Small-diameter low-loss optical fiber

Abstract

The invention provides a small-diameter low-loss optical fiber, and relates to the technical field of optical communication. The small-diameter low-loss optical fiber comprises a core layer, and the value range of the relative refractive index difference delta n1 of the core layer is 0.35%-0.65%. The wrapping layer wraps the outer side of the core layer; wherein the cladding comprises a first platform layer wrapping the core layer, the relative refractive index difference of the first platform layer is # imgabs0 #, r1 is the radius of the core layer, r2 is the radius of the first platform layer, delta n2 is the relative refractive index difference of the inner surface of the first platform layer, and delta n3 is the relative refractive index difference of the outer surface of the first platform layer; the first platform layer is wrapped with the sunken layer, and the numerical value range of the relative refractive index difference delta n4 of the sunken layer is-0.4%-0.6%. According to the small-diameter low-loss optical fiber provided by the invention, the strength of the optical fiber is remarkably improved and the overall performance of the optical fiber is optimized under the condition that the small size is maintained.

Description

Technical Field

[0001] This application relates to the field of optical communication technologies, and particularly to a small-diameter low-loss optical fiber. Background Art

[0002] An optical fiber is a slender and flexible material used for transmitting optical signals, and is widely applied in fields such as communication, medical treatment, and sensing. Its basic structure consists of a core and a cladding, and realizes efficient transmission of optical signals through the principle of total internal reflection.

[0003] The performance of an optical fiber not only depends on its material and manufacturing process, but is also closely related to its size and bending resistance. The diameter of an optical fiber usually affects its bending performance and installation flexibility. The bending resistance is a key index for measuring the flexibility and durability of an optical fiber in practical applications. According to the bending resistance, optical fibers can be divided into different grades, from low to high, namely A1, A2, and B3.

[0004] Currently, an optical fiber with a diameter of 200 microns can only reach grade A2 in terms of bending resistance, and its strength can only meet the screening strain requirement of 1%, which limits its wide use in high-stress applications. Summary of the Invention

[0005] In view of the above problems, embodiments of this application provide a small-diameter low-loss optical fiber, which significantly improves the strength of the optical fiber and optimizes the overall performance of the optical fiber while maintaining a small size.

[0006] To achieve the above object, embodiments of this application provide the following technical solutions:

[0007] The first aspect of this application provides a small-diameter low-loss optical fiber, including:

[0008] A core layer, where the numerical range of the relative refractive index difference Δn1 of the core layer is 0.35% - 0.65%;

[0009] A cladding, coated on the outside of the core layer; wherein, the cladding includes: a first platform layer, wrapped around the core layer, and the relative refractive index difference of the first platform layer is:

[0010]

[0011] wherein, r 1 is the radius of the core layer, r 2 is the radius of the first platform layer, Δn 2 is the relative refractive index difference of the inner surface of the first platform layer, and Δn 3 is the relative refractive index difference of the outer surface of the first platform layer;

[0012] A depression layer, wrapped outside the first platform layer, and the relative refractive index difference Δn 4The numerical range is -0.4% - 0.6%.

[0013] In a possible implementation, the cladding further includes:

[0014] A first buffer layer disposed between the first platform layer and the depressed layer; the relative refractive index difference of the first buffer layer is:

[0015]

[0016] where r 3 is the radius of the first buffer layer.

[0017] In a possible implementation, the cladding further includes:

[0018] A second platform layer wrapping outside the depressed layer, and the relative refractive index difference Δn 5 of the second platform layer has a numerical range of -0.2% to -0.4%.

[0019] In a possible implementation, the cladding further includes:

[0020] A second buffer layer disposed between the depressed layer and the second platform layer; the relative refractive index difference of the second buffer layer is:

[0021]

[0022] where r 4 is the radius of the depressed layer, and r 5 is the radius of the second buffer layer.

[0023] In a possible implementation, the cladding further includes:

[0024] An outer layer wrapping outside the second platform layer, and the relative refractive index difference Δn 6 of the outer layer is 0.

[0025] In a possible implementation, the core layer is doped with alkali metal ions.

[0026] In a possible implementation, the core layer further includes SiO 2 , GeO 2 and F, and the ratio of SiO 2 , GeO 2 , F and alkali metal ions is (1 - a - b - c):a:b:c, where the value range of a is 0.5% - 2.5%, the value range of b is 0.05% - 0.45%, and the value range of c is 0 - 0.25%.

[0027] In a possible implementation, it further includes: a coating layer coated on the outside of the cladding.

[0028] In a possible implementation, the coating layer includes:

[0029] An inner coating layer, coated on the outer side of the cladding, and the elastic modulus of the inner coating layer is less than or equal to 0.7 Mpa;

[0030] An outer coating layer, coated on the outer side of the inner coating layer, and the elastic modulus of the outer coating layer is greater than or equal to 750 Mpa.

[0031] The second aspect of the present application provides an optical fiber drawing device for preparing the small-diameter and low-loss optical fiber as described above. The optical fiber drawing device includes: a drawing furnace; a heat preservation device arranged on the outlet side of the drawing furnace; a coating device arranged on the outlet side of the heat preservation device; a bare fiber measuring device arranged between the drawing furnace and the heat preservation device, or arranged between the heat preservation device and the coating device, and used for measuring the size and the central position of the bare fiber.

[0032] In a possible implementation, it further includes:

[0033] A moisture removal device arranged between the heat preservation device and the coating device.

[0034] In a possible implementation, the moisture removal device has a moisture removal cavity, the moisture removal cavity communicates with the axial two ends of the moisture removal device, and the two ends of the moisture removal cavity are respectively an air inlet end and an air extraction end; from the center of the moisture removal cavity to the two ends of the moisture removal cavity, the cross-sectional area of the moisture removal cavity gradually increases.

