Single-mode optical fiber and method for manufacturing a single-mode optical fiber

Abstract

This application provides a single-mode optical fiber and a method for fabricating it. Specifically, the single-mode optical fiber comprises, from its center to its outer periphery: a core layer, an inner cladding, a first depressed cladding, a second depressed cladding, and an outer cladding. The refractive index of the core layer relative to the outer cladding is negatively correlated with its radius; the refractive index of the inner cladding relative to the outer cladding is negatively correlated with its radius, and the refractive index of the outer boundary of the inner cladding is less than that of the outer cladding; the refractive index of the first depressed cladding is less than that of the second depressed cladding; and the refractive index of the second depressed cladding is less than that of the outer cladding. The technical solution of this application can effectively solve the problem of large differences in attenuation coefficients in the C+L band of single-mode optical fibers.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to a single-mode optical fiber and a method for preparing a single-mode optical fiber. Background Technology

[0002] Wavelength Division Multiplexing (WDM) is a technology that combines two or more optical carrier signals of different wavelengths (carrying various information) at the transmitting end using a multiplexer (also called a multiplexer) and couples them into the same optical fiber for transmission. At the receiving end, a demultiplexer (also called a demultiplexer) separates the optical carriers of different wavelengths, and then the optical receiver performs further processing to recover the original signal. This technology of simultaneously transmitting two or more different wavelength optical signals in the same optical fiber is called wavelength division multiplexing. Currently, C-band-based WDM systems have begun large-scale commercial use, but with the continued rapid growth of network traffic, C-band (1530–1565nm) WDM systems will be unable to meet the network expansion requirements of emerging services. In recent years, the application of C+L band (1530-1625nm) has gradually matured. By extending the L band, the number of channels per fiber can be increased. Theoretically, it can accommodate 192 channels with a 50GHz spacing, increasing the system capacity by nearly 100%.

[0003] In related technologies, the attenuation coefficient of optical fiber is one of the most important performance indicators, largely determining the relay distance in optical fiber communication. In long-distance optical fiber transmission, the smaller the attenuation coefficient, the farther the optical signal can be transmitted, thus greatly reducing the need for relay stations and significantly lowering operating costs. Therefore, reducing optical power loss and mitigating the impact of optical fiber nonlinear effects have become the development direction of optical fiber communication.

[0004] Extending WDM applications to the L-band presents several challenges: due to the significant difference in attenuation coefficients between optical fibers in the C+L band, the optical signal-to-noise ratio (OSNR) can degrade by up to 3 dB when the fiber span is 100 km. This affects the transmission bandwidth of the optical fiber in the C+L band and also increases the cost and complexity of maintaining the transmission system. Summary of the Invention

[0005] This application provides a single-mode optical fiber and a method for fabricating a single-mode optical fiber, in order to solve the problem of the difference in attenuation coefficient between the C+L band and the L band of single-mode optical fiber.

[0006] On the one hand, this application provides a single-mode optical fiber, which includes, from the center to the periphery, a core layer, an inner cladding layer, a first depressed cladding layer, a second depressed cladding layer, and an outer cladding layer.

[0007] Among them, the refractive index of the core layer relative to the outer cladding layer is negatively correlated with the radius; the refractive index of the inner cladding layer relative to the outer cladding layer is negatively correlated with the radius, and the refractive index of the outer boundary of the inner cladding layer is less than that of the outer cladding layer; the refractive index of the first depressed cladding layer is less than that of the second depressed cladding layer; and the refractive index of the second depressed cladding layer is less than that of the outer cladding layer.

[0008] In some embodiments, the core layer is a silicon dioxide glass layer doped with germanium. The refractive index of the core layer relative to the cladding layer follows a linear or curvilinear function distribution with increasing radius, wherein the horizontal axis of the linear and curvilinear functions is the fiber radius, and the vertical axis of the linear and curvilinear functions is the refractive index of the core layer relative to the cladding layer.

[0009] In some embodiments, when the refractive index of the core layer relative to the cladding layer is distributed as a linear function with increasing radius, the angle between any point on the linear function and the horizontal axis is less than a preset angle α; when the refractive index of the core layer relative to the cladding layer is distributed as a curvilinear function with increasing radius, the angle between any point on the curvilinear function and the horizontal axis is less than a preset angle α.

[0010] In some embodiments, the preset angle α is between 15° and 35°.

[0011] In some embodiments, the refractive index difference Δ1 between the core center point and the outer cladding layer satisfies: 0.3% ≤ Δ1 ≤ 0.35%; and / or, the refractive index difference Δ2 between the core and inner cladding layer boundary and the outer cladding layer satisfies: 0.24% ≤ Δ1 ≤ 0.3%; and / or, the radius R1 of the core layer satisfies: 4μm ≤ R1 ≤ 7μm.

