Design method of bragg grating with multi-mode wavelength selection function
By setting reflection regions at different axial length positions of the grating fiber core and using differentiated grating period and radial refractive index distribution, a Bragg grating with multi-mode wavelength selection function was designed, which solved the problem of fixed wavelength spacing in traditional gratings and realized mode field separation and mode selection of fundamental mode and higher-order modes.
Patent Information
- Application Number
- CN202511291589.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-10
- Publication Date
- 2025-11-21
- Estimated Expiration
- 2045-09-10
AI Technical Summary
Traditional Bragg gratings have fixed wavelength spacing, which cannot be dynamically expanded or compressed according to actual needs, resulting in mode crosstalk and signal distortion. This is especially true in multimode fibers where the wavelength spacing between the fundamental mode and higher-order modes is less than 1 nm, making them difficult to separate.
A multi-mode wavelength selection Bragg grating is designed. By setting reflection regions at different axial length positions of the grating fiber core and using differentiated grating period and radial refractive index distribution, mode field separation and mode selection are achieved.
The mode field of the fundamental mode and higher-order modes is effectively separated, which improves the sensitivity of the grating, realizes active control of wavelength spacing and mode selection, and solves the problem of fixed wavelength spacing in traditional gratings.
Smart Images
Figure CN120821077B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of fiber optic grating design technology, and in particular, a Bragg grating design method with multi-mode wavelength selection function. Background Technology
[0002] As can be seen from the conventional grating Bragg condition, the wavelength spacing of a conventional grating (FBG) is... From grating period Difference in effective refractive index between modes It is determined that its design is based on a single grating period and the inherent material structure properties of optical fibers. This principle leads to the following limitations: because the grating period cannot be adjusted after manufacturing, and the effective refractive index difference between different modes is limited by the fiber material and geometric parameters (such as core diameter, doping distribution, etc.), the wavelength spacing of traditional gratings is strictly bound to the initial design value. It is impossible to dynamically expand the wavelength spacing according to actual needs to suppress mode crosstalk, nor can it compress the wavelength spacing to achieve high-density wavelength allocation. For example, in multimode fibers, the fundamental mode (LP) 01 ) and higher-order modes (LP) 11 The wavelength interval is often due to The tiny size (less than 1 nm) makes it difficult to separate optical signals in the overlapping spectral regions at the receiver, leading to inter-mode energy coupling and signal distortion. Therefore, a novel Bragg grating design that breaks through traditional design paradigms is needed to solve the problems of fixed wavelength spacing and insufficient mode selectivity. Summary of the Invention
[0003] To address the shortcomings of existing technologies, this invention proposes a Bragg grating design method with multi-mode wavelength selection functionality.
[0004] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:
[0005] On the one hand, a method for designing a Bragg grating with multi-mode wavelength selection is provided, including:
[0006] Step 1: Determine the target modes for the two target wavelengths of the Lagrange grating to be designed, which is the long wavelength LP of the first target wavelength. 01 Shortwave LP of the second target wavelength 11 model;
[0007] Step 2: Determine the grating period corresponding to the target mode;
[0008] Step 3: Set the reflection regions corresponding to the target modes of the two target wavelengths at different axial length positions of the grating fiber core;
[0009] Step four: Design the radial refractive index distribution of the reflection region corresponding to the target modes of the two target wavelengths to achieve mode field separation of the target modes of the two target wavelengths.
[0010] Furthermore, a Bragg grating designed based on the above-mentioned design method for a Bragg grating with multi-mode wavelength selection function is provided.
[0011] Compared with the prior art, the beneficial technical effects that the present invention can achieve are as follows:
[0012] The Bragg grating design method with multi-mode wavelength selection provided by this invention first determines the target modes of the two target wavelengths reflected by the Bragg grating to be designed, which is the long wavelength LP of the first target wavelength. 01 Shortwave LP of the second target wavelength 11 The method provided by this invention enables the design of Bragg gratings that effectively separate the fundamental mode and higher-order modes. Specifically, the reflection regions corresponding to the target modes of two target wavelengths are positioned at different axial lengths along the fiber core. That is, the reflection regions corresponding to the target modes of the two target wavelengths are located at different positions along the axial direction of the fiber core and have different grating periods. This differentiated grating period design significantly improves sensitivity compared to traditional gratings. Given the fiber structure and parameters of the Bragg grating to be designed, and after determining the target modes and grating periods for the target wavelengths, the Bragg grating to be designed is simulated using COMSOL software. The simulation designs the radial refractive index distribution of the reflection regions corresponding to the target modes of the two target wavelengths, achieving mode field separation. The final designed Bragg grating can output different modes at different wavelengths. Attached Figure Description
[0013] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.