[0035] In a possible implementation, the moisture removal channel is a symmetric structure, and from the center of the moisture removal cavity to the two ends of the moisture removal cavity, the cavity wall of the moisture removal cavity has an arc transition.

[0036] In a possible implementation, it further includes: a curing device arranged on the outlet side of the coating device.

[0037] The third aspect of the present application provides an adaptive adjustment method for an optical fiber drawing center, which is applied to the optical fiber drawing device as described above. The adaptive adjustment method includes:

[0038] Adjust the centers of the drawing furnace, the bare fiber measuring device, and the coating device to be on a straight line; measure the central position of the bare fiber through the bare fiber measuring device, and calculate the central position of the optical fiber through the central position of the bare fiber; according to the deviation between the calculated central position of the optical fiber and the center of the coating device, adjust the position of the bare fiber so that the concentricity between the central position of the optical fiber and the center position of the coating device is less than a preset value.

[0039] The small-diameter low-loss optical fiber, optical fiber drawing equipment, and adaptive adjustment method of an optical fiber drawing center provided by this application. The small-diameter low-loss optical fiber includes a core layer and a cladding layer wrapped outside the core layer. The cladding layer includes a first platform layer and a depressed layer. The first platform layer wraps outside the core layer, and the depressed layer wraps outside the first platform layer. Among them, the relative refractive index difference Δn of the core layer 1 has a numerical range of 0.35% - 0.65%. The relative refractive index difference of the first platform layer is:

[0040]

[0041] In the formula, r 1 is the radius of the core layer, r 2 is the radius of the first platform layer, Δn 2 is the relative refractive index difference of the inner surface of the first platform layer, and Δn 3 is the relative refractive index difference of the outer surface of the first platform layer. The relative refractive index difference Δn of the depressed layer 4 has a numerical range of -0.4% - 0.6%. In this way, through the gradient design of the relative refractive index difference between each part of the core layer and the cladding layer, the difference in the expansion coefficient between each part can be effectively reduced. With such a setting, while ensuring that the small-diameter low-loss optical fiber has a sufficient relative refractive index difference, the uniformity of the optical fiber viscosity and stress can be maintained, thereby effectively improving the bending resistance of the small-diameter low-loss optical fiber and optimizing the overall performance of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0043] Figure 1 It is a schematic structural diagram of the small-diameter low-loss optical fiber provided by the embodiment of this application;

[0044] Figure 2 It is a schematic cross-sectional refractive index structure diagram of the core layer and the cladding layer in the small-diameter low-loss optical fiber provided by the embodiment of this application;

[0045] Figure 3 It is a schematic structural diagram of the optical fiber drawing equipment provided by the embodiment of this application;

[0046] Figure 4 It is a schematic structural diagram of the moisture removal device in the optical fiber drawing equipment provided by the embodiment of this application;

[0047] Figure 5Flowchart of the steps of the adaptive adjustment method for the optical fiber drawing center provided by the embodiments of this application.

[0048] Explanation of reference numerals:

[0049] 10 - Small - diameter low - loss optical fiber;

[0050] 100 - Core layer; 200 - Cladding layer; 300 - Coating layer;

[0051] 210 - First platform layer; 220 - Sunken layer; 230 - First buffer layer; 240 - Second platform layer; 250 - Second buffer layer; 260 - Outer layer; 310 - Inner coating layer; 320 - Outer coating layer;

[0052] 20 - Optical fiber drawing equipment;

[0053] 21 - Drawing furnace; 22 - Rod feeder; 23 - Heat preservation device; 24 - Coating device; 25 - Humidity - removing device; 26 - Curing device; 27 - Bare fiber measuring device; 28 - Optical fiber measuring device; 29 - Winding device;

[0054] 251 - Humidity - removing chamber; 252 - Intake end; 253 - Exhaust end;

[0055] 30 - Preform. Detailed implementation manners

[0056] As described in the background art, the performance of an optical fiber is closely related to the size of the optical fiber and the bending resistance of the optical fiber. The principle of optical fiber bending resistance refers to the fact that after the optical fiber is bent, the light energy loss is small and continuous transmission can still be carried out. The total internal reflection principle is the basic principle for the continuous transmission of light energy in the optical fiber. However, in fact, part of the light energy also propagates in the cladding layer, but its transmission energy decreases rapidly with the distance from the core.

[0057] The phenomenon of bending loss in optical fibers occurs because after the optical fiber is bent, the total internal reflection transmission condition is damaged, and there are differences in the refractive indices of different modes and wavelengths. At this time, the transmission modes that do not meet the total internal reflection condition are converted into leakage modes and radiation modes, resulting in energy loss, which is the microscopic manifestation of bending loss.

[0058] As optical fibers have gradually been deployed from household to room - by - room, the usage scenarios of optical fibers have increased, and the bending radius of optical fibers has become smaller and smaller. As the bending radius of the optical fiber decreases, its bending loss increases exponentially. Therefore, it is very important to improve the bending resistance of optical fibers.

[0059] According to the current standards, the bending resistance levels of optical fibers can be classified from low to high as G.657.A1, G.657.A2, and G.657.B3. Among them, G.657.B3 has the highest bending resistance performance and can maintain extremely low losses even at a very small bending radius. It can be used in occasions where frequent bending or wiring in narrow spaces is required to ensure the stability and reliability of signal transmission.

[0060] Currently, the size of optical fibers meeting the G.657.B3 standard is usually 245μm. However, with the increasing tension of pipeline resources in urban infrastructure and the continuous pursuit of higher data transmission speeds, the market demand for small-sized optical fibers is increasing. The diameter of the coated small-sized optical fibers is usually between 180 and 200μm, which is more suitable for modern compact wiring environments.