[0012] In some embodiments, the refractive index difference Δ3 between the boundary of the inner cladding and the first recessed cladding and the outer cladding satisfies: -0.2% ≤ Δ3 ≤ -0.3%; the difference between the radius R2 of the inner cladding and the radius R1 of the core layer satisfies: 1μm ≤ R2 - R1 ≤ 2.4μm; the inner cladding is a silicon dioxide glass layer doped with germanium and fluorine.

[0013] In some embodiments, the refractive index difference Δ4 between the second cladding layer and the outer cladding layer satisfies: -0.05% ≤ Δ4 ≤ -0.15%; the difference between the radius R3 of the first cladding layer and the radius R2 of the inner cladding layer satisfies: 3μm ≤ R3 - R2 ≤ 7μm; the difference between the radius R4 of the second cladding layer and the radius R3 of the first cladding layer satisfies: 7.2μm ≤ R4 - R3 ≤ 13μm; both the first cladding layer and the second cladding layer are fluorine-doped silica glass layers.

[0014] On the other hand, this application provides a method for fabricating a single-mode optical fiber, which includes:

[0015] In a vapor phase evaporation apparatus, a core layer, an inner cladding layer, a first sunken cladding layer, and a second sunken cladding layer are prepared sequentially using a deposition method, so that the core layer, inner cladding layer, first sunken cladding layer, and second sunken cladding layer form a loose preform.

[0016] The porous preform is sintered at a high temperature of 1300℃~1500℃ in an atmosphere of halogen gas to form a transparent quartz rod.

[0017] Quartz rods are placed in a sintering furnace for sintering, and an outer cladding layer is formed on the outside of the quartz rod according to the preset outer cladding weight to obtain a preformed rod.

[0018] In some embodiments, after obtaining the preform, the method for fabricating a single-mode optical fiber further includes:

[0019] The preform is loaded into the drawing tower, heated, and melted from the tip of the cone.

[0020] The molten preform is drawn using a drawing process to form quartz fibers;

[0021] Quartz fibers are annealed in an annealing furnace and then naturally cooled to reduce the surface temperature of the quartz fibers to 45°C to 55°C.

[0022] An inner coating layer and an outer coating layer are formed sequentially on the outer side of the annealed quartz fiber.

[0023] In some embodiments, the step of placing the quartz rod in a sintering furnace for sintering specifically includes:

[0024] Place the quartz rod in the sintering furnace and raise the furnace temperature at a rate of 30°C to 50°C / min to the first preset temperature, and keep the quartz rod at the first preset temperature for 2 to 4 hours.

[0025] The furnace temperature of the sintering furnace is then raised to the second preset temperature within a preset time, and the quartz rod is held at the second preset temperature for 24 hours to complete the sintering.

[0026] In some embodiments, annealing the quartz fibers in an annealing furnace specifically includes:

[0027] The initial temperature of the annealing furnace is set between 1200℃ and 1400℃;

[0028] Quartz fibers are fed into an annealing furnace;

[0029] Using a temperature gradient between 50°C and 150°C, the temperature of the annealing furnace is gradually reduced until it drops to between 700°C and 900°C.

[0030] The single-mode optical fiber provided in this application comprises, from the center to the outer periphery, a core layer, an inner cladding, a first depressed cladding, a second depressed cladding, and an outer cladding. The refractive index of the core layer relative to the outer cladding is negatively correlated with the radius, and the refractive index of the inner cladding relative to the outer cladding is also negatively correlated with the radius. This arrangement causes the refractive indices of the core layer and the inner cladding to continuously change with increasing radius, making the attenuation coefficients of the single-mode fiber in the C+L band and the L band closer, thereby improving the transmission bandwidth of the fiber in the C+L band. Simultaneously, the refractive index of the outer boundary of the inner cladding is lower than that of the outer cladding, causing the refractive index of the inner cladding to gradually change to a state lower than that of the outer cladding, further reducing the difference in attenuation coefficients between the single-mode fiber in the C+L band and the L band, further improving the transmission bandwidth of the fiber in the C+L band. Attached Figure Description

[0031] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0032] Figure 1 A schematic diagram of the cross-sectional structure of a single-mode optical fiber provided in an embodiment of this application;

[0033] Figure 2 A schematic diagram of the refractive index profile of a single-mode optical fiber provided in an embodiment of this application;

[0034] Figure 3 Provided for the embodiments of this application Figure 2 A magnified schematic diagram of the structure at point A of a single-mode optical fiber;

[0035] Figure 4 A comparison diagram of the attenuation characteristics of single-mode optical fiber provided in the embodiments of this application and single-mode optical fiber in related technologies;

[0036] Figure 5 Loss decomposition diagram of the single-mode optical fiber provided in this application;

[0037] Figure 6 A flowchart illustrating the fabrication method of the single-mode optical fiber provided in the application.

[0038] Explanation of reference numerals in the attached figures:

[0039] 10 - Core layer; 20 - Inner cladding layer; 30 - First recessed cladding layer; 40 - Second recessed cladding layer; 50 - Outer cladding layer; 60 - Coating layer.

