Single-polarization photonic crystal fiber

Abstract

The present application relates to a single-polarization photonic crystal fiber having a plurality of circular air holes formed therein and extending axially through the single-polarization photonic crystal fiber. The plurality of circular air holes includes two large circular air holes, a plurality of small circular air holes, and a plurality of medium circular air holes. The single-polarization photonic crystal fiber has a circular cross-section, wherein the two large circular air holes are symmetrically distributed about the center of the cross-section. The plurality of small circular air holes are arranged around the two large circular air holes, forming a multi-layer polygonal air hole ring with increasing size from the inside out. The outermost layer of the hexagonal array comprises a plurality of medium circular air holes. The distance between the centers of two adjacent medium circular air holes and two adjacent small circular air holes is a fixed pitch, and the distance between the centers of the two large circular air holes is twice the pitch. The structure of the single-polarization photonic crystal fiber of the present application is simple and easy to manufacture.

Description

Technical Field

[0001] The present application belongs to the field of optical fiber technology, and in particular relates to a single-polarization photonic crystal fiber. Background Art

[0002] Photonic crystal fiber, also known as holey fiber, was proposed by Russell of the University of Bath in the UK in 1992. It is generally composed of undoped quartz and air holes, with the air holes periodically arranged in a uniform distribution along the axial direction across its cross-section. Photonic crystal fiber has attracted widespread attention and in-depth research due to its flexible structural design and outstanding advantages unmatched by conventional optical fibers, such as excellent temperature stability, low bending loss, good birefringence stability, low magnetic sensitivity, low optical noise, and insensitivity to radiation. It has broad application prospects in fields such as fiber optic sensing, optical communications, and nonlinear optics. In recent years, single-mode, single-polarization transmission has been achieved by adjusting the end-face structure of photonic crystal fibers, such as by employing localized doping and elliptical holes. For example, the cross-sectional structure of the photonic crystal fiber described in the Chinese patent "A Single-Mode, Single-Polarization Photonic Crystal Fiber with a Star-Shaped Arrangement of Small Circular Holes" (Publication No. CN110426780) includes circular air holes of three different diameters: large, medium, and small. However, the arrangement of the circular air holes does not achieve single-polarization performance under bending conditions.

[0003] Single-mode, single-polarization photonic crystal fiber only supports one polarization fundamental mode transmission, eliminating polarization mode coupling, polarization mode dispersion, and polarization-dependent loss. It can improve the stability of optical devices and optical transmission networks, and has broad application prospects in fiber optic sensing systems, fiber optic gyroscopes, and fiber optic hydrophones.

[0004] Existing photonic crystal fibers that achieve single-mode single-polarization transmission through local doping, small hole coupling, elliptical holes, etc. have complex manufacturing processes, high production costs, low yields, and are difficult to mass produce. They also lose their single-polarization performance under bending conditions. Summary of the Invention

[0005] The present application provides a single-polarization photonic crystal fiber to solve the problem in the prior art that single-polarization photonic crystal fibers cannot meet the use requirements under small bending diameters.

[0006] In order to solve the above technical problems, the present application proposes a single-polarization photonic crystal fiber, in which a plurality of circular air holes are formed axially through the single-polarization photonic crystal fiber, and the plurality of circular air holes include two large circular air holes, a plurality of small circular air holes and a plurality of medium circular air holes; the cross-section of the single-polarization photonic crystal fiber is circular, and on the cross-section, the two large circular air holes are symmetrically distributed left and right according to the center of the cross-section; the plurality of small circular air holes are arranged around the two large circular air holes, forming a multi-layer polygonal air hole ring with increasing size from the inside to the outside; the plurality of medium circular air holes are located in the outermost layer of the multi-layer polygonal air hole ring; the multi-layer polygonal air hole ring is arranged according to a regular hexagonal array, the distance between the centers of two adjacent medium circular air holes is a fixed pitch, the distance between the centers of the two large circular air holes is twice the pitch, and the distance between the centers of the plurality of medium circular air holes is also a fixed pitch.

[0007] In one embodiment, the diameters of the two large circular air holes are both 5.5 um±0.5 um.

