Optical fiber and its preparation method

Abstract

The present invention provides an optical fiber and a method for preparing the same, which relates to the field of optical communication technologies. The optical fiber includes, from inside to outside in sequence, a germanium-doped silica core layer, a separation layer, a fluorine-doped silica optical cladding layer, and an outer cladding layer. The separation layer is used to prevent the diffusion of germanium in the germanium-doped silica core layer and fluorine in the fluorine-doped silica optical cladding layer; wherein the fluorine-doped silica optical cladding layer is divided into three layers, which are, from inside to outside in sequence, a shallow fluorine-doped layer, a main fluorine-doped layer, and an auxiliary fluorine-doped layer, and the refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than the refractive index of the main fluorine-doped layer. Through the layered arrangement of the fluorine-doped silica optical cladding layer, the amount of fluorine doped in SiO2 has a process of gradually changing concentration in the radial direction. This changing process can make the viscosity of the optical fiber cross-section change gradually in the radial direction. This structure can reduce the generation of optical fiber stress while obtaining low macro-bending loss of the optical fiber, and obtain an optical fiber with low loss and low bending loss.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technologies, and particularly to an optical fiber and a preparation method thereof. Background Art

[0002] This section aims to provide background or context for the embodiments of the present invention described in the claims. The description herein is not admitted to be prior art merely because it is included in this section.

[0003] Due to its excellent bending resistance characteristics, G.657 optical fiber has been widely used in recent years. Its main structure includes a germanium-doped single germanium dioxide core layer, a single fluorine-doped silica optical cladding layer, and an outer cladding layer arranged from the inside out. In order to achieve the performance of small bending loss of the optical fiber itself, it is mainly achieved by reducing the mode field diameter of the optical fiber and increasing the depressed cladding; and the depressed cladding is achieved by doping the single fluorine-doped silica optical cladding layer with a fluorine element having a low refractive index.

[0004] Due to the doping of fluorine elements, some fluorine elements will be mixed with germanium elements having a high refractive index. Under the condition of achieving the same refractive index of the single germanium dioxide core layer, 10% - 15% more germanium elements will be doped than ordinary G.652 optical fiber. The increase in the doping of germanium elements will bring an increase in Rayleigh scattering. For the optical fiber produced under this condition, the loss in the 1310nm band is generally 0.010dB / km - 0.015dB / km higher than that of G.652 optical fiber. Therefore, an optical fiber is needed to ensure the problem of increased optical fiber attenuation caused by the mutual doping of germanium and fluorine elements between the single germanium dioxide core layer and the single fluorine-doped silica optical cladding layer. Summary of the Invention

[0005] One of the purposes of the present invention is to provide an optical fiber which has low attenuation and low bending loss at the same time.

[0006] The technical solution provided by the present invention is as follows:

[0007] An optical fiber includes, from the inside out, a single germanium-doped silica core layer, a separation layer, a single fluorine-doped silica optical cladding layer, and an outer cladding layer in sequence. The separation layer is used to prevent the mutual diffusion of germanium in the single germanium-doped silica core layer and fluorine in the single fluorine-doped silica optical cladding layer; wherein the single fluorine-doped silica optical cladding layer is divided into three layers, which are a shallow fluorine-doped layer, a main fluorine-doped layer, and an auxiliary fluorine-doped layer from the inside out. The refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than that of the main fluorine-doped layer.

[0008] Preferably, the refractive indices of adjacent two layers among the separation layer, the shallow fluorine-doped layer, the main fluorine-doped layer, and the auxiliary fluorine-doped layer change gradually, and the refractive index change within each 1μm is controlled to be 0.03% - 0.05%.

[0009] Preferably, the barrier layer is a pure SiO2 barrier layer.

[0010] Preferably, the refractive index of the germanium-doped silica core layer is 0.35% to 0.45%, and the thickness of the germanium-doped silica core layer is 4.0 μm to 4.5 μm.

[0011] Preferably, the relative refractive index of the barrier layer is -0.01% to 0.01%, and its thickness is 1.5 μm to 2 μm.