[0061] In view of this, the embodiments of the present application provide a small-diameter low-loss optical fiber, an optical fiber drawing device, and an adaptive adjustment method for an optical fiber drawing center. The small-diameter low-loss optical fiber includes a core layer and a cladding layer wrapped outside the core layer. The cladding layer includes a first platform layer and a depression layer. The first platform layer wraps outside the core layer, and the depression layer wraps outside the first platform layer. Among them, the value range of the relative refractive index difference Δn1 of the core layer is 0.35%-0.65%, and the relative refractive index difference of the first platform layer is:

[0062]

[0063] In the formula, r 1 is the radius of the core layer, r 2 is the radius of the first platform layer, Δn 2 is the relative refractive index difference of the inner surface of the first platform layer, and Δn 3 is the relative refractive index difference of the outer surface of the first platform layer. The value range of the relative refractive index difference Δn 4 of the depression layer is -0.4%-0.6%. In this way, through the gradient design of the relative refractive index difference between each part of the core layer and the cladding layer, the difference in the expansion coefficients between each part can be effectively reduced. With such a setting, while ensuring that the small-diameter low-loss optical fiber has a sufficient refractive index difference, the uniformity of the viscosity and stress of the optical fiber can be maintained, thereby effectively improving the bending resistance of the small-diameter low-loss optical fiber and optimizing the overall performance of the optical fiber.

[0064] In order to make the above-mentioned objects, features, and advantages of the embodiments of the present application more apparent and understandable, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0065] Figure 1 It is a schematic structural diagram of a small-diameter low-loss optical fiber provided by an embodiment of the present application. Refer to Figure 1 As shown, an embodiment of the present application provides a small-diameter low-loss optical fiber (hereinafter referred to as optical fiber), and the optical fiber 10 can be widely used in modern communication networks. Exemplarily, the optical fiber 10 can be used in Fiber to the Home (FTTH), data centers, and urban infrastructure to achieve high-density wiring in a limited space while ensuring low loss and high bandwidth. In addition, the optical fiber 10 is also suitable for 5G networks, industrial automation, the Internet of Things, and the aerospace and defense fields, providing reliable connections and efficient data transmission.

[0066] Refer to Figure 1 As shown, the optical fiber 10 includes a core layer 100 and a cladding layer 200. Among them, the core layer 100 is the central part of the optical fiber 10, has a relatively high refractive index, and can be used to transmit optical signals. The cladding layer 200 is coated on the outside of the core layer 100, can confine the optical signal in the core layer 100 through total internal reflection, and provides physical protection, reduces crosstalk, and at the same time enhances the bending resistance of the optical fiber. The core layer 100 and the cladding layer 200 work together to enable the optical fiber 10 to achieve efficient and reliable optical signal transmission in various applications, meeting the requirements of modern communication networks for high bandwidth and stability.

[0067] In this embodiment, by gradually changing the relative refractive index difference of the cladding layer 200 of the optical fiber 10, while maintaining a small size, the strength of the optical fiber 10 is significantly improved. The optical fiber 10 has better bending resistance and can reach the G.657B3 bending resistance grade.

[0068] Figure 2 It is a schematic cross-sectional refractive index structure diagram of the core layer and the cladding layer in the small-diameter low-loss optical fiber provided by an embodiment of the present application. Refer to Figure 2 As shown, the radius of the core layer 100 is between r 1 The value range of r 1 is 4.5 μm - 5.5 μm. The main matrix material of the core layer 100 is SiO 2 (silicon dioxide), SiO 2It has excellent optical transparency and mechanical strength, and its low-loss characteristic enables optical signals to propagate over long distances in the optical fiber 10 without significant attenuation. It should be noted that in the embodiments of the present application, pure SiO 2 is defined as the reference refractive index, and the relative refractive index difference is the difference between the refractive indices of the core layer 100 and the cladding layer 200 and the reference refractive index.

[0069] However, during the drawing process of the optical fiber 10, the materials of the core layer 100 and the cladding layer 200 need to be melted at high temperatures and formed into fibers. If the viscosity difference between the two is too large, it will lead to inconsistent material fluidity, thus affecting the geometry and optical performance of the optical fiber. In addition, too large a viscosity difference may also cause a significant difference in the thermal expansion coefficients between the core layer 100 and the cladding layer 200, thereby causing large internal stresses. Therefore, in order to reduce the viscosity of the core layer 100 and reduce the viscosity difference from the cladding layer 200, an appropriate amount of alkali metal ions can be doped into the core layer 100 to optimize the material properties and improve the overall performance of the optical fiber 10.

[0070] Exemplarily, potassium ions (K + ) can be added to the core layer 100. K + can break the silicon-oxygen bonds (Si-O) in the glass network structure, increase the fluidity of the material, and thus reduce the viscosity of the core layer 100.

[0071] In addition, the core layer 100 may also include germanium dioxide (GeO 2 ). The incorporation of GeO 2 can increase the refractive index of the core layer 100, thereby enhancing the confinement ability of optical signals in the core layer 100 and improving the bandwidth and transmission efficiency of the optical fiber 10. In addition, the doping of GeO 2 can also adjust the dispersion characteristics of the optical fiber 10 and optimize its performance at specific wavelengths. The doping of F can be used to reduce the refractive index of the optical fiber 10 and reduce the dispersion of the material, thereby controlling the mode field distribution of the optical fiber 10 and reducing the nonlinear effect.

[0072] By optimizing the ratios of SiO 2 , GeO 2 , F, and K + , low viscosity of the core layer 100 can be achieved while maintaining a high refractive index and low loss. Exemplarily, the ratios of SiO 2 , GeO 2 , F, and K + can be (1 - a - b - c):a:b:c, where the value range of a is 0.5% - 2.5%, the value range of b is 0.05% - 0.45%, and the value range of c is 0 - 0.25%.

