CN117538981A

CN117538981A - Broadband antiresonance hollow fiber

Info

Publication number: CN117538981A
Application number: CN202210923157.6A
Authority: CN
Inventors: 洪奕峰; 汪滢莹; 丁伟; 邓豪平; 高寿飞; 周锐; 童朝阳
Original assignee: Huawei Technologies Co Ltd; Jinan University
Current assignee: Huawei Technologies Co Ltd; Jinan University
Priority date: 2022-08-02
Filing date: 2022-08-02
Publication date: 2024-02-09
Also published as: WO2024027379A1

Abstract

The application discloses a broadband antiresonant hollow fiber in the field of optical communication, which can effectively widen the low-loss passband of the fiber by inhibiting the loss rise caused by mode interaction on the long wavelength side of the guided passband. The optical fiber may include: an outer cladding and an inner cladding; the outer cladding is of a hollow tubular structure, and the inner cladding is arranged inside the outer cladding; the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprising at least one sheet-like structure, opposite ends of each sheet-like structure being connected to the outer cladding.

Description

Broadband antiresonance hollow fiber

Technical Field

The application relates to the field of communication, in particular to a broadband antiresonant hollow-core optical fiber.

Background

Cables are an important transmission medium in communication systems for transmitting data in the communication systems. Typically, a cable includes a plurality of cable cores, and a transmission medium connecting two devices may be included in the multi-segment cable. Taking optical fiber as an example, optical fiber is used as an important communication medium, and is widely used in high-speed, large-capacity, low-delay communication systems and the like.

Hollow-core optical fibers, which are one of the leading edge products of the development of optical fiber optics, have been favored in many research fields for their excellent properties of low delay, low nonlinearity, low dispersion, high photodamage threshold, and flexible gas/liquid filling due to the light guiding in the hollow-core region. The transmission loss of the hollow fiber based on the antiresonant light guiding principle is smaller than 0.2dB/km thanks to the existing nested tube cladding structure design, and the best result achieved by the solid quartz fiber is achieved. However, due to the weak interaction between the air core mode and the quartz wall mode of the cladding nested tube in the anti-resonant hollow fiber, the transmission loss of the long wavelength side of the optical fiber light guide passband is degraded, and the low-loss transmission bandwidth of the light guide passband is narrowed to a certain extent, so that the low-loss transmission broadband potential possibly realized by the hollow fiber is still not sufficiently developed. Therefore, how to obtain an optical fiber with higher transmission efficiency is a problem to be solved.

Disclosure of Invention

The application discloses broadband antiresonant hollow fiber, through restraining the loss lifting that leads to because of mode interact in the long wavelength side of light guide passband, make the low-loss passband of optic fibre can be effectively widened.

In a first aspect, the present application provides a broadband antiresonant hollow core fiber comprising: an outer cladding and an inner cladding; the outer cladding is of a tubular structure, and the inner cladding is arranged inside the outer cladding; the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprises one or more sheet-like structures, namely each rotationally symmetrical structure comprises at least one sheet-like structure, and two opposite ends of each sheet-like structure are connected with the outer cladding.

Therefore, the broadband antiresonant hollow-core optical fiber provided by the application has the advantages that the internally arranged rotationally symmetrical structure is a sheet structure, the sheet structure can be understood as a non-tubular structure, the sheet structure is used as a cladding antiresonant unit, and the quartz resonant mode supported by the sheet structure has a lower coupling coefficient with an air fiber core mode, so that the interaction between the resonant mode supported by the sheet structure and the fiber core air mode can be restrained, and the low-loss transmission bandwidth is further widened. And compared with a tubular structure unit in a common antiresonant hollow fiber, the antiresonant hollow fiber has lower quality factor, can better inhibit the interaction between a supported resonant mode and a fiber core air mode, and further widens the low-loss transmission bandwidth.

In one possible embodiment, the difference between the curvatures of the respective positions in each sheet-like structure in the same rotationally symmetrical structure is within a first preset range. The first preset range may be determined from empirical values, or from errors in actually pulling the optical fiber, and typically a smaller range is determined, i.e. the curvatures of the various positions of the same sheet-like structure are as identical or close as possible.

It is understood that the curvature of the various locations in each sheet structure is as identical or as close as possible. Thereby being more in accordance with the category of optical fiber drawing based on fluid mechanics and thermodynamics and improving the preparation property of the optical fiber. So that the wide application of the optical fiber can be realized.

In one possible embodiment, each rotationally symmetrical structure comprises at least two layers of sheet-like structures with a curvature other than 0. It can be understood that at least two layers of lamellar structures in each rotationally symmetrical structure are curved lamellar structures, so that a resonant cavity can be avoided being formed in the rotationally symmetrical structure, mode interaction on the long wave side can be further weakened, and further narrowing of the light guide passband is avoided.

Therefore, in the embodiment of the application, the low-loss passband of the optical fiber can be effectively widened by arranging the sheet-shaped structure with a certain curvature and inhibiting the loss rise of the long wavelength side of the light guide passband caused by mode interaction.

In one possible embodiment, each rotating structure comprises at least one sheet-like structure with a curvature of 0 and at least one sheet-like structure with a curvature other than 0.

Therefore, in the embodiment of the application, a structure with the curvature of 0, namely a straight wall structure, can be arranged in the inner cladding, so that when the optical fiber is drawn, the air pressure introduced from two sides of the straight wall structure can be the same, the drawing difficulty is reduced, and the producibility of the optical fiber is improved.

In one possible embodiment, at least one sheet-like structure of curvature other than 0 in each rotating structure may be disposed on a side of the core adjacent to the inner cladding.

