阅读说明：本技术 一种细直径耦合器用980光纤 (980 optical fiber for thin-diameter coupler ) 是由 冯术娟 缪振华 孙周 徐亮 侯树虎 张静霞 赵霞 刘瑞林 卞新海 于 2019-10-14 设计创作，主要内容包括：本发明涉及一种小直径耦合器用光纤,包括有芯层、包层、涂覆层,芯层为掺锗Ge的二氧化硅石英玻璃层,所述芯层的直径D1为3.5-5μm,芯层与内包层的折射率差Δn1为0.014-0.017；所述包层分为内包层和外包层,内包层紧密环绕芯层,为锗、氟、磷共掺的二氧化硅石英玻璃层,内包层与外包层纯石英的折射率差Δ2为-0.0002-0,直径D2为5-15μm；外包层为纯石英层,厚度D3为79-81μm；涂覆层的厚度为160-190μm。本发明采用内包层和外包层的折射率基本一致的结构设计,光纤间的耦合为利用单模光纤间消逝场相互耦合的机理,熔融拉锥工艺使一根光纤内的一部分光耦合到另一根光纤中,实现特定分光比,从而减少信号光由于折射率波动造成的损失,达到降低光纤熔融拉制过程中附加损耗。(The invention relates to an optical fiber for a small-diameter coupler, which comprises a core layer, a cladding layer and a coating layer, wherein the core layer is a silica quartz glass layer doped with germanium Ge, the diameter D1 of the core layer is 3.5-5 mu m, and the refractive index difference delta n1 between the core layer and the inner cladding layer is 0.014-0.017; the cladding is divided into an inner cladding and an outer cladding, the inner cladding tightly surrounds the core layer and is a silica quartz glass layer doped with germanium, fluorine and phosphorus, the refractive index difference delta 2 between the inner cladding and the outer cladding pure quartz is-0.0002-0, and the diameter D2 is 5-15 microns; the outer cladding layer is a pure quartz layer with a thickness D3 of 79-81 μm; the thickness of the coating layer was 160-190 μm. The invention adopts the structural design that the refractive indexes of the inner cladding and the outer cladding are basically consistent, the coupling among the optical fibers is a mechanism of utilizing evanescent fields among single-mode optical fibers to be mutually coupled, and a fused tapering process enables one part of light in one optical fiber to be coupled into the other optical fiber, so that the specific splitting ratio is realized, the loss of signal light caused by refractive index fluctuation is reduced, and the additional loss in the optical fiber fusion drawing process is reduced.)

1. An optical fiber for a small-diameter coupler comprises a core layer, a cladding layer and a coating layer, wherein the core layer is a silica quartz glass layer doped with germanium Ge, and the optical fiber is characterized in that: the diameter D1 of the core layer is 3.5-5 μm, and the refractive index difference delta n1 between the core layer and the inner cladding layer is 0.014-0.017; the cladding is divided into an inner cladding and an outer cladding, the inner cladding tightly surrounds the core layer and is a silica quartz glass layer doped with germanium, fluorine and phosphorus, the refractive index difference delta 2 between the inner cladding and the pure quartz of the outer cladding is-0.0002-0, the diameter D2 is 15-35 mu m, and the thickness b is 5-15 mu m; the outer cladding layer is a pure quartz layer with a diameter D3 of 79-81 μm and a thickness c of 22.5-33.5 μm; the diameter of the coating layer is 160-190 μm.

2. An optical fiber for a small-diameter coupler according to claim 1, wherein: the core layer comprises SiCl4 and GeCl4 according to a fixed flow ratio, wherein the mol percentages of doping substances are respectively Si: 86 to 88 percent; 12-14% of Ge.

3. An optical fiber for a small-diameter coupler according to claim 1 or 2, wherein: the mol percentages of doping materials of the inner cladding are respectively Si: 95 to 98.5 percent; 0.5 to 1.5 percent of Ge; 0.5 to 2 percent of F; 0.5-2% of P, the flow rates of SiCl4, GeCl4, SF6 and POCL3 are distributed close to the core layer and towards the inner cladding layer direction according to Y1-a 1X + b1, Y2-a 2X + b2, Y3-b 3-a3X and Y4-a 4X + b4, wherein: y1, Y2, Y3 and Y4 are flow rates of final deposition X SiCl4, GeCl4, SF6 and POCL3, respectively, b1, b2, b3 and b4 are flow rates of initial SiCl4, GeCl4, SF6 and POCL3 close to the core layer, and a1, a2, a3 and a4 are increasing coefficients.

