Polarization-maintaining hollow-core optical fiber

Abstract

The invention discloses a polarization-maintaining hollow-core optical fiber. The polarization-maintaining hollow-core optical fiber comprises a hollow-core region (101), an outer cladding (301), a plurality of cladding tubes (201), unit walls (601) and unit spaces (701), the plurality of cladding tubes (201) comprise a first type of cladding tubes and a second type of cladding tubes, at least one layer of nested tubes (501, 502) is arranged in a unit space (701) of the first type of cladding tubes, and a plurality of crossing layers (401) are arranged in a unit space (701) of the second type of cladding tubes. The nesting tube structure and the crossing layer structure are configured in the same optical fiber in a mixed mode, and the birefringence effect is achieved through different constraint mechanisms of the two structures on an optical field. By adjusting the ratio of the wall thickness of the nested tube to the thickness of the crossing layer (401), the birefringence amount can be continuously adjusted in a large range, switching between a polarization maintaining mode and a polarization mode is achieved, and different application requirements are met.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, specifically to a hollow-core optical fiber that achieves polarization-maintaining characteristics using a hybrid structure, suitable for applications such as data center interconnection, long-distance optical fiber communication, quantum communication, high-power laser transmission, laser processing, medical laser transmission, optical fiber sensing, optical fiber gyroscopes, and scientific research. Background Technology

[0002] Antiresonant hollow fiber is a new type of optical fiber in which optical transmission mainly takes place in the air core. Compared with traditional solid fiber, it has significant advantages such as low delay, low nonlinearity, and low dispersion, and shows great application potential in optical communication, high-power laser transmission, precision sensing and other fields.

[0003] The working principle of antiresonant hollow fiber is based on the antiresonance effect: multiple tubular antiresonant units are arranged in the cladding region of the fiber. The wall thickness of these antiresonant units satisfies specific antiresonance conditions, thereby creating a strong reflection effect on light within a specific wavelength range, confining the light to the hollow core for transmission. Compared with traditional photonic bandgap hollow fiber, antiresonant hollow fiber has a wider operating bandwidth, a simpler structural design, and lower transmission loss.

[0004] In applications such as fiber optic gyroscopes, coherent optical communication, and interferometry, hollow-core optical fibers are required to possess polarization-maintaining properties, meaning they can maintain the stable transmission of light in a polarization state. However, existing polarization-maintaining hollow-core fibers generally suffer from problems such as difficulty in controlling birefringence and narrow operating bandwidth, which limit their widespread adoption in polarization-sensitive applications.

[0005] Therefore, there is an urgent need for a polarization-maintaining hollow fiber with adjustable birefringence and a simple structure. Summary of the Invention

[0006] The purpose of this invention is to provide a polarization-maintaining hollow fiber and an optical transmission system to solve the technical problem of the difficulty in controlling the birefringence of existing polarization-maintaining hollow fibers.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A polarization-maintaining hollow-core optical fiber, comprising:

[0009] Hollow region;

[0010] Outer layer;

[0011] Multiple cladding tubes are distributed around the hollow region and located inside the outer cladding layer;

[0012] Unit wall;

[0013] The unit space is defined by the cladding tube and the unit wall;

[0014] The plurality of cladding tubes include a first type of cladding tube and a second type of cladding tube:

[0015] The first type of cladding tube has at least one nested tube within its unit space;

[0016] The second type of cladding tube has multiple transverse layers within its unit space, which span the unit space and are connected to the unit wall at both ends.

[0017] The core innovation of this invention lies in the use of two different types of cladding tube structures: a nested tube structure and a transverse layer structure, mixed and configured within the same optical fiber. Because the two structures have different constraints on the optical field, when they are distributed along different directions, they will produce different effective refractive indices in two orthogonal polarization directions, thereby achieving a birefringence effect.

[0018] This invention reveals that when the thickness of the nested tube wall and the thickness of the transverse layer are similar, the effects of the two structures on the two orthogonal polarization states tend to be balanced, and the birefringence is close to zero. When there is a difference in their thicknesses, this balance is broken, resulting in significant birefringence. This mechanism of coordinating birefringence through two independent parameters is not present in existing single-structure polarization-maintaining fibers.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Birefringence is adjustable over a wide range. By adjusting the ratio of the wall thickness of the nested tube to the thickness of the transverse layer, the amount of birefringence can be continuously adjusted over a wide range to meet the polarization maintenance requirements of different applications.

[0021] (2) The polarization-maintaining mode and the polarization-inducing mode can be switched. When the thickness of the nested tube wall is similar to that of the transverse layer, the birefringence is large, which is suitable for polarization-maintaining transmission; when the thickness of the two is large, the loss difference between the two polarization states increases, the polarization extinction ratio increases, which is suitable for polarization-inducing applications.

[0022] (3) The structure is stable and easy to manufacture. The transverse layer structure provides excellent mechanical support, and the nested tube structure has mature technology. The combination of the two takes into account both optical performance and manufacturing feasibility.