In this embodiment, the sheet structure with curvature other than 0 may be disposed at the inner side near the fiber core, that is, the curved sheet structure may be disposed at the side near the fiber core, and the sheet structure with curvature 0 may be disposed at the side near the inner wall of the outer cladding, that is, the straight wall structure may be disposed at the side near the inner wall of the outer cladding, so that when the optical fiber is drawn, the air pressures at two sides of the straight wall may be the same, only different air pressures need to be filled at one side of the curved wall, which may reduce the drawing difficulty and improve the producibility of the optical fiber.

In one possible embodiment, the difference between the wall thicknesses at the respective positions of each sheet-like structure in the same rotationally symmetrical structure is within a second preset range.

In the embodiment of the application, the wall thickness at any position in the sheet structure is the same or close to the wall thickness, so that the category of drawing the optical fiber based on fluid mechanics and thermodynamics is met, and the preparation property of the optical fiber is improved.

In one possible embodiment, when a plurality of sheet-like structures are included in the same cycle, the difference between the wall thicknesses of the plurality of sheet-like structures is within a third preset range, which is typically a smaller range, such as a difference between the wall thicknesses that is within ±10%, i.e. the wall thicknesses of the different sheet-like structures in the same rotational symmetry structure are as identical or close as possible.

In one possible embodiment, the arrangement of the plurality of rotationally symmetrical structures inside the outer cladding is a rotationally symmetrical arrangement.

Therefore, the broadband antiresonant hollow fiber provided by the application can inhibit the loss lifting of the long wavelength side of the light guide passband due to mode interaction through the rotation arrangement of a plurality of rotation symmetrical structures, and the low-loss passband of the fiber can be effectively widened.

In one possible embodiment, the constituent materials of the outer cladding and the inner cladding may include one or more of the following: quartz, soft glass or plastic.

Therefore, in the embodiment of the application, the inner cladding layer and the outer cladding layer can be formed by a plurality of same or different light-permeable materials, so that the optical fiber is suitable for more scenes and the generalization property of the optical fiber is improved.

In one possible embodiment, the number of lamellar structures in each rotationally symmetrical structure is in the range of 2 to 6 layers.

Therefore, in the embodiment of the application, the number of the sheet-shaped structures in the rotationally symmetrical structure can be in the range of 2-6 layers, and the optical fiber can be prepared with lower preparation difficulty on the premise that the loss lifting caused by mode interaction on the long wavelength side of the light guide passband can be restrained, so that the generalization of the optical fiber provided by the application is improved.

In one possible embodiment, each rotationally symmetrical structure may further comprise one or more tubular structures disposed adjacent to the inner wall of the outer cladding and connected thereto. Because the tubular structure is arranged on the outer side of the thin-wall structure, the mode field overlapping degree of the tubular structure and the fiber core mode is low, and interaction between the supported tubular cladding mode and the fiber core mode is effectively reduced, so that the phenomenon of bandwidth narrowing is avoided to a certain extent.

In a second aspect, the present application provides a hollow core optical fiber comprising: an outer cladding and an inner cladding; the outer cladding is of a tubular structure, and the inner cladding is arranged inside the outer cladding; the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprises at least one sheet-shaped structure, two opposite ends of each sheet-shaped structure are connected with the outer cladding, and each rotationally structure comprises at least one sheet-shaped structure with 0 curvature and at least one sheet-shaped structure with non-0 curvature.

In one possible embodiment, at least one sheet-like structure of curvature other than 0 in each rotating structure is disposed on a side of the core adjacent to the inner cladding.

In a third aspect, the present application provides a transmitting device, including a transmitter and the broadband antiresonant hollow fiber according to any one of the first or second aspects, where the transmitter transmits a signal through the fiber, so as to implement optical signal transmission.

In a fourth aspect, the present application provides a receiving apparatus, including a receiver and a broadband antiresonant hollow fiber as shown in any one of the first aspect or the second aspect, where the receiver receives a signal through the fiber, so as to implement receiving an optical signal.

In a fifth aspect, the present application provides a communication system, including a transmitting device and a receiving device, where the transmitting device and the receiving device may be connected by a broadband antiresonant hollow fiber provided in any of the optional embodiments of the first aspect or the second aspect, so that the transmitting device and the receiving device may transmit an optical signal through the connected optical fiber.

Drawings

Fig. 1 is a schematic structural diagram of a communication system provided in the present application;

FIG. 2 is a schematic cross-sectional view of a broadband antiresonant hollow core fiber provided herein;

FIG. 3 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 4 is a schematic diagram of a loss spectrum of a broadband antiresonant hollow-core fiber according to the present disclosure;

FIG. 5 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 6 is a schematic diagram of a loss spectrum of another broadband antiresonant hollow-core fiber provided herein;

FIG. 7 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 8 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 9 is a schematic diagram of a loss spectrum of another broadband antiresonant hollow-core fiber provided herein;

FIG. 10 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 11 is a schematic diagram of a loss spectrum of another broadband antiresonant hollow-core fiber provided herein;

FIG. 12 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 13 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 14 is a schematic cross-sectional view of another broadband antiresonant hollow core fiber provided herein;

FIG. 15 is a schematic diagram of a loss spectrum of another broadband antiresonant hollow core fiber provided herein;

fig. 16 is a schematic diagram of a preparation flow of a broadband antiresonant hollow-core fiber provided in the present application.

