An optical fiber polarization beam splitter

Abstract

An embodiment of the present application provides an optical fiber polarization beam splitter, which relates to the technical field of optical fiber devices. The cross-section of the optical fiber polarization beam splitter along the radial direction is circular. The optical fiber polarization beam splitter includes: a core, an elliptical structure, and six cladding structures; the cross-section of the elliptical structure along the radial direction is an elliptical ring; on the radial cross-section, the center of the elliptical ring coincides with the center of the optical fiber polarization beam splitter; the core includes a first core and a second core; on the radial cross-section, the first core and the second core are arranged on both sides of the major axis of the elliptical ring, and the first core and the second core are centrosymmetric about the center of the elliptical ring; on the radial cross-section, the six cladding structures are arranged around the elliptical structure in the circumferential direction. The optical fiber polarization beam splitter of the present application realizes optical fiber performances such as polarization maintenance, polarization beam splitting, and single-mode output by introducing the elliptical structure and the cladding structure, and can better meet the requirements for the performance and stability of optical fiber devices.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber devices, and in particular to an optical fiber polarization beam splitter. Background Art

[0002] Fiber Polarization Beam Splitter (FPBS) is a fiber device that can separate the input optical signal into two mutually perpendicular polarization directions according to its polarization state and output them, or it can also be used to combine two optical signals with different polarization states into one output optical fiber. It has a wide range of applications in optical fiber communication systems, optical measurement, laser development, and optical fiber sensing technology. According to the different principles of polarization beam splitting, it can be divided into several types, such as birefringent crystal splitting type, waveguide coupled splitting type, polarization selective reflection type, and integrated optical device type. Among them, the waveguide coupled splitting type realizes the separation of polarization states through fused taper or waveguide design. It has attracted much attention due to its small size and flexible structural design, and is very suitable for the establishment of all-fiber communication and transmission systems. At present, most of the waveguide coupled splitting type optical fiber polarization beam splitters are designed based on ordinary communication optical fiber or photonic crystal fiber. Its scope of application is limited to the traditional scenario of splicing with ordinary communication optical fiber, and it is not suitable for the scenario of splicing with hollow core or all-solid core anti-resonant optical fiber. Hollow-core antiresonant fiber has attracted more and more attention because the light is confined in the air core, and has the characteristics of high fiber damage threshold and low transmission loss. It has become the most likely choice for the backbone fiber of the next generation of communication systems, and its applicable scenarios and scope of use will become larger and larger. Fully solid-core antiresonant fiber is an improvement and development of hollow-core antiresonant fiber. The introduction of low-refractive-index fiber materials in the fiber core is more conducive to the design and performance improvement of the fiber beam splitter structure. Its transmission loss is lower than that of traditional solid-core fiber, and its performance is better and easier to design. As a hot spot in the current research field of optical fibers, antiresonant fiber has attracted much attention and made breakthrough progress, but the research in the field of design of its supporting photonic devices has just started, which greatly limits the development and application of antiresonant fiber. It is urgent to study and design antiresonant fiber-type photonic devices, and the research and design of this type of polarization beam splitter is particularly urgent. In addition, the mid-infrared band is of great significance for applications in the fields of communication, medical treatment, and sensing. This not only reflects the advantages of the light in this band itself, but also contributes to the necessity of seizing technological dominance and establishing first-mover advantages. Therefore, the development of fiber photonic devices in this band is of great significance and urgency. Summary of the invention

[0003] The purpose of the embodiment of the present application is to provide a fiber polarization beam splitter, which adopts a fully solid-state anti-resonance design, which is of great significance for meeting the needs of industry development, developing fiber beam splitter technology, and improving polarization beam splitting and single-mode output characteristics. The specific technical solution is as follows:

[0004] This application provides an optical fiber polarization beam splitter. The cross-section of the optical fiber polarization beam splitter along the radial direction is circular.

[0005] The optical fiber polarization beam splitter includes: a core, an elliptical structure, and six cladding structures.

[0006] The cross-section of the elliptical structure along the radial direction is an elliptical ring; on the radial cross-section, the center of the elliptical ring coincides with the center of the optical fiber polarization beam splitter.

[0007] The core includes core one and core two; on the radial cross-section, core one and core two are arranged on both sides of the major axis of the elliptical ring, and core one and core two are centrosymmetric about the center of the elliptical ring.

[0008] On the radial cross-section, the six cladding structures are arranged around the elliptical structure in the circumferential direction.

