Dual-core hollow anti-resonant optical fiber and method of construction of polarization beam splitter

Abstract

This application provides a method for constructing a dual-core hollow anti-resonant optical fiber and a polarization beam splitter. The optical fiber includes an inner cladding assembly and an outer cladding tube surrounding the inner cladding assembly. The inner cladding assembly includes two parallel elliptical tubes and two first circular tube assemblies arranged in a non-contact manner, with a second circular tube assembly inside each elliptical tube. Each elliptical tube and each first circular tube assembly is tangent to the outer cladding tube. The cross-sections of the two elliptical tubes are mirror-symmetrical about the Y-axis, and the major axes of both elliptical tubes extend along the X-axis to divide the interior of the outer cladding tube into two symmetrical core regions. This application can effectively shorten the distance between the two symmetrical cores of the dual-core hollow anti-resonant optical fiber, thereby effectively reducing the overall length of the dual-core hollow anti-resonant optical fiber polarization beam splitter, achieving ultra-wide operating bandwidth and good single-mode operation characteristics, and improving the applicability of the polarization beam splitter.

Description

Technical Field

[0001] This application relates to the field of optical fiber technology, and in particular to a method for constructing a dual-core hollow anti-resonant optical fiber and a polarization beam splitter. Background Technology

[0002] Polarization beam splitters can split light into two beams with a single polarization state, and are fundamental optical devices in optical communication systems. Based on the coupling of the evanescent field between the two fiber cores, dual-core optical fibers can realize beam splitting and combining devices with multiple selectivity for optical power, wavelength, and polarization state. Traditional dual-core optical fibers are difficult to manufacture, have high requirements for fabrication process conditions, few variable parameters, a small range of variable refractive index difference between the core and cladding, and strong wavelength and polarization dependence. Therefore, beam splitters and combiners based on traditional dual-core optical fibers have narrow bandwidth, long device length, and strong wavelength and polarization dependence, making it difficult to meet the development requirements of ultra-high capacity, ultra-high speed, and ultra-low loss all-optical networks.

[0003] Meanwhile, compared to solid optical fibers, hollow optical fibers have lower dispersion and nonlinear coefficients, making them widely applicable in fields such as ultrashort pulse or high-power laser transmission, mid-infrared transmission, fiber optic gyroscopes, and terahertz systems. Furthermore, hollow optical fibers can be filled with gas or liquid, showing broad application prospects in pulse compression, supercontinuum spectroscopy generation, fiber optic sensing, and the development of novel optical devices.

[0004] In 2002, a hollow microstructure fiber with a Kagome cladding was proposed. While its structure is similar to photonic bandgap fiber, the requirement for cladding periodicity is less stringent, significantly reducing fabrication difficulty. The light guiding mechanism of the Kagome hollow microstructure fiber is based on confined coupling theory, hence it is called a hollow antiresonant fiber. The emergence of this fiber not only provides a new approach to reducing the fabrication difficulty of hollow microstructure fibers but also offers a new and effective way to improve the performance and structural innovation of hollow microstructure fiber devices. In 2017, a dual-core hollow antiresonant fiber was fabricated for the first time. Experimental testing of the fiber's coupling characteristics showed that the coupling length of this fiber reached 35 cm. Considering the application requirements of dual-core hollow antiresonant fibers in practical systems, wide bandwidth, short device length, high splitting ratio, and single-mode operation are important factors to consider during design.

[0005] Currently, dual-core hollow microstructure fiber polarization beam splitters are mainly based on bandgap microstructure fibers. Achieving energy coupling between the two cores is difficult, and the stringent conditions required for bandgap formation increase the fabrication complexity. Hollow-core antiresonant fibers, compared to hollow-core photonic bandgap fibers, have lower requirements for cladding periodicity and are easier to fabricate, offering greater structural design flexibility. Existing dual-core hollow antiresonant fiber polarization beam splitters suffer from excessively long distances between the two symmetrical cores, leading to an overall longer length that limits their applications and increases production costs. Summary of the Invention

[0006] In view of this, this application provides a dual-core hollow anti-resonant optical fiber, including: an inner cladding assembly, and an outer cladding tube sleeved outside the inner cladding assembly;

[0007] The inner cladding assembly includes two elliptical tubes and two first circular tube assemblies arranged in parallel without contact with each other, and each elliptical tube is provided with a second circular tube assembly; each elliptical tube and each first circular tube assembly is tangent to the outer cladding circular tube;

[0008] The cross-sections of the two elliptical tubes are mirror-symmetrical about the Y-axis, and the major axes of the two elliptical tubes extend along the X-axis to divide the interior of the outer cladding tube into two symmetrical core regions. The origin of the rectangular coordinate system corresponding to the X-axis and Y-axis is the center of the cross-section of the dual-core hollow anti-resonant optical fiber.

[0009] The two first circular tube assemblies are located in the two fiber core regions respectively, and the cross-sections of the two first circular tube assemblies are mirror-symmetrical about the X-axis.

[0010] Furthermore, the first circular tube assembly includes two first circular tubes and two second circular tubes arranged in parallel without contact with each other, and the inner diameter of the first circular tubes is larger than the inner diameter of the second circular tubes.

[0011] Two second circular tubes are spaced apart between two first circular tubes, and each of the first and second circular tubes is tangent to the outer cladding circular tube.

[0012] Furthermore, the second circular tube assembly includes two third circular tubes arranged in parallel without contact with each other, and the inner diameter of the third circular tubes is smaller than the inner diameter of the second circular tube.

[0013] The two third circular tubes are mirror-symmetrical about the major axis of the elliptical tube in which they are located, and each third circular tube extends along the minor axis of the elliptical tube, with the inner wall of each third circular tube being tangent to the elliptical tube.

[0014] Furthermore, the inner diameter of the second circular tube, the inner diameter of the first circular tube, the inner diameter of the third circular tube, and the major axis, minor axis, and ellipticity of the elliptical tube are each determined in advance based on their respective influence data on the characteristics of the dual-core hollow anti-resonant optical fiber.