Detailed Description

The following description of the technical solutions in the embodiments of the present application will be made with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

First, the broadband antiresonant hollow-core optical fiber provided by the present application can be applied to various communication systems, such as an optical communication network or a network combining an optical communication network and an electrical communication network. The electrical communication system may include digital subscriber lines (Digital Subscriber Line, DSL), asymmetric digital subscriber lines (ADSL, asymmetric Digital Subscriber Line), rate adaptive digital subscriber lines (rate adaptive digital subscriber line, RADSL), and the like. The optical communication network includes, but is not limited to: any one or a combination of a plurality of optical transport networks (optical transport network, OTN), optical access networks (optical access network, OAN), synchronous digital hierarchy (synchronous digital hierarchy, SDH), passive optical networks (passive optical network, PON), ethernet (Ethernet), or flexible Ethernet (FlexE), wavelength division multiplexing (wavelength division multiplexing, WDM) networks, etc.

Specifically, the communication system provided by the application can comprise a sending device and a receiving device, wherein the sending device and the receiving device can be connected through the broadband anti-resonance hollow fiber, and the data transmission can be performed by transmitting optical signals through the connected hollow fiber.

In general, in an optical fiber communication system, communication is mainly performed by using a common single mode optical fiber, and typical system components include a single mode transmitting device, a single mode communication optical fiber, a single mode optical amplifier, and a single mode optical receiving device, so as to respectively implement excitation, conduction, amplification, and demodulation of an optical signal, and transmit multiple wavelength channels in one optical fiber to respectively carry different user information through a wavelength division multiplexing technology.

Illustratively, taking a single-mode communication system as an example, the communication system of the optical fiber provided in the present application may be as shown in fig. 1. At the transmitting end, the single-mode wavelength division device can combine optical signals of a plurality of frequency bands into an air core optical fiber for transmission, and at the receiving end, the single-mode wavelength division device can divide the combined signal into optical signals of a plurality of frequency bands so as to realize optical signal transmission of a plurality of frequency bands through one optical fiber.

In addition, the same light splitting device can integrate a transmitting end and a receiving end, namely, the light splitting device can perform wave combination processing on the optical signals to be transmitted and can perform light splitting processing on the received optical signals, so that mutual transmission of the optical signals is realized.

Therefore, the hollow fiber provided by the application can be used for realizing lower transmission delay, lower transmission signal damage (dispersion/nonlinear damage and the like), wider optical signal transmission spectrum width and potential lower transmission loss, and as the hollow fiber and other single-mode devices have good compatibility, the hollow fiber and the single-mode wavelength division transceiver, the single-mode optical amplifier and the like can be directly realized in a mode of tail fiber fusion, butt joint and the like, so that the traditional single-mode wavelength division multiplexing communication system is improved in performance, and meanwhile, the extra insertion loss of the system is furthest reduced, and the development and introduction of various adaptation devices are reduced.

Specifically, for example, the communication system provided in the present application may be applied to a PON system, where the PON system may include an OLT, an ODN, and at least one ONU.

The ODN may comprise at least one optical splitter (splitter) and may further comprise optical fibers, which in turn may comprise, in particular, a backbone Fiber (feed Fiber), a distribution Fiber (distribution Fiber) and a drop Fiber (drop Fiber). The trunk optical fiber, that is, the optical fiber in which the OLT and the ODN are connected, and the distribution optical fiber and the branching optical fiber may also be referred to as a branch optical fiber. The branching optical fiber is an optical fiber connected between the optical splitter and the accessed ONU, and the distribution optical fiber is an optical fiber connected between the optical splitters in the ODN.

The ONU is used for receiving the data sent by the OLT, responding to the management command of the OLT and caching the Ethernet data of the user.

The OLT is a core component of the optical access network and is used to provide data for one or more ONUs that are accessed, provide management, etc. The OLT may be configured to send an optical signal to at least one ONU, receive information fed back by the ONU, and process information fed back by the ONU, or other data, etc.

Generally, the versatility of an optical fiber depends on whether it has optical characteristics of low transmission loss and wide light guide passband, which is of great importance for wide-ranging applications such as optical fiber-based optical communication, laser systems, interferometric sensing systems, spectroscopic analysis, etc., hollow-core optical fibers generally include an outer cladding and an inner hollow core, and their excellent characteristics of low delay, low nonlinearity, low dispersion, high photodamage threshold, and flexible gas/liquid filling due to light guide in the hollow core region are applied in many fields.

Due to the design of the nested tube cladding structure, the transmission loss of the hollow fiber based on the antiresonant light guiding principle is smaller than 0.2dB/km, and the best result achieved by the solid quartz fiber is achieved. However, due to the weak interaction between the air core mode and the quartz wall mode of the cladding nested tube in the anti-resonant hollow fiber, the transmission loss of the long wavelength side of the optical fiber light guide passband is degraded, and the low-loss transmission bandwidth of the light guide passband is narrowed to a certain extent, so that the low-loss transmission broadband potential possibly realized by the hollow fiber is still not sufficiently developed.

Therefore, the application provides a broadband antiresonant hollow-core optical fiber, a node-free multilayer non-tubular structural unit is selected to construct a cladding structure of the antiresonant hollow-core optical fiber, the interaction between an air core mode and a cladding quartz wall mode is obviously inhibited, the 1dB/km bandwidth showing the basic-order low-loss passband of the optical fiber can be about 305nm wider than that of a nested tube antiresonant hollow-core optical fiber under the same condition (3 dB/km bandwidth is 385nm wider than that of the nested tube structure), the optical fiber structure meets the category which can be realized by drawing the optical fiber based on the fluid mechanics and thermodynamic method, and the optical fiber has the advantages of preparability and can be widely applied.

Some of the commonly used hollow core optical fibers are first exemplified below.