[0012] Preferably, the refractive index of the shallow fluorine-doped layer is -0.04% to -0.07%, and the thickness is 2.5 μm to 4.2 μm.

[0013] Preferably, the refractive index of the main fluorine-doped layer is -0.08% to -0.15%, and the thickness of the main fluorine-doped layer is 5 μm to 8.5 μm.

[0014] Preferably, the refractive index of the auxiliary fluorine-doped layer is -0.01% to -0.07%, and the thickness is 2.5 to 4.2 μm.

[0015] Preferably, the outer cladding is a protective layer of the optical fiber, and the outer cladding is a pure SiO2 layer; the refractive index of the outer cladding is 0 to 0.005%, and its thickness is 41.1 μm to 49.0 μm.

[0016] Another object of the present invention is to provide an optical fiber manufacturing method for manufacturing the above-mentioned optical fiber, which includes the following steps:

[0017] S1: Prepare a germanium-doped core layer;

[0018] S2: Form a prefabricated barrier layer in a loose state on the outer periphery of the germanium-doped core layer by chemical vapor deposition. The prefabricated barrier layer can prevent the diffusion of germanium in the core layer and the diffusion of fluorine in the prefabricated single fluorine-doped silica optical cladding.

[0019] S3: Form a fluorine-doped prefabricated single fluorine-doped silica optical cladding on the outer periphery of the prefabricated barrier layer to obtain an optical fiber preform. The prefabricated single fluorine-doped silica optical cladding is formed by stacking in three layers, which are, from the inside to the outside, a prefabricated shallow fluorine-doped layer, a prefabricated main fluorine-doped layer, and a prefabricated auxiliary fluorine-doped layer, and finally obtain a single fluorine-doped silica optical cladding structure in which the refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than the refractive index of the main fluorine-doped layer.

[0020] S4: Obtain an optical fiber by subjecting the optical preform to an optical fiber melting and annealing process and an optical fiber coating and curing process.

[0021] Preferably, the density of the prefabricated barrier layer loose body is 0.3 g / cm 3 or more.

[0022] Compared with the prior art, an optical fiber provided by the present invention includes, from inside to outside in sequence, a germanium-doped silica core layer, a separation layer, a fluorine-doped silica optical cladding layer, and an outer cladding layer. The separation layer is used to prevent the diffusion of germanium in the germanium-doped silica core layer and fluorine in the fluorine-doped silica optical cladding layer. Among them, the fluorine-doped silica optical cladding layer is divided into three layers, which are, from inside to outside in sequence, a shallow fluorine-doped layer, a main fluorine-doped layer, and an auxiliary fluorine-doped layer. The refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than that of the main fluorine-doped layer. Through the setting of the separation layer, the cancellation of the refractive index caused by the migration of doping elements is reduced. And through the layered setting of the fluorine-doped silica optical cladding layer, the amount of fluorine doped in SiO2 has a process of gradually changing concentration in the radial direction. This changing process can make the viscosity of the optical fiber cross-section change gradually along the radial direction. This structure can reduce the generation of optical fiber stress while obtaining low macro-bending loss of the optical fiber, and obtain an optical fiber with low loss and low bending loss.

[0023] Through the shallow fluorine-doped layer and the auxiliary fluorine-doped layer that play a transitional role, the generation of stress caused by viscosity mismatch during the preparation of the optical fiber preform and the optical fiber drawing process is reduced, which facilitates the preparation of the optical fiber itself. And through the setting of the main fluorine-doped layer with a relatively low refractive index, the main fluorine-doped layer is used as a depressed cladding layer to achieve the reduction of the bending attenuation of the optical fiber. And in the present invention, the refractive index profile structure of the optical fiber does not adopt a deep fluorine-doped fluorine-doped silica optical cladding layer structure, which reduces the difficulty of the optical fiber preparation process and is conducive to mass production using the VAD and OVD processes. Description of the Drawings

[0024] The following further describes the present invention in detail with reference to the drawings and specific embodiments.