[0015] Furthermore, the inner diameter d1 of the second circular tube is 12.2 μm; the inner diameter d2 of the first circular tube is 14.6 μm; and the inner diameter d of the third circular tube is... s It is 4μm;

[0016] The major axis d of the elliptical tube a It is 28.8 μm, and the minor axis d b The value is 10 μm, and the ellipticity e is 0.35.

[0017] Furthermore, the inner radius of the outer cladding tube, and the wall thickness of the second, first, third, and elliptical tubes are predetermined based on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant optical fiber.

[0018] Furthermore, the inner radius R of the outer cladding circular tube n It is 30μm;

[0019] The wall thickness t of the second circular tube, the first circular tube, the third circular tube, and the elliptical tube is the same, which is 0.53 μm.

[0020] Another aspect of this application provides a method for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter, comprising:

[0021] The structural parameters of the aforementioned dual-core hollow anti-resonant optical fiber are respectively divided into the first structural parameter group and the second structural parameter group;

[0022] For the structural parameters in the first structural parameter group, values ​​are assigned to each structural parameter based on the influence data of each structural parameter on the characteristics of the dual-core hollow anti-resonant fiber; and values ​​are assigned to the structural parameters in the second structural parameter group to obtain a broadband dual-core hollow anti-resonant fiber polarization beam splitter containing the dual-core hollow anti-resonant fiber after the structural parameter assignment.

[0023] Furthermore, the first circular tube assembly includes two first circular tubes and two second circular tubes arranged in parallel without contact with each other; the second circular tube assembly includes two third circular tubes arranged in parallel without contact with each other.

[0024] The first set of structural parameters includes: the inner diameter d1 of the second circular tube, the inner diameter d2 of the first circular tube, and the inner diameter d of the third circular tube. s The major axis d of the elliptical tube a and ellipticity e;

[0025] Correspondingly, the step of assigning values ​​to each structural parameter in the first structural parameter group based on the influence data of each structural parameter on the characteristics of the dual-core hollow anti-resonant optical fiber includes:

[0026] Let d1 be the inner diameter of the second circular tube, d2 be the inner diameter of the first circular tube, and d be the inner diameter of the third circular tube. s The major axis d of the elliptical tube a Set initial values ​​for both the ellipticity e and the ellipticity e.

[0027] Assignment steps: Select one of the structural parameters in the first structural parameter group as the current target parameter, and fix the initial values ​​of the other structural parameters; assign different values ​​to the target parameter in sequence, and for each value of the target parameter and the initial values ​​of the other structural parameters, use a multiphysics simulation method based on the finite element method to simulate and calculate the dual-core hollow anti-resonant optical fiber, so as to obtain the characteristic influence data of each value of the target parameter on the dual-core hollow anti-resonant optical fiber, and select the optimal value among the values ​​of the target parameter based on the characteristic influence data, and determine the value of the target parameter as the optimal value;

[0028] Determine whether each structural parameter in the first structural parameter group has been assigned its optimal value. If not, return to the assignment step until all structural parameters in the first structural parameter group have been assigned their respective optimal values.

[0029] Furthermore, the second set of structural parameters includes: the inner radius R of the outer cladding tube. n The same wall thickness t of the second circular tube, the first circular tube, the third circular tube, and the elliptical tube;

[0030] Correspondingly, assigning values ​​to the structural parameters in the second structural parameter group includes:

[0031] Based on the pre-acquired data on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant optical fiber, the inner radius R of the outer cladding tube is determined. n And the value of the pipe wall thickness t.

[0032] The dual-core hollow anti-resonant optical fiber provided in this application includes: an inner cladding assembly, and an outer cladding circular tube sleeved outside the inner cladding assembly; the inner cladding assembly includes: two elliptical tubes and two first circular tube assemblies arranged parallel to each other in a non-contact manner, and each elliptical tube contains a second circular tube assembly; each elliptical tube and each first circular tube assembly is tangent to the outer cladding circular tube; the cross-sections of the two elliptical tubes are mirror-symmetrical about the Y-axis, and the major axes of the two elliptical tubes extend along the X-axis to divide the interior of the outer cladding circular tube into two symmetrical core regions, wherein the rectangular coordinates corresponding to the X-axis and Y-axis are... The origin is the center of the cross-section of the dual-core hollow anti-resonant fiber; the two first circular tube assemblies are respectively located in the two fiber core regions, and the cross-sections of the two first circular tube assemblies are mirror-symmetrical about the X-axis. This can effectively solve the problem of the overall length of the dual-core hollow anti-resonant fiber polarization beam splitter caused by the excessive distance between the two symmetrical fiber cores of the dual-core hollow anti-resonant fiber. It can effectively shorten the distance between the two symmetrical fiber cores of the dual-core hollow anti-resonant fiber, thereby effectively reducing the overall length of the dual-core hollow anti-resonant fiber polarization beam splitter, achieving ultra-wide operating bandwidth and good single-mode operation characteristics, and improving the applicability of the polarization beam splitter.

[0033] Additional advantages, objectives, and features of this application will be set forth in part in the description which follows, and will in part become apparent to those skilled in the art upon review of the following description, or may be learned by practice of the application. The objectives and other advantages of this application can be realized and obtained by means of the structures specifically pointed out in the specification and drawings.

[0034] Those skilled in the art will understand that the purposes and advantages that can be achieved with this application are not limited to those specifically described above, and that the above and other purposes that this application can achieve will be more clearly understood from the following detailed description. Attached Figure Description

[0035] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, do not constitute a limitation thereof. The components in the drawings are not drawn to scale but are merely for illustrating the principles of this application. For ease of illustration and description of certain parts of this application, corresponding portions in the drawings may be enlarged, i.e., may appear larger relative to other components in an exemplary device actually manufactured according to this application. In the drawings:

[0036] Figure 1 This is a schematic diagram of the structure of a dual-core hollow anti-resonant optical fiber in one embodiment of this application.

[0037] Figure 2 This is a schematic diagram illustrating the structural parameters in a dual-core hollow anti-resonant optical fiber according to one embodiment of this application.

