WO2011020315A1 - 一种抗弯曲多模光纤及其制造方法 - Google Patents

一种抗弯曲多模光纤及其制造方法 Download PDF

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WO2011020315A1
WO2011020315A1 PCT/CN2010/070778 CN2010070778W WO2011020315A1 WO 2011020315 A1 WO2011020315 A1 WO 2011020315A1 CN 2010070778 W CN2010070778 W CN 2010070778W WO 2011020315 A1 WO2011020315 A1 WO 2011020315A1
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refractive index
optical fiber
fluorine
cladding
fiber
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PCT/CN2010/070778
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English (en)
French (fr)
Inventor
张方海
曹蓓蓓
韩庆荣
拉吉·马泰
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长飞光纤光缆有限公司
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Priority to EP10737461.3A priority Critical patent/EP2420875A4/en
Priority to US12/839,396 priority patent/US8184936B2/en
Publication of WO2011020315A1 publication Critical patent/WO2011020315A1/zh

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0288—Multimode fibre, e.g. graded index core for compensating modal dispersion
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
    • C03B37/01807—Reactant delivery systems, e.g. reactant deposition burners
    • C03B37/01815—Reactant deposition burners or deposition heating means
    • C03B37/01823—Plasma deposition burners or heating means
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
    • C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
    • C03B37/01861—Means for changing or stabilising the diameter or form of tubes or rods
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03638—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only
    • G02B6/0365—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 3 layers only arranged - - +
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/08—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant
    • C03B2201/12—Doped silica-based glasses doped with boron or fluorine or other refractive index decreasing dopant doped with fluorine
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2201/00—Type of glass produced
    • C03B2201/06—Doped silica-based glasses
    • C03B2201/30—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi
    • C03B2201/31—Doped silica-based glasses doped with metals, e.g. Ga, Sn, Sb, Pb or Bi doped with germanium
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2203/00—Fibre product details, e.g. structure, shape
    • C03B2203/10—Internal structure or shape details
    • C03B2203/22—Radial profile of refractive index, composition or softening point
    • C03B2203/23—Double or multiple optical cladding profiles
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B2203/00—Fibre product details, e.g. structure, shape
    • C03B2203/10—Internal structure or shape details
    • C03B2203/22—Radial profile of refractive index, composition or softening point
    • C03B2203/26—Parabolic or graded index [GRIN] core profile
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/028—Optical fibres with cladding with or without a coating with core or cladding having graded refractive index
    • G02B6/0286—Combination of graded index in the central core segment and a graded index layer external to the central core segment
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
    • G02B6/03622—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only
    • G02B6/03633—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 2 layers only arranged - -

Definitions

  • the present invention relates to a multimode optical fiber for use in an access network or miniaturized optical device and a method of manufacturing the same, which has excellent bending resistance and belongs to the field of optical communication technology.
  • Multimode fiber especially high-bandwidth multimode fiber (such as OM3), has been widely used in medium and short-haul fiber-optic network systems (such as data centers and campus networks) due to its relatively low system construction cost.
  • the fiber In indoor and narrow wiring, the fiber is subject to high bending stresses, especially in applications where the fiber is too long to be wound in an increasingly smaller memory box that will withstand large bending stresses. Therefore, it is necessary to design and develop multimode fiber with anti-bending performance to meet the requirements of indoor fiber network laying and device miniaturization.
  • the anti-bending multimode fiber needs to have the following characteristics: 1.
  • the additional bending attenuation especially the macrobend additional attenuation) is small. There are many modes in the multimode fiber.
  • the high-order mode near the boundary of the multimode fiber core is easy to leak out from the core when the fiber is bent. Some of the light leaked from the core will return to the core, and some will be in the cladding. During transport, a portion will leak through the coating. As the bend radius decreases, the amount of light leaking from the core increases, and the attenuation of the fiber-optic transmission system increases, which can cause signal distortion and increase the possibility of bit errors in the system. 2. Fiber life is not affected at small bend radii. Anti-bending multimode fiber may work at a small bending radius for a long time, when the fiber is bent, outside the fiber
  • the _ E r side is inevitably subjected to tensile stress.
  • the magnitude of the stress can be expressed by the following formula: ⁇ + + f) where E is the Young's modulus of the quartz glass, R is the bending radius, r is the radius of the fiber, C th For painting Coating thickness.
  • E the Young's modulus of the quartz glass
  • R the bending radius
  • r the radius of the fiber
  • C th For painting Coating thickness.
  • the flexural multimode fiber must have good mechanical properties, that is, it has good mechanical reliability at a small bending radius to ensure its service life. This requires the fiber to have less residual stress and fewer defects. 3, with higher bandwidth, can meet the needs of 10Gb / s, or even 40Gb / s Ethernet.
  • the refractive index profile is mainly composed of "groove type” (shown in Figure 1) and "double-clad type” (shown in Figure 2).
  • U.S. Patents US20080166094A1, US20090169163A1 and US20090154888A1 are such designs.