[0009] In a possible implementation manner, each of the six cladding structures includes a cladding tube and an inserted tube.

[0010] The inserted tube is concentrically nested in the cladding tube; the cross-sections of the inserted tube and the cladding tube are both circular rings.

[0011] In a possible implementation manner, the six cladding structures include four cladding ones and two cladding twos.

[0012] On the radial cross-section, the four cladding ones are centrosymmetric about the center of the elliptical ring, and the distance from the common center of each cladding one to the major axis of the elliptical ring is the same.

[0013] On the radial cross-section, the line connecting the centers of the two cladding twos is perpendicular to the major axis of the elliptical ring, and the distance from the common center of each cladding two to the center of the elliptical ring is the same.

[0014] In a possible implementation manner, the diameter of the cross-section of the optical fiber polarization beam splitter along the radial direction is 100 μm.

[0015] In a possible implementation manner, the wall thickness of the elliptical ring is 0.5 μm, the semi-major axis of the inner ellipse is 18 μm, and the semi-minor axis is 1 μm.

[0016] In a possible implementation manner, the wall thickness of the cladding tube is 0.5 μm, and the inner circle radius is 11.6 μm;

[0017] The wall thickness of the inserted tube is 0.5 μm, and the inner circle radius is 0.3 μm.

[0018] In a possible implementation, the distance from the common center of each first cladding layer to the major axis of the elliptical ring is the same, which is 15 μm, and the distance from the common center of each first cladding layer to the minor axis of the elliptical ring is the same, which is 20 μm;

[0019] The distance from the common center of each second cladding layer to the center of the elliptical ring is 30 μm.

[0020] In a possible implementation, the elliptical structure is an elliptical tube, and the materials of the elliptical tube, the cladding tube and the embedded tube are all chalcogenide glass As2Se3.

[0021] In a possible implementation, the length of the fiber polarization beam splitter is 5 cm.

[0022] In a possible implementation, the wavelength of the incident light of the fiber polarization beam splitter is 2.955 μm to 3.045 μm.

[0023] Advantages of the embodiments of the present application:

[0024] The embodiments of the present application provide a fiber polarization beam splitter. The cross-section of the fiber polarization beam splitter along the radial direction is circular. The fiber polarization beam splitter includes: a core, an elliptical structure and six cladding structures; the cross-section of the elliptical structure along the radial direction is an elliptical ring; in the radial cross-section, the center of the elliptical ring coincides with the center of the fiber polarization beam splitter; the core includes a first core and a second core; in the radial cross-section, the first core and the second core are arranged on both sides of the major axis of the elliptical ring, and the first core and the second core are centrosymmetric about the center of the elliptical ring; in the radial cross-section, the six cladding structures are arranged around the elliptical structure in the circumferential direction. The fiber polarization beam splitter provided by the present application can achieve fiber performance such as polarization maintaining, polarization beam splitting and single-mode output by introducing the elliptical structure and the cladding structure, and can better meet the requirements for the performance and stability of fiber devices in practical applications. At the same time, the structural design of the all-solid anti-resonant fiber is not only more flexible, but also conducive to the development of different types of fiber devices. The fiber polarization beam splitter provided by the present application realizes the polarization beam splitting of light in the 3-μm band through the innovative design of the fiber structure. It is applicable to the connection and function realization of all current types of fibers such as ordinary communication fibers, photonic crystal fibers, hollow anti-resonant fibers and improved all-solid core anti-resonant fibers. It is the development and improvement of the existing beam splitter design technology and is of great significance for helping to build the closed-loop of the next-generation hollow fiber-based communication system.

[0025] Of course, it is not necessary for any product or method implementing the present application to achieve all the above advantages simultaneously. Description of the Drawings

[0026] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic structural diagram of an optical fiber polarization beam splitter provided by an embodiment of the present application;

[0028] Figure 2 It is a relationship curve diagram of the normalized output power of the first core and the second core of the optical fiber polarization beam splitter proposed by the present application changing with the propagation length;

[0029] Figure 3 It is a relationship curve diagram of the polarization extinction ratio of the optical fiber polarization beam splitter proposed by the present application changing with the propagation length;

[0030] Figure 4 It is a relationship curve diagram of the polarization extinction ratio of the optical fiber polarization beam splitter proposed by the present application changing with the wavelength at a fiber length of 5 cm;

[0031] Figure 5 It is a schematic diagram of a relationship curve of the high-order mode extinction ratio of the optical fiber polarization beam splitter proposed by the present application changing with the wavelength at a fiber length of 5 cm. Detailed implementation manners

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art based on the present application belong to the scope of protection of the present application.