[0014] Figure 1 This is a flowchart of a Bragg grating design method with multi-mode wavelength selection function in one embodiment;
[0015] Figure 2 LP propagating in a conventional grating 01 LP 11 LP 21 LP 02 The model field distribution diagram, in which Figure 2 (a) is LP01 Model field distribution diagram Figure 2 (b) is LP 11 Model field distribution diagram Figure 2 (c) is LP 21 Model field distribution diagram Figure 2 (d) is LP 02 Model field distribution diagram;
[0016] Figure 3 For LP 11 A schematic diagram showing the division of the radial cross section of the fiber core in the reflection region corresponding to the mode.
[0017] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation
[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0019] In one embodiment, a method for designing a Bragg grating with multi-mode wavelength selection is provided, comprising:
[0020] Step 1: Determine the target modes for the two target wavelengths of the Lagrange grating to be designed, which is the long wavelength LP of the first target wavelength. 01 Shortwave LP of the second target wavelength 11 model;
[0021] Step 2: Determine the grating period corresponding to the target mode;
[0022] Step 3: Set the reflection regions corresponding to the target modes of the two target wavelengths at different axial length positions of the grating fiber core;
[0023] Step four: Design the radial refractive index distribution of the reflection region corresponding to the target modes of the two target wavelengths to achieve mode field separation of the target modes of the two target wavelengths.
[0024] For the fiber core is , NA For a standard grating of 0.061, LP 01 and LP 11 The effective refractive index difference is 0.00035, therefore, with a finite grating period length, wavelength spacing is difficult to separate. To achieve wavelength spacing... Active regulation, with the preferred core diameter being... The optical fiber was used for mode modulation at 1080nm and 1050nm. COMSOL simulation was used to perform mode modulation on the fiber core. The modes propagating in a conventional grating with an NA of 0.061 include LP. 01 LP 11 LP 21 LP 02 Patterns, such as Figure 2 As shown. By Figure 2 It can be seen that LP 01 Patterns and LPs 11 Pattern, LP 11 Patterns and LPs 21 The mode fields of the model overlap significantly. Separate the LPs. 01 Patterns and LPs 11 Pattern, LP 11 Patterns and LPs 21 The pattern field can realize the LP 01 Pattern, LP 11 Mode-selective reflection. To achieve mode selection, the modes propagating in the fiber core must first be separated so that the refractive index modulation is related to the mode field integral of that mode. The reflectivity is significantly higher than other modes, thus achieving high reflectivity of the grating for that mode. Different modes correspond to different reflection regions of the grating, and different wavelengths correspond to different grating periods. In summary, by setting gratings with different periods in different reflection regions along the fiber core axis and designing the radial refractive index distribution of the reflection regions, mode separation can be achieved, realizing both mode selection and wavelength separation.
[0025] Bragg gratings control the self-coupling coefficients of different modes by selectively modulating the refractive index distribution of the fiber core.
[0026] ;
[0027] in, For wave vector, For the effective propagation constant, For the radial refractive index modulation variation of independent gratings, Let be the mode field distribution function of the model.
[0028] Based on the reflection characteristics of the Bragg grating, reflectivity R It can be approximated by the following formula:
[0029] ;
[0030] in, It is the coupling coefficient. L This is the effective length of the grating. For weak gratings (i.e., ... In smaller cases, reflectivity can be approximately proportional to Different grating periods are inscribed in different regions of the fiber core for different transmission wavelengths and desired modes. This allows for the active expansion or compression of wavelength spacing and mode selection, thereby solving the problem of fixed wavelength spacing in traditional gratings.
[0031] In one embodiment, a Bragg grating design method with multi-mode wavelength selection is proposed, with the goal of achieving 1080nm LP. 01 Mode and 1050nm LP 11 Strong self-coupling of modes is used to achieve wavelength separation and mode selection. Specifically, in step one, the target modes for the two target wavelengths are LP modes at 1050 nm. 11 Mode, 1080nm LP 01 model.
[0032] To achieve 1080nm LP 01 Mode and 1050nm LP 11 The strong self-coupling of the mode, as can be seen from the grating Bragg condition, in step two, the 1050nm LP 11 The mode corresponds to a grating period of 362nm, and the LP is 1080nm. 01 The grating period corresponding to the mode is 372nm.