  • the design principle is as follows: When the fiber is subjected to small bending, the light leaked from the core is limited to a larger proportion of the inner cladding and returned to the core, thereby effectively reducing the additional loss of the fiber macrobend.
  • the fiber corresponding to the refractive index profile shown in Fig. 1 has a high doping of the core layer due to high doping of the core layer, and the core layer and the depressed cladding are close to each other, and the expansion coefficients of the misdoped and fluorine-doped quartz glass vary greatly.
  • the internal fiber tends to have a large internal stress. Although the additional bending loss due to stress can be overcome by the depressed cladding, the internal stress will have a serious impact on the life of the fiber, and the profile of the fiber will be stressed when the fiber is bent. The distortion occurs and thus affects the transmission bandwidth of the fiber.
  • the fiber corresponding to the refractive index profile shown in Figure 2 is designed according to the material composition described in the U.S. patent, and will also Like the fiber corresponding to the refractive index profile shown in Fig. 1, it has a large internal stress. And this internal gravity is caused by the permanent stress caused by the difference in thermal expansion coefficient of each layer. It is difficult to eliminate it only by adjusting the process optimization annealing, and must be solved from the material composition and structural design.
  • the ITU - T G657 Appendix fiber cartridge to the standard have been introduced in the dynamic fatigue life of the optical parameters of the optical fiber n d, the higher the dynamic fatigue parameter n d, and located in the same bending radius The mechanical reliability of the fiber is higher under the length. Therefore, the effect of improving the fiber material composition and cross-sectional structure can be verified by testing the dynamic fatigue parameter n d of the fiber.
  • the fiber core refractive index profile must be approximately perfect parabola.
  • the method including the patent CN1183049C focuses on how to prepare a preform with a precise refractive index profile.
  • the fiber refractive index is compared with the refractive index distribution of the preform due to the residual stress and component diffusion. The rate distribution will be distorted. That is to say, even if the refractive index distribution of the preform is a perfect parabola, the refractive index distribution of the fiber after the fiber is drawn is difficult to maintain a perfect parabola.
  • Core rod a preform containing a core layer and a partial cladding
  • Radius the distance between the outer boundary of the layer and the center point
  • Refractive index profile The relationship between the refractive index of a fiber or an optical fiber preform (including a mandrel) and its radius;
  • Relative refractive index difference ⁇ and ⁇ 0 are the corresponding parts And pure silica glass refractive index, unless otherwise stated, lli is the maximum refractive index of each corresponding part; fluorine (F) contribution: the relative refractive index difference of fluorine-doped (F) quartz glass relative to pure quartz glass (A F ), thereby indicating the amount of fluorine (F) doped;
  • germanium (Ge) the relative refractive index difference (A Ge ) of germanium (Ge)-doped quartz glass relative to pure quartz glass, thereby indicating the amount of germanium (Ge) doped;
  • Casing a quartz glass tube that meets certain geometric and doping requirements
  • Power exponential refractive index profile A refractive index profile that satisfies the power exponential function below, where m is the refractive index of the fiber axis; r is the distance from the fiber axis; a is the fiber core radius; ⁇ is the distribution index; ⁇ is Core/package relative refractive index difference; A multi-mode optical fiber with reasonable structural design, high mechanical reliability of fiber, long service life and high bandwidth, and a manufacturing method thereof.
  • the core layer and the cladding layer are characterized in that the core layer radius R1 is 24 to 26 ⁇ m, the core layer refractive index profile is parabolic ( ⁇ is 1.9 to 2.2), and the maximum relative refractive index difference ⁇ 1 is 0.9 to 1.1%, and the core layer
  • the outer cladding consists of three parts, from the inside to the outside: the inner cladding radius R2 is 1.04 ⁇ 1.6 times the core radius R1, the relative refractive index difference ⁇ 2 is -0.01 ⁇ 0.01%, the intermediate cladding is the refractive index gradient
  • the cladding, the intermediate cladding radius R3 is 1.06 ⁇ 1.8 times of the core radius R1, the relative refractive index difference is gradually decreased from ⁇ 2 to ⁇ 4, and the outer cladding radius R4 is 2.38 ⁇ 2.63 times of the core radius R1, and the relative refractive index difference ⁇ 4 It is -0.20% ⁇ -0.40%.
  • the optimal scheme of the inner cladding radius R2 is 1.04 ⁇ of the core layer radius R1. 1.25 times.
  • the outer cladding relative refractive index difference ⁇ 4 is constant in the radial direction, or is gradual, and the gradation includes increasing the gradient from the inside to the outside or decreasing the gradation from the inside to the outside.
  • the optimal solution is to gradually increase the relative refractive index from the inside to the outside.
  • the relative refractive index difference ⁇ 4 of the outer cladding gradually increases from the inside to the outside, from -0.40% to -0.25%, or from -0.35% to -0.15%.
  • the relative refractive index difference ⁇ 4 of the outer cladding decreases from the inside to the outside, decreasing from -0.15 % to -0.35 %, or decreasing from -0.10% to -0.30%.