[0038] Figure 3 This is a schematic diagram of the first process for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter according to another embodiment of this application.

[0039] Figure 4 This is a second flowchart illustrating the construction method of a broadband dual-core hollow anti-resonant fiber polarization beam splitter according to another embodiment of this application.

[0040] Figure 5 This is a schematic diagram of the construction device for a broadband dual-core hollow anti-resonant fiber polarization beam splitter according to another embodiment of this application.

[0041] Figure 6 This is a schematic diagram showing the variation of coupling length and the difference in coupling length between the two polarization states with the inner diameter d2 of the first circular tube at a wavelength of 1.55 μm, provided in an application example of this application.

[0042] Figure 7 This is a schematic diagram showing the variation of the confinement loss and higher-order mode extinction ratio of the optical fiber at a wavelength of 1.55 μm with the inner diameter d2 of the first circular tube 3, provided in an application example of this application.

[0043] Figure 8 In an application example of this application, at a wavelength of 1.55 μm, the coupling length, the difference in coupling length, and the distance between the two elliptical tubes vary with the major axis d of the elliptical tubes. a A diagram illustrating the changes.

[0044] Figure 9 The application example provided in this application shows that, at a wavelength of 1.55 μm, the ratio of confinement loss to higher-order mode loss varies with the major axis d of the elliptical tube. a A diagram illustrating the changes.

[0045] Figure 10 This is a schematic diagram showing the variation of the fiber coupling length and the difference between the two coupling lengths with the ellipticity of the elliptic tube when the wavelength is 1.55μm, as provided in the application example of this application.

[0046] Figure 11 This is a schematic diagram showing the variation of confinement loss and higher-order mode loss ratio with the ellipticity e of the elliptic tube at a wavelength of 1.55 μm, provided in an application example of this application.

[0047] Figure 12 The graph shows the relationship between the coupling length of the x and y polarization states and the difference in the couple length between the two polarization states as a function of wavelength, as provided in the application examples of this application.

[0048] Figure 13 The graph shows the relationship between the normalized power in the first core region A and the second core region B as the light travels through the optical fiber when the optical fiber length is 8.15 cm, as provided in the application example of this application.

[0049] Figure 14 This is a graph showing the relationship between the extinction ratio and wavelength in an application example provided in this application.

[0050] Figure 15 This is a graph showing the relationship between fiber confinement loss and higher-order mode extinction ratio as a function of wavelength, provided in an application example of this application.

[0051] The attached icons are numbered as follows:

[0052] 1. Outer layer circular tube;

[0053] 2. Elliptical tube;

[0054] A. First fiber core region;

[0055] B. Second fiber core region;

[0056] 3. First circular tube;

[0057] 4. The second circular tube;

[0058] 5. The third circular tube. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the embodiments and accompanying drawings. Here, the illustrative embodiments and their descriptions are used to explain this application, but are not intended to limit it.

[0060] It should also be noted that, in order to avoid obscuring this application with unnecessary details, only the structures and / or processing steps closely related to the scheme according to this application are shown in the accompanying drawings, while other details that are not closely related to this application are omitted.

[0061] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, element, step, or component, but does not exclude the presence or addition of one or more other features, elements, steps, or components.

[0062] It should also be noted that, unless otherwise specified, the term "connection" in this article can refer not only to a direct connection, but also to an indirect connection involving an intermediary.

[0063] In the following description, embodiments of the present application will be illustrated with reference to the accompanying drawings. In the drawings, the same reference numerals represent the same or similar parts, or the same or similar steps.

[0064] In one or more embodiments of this application, the hollow anti-resonant fiber refers to a type of hollow fiber that confines light within a hollow structure for propagation based on a restricted coupling light guiding mechanism; the polarization beam splitter is a basic fiber optic device that can separate a beam of light into light with single x and y polarization states.

[0065] See Figure 1 To address the problem of excessively long distance between the two symmetrical cores of existing dual-core hollow anti-resonant optical fibers, which leads to increased device length, this application provides a dual-core hollow anti-resonant optical fiber. The dual-core hollow anti-resonant optical fiber can be used as a dual-core hollow anti-resonant optical fiber polarization beam splitter. Specifically, the dual-core hollow anti-resonant optical fiber includes the following components: an inner cladding assembly and an outer cladding tube 1 sleeved outside the inner cladding assembly.

[0066] The inner cladding assembly includes two elliptical tubes 2 and two first circular tubes 3 arranged in parallel without contact with each other, and each elliptical tube 2 is provided with a second circular tube 4; each elliptical tube 2 and each first circular tube 3 is tangent to the outer cladding circular tube 1;

[0067] The cross-sections of the two elliptical tubes 2 are mirror symmetrical about the Y-axis, and the major axes of the two elliptical tubes 2 extend along the X-axis to divide the interior of the outer cladding tube 1 into two symmetrical fiber core regions. The origin of the rectangular coordinate system corresponding to the X-axis and Y-axis is the center of the cross-section of the dual-core hollow anti-resonant optical fiber.

[0068] The two first circular tube 3 assemblies are located in the two fiber core regions, namely the first fiber core region A and the second fiber core region B, and the cross sections of the two first circular tube 3 assemblies are mirror-symmetrical about the X-axis.

[0069] It is understandable that existing dual-core hollow anti-resonant optical fibers have two large circular tubes arranged on the X-axis. This arrangement results in an excessively long distance between the two symmetrical fiber cores, leading to a longer device length. This limits the application scenarios and increases production costs. Therefore, to solve this problem, the dual-core hollow anti-resonant optical fiber provided in this application uses two elliptical tubes 2, with their cross-sections mirror-symmetrical about the Y-axis. The major axes of both elliptical tubes 2 extend along the X-axis, dividing the interior of the outer cladding circular tube 1 into two symmetrical core regions. This solves the aforementioned problem and shortens the core distance, thereby reducing the device length.

[0070] As can be seen from the above description, the dual-core hollow anti-resonant fiber provided in this application embodiment can effectively shorten the distance between the two symmetrical cores of the dual-core hollow anti-resonant fiber, thereby effectively reducing the overall length of the dual-core hollow anti-resonant fiber polarization beam splitter, achieving ultra-wide operating bandwidth and good single-mode operation characteristics, and improving the applicability of the polarization beam splitter.