[0033] In this embodiment, step four involves designing the radial refractive index distribution of the reflection region corresponding to the target modes of the two target wavelengths, including:
[0034] (1) Design of 1050nm LP 11 The radial refractive index distribution of the reflection region corresponding to the mode is as follows:
[0035] For 1050nm LP 11 The radial cross-section of the fiber core corresponding to the reflection region of the mode is divided into regions: such as Figure 3 As shown, with the fiber core center as the origin of the xy coordinate system (which is also the origin of the fiber core radial section), a central circular region and four circular arc regions centered on the fiber core center and symmetrically distributed about the x-axis and y-axis are determined within the fiber core radial section: Let... Let r1, r2, r3, r4, and r5 be the radius of the central circle with the fiber core center as its center, and r5 be the fiber core radius, the distance from the center to the outer ring, the distance from the center to the inner ring, the distance from the center to the outer diameter of the arc region, and the distance from the center to the inner diameter of the arc region, respectively. The angle between the edge of the arc region closest to the x-axis and the x-axis. The angle between the edge of the arc region furthest from the x-axis and the x-axis. Preferred parameter settings for this embodiment: They are respectively included angle They are respectively 、 .
[0036] 1050nm LP 11 The four circular arc regions in the radial cross-section of the fiber core corresponding to the mode are used as the radial refractive index modulation regions of the grating. The distance from the center of the fiber core to each of the four circular arc regions is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the circular arc region, where... The refractive index of the optical fiber matrix material SiO2 is taken as 1.45; This is an inherent refractive index added to the fiber core. This is an inherent refractive index added to the arc region. The distance from the center of the arc region to the center of the fiber core is the distance from the center of the arc region to the inner and outer arcs of the arc region. This represents a Gaussian function with a standard deviation of 0.3 and a total integral of 1. The second term represents the distance from any point in the four arc regions to the center of the fiber core. For the refractive index modulation term of the circular arc grating region, the Gaussian peak is located at the second term through Gaussian modulation. Pick At that time, the circular arc modulation region is matched with the 1050nm LP. 11 Mode field distribution of the mode, while suppressing LP at 1080nm 01 Pattern coupling enables pattern-selective reflection.
[0037] 1050nm LP 11 The central circular region in the radial cross-section of the fiber core corresponding to the mode's reflection region is the grating's inherent radial refractive index region. The distance from the center of the fiber core to this central circular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region, where... This represents the distance from any point in the central circular region to the center of the fiber core.
[0038] 1050nm LP 11 The annular region between the outer and inner rings in the radial section of the fiber core corresponding to the reflection region of the mode, the distance from the center of the fiber core to the annular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the annular region, where... This represents the distance from the center of the outer ring to the center of the inner ring. The center of the outer ring is the point within the ring that is equidistant from both the inner and outer rings. This indicates the refractive index modulation of the outer ring.
[0039] 1050nm LP 11 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the four arc regions, the central circle region, and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This determines the radial refractive index distribution in the other regions of the fiber core region besides the four arc regions, the central circle region, and the annular region between the outer and inner rings. This represents the distance from any point in the fiber core region other than the four arc regions, the central circle region, and the annular region between the outer and inner rings, to the center of the fiber core.
[0040] (2) Design of 1080nm LP 01 The radial refractive index distribution of the reflection region corresponding to the mode is as follows:
[0041] For 1080nm LP 01 The radial section of the fiber core corresponding to the reflection region is divided into regions: A central circular region is determined within the radial section of the fiber core, with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core. Let... Let r1, r2, and r3 be the radius of the central circle centered at the fiber core, and r1, r2, and r3 be the fiber core radius, the distance from the center to the outer ring, and the distance from the center to the inner ring, respectively. .
[0042] 1080nm LP 01 The central circular region of the fiber core radial cross-section corresponding to the mode is the grating radial refractive index modulation region, and the distance from the central circular region to the fiber core center is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region, where... The fourth term represents the distance from any point in the central circular region to the center of the fiber core. This is the gate region refractive index modulation term, which, through the fourth Gaussian modulation term, has a Gaussian peak located at... When the value is 0, the gate region and 1080nm LP are realized. 01 The mode field overlap of the mode is much higher than that of the 1050nm LP. 11 The mode field of the mode is used to reduce self-coupling of higher-order modes.
[0043] 1080nm LP 01The annular region between the outer and inner rings of the fiber core's radial cross-section corresponding to the reflection region of the mode is the inherent radial refractive index region of the fiber core. The distance from the center of the fiber core to the annular region between the outer and inner rings is... The point whose refractive index is obtained through This confirms the LP at 1080nm. 01 The radial refractive index distribution of the annular region between the outer and inner rings of the fiber core radial section corresponding to the mode.
