Ultra-low-loss and large-effective-area optical fiber and preparation method therefor

Abstract

An ultra-low-loss and large-effective-area optical fiber, sequentially comprising, from inside to outside, a core layer (10), an inner cladding layer (20), a depressed cladding layer (30) and an outer cladding layer (40), wherein the depressed cladding layer (30) comprises a deep depressed layer (31), a depressed step layer (32) and a depressed platform layer (33). The ultra-low-loss and large-effective-area optical fiber having a specific refractive index profile structure has a relatively good bending resistance performance, an optical-cable cutoff wavelength of no more than 1520 nm, and a relatively low macro-bending loss, and also has a relatively small difference in attenuation coefficients between a short-wavelength C-band of 1520 to 1565 nm and a long-wavelength L-band of 1565 to 1625 nm. The ultra-low-loss and large-effective-area optical fiber can meet the G.654.E optical-fiber standards, and can be used in ultra-high-voltage electric power communication, ultra-high-speed communication lines of submarine cables or land trunks, etc.

Description

Ultra-low loss large effective area optical fiber and preparation method thereof

[0001] This application is based on the Chinese application with CN application number 202311048448.6 and application date August 17, 2023, and claims its priority. The disclosed content of the CN application is again introduced as a whole into this application. Technical Field

[0002] The present invention relates to the field of optical communication technology, and in particular to an ultra-low loss large effective area optical fiber and a preparation method thereof. Background Art

[0003] A degraded signal-to-noise ratio and fiber nonlinearity are the primary factors limiting optical transmission distance. Reducing fiber loss can reduce the number of repeater stations, thereby reducing overall link loss and lowering construction costs. Increasing the effective area can mitigate nonlinear effects and increase input power, thereby improving fiber transmission performance. In addition to improving single-channel transmission capacity, increasing the number of wavelength division multiplexing (WDM) system channels and expanding the transmission band can also increase system capacity to meet growing business needs.

[0004] Currently, a step-type structure design is often used to reduce the loss of optical fiber. However, the attenuation coefficients of existing optical fibers vary greatly from short wavelength to long wavelength, and the attenuation consistency of the optical fiber's communication window needs to be improved.

[0005] Therefore, it is urgent to research and develop a low-loss optical fiber with a small difference in attenuation coefficient between the short wavelength C band 1520nm~1565nm and the long wavelength L band 1565nm~1625nm, which is of great significance for improving the transmission performance of optical fiber.

[0006] Summary of the Invention

[0007] The main purpose of the present invention is to provide an ultra-low loss large effective area optical fiber and its preparation method, so as to solve the problem in the prior art that the attenuation coefficient of optical fiber in the short wavelength to long wavelength range varies greatly and the communication window attenuation consistency of optical fiber is poor.

[0008] In order to achieve the above-mentioned object, the present invention provides an ultra-low loss large effective area optical fiber, which comprises a core layer, an inner cladding, a depressed cladding and an outer cladding from the inside out; the depressed cladding comprises a deep depressed layer, a depressed step layer and a depressed platform layer; the maximum relative refractive index difference of the core layer material is △1 max , the minimum relative refractive index difference of the inner cladding material is △2 min , the relative refractive index difference of the deep concave layer material is △3; the maximum relative refractive index difference of the concave step layer material is △4 max , and the minimum relative refractive index is △4 min, the maximum relative refractive index difference of the concave platform layer material is △5 max , and the minimum relative refractive index is △5 min ; △3<△2 min , △3<△4 min , and △3<△5 min ; r represents the radial distance from a certain position in the ultra-low loss large effective area optical fiber to the center of the optical fiber;

[0009] △1(r) represents the relative refractive index difference of the material at a certain position in the core layer from the center of the optical fiber. △1(r) and r satisfy the following relationship (1):

[0010] Where R0 represents the radius of the core layer, g represents the refractive index distribution parameter of the core layer, 2≤g≤6;

[0011] △2(r) represents the relative refractive index difference of the material at a certain position in the inner cladding from the center of the optical fiber. △2(r) and r satisfy the following relationship (2):

[0012] Wherein, R1 represents the radial distance between the contact interface between the inner cladding and the depressed cladding and the center of the optical fiber, h represents the refractive index distribution parameter of the inner cladding, 3≤h≤10;

[0013] △4(r) represents the relative refractive index difference between a certain position in the depressed step layer and the center of the optical fiber. △4(r) and r satisfy the following relationship (3):

[0014] Wherein, R2 represents the radial distance between the contact interface of the deep depression layer and the depression step layer and the center of the optical fiber, R3 represents the radial distance between the contact interface of the depression step layer and the depression platform layer and the center of the optical fiber, and m represents the refractive index distribution parameter of the depression step layer, 0.5≤m≤3;

[0015] △5(r) represents the relative refractive index difference between a certain position in the concave platform layer and the center of the optical fiber. △5(r) and r satisfy the following relationship (4):

[0016] Wherein, R4 represents the radial distance between the contact interface of the depressed terrace layer and the outer cladding and the center of the optical fiber, and n represents the refractive index distribution parameter of the depressed terrace layer, 0.5≤n≤3;

[0017] The outer cladding is a silicon dioxide layer, and the refractive index of the outer cladding is 0.

[0018] To achieve the above-mentioned objectives, another aspect of the present invention provides a method for preparing an ultra-low-loss large effective area optical fiber, the preparation method comprising: preparing an optical fiber preform, the optical fiber preform comprising, from the inside to the outside, a core layer preparation layer, an inner cladding preparation layer, a depressed cladding preparation layer, and an outer cladding preparation layer; and subjecting the optical fiber preform to a drawing annealing treatment so that the core layer preparation layer, the inner cladding preparation layer, the depressed cladding preparation layer, and the outer cladding preparation layer are sequentially transformed into the core layer, inner cladding, depressed cladding, and outer cladding defined above in this application, thereby obtaining an ultra-low-loss large effective area optical fiber.

[0019] By applying the technical solution of the present invention, by designing the depressed cladding of the above-mentioned specific cladding structure, and simultaneously designing the variation rules of the relative refractive index difference △1(r) of the core layer material, the relative refractive index difference △2(r) of the inner cladding material, the relative refractive index difference △4(r) of the depressed step layer material, and the relative refractive index difference △5(r) of the depressed platform layer material to satisfy equations (1) to (4), respectively, and limiting the relative refractive index difference △3 of the deep depressed layer material to be within the above-mentioned range, it is possible to effectively constrain the optical fiber waveguide transmission, improve the optical fiber attenuation performance, and enable the optical fiber to have higher bending resistance and an optical cable cutoff wavelength of no more than 1520 nm.

[0020] In summary, the ultra-low loss large effective area optical fiber with the above-mentioned specific refractive index profile structure provided by the present application has good bending resistance, an optical cable cut-off wavelength of no more than 1520nm, small macrobending loss, and a small difference in attenuation coefficient from the short wavelength C band 1520nm to 1565nm to the long wavelength L band 1565nm to 1625nm. It can meet the G.654.E optical fiber standard and can be used for ultra-high voltage power communications, submarine cables or land trunk ultra-high-speed communication lines, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0022] FIG1 shows a schematic cross-sectional view of the structure of the optical fiber prepared in Example 1;

[0023] FIG2 shows a cross-sectional view of the refractive index structure of the optical fiber prepared in Example 1;

[0024] FIG3 shows a schematic structural diagram of an optical fiber drawing and annealing device in a preferred embodiment of the present application;

[0025] FIG4 shows a schematic diagram of the structure of an apparatus used in the optical fiber preparation process in a preferred embodiment of the present application.

