Ultra-low-loss large-effective-area optical fiber and method of making same

Abstract

The application provides an ultra-low-loss large-effective-area optical fiber and a preparation method thereof. The ultra-low-loss large-effective-area optical fiber comprises, from inside to outside, a core layer, an inner cladding layer, a recessed cladding layer and an outer cladding layer; the recessed cladding layer comprises a deep recessed layer, a recessed step layer and a recessed platform layer. The ultra-low-loss large-effective-area optical fiber provided by the application has good bending resistance, a cable cutoff wavelength of not more than 1520 nm, small macro-bending loss, and small difference in attenuation coefficient from a short wavelength C band of 1520 nm to 1565 nm to a long wavelength L band of 1565 nm to 1625 nm, and can meet the G.654.E optical fiber standard and be used in extra-high voltage power communication, submarine cable or land trunk ultra-high speed communication lines.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and more specifically, to an ultra-low loss, large effective area optical fiber and its fabrication method. Background Technology

[0002] Degraded signal-to-noise ratio and nonlinear effects in optical fibers are the main factors limiting optical transmission distance. Reducing fiber loss can decrease the number of repeater stations, thereby reducing overall link loss and construction costs. Increasing the effective area can reduce nonlinear effects and increase input power, thus improving fiber transmission performance. In addition to improving single-channel transmission capacity, increasing the number of channels in wavelength division multiplexing (WDM) systems and expanding transmission bands can also increase system capacity, thereby meeting the ever-growing service demands.

[0003] Currently, step-index structures are often used to reduce fiber loss. However, existing optical fibers have significant differences in attenuation coefficients across short and long wavelength ranges, and the attenuation consistency within the communication window of optical fibers needs to be improved.

[0004] 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 fibers. Summary of the Invention

[0005] The main objective of this invention is to provide an ultra-low loss optical fiber with a large effective area and its fabrication method, in order to solve the problems of large differences in attenuation coefficients of optical fibers in the short-wavelength to long-wavelength range and poor attenuation consistency of optical fibers in the communication window in the prior art.

[0006] To achieve the above objectives, the present invention provides an ultra-low loss, large effective area optical fiber, which comprises, from the inside out, a core layer, an inner cladding, a recessed cladding, and an outer cladding; the recessed cladding includes a deep recessed layer, a recessed step layer, and a recessed plateau layer; the maximum relative refractive index difference of the core layer material is Δ1. max The minimum relative refractive index difference of the inner cladding material is Δ2. min The relative refractive index difference of the deep depression layer material is Δ3; the maximum relative refractive index difference of the depression step layer material is Δ4. max And the minimum relative refractive index is Δ4 min The maximum relative refractive index difference of the concave plateau layer material is Δ5. max And the minimum relative refractive index is Δ5 min ; △3 < △2 min △3 < △4 min And △3 < △5 min ;r represents the radial distance from the center of the fiber at a certain location in an ultra-low loss, large effective area optical fiber.

[0007] △1(r) represents the relative refractive index difference of the material at a certain location in the core layer from the center of the optical fiber. △1(r) and r satisfy the following relationship (1):

[0008]

[0009] Where R0 represents the radius of the core layer, g represents the refractive index distribution parameter of the core layer, and 2≤g≤6;

[0010] △2(r) represents the relative refractive index difference of the material at a certain location in the inner cladding from the center of the optical fiber. △2(r) and r satisfy the following relationship (2):

[0011]

[0012] Where R1 represents the radial distance from the contact interface between the inner cladding and the recessed cladding to the center of the fiber, and h represents the refractive index distribution parameter of the inner cladding, 3≤h≤10;

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

[0014]

[0015] Where R2 represents the radial distance from the contact interface between the deep recessed layer and the recessed step layer to the center of the optical fiber, R3 represents the radial distance from the contact interface between the recessed step layer and the recessed platform layer to the center of the optical fiber, and m represents the refractive index distribution parameter of the recessed step layer, 0.5≤m≤3.

[0016] △5(r) represents the relative refractive index difference of the material at a certain location in the recessed plateau layer from the center of the optical fiber. △5(r) and r satisfy the following relationship (4):

[0017]

[0018] Where R4 represents the radial distance from the contact interface between the recessed plateau layer and the outer cladding layer to the center of the optical fiber, and n represents the refractive index distribution parameter of the recessed plateau layer, 0.5≤n≤3;

[0019] The outer cladding layer is a silicon dioxide layer with a refractive index of 0.

[0020] To achieve the above objectives, another aspect of the present invention provides a method for fabricating an ultra-low loss, large effective area optical fiber. The method includes: fabricating an optical fiber preform, the preform comprising, from the inside out, a core pre-layer, an inner cladding pre-layer, a recessed cladding pre-layer, and an outer cladding pre-layer; and performing a drawing and annealing treatment on the optical fiber preform to transform the core pre-layer, inner cladding pre-layer, recessed cladding pre-layer, and outer cladding pre-layer into the core, inner cladding, recessed cladding, and outer cladding layers as defined above in this application, thereby obtaining an ultra-low loss, large effective area optical fiber.

[0021] By applying the technical solution of the present invention, by designing the above-mentioned specific cladding structure with a recessed cladding, and by designing the variation laws of the relative refractive index difference Δ1(r) of the core material, the relative refractive index difference Δ2(r) of the inner cladding material, the relative refractive index difference Δ4(r) of the recessed step layer material and the relative refractive index difference Δ5(r) of the recessed platform layer material to satisfy the relationships (1) to (4), and limiting the relative refractive index difference Δ3 of the deep recessed layer material to the above 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 high bending resistance and a cutoff wavelength of no more than 1520nm.

[0022] In summary, the ultra-low loss, large effective area optical fiber with the specific refractive index profile structure provided in this application has good bending resistance, a cable cutoff wavelength of no more than 1520nm, low macro-bending loss, and a small difference in attenuation coefficient between the short-wavelength C-band (1520nm-1565nm) and the long-wavelength L-band (1565nm-1625nm). It can meet the G.654.E optical fiber standard and can be used in ultra-high voltage power communication, submarine cables, or terrestrial trunk ultra-high speed communication lines. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0024] Figure 1 A schematic cross-sectional view of the optical fiber fabricated in Example 1 is shown.

[0025] Figure 2 A cross-sectional view of the refractive index structure of the optical fiber prepared in Example 1 is shown.

[0026] Figure 3 A schematic diagram of the structure of an optical fiber drawing and annealing apparatus according to a preferred embodiment of this application is shown;

[0027] Figure 4 The diagram shows a schematic of the apparatus used in the optical fiber fabrication process according to a preferred embodiment of this application.