[0025] Figure 1 It is a schematic cross-sectional view of an optical fiber in an embodiment of the present invention.

[0026] Figure 2 In the present invention Figure 1 Schematic diagram of the refractive index profile of the optical fiber.

[0027] Figure 3 It is the optical fiber attenuation parameter characteristics prepared by the VAD process with different densities of the separation layer in a loose state in the present invention.

[0028] Description of the reference numerals:

[0029] Germanium-doped silica 1 Interlayer 2 Shallow fluorine-doped layer 3 Main fluorine-doped layer 4 Auxiliary fluorine-doped layer 5 Cladding layer 6

[0030] The following specific embodiments will further illustrate the embodiments of the present invention in conjunction with the above drawings. Specific Embodiments

[0031] In order to more clearly understand the above objects, features and advantages of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the features in the embodiments of the present application can be combined with each other.

[0032] In the following description, many specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the embodiments of the present invention.

[0033] ″Rayleigh scattering″ herein belongs to a type of scattering, also known as ″molecular scattering″, which refers to the scattering of light waves by particles whose linear dimensions are much smaller than the wavelength.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the embodiments of the present invention belong. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present invention.

[0035] An optical fiber, as Figure 1 shown, includes a germanium-doped silica core layer 1, a fluorine-doped silica optical cladding layer, and an outer cladding layer 6. A barrier layer 2 for preventing the diffusion of germanium and fluorine is provided between the germanium-doped silica core layer 1 and the fluorine-doped silica optical cladding layer. By providing the barrier layer 2, during the preparation of the optical fiber preform and the optical fiber drawing process, the mixing of germanium in the germanium-doped silica core layer 1 and fluorine in the fluorine-doped silica optical cladding layer can be reduced. By blocking the fluorine in the fluorine-doped silica optical cladding layer from entering the germanium-doped silica core layer 1 through the barrier layer 2, the Rayleigh scattering in the optical fiber can be effectively reduced, thereby achieving low attenuation of the optical fiber itself; and at the same time, by providing the barrier layer 2, the fluorine in the fluorine-doped silica optical cladding layer is blocked, ensuring that the content of fluorine in the fluorine-doped silica optical cladding layer always remains constant, and avoiding the phenomenon that the bending loss increases due to the decrease in the fluorine content.

[0036] In some embodiments, the refractive index changes gradually between every two adjacent layers of the barrier layer 2, the shallow fluorine-doped layer 3, the main fluorine-doped layer 4, and the auxiliary fluorine-doped layer 5, and the refractive index change within every 1 μm is controlled to be 0.03% - 0.05%.

[0037] In some embodiments, the refractive index of the germanium-doped silica core layer 1 is 0.35% to 0.45%, and the radius of the germanium-doped silica core layer 1 is 4.0 μm to 4.5 μm. By limiting the refractive index and radius of the germanium-doped silica core layer 1, the germanium-doped silica core layer 1 can have a relatively good refractive index, ensuring that during use, there can be a relatively small transmission attenuation.

[0038] In some embodiments, in order to achieve the separation of the germanium-doped silica core layer 1 and the fluorine-doped silica optical cladding layer by the separation layer 2, the relative refractive index of the separation layer 2 is -0.01% to 0.01%, its thickness is 1.5 μm to 2 μm, and in some embodiments, the bulk density of the separation layer is 0.32 g / cm 3 ~0.35 g / cm 3 . In the present invention, the separation layer 2 plays a role in separation. On the one hand, physical separation is achieved through the separation layer 2, and on the other hand, it is achieved by controlling the density of this layer in the bulk state.

