Low-loss bend-resistant single-mode optical fiber

Abstract

A low-loss bend-resistant single-mode optical fiber (10), comprising, from the center toward the outside, a core layer (11), a first inner cladding layer (12), a second inner cladding layer (13), a depressed cladding layer (14), and an outer cladding layer (15) which are sequentially arranged. The outer radius of the first inner cladding layer (12) is R2, the width R2-R1 of the first inner cladding layer (12) ranges from 1 μm to 4 μm, and a relative refractive index difference Δ2 between the first inner cladding layer (12) and the outer cladding layer (15) ranges from -0.2% to 0%; the outer radius of the second inner cladding layer (13) is R3, the width R3-R2 of the second inner cladding layer (13) ranges from 1 μm to 4 μm, and a relative refractive index difference Δ3 between the second inner cladding layer (13) and the outer cladding layer (15) ranges from -0.1% to 0.1%; and the first inner cladding layer (12) and the second inner cladding layer (13) which have different refractive indices are arranged between the core layer (11) and the depressed cladding layer (14). By adjusting the difference value of a refractive index difference between the first inner cladding layer (12) and the second inner cladding layer (13), a zero-dispersion wavelength shifts towards a long wavelength direction, and the slope of the zero-dispersion wavelength is reduced, achieving compatibility with G.652 dispersion standard requirements.

Description

Low-loss bend-resistant single-mode optical fiber Technical Field

[0001] The present application relates to the field of communications, and in particular to a low-loss, bend-resistant single-mode optical fiber. Background Art

[0002] G.657 fiber was developed based on G.652 fiber to achieve fiber-to-the-home (FTTH) coverage. Its primary characteristic is its excellent bend resistance. Based on compatibility with G.652 fiber and minimum bend radius, G.657 fiber is divided into four subcategories: G.657.A1, G.657.A2, G.657.B2, and G.657.B3. G.657A fiber (G.657.A1 and G.657.A2) is compatible with G.652 fiber, while G.657B fiber (G.657.B2 and G.657.B3) is not fully compatible with G.652 fiber. G657B3, a highly bend-resistant single-mode fiber, is designed for applications requiring optical fiber communications within ultra-small bend radii. It exhibits very low additional bending loss within a 5mm bend radius, meeting the installation requirements of complex indoor and outdoor fiber-to-the-home (FTTH) cabling. It overcomes additional bending loss caused by corners, patch cord fixation, and high cable tension, ensuring stable operation of communication systems. The latest ITU-T G.657 standard imposes constraints on the dispersion-related performance (zero-dispersion wavelength and dispersion slope) of G.657.B3 fiber. While these requirements are still more relaxed than those of G.652 fiber, the increasingly complex application environments of G.657.B3 have led to higher performance requirements. Therefore, the new generation of G.657.B3 products require a maximum mode field diameter (MFD) and dispersion specifications compatible with G.652 fiber. When designing the G.657.B3 cross-section structure, it is necessary to comprehensively balance optical fiber transmission loss, mode field diameter, cutoff wavelength, macrobending loss, dispersion and other parameters according to standard requirements. The cross-section generally includes a core layer, an inner cladding, a deep depression layer and a pure silica outer cladding.

[0003] Existing G.657.B3 core profiles typically employ a step-type design, resulting in a significant stress transition between the core and cladding layers, leading to high attenuation. Furthermore, to ensure compatibility with the G.652 standard for fiber dispersion parameters and cable cutoff wavelength, the core width design is limited, resulting in a relatively small mode field diameter (typically less than 8.7μm, with a typical value of 8.4μm), making it incompatible with the G.652 mode field diameter. Furthermore, G.657.B3 fiber profiles typically incorporate a relatively wide inner cladding (typically 4.5 to 9μm) between the core and the depressed layer. This serves to minimize the impact of the depressed layer on MFD and dispersion performance. When fabricating this type of core rod profile using the in-tube method, a wide inner cladding reduces the cross-sectional area available for deposition of other structural layers, limiting the size of the final rod. Chinese patent application CN111807699A proposes a method for preparing a bend-resistant optical fiber. Its core layer has a typical step-index structure, and a large stress mutation between the core and cladding results in high attenuation and a small mode field diameter. Furthermore, each structural layer is prepared and assembled separately, resulting in a cumbersome and lengthy preparation process, making it unsuitable for mass production. Separately, Chinese patent application CN103345017B proposes a bend-insensitive single-mode optical fiber design. Its core layer also has a typical step-index structure, and a large stress mutation between the core and cladding results in high attenuation. Furthermore, to control the dispersion and bending loss ranges, the inner cladding width is designed to be relatively large, making it unsuitable for core rod preparation using the in-tube method.

