A hybrid S+C+L band optical fiber with single polarization and single-mode hollow core.

Abstract

This invention discloses a (S+C+L) band hybrid light-guiding type single-polarization single-mode hollow-core optical fiber, belonging to the field of optical fiber technology. It includes an outer sheath tube, eight cladding tubes with identical inner diameters and thicknesses, uniformly arranged around the center of the outer sheath tube and tightly attached to its inner side, a pair of negative curvature arc layers with identical radii of curvature and thicknesses, symmetrically distributed along the x and y axes, and a central region of the fiber. The two symmetrical negative curvature arc layers in this invention achieve single-polarization transmission of the y-polarized fundamental mode through a hybrid light-guiding mechanism of anti-resonance and total internal reflection. The eight cladding tubes regulate the transmission loss of other higher-order modes through an anti-resonance light-guiding mechanism, achieving single-mode transmission of the optical fiber. This invention exhibits excellent high birefringence and single-polarization single-mode characteristics in the (S+C+L) band, and the loss of different modes can be effectively controlled by adjusting the light-guiding capabilities of different light-guiding mechanisms.

Description

Technical Field

[0001] This invention relates to the field of microstructure optical fiber technology, and in particular to a (S+C+L) band hybrid light-guiding single-polarization single-mode hollow core optical fiber. Background Technology

[0002] In many fiber optic applications, maintaining extremely high stability of the beam polarization state is required, such as in fiber optic communication systems, fiber lasers, fiber coherent systems, and fiber optic gyroscopes. One solution is to use single-polarization single-mode fiber. This type of fiber can suppress the loss of the fundamental mode in a certain polarization direction, while allowing other modes to have very high losses. After transmission over a finite distance, these high-loss modes are filtered out, retaining only one fundamental mode, thus ensuring that the beam in the fiber always maintains a highly stable polarization state.

[0003] When designing single-polarization single-mode optical fibers, they can be categorized into refractive index total internal reflection type, photonic bandgap type, and anti-resonant type based on their light guiding mechanism. Each type of single-polarization single-mode microstructure fiber has its own advantages and significant drawbacks. For example, photonic bandgap type microstructure fibers can be used as hollow-core fibers to achieve single-polarization single-mode characteristics, but their structure is very complex, their bandwidth is narrow, and their fabrication process is very demanding. Refractive index total internal reflection type microstructure fibers can achieve high-performance birefringence and single-polarization single-mode characteristics, and are often designed as complex asymmetric or defective air-hole arrays. This structure poses a serious challenge to fiber drawing, and the fiber core is solid. Anti-resonant type microstructure fibers can be used as hollow-core fibers to achieve single-polarization single-mode characteristics, and their simple structure makes them easy to fabricate; however, it is difficult to achieve high birefringence in this type of fiber, and its single-polarization single-mode characteristics are limited.

[0004] To balance the advantages and disadvantages of various microstructure optical fibers, hybrid light guiding mechanism optical fibers have become a research hotspot. For example, Chinese patent with publication number "CN102279439A" discloses a hybrid light guiding single-polarization single-mode photonic crystal fiber with refractive index total internal reflection and photonic bandgap. However, this fiber is a solid fiber and does not have the advantages of hollow fiber. Moreover, the fiber has a narrow bandwidth in the communication band and a complex structure. In particular, maintaining the fiber bandgap requires high process requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a hybrid light-guiding single-polarization single-mode hollow fiber operating in the (S+C+L) band, in order to solve the problem that the structure and performance of current single-polarization single-mode fibers based on a single light-guiding mechanism cannot be balanced, improve the controllability of transmission loss of different modes of the fiber, improve birefringence and single-polarization single-mode performance, and reduce manufacturing process requirements.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention includes:

[0008] Outer sheath round tube;

[0009] A pair of negative curvature circular arc layers, the radius of curvature and thickness of the pair of negative curvature circular arc layers are exactly the same and they are symmetrically distributed along the x-axis and y-axis;

[0010] Eight cladding tubes, all with identical inner diameters and thicknesses, are evenly arranged around the center of the outer sheath tube and are tightly fitted to the inner side of the outer sheath tube; and

[0011] The central area of ​​the optical fiber.

[0012] Under the action of the refractive index total internal reflection and anti-resonance hybrid light guiding mechanism formed by the negative curvature arc layer, the light beam is highly constrained to form a transmission fundamental mode, in which the x-polarized fundamental mode has high confinement loss and the y-polarized fundamental mode has low confinement loss, enabling the optical fiber to achieve single polarization transmission characteristics.

[0013] Eight cladding tubes form an anti-resonant light guiding mechanism, allowing a large amount of high-order mode energy to leak into the cladding tubes, thus enabling the optical fiber to achieve single-mode transmission characteristics.