[0023] (4) High design flexibility. The performance of optical fiber can be flexibly optimized by adjusting parameters such as the number of nested tube layers, the number of cross layers, and the distribution of the two types of cladding tubes. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the polarization-maintaining hollow-core optical fiber of the present invention. In the figure: 101-hollow core region; 201-cladding tube; 301-outer cladding; 401-transverse layer; 501-first nested tube; 502-second nested tube; 601-unit wall; 701-unit space.

[0025] Figure 2 The curves show the birefringence Δn as a function of wall thickness, including two curves: a fixed cross-layer (401) thickness of 0.4µm and a scan of the nested tube wall thickness; and a fixed nested tube wall thickness of 0.4µm and a scan of the cross-layer (401) thickness.

[0026] Figure 3 This is a graph showing the polarization extinction ratio (PER) as a function of wall thickness, with the coordinates […]. Figure 2 correspond.

[0027] Figure 4 The graph shows the transmission loss of the two polarization states as a function of the wall thickness of the nested tube when the thickness of the transverse layer (401) is fixed at 0.4µm.

[0028] Figure 5 The graph shows the transmission loss of the two polarization states as a function of the thickness of the transverse layer (401) when the wall thickness of the nested tube is fixed at 0.4µm. Detailed Implementation

[0029] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0030] Example 1: Basic Configuration of Hybrid Structure

[0031] like Figure 1 As shown, this embodiment provides a polarization-maintaining hollow-core optical fiber, comprising:

[0032] Hollow core region (101): Located at the center of the optical fiber, with a circular cross-section and a diameter of approximately 30µm.

[0033] Outer cladding (301): Located on the outside of the cladding tube, made of quartz glass, with an outer diameter of approximately 125µm.

[0034] Cladding tube (201): Four cladding tubes are distributed around the hollow region (101), including two Class I cladding tubes and two Class II cladding tubes.

[0035] Type 1 cladding tubes: distributed along the first direction. Two layers of concentric nested tubes are provided in the unit space (701), including a first layer of nested tubes (501) and a second layer of nested tubes (502).

[0036] Type II cladding tubes: distributed along a second direction orthogonal to the first direction. Seven transverse layers (401) are provided in the unit space (701). The transverse layers are straight, spanning the unit space, and connected to the unit wall (601) at both ends.

[0037] Unit wall (601): is arc-shaped.

[0038] Unit space (701): The cavity region defined by the cladding tube (201) and the unit wall (601).

[0039] Example 2: Parameter tuning of birefringence properties

[0040] The structure of Example 1 was numerically analyzed using the finite element method. The simulation parameters are as follows:

[0041] Operating wavelength: 1550nm

[0042] Hollow region (101) diameter: 30µm

[0043] Outer diameter of cladding (301): 125µm

[0044] Number of cladding tubes (201): 4 (2 Class I cladding tubes, 2 Class II cladding tubes)

[0045] Type 1 cladding tube: with two nested tubes inside (501, 502)

[0046] Type II cladding tube: with 7 transverse layers (401)

[0047] The effects of the wall thickness of the nested tube and the thickness of the transverse layer (401) on the birefringence properties were studied through a systematic parameter scan.

[0048] Parameter group 1: Fixed cross-layer (401) thickness 0.4µm, scan nested tube wall thickness

[0049] like Figure 2 and Figure 4 As shown, when the wall thickness of the nested tube changes from 0.30µm to 0.70µm:

[0050] The birefringence Δn varies from 0 to 1.68 × 10⁻⁶. -3 When the wall thickness of the nested tube is approximately 0.43µm, Δn≈0, at which point the effects of the two structures on the optical field reach equilibrium; as the wall thickness deviates from this equilibrium point, Δn gradually increases.

[0051] The polarization extinction ratio (PER) reaches a peak of 14.8 dB at a nested tube wall thickness of 0.37 µm.

[0052] Low levels of loss can be achieved for both polarization states within a wall thickness range of 0.37–0.45 µm.

[0053] Parameter group 2: Fixed nested tube wall thickness 0.4µm, scan the thickness of the (401) cross layer.

[0054] like Figure 2 and Figure 5 As shown, when the thickness of the transverse layer (401) changes from 0.30µm to 0.70µm:

[0055] The birefringence Δn varies from 0 to 2.10 × 10⁻⁶. -3 When the thickness of the transverse layer (401) is approximately 0.37µm, Δn≈0; as the thickness of the transverse layer (401) increases, Δn increases significantly.

[0056] The polarization extinction ratio (PER) reaches a peak of approximately 12.9 dB across the (401) layer with a thickness of 0.43–0.44 µm.

[0057] Example 3: Three Preferred Configurations

[0058] Based on the above simulation results, the present invention provides the following three preferred parameter configurations:

[0059] Configuration A: High birefringence, low loss configuration

[0060] Nested tube wall thickness: 0.57µm; Transverse layer (401) thickness: 0.40µm.