[0040] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0041] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0042] Fiber optic communication uses light as the information carrier, transmitting it through the fiber core. However, not all light is suitable for fiber optic communication. Different wavelengths of light result in different transmission losses in optical fibers. The most commonly used band is called the C-band (1530nm–1565nm). The C-band exhibits the lowest loss and is widely used in metropolitan area networks, long-haul, ultra-long-haul, and submarine cable systems. The C-band is also frequently used in WDM (wavelength division multiplexing) systems. The adjacent L-band (1565nm–1625nm) has the second lowest loss and is also one of the mainstream choices in the industry. When the C-band is insufficient to meet bandwidth requirements, the L-band is used as a supplement. The L-band, from 1565nm to 1625nm, if calculated as 1570–1611nm, has a usable spectrum range of approximately 4.8THz. Therefore, the C+L band can achieve 192 wavelengths, with a spectrum bandwidth approaching 9.6THz, nearly doubling the transmission capacity.

[0043] Extending WDM applications to the L-band presents a challenge: significant differences in attenuation coefficients exist between the C+L bands of optical fibers. Specifically, single-mode fibers in related technologies can achieve a minimum attenuation coefficient below 0.19 dB / km in the C+L band (typically around 1575 nm), while the maximum attenuation coefficient in the L-band (typically around 1625 nm) can reach 0.22 dB / km, a difference of 0.03 dB / km. Even low-loss fibers, while achieving a minimum attenuation coefficient below 0.17 dB / km in the C+L band, still exhibit a maximum attenuation coefficient of 0.20 dB / km in the L-band, a difference of 0.03 dB / km.

[0044] Therefore, due to the difference in attenuation coefficient, the optical signal-to-noise ratio (OSNR) can degrade by up to 3dB when the fiber span is 100km, which brings higher costs and complexity to system gain and maintenance.

[0045] This application provides a single-mode optical fiber to solve the problem of large differences in attenuation coefficients in the C+L band of single-mode optical fibers in related technologies.

[0046] The following description, in conjunction with the accompanying drawings, illustrates an embodiment of a single-mode optical fiber provided in this application.

[0047] Figure 1This is a schematic diagram of the cross-sectional structure of a single-mode optical fiber provided in an embodiment of this application. Figure 2 This is a schematic diagram of the refractive index profile of a single-mode optical fiber provided in an embodiment of this application.

[0048] like Figure 1 and Figure 2 As shown, the single-mode fiber in this embodiment comprises, from the center to the outer periphery: a core layer 10, an inner cladding 20, a first depressed cladding 30, a second depressed cladding 40, and an outer cladding 50; wherein, the refractive index of the core layer 10 relative to the outer cladding 50 is negatively correlated with its radius; the refractive index of the inner cladding 20 relative to the outer cladding 50 is negatively correlated with its radius, and the refractive index of the outer boundary of the inner cladding 20 is less than the refractive index of the outer cladding 50; the refractive index of the first depressed cladding 30 is less than the refractive index of the second depressed cladding 40; and the refractive index of the second depressed cladding 40 is less than the refractive index of the outer cladding 50.

[0049] Using the technical solution of this embodiment, the single-mode optical fiber includes, from the center to the outer periphery, a core layer 10, an inner cladding 20, a first recessed cladding 30, a second recessed cladding 40, and an outer cladding 50. The refractive index of the core layer 10 relative to the outer cladding 50 is negatively correlated with the radius, and the refractive index of the inner cladding 20 relative to the outer cladding 50 is also negatively correlated with the radius. This arrangement causes the refractive indices of the core layer and the inner cladding to continuously change with the increase of the radius, making the attenuation coefficients of the single-mode optical fiber in the C-band and L-band closer, thereby improving the transmission bandwidth of the optical fiber in the C+L band. Simultaneously, the refractive index of the outer boundary of the inner cladding 20 is lower than that of the outer cladding 50, causing the refractive index of the inner cladding 20 to gradually change to a state lower than that of the outer cladding 50, thereby further reducing the difference in the attenuation coefficient of the single-mode optical fiber in the C+L band and further improving the transmission bandwidth of the optical fiber in the C+L band.

[0050] Specifically, Figure 5 This is a loss decomposition diagram of the single-mode optical fiber provided in this application.

[0051] like Figure 5 It can be seen that the attenuation of optical fiber in the C+L band (1520–1625 nm) can be considered as the result of the combined effects of Rayleigh scattering loss and infrared absorption loss. Rayleigh scattering is caused by refractive index fluctuations due to variations in material concentration (composition) or density (viscosity), and decreases with increasing wavelength. Infrared absorption loss is caused by the inherent vibrations of SiO2 molecules and increases with increasing wavelength.