[0028] The above figures include the following reference numerals:

[0029] 10. Core layer; 20. Inner cladding layer; 30. Recessed cladding layer; 31. Deep recessed layer; 32. Recessed stepped layer; 33. Recessed plateau layer; 40. Outer cladding layer; 51. First coating layer; 52. Second coating layer;

[0030] 100, Inner cavity heating section; 110, Preheating component; 120, Melting component; 200, Wire drawing and annealing section; 210, First annealing unit; 220, Second annealing unit; 300, Annealing tube; 301, Fiber optic annealing tube outlet. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0032] As described in the background section, existing optical fibers suffer from significant differences in attenuation coefficients across short to long wavelength ranges, resulting in poor attenuation consistency within the communication window and consequently, poor fiber transmission performance. To address these issues, this application provides an ultra-low-loss, large-effective-area optical fiber, such as... Figure 1 As shown, the ultra-low loss, large effective area optical fiber comprises, from the inside out, a core layer 10, an inner cladding 20, a recessed cladding 30, and an outer cladding 40; the recessed cladding 30 includes a deep recessed layer 31, a recessed step layer 32, and a recessed plateau layer 33; the maximum relative refractive index difference of the core layer 10 material is Δ1. max The minimum relative refractive index difference of the inner cladding 20 material is Δ2. min The relative refractive index difference of the deep recessed layer 31 material is Δ3; the maximum relative refractive index difference of the recessed step layer 32 material is Δ4. max And the minimum relative refractive index is Δ4 min The maximum relative refractive index difference of the material in the concave platform layer 33 is Δ5. max And the minimum relative refractive index is Δ5 min ; △3 < △2 min △3 < △4 min And △3 < △5 min ;r represents the radial distance from the center of the fiber at a certain location in an ultra-low loss, large effective area optical fiber.

[0033] △1(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. △1(r) and r satisfy the following relationship (1):

[0034]

[0035] Where R0 represents the radius of core layer 10, g represents the refractive index distribution parameter of core layer 10, and 2≤g≤6;

[0036] △2(r) represents the relative refractive index difference of the material at a certain location in the inner cladding 20 from the center of the optical fiber. △2(r) and r satisfy the following relationship (2):

[0037]

[0038] Where R1 represents the radial distance from the contact interface between the inner cladding 20 and the recessed cladding 30 to the center of the optical fiber, and h represents the refractive index distribution parameter of the inner cladding 20, 3≤h≤10.

[0039] △4(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. △4(r) and r satisfy the following relationship (3):

[0040]

[0041] Where R2 represents the radial distance from the contact interface between the deep recessed layer 31 and the recessed step layer 32 to the center of the optical fiber, R3 represents the radial distance from the contact interface between the recessed step layer 32 and the recessed platform layer 33 to the center of the optical fiber, and m represents the refractive index distribution parameter of the recessed step layer 32, 0.5≤m≤3.

[0042] △5(r) represents the relative refractive index difference of the material at a certain location in the recessed platform layer 33 from the center of the optical fiber. △5(r) and r satisfy the following relationship (4):

[0043]

[0044] Where R4 represents the radial distance from the contact interface between the recessed platform layer 33 and the outer cladding layer 40 to the center of the optical fiber, and n represents the refractive index distribution parameter of the recessed platform layer 33, 0.5≤n≤3.

[0045] The outer cladding layer 40 is a silicon dioxide layer with a refractive index of 0.

[0046] It should be noted that, in this application, the relative refractive index difference refers to the difference between the refractive index of a certain layer in an ultra-low loss, large effective area optical fiber and the refractive index of pure silicon dioxide material.

[0047] By designing the recessed cladding 30 of the above-mentioned specific cladding structure, and simultaneously designing the variation laws of the relative refractive index difference Δ1(r) of the core layer 10 material, the relative refractive index difference Δ2(r) of the inner cladding 20 material, the relative refractive index difference Δ4(r) of the recessed step layer 32 material and the relative refractive index difference Δ5(r) of the recessed platform layer 33 material to satisfy the relationships (1) to (4), and limiting the relative refractive index difference Δ3 of the deep recessed layer 31 material to the above 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 high bending resistance and a cutoff wavelength of no more than 1520nm.

[0048] In summary, the structure with the specific refractive index profile described above provided in this application (such as...) Figure 2 The ultra-low loss, large effective area optical fiber (as shown) has good bending resistance, a cable cutoff wavelength of no more than 1520nm, low macro-bending loss, and small attenuation coefficient differences between the short wavelength C-band (1520nm-1565nm) and the long wavelength L-band (1565nm-1625nm). It can meet the G.654.E optical fiber standard and can be used in ultra-high voltage power communication, submarine cables, or terrestrial trunk ultra-high speed communication lines.

[0049] In a preferred embodiment, △1 max It is 0.10–0.30%, △2 min The range is -0.25% to -0.35% for △3, -0.45% to -0.5% for △4. max The range is -0.20% to -0.25%, △4 min The range is -0.25% to -0.30%, △5 max The range is -0.30 to -0.35%, △5 min The range is -0.35% to -0.4%. △1 max △2 min △3, △4 max △4 min △5 max and △5 min Each and every one of the above-mentioned ranges, individually and independently, is beneficial for constraining fiber waveguide transmission, improving fiber attenuation performance, thereby improving fiber bending resistance, and reducing the difference in attenuation coefficient between short and long wavelength ranges.

[0050] 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 from the outer surface of the outer cladding 40 to 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, recessed cladding 30, and outer cladding 40 to the above ranges is beneficial to reducing 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 thus reducing the impact of additional stress on the optical fiber performance; at the same time, it is also beneficial to reduce the optical fiber attenuation in the long wavelength band and improve the bending resistance of the optical fiber.

[0051] In order to further control the cutoff wavelength of the optical fiber and reduce its macrobending loss, so that both performances are maintained at a good level, the ratio of R1 to R0 is preferably (1.4 to 2.0):1.

[0052] 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.

[0053] To further improve the overall performance of the optical fiber, preferably, the radial distance from the outer surface of the cladding 40 to the center of the optical fiber is 62-63 μm.

[0054] Doping with Ge and F elements helps weaken the silicon-oxygen bonds in quartz materials. At high temperatures, SiO2 chemical bonds are more easily broken, thus 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 recessed cladding 30 is made of SiO2 doped with F. Compared to other materials, using quartz materials doped with the aforementioned elements as the materials for the core layer 10, inner cladding 20, and recessed cladding 30 helps adjust the relative refractive index difference between the core layer 10 and each cladding layer, better meeting the specific fiber refractive index profile design.