[0033] First, the professional terms that may be used in the embodiments of the present application are explained:

[0034] An optical fiber, whose full name is optical fiber, is a medium that uses the principle of total internal reflection of light to transmit optical signals in a slender transparent fiber. An optical fiber mainly consists of a core, a cladding, and a coating layer. The core is the core part of the optical fiber, usually made of high-purity silica or other transparent materials, responsible for transmitting optical signals; the cladding tightly wraps around the outside of the core, and its refractive index is slightly lower than that of the core to ensure that the optical signal undergoes total internal reflection at the interface between the core and the cladding and does not leak to the outside; the coating layer is located on the outermost layer, mainly playing a role in protecting and enhancing the flexibility of the optical fiber to prevent the optical fiber from being damaged during bending or pulling.

[0035] Optical fiber polarization beam splitter, which is an optical device used to couple orthogonally linearly polarized light in one optical fiber into two optical fibers for output respectively, or to couple two orthogonally polarized light beams input from a polarization-maintaining fiber branch into a single-mode output optical fiber. Its working principle is to split the incident light beam so that the output light is output from two vibration directions perpendicular and parallel to the incident plane. The application scenarios of the optical fiber polarization beam splitter include: Polarization multiplexing / demultiplexing: In optical fiber communication, the polarization beam splitter is used to separate or combine optical signals with different polarization states to achieve information transmission and processing. In an optical amplifier, the polarization beam splitter can improve the extinction ratio and stability of the system. Optical fiber sensing: In optical fiber sensing applications, the polarization beam splitter is used to detect and measure various physical quantities such as temperature, strain, etc. Optical transmission: In long-distance optical transmission, the polarization beam splitter is used to improve the stability and reliability of the signal. The characteristics of the optical fiber polarization beam splitter include: Low insertion loss: The insertion loss is low, ensuring the integrity of the signal. High extinction ratio: It can effectively eliminate unwanted polarized light and improve the signal-to-noise ratio of the system. High stability and reliability: The structure is stable and can work reliably in various environments.

[0036] The infrared light band refers to electromagnetic waves with wavelengths between 0.7 micrometers and 25 micrometers, which can be further divided into near-infrared, mid-infrared, and far-infrared according to the wavelength range. Among them, mid-infrared light (wavelength range 2.5 micrometers to 5 micrometers) has important applications in spectroscopy, especially in the fields of material research, environmental monitoring, security detection, fire warning, etc. The mid-infrared band is located in the atmospheric absorption window, and the transmittance of most wavelengths is above 60%, which enables mid-infrared lasers to achieve long-distance transmission in the atmosphere and has important application value for remote sensing, detection, and other fields. The concentrated area of thermal radiation energy: At room temperature, blackbody radiation is mainly concentrated in the range of 4 micrometers to 20 micrometers, with the peak located near 10 micrometers. When the temperature rises, the energy of blackbody radiation gradually concentrates in the mid-infrared band, making the detection of blackbody radiation in the mid-infrared band an important technology.

[0037] A dual-core optical fiber refers to an optical fiber that contains two cores within the same cladding. Each core is an independent optical waveguide, equivalent to integrating two single-core optical fibers in one dual-core optical fiber. This type of optical fiber has a special refractive index distribution, breaking the refractive index distribution structure of conventional optical fibers and is commonly used as an optical transmission medium and for constructing new optical devices. Structure and characteristics: The transmission characteristics of a dual-core optical fiber not only depend on parameters such as the cladding refractive index, core refractive index, core radius, and the wavelength of the transmitted light, but also on the distance between the two cores. Changing the distance between the two cores affects the energy distribution between the two cores. In addition, the birefringence effect of a dual-core optical fiber also needs to be specifically analyzed as its waveguide structure does not have circular symmetry. Application scenarios of dual-core optical fibers include: High-speed data transmission between servers within a data center: In situations where multiple data channels need to be transmitted simultaneously, dual-core optical fiber jumpers can provide higher bandwidth and more stable transmission performance. Application scenarios requiring two-way communication: Dual-core optical fiber jumpers have advantages in saving space and reducing wiring complexity and are suitable for systems that require two-way communication.