[0052] The purpose of this application is not to maximally reduce the attenuation coefficient of optical fiber across all wavelengths, but rather to make the attenuation coefficients of optical fiber more similar across all wavelengths, i.e., to reduce the difference in attenuation coefficients across different wavelengths. Therefore, the above-described configuration can control the magnitude of Rayleigh scattering loss and infrared absorption loss to reduce the difference in attenuation coefficients between the C-band and L-band of single-mode fiber. Current technologies often focus on maximizing the reduction of Rayleigh scattering loss and infrared absorption loss to pursue lower attenuation coefficients, while neglecting the fact that appropriate infrared absorption loss helps balance the difference in attenuation coefficients between the C+L bands.

[0053] Specifically, such as Figure 1 and Figure 2 As shown, in this embodiment, the core layer is a silicon dioxide glass layer doped with germanium. The refractive index of the core layer 10 relative to the outer cladding layer 50 follows a linear or curvilinear function distribution with increasing radius. The horizontal axis of both the linear and curvilinear functions is the fiber radius, and the vertical axis of both functions is the refractive index of the core layer relative to the outer cladding layer.

[0054] In the above structure, the core layer 10 is a germanium-doped silica glass layer. Germanium doping increases the refractive index of the core layer 10, shifting the infrared absorption peak of the optical fiber from the L-band to the C-band, thereby reducing the attenuation coefficient difference in the C+L band of the single-mode fiber. Furthermore, the refractive index of the core layer 10 relative to the outer cladding 50 follows a linear or curvilinear distribution with increasing radius, causing the refractive index of the core layer 10 to gradually decrease. This results in a gradual transition of refractive index from the core layer 10 to the inner cladding 20, avoiding abrupt changes in refractive index and effectively reducing or suppressing the interface effect at the core layer 10-inner cladding 20 interface, thus improving bandwidth.

[0055] It should be noted that the core layer 10 is a silica glass layer doped with GeO2.

[0056] like Figure 1 As shown, in this embodiment, when the refractive index of the core layer 10 relative to the outer cladding layer 50 is distributed as a linear function with the increase of radius, the angle between any point on the linear function and the horizontal axis is less than a preset angle α.

[0057] When the refractive index of the core layer 10 relative to the outer cladding layer 50 follows a curve function distribution with the increase of radius, the angle between any point on the curve function and the horizontal axis is less than the preset angle α.

[0058] It should also be noted that, in this embodiment, the refractive index of the inner cladding layer 20 relative to the outer cladding layer 50 also exhibits a linear or curvilinear distribution with increasing radius. When the refractive index of the outer cladding layer relative to the outer cladding layer 50 exhibits a linear distribution with increasing radius, the angle between any point on the linear function and the horizontal axis is less than a preset angle α; similarly, when the refractive index of the core layer 10 relative to the outer cladding layer 50 exhibits a curvilinear distribution with increasing radius, the angle between any point on the curvilinear function and the horizontal axis is less than a preset angle α.

[0059] Specifically, Figure 3 Provided for the embodiments of this application Figure 2 A magnified schematic diagram of the structure at point A of a single-mode optical fiber.

[0060] like Figures 1 to 3 As shown, in this embodiment, the preset angle α is between 15° and 35°. That is, 15°≤α≤35°. For example, the specific values ​​that the preset angle α can take include, but are not limited to, 15°, 20°, 25°, and 30°.

[0061] When the refractive index of the outer cladding layer relative to the outer cladding layer 50 follows a linear function distribution with increasing radius, the angle between any point on the linear function and the horizontal axis is a preset angle α, which is between 15° and 35°. That is, when the refractive index of the outer cladding layer relative to the outer cladding layer 50 follows a linear function distribution with increasing radius, the slope of this linear function is less than a predetermined value, which is between -0.26 and -0.7. Similarly, when the refractive index of the core layer 10 relative to the outer cladding layer 50 follows a curvilinear function distribution with increasing radius, the angle between any point on the curvilinear function and the horizontal axis is less than a preset angle α, which is between 15° and 35°. That is, when the refractive index of the core layer 10 relative to the outer cladding layer 50 follows a curvilinear function distribution with increasing radius, the slope of any point on the curvilinear function is less than a predetermined value, which is between -0.26 and -0.7.

[0062] The above settings result in a slower decrease in the refractive index of the core layer 10, which helps to reduce the attenuation coefficient difference of single-mode fiber in the C+L band.

[0063] Furthermore, such as Figure 1 and Figure 2 As shown, in this embodiment, the refractive index difference Δ1 between the center point of the core layer 10 and the outer cladding 50 satisfies: 0.3% ≤ Δ1 ≤ 0.35%, which gives the core layer 10 a higher refractive index, causing the infrared absorption peak of the optical fiber to shift from the L-band to the C-band, thereby achieving the purpose of controlling infrared absorption loss. For example, specific values ​​for Δ1 may include, but are not limited to, 0.3%, 0.31%, 0.32%, 0.34%, and 0.35%.