[0014] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0015] This invention utilizes a novel hybrid light guiding mechanism to achieve free control of the loss between different modes of optical fiber. It fully leverages the advantages of the refractive index total internal reflection light guiding mechanism in generating ultra-high birefringence and the anti-resonance mechanism in efficiently controlling the transmission loss of different modes. It can obtain excellent high birefringence and single polarization single-mode characteristics in the (S+C+L) band. It has the advantages of relatively simple structure, single material, convenient drawing, and high manufacturing efficiency. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the cross-section of the (S+C+L) band hybrid light-guiding single-polarization single-mode hollow fiber disclosed in an embodiment of the present invention.

[0017] Figure 2 for Figure 1 The publicly available electric field intensity distribution diagrams for different modes of (S+C+L) band hybrid optical guide single-polarization single-mode hollow-core fiber at a wavelength of 1550 nm when the light is tangent to two negative curvature circular arc layers are shown. Figure 2 (a), (b), (c) and (d) represent the x-polarized fundamental mode, the y-polarized fundamental mode, the LP11 higher-order mode, and the LP12 higher-order mode, respectively.

[0018] Figure 3 for Figure 1 A schematic diagram of the effective refractive index of different modes in a (S+C+L) band hybrid light-guiding single-polarization single-mode hollow fiber when two negative curvature circular arc layers are tangent.

[0019] Figure 4 for Figure 1 A schematic diagram illustrating the confinement loss of different modes in a (S+C+L) band hybrid light-guiding single-polarization single-mode hollow fiber when two negative curvature circular arc layers are tangent.

[0020] Figure 5 for Figure 1 A schematic diagram showing the polarization mode loss ratio and higher-order mode loss ratio of a (S+C+L) band hybrid light-guiding single-polarization single-mode hollow fiber when two negative curvature circular arc layers are tangent.

[0021] Reference numerals: 1. Outer sheath tube; 2. Negative curvature arc layer; 3. Cladding tube; 4. Central region of optical fiber. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] An embodiment of the present invention is disclosed as follows: Figure 1 As shown, the structure includes: an outer sheath tube 1, a pair of negative curvature arc layers 2 with identical radii of curvature and thickness, symmetrically distributed along the x and y axes, eight cladding tubes 3 with identical inner diameters and thicknesses, uniformly arranged around the center of the outer sheath tube and tightly attached to the inner side of the outer sheath tube, and an optical fiber central region 4. Let the curvature of the negative curvature arc layers be R, the thickness be t2, the separation distance between them along the x-axis be H, the outer diameter of the cladding tubes be d, the thickness be t1, and the diameter of the optical fiber central region be D.

[0024] In one embodiment, the outer diameter d of the optical fiber cladding tube ranges from 11.0 to 16.0 μm, and the thickness t1 ranges from 0.20 to 0.24 μm, or 0.79 to 1.01 μm, or 1.56 to 1.72 μm. Furthermore, all eight cladding tubes are uniformly inscribed within the outer sheath tube.

[0025] In one embodiment, two negative curvature arc layers are grafted onto two cladding tubes, with a cladding tube spaced apart between the two cladding tubes. The two negative curvature arc layers can be tangent, with the tangency point located at the geometric center of the optical fiber, or they can be separated along the x-axis. The radius of curvature R of the optical fiber's negative curvature arc layers ranges from 12.0 to 22.0 μm, the thickness t2 ranges from 0.83 to 0.86 μm, and the separation distance H along the x-axis ranges from 0 to 0.55 μm.

[0026] In one embodiment, the thickness of the outer sheath tube of the optical fiber is set to be greater than 10 μm, and the base material of the outer sheath tube, the eight cladding tubes and the pair of negative curvature arc layers are all pure quartz glass, with the remaining internal space filled with air.

[0027] In one embodiment, the diameter of the central region of the optical fiber ranges from 24.0 to 30.0 μm.

[0028] The above describes the structure and parameters of the optical fiber. The working principle of the optical fiber will be explained below.

[0029] A pair of negative curvature arc layers symmetrical along the x-axis and y-axis form an anti-resonant layer, which forms the fundamental mode through an anti-resonant light guiding mechanism. Since the distance between these two negative curvature arc layers is very close, they can be equivalent to a solid quartz core. The light beam is highly constrained under the action of the refractive index total internal reflection and anti-resonant hybrid light guiding mechanism formed by the two negative curvature arc layers, forming the transmission fundamental mode. The fundamental mode is also affected by the refractive index total internal reflection light guiding mechanism, resulting in high birefringence characteristics of the two polarization modes. The x-polarized fundamental mode has a very high confinement loss, while the y-polarized fundamental mode has a lower confinement loss, enabling the optical fiber to achieve single polarization transmission characteristics.

[0030] The cladding tube also has an anti-resonance optical confinement mechanism. By setting reasonable parameters, the loss of the y-polarized fundamental mode can be effectively suppressed, while allowing a large amount of higher-order energy to leak into the cladding tube, increasing the loss of higher-order modes and realizing single-mode transmission.