[0038] An all-solid anti-resonant optical fiber is an optical fiber with an all-solid anti-resonant structure, combining the advantages of large mode field single-mode transmission and filtering characteristics. This optical fiber is prepared by a drilling-sleeving combined with high-temperature drawing technology, which can effectively suppress high-order modes and amplified spontaneous emission within a specific wavelength range, thereby improving the performance and application scope of the optical fiber. Characteristics and applications include: Large mode field single-mode transmission: The all-solid anti-resonant optical fiber has an extremely high high-order mode suppression ratio and is suitable for single-mode transmission systems, high-power fiber lasers, and amplifiers, etc. Filtering characteristics: By splicing an all-solid anti-resonant optical fiber in an amplifier, it can effectively suppress the amplified spontaneous emission of Yb 3+ ions (ytterbium ions). Preparation methods include: The all-solid anti-resonant optical fiber is prepared by a drilling-sleeving combined with high-temperature drawing technology. This technical route not only achieves low-cost and efficient preparation but can also further optimize the transmission band and filtering range of the optical fiber through thermal annealing treatment.

[0039] Chalcogenide glass is a glass material mainly composed of sulfides, selenides, and antimonides, and sometimes also includes oxides. It is an amorphous material formed by the combination of chalcogen elements (such as sulfur, selenium, tellurium) and other metal elements (such as gallium, germanium, etc.). Chalcogenide glass is black in color and has excellent mid- and far-infrared transmission performance, and is widely used in fields such as infrared night vision, infrared temperature measurement, and infrared thermal imaging. Composition and preparation method: The main components of chalcogenide glass include chalcogen elements such as sulfur, selenium, tellurium, and metal elements such as gallium, germanium, etc. Its preparation method usually adopts vacuum melting technology, melting high-purity raw materials at high temperature in a vacuum environment and quickly forming. This preparation method makes chalcogenide glass have excellent temperature-viscosity characteristics and is suitable for precision molding to produce optical components with complex surfaces. Chalcogenide glass has the following main characteristics: Optical properties: Chalcogenide glass has a high transmittance in the mid-wave and long-wave infrared bands, and the transmission band can cover three atmospheric windows of 1~3um, 3~5um, and 8~12um. Its far-infrared transmittance is greater than 64% (wavelength 8μm~12μm), and the transmittance can reach more than 95% after coating. The refractive index of chalcogenide glass is as high as 1.7-2.4, and the refractive index temperature coefficient is small, which is suitable for thermal defocus adjustment and chromatic aberration correction of infrared thermal imaging systems. Physical properties: Chalcogenide glass has a relatively high density (such as the density of IRG101 is 3.20g / cm³), and has good thermal stability and chemical stability, and can maintain image stability in the temperature range of -40℃~70℃. Processing method: Chalcogenide glass is produced by the melt quenching method, with high production efficiency, short cycle, and low cost. Its processing efficiency is more than 10 times higher than that of traditional diamond turning, and is suitable for mass production of optical components with complex surfaces. Chalcogenide glass is widely used in infrared optical systems, such as infrared night vision, infrared temperature measurement, and infrared thermal imaging. Due to its excellent performance and low-cost production method, chalcogenide glass has been widely used in the manufacture of infrared lenses, especially in fields such as security, automotive, and industrial vision.

[0040] In the prior art, mid-infrared fiber technology has important applications in the fields of mid-infrared laser generation and transmission, biomedical monitoring, environmental monitoring, etc. With the continuous development of technology, its application prospects will be even broader. Chalcogenide glass is a widely studied mid-infrared fiber material at present. Chalcogenide fibers perform excellently in supercontinuum generation, laser damage threshold control, and suppression of absorption loss and scattering loss. Hollow anti-resonant fibers are considered ideal mid-infrared fibers due to their advantages such as low loss and wide bandwidth. However, due to the viscosity-temperature characteristics of chalcogenide glass and the hollow structure of the fiber, it is challenging to fabricate high-quality chalcogenide hollow anti-resonant fibers. To construct a structurally stable anti-resonant fiber, considering the refractive index difference between chalcogenide glasses, two or more chalcogenide glasses can be selected as the fiber material to design all-solid anti-resonant fibers and fiber devices. A fiber polarization beam splitter is a fiber device that can separate an input optical signal into two optical signals with mutually perpendicular polarization directions according to its polarization state, and it has extensive applications in the fields of optical communication, laser, fiber sensing technology, etc. Currently, most of the fiber polarization beam splitters applied to the mid-infrared band are designed based on traditional solid-core communication fibers and photonic crystal fibers. The structural design of all-solid anti-resonant fibers is more flexible, which is beneficial to the development of different types of fiber devices. By introducing different cladding structures, fiber performances such as polarization maintenance, polarization beam splitting, and single-mode output can be achieved. At the same time, the all-solid fiber structure can better meet the requirements for the performance and stability of fiber devices in practical applications. From the perspective of practical applications, there is an urgent need to develop high-performance mid-infrared all-solid anti-resonant fibers and fiber devices to promote the development of mid-infrared all-solid anti-resonant fibers and related technologies. Therefore, the present application provides a mid-infrared dual-core all-solid anti-resonant fiber polarization beam splitter, and provides new ideas for the development of mid-infrared all-solid anti-resonant fibers and their devices.