[0044] 1080nm LP 01 In the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, the remaining regions are the inherent refractive index regions of the fiber. For a 1080nm LP... 01 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This confirms the LP at 1080nm. 01 The radial refractive index distribution of the fiber core region in the radial cross section of the reflection region corresponding to the mode, excluding the central circular region and the annular region between the outer and inner annular rings.
[0045] Preferred parameter settings in this embodiment: It is 1.45. It is 0.0031. It is 0.0005. It is 0.01. for , for .
[0046] LP reflecting 1050nm 11 The lengths L1 and L2 of the symmetrical circular arc grating in the mode are 0.198m and 0.0216m, respectively, reflecting 1080nm LP. 01 The lengths L3 and L4 of the central small circular grating in the mode are 0.0245m and 0.00267m, respectively.
[0047] For LP reflecting 1050nm 11 The symmetrical circular arc grating refractive index modulation region of the mode, LP 11 The mode self-coupling coefficient is approximately 15.12, LP 01 The mode self-coupling coefficient is approximately 1.80, and the LP at 1050 nm... 02 The mode self-coupling coefficient is approximately 4.01, and the LP at 1050 nm... 21The mode self-coupling coefficient is approximately 4.04. According to the reflectivity formula, when L1 is 0.198 m, the LP at 1050 nm... 11 The reflectivity of the mode is 99.0%, 1050nm LP 01 The reflectivity of the mode is 11.7%, 1050nm LP 02 The reflectivity of the mode is 43.7%, 1050nm LP 21 The reflectivity of the mode is 44.1%. When L1 is 0.0216 m, the LP at 1050 nm... 11 The reflectivity of the mode is 10.0%, 1050nm LP 01 The reflectivity of the mode is 0.15%, 1050nm LP 02 The reflectivity of the mode is 0.75%, 1050nm LP 21 The reflectivity of the mode is 0.76%. For an LP reflecting 1080nm... 01 The central small circular grating refractive index modulation region of the mode, 1080nm LP 01 The mode self-coupling coefficient is approximately 122.61, and the LP at 1080 nm... 11 The mode self-coupling coefficient is approximately 2.19, and the LP at 1080 nm... 02 The mode self-coupling coefficient is approximately 12.25.
[0048] According to the formula for calculating reflectance, when L3 is 0.0245 m, the reflectance at 1080 nm is... 01 The mode has a reflectivity of 99.0% and a LP wavelength of 1080nm. 11 The reflectivity of the mode is 0.287%, 1080nm LP 02 The reflectivity of the mode is 8.41%. When L4 is 0.00267 m, the LP at 1080 nm... 01 The reflectivity of the mode is 10.0%, 1080nm LP 11 The reflectivity of the mode is 0.00342%, 1080nm LP 02 The reflectance of the pattern is 0.1056%.
[0049] In summary, compared to 25 Conventional gratings, through differentiated grating period and refractive index modulation, enable LP at 1080nm. 01 Mode and 1050nm LP 11 The modes exhibit strong self-coupling, achieving both wavelength spacing extension and mode-selective reflection.
[0050] In another embodiment, a Bragg grating design method with multi-mode wavelength selection is proposed, with the goal of achieving 1080nm LP. 11Mode and 1050nm LP 01 Strong self-coupling of modes is used to achieve wavelength separation and mode selection. Specifically, in step one, the target modes for the two target wavelengths are LP modes at 1080nm. 11 mode, 1050nm LP 01 model.
[0051] To achieve 1080nm LP 11 Mode and 1050nm LP 01 The strong self-coupling of the mode, as can be seen from the grating Bragg condition, in step two, the 1080nm LP 11 The mode corresponds to a grating period of 372nm, and the LP is 1050nm. 01 The grating period corresponding to the mode is 362nm.
[0052] In this embodiment, step four involves designing the radial refractive index distribution of the reflection region corresponding to the target modes of the two target wavelengths, including:
[0053] (1) Design of 1080nm LP 11 The radial refractive index distribution of the reflection region corresponding to the mode is as follows:
[0054] For 1080nm LP 11 The radial cross-section of the fiber core corresponding to the reflection region of the mode is divided into regions: such as Figure 3 As shown, with the fiber core center as the origin of the xy coordinate system (which is also the origin of the fiber core radial section), a central circular region and four circular arc regions centered on the fiber core center and symmetrically distributed about the x-axis and y-axis are determined within the fiber core radial section: Let... Let r1, r2, r3, r4, and r5 be the radius of the central circle with the fiber core center as its center, and r5 be the fiber core radius, the distance from the center to the outer ring, the distance from the center to the inner ring, the distance from the center to the outer diameter of the arc region, and the distance from the center to the inner diameter of the arc region, respectively. The angle between the edge of the arc region closest to the x-axis and the x-axis. The angle between the edge of the arc region furthest from the x-axis and the x-axis. Preferred parameter settings for this embodiment: They are respectively included angle They are respectively 、 .