For example, by periodically arranging quartz nodes in a cladding region of the fiber cross-section, a photonic band gap can be created in which the fiber cladding region is not capable of guiding light over a particular propagation constant range. By means of the photonic band gap effect, the transverse resonance mode supported by the air fiber core in the center of the optical fiber can realize low-loss transmission in dB/km. The use of photonic band gap light guiding mechanism means that air core light guiding can only be achieved in band gap regions of limited wavelength width, even though according to related theory, the light guiding passband to bandwidth wavelength ratio of 0.3 of an optical fiber can be effectively widened by increasing the air filling ratio (> 0.95) of the optical fiber and reducing the wall thickness of the first quartz thin wall around the fiber core to 0.5 to 0.6 times the cladding thin wall. However, the actual preparation of the bandgap fiber structure is difficult to realize and is susceptible to process defects and structural disturbances. Because the photonic band gap bandwidth is limited, the optical fiber is difficult to realize broadband light guide, and the application of the optical fiber in the field of laser nonlinearity is greatly limited. On the other hand, the photonic band gap effect not only reduces the transmission loss of the fundamental mode in the air fiber core, but also reduces the transmission loss of the supported higher-order mode with high efficiency, so that the void optical fiber based on the photonic band gap light guide has poor mode purity, the application surface of the narrow-band multimode flexible waveguide is relatively limited, and the universality of the optical fiber is obviously insufficient.

For another example, hollow core optical fibers based on antiresonant reflection light guiding, whose light guiding mechanism intrinsic provides the advantage of a broad light guiding passband. When the cladding structure meets the resonance condition for the core mode, coherent constructive of the cladding region will result in significant light leakage from the core region, thus corresponding to loss spikes in the loss spectrum; whereas in the non-resonant wavelength region, local coherent cancellation of the cladding structure ties the optical energy into the core, thus corresponding to individual low-loss pass-bands in the loss spectrum. Because the optical fiber only has discrete resonant wavelength and does not support the air core transmission of light waves, the optical fiber is one of key technologies for realizing ultraviolet and mid-infrared light transmission. However, in hollow-core optical fibers based on tubular structures as cladding antiresonant units, there is a weak interaction between the air core mode on the long wavelength side of the light guide passband and the cladding quartz wall mode, and the rise of loss introduced by this interaction limits the light guide passband low-loss transmission bandwidth of the optical fiber. Hollow optical fibers adopting tubular cladding structures cannot fully excavate ultra-wideband low-loss potential based on an anti-resonant reflection light guide mechanism.

Also for example, another hollow-core antiresonant optical fiber is commonly used, which comprises an outer structure, and an inner space surrounded by the inner surface of the outer structure, in a radial direction from the outside to the inside of the optical fiber: a hollow region, and a plurality of closed cavities of the same structure except the hollow region; the radial section of the inner surface of the outer layer structure is a circle with a first radius; the closed cavities are spaced from each other along the circumferential direction of the inner surface of the outer layer structure and are uniformly distributed in the circumferential direction; each closed cavity comprises: the radial section of the outermost wall serving as the first thin wall is a sector or circle with a second radius; each closed cavity further comprises: and the end face of the second thin wall is a circular thin wall structure with a thin wall spacer in the middle. However, the nodes of the cladding microstructure of the optical fiber design exist not only at the connection part with the outer sleeve but also in the inner structure, so that the quartz mode loss in the optical fiber is obviously reduced, the interaction between the quartz mode loss and the fiber core air mode is obviously enhanced, and the phenomenon of oscillation exists in the loss spectrum. Meanwhile, due to the remarkable enhancement of interaction between the air mode and the quartz wall mode, the structure cannot realize broadband ultralow-loss light transmission.

In addition, another type of hollow anti-resonance optical fiber is commonly used, the cladding is a multilayer anti-resonance hollow optical fiber formed by a tube and a thin wall, the inner layer of the outer cladding is provided with a groove, and the cladding tube is tangent to the sleeve, so that the curvature of the wall of the cladding structure is uneven, and the preparation is difficult. Due to the lack of a significant break point, there is still a weak interaction between the air core mode and the cladding quartz wall mode on the long wavelength side of the light guide passband, and the loss introduced by this may raise the long wavelength loss and thus affect the light guide passband of the fiber.

Therefore, the common antiresonant hollow-core optical fiber adopts a tubular cladding structure, and although the structure can realize excellent single-mode performance and high-efficiency reduction of transmission loss, a circular structure on the cross section of the antiresonant hollow-core optical fiber also forms a ring-shaped resonant cavity, and a high quality factor leads to and strengthens weak interaction between a quartz mode concentrated on a thin wall of the optical field and an air core mode of the hollow-core optical fiber to a certain extent and the lifting of a long wavelength side of an optical fiber loss spectrum. The loss lifting phenomenon narrows the low-loss passband width of the anti-resonant hollow fiber, and the higher light guide passband width is difficult to realize. In addition, the design of the cladding structure of the embedded pipe needs to carry out sealing and inflation on each hole in the actual drawing process, and a plurality of different air pressures are usually needed to be inflated, so that the drawing difficulty is high.

The application provides a broadband antiresonant hollow fiber, or hollow fiber, which uses an inner cladding of a non-tubular structure, weakens the interaction between a quartz mode and an air fiber core mode in the fiber, and remarkably widens the low-loss light guide passband of the fiber.

Specifically, the optical fiber provided by the application may include an outer cladding layer and an inner cladding layer, the outer cladding layer is a hollow tubular structure, the inner cladding layer is disposed in the outer cladding layer, the inner cladding layer includes a plurality of rotationally symmetrical structures, the structures of each rotationally symmetrical structure are the same or are close to each other, each rotationally symmetrical structure includes at least one sheet-shaped structure, or is called a non-tubular structure, and two opposite sides of each sheet-shaped structure are connected with the outer cladding layer.