[0071] To further address the problems of high fiber confinement loss and inability to achieve single-mode operation in existing dual-core hollow anti-resonant optical fibers, the dual-core hollow anti-resonant optical fiber provided in this application embodiment includes the following components: two first circular tubes 3 and two second circular tubes 4 arranged in parallel without contact with each other, and the inner diameter of the first circular tube 3 is larger than the inner diameter of the second circular tube 4.

[0072] Two second circular tubes 4 are spaced apart between two first circular tubes 3, and each first circular tube 3 and second circular tube 4 is tangent to the outer cladding circular tube 1.

[0073] It is understandable that existing dual-core hollow anti-resonant optical fibers have three small circular tubes in each core region, which causes the dual-core hollow anti-resonant optical fibers to have large fiber confinement loss and cannot achieve single-mode operation. Therefore, the embodiments of this application can effectively reduce the fiber confinement loss of dual-core hollow anti-resonant optical fibers and support single-mode operation by setting two first circular tubes 3 and two second circular tubes 4 in parallel and non-contact with each other in each core region.

[0074] In order to further shorten the device length while achieving the same effect of reducing fiber confinement loss, in the dual-core hollow anti-resonant optical fiber provided in this application embodiment, the second circular tube 4 component includes: two third circular tubes 5 arranged in parallel without contact with each other, and the inner diameter of the third circular tube 5 is smaller than the inner diameter of the second circular tube 4.

[0075] The two third circular tubes 5 are mirror-symmetrical about the major axis of the elliptical tube 2 in which they are located, and each third circular tube 5 extends along the minor axis of the elliptical tube 2, and the inner wall of each third circular tube 5 is tangent to the elliptical tube 2.

[0076] Understandably, existing dual-core hollow anti-resonant optical fibers typically have a small tube inside a large circular tube arranged along the X-axis, which can effectively reduce fiber confinement loss. However, this can further increase the length of the device. In contrast, the embodiments of this application use two third circular tubes 5 arranged in parallel and non-contact with each other inside an elliptical tube. Compared with the prior art, this can further shorten the length of the dual-core hollow anti-resonant optical fiber while achieving the same effect of reducing fiber confinement loss.

[0077] To further meet the requirements of fiber polarization beam splitters regarding bandwidth, device length, splitting ratio, and single-mode operation conditions, in the dual-core hollow anti-resonant fiber provided in this application embodiment, the inner diameters of the second circular tube 4, the first circular tube 3, and the third circular tube 5, as well as the major axis, minor axis, and ellipticity of the elliptical tube 2, are pre-determined based on their respective influence data on the characteristics of the dual-core hollow anti-resonant fiber. This effectively improves the reliability and effectiveness of selecting the values ​​of the inner diameters of the second circular tube 4, the first circular tube 3, and the third circular tube 5, as well as the major axis, minor axis, and ellipticity of the elliptical tube 2, thereby improving the application performance of the polarization beam splitter.

[0078] To further meet the requirements of fiber polarization beam splitters regarding bandwidth, device length, splitting ratio, and single-mode operation, in the dual-core hollow anti-resonant fiber provided in this application embodiment, the inner radius of the outer cladding tube 1, and the wall thicknesses of the second tube 4, first tube 3, third tube 5, and elliptical tube 2 are predetermined based on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant fiber. This effectively improves the reliability and effectiveness of selecting the values ​​of the inner radius of the outer cladding tube 1 and the wall thicknesses of the second tube 4, first tube 3, third tube 5, and elliptical tube 2, thereby improving the application performance of the polarization beam splitter.

[0079] Based on this, and after extensive experiments and verifications, in the dual-core hollow anti-resonant optical fiber provided in the embodiments of this application, such as Figure 2 The preferred values ​​for each structural parameter of the dual-core hollow anti-resonant optical fiber shown are as follows:

[0080] (1) The inner diameter d1 of the second circular tube 4 is 12.2 μm;

[0081] (2) The inner diameter d2 of the first circular tube 3 is 14.6 μm;

[0082] (3) The inner diameter d of the third circular tube 5 s It is 4μm;

[0083] (4) The major axis d of the elliptical tube 2 a It is 28.8μm.

[0084] (5) The minor axis d of the elliptical tube 2 b It is 10μm.

[0085] (6) The ellipticity e of the elliptic tube 2 is 0.35.

[0086] (7) The inner radius R of the outer cladding tube 1 n It is 30μm;

[0087] (8) The wall thickness t of the second circular tube 4, the first circular tube 3, the third circular tube 5 and the elliptical tube 2 is the same, which is 0.53 μm.

[0088] It is understood that the preferred values ​​of the various structural parameters of the dual-core hollow anti-resonant optical fiber described above are only preferred embodiments of this application, and fine-tuning the structure or adjusting the values ​​of the structural parameters are also within the applicable range of the dual-core hollow anti-resonant optical fiber mentioned in this application.

[0089] In other words, the dual-core hollow anti-resonant fiber provided in this application embodiment, which can be used as a broadband dual-core hollow anti-resonant fiber polarization beam splitter, consists of an outer cladding circular tube 1 and an inner cladding ten-tube circular tube and an elliptical tube 2, with no contact between the outer and inner cladding. The inner and outer cladding are tangent, and the tangency points are symmetrically distributed at equal intervals along the inner wall of the outer cladding. The beam splitter structure is symmetrical about both the X and Y axes. The inner cladding structure includes two sizes of circular tubes and one size of elliptical tube 2, with the larger size... A circular tube (first circular tube 3) is positioned between a smaller circular tube (second circular tube 4) and an elliptical tube 2. The elliptical tube 2 is located on the X-axis of the beam splitter, dividing the fiber core region into a symmetrical first core region A and a second core region B. The elliptical tube 2 contains two smaller circular tubes (i.e., the third circular tube 5), which are located on the minor axis of the elliptical tube 2 and tangent to it. The wall material of the dual-core hollow anti-resonant optical fiber can be pure quartz glass. All the circular tubes in the inner cladding have the same wall thickness as the elliptical tube 2. The radius Rn of the outer cladding circular tube 1 is 30 μm; the inner diameter d1 of the second circular tube 4 in the inner cladding is 12.2 μm; the inner diameter d2 of the first circular tube 3 in the inner cladding is 14.6 μm; the wall thickness t is 0.53 μm; and the minor axis d of the elliptical tube 2 is... b Take 10μm, major axis d a Take 28.8 μm; the inner diameter d of the third circular tube 5 inside the elliptical tube 2. s Take 4μm.