[0061] Birefringence Δn: 5.49 × 10 -4 Polarization extinction ratio (PER): 14.1 dB.

[0062] Suitable for polarization-maintaining transmission applications that require both birefringence and loss.

[0063] Configuration B: Ultra-high birefringence configuration

[0064] Nested tube wall thickness: 0.40µm; Transverse layer (401) thickness: 0.65µm.

[0065] Birefringence Δn: 1.41 × 10 -3 .

[0066] Suitable for short-distance applications with extremely high requirements for birefringence.

[0067] Configuration C: High extinction ratio configuration

[0068] Nested tube wall thickness: 0.37µm; Transverse layer (401) thickness: 0.40µm.

[0069] Polarization extinction ratio (PER): 14.8 dB.

[0070] Suitable for polarizer or polarization filter applications.

[0071] Example 4: Variation in the number of nested tube layers

[0072] Different numbers of nested tubes can be set within the unit space (701) of the first type of cladding tube:

[0073] Single-layer nested tube (501): The structure is the simplest and the manufacturing difficulty is the lowest.

[0074] Double-layer nested tubes (501, 502): such as Figure 1 As shown, more reflective interfaces are provided, which can further optimize performance.

[0075] Three or more nested tubes: suitable for applications with extremely high loss requirements.

[0076] The selection of the number of nested tube layers needs to take into account both optical performance and manufacturing feasibility.

[0077] Example 5: Changes in the number and distribution of cladding tubes

[0078] The total number of cladding tubes (201) can be 3-20, preferably 3-8.

[0079] When the number of cladding tubes (201) is 4, as shown in Example 1, 2 first-class cladding tubes and 2 second-class cladding tubes are distributed in orthogonal directions, and the birefringence effect is significant.

[0080] When the number of cladding tubes (201) is 6, 3 first-class cladding tubes and 3 second-class cladding tubes can be alternately distributed.

[0081] The number of Type I cladding tubes and Type II cladding tubes can be the same or different, depending on the specific application requirements.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A polarization maintaining hollow core optical fiber, characterized by, Comprising: a hollow core region (101); an outer cladding (301); a plurality of cladding tubes (201) distributed around the hollow core region, inside the outer cladding; a cell wall (601); a cell space (701) defined by the cladding tubes (201) and the cell wall (601); wherein the plurality of cladding tubes (201) comprises a first type of cladding tube and a second type of cladding tube: at least one layer of nested tubes is arranged in the cell space of the first type of cladding tube; a plurality of cross layers (401) is arranged in the cell space of the second type of cladding tube, the cross layers cross the cell space and are connected to the cell wall (601) at both ends.

2. The hollow core optical fiber according to claim 1, characterized in that, The total number of cladding tubes (201) is 4, of which 2 are first type of cladding tubes and 2 are second type of cladding tubes; the first type of cladding tubes are distributed along a first direction, and the second type of cladding tubes are distributed along a second direction orthogonal to the first direction.

3. The hollow core optical fiber according to claim 1, characterized in that, The total number of cladding tubes (201) is 3-20.

4. The hollow core optical fiber according to claim 3, characterized in that, The total number of cladding tubes (201) is 3-8.

5. The hollow core fiber according to claim 1, characterized in that, The number of first type of cladding tubes is the same as the number of second type of cladding tubes.

6. The hollow core fiber according to claim 1, characterized in that, The wall thickness of the nested tubes ranges from 0.1 µm to 20 µm.

7. The hollow core optical fiber according to claim 6, characterized in that, The wall thickness of the nested tubes ranges from 0.3 µm to 0.7 µm.

8. The hollow core fiber according to claim 1, characterized in that, The thickness of the cross layers (401) ranges from 0.1 µm to 20 µm.

9. The hollow core optical fiber according to claim 8, characterized in that, The thickness of the cross layers (401) ranges from 0.3 µm to 0.7 µm.

10. The hollow core fiber according to claim 1, characterized in that, The ratio of the wall thickness of the nested tubes to the thickness of the cross layers (401) is 0.1 to 10.

11. The hollow core optical fiber according to claim 10, characterized in that, The ratio of the wall thickness of the nested tubes to the thickness of the cross layers (401) is 0.5 to 2.

0.

12. The hollow core fiber according to claim 1, characterized in that, One layer of nested tubes (501) is arranged in the cell space of the first type of cladding tube.

13. The hollow core fiber according to claim 1, characterized in that, Two or more layers of concentric nested tubes are arranged in the cell space of the first type of cladding tube, including a first layer of nested tubes (501) and a second layer of nested tubes (502).

14. An optical transmission system or apparatus, characterised by A system or device comprising the hollow core fiber as claimed in any one of claims 1 to 13 is used in one or more of the following applications: data center interconnection, long distance optical fiber communication, quantum communication, high power laser transmission, laser processing, medical laser transmission, optical fiber sensing, optical fiber gyroscope or scientific research.

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