  • each layer is (the schematic diagram of the doping profile is shown in Fig. 6):
  • the core layer is composed of quartz glass doped with (Ge) and fluorine (F), and the contribution of fluorine (F) is -0.03 ⁇ 0.02%;
  • the inner cladding layer is composed of quartz glass doped with (Ge) and fluorine (F).
  • the intermediate cladding layer is composed of fluorine-doped quartz glass, and the fluorine is gradually increased from the interface 32 to the outer interface 43 of the intermediate cladding layer; the outer cladding layer is composed of fluorine-doped quartz glass.
  • Chlorine (C1) is introduced by the reaction of silicon tetrachloride (SiCl 4 ), ruthenium tetrachloride ( GeCl 4 ) and oxygen ( 0 2 ) to form C1, and the fluctuation of its content has little effect on the performance of the fiber, and Under stable process conditions, the fluctuation of its content is not large, and it can be omitted and required.
  • a pure quartz glass liner is fixed on a plasma enhanced chemical vapor deposition (PCVD) lathe for doping deposition, and a fluorine-containing gas is introduced into the reaction gases silicon tetrachloride (SiCl 4 ) and oxygen (0 2 ).
  • PCVD plasma enhanced chemical vapor deposition
  • the reaction gas in the liner is ionized into a plasma by microwave, and finally deposited on the inner wall of the liner in the form of glass; according to the doping requirement of the fiber waveguide structure, by changing the flow rate of the doping gas in the mixed gas, Depositing the intermediate cladding layer, the inner cladding layer and the core layer; after the deposition is completed, the deposition tube is melted into a solid core rod by an electric heating furnace; then the core rod is etched by hydrofluoric acid (HF), and the liner of the outer core rod is etched After the layer is etched away, the optical fiber preform is prepared by using RIT process using synthetic fluorine-doped quartz glass as a sleeve, or an optical fiber preform is prepared by depositing an outer layer outside the core rod by using an OVD or VAD outer deposition deposition process;
  • the fluorine-containing gas is any one or more of C 2 F 6 , CF 4 , SiF 4 and SF 6 .
  • the refractive index distribution of the preform is corrected and compensated according to the refractive index distribution of the optical fiber and the refractive index distribution of the preform during the manufacture of the optical fiber preform, and the correction is performed.
  • the compensated preform can pull out the fiber with a precise refractive index profile.
  • the method of correcting and compensating the refractive index profile of the preform includes the following steps:
  • the refractive index distribution of the optical fiber preform is preliminarily designed
  • the reaction gas mixture is introduced into the liner and reacted therein to complete the deposition of the oxide forming the glass inside the liner to form an optical fiber preform;
  • step 8 Repeat steps 3 through 7, until the contrast difference in step 6 is within acceptable tolerances.
  • the dynamic fatigue parameter n d of the optical fiber of the invention is above 27; the bandwidth above 2000 MHz-km and even above 5000 MHz-km at the wavelength of 850 nm; the numerical aperture of the optical fiber is 0.195-0.230; at the wavelength of 850 nm, the bending radius is 10 mm
  • the additional bending loss caused by 1 ⁇ is less than 0.2dB, even reaching 0.03dB; the additional bending loss caused by the winding radius of 7.5mm around 1 ⁇ is less than 0.3dB, even reaching 0.05dB; bending around 1 ⁇ with a bending radius of 5mm
  • the additional loss is less than 1.0 dB, even reaching 0.3 dB.
  • a three-clad multimode fiber is designed, and a refractive index-graded intermediate cladding layer is introduced between the inner and outer cladding layers, and the fiber-bending addition is not only reduced by the reasonable composition of the material and the waveguide structure.
  • the attenuation improves the bending resistance of the optical fiber, and substantially eliminates the internal stress of the optical fiber, thereby greatly improving the mechanical properties of the optical fiber, and the service life of the optical fiber for a long period of time in a small radius state can also be ensured; 2.
  • the material composition of each layer of the invention makes the fiber have a functionally graded material composition and structure: from the core layer to the outer cladding interface, the viscosity gradually changes; in the inner cladding, from the outside to the inside, the fluorine-doped and erbium-doped gradual increase continuously, with a gradient change, making it The coefficient of expansion gradually increases; the intermediate cladding makes the refractive index and viscosity between the inner cladding and the outer cladding more moderate; the optimal refractive index of the outer cladding is that the refractive index gradually increases from the inside to the outside, that is, the fluorine is gradually added from the inside to the outside.
  • the viscosity gradually increases, It helps the outer layer to take more tension during the drawing process and reduce the influence of wire drawing on the fiber core.
  • the above material composition design can avoid the residual stress generated during the drawing process and enhance the mechanical properties of the optical fiber. 3.
  • the method of correcting and compensating the refractive index distribution of the preform can be controlled in a small range. The bandwidth performance of the optical fiber can be greatly improved; 4.
  • the manufacturing method of the invention is effective and suitable for mass production.