[0004] In view of the shortcomings of the above-mentioned existing technologies, technical personnel in this field need to consider how to design a reasonable optical fiber structure to ensure that the optical fiber has a large mode field diameter (effective area), low transmission loss and low bending loss characteristics while meeting the cutoff wavelength and dispersion requirements.

[0005] Summary of the Invention

[0006] In order to solve the problems in the prior art, the present application provides a low-loss bend-resistant single-mode optical fiber.

[0007] The present application provides a low-loss bend-resistant single-mode optical fiber, which comprises a core layer, a first inner cladding layer, a second inner cladding layer, a depressed cladding layer, and an outer cladding layer arranged in sequence from the center to the outside, wherein:

[0008] The outer radius of the first inner cladding is R2, the width R2-R1 of the first inner cladding is in a range of 1 μm to 4 μm, and the relative refractive index difference Δ2 between the first inner cladding and the outer cladding is in a range of -0.2% to 0%;

[0009] The outer radius of the second inner cladding is R3, the width R3-R2 of the second inner cladding ranges from 1 μm to 4 μm, and the relative refractive index difference Δ3 between the second inner cladding and the outer cladding ranges from -0.1% to 0.1%.

[0010] It can be understood that the low-loss, bend-resistant single-mode optical fiber of the present application has a first inner cladding and a second inner cladding with different refractive indices between the core layer and the depressed layer. By adjusting the difference in the refractive index between the first inner cladding and the second inner cladding, the zero dispersion wavelength is shifted toward the long wavelength direction, and the zero dispersion wavelength slope is reduced at the same time, which is compatible with the G.652 dispersion standard requirements.

[0011] In one embodiment, the radius R1 of the core layer ranges from 4 μm to 6 μm, the relative refractive index Δ1 between the top of the core layer and the outer cladding ranges from 0.30% to 0.45%, and the refractive index from the center of the core layer to the boundary of the core layer is linearly gradient.

[0012] It can be understood that the low-loss, bend-resistant single-mode optical fiber of the present application adopts a linear gradient design for the core refractive index profile. On the one hand, it can achieve a gradual change in physical properties and doping concentration, reduce the interface stress difference between the core and cladding to reduce attenuation; on the other hand, while maintaining the core refractive index difference and the cut-off wavelength less than or equal to 1260nm, a larger mode field diameter is obtained by increasing the core diameter to meet the requirements of G.657.B3 and G.652 standards.

[0013] In one embodiment, the relative refractive index difference Δ4 between the depressed cladding and the outer cladding ranges from -0.6% to -0.3%.

[0014] In one embodiment, the relative refractive index difference Δ3 between the second inner cladding and the outer cladding is lower than the relative refractive index difference Δ2 between the first inner cladding and the outer cladding.

[0015] In one embodiment, the outer radius of the depressed cladding is R4, and the width R4-R3 of the depressed cladding ranges from 6 μm to 10 μm.

[0016] In one embodiment, the outer radius of the outer cladding is R5, the width R5-R4 of the outer cladding ranges from 60 μm to 65 μm, and the material of the outer cladding is pure silicon dioxide.

[0017] In one embodiment, the core layer is a GE / F co-doped silica glass layer.

[0018] In one embodiment, the low-loss bend-resistant single-mode optical fiber has an application wavelength range of 1310 nm to 1625 nm.

[0019] In one embodiment, the mode field diameter of the low-loss bend-resistant single-mode optical fiber at 1310 nm is 8.7 μm to 9.2 μm, and the mode field diameter of the low-loss bend-resistant single-mode optical fiber at 1550 nm is 9.2 μm to 10 μm.

[0020] In one embodiment, the attenuation coefficient of the low-loss bend-resistant single-mode optical fiber at 1310 nm is less than or equal to 0.350 dB / km, and the attenuation coefficient of the low-loss bend-resistant single-mode optical fiber at 1550 nm is less than or equal to 0.21 dB / km.

[0021] In one embodiment, the zero dispersion wavelength range of the low-loss bend-resistant single-mode optical fiber is 1300 nm to 1324 nm, and the dispersion slope of the low-loss bend-resistant single-mode optical fiber at the zero dispersion wavelength is less than or equal to 0.092 ps / (nm 2 *km).

[0022] It can be understood that when using the improved in-tube chemical vapor deposition (MCVD) or plasma chemical vapor deposition (PCVD) in-tube process to prepare a narrow inner cladding width, the preparation size of the core layer is expanded as much as possible, thereby increasing the size of the finished preform rod and the output of single wire drawing. In addition, the in-tube deposition method can be completed in one cycle for each structural layer, and the pure silicon outer sleeve is directly drawn, and the preparation process is relatively simple.