The number of the rotationally symmetrical structures may be a plurality of, such as three, four or five, and the specific number of the arrangements may be determined according to the actual application scenario, which is not limited in this application.

Illustratively, taking three rotationally symmetrical structures as an example, the cross section of the optical fiber provided in the present application may be as shown in fig. 2, where the outer cladding has a tubular structure and is divided into an inner wall and an outer wall. Each of the rotationally symmetrical structures comprises a plurality of layers of lamellar structures, and two opposite sides of each lamellar structure are connected with the inner wall of the outer cladding.

The tubular structure can be understood as a circular cavity which is presented on the cross section, but not the tubular structure is a FP-like cavity with a low quality factor, namely, two ends of the cavity are two intersection points where the non-tubular structure is connected with the sleeve, so that compared with the non-tubular structure, the tubular structure is easier to bind light in the circular cavity, higher loss peaks are generated in the air mode, the loss peaks introduced by the interaction of the air mode and the quartz mode are lower, and therefore, the loss of the long wavelength side of the light guide passband can be reduced, and the working bandwidth is further widened.

In one possible embodiment, the difference between the curvatures of the respective positions in each sheet-like structure in the same rotationally symmetrical structure is within a first preset range. It will be appreciated that the curvature of each location of each sheet structure in the same rotationally symmetrical structure is the same or close to thereby more closely conform to the thermodynamic and hydrodynamic processes of fiber drawing, and render the structure viable for drawing.

In general, the first preset range may be determined according to an actual process accuracy, for example, when an optical fiber is drawn, a curvature of each sheet structure may deviate within a certain range due to an influence of a drawing process.

For example, the curvature of the thin walls in the inner cladding (i.e., the lamellar structure in the inner cladding) may be within a range of values including [ -1/(0.62 x R) _core ),1/(0.62*R _core )]Wherein R is _core The curvature difference at each location of each ply of the layered structure may be within + -3% for the core radius.

In one possible embodiment, each rotationally symmetrical structure comprises at least two layers of sheet-like structures with a curvature other than 0. It is understood that each rotationally symmetrical structure comprises one or more lamellar structures, wherein the curvature of at least two lamellar structures is different from 0, i.e. at least two lamellar structures are curved lamellar structures. Of course, each rotationally symmetrical structure may also comprise a sheet-like structure with a curvature of 0, i.e. a straight-walled sheet-like structure.

In one possible embodiment, to reduce the difficulty of drawing the optical fiber, each rotating structure includes at least one sheet-like structure with a curvature of 0 and at least one sheet-like structure with a curvature other than 0.

Optionally, at least one sheet-like structure of curvature other than 0 in each rotating structure is disposed on a side of the core adjacent to the inner cladding.

It can be appreciated that the present application also provides an easily drawn hollow core optical fiber, including: an outer cladding and an inner cladding; the outer cladding is of a tubular structure, and the inner cladding is arranged inside the outer cladding; the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprises at least one sheet-shaped structure, two opposite ends of each sheet-shaped structure are connected with the outer cladding, and each rotationally structure comprises at least one sheet-shaped structure with 0 curvature and at least one sheet-shaped structure with non-0 curvature.

In one possible embodiment, the difference between the wall thicknesses at the various positions in the same rotationally symmetrical structure is within a second predetermined range. It is understood that the wall thickness at each location in each sheet in each rotationally symmetrical structure is the same or close to, and more closely conforms to the thermodynamic and hydrodynamic processes of fiber drawing, making the structure viable for drawing.

In general, the second preset range may be determined according to the actual process accuracy, for example, when the optical fiber is drawn, the wall thickness at different positions of each sheet structure may deviate within a certain range due to the influence of the drawing process. For example, the wall thickness difference between the individual locations of the sheet structure may be within ±3%.

Furthermore, when a plurality of sheet-like structures are included in the optical fiber, the difference in wall thickness of the plurality of sheet-like structures may be within a third preset range. It will be appreciated that the wall thickness of the plurality of sheet-like structures in a rotationally symmetrical structure may be the same or close, e.g. the difference of the individual sheet-like structures may be within + -10%. Therefore, when the optical fiber is drawn, the wall thickness of each sheet structure is the same or close, so that the drawing is more convenient, and the preparation property of the optical fiber is improved.

Alternatively, the arrangement of the respective rotationally symmetrical structures in the inner cladding is a rotationally symmetrical arrangement. Therefore, the loss rise of the long wavelength side of the light guide passband of the optical fiber caused by mode interaction can be restrained through the symmetrical arrangement of the optical fiber, and therefore, the low-loss passband of the optical fiber can be effectively widened. For example, if N rotationally symmetrical structures are included in the inner cladding, the N rotationally symmetrical structures in the inner cladding satisfy N-fold rotational symmetry about the fiber axis, where N > 2.

Optionally, the materials of the outer cladding layer and the inner cladding layer may be the same or different, specifically the materials of the inner cladding layer and the outer cladding layer may include one or more materials such as quartz, soft glass or plastic, which may be used for transmitting an optical signal, and the materials have a certain light transmittance, so as to realize the transmission of the optical signal.

Further, alternatively, the number of layers of the sheet structure in each rotationally symmetrical structure may be selected in the range of 2-6 layers. Therefore, the optical fiber has drawing feasibility and can realize better bandwidth lifting effect.