[0041] The present application provides a fiber polarization beam splitter, which can be referred to Figure 1 , Figure 1 is a schematic structural diagram of a fiber polarization beam splitter provided by an embodiment of the present application. The reference numerals in the figure are as follows:

[0042] 1 - Core one; 2 - Core two; 3 - Elliptical tube; 4 - Cladding one; 5 - Cladding two; 6 - Insertion tube; 7 - Cladding tube.

[0043] Refer to Figure 1 , the cross-section of the fiber polarization beam splitter along the radial direction is circular;

[0044] The fiber polarization beam splitter includes: a core, an elliptical structure, and six cladding structures;

[0045] The cross-section of the elliptical structure along the radial direction is an elliptical ring; on the radial cross-section, the center of the elliptical ring coincides with the center of the fiber polarization beam splitter;

[0046] The core includes core one 1 and core two 2; in the radial cross-section, core one 1 and core two 2 are arranged on both sides of the major axis of the elliptical ring, and core one 1 and core two 2 are centrosymmetric about the center of the elliptical ring;

[0047] In the radial cross-section, the six cladding structures are arranged around the elliptical structure in the circumferential direction.

[0048] Among them, the fiber polarization beam splitter in the embodiments of the present application includes: a core. The fiber polarization beam splitter is an optical fiber device that can separate an input optical signal into two optical signals with mutually perpendicular polarization directions according to its polarization state. Specifically, the optical fiber device can be a mid-infrared optical fiber device and is applied to the mid-infrared band. Among them, mid-infrared optical fiber technology has important applications in the generation and transmission of mid-infrared lasers, biomedical monitoring, environmental monitoring, etc., and with the continuous development of technology, its application prospects will be broader.

[0049] Among them, the fiber polarization beam splitter in the embodiments of the present application further includes: an elliptical structure. The cross-section of the elliptical structure along the radial direction is an elliptical ring. In the radial cross-section, the center of the elliptical ring coincides with the center of the fiber polarization beam splitter. The center of the elliptical ring refers to the intersection point of the major axis and the minor axis of the elliptical ring. In the actual use process, the elliptical structure is an elliptical tube. The fiber polarization beam splitter provided by the present application constructs a symmetric dual-core optical fiber structure by introducing an elliptical structure. The dual-core means that the core includes core one 1 and core two 2. In the radial cross-section, core one 1 and core two 2 are arranged on both sides of the major axis of the elliptical ring, and core one 1 and core two 2 are centrosymmetric about the center of the elliptical ring. When light propagates in the optical fiber, two supermodes with the same polarization direction will undergo mode coupling, and the polarization beam splitting performance can be achieved by adjusting the ratio of the coupling lengths.

[0050] The fiber polarization beam splitter further includes six cladding structures. The fiber polarization beam splitter in the embodiments of the present application can form a hollow anti-resonant optical fiber by introducing an elliptical structure and a cladding structure. The hollow anti-resonant optical fiber is considered to be an ideal mid-infrared optical fiber due to its advantages such as low loss and wide bandwidth.

[0051] The fiber polarization beam splitter provided by the embodiments of the present application can be applied to the mid-infrared band. From the perspective of practical applications, the development of high-performance mid-infrared all-solid anti-resonant optical fibers and optical fiber devices can promote the development of mid-infrared all-solid anti-resonant optical fibers and related technologies. And the mid-infrared dual-core all-solid anti-resonant fiber polarization beam splitter provided by the present application can provide new ideas for the development of mid-infrared all-solid anti-resonant optical fibers and their devices.

[0052] It can be seen that the fiber optic polarization beam splitter provided by the present application can achieve fiber optic performance such as polarization maintenance, polarization beam splitting, and single-mode output by introducing an elliptical structure and a cladding structure, better meeting the requirements for the performance and stability of fiber optic devices in practical applications.