  • Figure 1 is a schematic diagram showing the refractive index profile of a conventional "groove-type" depressed cladding fiber.
  • Figure 2 is a schematic diagram showing the refractive index profile of a conventional "double-clad" depressed cladding fiber.
  • FIG 3 is a schematic cross-sectional view of a refractive index of an optical fiber according to an embodiment of the present invention.
  • Fig. 4 is a view showing a refractive index profile of an optical fiber (the outer layer is gradually doped with fluorine from the outside to the inside) according to another embodiment of the present invention.
  • Fig. 5 is a view showing the refractive index profile of the optical fiber of the third embodiment of the present invention (the outer layer is gradually doped with fluorine from the outside to the inside).
  • Figure 6 is a schematic cross-sectional view showing the doping of the optical fiber of the present invention. detailed description
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • a set of preforms and wire drawing are prepared, which adopts double-layer coating of multimode fiber and drawing speed of 600 m/min.
  • the structure and material composition of the fiber are shown in Table 1.
  • the macrobend additional loss is measured according to the FOTP-62 (IEC - 60793 - 1 - 47) method.
  • the fiber to be tested is wound around a certain diameter (for example: 10mm, 15mm, 20mm, 30mm, etc.), and then the circle is released to test the change of optical power before and after snoring, which is used as the macrobend additional loss of the fiber.
  • an Encircled Flux light injection condition was employed.
  • Encircled Flux light injection conditions can be obtained by: welding a 2 m long ordinary 50 micron core multimode fiber at the front end of the fiber to be tested, and winding a 25 mm diameter crucible in the middle of the fiber.
  • the fiber to be tested is an Encircled Flux light injection.
  • the full injection bandwidth is measured by the FOTP-204 method and the test uses full injection conditions.
  • the dynamic fatigue parameter n d value of the fiber is tested according to IEC 60793-1-33 using a two-point bending method.
  • Embodiment 2 is a diagrammatic representation of Embodiment 1:
  • This embodiment is an example of a multimode optical fiber in which a refractive index distribution of a preform is corrected and compensated according to a refractive index distribution of a fiber to thereby produce a precise refractive index distribution.
  • the gaseous SiCl 4 , GeCl 4 , C 2 F 6 and 02 are introduced into the quartz glass liner by PCVD, and deposited inside the tube.
  • the supply of SiCl 4 , GeCl 4 and 0 2 changes with time, while the supply of C 2 F 6 remains constant.
  • the refractive index distribution of the preform is tested to draw the preform into an optical fiber.
  • the refractive index distribution test is performed on the optical fiber, and the test result is compared with the refractive index distribution required by the predetermined optical fiber, and the distribution parameter ⁇ represents the refractive index distribution form of the optical fiber.
  • the refractive index of the preform is The distribution design is modified and the correction is achieved by changing the composition of the reaction gas mixture versus time in a subsequent deposition process. According to the method, the standard deviation of the refractive index profile a of the fiber is reduced from 0.05 to 0.008. Table 1: Structure and material composition of the fiber
  • Embodiment 3 is a diagrammatic representation of Embodiment 3
  • the pure quartz glass liner was fixed on a plasma enhanced chemical vapor deposition (PCVD) lathe for doping deposition.
  • PCVD plasma enhanced chemical vapor deposition
  • the reaction in the liner was carried out by microwave.
  • the gas ionization becomes a plasma, and finally deposits on the inner wall of the liner in the form of glass; according to the doping requirement of the fiber waveguide structure shown in FIG. 1, the depressed cladding layer is sequentially deposited by changing the flow rate of the doping gas in the mixed gas.
  • the inner cladding layer and the core layer are filled with fluorine-containing gas when depositing the outer depressed cladding layer, and fluorine (F) is doped, the inner cladding layer is pure quartz glass, and the germanium tetrachloride (GeC14) is introduced during the deposition of the core layer.
  • Error (Ge) doping to obtain a profile with an increased refractive index; after deposition, the deposition tube is melted into a solid mandrel by an electric heating furnace; then the fiber is made by using the RIT process using geometrically matched pure quartz glass as a sleeve.
  • Preforms The optical fiber preform was placed in a drawing tower and pulled into an optical fiber at a tension of 0.4 Newton, and two layers of ultraviolet-curable polyacrylic acid resin were coated on the surface of the optical fiber.
  • the core of the optical fiber is not fluorine-doped, and the inner cladding and the outer cladding are pure quartz glass.
  • a pure quartz glass liner was fixed on a plasma enhanced chemical vapor deposition (PCVD) lathe for doping deposition.
  • PCVD plasma enhanced chemical vapor deposition
  • SiCl 4 silicon tetrachloride
  • oxygen (0 2 )
  • ruthenium tetrachloride was introduced.
  • GeCl 4 is doped with germanium (Ge), the reaction gas in the liner is ionized into a plasma by microwave, and finally deposited on the inner wall of the liner in the form of glass; the doping of the fiber waveguide structure according to FIG.
