Figure 3 Schematic diagram of optical fiber orientation.

[0033] Figure 4 Schematic diagram of optical fiber parameters.

[0034] Figure 5 Schematic diagram of the first grating period.

[0035] Figure 6 It is a flow chart for designing grating parameters of grating scattering device.

[0036] Figure 7 This is the typical period distribution of a radial self-focusing grating device. The horizontal axis is the grating point number and the vertical axis is the grating point period, in microns.

[0037] Figure 8 This is a flow chart of machining radial self-focusing grating scattering devices by femtosecond direct writing method.

[0038] Fig. 9 It is a schematic diagram of the operation of a grating scattering device, with a fiber Bragg grating device below.

[0039] Fig.10 is the intensity distribution of the radiation mode in the focal plane. DETAILED DESCRIPTION

[0040] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0041] like Figure 1 , Figure 2 A radial self-focusing fiber grating scattering device, wherein a radiation mode is emitted from the device to form a focal plane perpendicular to the direction of the optical fiber, and several characteristic wavelengths emitted by the radiation mode are respectively converged into points or lines at the focal plane. The design of the grating scattering device is based on the grating diffraction formula, and the optimal processing parameters of the grating are dynamically found through a point-by-point iterative calculation method.

[0042] like Figure 3 , the grating diffraction formula is as follows: Where β is the diffracted light exit angle, α is the incident angle, λ is the incident wavelength, and d is the laser processing period.

[0043] like Figure 4 , showing the direction parallel to the optical fiber and the direction perpendicular to the optical fiber.

[0044] like Figure 5 ,In the design stage, the grating parameters generally refer to the period of the grating.,In the chirped scheme, the grating point spacing increases linearly, for example, the relationship between the point spacing abc is ba=cb;,In this design scheme, the period of the grating is not fixed, and the grating parameters are replaced by the grating point spacing, and the point spacing parameters are provided by the design method.

[0045] The present device is not necessarily restricted to the design limitations of chirped gratings.

[0046] First, several characteristic wavelengths are selected from the working band as research objects. These wavelengths are used to evaluate the imaging quality of the focal plane and are generally greater than one.

[0047] The relative position of the focal plane and the grating is selected. The focal plane can be at any angle relative to the optical fiber, such as parallel to the optical fiber direction, perpendicular to the optical fiber direction, at a certain angle to the optical fiber, etc. This algorithm can solve the required grating parameters.

[0048] like Figure 6 , the optimal processing parameter flow for designing the grating scattering device is:

[0049] Select the total number of processing points N required for the grating and calculate the first grating cycle;

[0050] After calculating the period, the total size of the diffusion circle formed by the current fiber Bragg grating in the focal plane is evaluated and minimized by adjusting the period of the current point;

[0051] After reaching the minimum value, the next cycle of cyclic calculation is performed;

[0052] When the grating period number reaches N, the calculation stops and the period value of each point of the grating is obtained;

[0053] At this point, the design of the grating device period is completed.

[0054] like Figure 7 , which is the typical period distribution of radial self-focusing grating device. The horizontal axis is the grating point number and the vertical axis is the grating point period, in micrometers.

[0055] like Figure 8 A method for processing a self-focusing grating scattering device, wherein the designed grating scattering device is processed by ultraviolet exposure method or femtosecond direct writing method, and the processing steps of the femtosecond direct writing method include:

[0056] Step 1: Place the optical fiber on the processing platform of femtosecond direct writing;

[0057] Step 2: Adjust the tension at both ends of the optical fiber to keep the tension at a set value, wherein the set value is 0.01 N to 20 N;

[0058] Step 3: Detect the shape of the processed optical fiber, determine the position of the optical fiber core, and the beginning and end processing positions;

[0059] Step 4: Determine the moving speed pattern of the translation stage through the data in step 3;

[0060] Step 5: Start processing, the translation stage moves according to the set method, and the laser shutter is opened synchronously to start processing;

[0061] Step 6: When the required length is reached, the processing process ends.

[0062] Furthermore, in the moving speed pattern of the translation stage in step 4, for a chirped grating, the translation stage is in uniformly accelerated motion; if it is not a chirped grating, the moving pattern of the translation stage is calculated by interpolation method.

[0063] like Fig. 9 ,The different line segments in the figure represent different wavelengths, which are focused on the focal plane at the same time.

[0064] Below is a fiber Bragg grating device, where the radiation mode is emitted from the device and forms a focal plane perpendicular to the direction of the optical fiber. The three line segments represent three characteristic wavelengths, which converge into points at the focal plane, realizing the radial self-focusing function.

[0065] like Fig.10, which is the intensity distribution diagram of the focal plane radiation mode. The spectrum of the optical fiber transmission light can be analyzed from this diagram.

[0066] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any person skilled in the art can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A self-focusing fiber Bragg grating scattering device, characterized in that it radiates The mode is emitted from the device, and the light emitted by the radiation mode is respectively gathered into points or lines at the focal plane according to its own wavelength. The design of the grating scattering device is based on the grating diffraction formula, and the optimal processing parameters of the grating are dynamically found through a point-by-point iterative calculation method; The grating diffraction formula is as follows: Where β is the diffracted light exit angle, α is the incident angle, λ is the incident wavelength, and d is the laser processing period; The process flow for designing the processing parameters of fiber Bragg grating scattering devices is: Select the total number of processing points N required for the fiber Bragg grating and calculate the first grating period; After calculating the period, the total size of the diffusion circle formed by the current fiber Bragg grating in the focal plane is evaluated and minimized by adjusting the period of the current point; After reaching the minimum value, the next cycle of cyclic calculation is performed; When the grating period number reaches N, the calculation stops and the period value of each point of the grating is obtained; At this point, the design of the grating device period is completed.

2. A self-focusing fiber Bragg grating scattering device according to claim 1, characterized in that The focal plane is perpendicular to the fiber grating, or is inclined or parallel to the fiber grating.

3. A self-focusing fiber Bragg grating scattering device according to claim 1, characterized in that The focal plane is a plane or a curved surface, and the curved surface is a spherical surface.

4. A method for processing a self-focusing fiber Bragg grating scattering device according to any one of claims 1 to 3, characterized in that The process is carried out by using an ultraviolet exposure method or a femtosecond direct writing method, wherein the femtosecond direct writing method comprises the following steps: Step 1: Place the optical fiber on the processing platform of femtosecond direct writing; Step 2: Adjust the tension at both ends of the optical fiber to keep the tension at a set value, wherein the set value is 0.01 N to 20 N; Step 3: Detect the shape of the processed optical fiber, determine the position of the optical fiber core, and the beginning and end processing positions; Step 4: Determine the moving speed pattern of the translation stage through the data in step 3; Step 5: Start processing, the translation stage moves according to the set method, and the laser shutter is opened synchronously to start processing; Step 6: When the required length is reached, the processing process ends.

5. The method for processing a self-focusing fiber Bragg grating scattering device according to claim 4, characterized in that The moving speed pattern of the translation stage in step 4 is that for a chirped grating, the translation stage is in uniform accelerated motion; if it is not a chirped grating, the moving pattern of the translation stage is calculated by interpolation.

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