[0053] In a possible implementation manner, the six cladding structures each include a cladding tube 7 and an insert tube 6; the insert tube 6 is concentrically nested in the cladding tube 7; the cross-sections of the insert tube 6 and the cladding tube 7 are both circular rings.

[0054] In a possible implementation manner, the six cladding structures include four first claddings 4 and two second claddings 5; in the radial cross-section, the four first claddings 4 are centrosymmetric about the center of the elliptical ring, and the distance from the common center of each first cladding 4 to the major axis of the elliptical ring is the same; in the radial cross-section, the line connecting the centers of the two second claddings 5 is perpendicular to the major axis of the elliptical ring, and the distance from the common center of each second cladding 5 to the center of the elliptical ring is the same.

[0055] Specifically, reference can be made to Figure 1 , Figure 1 which is a schematic structural diagram of the fiber optic polarization beam splitter provided by the embodiment of the present application, including a first core 1, a second core 2, an elliptical structure, and a cladding structure; the first core 1 and the second core 2 are centrosymmetric about the fiber center; the elliptical structure is an elliptical tube 3 with an elliptical ring cross-section; the elliptical tube 3 is located at the fiber center and is between the first core 1 and the second core 2; the major axis of the elliptical tube 3 is perpendicular to the line connecting the first core 1 and the second core 2; the cladding structure includes the first cladding 4 and the second cladding 5, with a total of six double-layer cladding tubes; the double-layer cladding tubes are exactly the same in size and shape, and each is composed of an insert tube 6 and a cladding tube 7; the insert tube 6 is concentrically nested in the cladding tube 7; the cross-sections of the insert tube 6 and the cladding tube 7 are both circular rings; the first cladding 4 includes four double-layer cladding tubes, and the four double-layer cladding tubes of the first cladding 4 are arranged circumferentially about the fiber center, and the perpendicular distance from the centers of the four double-layer cladding tubes to the major axis of the elliptical tube 3 is the same; the second cladding 5 includes two double-layer cladding tubes, and the two double-layer cladding tubes of the second cladding 5 are centrosymmetric about the fiber center, and the line connecting the centers of the two double-layer cladding tubes is perpendicular to the major axis of the elliptical tube 3.

[0056] The fiber optic polarization beam splitter provided by the present application introduces regularly arranged concentrically nested double-layer cladding tubes to form the cladding structure of the fiber optic. This design of concentrically nested double-layer cladding tubes can achieve the single-mode characteristic of the fiber optic while reducing the fiber optic loss.

[0057] During the actual use process, the structure of the fiber optic polarization beam splitter provided by the embodiment of the present application can be referred to the following embodiments.

[0058] In a possible implementation manner, the diameter of the radial cross-section of the fiber optic polarization beam splitter is 100 μm.

[0059] In a possible implementation, the wall thickness of the elliptical ring is 0.5 μm, the semi-major axis of the inner ellipse is 18 μm, and the semi-minor axis is 1 μm.

[0060] In a possible implementation, the wall thickness of the cladding tube 7 is 0.5 μm, and the inner circle radius is 11.6 μm; the wall thickness of the insert tube 6 is 0.5 μm, and the inner circle radius is 0.3 μm.

[0061] In a possible implementation, the distance from the common center of each cladding layer 4 to the major axis of the elliptical ring is the same, all being 15 μm, and the distance to the minor axis of the elliptical ring is the same, all being 20 μm; the distance from the common center of each cladding layer 5 to the center of the elliptical ring is all 30 μm.

[0062] In a possible implementation, the elliptical structure is an elliptical tube 3, and the materials of the elliptical tube 3, the cladding tube 7, and the insert tube 6 are all chalcogenide glass As2Se3.

[0063] Among them, chalcogenide glass is a mid-infrared optical fiber material that has been widely studied at present. Chalcogenide optical fibers perform excellently in supercontinuum generation, laser damage threshold control, and suppression of absorption loss and scattering loss. However, due to the viscosity-temperature characteristics of chalcogenide glass and the hollow core structure of the optical fiber, it is challenging to fabricate high-quality chalcogenide hollow anti-resonant optical fibers. To construct a structurally stable anti-resonant optical fiber, considering the refractive index difference between chalcogenide glasses, the inventors selected two or more chalcogenide glasses as the optical fiber material and designed an all-solid anti-resonant optical fiber and optical fiber devices.