[0055] In a preferred embodiment, the doping amount of Ge element in the optical fiber is 1.0–4.0 wt%, and the doping amount of F element is 0.01–0.3%, based on the total weight of the material in the core layer 10. Compared to other doping amounts, limiting the doping amount of Ge element in the core layer 10 to the above range is beneficial to reducing the Rayleigh scattering effect caused by GeO2, thereby reducing optical fiber attenuation. At the same time, limiting the doping amount of F element to the above range is beneficial to reducing the relative refractive index difference of the core layer 10 and also beneficial to reducing the viscosity of the core layer 10.

[0056] In a preferred embodiment, the doping amount of element F in the optical fiber is 0.01 to 1.0% based on the total weight of the material in the inner cladding 20. Compared to other doping amounts, limiting the doping amount of element F in the inner cladding 20 to the above range is beneficial to reducing the stress difference between the core layer 10 and the inner cladding 20, and between the inner cladding 20 and the recessed cladding 30, thereby helping to reduce the additional loss caused by stress.

[0057] In a preferred embodiment, the amount of F element doping in the optical fiber, based on the total weight of the material in the recessed cladding 30, is 0.3–2.0 wt%. Compared to other doping amounts, limiting the amount of F element doping in the recessed cladding 30 to the above range is beneficial for achieving a relative refractive index-depressed optical structure, achieving compatibility in terms of comprehensive performance such as attenuation coefficient, cutoff wavelength, and bending loss, while also helping to reduce the stress difference between the recessed layer and the core layer, thereby reducing the generation of additional attenuation.

[0058] In a preferred embodiment, the compressive stress of the core layer 10 to the inner cladding 20 is 40–100 MPa. The compressive stress values ​​within the range of the core layer 10 to the inner cladding 20 include, but are not limited to, the above range. Limiting them to the above range is beneficial for suppressing the propagation of internal micro-defects, reducing Rayleigh scattering, thereby reducing fiber attenuation, and also improving the tensile strength of the fiber.

[0059] In a preferred embodiment, within the radial range from the recessed step layer 32 to the recessed platform layer 33, the radial viscosity variation is no greater than 2% / μm, and the stress difference is no greater than 20%. Compared to other ranges, limiting the radial viscosity variation and stress difference to the above ranges is beneficial for reducing abrupt changes in stress in the optical fiber and for reducing additional attenuation.

[0060] The coating improves 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 coated with a first coating 51 and a second coating 52. Preferably, the materials of the first coating 51 and the second coating 52 are independently one or more of the group consisting of acrylic resin, epoxy resin, and silicone-modified acrylic resin.

[0061] 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 are each independently within, but not limited to, the above-mentioned ranges. Limiting them to these ranges is beneficial for improving the flexibility of the optical fiber; limiting the coefficient of friction of the outer surface of the second coating 52 to these ranges is beneficial for improving the wear resistance of the optical fiber, thus facilitating its application in the field of optical communication.

[0062] In a preferred embodiment, the optical fiber has a mode field diameter of 12–13 μm and an effective area of ​​120–130 μm at a wavelength of 1550 nm. 2 The optical fiber exhibits an attenuation coefficient ≤0.174dB / km at a wavelength of 1550nm; the difference in minimum attenuation coefficient between 1520nm and the wavelength range of 1520nm to 1625nm is Δα1520, where Δα1520 ≤ 0.02dB / km; the difference in minimum attenuation coefficient between 1625nm and the wavelength range of 1520nm to 1625nm is Δα1625, where Δα1625 ≤ 0.02dB / km; and the absolute value of the difference between Δα1520 and Δα1625 is not greater than 0.009dB / km. The optical fiber provided in this application has a large effective area and a small attenuation coefficient, exhibiting excellent transmission performance. Furthermore, the difference in attenuation coefficient between the short and long wavelength ranges is small, demonstrating excellent attenuation consistency within the communication window of the optical fiber.

[0063] The second aspect of this application also provides a method for fabricating an optical fiber, the method comprising: fabricating an optical fiber preform, the optical fiber preform comprising, from the inside out, a core layer 10 pre-preparation layer, an inner cladding layer 20 pre-preparation layer, a recessed cladding layer 30 pre-preparation layer, and an outer cladding layer 40 pre-preparation layer; and performing a drawing and annealing treatment on the optical fiber preform, so that the core layer 10 pre-preparation layer, the inner cladding layer 20 pre-preparation layer, the recessed cladding layer 30 pre-preparation layer, and the outer cladding layer 40 pre-preparation layer are sequentially transformed into the core layer 10, the inner cladding layer 20, the recessed cladding layer 30, and the outer cladding layer 40 in the optical fiber provided in this application, thereby obtaining the optical fiber provided in this application.

[0064] An optical fiber preform is prepared according to the specific refractive index profile structure provided in this application. The preparation process includes a deposition method commonly used in the art. After drawing and annealing the optical fiber preform, the optical fiber provided in this application is obtained. The optical fiber obtained in this application meets the G.654.E optical fiber standard and can be used in ultra-high voltage power communication, submarine cables, or terrestrial trunk ultra-high speed communication lines, etc.

[0065] In a preferred embodiment, the core layer 10 pre-layer is made of SiO2 doped with Ge and F, the inner cladding layer 20 pre-layer is made of SiO2 doped with F, and the recessed cladding layer 30 pre-layer is made of SiO2 doped with F. Compared to other materials, using quartz materials doped with the aforementioned elements as the materials for the core layer 10 pre-layer, inner cladding layer 20 pre-layer, and recessed cladding layer 30 pre-layer is beneficial for adjusting the relative refractive index difference of the core layer 10 and each cladding layer in the fabricated optical fiber, so as to better meet the aforementioned specific optical fiber refractive index profile design.

[0066] In a preferred embodiment, the doping amount of Ge element is 1.0 to 4.0 wt% and the doping amount of F element is 0.01 to 0.3% based on the total weight of the material in the preparatory layer of core layer 10. Compared with other doping amounts, limiting the doping amount of Ge element in the preparatory layer of core layer 10 to the above range is beneficial to reducing the Rayleigh scattering effect caused by GeO2, thereby helping to reduce fiber attenuation. At the same time, limiting the doping amount of F element to the above range is beneficial to reducing the relative refractive index difference of the obtained core layer 10, and also helps to reduce the viscosity of the obtained core layer 10.