  • the optical fiber preform is prepared by using the RIT process using synthetic fluorine-doped quartz glass as a sleeve. Place the fiber preform in the drawing tower at 0.4 Newtons The fiber core layer is not fluorine-doped.

Description

一种抗弯曲多模光纤及其制造方法
技术领域
本发明涉及一种用于接入网或小型化光器件中的多模光纤及其制造方 法， 该光纤具有优异的抗弯曲性能， 属于光通信技术领域。
背景技术
多模光纤， 特别是高带宽的多模光纤（比如 OM3 ) 由于系统建设成本 相对较低， 在中短距离光纤网络系统（比如数据中心和校园网等）中得到了 广泛的应用。 在室内及狭窄环境下的布线， 光纤经受较高的弯曲应力， 特别 是在应用中过长的光纤通常缠绕在越来越小型化的存储盒中，光纤将承受很 大的弯曲应力。 因此需要设计开发具有抗弯曲性能的多模光纤， 以满足室内 光纤网络铺设和器件小型化的要求。 与传统多模光纤相比，抗弯曲多模光纤 需具有以下特点： 1、 弯曲附加衰减（特别是宏弯附加衰减）要小。 多模光 纤里面传输有许多模式，靠近多模光纤芯子边界传输的高阶模很容易在光纤 弯曲时从芯子泄露出去，从芯子泄露出去的光一部分会返回芯子，一部分会 在包层中传输， 一部分会穿过涂覆层泄露出去。 当弯曲半径减小时， 从芯子 泄露出去的光会增加， 光纤传输系统的衰减就会增加，从而可能会导致信号 失真， 增加了系统出现误码的可能。 2、 小弯曲半径下光纤寿命不受影响。 抗弯曲多模光纤工作时可能长期处于小弯曲半径下， 当光纤弯曲时， 光纤外
_ E r 侧必然受到张应力的作用， 其应力大小可用下列公式表示： ^ + + f) 式中， E为石英玻璃的扬氏模量、 R为弯曲半径、 r为光纤的半径、 Cth为涂 覆层厚度。对于玻璃包层直径为 125微米和外径为 250微米的光纤， 当弯曲 半径减小至 6.5mm时， 光纤弯曲外侧将承受 0.69GPa ( lOOkpsi ) 的张应力， 已达到光纤的常用筛选张力。光纤弯曲引起的断裂一方面会发生在敷设过程 中， 将引起敷设成本的增加； 更严重的是发生在使用过程中， 这是因为光纤 在张应力作用下，微裂紋会扩张并可能最终导致光纤的断裂，特别是在 FTTx 的应用中将大大增加维护成本和影响系统的可靠性。 因此， 与普通多模光纤 相比， 抗弯曲多模光纤必须有很好的机械性能， 即在小弯曲半径状态下， 要 具有很好的机械可靠性以确保其使用寿命。这就要求光纤具有较小的残存应 力和较少的缺陷。 3、 具有较高带宽， 可以满足 10Gb/s, 甚至是 40Gb/s以太 网的需要。
降低光纤弯曲附加衰减的一个有效方法是采用下陷包层的设计，其折射 率剖面主要有 "壕沟型"（图 1所示）和"双包层型"（图 2所示） 两种。 美国 专利 US20080166094A1 , US20090169163A1和 US20090154888A1就是采用 的此类设计。 其设计原理为： 当光纤受到小的弯曲时， 从芯子泄露出去的光 会较大比例的限制在内包层并返回到芯子中，从而有效降低了光纤宏弯附加 损耗。
但是，如何保证此类光纤长期工作在小半径状态下的使用寿命，仍然有 待进一步的解决。图 1所示折射率剖面对应的光纤由于芯层高掺错而下陷包 层高掺氟，且芯层和下陷包层相距^艮近， 而掺错和掺氟石英玻璃的膨胀系数 相差很大， 光纤内部势必具有很大的内应力， 虽然因应力引起的弯曲附加损 耗可通过下陷包层进行克服，但内应力会对光纤的寿命产生严重影响，且当 光纤弯曲时其剖面结构因应力的作用而发生畸变进而影响光纤的传输带宽。 图 2所示折射率剖面对应的光纤按照该美国专利所述的材料组成设计，也会 同图 1所示折射率剖面对应的光纤一样，具有 ^艮大的内应力。 并且这种内引 力是由于各层的热膨胀系数不同所引起的永久性应力，很难仅仅通过调整工 艺优化退火来消除， 必须从材料组成和结构设计方面来解决。对于光纤寿命 的预测， 在 ITU - T G657光纤标准的附录中已有筒要介绍， 光纤的使用寿 命与光纤的动态疲劳参数 nd有关， 动态疲劳参数 nd越高， 在同等弯曲半径 和存放长度下， 光纤的机械可靠性就越高。 因此， 改进光纤材料组成和剖面 结构的效果可以通过测试光纤的动态疲劳参数 nd来检验。