[0026] Among them, the above-mentioned drawings include the following figure marks: 10, core layer; 20, inner cladding; 30, depressed cladding; 31, deep depressed layer; 32, depressed step layer; 33, depressed platform layer; 40, outer cladding; 51, first coating layer; 52, second coating layer; 100, inner cavity heating section; 110, preheating component; 120, melting component; 200, drawing annealing section; 210, first annealing unit; 220, second annealing unit; 300, annealing tube; 301, optical fiber annealing tube outlet. DETAILED DESCRIPTION

[0027] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0028] As described in the background art, existing optical fibers have large differences in attenuation coefficients from short wavelengths to long wavelengths, and the attenuation consistency of the communication window is poor, resulting in poor optical fiber transmission performance. In order to solve the above technical problems, the present application provides an ultra-low loss large effective area optical fiber, as shown in Figure 1. The ultra-low loss large effective area optical fiber includes, from the inside to the outside, a core layer 10, an inner cladding 20, a depressed cladding 30, and an outer cladding 40; the depressed cladding 30 includes a deep depressed layer 31, a depressed step layer 32, and a depressed platform layer 33; the maximum relative refractive index difference of the core layer 10 material is △1 max The minimum relative refractive index difference of the inner cladding 20 material is △2 min , the relative refractive index difference of the material of the deep concave layer 31 is △3; the maximum relative refractive index difference of the material of the concave step layer 32 is △4 max , and the minimum relative refractive index is △4 min , the maximum relative refractive index difference of the material of the concave platform layer 33 is △5 max , and the minimum relative refractive index is △5 min ; △3<△2 min , △3<△4 min , and △3<△5 min ; r represents the radial distance from a certain position in the ultra-low loss large effective area optical fiber to the center of the optical fiber;

[0029] Δ1(r) represents the relative refractive index difference of the material at a certain position in the core layer 10 from the center of the optical fiber. Δ1(r) and r satisfy the following relationship (1):

[0030] Wherein, R0 represents the radius of the core layer 10, g represents the refractive index distribution parameter of the core layer 10, 2≤g≤6;

[0031] Δ2(r) represents the relative refractive index difference of the material at a certain position in the inner cladding 20 from the center of the optical fiber. Δ2(r) and r satisfy the following relationship (2):

[0032] Wherein, R1 represents the radial distance between the contact interface between the inner cladding 20 and the depressed cladding 30 and the center of the optical fiber, h represents the refractive index distribution parameter of the inner cladding 20, and 3≤h≤10;

[0033] Δ4(r) represents the relative refractive index difference between a certain position in the recessed step layer 32 and the center of the optical fiber. Δ4(r) and r satisfy the following relationship (3):

[0034] Wherein, R2 represents the radial distance between the contact interface of the deep depressed layer 31 and the depressed step layer 32 and the center of the optical fiber, R3 represents the radial distance between the contact interface of the depressed step layer 32 and the depressed platform layer 33 and the center of the optical fiber, and m represents the refractive index distribution parameter of the depressed step layer 32, where 0.5≤m≤3;

[0035] Δ5(r) represents the relative refractive index difference between a certain position in the depressed platform layer 33 and the center of the optical fiber. Δ5(r) and r satisfy the following relationship (4):

[0036] Wherein, R4 represents the radial distance between the contact interface between the depressed platform layer 33 and the outer cladding layer 40 and the center of the optical fiber, and n represents the refractive index distribution parameter of the depressed platform layer 33, where 0.5≤n≤3;

[0037] The outer cladding layer 40 is a silicon dioxide layer, and the refractive index of the outer cladding layer 40 is zero.

[0038] It should be noted that the relative refractive index difference in this application refers to the difference between the refractive index of a layer in the ultra-low loss large effective area optical fiber and the refractive index of pure silica material.

[0039] By designing the depressed cladding 30 of the above-mentioned specific cladding structure, and simultaneously designing the variation rules of the relative refractive index difference △1(r) of the core layer 10 material, the relative refractive index difference △2(r) of the inner cladding 20 material, the relative refractive index difference △4(r) of the depressed step layer 32 material, and the relative refractive index difference △5(r) of the depressed platform layer 33 material to satisfy equations (1) to (4), respectively, and limiting the relative refractive index difference △3 of the deep depressed layer 31 material to be within the above-mentioned range, it is possible to effectively constrain the optical fiber waveguide transmission, improve the optical fiber attenuation performance, and make the optical fiber have higher bending resistance and a cut-off wavelength of no more than 1520nm.

[0040] In summary, the ultra-low loss large effective area optical fiber with the above-mentioned specific refractive index profile structure (as shown in Figure 2) provided by this application has good bending resistance, an optical cable cut-off wavelength not greater than 1520nm, small macrobending loss, and a small difference in attenuation coefficient from the short wavelength C band 1520nm~1565nm to the long wavelength L band 1565nm~1625nm. It can meet the G.654.E optical fiber standard and can be used for ultra-high voltage power communications, submarine cables or land trunk ultra-high-speed communication lines, etc.

[0041] In a preferred embodiment, Δ1 max 0.10~0.30%,△2 min -0.25~-0.35%, △3 is -0.45~-0.5%, △4 max -0.20~-0.25%,△4 min -0.25~-0.30%,△5 max -0.30~-0.35%,△5 min -0.35~-0.4%. △1 max ,△2 min , △3, △4 max ,△4 min ,△5 max and △5 min The above ranges are independently included but not limited to. Limiting them within the above ranges is beneficial to constraining the optical fiber waveguide transmission, improving the optical fiber attenuation performance, thereby improving the optical fiber's anti-bending performance, and reducing the difference in the attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band.

[0042] In a preferred embodiment, R0 is 5-7 μm, the difference between R1 and R0 is 3.5-5 μm, the difference between R4 and R1 is 30-40 μm, and the radial distance R5 between the outer surface of the outer cladding 40 and the center of the optical fiber is 50-65 μm. Compared to other ranges, limiting the radius or thickness of the core layer 10, inner cladding 20, depressed cladding 30, and outer cladding 40 to the above ranges helps reduce the viscosity difference between the core layer 10 and each cladding layer, thereby reducing the stress difference between the core layer 10 and each cladding layer, and further reducing the impact of additional stress on optical fiber performance. It also helps reduce optical fiber attenuation in the long wavelength band and improves the optical fiber's bending resistance.

[0043] In order to further control the cutoff wavelength of the optical fiber while reducing its macrobending loss, so that these two properties can be maintained at a relatively good level at the same time, preferably, the ratio of R1 to R0 is (1.4-2.0):1.

[0044] In order to further improve the bending resistance and optical performance of the optical fiber, preferably, the difference between R2 and R1 is 4.5-5.5 μm, the difference between R3 and R2 is 6-18 μm, and the difference between R4 and R3 is 5.5-22 μm.

[0045] In order to further improve the comprehensive performance of the optical fiber, preferably, the radial distance between the outer surface of the outer cladding 40 and the center of the optical fiber is 62-63 μm.

[0046] Doping with Ge and F elements both helps weaken the silicon-oxygen bonds in the quartz material, making SiO2 chemical bonds more susceptible to breaking at high temperatures, thereby reducing the glass viscosity at the same temperature. In a preferred embodiment, the core layer 10 is made of SiO2 doped with Ge and F, the inner cladding 20 is made of SiO2 doped with F, and the depressed cladding 30 is made of SiO2 doped with F. Compared to other materials, using quartz materials doped with these elements as the core layer 10, inner cladding 20, and depressed cladding 30 facilitates adjusting the relative refractive index differences between the core layer 10 and each cladding layer to better meet the specific optical fiber refractive index profile design described above.

[0047] In a preferred embodiment, the optical fiber has a Ge doping amount of 1.0 to 4.0 wt%, and a F doping amount of 0.01 to 0.3%, based on the total weight of the core layer 10. Compared to other doping amounts, limiting the Ge doping amount in the core layer 10 within the aforementioned range is beneficial for reducing the Rayleigh scattering effect caused by GeO2, thereby reducing optical fiber attenuation. Furthermore, limiting the F doping amount within the aforementioned range is beneficial for reducing the relative refractive index difference of the core layer 10 and reducing the viscosity of the core layer 10.