[0008] In one embodiment, the diameters of the plurality of medium circular air holes are all 3.2 um±0.5 um.

[0009] In one embodiment, the diameter of the small circular air hole is 2.2 um±0.5 um.

[0010] In one embodiment, the mesopore spacing is 4.4 um ± 0.5 um.

[0011] In one embodiment, the diameter of the cross section of the single-polarization photonic crystal fiber is 40 um, 60 um, 80 um or 125 um.

[0012] In one embodiment, the small circular air holes are located in the second layer of polygonal air hole ring from the outside to the inside.

[0013] In one embodiment, the single-polarization photonic crystal fiber is made of pure quartz material.

[0014] In one embodiment, the multiple small circular air holes form a multi-layer polygonal air hole ring with increasing size from the inside to the outside, and the outermost layer of the multi-layer polygon is a regular hexagon formed by medium circular air holes, and the medium circular air holes are not set at the six corners of the regular hexagon.

[0015] In one embodiment, the centers of the two large circular air holes are on the same horizontal line as the centers of the small circular air holes on their left and right sides.

[0016] Different from the prior art, the single-polarization photonic crystal fiber of the present application is formed with multiple circular air holes that axially penetrate the single-polarization photonic crystal fiber, and the multiple circular air holes include two large circular air holes, multiple small circular air holes, and multiple medium circular air holes. The cross section of the single-polarization photonic crystal fiber is circular. In the cross section, the two large circular air holes are symmetrically distributed according to the center of the cross section. The multiple small circular air holes are arranged around the two large circular air holes, forming a multi-layer polygonal air hole ring with increasing size from the inside to the outside. The multiple medium circular air holes are distributed in the outermost layer of the multi-layer polygonal air hole ring. The multi-layer polygonal air hole ring is arranged according to a regular hexagonal array. The distance between the centers of two adjacent small circular air holes and two adjacent medium circular air holes is a fixed pitch, and the distance between the centers of the two large circular air holes is twice the pitch. The present application can achieve different degrees of single polarization effect under different bending diameters by simply adjusting the position and size of the circular air holes, and the structure is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the exemplary embodiments of the present disclosure will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the accompanying drawings, several embodiments of the present disclosure are shown in an illustrative and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of an embodiment of the single-polarization photonic crystal fiber of the present application;

[0019] Figure 2 yes Figure 1 The single polarization performance test diagram of the single polarization photonic crystal fiber embodiment shown in FIG.

[0020] Figure 3 This is a schematic diagram of the cross-sectional structure of a common photonic crystal fiber;

[0021] Figure 4 yes Figure 3 The single polarization performance test diagram of ordinary photonic crystal fiber at different bending diameters is shown. DETAILED DESCRIPTION

[0022] The following will be combined with the accompanying drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the embodiments described are part of the embodiments of the present disclosure, not all of them. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present disclosure.

[0023] Below is the attached figure Figures 1-4 To describe this application. First refer to Figure 3, we can know the structure of air holes in existing common photonic crystal fibers, which are arranged around regular hexagons with air holes of the same size. A single size of air hole cannot guarantee single polarization characteristics, such as Figure 4 As shown in FIG, the limiting loss after bending is almost the same for both the slow axis and the fast axis, so this type of optical fiber cannot achieve the single polarization effect in a bent state.

[0024] Based on this, the present application designs two large circular air holes and multiple medium circular air holes to replace the conventional small circular air holes. Among them, the two large circular air holes make the fiber core produce a high birefringence effect. When bending, the fast-axis light will be coupled out of the fiber core, and the slow-axis light will continue to be transmitted in the fiber core in the form of a guided mode, thereby achieving a single polarization effect. The optical fiber of the present application utilizes the principle of bend-induced mode cutoff, which can achieve good single polarization performance within a specific bending diameter range. The bending diameter range of the single-polarization photonic crystal fiber is 5mm to 30mm.