In one possible embodiment, each rotationally symmetrical structure may further comprise one or more tubular structures disposed adjacent to the inner wall of the outer cladding and connected thereto. Since the mode field of the fiber core mode and the overlapping degree of the tubular structure are effectively reduced after the tubular structure is deployed on the first layer of thin-wall structure, the interaction between the quartz mode supported by the tubular structure and the fiber core air mode is also effectively reduced, and the phenomenon of loss lifting caused by the coupling between the air fiber core mode and the cladding quartz wall mode, which is common to the antiresonant hollow fiber based on the traditional tubular structure, is restrained to a certain extent.

For ease of understanding, the following exemplary effects of the fiber implementations provided herein are described.

In general, in hollow core fibers, the interaction between the air mode and the quartz mode can be described by a coupling mode approach. When two modes of coupling are considered, the coupling equation for the matrix description is as follows:

wherein the two-dimensional matrixβ ₁ And beta ₂ The propagation constant of the first two modes of interaction, C is the mode coupling coefficient. By matrix diagonalization operation, we can obtain the propagation constant beta 'of the two modes after interaction' ₁ And beta' ₂ The method comprises the following steps:

since the hollow fiber is a leaky mode system, the mode propagation constant calculated by us has an imaginary part, so that the coupling between modes can generate two effects according to different conditions.

When the imaginary part difference of the mode propagation constants of the two interactions is smaller than 2|C |, the real part curves of the effective refractive indexes of the modes are not intersected, and the phenomenon that the real part curves evolve with the change of the wavelength is reflected, and the phenomenon is called an anti-cross effect.

When the difference in the imaginary parts of the mode propagation constants of the two interactions is equal to or greater than 2|C |, there is an intersection of the real parts of the effective refractive indices of the modes, which is called a cross effect.

Loss spikes on the long wavelength side of the guided passband of the antiresonant hollow core fiber result from weak interactions between modes—cross effects. The crossover effect causes Lorentzian line type loss peaks due to phase matching at the wavelength locations where the effective refractive index curves between the air mode and the cladding quartz mode intersect. If we define subscript 1 in formulas (2) and (3) as air mode and subscript 2 as quartz mode, then the imaginary part of the propagation constant due to the crossover effect of air mode is changed to:

K= 2|C |formula (5)

Converted into loss (unit dB/km) as follows:

notably, in the coupling strength K ² When determining (the coupling strength is mainly determined by the mode field quartz overlapping degree and the fiber core size), the loss of the air mode in the antiresonant hollow fiber caused by the interaction with the quartz mode follows the square of the imaginary part of the Dan Yingmo propagation constantIncreasing and decreasing. Tubular structures are understood to mean circular cavities in cross-section rather than FP-like cavities of low quality factor (two ends of the cavity are the two intersection points where the non-tubular structure is connected to the sleeve), so that tubular structures more easily bind light into their circular cavities than non-tubular structures, which support quartz modes with smaller dimensionsThus resulting in higher loss peaks for the air mode. The selection of the non-tubular structure can provide a quartz mode with a larger sizeFurthermore, as can be seen from the formula (6), the hollow fiber provided by the application has lower loss peak caused by the interaction of the air mode and the quartz mode, so that the loss of the long wavelength side of the light guide passband can be reduced, and the working bandwidth can be further widened.

The following is an exemplary illustration of a specific fiber configuration.

Referring to fig. 3, another optical fiber provided herein is a schematic cross-sectional view.

Wherein, FIG. 3 shows an anti-resonance hollow fiber with triple rotation symmetry structure, the inner cladding of the fiber is composed of three layers of non-tubular structures, and the core size and the wall thickness of the cladding thin wall can be adjusted according to the applied working wavelength. For example, in this embodiment, the structural parameters of the fiber are selected to be 27.4 μm core diameter, 0.37 μm three thin wall thickness, and 12/9/9.2 μm thin wall pitch z1\z2\z3, respectively.

Compared with the anti-resonant hollow-core optical fiber based on the tubular structure commonly used under the same condition, as shown in fig. 4, the 1dB/km bandwidth 1080nm of the low-loss passband of the base order can be about 305nm wider than the embedded sleeve anti-resonant hollow-core optical fiber under the same condition (the 0.1dB/km bandwidth is 150nm wider than the embedded tube structure). In the simulation comparison, the diameter of the anti-resonance hollow fiber core based on the tubular structure is selected to be 30 mu m, and the wall thickness is 0.37 mu m for realizing more effective comparison. Therefore, the limited loss spectrum long wavelength side of the optical fiber provided by the application does not appear, loss lifting phenomenon caused by mode interaction is avoided, and the low-loss passband widening effect is remarkable.

Referring to fig. 5, another optical fiber provided herein is a schematic cross-sectional view.

In which, fig. 5 shows a non-tubular structure-based antiresonant hollow fiber with quadruple rotational symmetry, the inner cladding of the fiber is composed of three layers of non-tubular structures, and the core size and the wall thickness of the cladding thin wall can be adjusted according to the applied working wavelength. In this embodiment, the structural parameters of the optical fiber are selected to be 29 μm in core diameter, 0.37 μm in wall thickness of the three thin walls, and 7.7\7.7\7.1 μm in wall spacing z1\z2\z3, respectively.

Because of the non-tubular structure of the inner cladding in the hollow fiber, the limiting loss spectrum also obviously inhibits the obvious increase of the loss caused by the coupling between the air fiber core mode and the quartz wall mode of the cladding, which is common to the anti-resonance hollow fiber with the tubular structure, on the long wavelength side, so that the loss spectrum is flat and the low-loss passband is obviously widened.

The simulated constrained loss spectrum of the hollow-core fiber structure provided by the present application may be as shown in fig. 6, wherein the 1dB/km bandwidth 1000nm (3 dB/km bandwidth 1190 nm) of the fundamental low-loss passband.