[0067] In a preferred embodiment, the F element doping amount is 0.01 to 1.0% based on the total weight of the material in the inner cladding 20 pre-layer. Compared to other doping amounts, limiting the F element doping amount in the inner cladding 20 pre-layer to the above range is beneficial to reducing the stress difference between the core layer 10 and the inner cladding 20, and between the inner cladding 20 and the recessed cladding 30, thereby helping to reduce the additional loss caused by stress in the fabricated optical fiber.

[0068] In a preferred embodiment, the amount of element F is 0.3 to 2.0 wt% based on the total weight of the material in the preparatory layer of the recessed cladding 30. Compared to other doping amounts, limiting the amount of element F in the preparatory layer of the recessed cladding 30 to the above range is beneficial for achieving a relative refractive index-depressed optical structure, achieving compatibility in terms of comprehensive performance such as attenuation coefficient, cutoff wavelength, and bending loss, while also helping to reduce the stress difference between the recessed layer and the core layer, thereby reducing the generation of additional attenuation.

[0069] In a preferred embodiment, the fiber drawing and annealing process is performed using an optical fiber drawing and annealing device, such as... Figure 3As shown, the optical fiber drawing and annealing apparatus includes: an inner cavity heating section 100, a drawing and 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 traveling 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. The preheating component 110 and the melting component 120 are each independently arranged around the inner cavity in the circumferential direction and are parallel to each other. The drawing and annealing section 200 includes a first annealing unit 210 and a second annealing unit 220. 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 and the second annealing unit 220 are connected through the inner cavity heating section 100 in the coaxial direction. The annealing tube 300 is used to insert optical fibers. The second annealing unit 220 has an optical fiber annealing tube outlet 301 at its end furthest 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 and annealing process, the temperature of the preheating component 110 is set to T1, the temperature of the melting component 120 is set to T2 (1800–2000℃), the temperature of the first annealing unit 210 is set to T3, and the temperature of the second annealing unit 220 is set to T4 (1150–1250℃). Furthermore, T1, T2, T3, and T4 satisfy the following relationship: T2 > T3 > T4. 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℃.

[0070] When the fiber drawing and annealing device is in operation, the fiber preform is placed into the inner cavity. As the preheating component 110 and the melting component 120 preheat and melt the fiber preform, the heated and melted part of the fiber preform changes to a flowing 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 pulled out from the fiber annealing tube outlet 301. For optical fiber preforms made of specific materials (with Tg controlled within the aforementioned range), limiting the temperatures of the preheating component 110 and the melting component 120 within the aforementioned range, compared to other ranges, is beneficial for improving the efficiency of the optical fiber preform transitioning from a solid to a fluid state, and for obtaining optical fibers after drawing and annealing. Simultaneously, compared to other ranges, limiting the temperatures of the first annealing unit 210, the second annealing unit 220, and the optical fiber annealing tube outlet 301 within the aforementioned ranges is beneficial for producing optical fibers, reducing the likelihood of fiber breakage during drawing and reducing residual stress between layers in the optical fiber due to the drawing and annealing process. It also suppresses residual stress concentration in a specific location within the optical fiber and improves the attenuation performance of the fiber. Furthermore, compared to other ranges, limiting the temperature of the optical fiber annealing tube outlet 301 within the aforementioned range is beneficial for suppressing surface turbulence and for more precise control of the optical fiber diameter.

[0071] In summary, using the above-mentioned wire drawing and annealing device to perform the above-mentioned wire drawing and annealing treatment on the optical fiber preform is beneficial to improving the attenuation consistency of the optical fiber communication window.

[0072] In a preferred embodiment, the inner cavity heating section 100 includes two preheating components 110, each independently arranged around the inner cavity in the circumferential direction and parallel to each other, with their temperatures increasing sequentially along the travel direction of the optical fiber preform. Compared to a single preheating component 110, using two preheating components 110 and limiting their temperatures within the aforementioned range helps to further reduce temperature differences between different parts of the optical fiber preform during the fiber drawing process, further reduces stress differences between different parts, and thus helps to further improve the attenuation consistency of the optical fiber's communication window.

[0073] In a preferred embodiment, the inner cavity heating section 100 includes three melting components 120, each independently arranged around the inner cavity in a circumferential direction and parallel to each other, with their temperatures decreasing sequentially along the travel direction of the optical fiber preform. Compared to a single melting component 120, using three melting components 120 and limiting their temperatures within the aforementioned range helps to further reduce temperature differences between different parts of the optical fiber preform during the drawing process, further reduces stress differences between different parts, and thus helps to further improve the attenuation consistency of the optical fiber's communication window.

[0074] 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 and annealing device are each independently heated by graphite or coil heating, and each of the above components or annealing units is independently heated and controlled at temperature, and is connected to the host remote industrial control system for remote temperature adjustment.

[0075] In a preferred embodiment, the preheating component 110, melting component 120, first annealing unit 210, and second annealing unit 220 in the optical fiber drawing and annealing apparatus are each independently equipped with a temperature detector at a corresponding position for real-time monitoring of the optical fiber temperature at that position. Preferably, the preheating component 110, melting component 120, first annealing unit 210, and second annealing unit 220 are each independently equipped with a heat-insulating component on their outer periphery, and a water circulation cooling component is provided on the outer periphery of the heat-insulating component.

[0076] 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.

[0077] In a preferred embodiment, the inert gas introduction rate is 15–30 L / min. The inert gas introduction rate includes, but is not limited to, the above range. Limiting it to this range protects the heated graphite components inside the furnace, promotes thermal stability within the furnace, uniformly removes impurities from the furnace, and improves fiber strength and attenuation uniformity.

[0078] To further reduce the temperature difference between different parts of the optical fiber preform during the drawing process, further reduce the stress difference between different parts, and further improve the attenuation consistency of the optical fiber communication window, in a preferred embodiment, the shortest distance between the preheating component 110 and the melting component 120 is 200-500mm, the length of the annealing tube 300 in the region of the first annealing unit 210 is 100-300mm, and the length of the annealing tube 300 in the region of the second annealing unit 220 is 1000-2000mm.

[0079] In order to further reduce the temperature difference between different parts of the optical fiber preform during the drawing process, further reduce the stress difference between different parts, and further improve the attenuation consistency of the optical fiber communication window, in a preferred embodiment, when the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent components is 30-50 mm; and / or, when the inner cavity heating section 100 includes three melting components 120, the distance between two adjacent components is 20-40 mm.

[0080] In a preferred embodiment, during the wire drawing annealing process, the wire drawing tension is 50-180g, and the wire drawing tension and wire drawing rate satisfy the following relationship (5):

[0081]

[0082] Where F(v) represents the magnitude of the drawing tension corresponding to the drawing speed 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 speed, the unit is 350~1200m / min, α represents the tension adjustment coefficient, and 0.5≤α≤4.