另外，要使多模光纤具有很好的带宽， 光纤芯折射率剖面必须为近似完 美的抛物线。包括专利 CN1183049C在内的方法关注的是如何制备有精确折 射率分布的预制棒，然而在光纤拉制过程中，由于残存的应力和组分的扩散， 与预制棒折射率分布相比， 光纤折射率分布会发生畸变。 也就是说， 即使预 制棒折射率分布是完美的抛物线，拉成光纤后光纤折射率分布也 4艮难保持完 美的抛物线。 发明内容
为方便介绍本发明内容， 定义部分术语：
芯 棒： 含有芯层和部分包层的预制件；
半径： 该层外边界与中心点之间的距离；
折射率剖面： 光纤或光纤预制棒（包括芯棒）玻璃折射率与其半径之间 的关系；
相对折射率差：
Figure imgf000005_0001
ηι和 η0分别为各对应部 和纯二氧化硅玻璃折射率， 除非另做说明， lli为各对应部分的最大折射率； 氟（F ) 的贡献量： 掺氟（F )石英玻璃相对于纯石英玻璃的相对折射 率差值（AF ), 以此来表示掺氟（F )量；
锗（Ge ) 的贡献量： 掺锗（Ge )石英玻璃相对于纯石英玻璃的相对折 射率差值（AGe ), 以此来表示掺锗（Ge )量；
套 管： 符合一定几何和掺杂要求的石英玻璃管；
RIT工艺： 将芯棒插入套管中组成光纤预制棒；
幂指数律折射率剖面： 满足下面幂指数函数的折射率剖面， 其中， m 为光纤轴心的折射率； r为离开光纤轴心的距离； a为光纤芯半径； α为分布 指数； Δ为芯 /包相对折射率差；
Figure imgf000006_0001
种结构设计合理、 光纤的机械可靠性高、 使用寿命长的抗弯曲、 高带宽的多 模光纤及其制造方法。
本发明多模光纤的技术方案为：
包括有芯层和包层， 其特征在于芯层半径 R1为 24 ~ 26微米， 芯层折 射率剖面呈抛物线（ α为 1.9 ~ 2.2 ), 最大相对折射率差 Δ1为 0.9 ~ 1.1%, 芯层外的包层由三部分组成， 从内到外依次为： 内包层半径 R2为芯层半径 R1的 1.04 ~ 1.6倍， 相对折射率差 Δ2为 -0.01 ~ 0.01%, 中间包层为折射率 渐变包层， 中间包层半径 R3为芯层半径 R1的 1.06 ~ 1.8倍， 相对折射率差 由 Δ2递减渐变至 Δ4, 外包层半径 R4为芯层半径 R1的 2.38 ~ 2.63倍， 相 对折射率差 Δ4为 -0.20% ~ -0.40%。
按上述方案，所述的内包层半径 R2的最优方案为芯层半径 R1的 1.04 ~ 1.25倍。
按上述方案， 所述的外包层相对折射率差 Δ4沿径向为恒定的， 或者为 渐变的，渐变包括从内向外递增渐变或从内向外递减渐变。 最优方案为相对 折射率从内向外递增渐变。
按上述方案，所述的外包层相对折射率差 Δ4从内向外递增渐变，从 -0.40 %递增为 -0.25 % , 或者从 -0.35 %递增为 -0.15 %。
按上述方案，所述的外包层相对折射率差 Δ4从内向外递减渐变，从 -0.15 %递减为 -0.35 % , 或者从 -0.10 %递减为 -0.30 %。
按上述方案， 各层的材料组成为 （掺杂剖面示意图见图 6): 芯层由掺 错（Ge)和氟（F) 的石英玻璃组成， 氟（F) 的贡献量 AF为 -0.03±0.02%； 所述的内包层由掺错 (Ge)和氟（F)的石英玻璃组成， 从内包层外界面 32 至内界面 21, 掺氟和掺锗逐渐连续增加， 呈梯度变化； 所述的中间包层由 掺氟的石英玻璃组成，由中间包层内界面 32至外界面 43掺氟逐渐连续增加； 所述的外包层由掺氟的石英玻璃组成。
按上述方案， 所述的掺锗 （Ge) 和氟 （F) 石英玻璃的材料组分为 Si02-Ge02-F-Cl; 所述的掺氟（F)石英玻璃的材料组分为 Si02-F-Cl。
氯（ C1 )是由四氯化硅（ SiCl4 )、 四氯化锗（ GeCl4 )与氧气（ 02 )发生 反应生成 C1所引入的， 其含量的波动对光纤的性能影响不大， 且在稳定的 工艺条件下其含量的波动也不大， 可不作要求和控制。
本发明多模光纤制造方法的技术方案为：