[0023] It can be understood that the principle of the low-loss bend-resistant single-mode optical fiber and the G.657.B3 optical fiber profile design of the present application is to achieve the lowest possible transmission loss, the dispersion value in line with the G.652 standard, and the larger mode field diameter to reduce the connection loss with the conventional G.652 optical fiber, while meeting the cable cutoff wavelength less than or equal to 1260nm and low bending loss under a small bending radius. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG1 is a schematic cross-sectional view of an optical fiber provided in an embodiment of the present application.

[0025] FIG2 is a schematic diagram of the refractive index distribution of the optical fiber provided in an embodiment of the present application.

[0026] FIG3 is a schematic diagram of the preparation process of the optical fiber provided in an embodiment of the present application.

[0027] FIG4 is a schematic diagram showing the measured cross-sectional structure of an existing G.657.B3 optical fiber.

[0028] FIG5 is a schematic diagram of the measured cross-sectional structure of the low-loss bend-resistant single-mode optical fiber designed in this application.

[0029] Description of main component symbols

[0030] Low-loss bend-resistant single-mode optical fiber 10

[0031] Core layer 11

[0032] The first inner cladding layer 12

[0033] Second inner cladding 13

[0034] Depressed cladding 14

[0035] Outer layer 15

[0036] The following specific implementation methods will further illustrate this application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0037] The following description will refer to the accompanying drawings to more fully describe the contents of this application. Shown in the accompanying drawings are exemplary embodiments of the present application. However, the present application can be implemented in many different forms and should not be interpreted as being limited to the exemplary embodiments set forth herein. These exemplary embodiments are provided to make this application thorough and complete and to fully convey the scope of this application to those skilled in the art. Similar figure numerals represent identical or similar components. The terms used herein are only used for the purpose of describing specific exemplary embodiments and are not intended to limit this application. As used herein, unless the context clearly indicates otherwise, the singular forms "one", "an" and "the" are intended to also include plural forms. In addition, when used herein, "includes" and / or "comprising" and / or "having", integers, steps, operations, components and / or components, but do not exclude the presence or addition of one or more other features, regions, integers, steps, operations, components and / or their groups. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. In addition, unless otherwise expressly defined herein, terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the relevant art and the content of this application, and should not be interpreted as idealized or overly formal. The following will describe exemplary embodiments with reference to the accompanying drawings. It should be noted that the components depicted in the reference drawings are not necessarily shown to scale; and identical or similar components will be given the same or similar reference numerals or similar technical terms.

[0038] Typically, existing G.657.B3 core profiles employ a stepped design, resulting in a significant stress transition between the core and cladding layers, leading to high attenuation. Furthermore, to ensure compatibility with the G.652 standard for fiber dispersion parameters and cable cutoff wavelength, the core width is limited, resulting in a relatively small mode field diameter (typically less than 8.7μm, with a typical value of 8.4μm), making it incompatible with the G.652 mode field diameter. Furthermore, G.657.B3 fiber profiles typically incorporate a relatively wide inner cladding (typically 4.5-9μm) between the core and the depressed layer, primarily to minimize the impact of the depressed layer on MFD and dispersion performance. When fabricating this type of core rod profile using the in-tube method, a wide inner cladding reduces the cross-sectional area available for deposition of other structural layers, limiting the size of the final rod. How to achieve a large mode field diameter (effective area), low transmission loss, and low bending loss through appropriate fiber structural design while meeting cutoff wavelength and dispersion requirements is a question for those skilled in the art.

[0039] Correspondingly, the present application provides a low-loss, bend-resistant single-mode optical fiber, which includes a core layer, a first inner cladding layer, a second inner cladding layer, a depressed cladding layer, and an outer cladding layer arranged in sequence from the center to the outside. The radius R1 of the core layer ranges from 4 μm to 6 μm, the relative refractive index Δ1 between the top of the core layer and the outer cladding ranges from 0.30% to 0.45%, and the refractive index from the center of the core layer to the boundary of the core layer changes linearly. It should be noted here that the calculation of the relative refractive index can be expressed as: Where n1 is the refractive index of the current layer, and n2 is the refractive index of the pure silica outer cladding. The outer radius of the first inner cladding is R2, the width of the first inner cladding (R2-R1) ranges from 1μm to 4μm, and the relative refractive index difference Δ2 between the first inner cladding and the outer cladding ranges from -0.2% to 0%. The outer radius of the second inner cladding is R3, the width of the second inner cladding (R3-R2) ranges from 1μm to 4μm, and the relative refractive index difference Δ3 between the second inner cladding and the outer cladding ranges from -0.1% to 0.1%. The relative refractive index difference Δ4 between the depressed cladding and the outer cladding ranges from -0.6% to -0.3%. The outer cladding is made of pure silica.