[0083] The drawing tension includes, but is not limited to, the above-mentioned range. Limiting it to the above-mentioned range is beneficial to improve the fiber obtained by drawing and annealing to meet the above-mentioned refractive index profile structure of this application. At the same time, it makes the variation law of the relative refractive index difference Δ1(r) of the core layer 10 material, the relative refractive index difference Δ2(r) of the inner cladding layer 20 material, the relative refractive index difference Δ4(r) of the recessed step layer 32 material and the relative refractive index difference Δ5(r) of the recessed platform layer 33 material respectively satisfy the relationship (1) to (4). This is beneficial to more accurately control the relative refractive index difference of each layer, thereby improving the transmission performance of the fiber, reducing the difference in attenuation coefficient of the fiber from short wavelength to long wavelength, and improving the attenuation consistency of the fiber's communication window.

[0084] In a preferred embodiment, the fiber drawing tension is monitored in real time using a non-contact tension testing device. This device detects minute vibrations in the optical fiber to determine the magnitude of the tension acting on it. A schematic diagram of the device structure used in the optical fiber fabrication process during monitoring is shown below. Figure 4 As shown, this device further incorporates a non-contact tension testing device and a coating cup based on the fiber drawing and annealing apparatus. The coating cup is a container for coating the first coating layer 51 and the second coating layer 52. The non-contact tension meter is positioned between the fiber optic annealing tube outlet 301 and the coating cup, preferably slightly above it. The distance between the non-contact tension testing device and the fiber optic annealing tube outlet 301 is H1, and the distance between the non-contact tension testing device and the coating cup is H2. Preferably, H2 / H1 is (2-3):1. Compared to other ranges, limiting the ratio of H2 to H1 within the above range is beneficial for improving the accuracy of the measured drawing tension.

[0085] In a preferred embodiment, the optical fiber preform is cylindrical or rod-shaped, and its diameter is 60–200 mm. The shape and size of the optical fiber preform include, but are not limited to, the above range. Limiting it to the above range facilitates drawing and annealing processes and is beneficial for producing optical fibers with specific shapes suitable for optical communication applications, such as ultra-high voltage power communication, submarine cables, or terrestrial trunk ultra-high-speed communication lines.

[0086] 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; and when the diameter of the optical fiber preform is 160–200 mm, the drawing tension is 130–180 g. Using the above-mentioned preferred range of drawing tension for optical fiber preforms of different diameters allows for more precise control of the distribution of doping elements within each preform layer. This, in turn, allows for more precise control of the relative refractive index difference between the core layer 10 and each cladding layer in the fabricated optical fiber. This, in turn, improves the transmission performance of the optical fiber, reduces the difference in attenuation coefficient between short and long wavelength ranges, and enhances the attenuation consistency within the communication window of the optical fiber.

[0087] 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℃, and 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℃, and T4 is 1150–1250℃, and the drawing tension is 50–120g; when T g When the temperature is 1460~1550℃, T1 is 1350~1450℃, T2 is 1900~2200℃, T3 is 1560~1650℃, and T4 is 1150~1250℃, and the drawing tension is 80~180g.

[0088] For optical fiber preforms with different Tg or materials, using the above-mentioned preferred range of drawing tension for processing is beneficial to more accurately control the distribution of doping elements inside each preform layer, thereby enabling more accurate control of the relative refractive index difference between the core layer 10 and each cladding layer in the optical fiber, which in turn helps to improve the transmission performance of the optical fiber, reduce the difference in attenuation coefficient between the short and long wavelength ranges, and improve the attenuation consistency of the optical fiber communication window.

[0089] In a preferred embodiment, after the wire drawing and annealing process, a first coating process and a second coating process are performed sequentially, wherein the first coating process and the second coating process are performed by ultraviolet curing coating method.

[0090] In a preferred embodiment, during the first and second coating processes, the ultraviolet light source used has a center wavelength range of 365nm to 405nm, is a line light source in the direction parallel to the fiber's travel direction, and has an effective light source length of over 800mm. The distance between the light source and the fiber is set to 30 to 80mm, and the light source output power is infinitely adjustable from 10% to 100%, increasing with the fiber drawing rate to ensure that the ultraviolet irradiation energy obtained by the inner and outer layers reaches 400 to 600mJ / cm². 2 To ensure uniform curing of the inner and outer layers, nitrogen is used for protection within the fiber optic curing channel, and compressed air is introduced. The preferred nitrogen to compressed air flow ratio is (15-20):1, and the total air inlet flow rate is 15-30 L / min. Oil fumes and volatiles are extracted, with the protective gas inlet flow rate to the extraction flow rate being (3-5):1.

[0091] In the first and second coating processes described above, introducing nitrogen helps reduce the inhibition of the resin curing reaction by oxygen and increases the curing rate; introducing compressed air helps promote the ablation of oil fume volatiles and improves the friction properties of the outer surface of the second coating 52, thereby facilitating the adhesion of the subsequent coloring layer.

[0092] 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 and second coating treatments are respectively within, but not limited to, the above ranges. Limiting them within the above ranges is beneficial to reducing the microbending additional loss of the optical fiber, thereby improving the bending resistance of the optical fiber.

[0093] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0094] Example 1

[0095] A method for fabricating an optical fiber, comprising:

[0096] (1) Fabrication of optical fiber preform: In a reactor, the basic gas and dopant gas are deposited by MCVD deposition. The basic gases SiCl4, H2 and O2 are introduced, and the inert gas Ar or He is introduced into the reaction chamber as the carrier gas. GeCl4 gas and CF4 are introduced. The deposition temperature is 1450℃. After deposition for 24 hours, the optical fiber preform is obtained after sintering at 1550℃ for 4 hours. The optical fiber preform is cylindrical with a diameter of 155mm and a glass transition temperature Tg of 1360℃.

[0097] (2) Wire drawing and annealing process: using the following... Figure 3 The fiber drawing and annealing process shown is performed using a fiber drawing and annealing apparatus. The inner cavity heating section 100 includes two adjacent preheating components 110, which are independently arranged around the inner cavity in the circumferential direction and are parallel to each other, with a distance of 40 mm between them. The temperatures of the two preheating components 110 are set to 1310℃ and 1340℃ respectively along the traveling direction of the fiber preform. The inner cavity heating section 100 also includes three melting components 120, which are independently arranged around the inner cavity in the circumferential direction and are parallel to each other. The distance between two adjacent parts is 30mm. The temperatures of the three melting parts 120 along the direction of fiber preform travel are set to 1800℃, 1850℃ and 1900℃ respectively. The temperature T3 of the first annealing unit 210 is set to 1480℃ and the temperature T4 of the second annealing unit 220 is set to 1250℃. Under the above temperature conditions, the fiber is drawn and annealed. During this process, the fiber travels downward from the annealing tube 300 due to gravity and is finally pulled out from the fiber annealing tube outlet 301.