[0039] In some embodiments, as Figure 1 shown, the fluorine-doped silica optical cladding layer is divided into three layers. Here, from the inside to the outside, the fluorine-doped silica optical cladding layer is successively the lightly fluorine-doped layer 3, the main fluorine-doped layer 4, and the auxiliary fluorine-doped layer 5; and the refractive indices of the lightly fluorine-doped layer 3 and the auxiliary fluorine-doped layer 5 are both greater than the refractive index of the main fluorine-doped layer 4; here, the refractive indices and thicknesses of each layer are as follows: the refractive index of the main fluorine-doped layer 4 is -0.08% to -0.15%, and the thickness of the main fluorine-doped layer 4 is 5 μm to 8.5 μm; the refractive index of the lightly fluorine-doped layer 3 is -0.04% to -0.07%, and the thickness is 2.5 μm to 4.2 μm; the refractive index of the auxiliary fluorine-doped layer 5 is -0.01% to -0.07%, and the thickness is 2.5 to 4.2 μm. By adopting the method of interlayer jump, the viscosity of the fiber cross-section shows a gradually changing trend along the radial direction through the gradual change of the fluorine doping amount in the fluorine-doped silica optical cladding layer, so that the attenuation of the long wavelength in the optical fiber is significantly reduced. The attenuation of the G.657 optical fiber with this structure in the 1550 nm band is 0.008 dB / km to 0.013 dB / km lower than that of the G.657 optical fiber without this structure, and the general attenuation value can reach below 0.178 dB / km; and in this embodiment, by defining the main fluorine-doped layer 4 as the part with the lowest refractive index in the fiber cross-section direction, it mainly confines the light of the germanium-doped silica core layer 1, while the lightly fluorine-doped layer 3 and the auxiliary fluorine-doped layer 5 located on both sides of the main fluorine-doped layer 4 mainly play an auxiliary confinement role.

[0040] In some embodiments, as Figure 1As shown, it further includes an outer cladding layer 6 located on the outermost side. During use, the outer cladding layer 6 serves as a mechanical protection layer for the optical fiber. The outer cladding layer 6 is a pure SiO2 layer, with a refractive index of 0 to 0.005%, and a thickness of 41.1μm to 49.0μm. In this way, the inner single-doped germanium dioxide core layer 1 and the single-doped fluorine dioxide optical cladding layer are protected by the setting of the outer cladding layer 6.

[0041] The structures of the low-attenuation and low-bending-loss optical fibers provided in Examples 1 to 10 are basically the same as the above specific embodiments, and the differences lie in the refractive indices and specific thickness ratios between the layers, which are specifically manifested as follows:

[0042]

[0043]

[0044] The low-attenuation and low-bending-loss optical fiber provided in the above embodiments can be realized by processes such as VAD, OVD, MCVD, and PCVD, and its specific effects are as follows:

[0045]

[0046] Through the setting of the isolation layer 2 in the optical fiber provided by the present invention, during the preparation of the optical fiber preform and the optical fiber drawing process, the mixing of germanium in the single-doped germanium dioxide core layer 1 and fluorine in the single-doped fluorine dioxide optical cladding layer can be reduced. By blocking the fluorine in the single-doped fluorine dioxide optical cladding layer from entering the single-doped germanium dioxide core layer 1 through the isolation layer 2, the Rayleigh scattering in the optical fiber can be effectively reduced, thereby achieving the low attenuation of the optical fiber itself; through the setting of the isolation layer 2, the fluorine in the single-doped fluorine dioxide optical cladding layer is blocked, ensuring that the content of fluorine in the single-doped fluorine dioxide optical cladding layer always remains constant, and avoiding the phenomenon that the bending loss increases due to the decrease in the fluorine content.

[0047] Moreover, it can be obtained from the table that for the G.657 optical fiber adopting the refractive index profile structure of the present invention, when the mode field diameter (MFD) at 1310nm is 8.58μm, the typical attenuation value at 1310nm is 0.318dB / km, the typical attenuation value at 1550nm is 0.177dB / km, the typical bending loss value at 1550nm / R7.5 is 0.048dB, and the typical bending loss value at 1625nm / R7.5 is 0.128dB, that is, while ensuring low attenuation, low bending loss is also ensured.

[0048] Example Eleven:

[0049] The present invention also provides a method for preparing an optical fiber, which is used to prepare the optical fiber in the above technical solution, and its specific steps are as follows:

[0050] S1: Prepare a germanium-doped core layer: The germanium-doped core layer is initially deposited on a target rod by introducing 3 - 10 g / min of SiCl4 and 200 - 400 mg / min of GeCl4.