[0040] Therefore, the low-loss, bend-resistant single-mode optical fiber of the present application adopts a linear gradient design for the core refractive index profile. On the one hand, it can achieve a gradual change in physical properties and doping concentration, reduce the interfacial stress difference between the core and cladding layers to reduce attenuation; on the other hand, while maintaining the core refractive index difference and the cutoff wavelength less than or equal to 1260nm, a larger mode field diameter is obtained by increasing the core diameter to meet the requirements of the G.657.B3 and G.652 standards. At the same time, the low-loss, bend-resistant single-mode optical fiber of the present application provides a first inner cladding and a second inner cladding with different refractive indices between the core layer and the depressed layer. By adjusting the difference in the refractive index difference between the first inner cladding and the second inner cladding, the zero dispersion wavelength is shifted toward the longer wavelength direction, while reducing the zero dispersion wavelength slope, which is compatible with the G.652 dispersion standard requirements. The low-loss bend-resistant single-mode optical fiber of this application, the principle of G.657.B3 optical fiber profile design is to achieve the lowest possible transmission loss, the dispersion value that meets the G.652 standard, and the larger mode field diameter, while meeting the cable cutoff wavelength less than or equal to 1260nm and low bending loss under a small bending radius, so as to reduce the connection loss with conventional G.652 optical fiber.

[0041] As those skilled in the art will appreciate, modified in-tube chemical vapor deposition (MCVD) and plasma chemical vapor deposition (PCVD) are two common optical fiber preform manufacturing processes. The MCVD process uses liquid raw materials such as SiCl₄ and GeCl₄, which undergo an oxidation reaction at high temperature to produce SiO₂, B₂O₃, GeO₂, and P₂O₅ micropowders, which are then deposited on the inner wall of a quartz reaction tube. The deposition process requires precise control of the dopant flow rate to achieve the desired refractive index profile. This method is currently a reliable and reliable method for producing high-quality quartz glass optical fibers. The inner cladding and core glass are deposited within a single quartz tube, in a fully enclosed, ultra-purified system. The resulting preform is of exceptionally high purity, enabling the production of high-quality single-mode and multimode optical fibers. The PCVD process uses microwaves as a heat source. The reaction mechanism involves microwaves activating a gas to generate plasma, ionizing the reactant gas. The ionized reactant gas forms charged ions. The heat released by the recombination of the charged ions melts the gaseous reactants, forming a thin, transparent layer of deposited quartz glass. The preparation of core rods using PCVD also involves two basic steps: deposition and rod formation. PCVD has high deposition efficiency and precise control of the refractive index profile, enabling the production of optical fibers with complex refractive index structures and profiles (each layer can be deposited as small as 0.1 μm, while MCVD can deposit layers as small as tens to 100 μm). However, the deposition rate is low, and the raw material requirements are high, requiring a liner tube.

[0042] The following describes exemplary embodiments with reference to the accompanying drawings. It should be noted that the components depicted in the accompanying drawings are not necessarily shown to scale; and the same or similar components will be given the same or similar reference numerals or similar technical terms.

[0043] The specific implementation methods of the present application are further described in detail below with reference to the accompanying drawings.

[0044] As shown in Figures 1 and 2, the present application provides a low-loss bend-resistant single-mode optical fiber 10, which includes a core layer 11, a first inner cladding 12, a second inner cladding 13, a depressed cladding 14 and an outer cladding 15 arranged in sequence from the center to the outside.

[0045] The radius R1 of the core layer 11 ranges from 4 μm to 6 μm. The relative refractive index Δ1 between the top of the core layer 11 and the outer cladding layer 15 ranges from 0.30% to 0.45%, and the refractive index changes linearly from the center of the core layer 11 to the edge of the core layer 11.

[0046] The outer radius of the first inner cladding 12 is R2, and the width R2-R1 of the first inner cladding 12 ranges from 1 μm to 4 μm. The relative refractive index difference Δ2 between the first inner cladding 12 and the outer cladding 15 ranges from -0.2% to 0%.

[0047] The outer radius of the second inner cladding 13 is R3, the width R3-R2 of the second inner cladding 13 ranges from 1 μm to 4 μm, and the relative refractive index difference Δ3 between the second inner cladding 13 and the outer cladding 15 ranges from -0.1% to 0.1%.