4. An optical fiber for a small-diameter coupler according to claim 3, wherein: the cut-off wavelength of the optical fiber is 870-970 nm.

5. An optical fiber for a small-diameter coupler according to claim 3, wherein: the MFD of the fiber is 3.7-4.3 μm in the wavelength range of 980 nm.

6. An optical fiber for a small-diameter coupler according to claim 3, wherein: the MFD of the optical fiber is 5.8-6.6 μm in the 1550nm wavelength range.

7. An optical fiber for a small-diameter coupler according to claim 3, wherein: the attenuation of the optical fiber is less than or equal to 2.5dB/km in the wavelength range of 980 nm.

8. An optical fiber for a small-diameter coupler according to claim 3, wherein: the attenuation of the optical fiber is less than or equal to 1dB/km in the 1550nm wavelength range.

9. An optical fiber for a small-diameter coupler according to claim 3, wherein: the macrobend loss of the optical fiber is less than or equal to 0.01dB (phi 20mm-1 circle) in the 1550nm wavelength range.

10. An optical fiber for a small-diameter coupler according to claim 3, wherein: the additional loss of the optical fiber in the fusion tapering process is less than or equal to 0.1 dB.

Technical Field

The invention relates to a 980-fiber used for a coupler with a small diameter, which is used for preparing a small coupler and has stable and superior performance in a high-temperature fused cone coupling process. Belongs to the technical field of optical fibers.

Background

Recently, some experts at home and abroad propose a new concept that 980nm is the most commonly used wavelength band as a communication window, and the advantages of the new concept are that the light source and related devices are quite mature and cheap, and the cost of the optical network can be effectively reduced by using the wavelength band. Compared with 1310nm and 1550nm windows, the loss of light in the 980nm window is increased, the distance for transmitting signals is limited, and therefore, the optical fiber coupler cannot be used for long-distance or even medium-distance transmission, but can meet the requirement of manufacturing a coupler, and the optical fiber coupler is an important device for realizing optical signal splitting and combining in an optical network and an optical sensing system. The method has important application in optical fiber communication, optical fiber sensing and optical fiber measurement. With the rapid development of optical fiber communication technology, the application of optical fiber devices in the field of optical communication is also more and more extensive, wherein the optical fiber coupler has become the most widely applied optical fiber passive device. The optical fiber coupler plays a crucial role in realizing the splitting, combining, inserting and distributing of optical signals, is a multifunctional and multipurpose device and is one of the most important optical passive devices. Fiber couplers have been greatly developed since the 1982 Jensen reported theory on nonlinear directional couplers. The manufacturing method of the optical fiber coupling device mainly comprises an etching method, a grinding and polishing method and a fused tapering method. The melting tapering method is that two optical fibers or more optical fibers with coating layers removed are closed in a certain mode, melted under high-temperature heating and simultaneously stretched towards two sides, and finally a special waveguide device with a biconical structure is formed in a heating zone. When the two fibers are fused, the input optical signal enters the two fibers from one fiber. The method has the advantages of extremely low loss, good stability, suitability for batch production and the like, and is generally adopted in the large-scale production of the coupler. With the miniaturization of devices, higher demands are made on the miniaturization of the size of an optical fiber for a coupler and the bending resistance of the optical fiber.

The invention patent in China with the patent number of CN101639549 is a single-mode optical fiber for a 980nm transmission window, which is only suitable for the single-mode optical fiber required by the last kilometer of FTTH transmission in a communication FTTH system and is not suitable for a coupler. The application number CN201710344555.1 discloses a fused biconical taper type bend insensitive single mode fiber, which is suitable for the development and application of fiber coupler and fiber sensor, and the outer diameter of the fiber is 124-.

Disclosure of Invention

The invention aims to solve the technical problem of providing the optical fiber for the small-diameter coupler in the prior art, the proper optical fiber structure and component design is achieved by adjusting the doping mole percentage ratio of the core layer and the inner cladding of the optical fiber, the additional loss in the optical fiber coupling process is less than 0.1dB, and the bending performance is good. The optical fiber is suitable for couplers and splitters of various wave bands (C wave band and L wave band) produced by a fused biconical taper technology, and can be applied to pump/signal wavelength division multiplexers for EDFAs (erbium doped fiber amplifiers), CATV (community antenna television) optical fiber couplers, Tap coupler taps, ultra-small packaged optical fiber devices, two-way wave combiners and wave splitters, and low-loss couplers/ultra-short mixed couplers.