[0048] In a preferred embodiment, the F doping amount in the optical fiber is 0.01 to 1.0%, based on the total weight of the material of the inner cladding 20. Compared to other doping amounts, limiting the F doping amount in the inner cladding 20 to the aforementioned range is beneficial for reducing stress differences between the core layer 10 and the inner cladding 20, and between the inner cladding 20 and the depressed cladding 30, thereby reducing additional losses caused by stress.

[0049] In a preferred embodiment, the F doping amount in the optical fiber is 0.3 to 2.0 wt%, based on the total weight of the material in the depressed cladding 30. Compared to other doping amounts, limiting the F doping amount in the depressed cladding 30 to this range is beneficial for achieving a relatively depressed refractive index optical structure, ensuring compatibility of comprehensive performance characteristics such as attenuation coefficient, cutoff wavelength, and bending loss. It also helps reduce the stress difference between the depressed layer and the core layer, thereby reducing the generation of additional attenuation.

[0050] In a preferred embodiment, the compressive stress from the core layer 10 to the inner cladding layer 20 is 40 to 100 MPa. The compressive stress value from the core layer 10 to the inner cladding layer 20 includes, but is not limited to, the aforementioned range. Limiting the compressive stress within the aforementioned range helps suppress the expansion of internal micro-defects, reduces Rayleigh scattering, and thereby reduces optical fiber attenuation. It also helps improve the optical fiber's tensile strength.

[0051] In a preferred embodiment, the radial viscosity variation range from the recessed step layer 32 to the recessed platform layer 33 is no greater than 2% / μm, and the stress difference is no greater than 20%. Compared to other ranges, limiting the radial viscosity variation range and stress difference to the above ranges helps reduce sudden stress changes in the optical fiber and reduces additional attenuation.

[0052] The coating arrangement helps improve the overall performance of the optical fiber, such as its flexibility. In a preferred embodiment, the outer surface of the outer cladding 40 is further sequentially coated with a first coating 51 and a second coating 52. Preferably, the materials of the first coating 51 and the second coating 52 independently include, but are not limited to, one or more of the group consisting of acrylic resin, epoxy resin, and silicone-modified acrylic resin.

[0053] In a preferred embodiment, the elastic modulus of the first coating 51 is 0.3-0.5 MPa, the elastic modulus of the second coating 52 is 500-1000 MPa, and the coefficient of friction of the outer surface of the second coating 52 is 0.1-0.3. The elastic moduli of the first coating 51 and the second coating 52 independently include, but are not limited to, the aforementioned ranges. Limiting the elastic moduli to within these ranges helps improve the flexibility of the optical fiber; limiting the coefficient of friction of the outer surface of the second coating 52 to within these ranges helps improve the wear resistance of the optical fiber, facilitating its application in the field of optical communications.

[0054] In a preferred embodiment, the mode field diameter of the optical fiber at a wavelength of 1550 nm is 12 to 13 μm, and the effective area is 120 to 130 μm. 2The attenuation coefficient of the optical fiber at a wavelength of 1550nm is ≤0.174dB / km. The difference in the minimum attenuation coefficient of the optical fiber at 1520nm and within the wavelength range of 1520nm to 1625nm is △α1520, △α1520≤0.02dB / km. The difference in the minimum attenuation coefficient of the optical fiber at 1625nm and within the wavelength range of 1520nm to 1625nm is △α1625, △α1625≤0.02dB / km, and the absolute value of the difference between △α1520 and △α1625 is no more than 0.009dB / km. The optical fiber provided in this application has a large effective area and a small attenuation coefficient, and has excellent transmission performance. In addition, the difference in attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band is small, and the optical fiber has excellent attenuation consistency in the communication window.

[0055] A second aspect of the present application further provides a method for preparing an optical fiber, comprising: preparing an optical fiber preform, the optical fiber preform comprising, from the inside out, a core layer 10 preparatory layer, an inner cladding layer 20 preparatory layer, a depressed cladding layer 30 preparatory layer, and an outer cladding layer 40 preparatory layer; and performing a drawing annealing treatment on the optical fiber preform so that the core layer 10 preparatory layer, the inner cladding layer 20 preparatory layer, the depressed cladding layer 30 preparatory layer, and the outer cladding layer 40 preparatory layer are sequentially transformed into the core layer 10, inner cladding layer 20, depressed cladding layer 30, and outer cladding layer 40 in the optical fiber provided herein, thereby obtaining the optical fiber provided herein.

[0056] An optical fiber preform is prepared using the specific refractive index profile structure provided herein. The preparation process includes a deposition method commonly used in the art. The optical fiber preform is then subjected to a drawing and annealing process to obtain the optical fiber provided herein. The optical fiber produced herein meets the G.654.E optical fiber standard and can be used in ultra-high voltage power communications, submarine cables, or terrestrial trunk ultra-high-speed communication lines.

[0057] In a preferred embodiment, the material for the preliminary layer of the core layer 10 is SiO2 doped with Ge and F, the material for the preliminary layer of the inner cladding 20 is SiO2 doped with F, and the material for the preliminary layer of the depressed cladding 30 is SiO2 doped with F. Compared to other materials, using quartz materials doped with the aforementioned elements as the materials for the preliminary layers of the core layer 10, the preliminary layers of the inner cladding 20, and the preliminary layers of the depressed cladding 30 facilitates adjusting the relative refractive index difference between the core layer 10 and each cladding layer in the resulting optical fiber, thereby better meeting the aforementioned specific optical fiber refractive index profile design.

[0058] In a preferred embodiment, the Ge doping amount is 1.0-4.0 wt %, and the F doping amount is 0.01-0.3 wt %, based on the total weight of the material in the preliminary layer of the core layer 10. Compared to other doping amounts, limiting the Ge doping amount in the preliminary layer of the core layer 10 within the above range is beneficial for reducing the Rayleigh scattering effect caused by GeO2, thereby reducing optical fiber attenuation. Furthermore, limiting the F doping amount within the above range is beneficial for reducing the relative refractive index difference of the resulting core layer 10 and reducing the viscosity of the resulting core layer 10.

[0059] In a preferred embodiment, the F doping amount of the preliminary layer of the inner cladding 20 is 0.01 to 1.0% by weight, based on the total weight of the material. Compared to other doping amounts, limiting the F doping amount in the preliminary layer of the inner cladding 20 to the above range is beneficial for reducing the stress difference between the resulting core layer 10 and the inner cladding 20, and between the resulting inner cladding 20 and the depressed cladding 30, thereby reducing the additional loss caused by stress in the resulting optical fiber.

[0060] In a preferred embodiment, the F doping amount in the preliminary layer of the depressed cladding 30 is 0.3 to 2.0 wt %, based on the total weight of the material. Compared to other doping amounts, limiting the F doping amount in the preliminary layer of the depressed cladding 30 to this range is beneficial for achieving a relatively depressed refractive index optical structure, ensuring compatibility of comprehensive performance characteristics such as attenuation coefficient, cutoff wavelength, and bending loss. It also helps reduce the stress difference between the depressed layer and the core layer, thereby reducing the generation of additional attenuation.