[0090] In other words, for existing dual-core hollow anti-resonant fiber polarization beam splitters with coupling lengths as long as 35cm and without considering issues such as device operating bandwidth and single-mode operation conditions, this application proposes a dual-core hollow anti-resonant fiber with no inner cladding node to address the requirements of fiber polarization beam splitters on bandwidth, device length, splitting ratio, and single-mode operation conditions.

[0091] To further improve the reliability and efficiency of the construction process of a broadband dual-core hollow anti-resonant fiber polarization beam splitter, based on the broadband dual-core hollow anti-resonant fiber provided in the foregoing embodiments, this application also provides an embodiment of a method for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter, see [link to embodiment]. Figure 3 The method for constructing the broadband dual-core hollow anti-resonant fiber polarization beam splitter specifically includes the following:

[0092] Step 100: Divide the various structural parameters of the dual-core hollow anti-resonant optical fiber into the first structural parameter group and the second structural parameter group respectively.

[0093] Step 200: For the structural parameters in the first structural parameter group, assign values ​​to each structural parameter based on the characteristic influence data of each structural parameter on the dual-core hollow anti-resonant fiber; and assign values ​​to the structural parameters in the second structural parameter group to obtain a broadband dual-core hollow anti-resonant fiber polarization beam splitter containing the assigned structural parameters of the dual-core hollow anti-resonant fiber.

[0094] To further improve the reliability and effectiveness of the numerical selection of the first structural parameter set, thereby enhancing the application performance of the polarization beam splitter, in the construction method of the broadband dual-core hollow anti-resonant fiber polarization beam splitter provided in this application embodiment, the first circular tube 3 assembly includes: two first circular tubes 3 and two second circular tubes 4 arranged parallel to each other without contact; the second circular tube 4 assembly includes: two third circular tubes 5 arranged parallel to each other without contact; the first structural parameter set includes: the inner diameter d1 of the second circular tube 4, the inner diameter d2 of the first circular tube 3, and the inner diameter d of the third circular tube 5. s The major axis d of the elliptical tube 2 a minor axis d b and ellipticity e; see also Figure 4 Step 200 in the construction method of the broadband dual-core hollow anti-resonant fiber polarization beam splitter specifically includes the following:

[0095] Step 210: Define the inner diameter d1 of the second circular tube, the inner diameter d2 of the first circular tube, and the inner diameter d of the third circular tube. s The major axis d of the elliptical tube a minor axis d b Set initial values ​​for both the ellipticity e and the ellipticity e.

[0096] Step 220: Assignment Step: Select one of the structural parameters in the first structural parameter group as the current target parameter, and fix the initial values ​​of the other structural parameters; assign different values ​​to the target parameter in sequence, and for each value of the target parameter and the initial values ​​of the other structural parameters, use a multiphysics simulation method based on the finite element method to simulate and calculate the dual-core hollow anti-resonant optical fiber, so as to obtain the characteristic influence data of each value of the target parameter on the dual-core hollow anti-resonant optical fiber, and select the optimal value among the values ​​of the target parameter based on the characteristic influence data, and determine the value of the target parameter as the optimal value;

[0097] Step 230: Determine whether each structural parameter in the first structural parameter group has been assigned an optimal value. If not, return to the assignment step until all structural parameters in the first structural parameter group have been assigned their respective optimal values.

[0098] To further improve the reliability and effectiveness of the numerical selection of the second structural parameter set, and thus enhance the application performance of the polarization beam splitter, in the construction method of the broadband dual-core hollow anti-resonant fiber polarization beam splitter provided in this application embodiment, the second structural parameter set includes: the inner radius R of the outer cladding circular tube 1. n The same wall thickness t is also found in the second circular tube 4, the first circular tube 3, the third circular tube 5, and the elliptical tube 2; see also Figure 4 Step 200 in the method for constructing the broadband dual-core hollow anti-resonant fiber polarization beam splitter further includes the following:

[0099] Step 240: Based on the pre-acquired data on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant optical fiber, determine the inner radius R of the outer cladding tube. n And the value of the pipe wall thickness t.

[0100] From a software perspective, this application also provides a construction apparatus for performing a broadband dual-core hollow anti-resonant fiber polarization beam splitter in all or part of the dual-core hollow anti-resonant fiber, see [link to relevant documentation]. Figure 5 The construction device for the broadband dual-core hollow anti-resonant fiber polarization beam splitter specifically includes the following components:

[0101] The structural parameter division module 10 is used to divide the various structural parameters of the dual-core hollow anti-resonant optical fiber into the first structural parameter group and the second structural parameter group, respectively.

[0102] The structural parameter assignment module 20 is used to assign values ​​to the structural parameters in the first structural parameter group based on the characteristic influence data of each structural parameter on the dual-core hollow anti-resonant fiber; and to assign values ​​to the structural parameters in the second structural parameter group to obtain a broadband dual-core hollow anti-resonant fiber polarization beam splitter containing the dual-core hollow anti-resonant fiber after the structural parameter assignment.

[0103] The embodiments of the broadband dual-core hollow anti-resonant fiber polarization beam splitter construction device provided in this application can be used to execute the processing flow of the embodiments of the broadband dual-core hollow anti-resonant fiber polarization beam splitter construction method described above. Its functions will not be repeated here, but can be referred to the detailed description of the embodiments of the broadband dual-core hollow anti-resonant fiber polarization beam splitter construction method described above.