[0055] 1080nm LP 11 The four circular arc regions in the radial cross-section of the fiber core corresponding to the mode are used as the radial refractive index modulation regions of the grating. The distance from the center of the fiber core to each of the four circular arc regions is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the circular arc region, where... The refractive index of the optical fiber matrix material SiO2 is taken as 1.45; This is an inherent refractive index added to the fiber core. This is an inherent refractive index added to the arc region. The distance from the center of the arc region to the center of the fiber core is the distance from the center of the arc region to the inner and outer arcs of the arc region. This represents a Gaussian function with a standard deviation of 0.3 and a total integral of 1. The second term represents the distance from any point in the four arc regions to the center of the fiber core. For the refractive index modulation term of the circular arc grating region, the Gaussian peak is located at the second term through Gaussian modulation. Pick At that time, the circular arc modulation region is matched with the 1080nm LP. 11 Mode field distribution of the mode, while suppressing LP at 1050 nm 01 Mode coupling enables mode-selective reflection;
[0056] 1080nm LP 11 The central circular region in the radial cross-section of the fiber core corresponding to the mode's reflection region is the grating's inherent radial refractive index region. The distance from the center of the fiber core to this central circular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region, where... This represents the distance from any point in the central circular region to the center of the fiber core;
[0057] 1080nm LP 11 The annular region between the outer and inner rings in the radial section of the fiber core corresponding to the reflection region of the mode, the distance from the center of the fiber core to the annular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the annular region, where... This represents the distance from the center of the outer ring to the center of the inner ring. The center of the outer ring is the point within the ring that is equidistant from both the inner and outer rings. This indicates refractive index modulation of the outer ring, increasing the refractive index of the outer ring to make LP 21 The pattern is confined within the outer ring to prevent it from interacting with the LP. 11 Pattern overlap.
[0058] 1080nm LP 11The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the four arc regions, the central circle region, and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This determines the radial refractive index distribution in the other regions of the fiber core region besides the four arc regions, the central circle region, and the annular region between the outer and inner rings.
[0059] (2) Design of 1050nm LP 01 The radial refractive index distribution of the reflection region corresponding to the mode is as follows:
[0060] For 1050nm LP 01 The radial section of the fiber core corresponding to the reflection region is divided into regions: A central circular region is determined within the radial section of the fiber core, with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core. Let... Let r1, r2, and r3 be the radius of the central circle centered at the fiber core, and r1, r2, and r3 be the fiber core radius, the distance from the center to the outer ring, and the distance from the center to the inner ring, respectively. .
[0061] 1050nm LP 01 The central circular region of the fiber core radial cross-section corresponding to the mode is the grating radial refractive index modulation region, and the distance from the central circular region to the fiber core center is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region, where... The fourth term represents the distance from any point in the central circular region to the center of the fiber core. This is the gate region refractive index modulation term, which, through the fourth Gaussian modulation term, has a Gaussian peak located at... When the value is 0, the gate region and 1050nm LP are realized. 01 The mode field overlap of the mode is much higher than that of the 1080nm LP. 11 The mode field of the mode is used to reduce self-coupling of higher-order modes.
[0062] 1050nm LP 01 The annular region between the outer and inner rings of the fiber core's radial cross-section corresponding to the reflection region of the mode is the inherent radial refractive index region of the fiber core. The distance from the center of the fiber core to the annular region between the outer and inner rings is... The point whose refractive index is obtained through This confirms the LP at 1050nm. 01 The radial refractive index distribution of the annular region between the outer and inner rings of the fiber core radial section corresponding to the mode, where... This represents the distance from any point in the annular region between the outer and inner annular rings to the center of the fiber core.
[0063] 1050nm LP 01 In the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, the remaining regions are the inherent refractive index regions of the fiber. For a 1050nm LP... 01 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This confirms the LP at 1050nm. 01 The radial refractive index distribution of the fiber core radial cross-section corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, is shown below. This represents the distance from any point in the fiber core region other than the central circular region and the annular region between the outer and inner annular rings to the center of the fiber core.