[0061] In a preferred embodiment, the drawing annealing treatment is performed using an optical fiber drawing annealing device, as shown in FIG3 , the optical fiber drawing annealing device includes: an inner cavity heating section 100, a drawing annealing section 200 and an annealing tube 300. The inner cavity heating section 100 is used to heat the optical fiber preform; the inner cavity heating section 100 has an inner cavity, and according to the moving direction of the optical fiber preform, at least one preheating component 110 and at least one melting component 120 are sequentially arranged in the inner cavity, and the preheating component 110 and the melting component 120 are independently arranged in the circumferential direction of the inner cavity and are parallel to each other; the drawing annealing section 200 includes a first annealing unit 210 and a second annealing unit 220, and the first annealing unit 210 and the second annealing unit 220 are coaxially arranged with the inner cavity heating section 100, and the first annealing unit 210, the second annealing unit 220 and the inner cavity heating section 100 are coaxially arranged to penetrate the annealing tube. Tube 300, annealing tube 300 is used to insert the optical fiber; the second annealing unit 220 is provided with an optical fiber annealing tube outlet 301 at one end away from the first annealing unit 210, and the temperature at the interface between the second annealing unit 220 and the first annealing unit 210 is higher than the temperature of the optical fiber annealing tube outlet 301; during the drawing annealing process, the temperature of the preheating component 110 is set to T1, the temperature of the melting component 120 is set to T2, T2 is 1800-2000°C, the temperature of the first annealing unit 210 is T3, the temperature of the second annealing unit 220 is T4, T4 is 1150-1250°C, and T1, T2, T3 and T4 satisfy the following relationship: T2>T3>T g >T1>T4, where T g Indicates the glass transition temperature of the optical fiber preform; T3 and T g The difference is 50~100℃.

[0062] When the drawing annealing device is in operation, the optical fiber preform is placed in the inner cavity. As the preheating component 110 and the melting component 120 preheat and melt the optical fiber preform, the heated and melted portion of the optical fiber preform changes into a fluid state and moves along the annealing tube 300 toward the first annealing unit 210 until it enters the second annealing unit 220 and is finally drawn out from the optical fiber annealing tube outlet 301. For optical fiber preforms made of specific materials (with Tg controlled within the above range), limiting the temperatures of the preheating component 110 and the melting component 120 within the above range, compared to other ranges, is beneficial for improving the efficiency of the optical fiber preform's transition from a solid state to a fluid state, and is beneficial for obtaining optical fiber after the drawing annealing process. Furthermore, limiting the temperatures of the first annealing unit 210, the second annealing unit 220, and the optical fiber annealing tube outlet 301 within the above range, compared to other ranges, is beneficial for obtaining optical fiber, reducing fiber breakage during the drawing process, and reducing residual stress between layers in the optical fiber due to the drawing annealing process. This also suppresses the concentration of residual stress in a specific location within the optical fiber, and is beneficial for improving the attenuation performance of the optical fiber. Furthermore, limiting the temperature of the optical fiber annealing tube outlet 301 within the above range, compared to other ranges, is beneficial for suppressing surface turbulence and more accurately controlling the optical fiber diameter.

[0063] In summary, using the above-mentioned drawing and annealing device to perform the above-mentioned drawing and annealing treatment on the optical fiber preform is beneficial to improving the attenuation consistency of the communication window of the optical fiber.

[0064] In a preferred embodiment, the inner cavity heating section 100 includes two preheating components 110, each independently disposed circumferentially and parallel to the inner cavity. The temperatures of the two components increase sequentially along the direction of travel of the optical fiber preform. Compared to a single preheating component 110, employing two preheating components 110 and limiting their temperatures to the aforementioned range further reduces temperature variations among various parts of the optical fiber preform during the drawing process, further reducing stress variations among these parts, and thereby further improving the attenuation consistency of the optical fiber's communication window.

[0065] In a preferred embodiment, the inner cavity heating section 100 includes three melting components 120, each independently arranged circumferentially and parallel to the inner cavity. The temperatures of the three melting components decrease sequentially along the direction of travel of the optical fiber preform. Compared to a single melting component 120, employing three melting components 120 and limiting their temperatures to the aforementioned range further reduces temperature variations among various parts of the optical fiber preform during the drawing process, further reducing stress variations among these parts, and thereby further improving the attenuation consistency of the optical fiber's communication window.

[0066] In a preferred embodiment, the preheating component 110, the melting component 120, the first annealing unit 210 and the second annealing unit 220 in the optical fiber drawing annealing device are each independently heated by graphite heating or coil heating, and each of the above components or annealing units is independently heated and temperature-controlled, and is connected to the host remote industrial control system to remotely adjust the temperature.

[0067] In a preferred embodiment, the preheating unit 110, the melting unit 120, the first annealing unit 210, and the second annealing unit 220 in the optical fiber drawing and annealing apparatus are each independently provided with a temperature detector at a corresponding location for real-time monitoring of the temperature of the optical fiber at the corresponding location. Preferably, the preheating unit 110, the melting unit 120, the first annealing unit 210, and the second annealing unit 220 are each independently provided with a heat-insulating component on their periphery, and a water-circulating cooling component is provided on their periphery.

[0068] In a preferred embodiment, an inert gas is introduced into the inner cavity during the wire drawing annealing process. Preferably, the inert gas includes but is not limited to argon, or a mixture of argon and helium.

[0069] In a preferred embodiment, the inert gas is introduced at a rate of 15 to 30 L / min. This inert gas introduction rate includes, but is not limited to, the aforementioned range. Limiting the inert gas introduction rate within this range not only protects the heated graphite components within the furnace, but also helps stabilize the thermal field within the furnace, uniformly removes impurities from the furnace, and improves optical fiber strength and attenuation uniformity.

[0070] In order to further reduce the temperature difference between various parts of the optical fiber preform during the drawing process, further reduce the stress difference between various parts, and further improve the attenuation consistency of the communication window of the optical fiber, in a preferred embodiment, the shortest distance between the preheating component 110 and the melting component 120 is 200-500 mm, the length of the area where the annealing tube 300 is located in the first annealing unit 210 is 100-300 mm, and the length of the area where the annealing tube 300 is located in the second annealing unit 220 is 1000-2000 mm.

[0071] In order to further reduce the temperature difference between various parts of the optical fiber preform during the drawing process, further reduce the stress difference between various parts, and further improve the attenuation consistency of the communication window of the optical fiber, in a preferred embodiment, when the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent ones is 30 to 50 mm; and / or, when the inner cavity heating section 100 includes three melting components 120, the distance between two adjacent ones is 20 to 40 mm.

[0072] In a preferred embodiment, during the drawing annealing process, the drawing tension is 50 to 180 g, and the drawing tension and the drawing rate satisfy the following relationship (5):

[0073] Among them, F(v) represents the size of the drawing tension corresponding to the drawing rate v, F0 represents the minimum drawing tension, F1 represents the maximum drawing tension, the units of F(v), F0 and F1 are all g, v2 represents the maximum drawing rate, the unit is 350~1200m / min, α represents the tension adjustment coefficient, and 0.5≤α≤4.

[0074] The drawing tension includes but is not limited to the above range. Limiting it within the above range is beneficial to improving the drawing annealing treatment to obtain an optical fiber that meets the above-mentioned refractive index profile structure of the present application, and at the same time, the change rules of the relative refractive index difference △1(r) of the core layer 10 material, the relative refractive index difference △2(r) of the inner cladding 20 material, the relative refractive index difference △4(r) of the recessed step layer 32 material, and the relative refractive index difference △5(r) of the recessed platform layer 33 material respectively satisfy the relationships (1) to (4), which is beneficial to more accurately control the relative refractive index difference of each layer, thereby improving the transmission performance of the optical fiber, reducing the difference in the attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band, and improving the attenuation consistency of the communication window of the optical fiber.