[0048] The outer radius of the depressed cladding 14 is R4, the width R4-R3 of the depressed cladding 14 ranges from 6 μm to 10 μm, and the relative refractive index difference Δ4 between the depressed cladding 14 and the outer cladding 15 ranges from -0.6% to -0.3%.

[0049] The outer radius of the outer cladding 15 is R5, and the width R5-R4 of the outer cladding 15 ranges from 60 μm to 65 μm. The refractive index of the outer cladding 15 is nc, and the material of the outer cladding 15 is pure silicon dioxide.

[0050] It can be understood that the low-loss, bend-resistant single-mode optical fiber 10 of the present application has a linear gradient design for the refractive index profile of the core layer 11. On the one hand, it can achieve a gradient of physical properties and doping concentration, reduce the interface stress difference between the core and cladding layers to reduce attenuation; on the other hand, while maintaining the refractive index difference of the core layer 11 and the cut-off wavelength less than or equal to 1260 nm, a larger mode field diameter is obtained by increasing the core diameter to meet the requirements of G.657.B3 and G.652 standards.

[0051] It can be understood that the low-loss bend-resistant single-mode optical fiber 10 of the present application is provided with a first inner cladding 12 and a second inner cladding 13 with a difference in refractive index between the core layer 11 and the depressed layer. By adjusting the difference in the refractive index between the first inner cladding 12 and the second inner cladding 13, the zero dispersion wavelength is shifted toward the long wavelength direction, and the zero dispersion wavelength slope is reduced at the same time, which is compatible with the G.652 dispersion standard requirements.

[0052] In one embodiment, the core layer 11 is a Ge / F co-doped silica glass layer; the refractive index distribution of the core layer 11 can be changed by doping F and Ge elements.

[0053] In one embodiment, the radius R1 of the core layer 11 may be 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, or 5.9 μm. The relative refractive index Δ1 between the top of the core layer 11 and the outer cladding layer 15 may be 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, 0.41%, 0.42%, 0.43%, or 0.44%.

[0054] In one embodiment, the width R2-R1 of the first inner cladding 12 may further be 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, or 3.9 μm. The value of the relative refractive index difference Δ2 between the first inner cladding 12 and the outer cladding 15 can further be -0.01%, -0.02%, -0.03%, -0.04%, -0.05%, -0.06%, -0.07%, -0.08%, -0.09%, -0.11%, -0.12%, -0.13%, -0.14%, -0.15%, -0.16%, -0.17%, -0.18%, and -0.19%; the refractive index distribution of the first inner cladding 12 can be changed by doping F and Ge elements.

[0055] In one embodiment, the width R3-R2 of the second inner cladding 13 may further be 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, or 3.9 μm. The value of the relative refractive index difference Δ3 between the second inner cladding 13 and the outer cladding 15 can further be -0.01%, -0.02%, -0.03%, -0.04%, -0.05%, -0.06%, -0.07%, -0.08%, -0.09%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%; the refractive index distribution of the second inner cladding 13 can be changed by doping F and Ge elements.

[0056] In one embodiment, the relative refractive index difference Δ3 between the second inner cladding 13 and the outer cladding 15 is lower than the relative refractive index difference Δ2 between the first inner cladding 12 and the outer cladding 15. That is, when considering actual design, the relative refractive index difference Δ2 between the first inner cladding 12 and the outer cladding 15 and the relative refractive index difference Δ3 between the second inner cladding 13 and the outer cladding 15 are selected to meet the above design requirements.

[0057] In one embodiment, the width R4-R3 of the depressed cladding 14 may further be 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, 7.7 μm, 7.8 μm, 7.9 μm, 8.1 μm, 8.2 μm, 8.3 μm, 8.4 μm, 8.5 μm, 8.6 μm, 8.7 μm, 8.8 μm, 8.9 μm, 9.1 μm, 9.2 μm, 9.3 μm, 9.4 μm, 9.5 μm, 9.6 μm, 9.7 μm, 9.8 μm, or 9.9 μm. The relative refractive index difference Δ4 between the depressed cladding 14 and the outer cladding 15 can further be -0.31%, -0.32%, -0.33%, -0.34%, -0.35%, -0.36%, -0.37%, -0.38%, -0.39%, -0.41%, -0.42%, -0.43%, -0.44%, -0.45%, -0.46%, -0.47%, -0.48%, -0.49%, -0.51%, -0.52%, -0.53%, -0.54%, -0.55%, -0.56%, -0.57%, -0.58%, and -0.59%. The refractive index distribution of the depressed cladding 14 can be changed by doping F element.