[0064] Among them, the wall materials of the above-mentioned elliptical tube 3, insert tube 6, and cladding tube 7 are all chalcogenide glass As2Se3, and the materials of the remaining optical fiber parts are all chalcogenide glass As2S3. The refractive indices of chalcogenide glasses As2Se3 and As2S3 can both be described by the Sellmeier equation,

[0065] ,

[0066] Among them, is the item serial number, and is the i Sellmeier coefficient of the item, λ is the optical wavelength, and n(λ) is the refractive index of the material at the optical wavelength λ. For As2Se3, when taking = 1, 2, 3, and the parameter values in its Sellmeier equation are A1 = 4.994871876241, A2 = 0.120715248481, A3 = 1.712368530625, λ1 = 0.24164 μm, λ2 = 19 μm, λ3 = 0.48328 μm; for As2S3, when taking = 1, 2, and the parameter values in its Sellmeier equation are A1 = 4.626261968807459, A2 = 1.16819527529024, λ1 = -0.2690645648975598 μm, λ2 = -31.3101221206341 μm.

[0067] As Figure 2 shown, there is a trigonometric function relationship between the normalized output power of the core light and the propagation distance. When the propagation distance is 5 cm, the normalized output power of the x-polarized light in core 1 reaches the maximum, approaching 1; while the normalized output power of the y-polarized light reaches the minimum, approaching 0. At this time, the normalized output power of the x-polarized light in core 2 approaches 0, and the normalized output power of the y-polarized light approaches 1. The normalized output power of the polarized light in the two cores is completely opposite. This means that when light travels 5 cm in this fiber, core 1 only outputs x-polarized light, and core 2 only outputs y-polarized light. Combining Figure 3 , when the propagation distance is 5 cm, the polarization extinction ratio of the fiber reaches the minimum, which is -58.3 dB. When the value of the polarization extinction ratio is lower than -20 dB, it is considered that the beam splitter has good beam splitting performance. Therefore, this beam splitter has good beam splitting performance at 3 μm.

[0068] The fiber polarization beam splitter proposed in this application is designed based on an all-solid anti-resonant fiber. Two chalcogenide glasses, As2Se3 and As2S3, which have refractive index differences and excellent performance in the mid-infrared band, are selected as the fiber materials, and light is confined to propagate in the dielectric core.

[0069] In a possible implementation, the length of the fiber polarization beam splitter is 5 cm. The 5-cm-long fiber can achieve polarization beam splitting and single-mode output in the wavelength range of 2.955 μm to 3.045 μm, and the high-order mode extinction ratio is higher than 1000. At a wavelength of 3 μm, the polarization extinction ratio can reach -58.3 dB. Here, the fiber in this application is the fiber polarization beam splitter.

[0070] As Figure 4As shown, when the fiber length is 5 cm, the polarization extinction ratio of the fiber is lower than -20 dB in the wavelength range of 2.955 μm to 3.045 μm. At a wavelength of 3 μm, the polarization extinction ratio can reach -58.3 dB. This shows that it has the ability of polarization beam splitting in this wavelength band. Here, the fiber in this application is the fiber polarization beam splitter.

[0071] As Figure 5 shown, when the fiber length is 5 cm, the mode loss and extinction ratio of the fiber in the 3-μm wavelength band. A total of six curves are shown, and the two curves in the upper half of the figure show the minimum loss and extinction ratio of the high-order modes of the fiber, and the four curves in the lower half of the figure show the fiber losses of the fiber in the x-polarized even mode, x-polarized odd mode, y-polarized even mode, and y-polarized odd mode. The directions of the arrows in the three regions A, B, and C shown in the figure indicate the specific corresponding ordinates of each curve. It can be seen from the figure that the loss of the supermode (x-polarized even mode, x-polarized odd mode, y-polarized even mode, y-polarized odd mode) of the fiber in this wavelength band is lower than 10 -2 dB / m, while the extinction ratio of the high-order modes is higher than 10 3 . This shows that this fiber has the performance of low loss and single-mode transmission. Here, the fiber in this application is the fiber polarization beam splitter.

[0072] In a possible implementation manner, the wavelength of the incident light of the fiber polarization beam splitter is 2.955 μm to 3.045 μm.