[0075] In a preferred embodiment, the drawing tension is monitored in real time using a non-contact tension testing device. The non-contact tension testing device can obtain the tension applied to the optical fiber by detecting the tiny vibrations of the optical fiber. During the monitoring process, a schematic diagram of the device structure used in the optical fiber preparation process is shown in FIG4 , which further introduces a non-contact tension testing device and a coating cup on the basis of the optical fiber drawing annealing device, wherein the coating cup refers to a container for coating the first coating 51 and the second coating 52. The non-contact tension meter is arranged between the optical fiber annealing tube outlet 301 and the coating cup, and preferably in an upper position. The distance between the non-contact tension testing device and the optical fiber annealing tube outlet 301 of the optical fiber drawing annealing device is H1, and the distance between the non-contact tension testing device and the coating cup is H2, preferably H2 / H1 is (2 to 3): 1. Compared with other ranges, limiting the ratio of H2 to H1 within the above range is conducive to improving the accuracy of the measured drawing tension.

[0076] In a preferred embodiment, the optical fiber preform is cylindrical or rod-shaped, with a diameter of 60 to 200 mm. The shape and size of the optical fiber preform include, but are not limited to, the aforementioned ranges. Limiting the shape and size of the optical fiber preform to within the aforementioned ranges facilitates drawing and annealing processes and facilitates the production of optical fibers with specific shapes suitable for optical communication applications, such as ultra-high voltage power communications, submarine cables, or terrestrial trunk ultra-high-speed communication lines.

[0077] In a preferred embodiment, when the diameter of the optical fiber preform is 60-80 mm, the drawing tension is 50-100 g; when the diameter of the optical fiber preform is 120-150 mm, the drawing tension is 90-130 g; when the diameter of the optical fiber preform is 160-200 mm, the drawing tension is 130-180 g. For optical fiber preforms of different diameters, using the drawing tension within the above preferred range for processing is conducive to more accurately controlling the distribution of doping elements inside each preparatory layer, thereby more accurately controlling the relative refractive index difference between the core layer 10 and each cladding layer in the obtained optical fiber, thereby improving the transmission performance of the optical fiber, reducing the difference in attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band, and improving the attenuation consistency of the optical fiber's communication window.

[0078] In a preferred embodiment, when T g When the temperature is 1360-1450℃, T1 is 1300-1350℃, T2 is 1800-2000℃, T3 is 1460-1500℃, T4 is 1150-1250℃, and the drawing tension is 60-130g; when T g When the temperature is 1310-1350℃, T1 is 1260-1300℃, T2 is 1800-2000℃, T3 is 1360-1450℃, T4 is 1150-1250℃, and the drawing tension is 50-120g; when T g When the temperature is 1460-1550°C, T1 is 1350-1450°C, T2 is 1900-2200°C, T3 is 1560-1650°C, T4 is 1150-1250°C, and the drawing tension is 80-180g.

[0079] For optical fiber preforms with different Tg or materials, using the drawing tension within the above-mentioned preferred range for processing is conducive to more accurately controlling the distribution of doping elements inside each preparatory layer, thereby more accurately controlling the relative refractive index difference between the core layer 10 and each cladding in the obtained optical fiber, thereby improving the transmission performance of the optical fiber, reducing the difference in the attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band, and improving the attenuation consistency of the optical fiber's communication window.

[0080] In a preferred embodiment, the wire drawing annealing treatment further includes a first coating treatment and a second coating treatment in sequence, and the first coating treatment and the second coating treatment are performed by an ultraviolet curing coating method.

[0081] In a preferred embodiment, the UV light source used in the first and second coating processes has a central wavelength range of 365nm to 405nm, is a linear light source parallel to the direction of travel of the optical fiber, and has an effective light source length of more than 800mm. The distance between the light source and the optical fiber is set to 30 to 80mm, and the light source output power is steplessly adjusted from 10 to 100%, and increases with the increase in the drawing rate, ensuring that the UV radiation energy received by the inner and outer layers reaches 400 to 600mJ / cm 2 , ensuring uniform curing of both inner and outer layers. Nitrogen is used to shield the fiber curing channel, and compressed air is introduced. The preferred nitrogen to compressed air flow ratio is (15-20):1, and the total air flow rate is 15-30 L / min. To exhaust volatile oil fumes, the ratio of shielding gas inlet flow to exhaust flow is (3-5):1.

[0082] During the above-mentioned first coating treatment and second coating treatment, the introduction of nitrogen is beneficial to reducing the inhibition of oxygen on the resin curing reaction and increasing the curing rate; the introduction of compressed air is beneficial to promoting the ablation of oil fume volatiles on the one hand, and on the other hand, it is beneficial to improve the friction performance of the outer surface of the second coating 52, thereby facilitating the adhesion of the subsequent coloring layer.

[0083] In a preferred embodiment, the curing degree of the first coating treatment is 90-92%, and the curing degree of the second coating treatment is 90-95%. The curing degrees of the first coating treatment and the second coating treatment include, but are not limited to, the above-mentioned ranges. Limiting the curing degrees of the first coating treatment and the second coating treatment to the above-mentioned ranges is beneficial for reducing the microbend loss of the optical fiber, thereby improving the bending resistance of the optical fiber.

[0084] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0085] Example 1

[0086] A method for preparing an optical fiber, comprising:

[0087] (1) Preparation of optical fiber preform: In a reaction furnace, the basic gas and dopant gas are deposited by MCVD deposition method. The basic gases SiCl4, H2 and O2 are introduced into the reaction chamber, and inert gas Ar or He is introduced as a carrier gas. GeCl4 gas and CF4 are introduced. The deposition temperature is 1450°C. After 24 hours of deposition, the optical fiber preform is sintered at 1550°C for 4 hours to obtain the optical fiber preform. The optical fiber preform is cylindrical with a diameter of 155 mm and a glass transition temperature Tg of 1360°C.

[0088] (2) Drawing annealing process: The drawing annealing process is performed using the optical fiber drawing annealing device shown in FIG3 . The inner cavity heating section 100 includes two adjacent preheating components 110, and the two components are independently arranged around the circumference of the inner cavity and are parallel to each other. The distance between the two components is 40 mm. The temperatures of the two preheating components 110 are set to 1310°C and 1340°C in the direction of travel of the optical fiber preform. The inner cavity heating section 100 includes three melting components 120, and the three components are independently arranged around the circumference of the inner cavity. The three melting components 120 are arranged in parallel in the direction of the optical fiber preform, with a distance of 30 mm between each two adjacent components. The temperatures of the three melting components 120 are set to 1800° C., 1850° C., and 1900° C., respectively, along the traveling direction of the optical fiber preform. The temperature T3 of the first annealing unit 210 is set to 1480° C., and the temperature T4 of the second annealing unit 220 is set to 1250° C. Under the above temperature conditions, a drawing annealing process is performed. During this process, the optical fiber moves downward from the annealing tube 300 due to gravity and is finally drawn out from the optical fiber annealing tube outlet 301.

[0089] During this process, a non-contact tension tester monitors the drawing tension in real time (as shown in Figure 4). The drawing tension is controlled at 130g and the drawing rate is 800m / min. Finally, a first coating 51 and a second coating 52 are sequentially applied to the outer surface of the outer cladding 40. After curing with 365nm to 395nm UV light, the optical fiber is drawn and wound into a coil. The first coating 51 is an acrylic resin layer, and the second coating 52 is an acrylic resin layer.

[0090] A schematic cross-sectional view of the structure of the optical fiber produced in Example 1 is shown in FIG1 . The optical fiber comprises, from the inside out, a core layer 10, an inner cladding layer 20, a depressed cladding layer 30, and an outer cladding layer 40. The depressed cladding layer 30 comprises a deep depressed layer 31, a depressed step layer 32, and a depressed terrace layer 33. The core layer 10 is made of SiO2 doped with Ge and F, with the Ge doping amount being 2.1 wt% and the F doping amount being 0.1 wt% based on the total weight of the core layer 10. The inner cladding 20 is made of SiO2 doped with F, with the F doping amount being 0.45 wt% based on the total weight of the inner cladding 20. The depressed cladding 30 is made of SiO2 doped with F, with the F doping amount being 1.2 wt% based on the total weight of the depressed cladding 30.