[0064] Preferred parameter settings in this embodiment: It is 1.45. It is 0.0031. It is 0.0005. It is 0.01. for , for .
[0065] LP reflecting 1080nm 11 The lengths L5 and L6 of the symmetrical circular arc grating in the mode are 0.205m and 0.0224m, respectively, reflecting 1050nm LP. 01 The lengths L7 and L8 of the central small circular grating in the pattern are 0.0237m and 0.0026m, respectively.
[0066] For 1080nm LP 11 Symmetrical circular arc grating refractive index modulation region of the mode, 1080nm LP 11 The mode self-coupling coefficient is approximately 14.60, and the LP at 1080 nm... 01 The mode self-coupling coefficient is approximately 1.75, and the LP at 1080 nm... 02 The mode self-coupling coefficient is approximately 3.90, and the LP at 1080 nm... 21 The mode self-coupling coefficient is approximately 3.93. According to the reflectivity formula, when L5 is 0.205 m, the LP at 1080 nm... 11 The mode has a reflectivity of 99.0% and a LP wavelength of 1080nm.01 The reflectivity of the mode is 11.8%, 1080nm LP 02 The reflectivity of the mode is 44.1%, 1080nm LP 21 The reflectivity of the mode is 44.6%. When L6 is 0.0224m, the LP at 1080nm... 11 The reflectivity of the mode is 10.0%, 1080nm LP 01 The reflectivity of the mode is 0.154%, 1080nm LP 02 The reflectivity of the mode is 0.762%, 1080nm LP 21 The reflectance of the pattern is 0.771%.
[0067] For 1050nm LP 01 The central small circular grating refractive index modulation region of the mode, 1050nm LP 01 The mode self-coupling coefficient is approximately 126.12, and the LP at 1050 nm... 11 The mode self-coupling coefficient is approximately 2.26, and the LP at 1050 nm... 02 The mode self-coupling coefficient is approximately 12.61. According to the reflectivity formula, when L7 is 0.0237m, the LP at 1050nm... 01 The reflectivity of the mode is 99.0%, 1050nm LP 11 The reflectivity of the mode is 0.286%, 1050nm LP 02 The reflectivity of the mode is 8.35%. When L8 is 0.0026m, the LP at 1050nm... 01 The reflectivity of the mode is 10.0%, 1050nm LP 11 The reflectivity of the mode is 0.00345%, 1050nm LP 02 The reflectance of the pattern is 0.107%.
[0068] In summary, compared to 25 Conventional gratings, through differentiated grating period and refractive index modulation, enable LP at 1050nm. 01 mode and 1080nm LP 11 The modes exhibit strong self-coupling, achieving both wavelength spacing extension and mode-selective reflection.
[0069] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.
Claims
1. A method for designing Bragg gratings with multi-mode wavelength selection, characterized in that, include: Step 1: Determine the target modes for the two target wavelengths of the Lagrange grating to be designed, which is the long wavelength LP of the first target wavelength. 01 Shortwave LP of the second target wavelength 11 The target modes for the two target wavelengths are LP at 1050 nm. 11 Mode, 1080nm LP 01 model; Step two: Determine the grating period corresponding to the target mode, where the 1050nm LP 11 The mode corresponds to a grating period of 362nm, and the LP is 1080nm. 01 The grating period corresponding to this mode is 372 nm; Step 3: Set the reflection regions corresponding to the target modes of the two target wavelengths at different axial length positions of the grating fiber core; Step four involves designing the radial refractive index distribution of the reflection regions corresponding to the target modes of the two target wavelengths to achieve mode field separation, including: (1) Design of 1050nm LP 11 The radial refractive index distribution of the reflection region corresponding to the mode is as follows: For 1050nm LP 11 The radial section of the fiber core corresponding to the reflection region is divided into regions: with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core, a central circular region and four circular arc regions centered on the center of the fiber core and symmetrically distributed about the x-axis and about the y-axis are determined in the radial section of the fiber core: Let... Let r1, r2, r3, r4, and r5 be the radius of the central circle with the fiber core center as its center, and r5 be the fiber core radius, the distance from the center to the outer ring, the distance from the center to the inner ring, the distance from the center to the outer diameter of the arc region, and the distance from the center to the inner diameter of the arc region, respectively. The angle between the edge of the arc region closest to the x-axis and the x-axis. The angle between the edge of the arc region furthest from the x-axis and the x-axis. <r5<r4<r3<r2<r1; 1050nm LP 11 The four circular arc regions in the radial cross-section of the fiber core