The technical scheme adopted by the invention for solving the problems is as follows: an optical fiber for a small-diameter coupler comprises a core layer, a cladding layer and a coating layer. The core layer is a germanium Ge-doped silica quartz glass layer, the diameter D1 of the core layer is 3.5-5 μm, and the refractive index difference delta n1 between the core layer and the inner cladding is 0.014-0.017; the cladding is divided into an inner cladding and an outer cladding, the inner cladding tightly surrounds the core layer and is a silica quartz glass layer doped with germanium, fluorine and phosphorus, the refractive index difference delta 2 between the inner cladding and the pure quartz of the outer cladding is-0.0002-0, the diameter D2 is 15-35 mu m, and the thickness b is 5-15 mu m; the outer cladding layer is a pure quartz layer with a diameter D3 of 79-81 μm and a thickness c of 22.5-33.5 μm; the thickness of the coating layer was 160-190 μm.

Preferably, the SiCl4 and the GeCl4 in the core layer are mixed according to a fixed flow ratio, and the mol percentages of doping substances of the SiCl4 and the GeCl4 are respectively Si: 86 to 88 percent; 12-14% of Ge.

Preferably, the mol percentages of the doping materials of the inner cladding are respectively Si: 95 to 98.5 percent; 0.5 to 1.5 percent of Ge; 0.5 to 2 percent of F; 0.5-2% of P, the flow rates of SiCl4, GeCl4, SF6 and POCL3 are distributed close to the core layer and towards the inner cladding layer direction according to Y1-a 1X + b1, Y2-a 2X + b2, Y3-b 3-a3X and Y4-a 4X + b4, wherein: y1, Y2, Y3 and Y4 are flow rates of final deposition X SiCl4, GeCl4, SF6 and POCL3, respectively, b1, b2, b3 and b4 are flow rates of initial SiCl4, GeCl4, SF6 and POCL3 close to the core layer, and a1, a2, a3 and a4 are increasing coefficients.

Wherein: the influence factors of the a1 coefficient are related to the flow rate of the initial silicon tetrachloride, the size specification of the tube, the deposition efficiency of the silicon tetrachloride, the moving speed of the flame torch and the like; the influence factors of the a2 coefficient are related to the flow rate of the initial germanium tetrachloride, the size specification of the tube, the deposition efficiency of the germanium tetrachloride, the moving speed of the flame burner, the contribution rate of the germanium dioxide which is the reaction product of the germanium tetrachloride to the refractive index and the like; the influence factors of the a3 coefficient are related to the flow of the initial sulfur hexafluoride, the size specification of the tube, the deposition efficiency of the sulfur hexafluoride, the moving speed of the flame torch, the contribution rate of the generated fluoride to the refractive index and the like; the factor a4 is related to the initial phosphorus oxychloride flow, the tube size, the deposition efficiency of phosphorus oxychloride, the moving speed of the flame burner, the refractive index contribution rate of the generated phosphorus pentoxide, and the like.

Preferably, the cut-off wavelength of the optical fiber is 870-970 nm.

Preferably, the MFD of the optical fiber is 3.7-4.3 μm in the 980nm wavelength range.

Preferably, the MFD of the optical fiber is 5.8-6.6 μm in the 1550nm wavelength range.

Preferably, the attenuation of the optical fiber is less than or equal to 2.5dB/km in the 980nm wavelength range.

Preferably, the attenuation of the optical fiber is less than or equal to 1dB/km in the 1550nm wavelength range.

Preferably, the macrobend loss of the optical fiber is less than or equal to 0.01dB (phi 20mm-1 turn) in the 1550nm wavelength range.

Preferably, the fusion tapering process additional loss of the optical fiber is less than or equal to 0.1 dB.