[0073] The relative refractive index difference Δn of the core layer 100 1The numerical range is 0.35% - 0.65%. The relatively high refractive index difference enables the optical signal to effectively propagate in the core layer 100 through total internal reflection, which helps improve the bandwidth and transmission efficiency of the optical fiber 10 while reducing signal attenuation.

[0074] Continue to refer to Figure 2 As shown, the cladding 200 includes a first platform layer 210 and a depressed layer 220. Among them, the first platform layer 210 wraps around the outside of the core layer 100, and its radius is r 2 , and the thickness of the first platform layer 210 is r 2 -r 1， The value range of which is 3.5 μm - 5.5 μm 。 The first platform layer 210 can also be composed of SiO 2 , GeO 2 , F and K + . The proportion of SiO 2 , GeO 2 , F and K + is (1 - a - b - c): a: b: c, where the value range of a is 0.2% - 1%, the value range of b is 0.05% - 0.2%, and the value range of c is 0 - 0.15%.

[0075] The first platform layer 210 can be prepared by chemical vapor deposition technology. Exemplarily, the first platform layer 210 can be prepared by methods such as vapor axial deposition (VAD), modified chemical vapor deposition (MCVD), plasma chemical vapor deposition (PCVD), etc. This embodiment does not make specific limitations on this.

[0076] Continue to refer to Figure 2 As shown, the relative refractive index difference of the first platform layer 210 is:

[0077]

[0078] Among them, Δn 2 is the relative refractive index difference of the inner surface of the first platform layer 210, and its range is 0% - 0.3%. Δn 3 is the relative refractive index difference of the outer surface of the first platform layer 210, and its range is 0% - 0.2%. r is the position of any point in the first platform layer 210. With such a setting, in the radial direction of the optical fiber, a gradually changing gradient design of the relative refractive index difference of different parts in the first platform layer 210 realizes a smooth refractive index transition from the core layer 100 to the cladding 200, which helps reduce the reflection and scattering of optical signals at the layer interface, improve the transmission efficiency and signal quality. Moreover, the gradual change of the relative refractive index difference can effectively reduce the phenomenon of internal stress concentration and microbending loss in the optical fiber 10, reduce the fracture risk of the optical fiber 10 when bent, and thus improve the durability and bending resistance of the optical fiber 10.

[0079] The depressed layer 220 is wrapped outside the first platform layer 210, and the radius of the depressed layer 220 is r 4 , and its thickness is r 4 -r 3 , r 4 -r 3 The value range of r is 4.5 μm - 10 μm. The depressed layer 220 can be composed of SiO 2 and F, and the ratio of SiO 2 to F is (1 - a):a, where the value range of a is 1% - 2%. Exemplarily, the depressed layer 220 can be deposited by using one of VAD and MCVD.

[0080] The relative refractive index difference of the depressed layer 220 is Δn 4 , Δn 4 The range of Δn is -0.4% - -0.6%. The depressed layer 220 has a lower refractive index, which can effectively limit the light propagation path and prevent light from leaking outside the cladding 200, thereby ensuring the effective confinement and transmission of optical signals in the core layer 100.

[0081] Continuing to refer to Figure 2 shown in the figure, the cladding 200 may further include a first buffer layer 230. The first buffer layer 230 is disposed between the first platform layer 210 and the depressed layer 220, and its radius is r 3 , and the thickness is r 3 -r 2， r 3 -r 2 The value range of r is 0 μm - 4.5 μm. The first buffer layer 230 can be composed of SiO 2 and F, and the ratio of SiO 2 to F is (1 - a):a, where the value range of a is 0.5% - 1.5%. The first buffer layer 230 can also be deposited by using one of VAD and MCVD.

[0082] The relative refractive index difference of the first buffer layer 230 is:

[0083]

[0084] where r is the position of any point in the first buffer layer 230. The first buffer layer 230 can smooth the transition of the relative refractive index difference between the first platform layer 210 and the depressed layer 220, so that the relative refractive index difference between the two can change gradually, thereby helping to relieve the mechanical stress caused by the different thermal expansion coefficients of the materials and improving the mechanical stability of the optical fiber 10.

[0085] In addition, the cladding 200 may further include a second platform layer 240 disposed outside the depressed layer 220 with a radius of r 6 and a thickness of r 6 -r 5 r 6 -r 5 where the value range of r is 4.5 μm - 15 μm. The second platform layer 240 may be composed of SiO 2 and F, and the ratio of SiO 2 to F is (1 - a):a, where the value range of a is 0.2% - 0.6%. The second platform layer 240 may also be deposited by using one of VAD and MCVD.

[0086] The relative refractive index difference of the second platform layer 240 is Δn 5 with a value range of -0.2% to -0.4%. The second platform layer 240 can effectively adjust the mode field distribution of the optical fiber 10, so that when the diameter of the core layer 100 is increased to expand the mode field diameter, the cable cut-off wavelength of the optical fiber remains within the standard range (e.g., below 1260 nm). Thus, the normal operation of the optical fiber 10 within the standard wavelength band can be ensured.

[0087] Continuing to refer to Figure 2 as shown, the cladding 200 may further include a second buffer layer 250 disposed between the depressed layer 220 and the second platform layer 240. The second buffer layer 250 has a radius of r 5 and a thickness of r 5 -r 4 with a value range of 4.5 μm - 15 μm. The second buffer layer 250 may also be composed of SiO 2 and F, and the ratio of SiO 2 to F is (1 - a):a, where the value range of a is 0.8% - 1.2%. Exemplarily, the second platform layer 240 may also be deposited by using one of VAD and MCVD.