[0104] To further illustrate this solution, this application also provides a specific application example of constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter, which specifically includes the following:

[0105] S1: A novel structure for setting up a dual-core optical fiber, corresponding to the structural improvement part of the dual-core hollow anti-resonant optical fiber mentioned in the previous embodiment;

[0106] S2: Set some initial structural parameters corresponding to the above-mentioned novel structure of dual-core hollow anti-resonant optical fiber;

[0107] For example, the initial structural parameters of the dual-core hollow anti-resonant optical fiber are set as follows: the inner diameter d1 of the second circular tube 4 is 12.2 μm; the inner diameter d2 of the first circular tube 3 is 14.6 μm; the inner diameter ds of the third circular tube 5 is 4 μm; and the major axis d of the elliptical tube 2 is... a The elliptic tube 2 has a minor axis of 28.8 μm, a minor axis of db of 10 μm, and an ellipticity e of 0.35.

[0108] S3: Among the structural parameters initially set in S2, first determine a target parameter, fix the other initial structural parameters of the optical fiber, and study the influence of the target parameter on the characteristics of the optical fiber to determine the optimal parameter value for each parameter. Specifically:

[0109] (1) The optical fiber is simulated and calculated using COMSOL software (multiphysics simulation platform) based on the finite element method to determine the effect of the diameter of the cladding tube on the loss of the fundamental mode and higher-order modes of the optical fiber. The effective refractive indices of the fundamental mode and even mode of the x and y polarization states are substituted into the following formula (1) to determine the effect of the diameter d2 of the cladding tube on the coupling length of the optical fiber, so as to determine the optimal value of the inner diameter d2 of the first circular tube 3.

[0110] (2) The optical fiber was simulated and calculated using COMSOL software based on the finite element method to determine the major axis diameter d of the elliptical tube. a The influence of the gap between the two elliptical tubes, considering single-mode operation characteristics and fiber confinement loss, is used to determine the major axis d of elliptical tube 2. a The optimal value;

[0111] (3) The optical fiber was simulated and calculated using COMSOL software based on the finite element method to determine the influence of the ellipticity e of the elliptic tube on the coupling length of the optical fiber, and the optimal value of the ellipticity e of the elliptic tube 2 was determined with the goal of optimizing the single-mode characteristics of the optical fiber.

[0112] (4) The effect of the change of the inner diameter d1 of the second circular tube 4 on the fiber coupling length and the limitation loss is similar to the effect of the inner diameter d2 of the first circular tube 3. The optimal value of the inner diameter d1 of the second circular tube 4 is determined.

[0113] S4: Considering the fiber size, coupling length, and operating wavelength range, the inner radius R of the outer cladding tube 1 of the fiber is... n The diameter of the tube and the wall thickness t are preset to R respectively. n =30μm and t=0.53μm.

[0114] The specific explanation for step S3 is as follows:

[0115] According to coupled-mode theory, four supermodes exist in a dual-core optical fiber, including odd and even modes in the x-polarization state and odd and even modes in the y-polarization state. As light propagates along the fiber, modes of the same polarization state will periodically transfer between the two cores. Coupling length. This represents the length of light in an optical fiber when it has completely transferred from one fiber core to another, indicating a certain polarization state. As shown in the following formula:

[0116]

[0117] Where λ is the wavelength in free space. and These represent the effective refractive indices of the fundamental modes in the x and y polarization states (the effective refractive indices of the fundamental modes in the x and y polarization states) and the effective refractive indices of the even modes in the x and y polarization states (i.e., the effective refractive indices of the even modes in the x and y polarization states), respectively.

[0118] As incident light propagates along the optical fiber, energy is coupled from one fiber core to another. If light with power pin is incident on fiber core A, the normalized output power can be calculated using the following formula:

[0119]

[0120]

[0121] in, and These represent the energy in the first core region A and the second core region B at the fiber output end, respectively. and These represent the energies of the x- and y-polarized light in the first core region A of the optical fiber output end, respectively. and These represent the energies of the x- and y-polarized light in the second core region B of the optical fiber output end, respectively. and , respectively, represent the energies of the x and y polarization states in the incident light.

[0122] When the transmission distance is set to L, the coupling coefficient C corresponding to the x and y polarization states x and C y Defined as:

[0123]

[0124]

[0125] in, For the wave number of light, These are the refractive indices corresponding to the even and odd modes of the x-polarized state and the even and odd modes of the y-polarized state, respectively. and These are the coupling lengths corresponding to the x and y polarized light, respectively.

[0126] The extinction ratio, as one of the important parameters for evaluating the performance of a polarization beam splitter, is defined as the ratio of the normalized power between light of one polarization state and light of another polarization state in the same fiber core. It is mainly used to describe the degree of separation between two polarized beams.

[0127]

[0128] in, and These represent the energy of the x-polarized light and the energy of the y-polarized light in the first fiber core region A at the output port, respectively. When the extinction ratio is greater than 20 dB, the energy of the y-polarized light in the first fiber core region A at the output port is more than 100 times that of the x-polarized light. At this point, the polarization beam splitter is generally considered to have good working effect. Therefore, the wavelength range with an extinction ratio greater than 20 dB is generally considered to be the operating bandwidth of the polarization beam splitter.

[0129] By fixing other optical fiber parameters, the influence of one of these parameters on the fiber's properties is studied. The initial structural parameters of the optical fiber are set as: R n =30μm, d1=12.2μm, d2=14.6μm, d a =28.8μm, e=0.35 and t=0.53μm, the influence of the inner diameter d2 of the first circular tube 3 on the fiber coupling length and confinement loss was studied. From Figure 6 It can be seen that the coupling lengths corresponding to the x and y polarization states in the optical fiber and the difference ΔL between the coupling lengths of the two polarization states C The value gradually decreases as the inner diameter d2 of the first circular tube 3 increases, but the change is small.