[0098] This process employs a non-contact tension testing device to monitor the wire drawing tension in real time (e.g., Figure 4 As shown, the fiber is drawn with a tension of 130g and a drawing speed of 800m / min. Finally, a first coating 51 and a second coating 52 are sequentially coated on the outer surface of the cladding 40. After curing with ultraviolet light at 365nm–395nm, the fiber is drawn and wound into a coil to obtain the optical fiber. The first coating 51 is an acrylic resin layer, and the second coating 52 is an acrylic resin layer.

[0099] A schematic diagram of the cross-sectional structure of the optical fiber obtained in Example 1 is shown below. Figure 1As shown, the optical fiber comprises, from the inside out, a core layer 10, an inner cladding 20, a recessed cladding 30, and an outer cladding 40. The recessed cladding 30 includes a deep recessed layer 31, a recessed step layer 32, and a recessed plateau layer 33. The core layer 10 is made of SiO2 doped with Ge and F, with Ge doping at 2.1 wt% and F doping at 0.1 wt% of the total weight of the core layer 10 material. The inner cladding 20 is made of SiO2 doped with F, with F doping at 0.45 wt% of the total weight of the inner cladding 20 material. The recessed cladding 30 is made of SiO2 doped with F, with F doping at 1.2 wt% of the total weight of the recessed cladding 30 material.

[0100] The cross-sectional view of the refractive index structure of the optical fiber prepared in Example 1 is shown below. Figure 2 As shown, the relative refractive index difference Δ1(r) of the core layer 10 material, the relative refractive index difference Δ2(r) of the inner cladding layer 20 material, the relative refractive index difference Δ4(r) of the recessed step layer 32 material, and the relative refractive index difference Δ5(r) of the recessed platform layer 33 material satisfy the relationships (1) to (4) defined above. 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 Δ1 of the core layer 10 material in relationship (1) is... max The value 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 Δ2 of the inner cladding 20 material in equation (2) is 0.2%. min The refractive index 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 Δ4 of the material in the recessed step layer 32 in equation (3) is Δ4. max The minimum relative refractive index is -0.20%, Δ4. min The refractive index distribution parameter m of the recessed step layer 32 is -0.30%, R2 is 16.16 μm, R3 is 26.56 μm, and the maximum relative refractive index difference Δ5 of the material of the recessed platform layer 33 in equation (4) is 2. max It is -0.30%, and the minimum relative refractive index Δ5 min The refractive index is -0.35%, R4 is 44.16 μm, and the refractive index distribution parameter n of the concave plateau layer 33 is 2.

[0101] Example 2

[0102] 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. The material of the core layer 10 is SiO2 doped with Ge and F elements. The doping amount of Ge element is 3.2 wt% and the doping amount of F element is 0.2 wt% based on the total weight of the material of the core layer 10. The doping amount of F element is 0.65 wt% based on the total weight of the material of the inner cladding layer 20. The doping amount of F element is 2.0 wt% based on the total weight of the material of the recessed cladding layer 30. In step (2), the wire drawing tension is controlled at 120 g and the wire drawing rate is 650 m / min for wire drawing.

[0103] Example 3

[0104] 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. The material of the core layer 10 is SiO2 doped with Ge and F elements. The doping amount of Ge element is 2.6 wt% and the doping amount of F element is 0.15 wt% based on the total weight of the material of the core layer 10. The doping amount of F element is 0.65 wt% based on the total weight of the material of the inner cladding layer 20. The doping amount of F element is 1.2 wt% based on the total weight of the material of the recessed cladding layer 30. In step (2), the wire drawing tension is controlled at 142 g and the wire drawing rate is 1000 m / min for wire drawing.

[0105] Example 4

[0106] Step (1) is the same as in Example 1. The difference from Example 1 is that the wire tension in step (2) is 50g and the wire drawing speed is 350m / min.

[0107] Example 5

[0108] Step (1) is the same as in Example 1. The difference from Example 1 is that the wire tension in step (2) is 180g and the wire drawing speed is 1200m / min.

[0109] Example 6

[0110] Step (1) is the same as in Example 1. The difference from Example 1 is that the wire tension in step (2) is 200g and the wire drawing speed is 1500m / min.

[0111] Example 7

[0112] Step (1) is the same as in Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent components is 30mm, and the temperatures are set to 1330℃ and 1350℃ respectively; the inner cavity heating section 100 includes three melting components 120, and the three are independently arranged around the inner cavity in the circumferential direction and are parallel to each other, the distance between two adjacent components is 20mm, and the temperatures are set to 1900℃, 1950℃ and 2000℃ respectively; the temperature T3 of the first annealing unit 210 is set to 1480℃, and the temperature T4 of the second annealing unit 220 is set to 1250℃.

[0113] Example 8

[0114] Step (1) is the same as in Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, the distance between two adjacent components is 50mm, and the temperatures are set to 1300℃ and 1320℃ respectively; the inner cavity heating section 100 includes three melting components 120, and the three are independently arranged around the inner cavity in the circumferential direction and are parallel to each other, the distance between two adjacent components is 40mm, and the temperatures are set to 1800℃, 1850℃ and 1900℃ respectively; the temperature T3 of the first annealing unit 210 is set to 1480℃, and the temperature T4 of the second annealing unit 220 is set to 1250℃.

[0115] Example 9

[0116] Step (1) is the same as in Example 1, except that: the inner cavity heating section 100 includes two preheating components 110, with a distance of 70 mm between adjacent components, and the temperatures are set to 1200℃ and 1250℃ respectively; the inner cavity heating section 100 includes three melting components 120, which are independently arranged around the inner cavity in the circumferential direction and are parallel to each other, with a distance of 60 mm between adjacent components, and the temperatures are set to 1750℃, 1800℃ and 1850℃ respectively; the temperature T3 of the first annealing unit 210 is set to 1480℃ and the temperature T4 of the second annealing unit 220 is set to 1250℃.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that the optical fiber preform does not include the recessed cladding 30 pre-fabrication layer, and the resulting optical fiber includes, from the inside out, a core layer 10, an inner cladding 20, and an outer cladding 40. The core layer 10 pre-fabrication layer, the inner cladding 20 pre-fabrication layer, and the outer cladding 40 pre-fabrication layer are the same as those in Example 1.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the optical fiber preform does not include the recessed step layer 32 and the recessed platform layer 33 preform. The resulting optical fiber includes, from the inside out, a core layer 10, an inner cladding layer 20, a deep recessed layer 31, and an outer cladding layer 40. The core layer 10 preform, the inner cladding layer 20 preform, the deep recessed layer 31 preform, and the outer cladding layer 40 preform are the same as in Example 1.