将纯石英玻璃衬管固定在等离子体增强化学气相沉积（PCVD)车床上 进行掺杂沉积， 在反应气体四氯化硅（SiCl4)和氧气（02) 中， 通入含氟 的气体， 引进氟（F)掺杂， 通入四氯化锗（GeCl4) 以引入错 (Ge)掺杂， 通过微波使衬管内的反应气体离子化变成等离子体，并最终以玻璃的形式沉 积在衬管内壁； 根据所述光纤波导结构的掺杂要求，通过改变混合气体中掺 杂气体的流量， 依次沉积中间包层、 内包层和芯层； 沉积完成后， 用电加热 炉将沉积管熔缩成实心芯棒； 然后采用氢氟酸（HF )对芯棒进行腐蚀， 把 芯棒外部的衬管层腐蚀掉后， 以合成的掺氟石英玻璃为套管采用 RIT 工艺 制得光纤预制棒， 或采用 OVD或 VAD外包沉积工艺在芯棒外沉积外包层 制得光纤预制棒；将光纤预制棒置于拉丝塔以 0.2 ~ 0.4牛顿的低张力拉成光 纤， 在光纤表面涂覆内外两层紫外固化的聚丙稀酸树脂即成。
按上述方案， 所述的含氟气体为 C2F6、 CF4、 SiF4和 SF6的任意一种或 多种。
按上述方案， 为制造有精确折射率分布的多模光纤，在制造光纤预制棒 过程中根据光纤折射率分布与预制棒折射率分布对比，对预制棒折射率分布 进行修正和补偿，经过修正和补偿后的预制棒可以拉出精确折射率分布的光 纤。 该对预制棒折射率分布进行修正和补偿的方法包括下列步骤：
1.根据光纤折射率分布， 初步设计光纤预制棒折射率分布；
2.精确调节制备目标预制棒所用气体混合物的组成和供给速率，使其与 步骤 1决定的折射率分布相符合；
3.根据上一步骤确定的条件，将反应气体混合物引入衬管并在其内进行 反应， 完成衬管内部形成玻璃的氧化物的沉积， 制成光纤预制棒；
4.对步骤 3沉积工艺得到的预制棒进行精确折射率分布的测量，并把该 预制棒拉成光纤；
5.对步骤 4得到的光纤进行精确折射率分布的测量；
6.根据光纤的测试结果优化设计待制造光纤所要求的折射率分布，并与 步骤 5测量的光纤折射率分布进行对比， 如果对比差别超过规定公差范围， 则根据对比结果对预制棒折射率分布设计进行修正；
7.在后续沉积工艺中，改变反应气体混合物的组成与时间的关系来实现 步骤 6对预制棒折射率分布设计的修正；
8.重复步骤 3 ~ 7, 直至步骤 6的对比差别在可接受的规定公差之内。 为了增强步骤 4和 5实施的折射率分布测量的精度，优选在许多不同纵 向位置， 许多不同角度进行测量（至少 X和 y两个方向）， 并将得到的数值 取平均值。
本发明光纤的动态疲劳参数 nd在 27 以上； 在 850nm波长具有 2000 MHz-km 以上， 甚至 5000MHz-km 以上的带宽； 光纤的数值孔径为 0.195-0.230; 在 850nm波长处， 以 10毫米弯曲半径绕 1圏导致的弯曲附加 损耗小于 0.2dB, 甚至达到 0.03dB; 以 7.5毫米弯曲半径绕 1圏导致的弯曲 附加损耗小于 0.3dB, 甚至达到 0.05dB; 以 5毫米弯曲半径绕 1圏导致的弯 曲附加损耗小于 l.OdB, 甚至达到 0.3dB。
本发明的有益效果在于： 1、 设计出一种三包层多模光纤， 在内外包层 之间引入了折射率渐变中间包层，通过材料和波导结构的合理组成， 不仅降 低了光纤弯曲附加衰减，提高了光纤的抗弯曲性能， 而且基本消除了光纤内 部应力， 大大提高了光纤的机械性能， 光纤长期工作在小半径状态下的使用 寿命也能得到保证； 2、 本发明各层材料组成的设计使光纤具有功能梯度材 料组成和结构： 从芯层到内包层外界面， 粘度逐渐变化； 在内包层中， 从外 至内， 掺氟和掺锗逐渐连续增加， 呈梯度变化， 使其膨胀系数逐渐增大； 中 间包层使内包层和外包层之间的折射率和粘度平緩过度；外包层折射率最优 方案为折射率从内向外逐渐增加，即从内向外掺氟逐渐较少、粘度逐渐增加， 有助于外包层在拉丝过程中承担更多张力， 减少拉丝对光纤芯子的影响。上 述材料组成设计可以避免拉丝过程中产生残余应力， 增强了光纤的机械性 能； 3、 采用对预制棒折射率分布进行修正和补偿的方法， 光纤折射率分布 的公差可以控制在很小的范围之内， 光纤的带宽性能可以得到大幅提高； 4、 本发明制造方法筒便有效， 适用于大规模生产。 附图说明
图 1 是现有 "壕沟型"下陷包层光纤的折射率剖面示意图。
图 2 是现有 "双包层型"下陷包层光纤的折射率剖面示意图。
图 3 是本发明一个实施例的光纤折射率剖面示意图。