[0058] In one embodiment, the width R5-R4 of the outer cladding layer 15 may further be 61.1 μm, 61.2 μm, 61.3 μm, 61.4 μm, 61.5 μm, 61.6 μm, 61.7 μm, 61.8 μm, 61.9 μm, 62.1 μm, 62.2 μm, 62.3 μm, 62.4 μm, 62.5 μm, 62.6 μm, 62.7 μm, 62.8 μm, 62.9 μm. , 63.1μm, 63.2μm, 63.3μm, 63.4μm, 63.5μm, 63.6μm, 63.7μm, 63.8μm, 63.9μm, 64.1μm, 64.2μm, 64.3μm, 64.4μm, 64.5μm, 64.6μm, 64.7μm, 64.8μm, 64.9μm, a typical value of the width R5-R4 of the outer cladding 15 may be 62.5μm.

[0059] In one embodiment, the low-loss bend-resistant single-mode optical fiber 10 provided in the present application has an application wavelength range of 1310 nm to 1625 nm.

[0060] In one embodiment, the mode field diameter of the low-loss bend-resistant single-mode optical fiber 10 provided in the present application at 1310 nm is 8.7 μm to 9.2 μm, and the mode field diameter of the low-loss bend-resistant single-mode optical fiber 10 provided in the present application at 1550 nm is in the range of 9.2 μm to 10 μm.

[0061] In one embodiment, the attenuation coefficient of the low-loss bend-resistant single-mode optical fiber 10 provided in the present application at 1310 nm is less than or equal to 0.350 dB / km, and the attenuation coefficient of the low-loss bend-resistant single-mode optical fiber 10 provided in the present application at 1550 nm is less than or equal to 0.21 dB / km.

[0062] In one embodiment, the zero dispersion wavelength range of the low-loss bend-resistant single-mode optical fiber 10 provided by the present application is 1300 nm to 1324 nm, and the dispersion slope of the low-loss bend-resistant single-mode optical fiber 10 provided by the present application at the zero dispersion wavelength is less than or equal to 0.092 ps / (nm 2 *km).

[0063] In one embodiment, the core layer 11 , the first inner cladding layer 12 , the second inner cladding layer 13 and the depressed cladding layer 14 are prepared by using a modified in-tube chemical vapor deposition method or a plasma chemical vapor deposition method.

[0064] It can be understood that under the condition of using the improved in-tube chemical vapor deposition (MCVD) or plasma chemical vapor deposition (PCVD) in-tube process to prepare a narrow inner cladding width, the preparation size of the core layer 11 is expanded as much as possible, thereby increasing the size of the finished preform rod and the output of single wire drawing. In addition, the preparation of each structural layer by in-tube deposition can be completed within one cycle, matching the direct drawing of the pure silicon outer sleeve, and the preparation process is relatively simple.

[0065] It can be understood that the principle of the low-loss bend-resistant single-mode optical fiber 10 and the G.657.B3 optical fiber profile design of the present application is to achieve the lowest possible transmission loss, the dispersion value that complies with the G.652 standard, and the larger mode field diameter to reduce the connection loss with the conventional G.652 optical fiber, while meeting the cable cutoff wavelength less than or equal to 1260nm and low bending loss under a small bending radius.

[0066] The low-loss, bend-resistant single-mode optical fiber prepared in this application can meet or exceed the G.657.B3 industry standard in various performance indicators and has a large MFD (MFD@1300nm~8.9) and dispersion performance compatible with G.652 optical fiber. Typical values ​​of the low-loss, bend-resistant single-mode optical fiber performance test are shown in Table 1:

[0067] Table 1 Typical values ​​of the performance test of low-loss bend-resistant single-mode optical fiber in this application

[0068] The performance indicators of the low-loss bend-resistant single-mode optical fiber described in the aforementioned embodiment are as follows: attenuation @1310nm ≤ 0.35dB / km, attenuation @1550nm ≤ 0.21dB / km, mode field diameter @1310nm ~ 8.6μm, mode field diameter @1550nm ~ 9.6μm, optical cable cutoff wavelength ≤ 1260nm, at 1550nm, macrobending loss for 10mm radius-1 turn ≤ 0.03dB, macrobending loss for 7.5mm radius-1 turn ≤ 0.08dB, and macrobending loss for 5mm radius-1 turn ≤ 0.15dB.