[0025] Specifically, the structure of this embodiment can be referred to Figure 1 First, in this embodiment, the single-polarization photonic crystal fiber is made of pure quartz material to form a photonic crystal fiber. A plurality of circular air holes are formed in the single-polarization photonic crystal fiber, extending axially through the fiber. The plurality of circular air holes includes two large circular air holes, a plurality of medium circular air holes, and a plurality of small circular air holes.

[0026] The cross section of the single-polarization photonic crystal fiber is circular. On the cross section, two large circular air holes are symmetrically distributed around the center of the cross section; multiple small circular air holes are arranged around the two large circular air holes, forming a multi-layer polygonal air hole ring with increasing size from the inside to the outside; multiple medium circular air holes are distributed in the outermost layer of the multi-layer polygonal air hole ring.

[0027] Multiple small circular air holes are arranged in a regular hexagonal array. The distance between the centers of two adjacent small circular air holes and two adjacent medium circular air holes is a fixed pitch, and the distance between the centers of the two large circular air holes is twice the pitch. The centers of the two large circular air holes are on the same horizontal line as the centers of the small circular air holes on their left and right. The regular hexagon formed by the medium circular air holes in the outermost layer does not have the medium circular air holes at the six corners of the regular hexagon. The diameter d1 of the two large circular air holes is 5.5um ± 0.5um, and the diameter d2 of the multiple medium circular air holes is 3.2um ± 0.5um. The diameter of the multiple small circular air holes d3 is 2.2um ± 0.5um. The distance L between the medium circular air holes is 4.4um ± 0.5um.

[0028] The size of the small circular air hole d3 and the medium pitch L determine the single-mode properties and low confinement loss of the single-polarization photonic crystal fiber of this embodiment. The design of the large circular air hole d1 determines the fiber's polarization-maintaining properties, which affects both the single-polarization effect and its single-polarization performance during bending. The size of the medium circular air hole d2 determines the low bend-confinement loss of the fiber of this embodiment. When d1, d2, and d3 are within the parameter range of this embodiment, good single-polarization performance can be achieved within a bending diameter range of 5 mm to 30 mm.

[0029] The single polarization in the bent state of this embodiment can be obtained by Figure 2 As is known, the limiting losses in the fast and slow axes can vary by several orders of magnitude at different bend diameters. In this embodiment, only one layer of circular air holes is provided. While enabling the fiber to achieve bend-resistant single polarization through parameter design, this greatly simplifies the structure and reduces the difficulty of the manufacturing process. The parameter control technology for multiple holes is relatively mature, resulting in a high production yield. Other single-polarization photonic crystal fiber structures, such as elliptical air holes, triangular air holes, and multiple nanoscale air holes, are currently difficult to achieve with current technology.

[0030] The arrangement structure of the circular air holes in this embodiment is applicable to single-polarization photonic crystal fibers with a cross-sectional diameter D of 40 um, 60 um, 80 um, or 125 um.

[0031] The single-polarization photonic crystal fiber of the present invention has multiple circular air holes formed axially through the single-polarization photonic crystal fiber. The multiple circular air holes include two large circular air holes, multiple small circular air holes, and multiple medium circular air holes. The single-polarization photonic crystal fiber has a circular cross-section. In the cross-section, the two large circular air holes are symmetrically distributed about the center of the cross-section. The multiple small circular air holes are arranged around the two large circular air holes, forming a multi-layer polygonal air hole ring with increasing size from the inside out. The multiple medium circular air holes are distributed in the outermost layer of the multi-layer polygonal air hole ring. The multi-layer polygonal air hole ring is arranged according to a regular hexagonal array. The distance between the centers of two adjacent small circular air holes and two adjacent medium circular air holes is a fixed pitch, and the distance between the centers of the two large circular air holes is twice the distance between the centers of the medium holes. The present invention can achieve single polarization by simply adjusting the position and size of the circular air holes, resulting in a simple structure. In addition, by designing the size of the air holes, it can achieve strong bending resistance.