[0088] The relative refractive index difference of the second buffer layer 250 is:

[0089]

[0090] where r is the position of any point in the second buffer layer 250. The second buffer layer 250 can further optimize the transition of the relative refractive index difference, reduce the optical loss and stress difference in the optical fiber 10, and contribute to improving the overall transmission performance of the optical fiber 10.

[0091] In addition, the cladding 200 may further include an outer layer 260 wrapped around the second platform layer 240, and the outer layer 260 can provide excellent mechanical protection and environmental barrier for the cladding 200. Wherein, the radius of the outer layer 260 is r 6 , r 6 has a value range of 62 μm - 63 μm. The outer layer 260 can be a pure silicon layer, and its relative refractive index difference is Δn 6 , Δn 6 has a value of 0. Exemplarily, the outer layer 260 can be rapidly deposited by using the OVD technology of silica.

[0092] Referring to Figure 1 as shown, the optical fiber 10 further includes a coating layer 300, and the coating layer 300 can protect the glass structure of the optical fiber 10 from physical and chemical damages of the external environment. The density of the coating layer 300 is 0.95 g / cm - 1.3 g / cm, which can ensure the mechanical properties and optical transparency of the coating layer 300 without adding too much weight.

[0093] Exemplarily, the coating layer 300 can be composed of an acrylic resin coating. The acrylic resin has good optical transparency, which can ensure that the coating layer 300 will not cause interference or loss to the transmission of optical signals, and helps to maintain the high transmission efficiency of the optical fiber 0. In addition, the acrylic resin has good chemical resistance and weather resistance, can resist the erosion of moisture, chemicals and ultraviolet rays, and the acrylic resin can provide strong mechanical protection, and can effectively resist external physical damages such as scratches, impacts and bending.

[0094] Specifically, the coating layer 300 may include an inner coating layer 310, and the inner coating layer 310 is coated on the outer side of the cladding 200. The elastic modulus of the inner coating layer 310 can be less than or equal to 0.7 MPa, and the elongation at break can be greater than or equal to 130%. The low elastic modulus and high elongation at break can endow the inner coating layer 310 with good flexibility, enabling it to withstand large bending and stretching during installation and operation without being easily broken, thereby providing a buffering effect for the optical fiber 10, being able to effectively absorb and relieve external impacts and vibrations, and protecting the core layer 100 and the cladding 200 from mechanical stress damages. In addition, the coating viscosity of the inner coating layer 310 can be set to 1500 mPa·s - 6000 mPa·s to ensure the uniformity and stability during the coating process and avoid the instability of the optical fiber performance caused by the non-uniformity of the inner coating layer 310.

[0095] The coating layer 300 may further include an outer coating layer 320, which is coated on the outer side of the inner coating layer 310. Its elastic modulus can be greater than or equal to 750 MPa, and the elongation at break can be greater than or equal to 10%. The high elastic modulus and moderate elongation at break endow the outer coating layer 320 with relatively high rigidity, which can provide a strong external protection for the optical fiber 10, significantly enhancing the overall mechanical strength of the optical fiber 10 and enabling the optical fiber to resist physical damage from the external environment. In addition, the outer coating layer 320 has good abrasion resistance and can resist wear and tear during long-term use, which enables the optical fiber 10 to maintain its integrity and function under harsh environmental conditions. Of course, the characteristic of high elastic modulus makes the material of the outer coating layer 320 more dense, thus, it can form an effective barrier to prevent the intrusion of external factors such as moisture, chemicals and ultraviolet rays, and extend the service life of the optical fiber 10. The coating viscosity of the outer coating layer 320 can be set to 3000 mPa·s - 8000 mPa·s. The relatively high viscosity can ensure the thickness and uniformity of the outer coating layer 320, thereby providing effective physical and environmental protection for the optical fiber 10.

[0096] Figure 3 The following is a schematic structural diagram of the optical fiber drawing equipment provided by the embodiment of the present application. Refer to Figure 3 As shown, the embodiment of the present application also provides an optical fiber drawing equipment 20, which is used to prepare the aforementioned optical fiber 10.

[0097] The optical fiber drawing equipment 20 includes a drawing furnace 21. The drawing furnace 21 can be an induction drawing furnace or a graphite drawing furnace, and the embodiment of the present application does not make specific limitations on this. The drawing furnace 21 can provide a stable and efficient heating environment, and can heat the preform 30 composed of the core layer 100 and the cladding layer 200 to the softening point, so that the preform 30 can be drawn into a bare fiber with the required diameter and optical characteristics under the action of gravity and tension. Exemplarily, the temperature of the drawing furnace 21 can be set to 1900 °C to 2300 °C.

[0098] In order to protect the bare fiber material during the drawing process, the drawing furnace 21 can be filled with a protective gas, such as argon or helium. Or, it can also be a mixed gas of argon and helium, where the proportion of argon is not less than 50%. The flow rate of the mixed gas can be controlled at 15 L / min - 40 L / min to maintain a stable gas environment, and at the same time, the oxygen content can be controlled below 200 ppm to prevent oxidation reactions and ensure the purity and optical performance of the bare fiber material. The drawing speed can be set to not less than 50 m / min to improve production efficiency and ensure the consistency of the diameter and optical characteristics of the bare fiber.

[0099] A rod feeder 22 is provided at the upper end of the drawing furnace 21. The rod feeder 22 can be used to clamp the preform 30 and slowly and stably feed the preform 30 into the drawing furnace 21 at a set speed.

[0100] Continue to refer to Figure 3 As shown, the optical fiber drawing device 20 further includes a heat preservation device 23, which is arranged on the outlet side of the drawing furnace 21 and can provide a stable thermal environment, helping to prevent the influence of temperature fluctuations on the diameter and optical properties of the bare fiber, thereby improving production efficiency and product quality.