[0121] Comparative Example 3

[0122] The difference from Example 1 is that the doping amount of F element in the pre-layer material of the deep recessed layer 31 in step (1) is changed so that the relative refractive index difference Δ3 of the pre-layer material of the deep recessed layer 31 in the optical fiber is -0.55%. The materials of the pre-layer material of the core layer 10, the pre-layer material of the inner cladding layer 20, the pre-layer material of the recessed step layer 32, the pre-layer material of the recessed platform layer 33, and the pre-layer material of the outer cladding layer 40 are the same as those in Example 1.

[0123] The 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 embodiments of this application are shown in Table 1, and the test results of each performance are shown in Table 2 and Table 3, respectively.

[0124] Table 1

[0125]

[0126]

[0127] Table 2

[0128]

[0129] Table 3

[0130] Mode field diameter @1550nm / μm 13.8 12.9 12.6 22m optical cable cutoff wavelength / nm 1580 1532 1544 Attenuation coefficient @1550nm, dB / km 0.192 0.178 0.173 The absolute value of the difference between Δα1520 and Δα1625, in dB / km 0.015 0.013 0.011

[0131] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0132] Comparing Example 1 with Comparative Examples 1 to 3, it can be seen that the optical fiber cutoff wavelength of the optical fibers prepared in Comparative Examples 1 to 3 is greater than 1520 nm, and the attenuation coefficient of the optical fibers prepared in Comparative Examples 1 to 3 is greater than that of Example 1, and the absolute value of the difference between Δα1520 and Δα1625 is also greater than that of Example 1. Therefore, by designing the recessed cladding 30 of the specific cladding structure of this application, and by designing the variation law of the relative refractive index difference Δ1(r) of the core layer 10 material, the relative refractive index difference Δ2(r) of the inner cladding 20 material, the relative refractive index difference Δ4(r) of the recessed step layer 32 material, and the relative refractive index difference Δ5(r) of the recessed platform layer 33 material to satisfy the above-mentioned relationship (1) to (4) provided in this application, and limiting the relative refractive index difference Δ3 of the deep recessed layer 31 material to the range of this 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 high bending resistance and an optical fiber cutoff wavelength of no more than 1520 nm.

[0133] Comparing Examples 1, 4 to 6, it can be seen that during the drawing and annealing process, the compressive stress values ​​of the core layer 10 to the inner cladding 20 were adjusted by changing the drawing tension and drawing rate. Under the action of 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 propagation of microcracks and reduce Rayleigh scattering loss. However, excessive drawing tension will cause an increase in the radial stress variation amplitude from the inner cladding to the recessed cladding, which is not conducive to the uniformity control of the attenuation coefficient. Moreover, the optical fiber cutoff wavelengths of the optical fibers obtained in Examples 1, 4 to 6 are all less than 1520nm, while the absolute values ​​of the attenuation coefficient and the difference between Δα1520 and Δα1625 at 1550nm of the optical fiber obtained in Example 6 are greater than those in Examples 1, 4, and 5, respectively. Therefore, compared with other ranges, limiting the drawing tension to the preferred range of this application is beneficial to controlling the radial stress variation amplitude, thereby improving the transmission performance of the optical fiber, reducing the difference in the attenuation coefficient of the optical fiber from the short wavelength range to the long wavelength range, and improving the attenuation consistency of the optical fiber's communication window.

[0134] Comparing Examples 1, 7 to 9, it can be seen that the compressive stress values ​​of the core layer 10 to the inner cladding layer 20 in the optical fiber prepared in Example 9 are significantly greater than those in Examples 1, 7, and 8. This indicates that the tensile strength of the optical fiber prepared in Example 9 is worse. Therefore, the compressive stress values ​​in the range of the core layer 10 to the inner cladding layer 20 include, but are not limited to, the range of this application. Limiting them to this range is beneficial for reducing optical fiber attenuation and also for improving the tensile strength of the optical fiber. Furthermore, the attenuation coefficient at 1550 nm and the absolute values ​​of the difference between Δα1520 and Δα1625 in the optical fiber prepared in Example 9 are both greater than those in Examples 1, 7, and 8, respectively. Therefore, compared to other ranges, limiting 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 to the preferred range of this application is beneficial to further reduce the temperature difference of each part in the optical fiber preform during the drawing process, further reduce the stress difference of each part, and further improve the attenuation consistency of the optical fiber communication window.

[0135] It should be noted that the terms "first," "second," etc., used 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 sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0136] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should 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 out, a core layer (10), an inner cladding layer (20), a recessed cladding layer (30), and an outer cladding layer (40); the recessed cladding layer (30) comprises a deep recessed layer (31), a recessed step layer (32), and a recessed plateau layer (33); the maximum relative refractive index difference of the core layer (10) material is Δ1. max The minimum relative refractive index difference of the inner cladding (20) material is Δ2. min The relative refractive index difference of the deep recessed layer (31) material is Δ3; the maximum relative refractive index difference of the recessed step layer (32) material is Δ4. max And the minimum relative refractive index is Δ4 min The maximum relative refractive index difference of the material in the recessed platform layer (33) is Δ5. max And the minimum relative refractive index is Δ5 min ; △3 < △2 min △3 < △4 min And △3 < △5 min ;r represents the radial distance from the center of the fiber at a certain location in the ultra-low loss, large effective area optical fiber. △1(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 △1(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; △2(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 △2(r) and r satisfy the following relationship (2): Wherein, R1 represents the radial distance between the contact interface of the inner cladding (20) and the recessed cladding (30) and the center of the optical fiber, and h represents the refractive index distribution parameter of the inner cladding (20), 3≤h≤10; △4(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 △4(r) and r satisfy the following relationship (3): Wherein, R2 represents the radial distance from the contact interface between the deep recessed layer (31) and the recessed step layer (32) to the center of the optical fiber, R3 represents the radial distance from the contact interface between the recessed step layer (32) and the recessed platform layer (33) to the center of the optical fiber, and m represents the refractive index distribution parameter of the recessed step layer (32), 0.5≤m≤3; △5(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 △5(r) and r satisfy the following relationship (4): Wherein, R4 represents the radial distance between the contact interface between the recessed 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 recessed platform layer (33), 0.5≤n≤3; The outer cladding layer (40) is a silicon dioxide layer, and the refractive index of the outer cladding layer (40) is 0.