[0091] The refractive index structure cross-section of the optical fiber obtained in Example 1 is shown in FIG2 , wherein the relative refractive index difference △1(r) of the core layer 10 material, the relative refractive index difference △2(r) of the inner cladding layer 20 material, the relative refractive index difference △4(r) of the recessed step layer 32 material, and the relative refractive index difference △5(r) of the recessed platform layer 33 material respectively satisfy the above-defined equations (1) to (4). Parameters such as the radius and relative refractive index difference of each layer in the optical fiber are shown in Table 1. As shown in Table 1, the maximum relative refractive index difference △1 of the core layer 10 material in equation (1) is max is 0.2%, the radius R0 of the core layer 10 is 6.2 μm, and the refractive index distribution parameter g of the core layer 10 is 4; the minimum relative refractive index difference △2 of the material of the inner cladding 20 in the relationship (2) is min is -0.32%, R1 is 11.16 μm, and the refractive index distribution parameter h of the inner cladding 20 is 4; the maximum relative refractive index difference △4 of the material of the recessed step layer 32 in the relationship (3) max -0.20%, minimum relative refractive index △4 min is -0.30%, R2 is 16.16 μm, R3 is 26.56 μm, and the refractive index distribution parameter m of the concave step layer 32 is 2; the maximum relative refractive index difference △5 of the material of the concave platform layer 33 in the relationship (4) is max -0.30%, and the minimum relative refractive index △5 min is -0.35%, R4 is 44.16 μm, and the refractive index distribution parameter n of the recessed terrace layer 33 is 2.

[0092] Example 2

[0093] The difference from Example 1 is that: in step (1), the doping amount in each layer is changed so that the relative refractive index difference is the value shown in Table 1, wherein the material of the core layer 10 is SiO2 doped with Ge and F elements, and the doping amount of Ge element is 3.2wt% and the doping amount of F element is 0.2wt% based on the total weight of the material of the core layer 10; the doping amount of F element is 0.65wt% based on the total weight of the material of the inner cladding 20; and the doping amount of F element is 2.0wt% based on the total weight of the material of the depressed cladding 30; in step (2), the drawing tension is controlled to 120g and the drawing rate is 650m / min for drawing.

[0094] Example 3

[0095] The difference from Example 1 is that: in step (1), the doping amount in each layer is changed so that the relative refractive index difference is the value shown in Table 1, wherein the material of the core layer 10 is SiO2 doped with Ge and F elements, and the doping amount of Ge element is 2.6wt% and the doping amount of F element is 0.15wt% based on the total weight of the material of the core layer 10; the doping amount of F element is 0.65wt% based on the total weight of the material of the inner cladding 20; and the doping amount of F element is 1.2wt% based on the total weight of the material of the depressed cladding 30; in step (2), the drawing tension is controlled to 142g and the drawing rate is 1000m / min for drawing.

[0096] Example 4

[0097] Step (1) is the same as Example 1, and the difference from Example 1 is that the drawing tension in step (2) is 50 g and the drawing rate is 350 m / min.

[0098] Example 5

[0099] Step (1) is the same as Example 1, and the difference from Example 1 is that the drawing tension in step (2) is 180 g and the drawing rate is 1200 m / min.

[0100] Example 6

[0101] Step (1) is the same as Example 1, and the difference from Example 1 is that the drawing tension in step (2) is 200 g and the drawing rate is 1500 m / min.

[0102] Example 7

[0103] Step (1) is the same as Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent ones is 30 mm, and the temperatures are set to 1330°C and 1350°C respectively; the inner cavity heating section 100 includes three melting components 120, and the three are independently arranged in the circumferential direction of the inner cavity and parallel to each other, the distance between two adjacent ones is 20 mm, and the temperatures are set to 1900°C, 1950°C and 2000°C respectively; the temperature T3 of the first annealing unit 210 is set to 1480°C, and the temperature T4 of the second annealing unit 220 is set to 1250°C.

[0104] Example 8

[0105] Step (1) is the same as Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent ones is 50 mm, and the temperatures are set to 1300°C and 1320°C respectively; the inner cavity heating section 100 includes three melting components 120, and the three are independently arranged in the circumferential direction of the inner cavity and parallel to each other, the distance between two adjacent ones is 40 mm, and the temperatures are set to 1800°C, 1850°C and 1900°C respectively; the temperature T3 of the first annealing unit 210 is set to 1480°C, and the temperature T4 of the second annealing unit 220 is set to 1250°C.

[0106] Example 9

[0107] Step (1) is the same as Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, the distance between adjacent two is 70 mm, and the temperatures are set to 1200°C and 1250°C respectively; the inner cavity heating section 100 includes three melting components 120, and the three are independently arranged in the circumferential direction of the inner cavity and parallel to each other, the distance between adjacent two is 60 mm, and the temperatures are set to 1750°C, 1800°C and 1850°C respectively; the temperature T3 of the first annealing unit 210 is set to 1480°C, and the temperature T4 of the second annealing unit 220 is set to 1250°C.

[0108] Comparative Example 1

[0109] The difference from Example 1 is that the optical fiber preform does not include a preliminary layer for the depressed cladding 30. Instead, the resulting optical fiber comprises, from the inside out, a core layer 10, an inner cladding 20, and an outer cladding 40. The preliminary layers for the core layer 10, the inner cladding 20, and the outer cladding 40 are identical to those in Example 1.

[0110] Comparative Example 2

[0111] The difference from Example 1 is that the optical fiber preform does not include a preparatory layer for the depressed step layer 32 or a preparatory layer for the depressed terrace layer 33. Instead, the resulting optical fiber comprises, from the inside out, a core layer 10, an inner cladding layer 20, a deep depressed layer 31, and an outer cladding layer 40. The preparatory layers for the core layer 10, the inner cladding layer 20, the deep depressed layer 31, and the outer cladding layer 40 are the same as those in Example 1.

[0112] Comparative Example 3

[0113] The difference from Example 1 is that the F doping level in the material of the preparatory layer of deep depressed layer 31 in step (1) is changed so that the relative refractive index difference Δ3 of the material of deep depressed layer 31 in the resulting optical fiber is -0.55%. The materials for the preparatory layer of core layer 10, the preparatory layer of inner cladding layer 20, the preparatory layer of depressed step layer 32, the preparatory layer of depressed terrace layer 33, and the preparatory layer of outer cladding layer 40 are the same as those in Example 1.

[0114] Parameters such as the radius and relative refractive index difference of each layer in the ultra-low loss large effective area optical fiber prepared in all the above embodiments of this application are shown in Table 1, and the performance test results are shown in Table 2 and Table 3 respectively.

[0115] Table 1

[0116] Table 2

[0117] Table 3

[0118] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0119] Comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the optical fiber cable cutoff wavelengths of the optical fibers prepared in Comparative Examples 1 to 3 are all greater than 1520 nm, and the attenuation coefficients of the optical fibers prepared in Comparative Examples 1 to 3 are all greater than that of Example 1, and the absolute values ​​of the differences between △α1520 and △α1625 are all greater than those of Example 1. It can be seen that by designing the depressed cladding 30 of the specific cladding structure of the present application, and at the same time designing the variation rules of the relative refractive index difference △1(r) of the core layer 10 material, the relative refractive index difference △2(r) of the inner cladding 20 material, the relative refractive index difference △4(r) of the depressed step layer 32 material, and the relative refractive index difference △5(r) of the depressed platform layer 33 material to respectively satisfy the above-mentioned relationship equations (1) to (4) provided in the present application, and limiting the relative refractive index difference △3 of the deep depressed layer 31 material to be within the scope of the present application, it is possible to effectively constrain the optical fiber waveguide transmission, improve the optical fiber attenuation performance, and enable the optical fiber to have higher bending resistance and an optical cable cutoff wavelength of no more than 1520 nm.