[0073] This application proposes a dual-core all-solid anti-resonant fiber polarization beam splitter based on the composite structure of chalcogenide glass and applied to the mid-infrared 3-μm wavelength band. Two chalcogenide glasses with refractive index differences in the mid-infrared band are selected as the fiber materials. A double-core fiber is constructed by adding an elliptical structure at the fiber core position, and a concentric nested double-cladding tube is introduced as the anti-resonant fiber cladding structure. Finally, a mid-infrared all-solid anti-resonant fiber polarization beam splitter with low loss, polarization beam splitting, and single-mode output characteristics is realized.

[0074] Specifically, compared with the prior art, this application has at least the following gain effects;

[0075] 1. The fiber polarization beam splitter proposed in this application is designed based on an all-solid anti-resonant fiber. Two chalcogenide glasses As2Se3 and As2S3 with refractive index differences and excellent performance in the mid-infrared band are selected as the fiber materials, and light is confined to the dielectric core for transmission;

[0076] 2. The fiber polarization beam splitter provided in this application constructs a symmetric double-core fiber structure by introducing an elliptical structure. When light propagates in the fiber, mode coupling occurs between two supermodes in the same polarization direction, and the polarization beam splitting performance is achieved by adjusting the ratio of the coupling lengths;

[0077] 3. The fiber optic polarization beam splitter provided by the present application introduces regularly arranged concentric nested double cladding tubes to form the cladding structure of the optical fiber. This design of the concentric nested double cladding tubes can achieve the single-mode characteristic of the optical fiber while reducing the optical fiber loss;

[0078] 4. The fiber optic polarization beam splitter provided by the present application can simultaneously achieve polarization beam splitting and single-mode output in the mid-infrared 3-μm band, and the high-order mode extinction ratio is higher than 1000. At a wavelength of 3 μm, the polarization extinction ratio can reach -58.3 dB.

[0079] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0080] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0081] The above description is only a preferred embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are included in the protection scope of the present application.

Claims

1. A fiber polarization beam splitter, characterized in that: The optical fiber polarization beam splitter is a dual-core all-solid-state anti-resonant optical fiber polarization beam splitter, and the cross section of the optical fiber polarization beam splitter along the radial direction is circular. The optical fiber polarization beam splitter comprises: a fiber core, an elliptical structure and six cladding structures; The cross section of the elliptical structure along the radial direction is an elliptical ring, and the elliptical structure is an elliptical tube; in the radial cross section, the center of the elliptical ring coincides with the center of the optical fiber polarization beam splitter; The fiber core includes a fiber core 1 and a fiber core 2; in a radial cross section, the fiber core 1 and the fiber core 2 are arranged on both sides of the long axis of the elliptical ring, and the fiber core 1 and the fiber core 2 are centrally symmetrical along the center of the elliptical ring; In a radial cross section, the six cladding structures are arranged around the elliptical structure along the circumferential direction; the six cladding structures each include a cladding tube and a nested tube; the nested tube is concentrically nested in the cladding tube; the cross sections of the nested tube and the cladding tube are both circular rings; The six cladding structures include four claddings 1 and two claddings 2; in a radial cross section, the four claddings 1 are centrally symmetrical along the center of the elliptical ring, and the distance from the common center of each cladding 1 to the long axis of the elliptical ring is the same; in a radial cross section, a line connecting the centers of two claddings 2 is perpendicular to the long axis of the elliptical ring, and the distance from the common center of each cladding 2 to the center of the elliptical ring is the same; Among them, the materials of the elliptical tube, the cladding tube and the nested tube are all chalcogenide glass As2Se3, and the materials of the other optical fiber parts are all chalcogenide glass As2S3; the wall thickness of the elliptical ring is 0.5μm, the semi-major axis of the inner ellipse is 18μm, and the semi-minor axis is 1μm; the wall thickness of the cladding tube is 0.5μm, and the inner circle radius is 11.6μm; the wall thickness of the nested tube is 0.5μm, and the inner circle radius is 0.3μm; the length of the optical fiber polarization beam splitter is 5cm; the distance from the common center of each cladding one to the major axis of the elliptical ring is the same, both 15μm, and the distance to the minor axis of the elliptical ring is the same, both 20μm; the distance from the common center of each cladding two to the center of the elliptical ring is 30μm.

2. The optical fiber polarization beam splitter according to claim 1, characterized in that: The diameter of the radial cross section of the optical fiber polarization beam splitter is 100 μm.

3. The optical fiber polarization beam splitter according to claim 1, characterized in that: The wavelength of the incident light of the optical fiber polarization beam splitter is 2.955 μm to 3.045 μm.

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