[0069] Understandably, optical fiber bending loss is closely related to the core refractive index and the depth and width of the depressed layer. To achieve low bending loss at the small bend radius required by G.657.B3, a higher core refractive index is required, along with a deeper and wider depressed layer located close to the core. The core is typically doped with GeO2 to increase its refractive index. The absorption loss and Rayleigh scattering caused by GeO2 doping are the primary contributors to high fiber attenuation. Therefore, during core rod preparation, it is important to find an appropriate GeO2 content within a certain range. While meeting the large mode field diameter requirement of G.657.B3, a traditional step-index core design can easily lead to a cutoff wavelength exceeding 1260nm due to the increased refractive index. However, a gradient core design, while maintaining the same refractive index and cutoff wavelength, allows the core boundary points to be further widened, thereby achieving a larger mode field diameter. A depressed layer that is too deep or too wide can also easily cause the cable cutoff wavelength to exceed 1260nm. In addition, if the depressed layer is close to the core layer, the mode field diameter will be reduced, the zero dispersion wavelength will be lowered, and the zero dispersion wavelength slope will increase. Therefore, the traditional design has a wider radius inner cladding layer (typical width is 4.5 to 9μm) between the depressed layer and the core layer to play a role in adjusting the dispersion and mode field diameter.

[0070] As can be understood, the use of a deeper and wider recessed structure achieves a larger effective relative refractive index difference (Δn) while reducing the core's refractive index difference and Ge content, thus achieving low bending losses. This also reduces fiber attenuation due to the reduced Ge content in the core. The presence of the recessed layer significantly affects the fiber's dispersion parameters and mode field diameter. Therefore, G.657.B3 incorporates an inner cladding layer within the core and recessed diameter to mitigate the impact of the recess on key fiber properties (mode field diameter and dispersion). Ultimately, by adjusting the refractive index profile of each structural layer, optimal optical parameters can be achieved.

[0071] Implementation steps:

[0072] As shown in FIG3 , the general steps of the preparation and production process of the low-loss bend-resistant single-mode optical fiber of the present application can be: optical fiber profile design (design parameters are as described in the above embodiment); MCVD / PCVD preparation of core rod; outer cladding matching; coating matching drawing; optical fiber performance testing.

[0073] Specifically, a prefabricated core rod is prepared using an improved in-tube chemical vapor deposition (MCVD) or plasma chemical vapor deposition (PCVD) process. The core rod comprises a core layer, a first inner cladding layer, a second inner cladding layer, a recessed layer, and a portion of a pure silicon outer cladding layer (composed of a pure silicon quartz tube). A pure silicon quartz tube is used as a deposition substrate, SiCl4 and O2 are used as SiO2 raw materials, SiF4, SF6, C2F6, or CF4 are used as fluorine doping materials, and GeCl4 is used as Ge doping materials. A reciprocating oxyhydrogen torch or plasma is used as a heat source to sequentially deposit the recessed layer, second inner cladding layer, first inner cladding layer, and core layer on the inner surface of the pure silicon quartz substrate by controlling the concentration of each doping element within the tube. The deposition tube is then melted and shrunk at high temperature to a suitable inner diameter. Before the inner diameter is shrunk, SF6, C2F6, and O2 are introduced to etch away impurities adhering to the inner diameter surface under heating from the oxyhydrogen torch or graphite furnace. Finally, the tube is melted and shrunk at high temperature to form a solid core rod. A pure quartz sleeve is used as the outer sleeve (outer cladding) or a pure matching drawing is prepared through the OVD process, and the optical fiber is obtained by high-temperature drawing.

[0074] The relevant parameters are adjusted according to the above implementation steps, corresponding to Examples 1 to 4 and Comparative Examples 1 and 2. Among them, Comparative Example 1 adopts a single inner cladding design (no second inner cladding is provided), and the refractive index of the core layer of Comparative Example 2 does not adopt a linear gradient design; the test results of the cross-sectional structures and corresponding optical parameters in Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Tables 2 and 3.

[0075] Table 2 Parameters of optical fibers with different structural designs

[0076] Table 3 Test performance of optical fibers with different structural parameters

[0077] As shown in Examples 1 to 4, as well as Comparative Examples 1 and 2, the refractive index difference between the first and second inner cladding layers significantly affects the zero-dispersion wavelength and the zero-dispersion wavelength slope. At the same inner cladding width, increasing the refractive index difference between the two layers can shift the zero-dispersion wavelength toward longer wavelengths while simultaneously reducing the zero-dispersion wavelength slope, allowing the dispersion parameters to meet the G.652 standard. If the refractive index difference between the two layers is close or identical, the dispersion parameters are likely to exceed the standard while the inner cladding width remains unchanged, requiring a significant increase in the inner cladding width to bring the dispersion parameters within the standard range. As shown in Examples 1 and 4, while increasing the core layer's refractive index improves bending loss, the cable's cutoff wavelength is likely to exceed the standard. Furthermore, an increase in Ge concentration also significantly increases Rayleigh scattering loss. It can be seen from Example 1 and Comparative Example 2 (the core layer adopts a stepped design) that, at the same core layer height, in order to control the cable cutoff wavelength ≤ 1260nm, the design value of the stepped core layer width is reduced, the MFD decreases significantly, and is close to the standard lower limit. In addition, due to the obvious stress mutation between the core layer and the cladding, the attenuation increase is more obvious.