[0101] In addition, the optical fiber drawing device 20 further includes a coating device 24, which is arranged on the outlet side of the heat preservation device 23 and is used for coating the bare fiber. Specifically, the coating method of the inner coating layer 310 and the outer coating layer 320 by the coating device 24 can be selected from at least one of wet-wet coating or wet-dry coating.

[0102] Among them, the wet-wet coating method usually includes a coating die, which can be used for coating the inner coating layer 310 and the outer coating layer 320 at the same time, effectively reducing the coating steps and improving production efficiency.

[0103] The wet-dry coating method usually includes two coating dies, one for coating the inner coating layer 310 and the other for coating the outer coating layer 320. This coating method can better control the quality and thickness of the inner coating layer 310 and the outer coating layer 320, ensuring the uniformity and quality of the inner coating layer 310 and the outer coating layer 320. In actual production, the suitable coating method can be selected according to requirements, and this embodiment does not make specific restrictions on this.

[0104] During coating, the ratio of the thickness of the inner coating layer 310 to the outer coating layer 320 can be set between 0.67 and 1.2. Exemplarily, the ratio of the thickness of the inner coating layer 310 to the outer coating layer 320 can be 0.8-0.95. In this way, by optimizing the thickness ratio of the inner coating layer 310 and the outer coating layer 320, the performance and durability of the optical fiber 10 can be maximized without increasing the total diameter of the optical fiber 10, enabling the optical fiber 10 to resist physical damage from the external environment and maintain a certain flexibility to adapt to dynamic environments such as bending and torsion.

[0105] It should be noted that after the bare fiber comes out of the heat preservation device 23, due to the relatively high surface temperature of the bare fiber, and the drawing environment usually requires conditions of a relative humidity of 50% - 80% and a temperature of 21°C - 25°C. Such environmental conditions help to reduce dust, but at the same time, it also causes water vapor to easily condense on the outer surface of the bare fiber. The presence of water vapor will interfere with the uniform adhesion of the coating material, reducing the quality of the coating layer 300 and the mechanical properties of the optical fiber. Therefore, before entering the coating device 24, the surface of the bare fiber can be pretreated to reduce the adhesion of water vapor on the surface of the bare fiber.

[0106] Figure 4The structural schematic diagram of the moisture removal device in the optical fiber drawing equipment provided by the embodiment of the present application. Refer to Figure 4 As shown, the optical fiber drawing equipment 20 may further include a moisture removal device 25, and the moisture removal device 25 is arranged between the heat preservation device 23 and the coating device 24. The moisture removal device 25 has a moisture removal cavity 251, and the moisture removal cavity 251 communicates with both axial ends of the moisture removal device 25.

[0107] Both ends of the moisture removal cavity 251 are respectively an air inlet end 252 and an air extraction end 253. Gas can be injected from the air inlet end 252 and discharged from the air extraction end 253. Among them, an air extraction pump (not shown in the figure) is connected below the air extraction end 253, and the air extraction pump can adjust the flow rate of the gas so that the flow rate of the gas is slightly greater than the drawing speed. With such a setting, it can ensure that a stable flow state is formed in the moisture removal cavity 251, avoid fluctuations in the air flow, help to uniformly remove the water vapor on the surface of the bare fiber, and ensure the dryness of the fiber surface.

[0108] Exemplarily, the gas can be nitrogen or compressed air, and the temperature of the gas can be between 30°C and 300°C. In this way, the high-temperature and dry gas can effectively eliminate the water vapor on the surface of the bare fiber, and moreover, the arc-shaped design of the moisture removal cavity 251 can also keep the bare fiber stable when passing through the moisture removal device 25, prevent shaking, and ensure the uniformity and stability of the subsequent coating process.

[0109] The moisture removal cavity 251 can be set to a structure that is wide at both ends and narrow in the middle. That is to say, from the center of the moisture removal cavity 251 to both ends of the moisture removal cavity 251, the cross-sectional area of the moisture removal cavity 251 gradually increases. Exemplarily, the length of the moisture removal device 25 can be between 0.5 m and 2 m, the width at the center of the moisture removal cavity 251 can be set between 1 cm and 2 cm, and the width at both ends of the moisture removal cavity 251 can be set between 2 cm and 4 cm.

[0110] In a possible implementation manner, the moisture removal cavity 251 can be set to a symmetric structure, and from the center of the moisture removal cavity 251 to both ends of the moisture removal cavity 251, the cavity wall of the moisture removal cavity 251 has an arc transition. With such a setting, it helps to smoothly guide the air flow, reduce the occurrence of turbulence, and helps to improve the stability of the air flow. In addition, the design of the arc-shaped structure can also make the distribution of the air flow more uniform. Thus, the gas can effectively cover the surface of the bare fiber, ensure the rapid evaporation of the water vapor on the surface of the bare fiber, and improve the drying efficiency.

[0111] Continue to refer to Figure 3As shown, the optical fiber drawing device 20 may also be provided with a curing device 26. The curing device 26 can rapidly cure the coating layer 300 through a specific curing process, thereby improving the mechanical strength of the optical fiber. Specifically, the curing process can adopt ultraviolet curing (abbreviated as UV) or light emitting diode curing (abbreviated as LED). To improve the curing efficiency and quality, the curing environment can be isolated using non-oxygen gases. Exemplarily, a gas such as nitrogen, helium, argon, or a mixed gas of any proportion of them can be used. These gases can effectively prevent the inhibitory effect of oxygen on the curing reaction and ensure the smooth progress of the curing process.