In addition, besides broadband light guiding characteristics, bending loss and mode purity of the optical fiber provided by the application are calculated through simulation, and the optical fiber is compared with a nested tube optical fiber with a common 5-fold rotationally symmetrical structure, as shown in fig. 7. Because the bending characteristics are not designed in a targeted way, the bending loss of the hollow fiber is slightly higher than that of a common nested tube fiber. In another aspect, the optical fibers provided herein are superior to conventional nested-tube optical fibers in mode purity, e.g., higher loss ratio of higher order modes to fundamental modes up to 302, than 231 of conventional nested-tube optical fibers. Therefore, the bending characteristic and the mode characteristic of the optical fiber can be enhanced or reduced by adjusting the structural parameters, and the design for the optical characteristics depends on the specific application scene and the application requirement.

Referring to fig. 8, a schematic cross-sectional view of another optical fiber is provided herein for an easily drawn hollow core optical fiber.

The hollow fiber is an anti-resonance hollow fiber with a triple rotation symmetrical structure, the inner cladding of the fiber is formed by three layers of sheet structures, the sheet structures are not contacted, the fiber core size and the wall thickness of the cladding thin wall can be adjusted according to the applied working wavelength, in the embodiment, the structural parameters of the fiber are selected to be 30.02 mu m of fiber core diameter, 1.2 mu m of three layers of thin wall thickness, and the thin wall interval z1\z2\z3 is 15.22/9.25/9.98 mu m respectively.

In the aspect of the drawing difficulty of the optical fiber, compared with the optical fiber based on the nested tube cladding structure of the current mainstream, the structure of the embodiment can be realized by only filling 1/2 of two different air pressures in the optical fiber drawing process, and the first layer of negative curvature thin wall of the fiber core outwards can be gapped or tangential or intersected, and the position of the thin wall has little influence on the performance of the optical fiber, so that the drawing difficulty can be effectively reduced.

For example, as shown in FIG. 9, the optical fiber structure of the present embodiment can realize low-loss light guide with loss bandwidth 1520-1640nm below 0.1dB/km, and ultra-low loss with loss of 0.08dB/km at 1560 nm.

Referring to fig. 10, another optical fiber provided herein is a schematic cross-sectional view.

In this embodiment, the structural parameter of the optical fiber is selected to be the core diameter of 30.02 μm, the thickness of the three thin walls of 1.2 μm, and the spacing z1\z2\z3\z4 of the thin walls of 13.31\6.81\6.46\7.66 μm respectively.

For example, as shown in FIG. 11, the optical fiber structure of the present embodiment can realize broadband light guide with a loss bandwidth of 1350-1800nm below 0.1dB/km, and ultra-low loss with a loss of 0.004dB/km at 1600 nm.

In addition, the application also provides structures of some hollow-core optical fibers.

In fig. 12, the antiresonant hollow-core optical fiber based on the non-tubular structure with five-fold rotational symmetry is shown, which comprises the antiresonant hollow-core optical fiber with five-fold rotational symmetry formed by the non-tubular structure, namely the rotationally symmetric structure, and considering the light guiding of the wide band with low loss, the quartz thin wall of the optical fiber cladding is required to meet the wall thickness of the first-order antiresonant band (for example, the wall thickness is only hundreds of nanometers for near infrared wavelength).

Referring to fig. 13, an anti-resonant hollow core fiber constructed of thin walls and straight walls of positive curvature that satisfy triple rotational symmetry is shown in fig. 13. The structure needs to be inflated and pressurized in the fiber core area in the aspect of preparing the optical fiber, and the wall thickness required by the first-order antiresonant band is convenient to realize.

Therefore, the hollow fiber can solve the problems of loss lifting and narrowing of a light guide passband caused by interaction between an air fiber core mode and a cladding quartz wall mode in the common anti-resonance hollow fiber with a tubular structure. The multilayer anti-resonance hollow optical fiber with different rotational symmetry and different curvatures (positive curvature, negative curvature and straight wall) arranged in a non-tubular structure can inhibit the loss lifting of the long wavelength side of the light guide passband due to mode interaction. Thus, the low loss passband of the fiber can be effectively widened. Meanwhile, the optical fiber structural design provided by the application meets the requirements that the curvature of any position of each layer of glass wall of the cladding is the same, and the wall thickness is the same, so that the optical fiber structural design meets the category of optical fiber drawing based on fluid mechanics and thermodynamics. Therefore, the optical fiber design provided by the application has universality and preparability, and compared with the anti-resonance hollow fiber based on the tubular structure, the hollow fiber provided by the application is more suitable for a wavelength division multiplexing optical fiber communication system and other related applications, and can be suitable for wider application scenes.

In addition, in one possible embodiment, in the inner cladding layer of the hollow-core optical fiber provided by the application, each rotationally symmetrical structure is not only provided with a sheet structure, but also provided with a tubular structure, i.e. the sheet structure and the tubular structure can be combined to form the rotationally symmetrical structure.

For example, referring to fig. 14, a schematic structural diagram of a hollow fiber is provided herein.

FIG. 14 is a cross-sectional view of an antiresonant hollow-core fiber having triple rotational symmetry and a thin-walled structure for the first layer near the core side. The inner cladding of the optical fiber consists of a thin wall and a layer of uniformly arranged pipe structure, and the fiber core size and the wall thickness and the inner diameter of the thin wall of the cladding and the pipe structure can be adjusted according to the applied working wavelength. For example, the structural parameters of the optical fiber are selected to be 30 μm in core diameter, 0.37 μm in wall thickness of the three thin walls, 78.8 μm in arc length corresponding to the first thin wall, 173.8 μm in inner diameter, and 16.8 μm in inner diameter of the tube structure.