[0032] In the above description of this specification, unless otherwise expressly specified or limited, terms such as "fixed," "mounted," "connected," or "connected" should be understood broadly. For example, the term "connected" can refer to a fixed connection, a removable connection, or an integral connection; a mechanical connection or an electrical connection; a direct connection or an indirect connection through an intermediate medium; or the internal connection between two elements or the interaction between two elements. Therefore, unless otherwise expressly defined in this specification, those skilled in the art can understand the specific meanings of the above terms in this application based on the specific circumstances.

[0033] According to the above description of this specification, those skilled in the art can also understand the terms used below, such as "upper", "lower", "front", "back", "left", "right", "length", "width", "thickness", "vertical", "horizontal", "top", "bottom"

[0034] Terms indicating orientation or positional relationships, such as "inside", "outside", "axial", "radial", "circumferential", "center", "longitudinal", "lateral", "clockwise" or "counterclockwise", are based on the orientation or positional relationships shown in the drawings of this specification. They are only for the purpose of facilitating the explanation of the scheme of this application and simplifying the description, and do not explicitly or implicitly indicate that the devices or elements involved must have the specific orientation, be constructed and operate in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms cannot be understood or interpreted as limitations on the scheme of this application.

[0035] In addition, the terms "first" or "second" used in this specification to refer to numbers or ordinal numbers are used for descriptive purposes only and should not be understood as explicitly or implicitly indicating relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of this specification, "plurality" means at least two, such as two, three or more, etc., unless otherwise clearly specified.

[0036] Although this specification has shown and described a plurality of embodiments of the present application, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Those skilled in the art will think of many changes, modifications and alternatives without departing from the thought and spirit of the present application. It should be understood that in the process of practicing the present application, various alternatives to the embodiments of the present application described herein may be adopted. The appended claims are intended to define the scope of protection of the present application and therefore cover modular compositions, equivalents or alternatives within the scope of these claims.

Claims

1. A single-polarization photonic crystal fiber, characterized in that: When the single-polarization photonic crystal fiber is bent, the fast-axis light is coupled out of the fiber core and cut off, while the slow-axis light continues to propagate in the fiber core in the form of a guided mode. The bending diameter of the single-polarization photonic crystal fiber ranges from 5 mm to 30 mm. The single-polarization photonic crystal fiber is formed with a plurality of circular air holes axially penetrating the single-polarization photonic crystal fiber. The plurality of circular air holes include two large circular air holes, a plurality of small circular air holes, and a plurality of medium circular air holes. The cross section of the single-polarization photonic crystal fiber is circular. On the cross section, the two large circular air holes are symmetrically distributed around the center of the cross section. The multiple small circular air holes are arranged around the two large circular air holes to form a multi-layer polygonal air hole ring with increasing size from the inside to the outside. The multiple medium circular air holes are distributed in the outermost layer of the multi-layer polygonal air hole ring formed by the small circular air holes. The outermost layer of the medium circular air holes forms a regular hexagon, and the medium circular air holes are not provided at the six corners of the regular hexagon. The plurality of small circular air holes are arranged in a regular hexagonal array, the distance between the centers of two adjacent small circular air holes is a fixed pitch, the distance between the centers of two adjacent medium circular air holes is also the same pitch, and the distance between the centers of the two large circular air holes is twice the pitch; The diameters of the two large circular air holes are both 5.5um±0.5um; the diameters of the multiple medium circular air holes are both 3.2um±0.5um; and the diameters of the multiple small circular air holes are both 2.2um±0.5um.

2. The single-polarization photonic crystal fiber according to claim 1, characterized in that The hole pitch is 4.4um±0.5um.

3. The single-polarization photonic crystal fiber according to claim 1, characterized in that The diameter of the cross section of the single-polarization photonic crystal fiber is 40um, 60um, 80um or 125um.

4. The single-polarization photonic crystal fiber according to claim 1, wherein: The plurality of medium circular air holes are located at the outermost layer of the polygonal air hole ring.

5. The single-polarization photonic crystal fiber according to claim 1, characterized in that: The single-polarization photonic crystal fiber is made of pure quartz material.

6. The single-polarization photonic crystal fiber according to claim 1, characterized in that: The centers of the two large circular air holes are on the same horizontal line as the centers of the small circular air holes on their left and right.

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