[0064] Furthermore, such as Figure 1 and Figure 2As shown, the refractive index difference Δ2 between the core layer 10 and the inner cladding 20 and the outer cladding 50 satisfies: 0.24% ≤ Δ2 ≤ 0.3%. The radius R1 of the core layer 10 satisfies: 4μm ≤ R1 ≤ 7μm.

[0065] Furthermore, such as Figure 1 and Figure 2 As shown, in this embodiment, the refractive index difference Δ3 between the boundary of the inner cladding layer 20 and the first recessed cladding layer 30 and the outer cladding layer 50 satisfies: -0.2% ≤ Δ3 ≤ -0.3%; the difference between the radius R2 of the inner cladding layer 20 and the radius R1 of the core layer 10 satisfies: 1μm ≤ R2 - R1 ≤ 2.4μm; the inner cladding layer 20 is a silicon dioxide glass layer doped with germanium and fluorine, specifically, the germanium is GeO2 or GeCl4, and the fluorine is one or more of CF4, C2F6, SiF4, and SF4.

[0066] Furthermore, such as Figure 1 and Figure 2 As shown, in this embodiment, the refractive index difference Δ4 between the second recessed cladding 40 and the outer cladding 50 satisfies: -0.05% ≤ Δ4 ≤ -0.15%; the difference between the radius R3 of the first recessed cladding 30 and the radius R2 of the inner cladding 20 satisfies: 3μm ≤ R3 - R2 ≤ 7μm; the difference between the radius R4 of the second recessed cladding 40 and the radius R3 of the first recessed cladding 30 satisfies: 7.2μm ≤ R4 - R3 ≤ 13μm.

[0067] It should be noted that both the first sunken cladding layer 30 and the second sunken cladding layer 40 are silicon dioxide glass layers doped with fluorine.

[0068] It should also be noted that, in this embodiment, a coating layer 60 is further wrapped around the outer cladding of the single-mode fiber. The diameter of the coating layer 60 is 245±10μm. The concentricity error between the coating layer 60 and the outer cladding 50 is less than or equal to 12μm. Optionally, the diameter of the coating layer 60 is 200±10μm, and the concentricity error between the coating layer 60 and the outer cladding 50 is less than or equal to 10μm.

[0069] To further illustrate this application, the single-mode optical fiber provided in this application will be described in detail below with reference to embodiments.

[0070] Example 1

[0071] R1 is 4.8 μm; R2-R1 is 1.8 μm; R3-R2 is 4.8 μm; R4-R3 is 8.5 μm; Δ1 is 0.31%; Δ2 is 0.26%; Δ3 is -0.22%; Δ4 is ​​-0.14%.

[0072] The optical and transmission characteristics of the optical fiber were tested as follows: the cutoff wavelength was 1178.3 nm; the mode field diameter at 1310 nm was 9.16 nm; the attenuation coefficient at 1520 nm was 0.189 dB / km; the attenuation coefficient at 1550 nm was 0.182 dB / km; the attenuation coefficient at 1575 nm was 0.181 dB / km; and the attenuation coefficient at 1625 nm was 0.192 dB / km. The attenuation was lowest in the 1520 nm and 1520–1625 nm bands. The difference between the minimum values ​​is 0.008 dB / km; the difference between the minimum attenuation values ​​in the 1625 nm and 1520–1625 nm bands is 0.011 dB / km; the macrobending loss R15×10 turns @1550 nm is 0.021 dB; the macrobending loss R15×10 turns @1625 nm is 0.07 dB; the macrobending loss R10×1 turns @1550 nm is 0.146 dB; and the macrobending loss R10×1 turns @1625 nm is 0.314 dB.

[0073] Example 2

[0074] R1 is 5.7 μm; R2-R1 is 1.4 μm; R3-R2 is 5.1 μm; R4-R3 is 10.7 μm; Δ1 is 0.32%; Δ2 is 0.29%; Δ3 is -0.25%; Δ4 is ​​-0.11%.

[0075] The optical and transmission characteristics of the optical fiber were tested as follows: the cutoff wavelength was 1211.7 nm; the mode field diameter at 1310 nm was 9.31 nm; the attenuation coefficient at 1520 nm was 0.193 dB / km; the attenuation coefficient at 1550 nm was 0.184 dB / km; the attenuation coefficient at 1575 nm was 0.183 dB / km; the attenuation coefficient at 1625 nm was 0.193 dB / km; and the attenuation within the 1520 nm and 1520–1625 nm bands was [not specified]. The difference in minimum values ​​is 0.01 dB / km; the difference in minimum attenuation between 1625 nm and 1520–1625 nm bands is 0.01 dB / km; macrobending loss R15×10 turns @1550 nm is 0.084 dB; macrobending loss R15×10 turns @1625 nm is 0.185 dB; macrobending loss R10×1 turns @1550 nm is 0.152 dB; macrobending loss R10×1 turns @1625 nm is 0.409 dB.