In terms of loss characteristics, thanks to the selection of the cladding structure closest to the core side as a thin-walled structure, as shown in fig. 15, the corresponding limited loss spectrum suppresses to some extent the increase in loss due to the coupling between the air core mode and the cladding quartz wall mode, which is common for antiresonant hollow-core fibers of tubular structure, on the long wavelength side. The fundamental low-loss passband of the hollow-core fiber of FIG. 14 was calculated to have a bandwidth of 975nm (3 dB/km 1140 nm) at 1dB/km, thus allowing low-loss bandwidth improvement.

In addition, the hollow-core optical fiber provided by the application has higher manufacturability. For ease of understanding, the drawing method of the hollow-core optical fiber provided in the application is described below as an example.

Referring to fig. 16, a modified stack-draw process may be used to produce non-tubular building blocks for stacking of fiber structures by laser machining, 3D printing, or chemical etching. And then a two-step drawing method required by the traditional microstructure optical fiber preparation is used, firstly, the structure is piled and drawn into a fine rod (can) with a millimeter scale and a structure, and then the fine rod is drawn into an optical fiber (fiber) with a micrometer scale by combining with accurate air pressure regulation, so that the final optical fiber can be obtained.

Therefore, the hollow fiber provided by the application comprises a multi-layer sheet structure, and the curvature and the wall thickness of each position of the sheet structure are the same or close, so that the hollow fiber accords with the category of fiber drawing based on fluid mechanics and thermodynamics when being drawn, and has higher universality and producibility.

It should be noted that the terms "first," "second," "third," "fourth," and the like in the description and claims of this application and in the above figures, if any, are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments described herein may be implemented in other sequences than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In this application, unless specifically stated and limited otherwise, the terms "mounted," "connected," "secured," "disposed," and the like are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, or can be communicated between two elements or the interaction relationship between the two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art as the case may be.

In the description of the present application, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate description of the present application and simplify the description, and do not indicate or imply that the device or element being referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the application.

Certain terms are used throughout the description and claims to refer to particular components. Those of skill in the art will appreciate that a hardware manufacturer may refer to the same component by different names. The present specification and claims do not take the form of an element or components as a functional element or components as a rule. The inclusion or inclusion in the specification and claims should be construed to be an open-ended term and should be interpreted to include, but not limited to, or include, but not limited to.

The foregoing description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, since it is intended that all modifications, equivalents, improvements, etc. that fall within the spirit and scope of the invention.

Claims

1. A broadband antiresonant hollow core fiber comprising: an outer cladding and an inner cladding;

the outer cladding is of a tubular structure, and the inner cladding is arranged inside the outer cladding;

the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprises at least one sheet-like structure, and opposite ends of each sheet-like structure are connected with the outer cladding.

2. The optical fiber according to claim 1, wherein the difference between the curvatures at the respective positions in each sheet-like structure in the same rotationally symmetrical structure is within a first predetermined range.

3. An optical fiber according to claim 1 or 2, wherein each rotationally symmetrical structure comprises at least two sheet-like structures having a curvature other than 0.

4. An optical fiber according to claim 1 or 2, wherein each of the rotating structures comprises at least one sheet-like structure having a curvature of 0 and at least one sheet-like structure having a curvature other than 0.

5. The optical fiber of claim 3 or 4, wherein at least one sheet-like structure of curvature other than 0 in each of the rotating structures is disposed on a side of the core adjacent to the inner cladding.

6. The optical fiber according to any one of claims 1 to 5, wherein the difference between the wall thicknesses at the respective positions of each of the sheet-like structures in the same rotationally symmetrical structure is within a second preset range.

7. The optical fiber according to any one of claims 1 to 6, wherein when a plurality of sheet-like structures are included in each rotationally symmetrical structure, a difference between wall thicknesses of the plurality of sheet-like structures is within a third preset range.

8. The optical fiber of any of claims 1-7, wherein the arrangement of the plurality of rotationally symmetrical structures inside the outer cladding is a rotationally symmetrical arrangement.

9. The optical fiber of any one of claims 1-8, wherein the constituent materials of the outer cladding and the inner cladding may include one or more of: quartz, soft glass or plastic.

10. The optical fiber according to any one of claims 1-9, wherein the number of lamellar structures in each rotationally symmetrical structure is in the range of 2 to 6 layers.

11. The optical fiber according to any one of claims 1-10, further comprising a tubular structure in each rotationally symmetrical structure, the tubular structure being arranged in connection with an inner wall of the outer cladding.

12. A hollow-core optical fiber, comprising: an outer cladding and an inner cladding;

the inner cladding comprises a plurality of rotationally symmetrical structures, each rotationally symmetrical structure comprises at least one sheet-shaped structure, two opposite ends of each sheet-shaped structure are connected with the outer cladding, and each rotationally symmetrical structure comprises at least one sheet-shaped structure with 0 curvature and at least one sheet-shaped structure with non-0 curvature.

13. The optical fiber of claim 12, wherein at least one sheet-like structure of curvature other than 0 in each of the rotating structures is disposed on a side of the core adjacent to the inner cladding.

14. A transmitting device comprising a transmitter and an optical fiber according to any one of claims 1-13, the transmitter transmitting a signal over the optical fiber.

15. A receiving device comprising a receiver and an optical fiber according to any one of claims 1-13, the receiver receiving a signal via the optical fiber.

16. A communication system comprising a transmitting device and a receiving device, the transmitting device and the receiving device being connected by an optical fiber according to any one of claims 1-13.