corresponding to the mode are used as the radial refractive index modulation regions of the grating. The distance from the center of the fiber core to each of the four circular arc regions is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the circular arc region, where... The refractive index of the optical fiber matrix material SiO2 is taken as 1.45; This is an inherent refractive index added to the fiber core. This is an inherent refractive index added to the arc region. The distance from the center of the arc region to the center of the fiber core is the distance from the center of the arc region to the inner and outer arcs of the arc region. This represents a Gaussian function with a standard deviation of 0.3 and a total integral of 1. 1050nm LP 11 The central circular region in the radial cross-section of the fiber core corresponding to the mode's reflection region is the grating's inherent radial refractive index region. The distance from the center of the fiber core to this central circular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region; 1050nm LP 11 The annular region between the outer and inner rings in the radial section of the fiber core corresponding to the reflection region of the mode, the distance from the center of the fiber core to the annular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the annular region, where... This represents the distance from the center of the outer ring to the center of the inner ring. The center of the outer ring is the point within the ring that is equidistant from both the inner and outer rings. This indicates the refractive index modulation of the outer ring; 1050nm LP 11 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the four arc regions, the central circle region, and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This determines the radial refractive index distribution in other regions of the fiber core region besides the four arc regions, the central circle region, and the annular region between the outer and inner rings; (2) Design of 1080nm LP 01 The radial refractive index distribution of the reflection region corresponding to the mode is as follows: For 1080nm LP 01 The radial section of the fiber core corresponding to the reflection region is divided into regions: A central circular region is determined within the radial section of the fiber core, with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core. Let... Let r1, r2, and r3 be the radius of the central circle centered at the fiber core, and r1, r2, and r3 be the fiber core radius, the distance from the center to the outer ring, and the distance from the center to the inner ring, respectively. <r3<r2<r1; 1080nm LP 01 The central circular region of the fiber core radial cross-section corresponding to the mode is the grating radial refractive index modulation region, and the distance from the central circular region to the fiber core center is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the central circular region; 1080nm LP 01 The annular region between the outer and inner rings of the fiber core's radial cross-section corresponding to the reflection region of the mode is the inherent radial refractive index region of the fiber core. The distance from the center of the fiber core to the annular region between the outer and inner rings is... The point whose refractive index is obtained through This confirms the LP at 1080nm. 01 The radial refractive index distribution of the annular region between the outer and inner annular rings of the fiber core radial section corresponding to the mode; 1080nm LP 01 In the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, the remaining regions are the inherent refractive index regions of the fiber. For a 1080nm LP... 01 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This confirms the LP at 1080nm. 01 The radial refractive index distribution of the fiber core region in the radial cross section of the reflection region corresponding to the mode, excluding the central circular region and the annular region between the outer and inner annular rings.
2. The Bragg grating design method with multi-mode wavelength selection function according to claim 1, characterized in that, 、 r1, r2, r3, r4, and r5 are respectively 2 、 12.5 12 11 、 7.1 、 6.1 included angle They are respectively 、 .
3. The Bragg grating design method with multi-mode wavelength selection function according to claim 2, characterized in that, It is 1.
45. It is 0.0031. It is 0.0005. It is 0.
01. It is 6.6 , It is 11.5 .
4. A Bragg grating, characterized in that, It was designed based on the Bragg grating design method with multi-mode wavelength selection function as described in claim 1.