[0076] Example 3

[0077] R1 is 5.3 μm; R2-R1 is 1.9 μm; R3-R2 is 5.3 μm; R4-R3 is 10.1 μm; Δ1 is 0.33%; Δ2 is 0.3%; Δ3 is -0.26%; Δ4 is ​​-0.1%.

[0078] The optical and transmission characteristics of the optical fiber were tested as follows: the cutoff wavelength was 1227.3 nm; the mode field diameter at 1310 nm was 9.22 nm; the attenuation coefficient at 1520 nm was 0.194 dB / km; the attenuation coefficient at 1550 nm was 0.189 dB / km; the attenuation coefficient at 1575 nm was 0.188 dB / km; and the attenuation coefficient at 1625 nm was 0.200 dB / km. The attenuation was lowest in the 1520 nm and 1520–1625 nm bands. The difference between the minimum values ​​is 0.006 dB / km; the difference between the minimum attenuation values ​​in the 1625 nm and 1520–1625 nm bands is 0.012 dB / km; the macrobending loss R15×10 turns @1550 nm is 0.037 dB; the macrobending loss R15×10 turns @1625 nm is 0.114 dB; the macrobending loss R10×1 turns @1550 nm is 0.221 dB; and the macrobending loss R10×1 turns @1625 nm is 0.531 dB.

[0079] It should be noted that the specific testing method is existing technology, and will not be described in detail here. The parameters in Examples 1 to 3 are shown in Table 1:

[0080] Table 1

[0081]

[0082] The optical and transmission characteristics test results of optical fibers show that the cutoff wavelength λ of the optical fiber cable is... CC ≤1260nm, with a mode field diameter ranging from 8.8 to 9.6µm at 1310nm.

[0083] The optical fiber has an attenuation coefficient of less than or equal to 0.20 dB / km in the 1520–1625 nm wavelength band. Specifically, the attenuation coefficient at 1550 nm is less than or equal to 0.19 dB / km, and the attenuation coefficient at 1625 nm is less than or equal to 0.20 dB / km. The difference between the minimum attenuation values ​​in the 1520 nm and 1520–1625 nm wavelength bands is less than or equal to 0.012 dB / km, and the difference between the minimum attenuation values ​​in the 1625 nm and 1520–1625 nm wavelength bands is less than or equal to 0.012 dB / km. When the optical fiber is loosely wound 10 times with a radius of 15 mm, the bending loss at 1550 nm is less than or equal to 0.25 dB, and the bending loss at 1625 nm is less than or equal to 1.0 dB. When loosely wound 1 time with a radius of 10 mm, the bending loss at 1550 nm is less than or equal to 0.75 dB, and the bending loss at 1625 nm is less than or equal to 1.5 dB.

[0084] On the other hand, this application provides a method for fabricating a single-mode optical fiber.

[0085] The method for fabricating single-mode optical fiber provided in the embodiments of this application is described below with reference to the accompanying drawings.

[0086] Figure 6 A flowchart illustrating the fabrication method of the single-mode optical fiber provided in the application.

[0087] like Figure 6 As shown, the method for fabricating single-mode optical fiber in this embodiment is used to fabricate the above-mentioned single-mode optical fiber, and specifically includes:

[0088] Step S100: In a vapor phase evaporation apparatus, a core layer 10, an inner cladding layer 20, a first sunken cladding layer 30, and a second sunken cladding layer 40 are prepared sequentially by deposition, so that the core layer 10, the inner cladding layer 20, the first sunken cladding layer 30, and the second sunken cladding layer 40 form a loose preform.

[0089] Step S200: The porous preform is sintered at a high temperature of 1300℃~1500℃ in an atmosphere of halogen gas to form a transparent quartz rod.

[0090] Step S300: Place the quartz rod in a sintering furnace for sintering, and form an outer cladding layer 50 on the outside of the quartz rod according to the preset weight of the outer cladding layer 50 to obtain a preformed rod.

[0091] In step S100, a deposition method is used to prepare the core layer 10, inner cladding layer 20, first depressed cladding layer 30, and second depressed cladding layer 40. Specifically, SiCl4, GeCl4, and any one or more of CF4, C2F6, SiF4, and SF4 are used as dopants. Through a gas-phase evaporation device, combined with real-time monitoring by a PLC, the gas flow rate and ratio are controlled to sequentially deposit the core layer 10, inner cladding layer 20, first depressed cladding layer 30, and second depressed cladding layer 40, conforming to the refractive index structure design, to form a porous preform. Compared with the traditional gas-blowing bubbling method, the deposition method can effectively reduce flow rate fluctuations, and is particularly suitable for the preparation of preforms with multi-layer refractive index profile structures.

[0092] Steps S200 and S300 enable the optical fiber to be vitrified while effectively extending the heat treatment time per unit area, eliminating a large number of micro-defects in the glass forming process, improving the stress distribution of the rod, and thus eliminating Rayleigh scattering and absorption loss caused by the inhomogeneity of the quartz structure.