2. The ultra-low loss, large effective area optical fiber according to claim 1, characterized in that, The △1 max The value is 0.10% to 0.30%, and the △2 min The value is -0.25% to -0.35%, Δ3 is -0.45% to -0.5%, and Δ4 is... max The value is -0.20% to -0.25%, and the △4 min The value is -0.25% to -0.30%, and the △5 max The value is -0.30% to -0.35%, and the △5 min The range 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 5-7 μm; the difference between R1 and R0 is 3.5-5 μm, preferably the ratio of R1 to R0 is (1.4-2.0):1; the difference between R4 and R1 is 30-40 μm, preferably the difference between R2 and R1 is 4.5-5.5 μm, preferably the difference between R3 and R2 is 6-18 μm, preferably the difference between R4 and R3 is 5.5-22 μm; the radial distance R5 from the outer surface of the outer cladding (40) to the center of the optical fiber is 50-65 μm, preferably 62-63 μm.

4. The ultra-low loss, large effective area optical fiber according to any one of claims 1 to 3, characterized in that, The core layer (10) is made of SiO2 doped with Ge and F elements, the inner cladding layer (20) is made of SiO2 doped with F elements, and the recessed cladding layer (30) is made of 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 in the core layer (10), the doping amount of Ge element is 1.0–4.0 wt%, and the doping amount of F element is 0.01–0.3%; and / or, The doping amount of F element is 0.01 to 1.0% based on the total weight of the material in the inner cladding (20); and / or, The amount of F element doped is 0.3 to 2.0 wt% based on the total weight of the material in the recessed 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 of 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 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 further covered 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 coefficient of friction 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 12–13 μm and an effective area of ​​120–130 μm at a wavelength of 1550 nm. 2 ; and / or, The ultra-low loss, large effective area optical fiber has an attenuation coefficient ≤0.174dB / km at a wavelength of 1550nm; and / or, The difference in minimum attenuation coefficient between the ultra-low loss, large effective area optical fiber at 1520 nm and in the wavelength range of 1520 nm to 1625 nm is Δα1520, where Δα1520 ≤ 0.02 dB / km; the difference in minimum attenuation coefficient between 1625 nm and in the wavelength range of 1520 nm to 1625 nm is Δα1625, where Δα1625 ≤ 0.02 dB / km; and the absolute value of the difference between Δα1520 and Δα1625 is not greater than 0.009 dB / km.

9. A method for fabricating an ultra-low loss, large effective area optical fiber, characterized in that, The preparation method includes: Fabricating an optical fiber preform, the optical fiber preform comprising, from the inside out, a core layer preparation layer, an inner cladding layer preparation layer, a recessed cladding layer preparation layer, and an outer cladding layer preparation layer; The optical fiber preform is subjected to a drawing and annealing process so that the core layer pre-layer, the inner cladding pre-layer, the recessed cladding pre-layer and the outer cladding pre-layer are sequentially transformed into the core layer (10), the inner cladding (20), the recessed cladding (30) and the outer cladding (40) in claim 1, thereby obtaining the ultra-low loss large effective area optical fiber.

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

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

12. The method for fabricating ultra-low loss, large effective area optical fiber according to any one of claims 9 to 11, characterized in that, The fiber drawing and annealing process is performed using an optical fiber drawing and annealing device, which includes: 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 at least one preheating component (110) and at least one melting component (120) are sequentially arranged in the inner cavity according to the traveling direction of the optical fiber preform. The preheating component (110) and the melting component (120) are each independently arranged around the inner cavity in the circumferential direction and are parallel to each other. A drawing and annealing section (200) includes 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) are coaxially arranged, and an annealing tube (300) is provided through the first annealing unit (210), the second annealing unit (220) and the inner cavity heating section (100) in the coaxial direction. The annealing tube (300) is used to insert optical fibers. The second annealing unit (220) has 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 process, the temperature of the preheating component (110) is set to T1, the temperature of the melting component (120) is set to T2, where T2 is 1800–2200°C, the temperature of the first annealing unit (210) is set to T3, and the temperature of the second annealing unit (220) is set to T4, where T4 is 1150–1250°C. Furthermore, T1, T2, T3, and T4 satisfy the following relationship: T2 > T3 > T4. g >T1>T4, where T g The T3 represents the glass transition temperature of the optical fiber preform; the T3 and the T g The difference is 50-100℃.

13. The method for fabricating ultra-low loss, large effective area optical fiber according to claim 12, characterized in that, The inner cavity heating section (100) includes two preheating components (110), each independently arranged around the inner cavity in the circumferential direction and parallel to each other, with their temperatures increasing sequentially along the travel direction of the optical fiber preform; and / or, The inner cavity heating section (100) includes three melting components (120), which are independently arranged around the inner cavity in the circumferential direction and are parallel to each other. The temperature of the three components decreases sequentially along the travel direction of the optical fiber preform.

14. The method for fabricating 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 annealing tube (300) in the region of the first annealing unit (210) is 100-300 mm, and the length of the annealing tube (300) in the region of the second annealing unit (220) is 1000-2000 mm.

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

16. The method for fabricating 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 process, the wire drawing tension is 50-180g, and the wire drawing tension and wire drawing speed satisfy the following relationship (5): Wherein, F(v) represents the magnitude of the drawing tension corresponding to the drawing speed v, F0 represents the minimum drawing tension, F1 represents the maximum drawing tension, the unit of F(v), F0 and F1 is g, v2 represents the maximum drawing speed, the unit is 350~1200m / 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 fabricating 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 60-200 mm. Preferably, when the diameter of the optical fiber preform is 60-80mm, the drawing tension is 50-100g; when the diameter of the optical fiber preform is 120-150mm, the drawing tension is 90-130g; and when the diameter of the optical fiber preform is 160-200mm, the drawing tension is 130-180g.

18. The method for fabricating 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℃, T1 is 1300-1350℃, T2 is 1800-2000℃, T3 is 1460-1500℃, T4 is 1150-1250℃, and the drawing tension is 60-130g. When the 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 the T g When the temperature is 1460-1550℃, T1 is 1350-1450℃, T2 is 1900-2200℃, T3 is 1560-1650℃, T4 is 1150-1250℃, and the drawing tension is 80-180g.

19. The method for fabricating ultra-low loss, large effective area optical fiber according to any one of claims 9 to 11, characterized in that, The wire drawing and annealing process is followed by a first coating process and a second coating process, which are performed using a UV curing coating method.

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