[0051] S2: Form a prefabricated isolation layer in a loose state on the outer periphery of the germanium-doped core layer by chemical vapor deposition, and form a prefabricated single-fluorine-doped silica optical cladding on the outer periphery of the prefabricated isolation layer to obtain an optical fiber preform. In this embodiment, the viscosity of the prefabricated isolation layer is close to that of the germanium-doped core, and the prefabricated isolation layer can effectively prevent the diffusion of germanium in the core layer and the diffusion of fluorine in the prefabricated single-fluorine-doped silica optical cladding.

[0052] During the preparation process, by using the isolation layer 2 formed by chemical vapor deposition, as a physical barrier, it can effectively prevent the situation of refractive index cancellation caused by the mutual doping of germanium in the single-germanium-doped silica core layer 1 and fluorine in the single-fluorine-doped silica optical cladding at high temperatures, thereby reducing the concentration of dopants in the single-germanium-doped silica core layer 1 or the single-fluorine-doped silica optical cladding. This reduction in concentration can, on the one hand, reduce material scattering, and on the other hand, reduce material stress, which is beneficial to reducing the attenuation coefficient of optical fiber transmission.

[0053] In some embodiments, the loose density of the prefabricated isolation layer is 0.32 g / cm 3 ~0.35 g / cm 3 , as Figure 3 shown, Figure 3 shows the optical fiber attenuation parameter characteristics prepared by the VAD process at different densities in the loose state of the isolation layer 2. Here, it can be obtained that when the loose density is above 0.3 g / cm Figure 3 , the attenuations at 1310 nm and 1550 nm both reach relatively low values, and when the density in the loose state is between 0.32 g / cm 3 ~0.35 g / cm 3 ~0.35 g / cm 3 , the attenuation value reaches the lowest.

[0054] In this embodiment, the prefabricated single-fluorine-doped silica optical cladding is formed by stacking in three layers, which are, from the inside out, a prefabricated shallow-fluorine-doped layer, a prefabricated main-fluorine-doped layer, and a prefabricated auxiliary-fluorine-doped layer. Finally, a single-fluorine-doped silica optical cladding structure is obtained where the refractive indices of the shallow-fluorine-doped layer 3 and the auxiliary-fluorine-doped layer 5 are both greater than that of the main-fluorine-doped layer 4. In this way, by setting the concentration change of the single-fluorine-doped silica optical cladding, without using a deeply fluorine-doped single-fluorine-doped silica optical cladding structure, the manufacturing process of the optical fiber is made easier, which is beneficial to large-scale production using the VAD and OVD processes.

[0055] S3 obtains an optical fiber through an optical fiber melting and annealing process and an optical fiber coating and curing process:

[0056] In this process, for the optical fiber melting and annealing process: the preform enters the drawing furnace from the top of the drawing furnace, the temperature inside the furnace body of the drawing furnace is set at 2000 - 2200 °C, the preform is melted and drawn in the furnace body of the drawing furnace, and the drawing speed is greater than 2000 m / min; after drawing is completed, the optical fiber enters the heat preservation and annealing furnace, the temperature of the heating element in the heat preservation and annealing furnace is controlled at 900 - 1300 °C, and a gradient temperature field of 800 - 1200 °C is formed in the annealing and heat preservation furnace, and the optical fiber gradually cools down in the heat preservation and annealing furnace to basically release the internal stress.

[0057] For the optical fiber coating and curing process: after the optical fiber enters the coater for coating, it immediately enters the ultraviolet curing furnace. The ambient temperature is 20 - 28 °C, the ambient humidity is 40 - 60%, the power of the ultraviolet curing furnace is controlled at 70 - 95%, and an exhaust system is used in the ultraviolet curing furnace to extract the cured volatiles of the coating on the surface of the optical fiber and remove harmful gases to form the final optical fiber.