[0093] Furthermore, in this embodiment, after the preform is obtained in step S300, the method for fabricating single-mode optical fiber further includes:

[0094] Step S400: Load the preform into the drawing tower, heat the preform, and melt the preform starting from the cone tip;

[0095] Step S500: The molten preform is drawn using a drawing process to form quartz fibers;

[0096] Step S600: The quartz fiber is fed into an annealing furnace for annealing, and then the quartz fiber is naturally cooled so that the surface temperature of the quartz fiber is reduced to 45°C to 55°C, preferably 50°C.

[0097] Step S700: An inner coating layer and an outer coating layer are formed sequentially on the outer side of the annealed quartz fiber.

[0098] Specifically, in step S700, the inner coating layer and the outer coating layer are acrylic resin materials, wherein the modulus of the inner coating layer is less than that of the outer coating layer, the elastic modulus of the inner coating layer after curing is less than 0.8 MPa, and the elastic modulus of the outer coating layer after curing is greater than 700 MPa.

[0099] Furthermore, in this embodiment, step S300, which involves placing the quartz rod in a sintering furnace for sintering, specifically includes the following steps:

[0100] Step S310: Place the quartz rod in the sintering furnace and raise the furnace temperature at a rate of 30°C to 50°C / min to the first preset temperature, and keep the quartz rod at the first preset temperature for 2 hours to 4 hours.

[0101] Step S320: Raise the furnace temperature of the sintering furnace to the second preset temperature within a preset time, and keep the quartz rod at the second preset temperature for 24 hours to complete the sintering.

[0102] It should be noted that the sintering furnace has a vacuum power supply, which can create a certain degree of vacuum in the sintering chamber. The sintering process of the quartz rod in the sintering furnace is carried out in an environment with a certain degree of vacuum.

[0103] Furthermore, in this embodiment, step S600, which involves annealing the quartz fiber in an annealing furnace, specifically includes:

[0104] Step S610: Set the initial temperature of the annealing furnace between 1200°C and 1400°C;

[0105] Step S620: Feed the quartz fiber into the annealing furnace;

[0106] Step S630: Using a temperature gradient between 50°C and 150°C, gradually reduce the temperature of the annealing furnace until the temperature of the annealing furnace drops to between 700°C and 900°C.

[0107] It should be noted that the first preset temperature mentioned above is between 400℃ and 600℃; for example, the first preset temperature is 400℃, 420℃, 450℃, 500℃, 550℃ or 600℃.

[0108] The preset time is between 1 hour and 2 hours. For example, the preset time is 1 hour, 1.5 hours or 3 hours.

[0109] The second preset temperature is between 1200°C and 1300°C. For example, the second preset temperature is 1200°C, 1250°C, 1275°C or 1300°C.

[0110] Figure 4 A comparison diagram of the attenuation characteristics of the single-mode fiber provided in the embodiments of this application and the single-mode fiber in related technologies.

[0111] like Figure 4 As shown, the single-mode fiber prepared by the above method exhibits optimized attenuation performance in the C+L band, demonstrating superior attenuation flatness compared to ordinary single-mode fiber. The role of germanium-10 doping in the core layer is to shift the infrared absorption peak of SiO2 from the L band to the C band by increasing the refractive index, thereby controlling infrared absorption loss. The graded refractive index design further facilitates attenuation control at different wavelengths.

[0112] The first depressed cladding ensures good bending resistance of the optical fiber, primarily compensating for insufficient bending resistance. Improving bending resistance based on the first depressed cladding is a common practice, but it also increases the cutoff wavelength. This embodiment, by setting an inner cladding with a gradually decreasing refractive index between the first depressed cladding and the core layer, effectively controls the cutoff wavelength while satisfying trench mode confinement.

[0113] In the description of this application, it should be understood that the terms "center", "longitudinal", "length", "width", "upper", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0114] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. In this application, unless otherwise expressly specified and limited, the terms "installation," "fastening," "connection," "fixing," etc., should be interpreted broadly. For example, they may refer to a fixed connection, a detachable connection, or an integral part; they may refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they may refer to a direct connection or an indirect connection through an intermediate medium; they may refer to the internal communication of two elements or the interaction between two elements, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0115] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0116] In this specification, the use of terms such as "optionally," "optionally implemented," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. The illustrative expressions of the above terms in this specification do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A single-mode optical fiber, characterized in that, The single-mode optical fiber comprises, from the center to the outer periphery, a core layer (10), an inner cladding layer (20), a first recessed cladding layer (30), a second recessed cladding layer (40), and an outer cladding layer (50). The refractive index of the core layer (10) relative to the outer cladding layer (50) is negatively correlated with its radius; The refractive index of the inner cladding (20) relative to the outer cladding (50) is negatively correlated with the radius, and the refractive index of the outer boundary of the inner cladding (20) is less than that of the outer cladding (50). The refractive index difference Δ2 between the boundary between the core layer (10) and the inner cladding layer (20) and the outer cladding layer (50) satisfies: 0.24%≤Δ2≤0.3%; The refractive index of the first depressed cladding (30) is less than that of the second depressed cladding (40); The refractive index of the second recessed cladding (40) is less than that of the outer cladding (50); The refractive index of the core layer (10) relative to the outer cladding layer (50) is distributed as a linear function or a curve function with increasing radius, wherein the horizontal axis of the linear function and the curve function are both the fiber radius, and the vertical axis of the linear function and the curve function are both the refractive index of the core layer (10) relative to the outer cladding layer (50); When the refractive index of the core layer (10) relative to the outer cladding layer (50) is distributed as a linear function with the increase of radius, the angle between any point on the linear function and the horizontal axis is less than a preset angle α. When the refractive index of the core layer (10) relative to the outer cladding layer (50) is distributed as a curve function with the increase of radius, the angle between any point on the curve function and the horizontal axis is less than a preset angle α. The preset angle α is between 15° and 35°.