5. A method for designing Bragg gratings with multi-mode wavelength selection, characterized in that, include: Step 1: Determine the target modes for the two target wavelengths of the Lagrange grating to be designed, which is the long wavelength LP of the first target wavelength. 01 Shortwave LP of the second target wavelength 11 The target modes for the two target wavelengths are LP at 1080 nm. 11 Mode, 1050nm LP 01 model; Step two: Determine the grating period corresponding to the target mode, where the 1080nm LP 11 The mode corresponds to a grating period of 372nm, and the LP is 1050nm. 01 The grating period corresponding to this mode is 362 nm; Step 3: Set the reflection regions corresponding to the target modes of the two target wavelengths at different axial length positions of the grating fiber core; Step four involves designing the radial refractive index distribution of the reflection regions corresponding to the target modes of the two target wavelengths to achieve mode field separation, including: (1) Design of 1080nm LP 11 The radial refractive index distribution of the reflection region corresponding to the mode is as follows: For 1080nm LP 11 The radial section of the fiber core corresponding to the reflection region is divided into regions: with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core, a central circular region and four circular arc regions centered on the center of the fiber core and symmetrically distributed about the x-axis and about the y-axis are determined in the radial section of the fiber core: Let... Let r1, r2, r3, r4, and r5 be the radius of the central circle with the fiber core center as its center, and r5 be the fiber core radius, the distance from the center to the outer ring, the distance from the center to the inner ring, the distance from the center to the outer diameter of the arc region, and the distance from the center to the inner diameter of the arc region, respectively. The angle between the edge of the arc region closest to the x-axis and the x-axis. The angle between the edge of the arc region furthest from the x-axis and the x-axis. <r5<r4<r3<r2<r1; 1080nm LP 11 The four circular arc regions in the radial cross-section of the fiber core corresponding to the mode are used as the radial refractive index modulation regions of the grating. The distance from the center of the fiber core to each of the four circular arc regions is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the circular arc region, where... The refractive index of the optical fiber matrix material SiO2 is taken as 1.45; This is an inherent refractive index added to the fiber core. This is an inherent refractive index added to the arc region. The distance from the center of the arc region to the center of the fiber core is the distance from the center of the arc region to the inner and outer arcs of the arc region. This represents a Gaussian function with a standard deviation of 0.3 and a total integral of 1. 1080nm LP 11 The central circular region in the radial cross-section of the fiber core corresponding to the mode's reflection region is the grating's inherent radial refractive index region. The distance from the center of the fiber core to this central circular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution in the central circular region; 1080nm LP 11 The annular region between the outer and inner rings in the radial section of the fiber core corresponding to the reflection region of the mode, the distance from the center of the fiber core to the annular region is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the annular region, where... This represents the distance from the center of the outer ring to the center of the inner ring. The center of the outer ring is the point within the ring that is equidistant from both the inner and outer rings. This indicates the refractive index modulation of the outer ring; 1080nm LP 11 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the four arc regions, the central circle region, and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This determines the radial refractive index distribution in other regions of the fiber core region besides the four arc regions, the central circle region, and the annular region between the outer and inner rings; (2) Design of 1050nm LP 01 The radial refractive index distribution of the reflection region corresponding to the mode is as follows: For 1050nm LP 01 The radial section of the fiber core corresponding to the reflection region is divided into regions: A central circular region is determined within the radial section of the fiber core, with the center of the fiber core as the center and also the origin of the xy coordinate system of the radial section of the fiber core. Let... Let r1, r2, and r3 be the radius of the central circle centered at the fiber core, and r1, r2, and r3 be the fiber core radius, the distance from the center to the outer ring, and the distance from the center to the inner ring, respectively. <r3<r2<r1; 1050nm LP 01 The central circular region of the fiber core radial cross-section corresponding to the mode is the grating radial refractive index modulation region, and the distance from the central circular region to the fiber core center is... The point whose refractive index is obtained through This determines the radial refractive index distribution of the central circular region; 1050nm LP 01 The annular region between the outer and inner rings of the fiber core's radial cross-section corresponding to the reflection region of the mode is the inherent radial refractive index region of the fiber core. The distance from the center of the fiber core to the annular region between the outer and inner rings is... The point whose refractive index is obtained through This confirms the LP at 1050nm. 01 The radial refractive index distribution of the annular region between the outer and inner annular rings of the fiber core radial section corresponding to the mode; 1050nm LP 01 In the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, the remaining regions are the inherent refractive index regions of the fiber. For a 1050nm LP... 01 The distance from the fiber core center to the other regions in the radial cross-section of the fiber core corresponding to the mode, excluding the central circular region and the annular region between the outer and inner rings, is: The point whose refractive index is obtained through This confirms the LP at 1050nm. 01 The radial refractive index distribution of the fiber core region in the radial cross section of the reflection region corresponding to the mode, excluding the central circular region and the annular region between the outer and inner annular rings.
6. The Bragg grating design method with multi-mode wavelength selection function according to claim 5, characterized in that, 、 r1, r2, r3, r4, and r5 are respectively 2 、 12.5 12 11 、 7.1 、 6.1 included angle They are respectively 、 .
7. The Bragg grating design method with multi-mode wavelength selection function according to claim 6, characterized in that, It is 1.
45. It is 0.0031. It is 0.0005. It is 0.
01. It is 6.6 , It is 11.5 .
8. A Bragg grating, characterized in that, It was designed based on the Bragg grating design method with multi-mode wavelength selection function as described in claim 5.
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Multimode long period fiber Bragg grating machined by ultrafast laser direct writing
US20060093012A1