For the convenience of describing the present invention, the following definitions are provided in part:

function of fluorine doping: fluorine doping of quartz glass to reduce the refractive index difference of pure quartz glass

The effect of germanium doping: germanium is doped into quartz glass to improve the refractive index difference of pure quartz glass

Effect of phosphorus doping: the phosphorus is doped into the quartz glass, so that the viscosity of pure quartz in the deposition process is reduced, and the refractive index difference of the quartz glass is improved

And (3) optical fiber core layer: a central portion of the fiber, which is the primary carrier of the waveguide transmission;

optical fiber cladding: a glass layer surrounding the core layer, the glass layer serving primarily to protect the core layer;

coating the optical fiber: a resin coating layer surrounding the cladding layer, the resin coating layer mainly serving as a reinforcing member;

refractive index profile: the relationship between the refractive index of each glass component in the fiber and its radius.

ni and n0 are the refractive index of the corresponding part and the refractive index of pure silica quartz glass, respectively.

The refractive index difference of the optical fiber core layer and the inner cladding layer is △ n1, for example, the refractive index difference of the optical fiber core layer and the inner cladding layer is n1, and the refractive index of the inner cladding layer is n2, the refractive index difference of the core layer relative to the inner cladding layer is △ n1 which is n1-n 2;

and the refractive index difference of the cladding is △ n2, namely the refractive index difference between the inner cladding of the optical fiber and pure quartz, if the refractive index of the inner cladding is n2 and the refractive index of the pure quartz is n0, the refractive index difference of the core layer relative to the inner cladding is △ n2 ═ n2-n 0.

Compared with the prior art, the invention has the advantages that:

1. the core layer of the optical fiber is high Ge-doped quartz, so that the refractive index difference between the core layer and the inner cladding is improved, the structural design of the core diameter is reduced, and the bending performance of the optical fiber is improved.

2. The optical fiber fusion-drawing device adopts a structural design that the refractive indexes of an inner cladding and an outer cladding are basically consistent, the coupling between optical fibers is a mechanism that evanescent fields between single-mode optical fibers are mutually coupled, a fusion-drawing process enables a part of light in one optical fiber to be coupled into the other optical fiber, a specific splitting ratio is realized, because signal light in a coupler is transmitted in the cladding, if the refractive index difference between the cladding is reduced, the refractive indexes of the inner cladding and the outer cladding are basically consistent, the loss of the signal light caused by refractive index fluctuation is reduced, and the additional loss in the optical fiber fusion-drawing process is reduced.

3. The co-doping technology of high germanium doping amount of the core layer and low germanium, phosphorus and fluorine doping of the inner cladding layer is adopted to achieve viscosity matching of the core layer and the inner cladding layer, and in the drawing process, the stress of the core layer of the optical fiber is reduced to achieve reduced attenuation of the optical fiber;

4. the technology of co-doping germanium with high germanium content in the core layer and low germanium, phosphorus and fluorine in the inner cladding layer is suitable for the welding process, the high germanium-doped region of the core layer is quickly diffused to the inner cladding layer region at high temperature, the diameter of a mode field is increased, and therefore the welding loss is reduced when the optical fiber is welded with other optical fibers.

Drawings

FIG. 1 is a schematic radial cross-section of an optical fiber according to one embodiment of the present invention.

FIG. 2 is a schematic representation of a refractive index profile of an optical fiber according to one embodiment of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

The optical fiber for the small-diameter coupler in the embodiment of the invention comprises a core layer, a cladding layer and a coating layer, wherein the core layer is a silica (SiO2) quartz glass layer doped with germanium Ge, the diameter D1 of the core layer is 3.5-5 mu m, and the refractive index difference delta n1 between the core layer and the inner cladding layer is 0.014-0.017; the cladding has 2 layers, the inner cladding surrounds the core layer closely, it is silica quartz glass layer of germanium, fluorine, phosphorus codoped, the refractive index difference delta 2 with the pure quartz of the outer cladding is-0.0002-0, the diameter D2 is 15-35 μm, its thickness b is 5-15 um; the outer cladding layer is a pure quartz layer with a diameter D3 of 79-81 μm and a thickness c of 22.5-33.5 μm; the diameter of the coating layer is 160-190 μm.

According to the technical scheme, the parameters of the optical fiber are designed within the specified range, the core rod is manufactured by the MCVD process and the PCVD process which are well known, and the whole wire-drawing rod is manufactured by the outer covering process such as the sleeve process, the OVD process or the VAD process. After the preform is prepared, the optical fiber is drawn on a drawing tower. The drawing speed is 800-1200 m/min, and the drawing tension of the bare optical fiber is 110-160 g.