2. The single-mode optical fiber according to claim 1, characterized in that, The core layer (10) is a silicon dioxide glass layer doped with germanium.

3. The single-mode optical fiber according to claim 1 or 2, characterized in that, The refractive index difference Δ1 between the center point of the core layer (10) and the outer cladding layer (50) satisfies: 0.3% ≤ Δ1 ≤ 0.35%; And / or, the radius R1 of the core layer (10) satisfies: 4μm≤R1≤7μm.

4. The single-mode optical fiber according to claim 1, characterized in that, The refractive index difference Δ3 between the boundary of the inner cladding (20) and the first recessed cladding (30) and the outer cladding (50) satisfies: -0.2% ≤ Δ3 ≤ -0.3%; The difference between the radius R2 of the inner cladding (20) and the radius R1 of the core layer (10) satisfies: 1μm≤R2-R1≤2.4μm; The inner cladding layer (20) is a silicon dioxide glass layer doped with germanium and fluorine.

5. The single-mode optical fiber according to claim 1, characterized in that, The refractive index difference Δ4 between the second recessed cladding (40) and the outer cladding (50) satisfies: -0.05% ≤ Δ4 ≤ -0.15%; The difference between the radius R3 of the first sunken cladding layer (30) and the radius R2 of the inner cladding layer (20) satisfies: 3μm≤R3-R2≤7μm; The difference between the radius R4 of the second sunken cladding (40) and the radius R3 of the first sunken cladding (30) satisfies: 7.2μm≤R4-R3≤13μm; Both the first sunken cladding layer (30) and the second sunken cladding layer (40) are silicon dioxide glass layers doped with fluorine.

6. A method for fabricating a single-mode optical fiber, characterized in that, For fabricating the single-mode optical fiber according to any one of claims 1 to 5, comprising: In a vapor phase evaporation apparatus, the core layer (10), the inner cladding layer (20), the first sunken cladding layer (30) and the second sunken cladding layer (40) are prepared sequentially by deposition, so that the core layer (10), the inner cladding layer (20), the first sunken cladding layer (30) and the second sunken cladding layer (40) form a loose preform; The porous preform is sintered at a temperature of 1300℃ to 1500℃ in an atmosphere of halogen gas to form a transparent quartz rod. The quartz rod is placed in a sintering furnace for sintering, and an outer cladding layer (50) is formed on the outside of the quartz rod according to the preset weight of the outer cladding layer (50) to obtain a preformed rod.

7. The method for fabricating a single-mode optical fiber according to claim 6, characterized in that, After the step of obtaining the preform, the method for fabricating the single-mode optical fiber further includes: The preform is loaded into the drawing tower, heated, and melted from the tip of the cone. The molten preform is drawn using a drawing process to form quartz fibers; The quartz fiber is annealed in an annealing furnace and then naturally cooled to reduce the surface temperature of the quartz fiber to 45°C to 55°C. An inner coating layer and an outer coating layer are sequentially formed on the outer side of the annealed quartz fiber.

8. The method for fabricating a single-mode optical fiber according to claim 6, characterized in that, The step of placing the quartz rod in a sintering furnace for sintering specifically includes: The quartz rod is placed in a sintering furnace, and the furnace temperature is uniformly increased to a first preset temperature at a rate of 30°C to 50°C / min, and the quartz rod is held at the first preset temperature for 2 hours to 4 hours. The furnace temperature of the sintering furnace is raised to a second preset temperature within a preset time, and the quartz rod is kept at the second preset temperature for 24 hours to complete the sintering.

9. The method for fabricating a single-mode optical fiber according to claim 7, characterized in that, The quartz fiber is annealed in an annealing furnace, specifically including: The initial temperature of the annealing furnace is set between 1200°C and 1400°C; The quartz fiber is fed into an annealing furnace; Using a temperature gradient between 50°C and 150°C, the temperature of the annealing furnace is gradually reduced until it drops to between 700°C and 900°C.

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