[0058] The method for preparing an optical fiber provided by the present invention separates germanium in the core layer and fluorine in the single-doped fluorine silica optical cladding through the isolation layer in the loose state, thereby effectively avoiding the situation where the two elements are mixed with each other, resulting in an increase in the attenuation coefficient or bending loss of the optical fiber.

[0059] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. The above embodiments are only used to explain the claims. However, the protection scope of the present invention is not limited to the specification. Any change or replacement that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention is included in the protection scope of the present invention.

Claims

1. An optical fiber, characterized in that: It includes, from inside to outside in sequence, a germanium-doped silica core layer, a separation layer, a fluorine-doped silica optical cladding layer, and an outer cladding layer. The separation layer is used to prevent the mutual diffusion of germanium in the germanium-doped silica core layer and fluorine in the fluorine-doped silica optical cladding layer. Among them, the fluorine-doped silica optical cladding layer is divided into three layers, which are, from inside to outside in sequence, a shallow fluorine-doped layer, a main fluorine-doped layer, and an auxiliary fluorine-doped layer. The refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than that of the main fluorine-doped layer. The refractive indices gradually change between every two adjacent layers among the separation layer, the shallow fluorine-doped layer, the main fluorine-doped layer, and the auxiliary fluorine-doped layer, and the refractive index change within every 1 μm is controlled to be 0.03% - 0.05%.

2. The optical fiber according to claim 1, characterized in that: The separation layer is a pure SiO2 separation layer.

3. The optical fiber according to claim 1, characterized in that: The refractive index of the germanium-doped silica core layer is 0.35% - 0.45%, and the radius of the germanium-doped silica core layer is 4.0 μm - 4.5 μm.

4. The optical fiber according to claim 1, characterized in that: The relative refractive index of the separation layer is -0.01% - 0.01%, and its thickness is 1.5 μm - 2 μm.

5. The optical fiber according to claim 1, characterized in that: The refractive index of the shallow fluorine-doped layer is -0.04% - 0.07%, and its thickness is 2.5 μm - 4.2 μm.

6. The optical fiber according to claim 1, characterized in that: The refractive index of the main fluorine-doped layer is -0.08% - 0.15%, and the thickness of the main fluorine-doped layer is 5 μm - 8.5 μm.

7. The optical fiber according to claim 1, characterized in that: The refractive index of the auxiliary fluorine-doped layer is -0.01% - 0.07%, and its thickness is 2.5 - 4.2 μm.

8. The optical fiber according to claim 1, characterized in that: The outer cladding layer is a protective layer of the optical fiber, and the outer cladding layer is a pure SiO2 layer; the refractive index of the outer cladding layer is 0 - 0.005%, and its thickness is 41.1 μm - 49.0 μm.

9. A method for preparing an optical fiber, which is used for preparing the optical fiber according to any one of claims 1-7, characterized in that: It includes the following steps: S1: Prepare a germanium-doped core layer. S2: Form a loose prefabricated separation layer on the outer periphery of the germanium-doped core layer by chemical vapor deposition. The prefabricated separation layer can prevent the diffusion of germanium in the core layer and the diffusion of fluorine in the prefabricated fluorine-doped silica optical cladding layer. S3: Form a fluorine-doped prefabricated fluorine-doped silica optical cladding layer on the outer periphery of the prefabricated separation layer to obtain an optical fiber preform. The prefabricated fluorine-doped silica optical cladding layer is formed by stacking three layers, which are, from inside to outside in sequence, a prefabricated shallow fluorine-doped layer, a prefabricated main fluorine-doped layer, and a prefabricated auxiliary fluorine-doped layer, and finally obtain a fluorine-doped silica optical cladding layer structure in which the refractive indices of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are both greater than that of the main fluorine-doped layer. S4: Obtain an optical fiber from the optical preform through an optical fiber melting and annealing process and an optical fiber coating and curing process.

10. The method for preparing an optical fiber according to claim 9, characterized in that: The loose density of the prefabricated partition layer is 0.3 g / cm 3 or more.

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