[0130] Figure 7 The confinement loss and higher-order mode extinction ratio of the optical fiber at a wavelength of 1.55 μm are shown as a function of the inner diameter d2 of the first circular tube 3. It can be seen that the confinement loss of the fundamental mode in the fiber core increases slowly with the increase of the cladding tube diameter, while the confinement loss of the higher-order modes first increases and then decreases. Figure 7The region where the d2 value between 14 and 15 intersects with the horizontal line indicating a higher-order mode extinction ratio of 100 represents the cladding tube diameter range where the higher-order mode extinction ratio is greater than 100. When the cladding tube diameter is between 11.72 μm and 12.3 μm, the higher-order mode extinction ratio is greater than 100, and it reaches its maximum value of 300 when d2 = 14.6 μm. In summary, the optimal d2 value for a large cladding tube diameter is 14.6 μm.

[0131] In the proposed fiber structure, the core region is divided into two symmetrical core regions, A and B, by introducing two elliptical tubes. The coupling mode between the two cores depends on the air gap between the two elliptical tubes. Therefore, the size of the elliptical tubes and the gap between them significantly affect the coupling characteristics of the fiber. Figure 8 It can be seen that, with other structural parameters kept constant, as the major axis d of the elliptical tube 2... a As the air gap increases, the distance between the two elliptical tubes decreases linearly, meaning the gap between them narrows. With this narrowing, the coupling between the two fiber cores becomes more difficult, and the coupling length increases accordingly. Furthermore, the change in the major axis diameter of the elliptical tubes has a significant impact on the coupling length in the x-polarization state.

[0132] from Figure 9 It can be seen that the maximum limiting loss of the fundamental mode initially decreases with the increase of the major axis diameter of the elliptical tube, and then decreases further as the major axis d of the elliptical tube 2 increases. a When the wavelength is greater than 28.4 μm, the confinement loss remains essentially unchanged. Simultaneously, the minimum confinement loss and extinction ratio of higher-order modes exhibit the same trend with increasing major axis diameter of the elliptical tube: both first increase and then decrease. Within the wavelength range of 11.3 μm to 12.8 μm, the extinction ratio of higher-order modes is greater than 100. Considering both single-mode operation characteristics and fiber confinement loss, the major axis d of elliptical tube 2... a The optimal value is 28.8 μm.

[0133] When other structural parameters of the optical fiber are fixed, the ellipticity of the elliptical tube is changed, that is, the minor axis d of the elliptical tube 2 is changed. b . Figure 10 When the wavelength is 1.55 μm, the fiber coupling length and the difference between the two coupling lengths vary with the ellipticity of the elliptic tube. When the major axis of the elliptic tube is fixed, that is, when the distance between the two elliptic tubes is fixed, the change in ellipticity has little effect on the coupling channel between the two fiber cores. Therefore, the ellipticity of the fiber elliptic tube has no significant effect on the fiber coupling length.

[0134] from Figure 11It can be seen that the higher-order mode extinction ratio first increases and then decreases with increasing ellipticity. Therefore, the single-mode characteristics of the optical fiber can be optimized by adjusting the ellipticity of the elliptical tube. When the ellipticity of the elliptical tube is between 0.32 and 0.42, the higher-order mode extinction ratio of the optical fiber is greater than 100, reaching its maximum value at e = 0.35. Considering all factors, the optimal ellipticity of the elliptical tube is 0.35.

[0135] Based on the preceding discussion, the optimal values ​​for the fiber optic structure parameters are: R n =30μm, d1=12.2μm, d2=14.6μm, d s =4μm, d a =28.8μm, e=0.35 and t=0.53μm. Under these fiber structure parameters, the coupling lengths of the two polarization states and the difference between their coupling lengths vary with wavelength as follows: Figure 12 As shown, the coupling length of the y-polarization state is much greater than that of the x-polarization state. Due to the difference in coupling lengths between the two polarization states, light of both polarization states can be separated after propagating a certain distance in the optical fiber. Furthermore, the difference in coupling lengths between the two polarization states varies relatively flat with wavelength, which means that the polarization beam splitter based on the proposed dual-core fiber can achieve a wide bandwidth.

[0136] Substituting the coupling length into equations (2) and (3), we obtain the states of the x-polarized and y-polarized light as they propagate along the optical fiber after a beam of light is incident from the first core region A. The x-polarized and y-polarized light couple back and forth between the first core region A and the second core region B at their respective coupling rates. (See also...) Figure 13 The normalized power corresponding to the two polarization states in fiber core A and The difference between them, and the normalized power corresponding to the two polarization states in fiber core B. and The difference between them all reaches its maximum at 8.15 cm. Therefore, an 8.15 cm long optical fiber of this application is selected as the fiber polarization beam splitter.

[0137] The extinction ratio of the x- and y-polarized light in the optical fiber is calculated using formula (4). Figure 14 As shown, the optical fiber has a working bandwidth of 355nm under the condition that the extinction ratio of x and y polarization states is higher than 20dB, covering a wavelength range from 1.285μm to 1.64μm. This working band includes two commonly used wavelengths, 1.31μm and 1.55μm.

[0138] like Figure 15As shown, the fundamental mode loss of this fiber is relatively flat, around 2 dB / m, except near the resonant wavelength. Meanwhile, the lowest loss of higher-order modes remains above 500 dB / m. The extinction ratio of higher-order modes is higher than 100 in the wavelength range of 1.23 μm to 1.72 μm. This wavelength range covers the entire operating band of the polarization beam splitter, indicating that the polarization beam splitter based on the proposed fiber has excellent single-mode characteristics.

[0139] In summary, the broadband dual-core hollow anti-resonant fiber polarization beam splitter constructed using the method provided in this application example has an operating bandwidth of 355nm, covering a wavelength range from 1.285μm to 1.64μm, under the condition that the extinction ratio of x and y polarization states is higher than 20dB. This operating band includes two commonly used wavelengths, 1.31μm and 1.55μm.

[0140] The broadband dual-core hollow anti-resonant fiber polarization beamsplitter of this application exhibits a relatively flat loss of approximately 2 dB / m, except near the resonant wavelength. Simultaneously, the lowest loss of higher-order modes remains above 500 dB / m. The extinction ratio of higher-order modes exceeds 100 in the wavelength range of 1.23 μm to 1.72 μm. This wavelength range covers the entire operating band of the polarization beamsplitter, demonstrating that the polarization beamsplitter based on the proposed fiber possesses excellent single-mode characteristics.