[0112] The curing device 26 may include a plurality of curing furnaces (not shown in the figure). To ensure a stable protective atmosphere of the gas in the curing furnace, the gas flow rate in a single curing furnace can be controlled within 15L - 30L, and the oxygen content in the curing environment is less than 50ppm to reduce the interference of oxygen on the curing reaction. During the curing process, when the optical fiber 10 passes through different curing furnaces, the exposure time to the air shall not exceed 0.04s to prevent the influence of water vapor and other pollutants on the surface of the optical fiber. After being cured by the curing furnace, the curing degree of the inner coating layer 310 of the optical fiber can reach 87% - 92%, and the curing degree of the outer coating layer 320 needs to reach 90% - 100%, and the curing degree of the outer coating layer 320 shall not be lower than that of the inner coating layer 310. In this way, high-quality curing of the optical fiber coating layer 300 can be ensured, and the mechanical strength and environmental adaptability of the optical fiber 10 can be improved.

[0113] In addition, the optical fiber drawing device 20 further includes a bare fiber measuring device 27 and an optical fiber measuring device 28. The bare fiber measuring device 27 is arranged between the drawing furnace 21 and the heat preservation device 23, or the bare fiber measuring device 27 can also be arranged between the heat preservation device 23 and the coating device 24. The bare fiber measuring device 27 can be used to measure the central position of the bare fiber. Of course, the bare fiber measuring device 27 also accurately measures the diameter of the drawn bare fiber to ensure that the diameter of the bare fiber meets the process requirements. In the embodiment of the present application, the diameter of the bare fiber is also the diameter of the outer layer, with a size of 124μm - 126μm.

[0114] The optical fiber measuring device 28 is arranged on the outlet side of the coating device 24 and can measure the optical fiber 10 again after coating and curing, including the detection of parameters such as diameter and ellipticity, to ensure that the final quality of the optical fiber meets the standards and meets the requirements of application fields such as communication. In the embodiment of the present application, the size of the optical fiber 10 is 180μm - 200μm.

[0115] Continue to refer to Figure 3As shown, the optical fiber drawing device 20 further includes a winding device 29. The winding device 29 is disposed at the end of the optical fiber drawing device 20 and is responsible for neatly winding the optical fiber 10 after drawing, coating, and curing onto a reel, so that the optical fiber 10 can be conveniently stored, transported, and further processed. The winding device 29 needs to precisely control the winding tension and speed to ensure that the optical fiber 10 is not damaged during the winding process. Exemplarily, the winding device 29 may be provided with a tension controller (not shown in the figure), and the tension controller can monitor and adjust the winding tension in real time to ensure that the optical fiber 10 maintains an appropriate tension during the winding process and avoid the situation that the optical fiber 10 becomes loose or is overstretched.

[0116] Figure 5 It is a step flowchart of the adaptive adjustment method for the optical fiber drawing center provided by the embodiment of the present application. Refer to Figure 5 As shown, the embodiment of the present application further provides an adaptive adjustment method for an optical fiber drawing center (hereinafter referred to as the adjustment method), and this adjustment method is used for the aforementioned optical fiber drawing device 20.

[0117] The optical fiber 10 provided by the embodiment of the present application reduces the thickness of the coating layer 300, so higher requirements are put forward for the consistency of coating. The concentricity of the cladding 200 - coating layer 300 (i.e., the distance between the center of the cladding 200 and the center of the coating layer 300) can be used to measure the consistency of coating. The smaller the concentricity of the cladding 200 - coating layer 300, the better the consistency of coating. A uniform coating layer 300 can reduce the signal loss of the optical fiber when it is slightly bent. And, a uniform coating layer 300 can reduce the stress concentration phenomenon and improve the overall mechanical strength of the optical fiber 10. The adjustment method can ensure that the central position of the optical fiber 10 always remains consistent during the drawing process through high-precision measurement and real-time adjustment, thereby improving the uniformity and consistency of the coating layer 300, and ultimately enhancing the quality and performance of the optical fiber 10.

[0118] Specifically, the adjustment method includes the following steps:

[0119] S100. Adjust the centers of the drawing furnace, the bare fiber measuring device, the coating device, and the optical fiber measuring device to be on a straight line.

[0120] First, ensure that the centers of the drawing furnace 21, the bare fiber measuring device 27, the coating device 24, and the optical fiber measuring device 28 are on a straight line.

[0121] Move the optical fiber preform 30 to the rod feeder 22, and adjust the position of the rod feeder 22 so that the lower tip of the optical fiber preform 30 is aligned with the center of the drawing furnace 21.

[0122] S200. Measure the central position of the bare fiber through the bare fiber measuring device, and calculate the central position of the optical fiber based on the central position of the bare fiber.

[0123] Measure the central position of the bare fiber through the bare fiber measuring device 27. Assume that the bare fiber measurement period is t (indicating that the point position is measured every t time). When the number of measurement points reaches n (50 ≤ n ≤ 500), the central control system starts to automatically calculate the central position of the optical fiber 10 based on the statistical data. Exemplarily, the K-point center algorithm can be used to obtain the best value through iteration, so as to obtain the relatively most accurate central position of the optical fiber 10.

[0124] S300. Adjust the position of the bare fiber according to the deviation between the calculated central position of the optical fiber and the center of the coating device, so that the concentricity between the central position of the optical fiber and the center position of the coating device is less than a preset value.

[0125] The central control system issues an adjustment instruction according to the deviation value between the measured central position of the optical fiber 10 and the center of the coating device 24, and controls the rod feeder 22 to make adjustments. The rod feeder 22 realizes precise position adjustment through a stepping motor (not shown in the figure) and a lead screw (not shown in the figure), so as to ensure that the concentricity value between the central position of the optical fiber 10 and the center position of the coating device 24 is less than the preset value of 5 μm. Exemplarily, the preset value of the concentricity can be set to 2 μm. In this way, the uniformity of the coating layer 300 can be guaranteed, which helps to improve the overall performance, durability and reliability of the optical fiber 10.