[0120] Comparing Examples 1, 4 to 6, it can be seen that during the drawing annealing process, the compressive stress value from the core layer 10 to the inner cladding 20 is adjusted by changing the drawing tension and the drawing rate. Under the action of the drawing tension, the outer cladding retains tensile stress, which in turn acts on the inner cladding to form compressive stress. The compressive stress can prevent the expansion of microcracks and reduce Rayleigh scattering loss. However, excessive drawing tension will cause the radial stress variation from the inner cladding to the depressed cladding to increase, which is not conducive to the control of the attenuation coefficient uniformity. Moreover, the optical fiber cable cutoff wavelength of the optical fiber prepared in Examples 1, 4 to 6 is less than 1520nm, and the attenuation coefficient of the optical fiber prepared in Example 6 at 1550nm and the absolute value of the difference between △α1520 and △α1625 are greater than those of Examples 1, 4 and 5, respectively. It can be seen that, compared with other ranges, limiting the drawing tension to the preferred range of the present application is beneficial to controlling the radial stress variation, thereby improving the transmission performance of the optical fiber, reducing the difference in the attenuation coefficient of the optical fiber from the short wavelength band to the long wavelength band, and improving the attenuation consistency of the optical fiber communication window.

[0121] Comparing Examples 1, 7, and 9, it can be seen that the compressive stress value from the core layer 10 to the inner cladding 20 of the optical fiber produced in Example 9 is significantly greater than that of Examples 1, 7, and 8, indicating that the optical fiber produced in Example 9 has poorer tensile strength. This indicates that the compressive stress value from the core layer 10 to the inner cladding 20 includes, but is not limited to, the range of this application. Limiting the compressive stress value to this range is beneficial for reducing optical fiber attenuation and improving tensile strength. Furthermore, the attenuation coefficient at 1550 nm and the absolute value of the difference between Δα1520 and Δα1625 of the optical fiber produced in Example 9 are both greater than those of Examples 1, 7, and 8, respectively. It can be seen that, compared with other ranges, the temperature T3 of the first annealing unit 210, the temperature T4 of the second annealing unit 220, the distance between two adjacent preheating components 110 in the inner cavity heating section 100 and the temperature of each component, and the distance between two adjacent melting components 120 and the temperature of each component are limited to the preferred range of the present application. This is conducive to further reducing the temperature difference between various parts of the optical fiber preform during the drawing process, further reducing the stress difference between various parts, and further improving the attenuation consistency of the communication window of the optical fiber.

[0122] It should be noted that the terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

[0123] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. An ultra-low loss large effective area optical fiber, characterized in that: The ultra-low loss large effective area optical fiber comprises, from the inside to the outside, a core layer (10), an inner cladding layer (20), a depressed cladding layer (30) and an outer cladding layer (40); the depressed cladding layer (30) comprises a deep depressed layer (31), a depressed step layer (32) and a depressed platform layer (33); the maximum relative refractive index difference of the material of the core layer (10) is △1 max The minimum relative refractive index difference of the inner cladding (20) material is △2 min The relative refractive index difference of the material of the deep concave layer (31) is △3; the maximum relative refractive index difference of the material of the concave step layer (32) is △4 max , and the minimum relative refractive index is △4 min The maximum relative refractive index difference of the material of the concave platform layer (33) is △5 max , and the minimum relative refractive index is △5 min ; △3<△2 min , △3<△4 min , and △3<△5 min ; r represents the radial distance from a certain position in the ultra-low loss large effective area optical fiber to the center of the optical fiber; Δ1(r) represents the relative refractive index difference of the material at a certain position in the core layer (10) from the center of the optical fiber, and the Δ1(r) and r satisfy the following relationship (1): Wherein, R0 represents the radius of the core layer (10), g represents the refractive index distribution parameter of the core layer (10), and 2≤g≤6; Δ2(r) represents the relative refractive index difference of the material at a certain position in the inner cladding (20) from the center of the optical fiber, and the Δ2(r) and r satisfy the following relationship (2): Wherein, R1 represents the radial distance between the contact interface between the inner cladding (20) and the depressed cladding (30) and the center of the optical fiber, h represents the refractive index distribution parameter of the inner cladding (20), and 3≤h≤10; Δ4(r) represents the relative refractive index difference of the material at a certain position in the recessed step layer (32) from the center of the optical fiber, and the Δ4(r) and r satisfy the following relationship (3): Wherein, R2 represents the radial distance between the contact interface between the deep depression layer (31) and the depression step layer (32) and the center of the optical fiber, R3 represents the radial distance between the contact interface between the depression step layer (32) and the depression platform layer (33) and the center of the optical fiber, and m represents the refractive index distribution parameter of the depression step layer (32), 0.5≤m≤3; Δ5(r) represents the relative refractive index difference of the material at a certain position in the recessed platform layer (33) from the center of the optical fiber, and the Δ5(r) and r satisfy the following relationship (4): Wherein, R4 represents the distance between the contact interface between the recessed platform layer (33) and the outer cladding layer (40) and the optical fiber The radial distance from the center, n represents the refractive index distribution parameter of the concave platform layer (33), 0.5≤n≤3; The outer cladding (40) is a silicon dioxide layer, and the refractive index of the outer cladding (40) is 0.

2. The ultra-low loss large effective area optical fiber according to claim 1, characterized in that: △1 max is 0.10~0.30%, said △2 min is -0.25~-0.35%, the △3 is -0.45~-0.5%, the △4 max is -0.20~-0.25%, the △4 min is -0.25~-0.30%, the △5 max is -0.30~-0.35%, the △5 min It is -0.35 to -0.4%.

3. The ultra-low loss large effective area optical fiber according to claim 1, characterized in that: The R0 is 5 to 7 μm; the difference between the R1 and the R0 is 3.5 to 5 μm, and preferably the ratio of the R1 to the R0 is (1.4 to 2.0):1; the difference between the R4 and the R1 is 30 to 40 μm, and preferably the difference between the R2 and the R1 is 4.5 to 5.5 μm, and preferably the difference between the R3 and the R2 is 6 to 18 μm, and preferably the difference between the R4 and the R3 is 5.5 to 22 μm; the radial distance R5 between the outer surface of the outer cladding (40) and the center of the optical fiber is 50 to 65 μm, and preferably 62 to 63 μm.

4. The ultra-low loss large effective area optical fiber according to any one of claims 1 to 3, characterized in that: The material of the core layer (10) is SiO2 doped with Ge and F elements, the material of the inner cladding (20) is SiO2 doped with F elements, and the material of the recessed cladding (30) is SiO2 doped with F elements.

5. The ultra-low loss large effective area optical fiber according to claim 4, characterized in that: In the ultra-low loss large effective area optical fiber, based on the total weight of the material of the core layer (10), the doping amount of the Ge element is 1.0-4.0wt%, and the doping amount of the F element is 0.01-0.3%; and / or, The doping amount of the F element is 0.01 to 1.0% based on the total weight of the material of the inner cladding (20); and / or, The doping amount of the F element is 0.3-2.0 wt % based on the total weight of the material of the depressed cladding (30).

6. The ultra-low loss large effective area optical fiber according to any one of claims 1 to 5, characterized in that: The compressive stress from the core layer (10) to the inner cladding layer (20) is 40 to 100 MPa; and / or, within the radial range from the recessed step layer (32) to the recessed platform layer (33), the radial viscosity variation range is no greater than 2% / μm, and the stress difference is no greater than 20%.

7. The ultra-low loss large effective area optical fiber according to claim 6, characterized in that: The outer surface of the outer coating (40) is also coated with a first coating (51) and a second coating (52) in sequence, the elastic modulus of the first coating (51) is 0.3 to 0.5 MPa, the elastic modulus of the second coating (52) is 500 to 1000 MPa, and the friction coefficient of the outer surface of the second coating (52) is 0.1 to 0.