[0141] It should be clarified that this application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of this application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of this application.

[0142] In this application, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with or in place of features of other embodiments.

[0143] The above description is merely a preferred embodiment of this application and is not intended to limit this application. For those skilled in the art, various modifications and variations can be made to the embodiments of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A dual-core hollow anti-resonant optical fiber, characterized in that, include: Inner cladding assembly, and outer cladding tube sleeved outside the inner cladding assembly; The inner cladding assembly includes two elliptical tubes and two first circular tube assemblies arranged in parallel without contact with each other, and each elliptical tube is provided with a second circular tube assembly; each elliptical tube and each first circular tube assembly is tangent to the outer cladding circular tube; The cross-sections of the two elliptical tubes are mirror-symmetrical about the Y-axis, and the major axes of the two elliptical tubes extend along the X-axis to divide the interior of the outer cladding tube into two symmetrical core regions. The origin of the rectangular coordinate system corresponding to the X-axis and Y-axis is the center of the cross-section of the dual-core hollow anti-resonant optical fiber. The two first circular tube assemblies are respectively located in the two fiber core regions, and the cross sections of the two first circular tube assemblies are mirror-symmetrical about the X-axis. The first circular tube assembly includes two first circular tubes and two second circular tubes arranged in parallel without contact with each other, wherein the inner diameter of the first circular tubes is larger than the inner diameter of the second circular tubes. Two second circular tubes are spaced apart between two first circular tubes, and each of the first and second circular tubes is tangent to the outer cladding circular tube; The second circular tube assembly includes two third circular tubes arranged in parallel without contact with each other, wherein the inner diameter of the third circular tubes is smaller than the inner diameter of the second circular tubes. The two third circular tubes are mirror-symmetrical about the major axis of the elliptical tube in which they are located, and each third circular tube extends along the minor axis of the elliptical tube, with the inner wall of each third circular tube being tangent to the elliptical tube.

2. The dual-core hollow anti-resonant optical fiber according to claim 1, characterized in that, The inner diameter of the second circular tube, the inner diameter of the first circular tube, the inner diameter of the third circular tube, and the major axis, minor axis, and ellipticity of the elliptical tube are determined in advance based on their respective influence data on the characteristics of the dual-core hollow anti-resonant optical fiber.

3. The dual-core hollow anti-resonant optical fiber according to claim 2, characterized in that, The inner diameter d1 of the second circular tube is 12.2 μm; the inner diameter d2 of the first circular tube is 14.6 μm; the inner diameter d of the third circular tube is... s It is 4μm; The major axis d of the elliptical tube a It is 28.8 μm, and the minor axis d b The value is 10 μm, and the ellipticity e is 0.

35.

4. The dual-core hollow anti-resonant optical fiber according to claim 1, characterized in that, The inner radius of the outer cladding tube, as well as the wall thickness of the second, first, third, and elliptical tubes, are predetermined based on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant optical fiber.

5. The dual-core hollow anti-resonant optical fiber according to claim 4, characterized in that, The inner radius R of the outer cladding tube n It is 30μm; The wall thickness t of the second circular tube, the first circular tube, the third circular tube, and the elliptical tube is the same, which is 0.53 μm.

6. A method for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter, characterized in that, include: Each structural parameter of the dual-core hollow anti-resonant optical fiber as described in any one of claims 1 to 5 is respectively assigned to the first structural parameter group and the second structural parameter group; For the structural parameters in the first group of structural parameters, values ​​are assigned to each structural parameter based on the data on the influence of each structural parameter on the characteristics of the dual-core hollow anti-resonant optical fiber. The structural parameters in the second structural parameter group are then assigned values ​​to obtain a broadband dual-core hollow anti-resonant fiber polarization beam splitter containing the assigned structural parameters.

7. The method for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter according to claim 6, characterized in that, The first circular tube assembly includes two first circular tubes and two second circular tubes arranged in parallel without contact with each other; the second circular tube assembly includes two third circular tubes arranged in parallel without contact with each other. The first set of structural parameters includes: the inner diameter d1 of the second circular tube, the inner diameter d2 of the first circular tube, and the inner diameter d of the third circular tube. s The major axis d of the elliptical tube a and ellipticity e; Correspondingly, the step of assigning values ​​to each structural parameter in the first structural parameter group based on the influence data of each structural parameter on the characteristics of the dual-core hollow anti-resonant optical fiber includes: Let d1 be the inner diameter of the second circular tube, d2 be the inner diameter of the first circular tube, and d be the inner diameter of the third circular tube. s The major axis d of the elliptical tube a Set initial values ​​for both the ellipticity e and the ellipticity e. Assignment steps: Select one of the structural parameters in the first structural parameter group as the current target parameter, and fix the initial values ​​of the other structural parameters; assign different values ​​to the target parameter in sequence, and for each value of the target parameter and the initial values ​​of the other structural parameters, use a multiphysics simulation method based on the finite element method to simulate and calculate the dual-core hollow anti-resonant optical fiber, so as to obtain the characteristic influence data of each value of the target parameter on the dual-core hollow anti-resonant optical fiber, and select the optimal value among the values ​​of the target parameter based on the characteristic influence data, and determine the value of the target parameter as the optimal value; Determine whether each structural parameter in the first structural parameter group has been assigned its optimal value. If not, return to the assignment step until all structural parameters in the first structural parameter group have been assigned their respective optimal values.

8. The method for constructing a broadband dual-core hollow anti-resonant fiber polarization beam splitter according to claim 7, characterized in that, The second set of structural parameters includes: the inner radius R of the outer cladding tube. n The same wall thickness t of the second circular tube, the first circular tube, the third circular tube, and the elliptical tube; Correspondingly, assigning values ​​to the structural parameters in the second structural parameter group includes: Based on the pre-acquired data on the dimensions, coupling length, and operating wavelength range of the dual-core hollow anti-resonant optical fiber, the inner radius R of the outer cladding tube is determined. n And the value of the pipe wall thickness t.

Images