[0031] Therefore, the optical fiber proposed in this embodiment adopts a single refractive index total internal reflection light guiding mechanism and a double anti-resonance light guiding mechanism to achieve free control of the transmission loss of different modes of the optical fiber, so as to obtain the high birefringence characteristics that cannot be achieved by the current pure anti-resonance light guiding mechanism optical fiber, improve the single polarization single-mode performance, and reduce the manufacturing process requirements.

[0032] The following describes a specific embodiment. In this embodiment, the structural parameters of the optical fiber are assumed to be D = 25.2 μm, R = 19 μm, d = 14 μm, t1 = 1.64 μm, t2 = 0.84 μm, and H = 0 μm, that is, the negative curvature arc layers are externally tangent to each other along the x-axis.

[0033] like Figure 2 As shown, when the operating wavelength is 1550 nm, the electric field energy of the y-polarized fundamental mode is well confined within the fiber core, while a significant amount of electric field energy in other modes leaks along the glass tube into the cladding. The confinement loss of the y-polarized fundamental mode is 6.86 × 10⁻⁶. -4 dB / m, while the confinement losses of the x-polarized fundamental mode, higher-order modes LP11 and LP12 are 4836.19 dB / m, 268.68 dB / m and 307.26 dB / m, respectively.

[0034] like Figure 3As shown, the operating wavelength range is 1450–1650 nm, and there is a large effective refractive index difference between the x-polarized fundamental mode and the y-polarized fundamental mode, with birefringence as high as 10. -2 The birefringence is on the order of magnitude of 0.0196 when the working wavelength is 1550nm.

[0035] Figure 4 As shown, when the working wavelength range is 1450-1700nm, the confinement loss variation curves between different modes show that within the set wavelength range, the optical fiber only has low confinement loss for the y-polarized base mode. Other modes cannot be effectively transmitted in this optical fiber due to the extremely high confinement loss, thus exhibiting the characteristics of single polarization and single mode.

[0036] The ratio between the transmission polarization mode loss of an optical fiber and the minimum loss of the cut-off polarization mode and the cut-off higher-order mode is an important performance parameter for evaluating the single-polarization single-mode characteristics of the fiber. When the ratio is greater than 100, it indicates that the fiber has single-polarization single-mode characteristics, and the larger the ratio, the better the single-polarization single-mode characteristics. Figure 5 As shown, the optical fiber maintains excellent single-polarization, single-mode characteristics in the wavelength range of 1481–1662 nm, and the polarization mode loss ratio is as high as 7.05 × 10⁻⁶ when the operating wavelength is 1550 nm. 6 The high-order mode loss ratio is as high as 3.92×10. 5 Furthermore, it maintains single polarization characteristics over a longer range in the short wavelength direction.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hybrid S+C+L band optical fiber for single-polarization, single-mode hollow core, characterized in that, include: Outer sheath round tube (1); A pair of negative curvature circular arc layers (2), the curvature radius and thickness of the pair of negative curvature circular arc layers (2) are exactly the same and are symmetrically distributed along the x-axis and y-axis; Eight cladding tubes (3) have the same inner diameter and thickness and are evenly arranged around the center of the outer sheath tube (1) and are closely attached to the inner side of the outer sheath tube (1); as well as Fiber optic central region (4); Under the action of the refractive index total internal reflection and anti-resonance hybrid light guiding mechanism formed by the negative curvature arc layer (2), the light beam is highly constrained to form a transmission fundamental mode, in which the x-polarized fundamental mode has high confinement loss and the y-polarized fundamental mode has low confinement loss, enabling the optical fiber to achieve single polarization transmission characteristics. The negative curvature arc layer (2) is grafted onto the two cladding round tubes (3), with a cladding round tube spaced between the two cladding round tubes; The eight cladding tubes (3) constitute an anti-resonance light guiding mechanism, and a large amount of high-order mode energy leaks into the cladding tubes (3), enabling the optical fiber to achieve single-mode transmission characteristics.

2. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to claim 1, characterized in that, The shortest distance between the two negative curvature circular arc layers in the x-axis direction is H, where 0.00μm≤H≤0.55μm.

3. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to claim 1, characterized in that, The outer sheath tube, the negative curvature arc layer, and the cladding tube are all made of pure quartz, while other areas are filled with air.

4. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to claim 1 or 2, characterized in that, The radius of curvature of the negative curvature arc layer is R, 12.0μm≤R≤22.0μm, and the thickness of the negative curvature arc layer is t2, 0.83μm≤t2≤0.86μm.

5. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to any one of claims 1 to 3, characterized in that, The outer diameter of the cladding tube is d, 11.0μm≤d≤16.0μm, and the thickness of the cladding tube is t1, 0.79μm≤t1≤1.01μm. All eight cladding tubes are uniformly tangent to the outer sheath tube.

6. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to claim 1, characterized in that, The diameter of the central region of the optical fiber is D, where 24.0 μm ≤ D ≤ 30.0 μm.

7. The S+C+L band hybrid light-guiding single-polarization single-mode hollow-core optical fiber according to claim 1, characterized in that, The outer sheath tube has a thickness greater than 10 μm.

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