3.

8. The ultra-low loss large effective area optical fiber according to any one of claims 1 to 7, characterized in that: The ultra-low loss large effective area optical fiber has a mode field diameter of 12 to 13 μm at a wavelength of 1550 nm and an effective area of ​​120 to 130 μm. 2 and / or, The attenuation coefficient of the ultra-low loss large effective area optical fiber at a wavelength of 1550nm is ≤0.174dB / km; and / or, The difference in the minimum attenuation coefficient of the ultra-low loss large effective area optical fiber at 1520nm and in the wavelength range of 1520nm to 1625nm is △α1520, △α1520≤0.02dB / km, the difference in the minimum attenuation coefficient at 1625nm and in the wavelength range of 1520nm to 1625nm is △α1625, △α1625≤0.02dB / km, and the absolute value of the difference between the △α1520 and the △α1625 is not greater than 0.009dB / km.

9. A method for preparing an ultra-low loss large effective area optical fiber, characterized in that: The preparation method comprises: preparing an optical fiber preform, wherein the optical fiber preform comprises, from inside to outside, a core layer preparation layer, an inner cladding preparation layer, a depressed cladding preparation layer, and an outer cladding preparation layer; The optical fiber preform is subjected to a drawing annealing treatment so that the core layer preparation layer, the inner cladding preparation layer, the depressed cladding preparation layer and the outer cladding preparation layer are sequentially transformed into the core layer (10), inner cladding (20), depressed cladding (30) and outer cladding (40) in claim 1, thereby obtaining the ultra-low loss large effective area optical fiber.

10. The method for preparing an ultra-low loss large effective area optical fiber according to claim 9, characterized in that: The material of the core layer preparation layer is SiO2 doped with Ge and F elements, the material of the inner cladding preparation layer is SiO2 doped with F elements, and the material of the recessed cladding preparation layer is SiO2 doped with F elements.

11. The method for preparing an ultra-low loss large effective area optical fiber according to claim 10, characterized in that: Based on the total weight of the material of the core preparation layer, the doping amount of Ge element is 1.0-4.0wt%, and the doping amount of F element is 0.01-0.3%; and / or, The doping amount of F element is 0.01-1.0% based on the total weight of the material of the inner cladding preparation layer; and / or, The doping amount of the F element is 0.3-2.0 wt % based on the total weight of the material of the recessed cladding preparation layer.

12. The method for preparing an ultra-low loss large effective area optical fiber according to any one of claims 9 to 11, characterized in that: The optical fiber drawing annealing treatment is performed by using an optical fiber drawing annealing device, and the optical fiber drawing annealing device comprises: An inner cavity heating section (100) is used to heat the optical fiber preform; the inner cavity heating section (100) has an inner cavity, and according to the moving direction of the optical fiber preform, at least one preheating component (110) and at least one melting component (120) are sequentially arranged in the inner cavity, and the preheating component (110) and the melting component (120) are independently arranged in a circumferential direction of the inner cavity and are parallel to each other; A wire drawing annealing section (200), the wire drawing annealing section (200) comprising a first annealing unit (210) and a second annealing unit (220), the first annealing unit (210), the second annealing unit (220) and the inner cavity heating section (100) being coaxially arranged, and an annealing tube (300) being coaxially arranged between the first annealing unit (210), the second annealing unit (220) and the inner cavity heating section (100), the annealing tube (300) being used for inserting an optical fiber; the second annealing unit (220) is provided with an optical fiber annealing tube outlet (301) at one end away from the first annealing unit (210), and the temperature at the interface between the second annealing unit (220) and the first annealing unit (210) is higher than the temperature of the optical fiber annealing tube outlet (301); During the wire drawing annealing treatment, the temperature of the preheating component (110) is set to T1, the temperature of the melting component (120) is set to T2, the temperature of T2 is 1800-2200° C., the temperature of the first annealing unit (210) is T3, the temperature of the second annealing unit (220) is T4, the temperature of T4 is 1150-1250° C., and the T1, T2, T3 and T4 satisfy the following relationship: T2>T3>T4 g >T1>T4, where T g represents the glass transition temperature of the optical fiber preform; T3 and T g The difference is 50~100℃.

13. The method for preparing an ultra-low loss large effective area optical fiber according to claim 12, characterized in that: The inner cavity heating section (100) comprises two preheating components (110), and the two preheating components (110) are independently arranged in a circumferential direction of the inner cavity and are parallel to each other, and the temperatures of the two components are increased in sequence along the moving direction of the optical fiber preform; and / or, The inner cavity heating section (100) comprises three melting components (120), and the three melting components are independently arranged in the circumferential direction of the inner cavity and are parallel to each other, and the temperatures of the three melting components decrease in sequence along the moving direction of the optical fiber preform.

14. The method for preparing an ultra-low loss large effective area optical fiber according to claim 12, characterized in that: The shortest distance between the preheating component (110) and the melting component (120) is 200-500 mm, the length of the area where the annealing tube (300) is located in the first annealing unit (210) is 100-300 mm, and the length of the area where the annealing tube (300) is located in the second annealing unit (220) is 1000-2000 mm.

15. The method for preparing an ultra-low loss large effective area optical fiber according to claim 13, characterized in that: When the inner cavity heating section (100) comprises two preheating components (110), the distance between two adjacent preheating components (110) is 30 to 50 mm; and / or, When the inner cavity heating section (100) includes three melting components (120), the distance between two adjacent ones is 20 to 40 mm.

16. The method for preparing an ultra-low loss large effective area optical fiber according to any one of claims 12 to 15, characterized in that: During the wire drawing annealing treatment, the wire drawing tension is 50 to 180 g, and the wire drawing tension and the wire drawing rate satisfy the following relationship (5): Wherein, F(v) represents the magnitude of the drawing tension corresponding to the drawing rate v, F0 represents the minimum drawing tension, F1 represents the maximum drawing tension, the units of F(v), F0 and F1 are all g, v2 represents the maximum drawing rate, the unit is 350-1200 m / min, α represents the tension adjustment coefficient, and 0.5≤α≤4; Preferably, the wire drawing tension is monitored in real time using a non-contact tension testing device.

17. The method for preparing an ultra-low loss large effective area optical fiber according to claim 16, characterized in that: The optical fiber preform is cylindrical or rod-shaped, and the diameter of the optical fiber preform is 60 to 200 mm; Preferably, when the diameter of the optical fiber preform is 60-80 mm, the drawing tension is 50-100 g; when the diameter of the optical fiber preform is 120-150 mm, the drawing tension is 90-130 g; when the diameter of the optical fiber preform is 160-200 mm, the drawing tension is 130-180 g.

18. The method for preparing an ultra-low loss large effective area optical fiber according to claim 16, characterized in that: When the T g When the temperature is 1360-1450°C, T1 is 1300-1350°C, T2 is 1800-2000°C, T3 is 1460-1500°C, T4 is 1150-1250°C, and the wire drawing tension is 60-130g; When the T g When the temperature is 1310-1350°C, T1 is 1260-1300°C, T2 is 1800-2000°C, The T3 is 1360-1450°C, the T4 is 1150-1250°C, and the wire drawing tension is 50-120g; When the T g When the temperature is 1460-1550°C, T1 is 1350-1450°C, T2 is 1900-2200°C, T3 is 1560-1650°C, T4 is 1150-1250°C, and the wire drawing tension is 80-180g.

19. The method for preparing an ultra-low loss large effective area optical fiber according to any one of claims 9 to 11, characterized in that: The wire drawing annealing treatment further includes a first coating treatment and a second coating treatment in sequence, wherein the first coating treatment and the second coating treatment are performed by an ultraviolet curing coating method.

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