[0078] 4 and 5 , FIG4 is a schematic diagram of a measured cross-sectional structure of an existing G.657.B3 optical fiber, and FIG5 is a schematic diagram of a measured cross-sectional structure of a low-loss, bend-resistant single-mode optical fiber (G.657.B3 optical fiber) designed in this application.

[0079] It can be understood that the low-loss, bend-resistant single-mode optical fiber designed in this application adopts a linear gradient design of the core layer, which, on the one hand, realizes a gradient of physical properties and doping concentration, reduces the interface stress difference between the core and cladding to reduce attenuation, and at the same time obtains a larger mode field diameter by increasing the core diameter, providing a new single-mode optical fiber design method that is compatible with G.652 and G.657.B3 and has low attenuation, large effective area, and low bending loss performance.

[0080] It can be understood that the design of the present application sets a first inner cladding layer and a second inner cladding layer with different refractive indices between the core layer and the recessed layer. Under the condition of using the in-tube method to prepare a narrow inner cladding width, the preparation size of the core layer part is expanded as much as possible, the size of the finished preform rod and the single wire drawing output are increased, the preparation process is relatively simple, and it is suitable for mass production.

[0081] The specific embodiments of the present application have been described above with reference to the accompanying drawings. However, those skilled in the art will appreciate that various modifications and substitutions may be made to the specific embodiments of the present application without departing from the spirit and scope of the present application. Such modifications and substitutions are intended to fall within the scope of the present application.

Claims

1. A low-loss bend-resistant single-mode optical fiber, characterized in that: The low-loss bend-resistant single-mode optical fiber comprises a core layer, a first inner cladding layer, a second inner cladding layer, a depressed cladding layer and an outer cladding layer arranged in sequence from the center to the outside, wherein: The outer radius of the first inner cladding is R2, the width R2-R1 of the first inner cladding is in a range of 1 μm to 4 μm, and the relative refractive index difference Δ2 between the first inner cladding and the outer cladding is in a range of -0.2% to 0%; The outer radius of the second inner cladding is R3, the width R3-R2 of the second inner cladding ranges from 1 μm to 4 μm, and the relative refractive index difference Δ3 between the second inner cladding and the outer cladding ranges from -0.1% to 0.1%.

2. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The radius R1 of the core layer ranges from 4 μm to 6 μm, the relative refractive index Δ1 between the top of the core layer and the outer cladding ranges from 0.30% to 0.45%, and the refractive index from the center of the core layer to the boundary of the core layer changes linearly.

3. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The relative refractive index difference Δ4 between the depressed cladding and the outer cladding ranges from -0.6% to -0.3%.

4. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The relative refractive index difference Δ3 between the second inner cladding and the outer cladding is lower than the relative refractive index difference Δ2 between the first inner cladding and the outer cladding.

5. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The outer radius of the depressed cladding is R4, and the width R4-R3 of the depressed cladding is in a range of 6 μm to 10 μm.

6. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The outer radius of the outer cladding is R5, the width R5-R4 of the outer cladding ranges from 60 μm to 65 μm, and the material of the outer cladding is pure silicon dioxide.

7. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The core layer is a GE / F co-doped silica glass layer.

8. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The application wavelength range of the low-loss bend-resistant single-mode optical fiber is 1310 nm to 1625 nm.

9. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The mode field diameter of the low-loss bend-resistant single-mode optical fiber at 1310 nm is 8.7 μm to 9.2 μm, and the mode field diameter of the low-loss bend-resistant single-mode optical fiber at 1550 nm is in the range of 9.2 μm to 10 μm.

10. The low-loss bend-resistant single-mode optical fiber according to claim 1, wherein: The attenuation coefficient of the low-loss bend-resistant single-mode optical fiber at 1310 nm is less than or equal to 0.350 dB / km, and the attenuation coefficient of the low-loss bend-resistant single-mode optical fiber at 1550 nm is less than or equal to 0.21 dB / km; the zero dispersion wavelength range of the low-loss bend-resistant single-mode optical fiber is 1300 nm to 1324 nm, and the dispersion slope of the low-loss bend-resistant single-mode optical fiber at the zero dispersion wavelength is less than or equal to 0.092 ps / (nm 2 *km).

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