[0126] It should be noted that during the movement of the preform 30, the moving speed of the rod feeder 22 is controlled within 0.5 mm / s, so that the accuracy and stability of the adjustment can be ensured. The movement of the entire preform 30 is completed within the preset time nt.

[0127] Taking nt as a cycle, repeatedly perform the above measurement and adjustment operations. Thus, it can be ensured that the concentricity value between the central position of the optical fiber 10 and the center position of the coating device 24 always remains within the preset range. Through this adjustment method, the coating consistency of the optical fiber 10 can be significantly improved, signal attenuation can be reduced, mechanical strength and environmental adaptability can be improved, so as to ensure the high performance and stability of the optical fiber 10 under various use conditions.

[0128] The embodiments or implementation manners in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0129] In the description of this specification, the descriptions with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A small-diameter, low-loss optical fiber, characterized in that: include: A core layer, wherein the relative refractive index difference Δn1 of the core layer has a value ranging from 0.35% to 0.65%; A cladding layer is coated on the outside of the core layer; wherein the cladding layer comprises: The first platform layer is wrapped outside the core layer, and the relative refractive index difference of the first platform layer is: Wherein, r1 is the radius of the core layer, r2 is the radius of the first platform layer, Δn2 is the relative refractive index difference of the inner surface of the first platform layer, and Δn3 is the relative refractive index difference of the outer surface of the first platform layer; The depressed layer is wrapped outside the first platform layer, and the relative refractive index difference Δn4 of the depressed layer has a value ranging from -0.4% to 0.6%.

2. The small-diameter low-loss optical fiber according to claim 1, characterized in that: The cladding also includes: A first buffer layer, disposed between the first platform layer and the depression layer; The relative refractive index difference of the first buffer layer is: Wherein, r3 is the radius of the first buffer layer.

3. The small-diameter low-loss optical fiber according to claim 1, characterized in that: The cladding also includes: The second platform layer is wrapped outside the depressed layer, and the relative refractive index difference Δn5 of the second platform layer has a value ranging from -0.2% to -0.4%.

4. The small-diameter low-loss optical fiber according to claim 3, characterized in that: The cladding also includes: a second buffer layer, disposed between the depression layer and the second platform layer; The relative refractive index difference of the second buffer layer is: Wherein, r4 is the radius of the depression layer, and r5 is the radius of the second buffer layer.

5. The small-diameter low-loss optical fiber according to claim 3, characterized in that: The cladding also includes: The outer layer is wrapped around the second platform layer, and the relative refractive index difference Δn6 of the outer layer is 0.

6. The small-diameter low-loss optical fiber according to any one of claims 1 to 5, characterized in that: The core layer is doped with alkali metal ions.

7. The small-diameter low-loss optical fiber according to claim 6, characterized in that: The core layer also includes SiO2, GeO2 and F, and the ratio of SiO2, GeO2, F and the alkali metal ions is (1-abc):a:b:c, wherein the value range of a is 0.5%-2.5%, the value range of b is 0.05%-0.45%, and the value range of c is 0-0.25%.

8. The small-diameter low-loss optical fiber according to any one of claims 1 to 5, characterized in that: Also includes: The coating layer is coated on the outer side of the cladding layer.

9. The small-diameter low-loss optical fiber according to claim 8, characterized in that: The coating layer comprises: An inner coating layer, coated on the outer side of the cladding layer, wherein the elastic modulus of the inner coating layer is less than or equal to 0.7 Mpa; The outer coating layer is coated on the outer side of the inner coating layer, and the elastic modulus of the outer coating layer is greater than or equal to 750Mpa.

10. An optical fiber drawing device for preparing the small-diameter low-loss optical fiber according to any one of claims 1 to 9, characterized in that: The optical fiber drawing equipment comprises: Wire drawing furnace; A heat preservation device, arranged at the outlet side of the wire drawing furnace; A coating device, arranged at the outlet side of the heat preservation device; The bare fiber measuring device is arranged between the drawing furnace and the heat preservation device, or between the heat preservation device and the coating device, and is used to measure the size of the bare fiber and the center position of the bare fiber.

11. The optical fiber drawing equipment according to claim 10, characterized in that: Also includes: The dehumidification device is arranged between the heat preservation device and the coating device.

12. The optical fiber drawing equipment according to claim 10, characterized in that: The dehumidification device has a dehumidification cavity, which is connected to two axial ends of the dehumidification device, and the two ends of the dehumidification cavity are respectively an air inlet end and an air extraction end; The cross-sectional area of ​​the dehumidification chamber gradually increases from the center of the dehumidification chamber to the two ends of the dehumidification chamber.

13. The optical fiber drawing equipment according to claim 12, characterized in that: The dehumidification chamber is a symmetrical structure, and the chamber wall of the dehumidification chamber has an arc-shaped transition from the center of the dehumidification chamber to the two ends of the dehumidification chamber.

14. The optical fiber drawing equipment according to any one of claims 10 to 13, characterized in that: Also includes: The curing device is arranged at the outlet side of the coating device.

15. An adaptive adjustment method for an optical fiber drawing center, applied to the optical fiber drawing equipment according to any one of claims 10 to 13, characterized in that: The adaptive adjustment method comprises: Adjust the center of the drawing furnace, the center of the bare fiber measuring device, and the center of the coating device to be in a straight line; Measuring the center position of the bare fiber by the bare fiber measuring device, and calculating the center position of the optical fiber by the center position of the bare fiber; According to the measured deviation between the center position of the optical fiber and the center of the coating device, the position of the bare fiber is adjusted so that the concentricity between the center position of the optical fiber and the center position of the coating device is less than a preset value.

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