图 4 是本发明另一个实施例的光纤折射率剖面 （外包层掺氟从外向内 逐渐减少）示意图。
图 5 是本发明第三个实施例的光纤折射率剖面 （外包层掺氟从外向内 逐渐增加）示意图。
图 6是本发明光纤的掺杂剖面示意图。 具体实施方式
下面将给出详细的实施例并结合附图， 对本发明作进一步的说明。
实施例一：
按本发明所述方法，制备了一组预制棒并拉丝， 采用多模光纤的双层涂 覆和 600米 /分钟的拉丝速度， 光纤的结构和材料组成见表 1 , 光纤的主要性 能参数见表 2。
宏弯附加损耗是根据 FOTP - 62 ( IEC - 60793 - 1 - 47 )方法测得的， 被测光纤按一定直径（比如： 10mm, 15mm, 20mm, 30mm等等）绕一圏， 然后将圓圏放开， 测试打圏前后光功率的变化， 以此作为光纤的宏弯附加损 耗。测试时，采用环形通量（Encircled Flux )光注入条件。环形通量（ Encircled Flux )光注入条件可以通过以下方法获得： 在被测光纤前端熔接一段 2米长 的普通 50微米芯径多模光纤， 并在该光纤中间绕一个 25毫米直径的圏， 当 满注入光注入该光纤时， 被测光纤即为环形通量（ Encircled Flux )光注入。
满注入带宽是 居 FOTP - 204方法测得的， 测试采用满注入条件。 为了准确评价光纤的机械性能， 按 IEC 60793-1-33 , 采用两点弯曲的方 法测试光纤的动态疲劳参数 nd值。
实施例二：
本实施例为根据光纤折射率分布对预制棒折射率分布进行修正和补偿， 从而制造精确折射率分布的多模光纤的实例。
根据初步设计的多模光纤预制棒折射率分布， 采用 PCVD工艺， 将气 态 SiCl4、 GeCl4、 C2F6和 02引入石英玻璃衬管， 在管内部进行沉积。 SiCl4、 GeCl4和 02的供给随时间变化， 而 C2F6的供给保持恒定。 沉积结束后， 熔 缩成实心棒， 并测试预制棒的折射率分布， 把预制棒拉成光纤。 然后对光纤 进行折射率分布测试， 测试结果与预定的光纤所要求的折射率分布进行比 对， 以分布参数 α表示光纤折射率分布形式， 如果分布参数 α偏离过大， 则 对预制棒折射率分布设计进行修正， 并在后续沉积工艺中， 改变反应气体混 合物的组成与时间的关系来实现该修正。按照本方法， 光纤折射率分布参数 a的标准差从 0.05降到了 0.008。 表 1: 光纤的结构和材料组成
Figure imgf000012_0001
表 2: 光纤的主要性能参数
Figure imgf000013_0001
实施例三：
为了说明本发明的效果， 采用 PCVD工艺， 按照美国专利所述光纤剖 面结构和材料组成制作了一些光纤样品， 并进行了动态疲劳参数 nd的测试。 为了消除涂覆层对试验结果的影响， 所有光纤采用了相同类型、尺寸相近的 涂覆层。 光纤拉丝速度和拉丝张力也基本相同。
试验 A:
采用 PCVD工艺制作了一些折射率剖面如图 1所示的光纤样品， 并进 行了 nd测试。 试验过程及光纤测试结果如下：
将纯石英玻璃衬管固定在等离子体增强化学气相沉积（PCVD )车床上 进行掺杂沉积， 在反应气体四氯化硅（SiCl4 )和氧气（02 ) 中， 通过微波 使衬管内的反应气体离子化变成等离子体，并最终以玻璃的形式沉积在衬管 内壁； 根据图 1所示光纤波导结构的掺杂要求，通过改变混合气体中掺杂气 体的流量， 依次沉积下陷包层， 内包层和芯层， 在沉积外下陷包层时通入含 氟的气体， 引进氟（F )掺杂， 内包层为纯石英玻璃， 在沉积芯层时通入四 氯化锗（ GeC14 )引入错 ( Ge )掺杂以获得折射率增加的剖面； 沉积完成后， 用电加热炉将沉积管熔缩成实心芯棒；然后以几何尺寸匹配的纯石英玻璃为 套管采用 RIT工艺制得光纤预制棒。将光纤预制棒置于拉丝塔以 0.4牛顿的 张力拉成光纤， 在光纤表面涂覆内外两层紫外固化的聚丙稀酸树脂。
光纤芯层不掺氟， 内包层和外包层均为纯石英玻璃。
光纤剖面参数及光纤动态疲劳参数 nd测试结果见表 3。 表 3: "壕沟型"光纤剖面参数及光纤动态疲劳参数 nd测试结果
Figure imgf000015_0001
采用 PCVD工艺制作了一些折射率剖面如图 2所示的光纤样品， 并进 行了 nd测试。 试验过程及光纤测试结果如下：
将纯石英玻璃衬管固定在等离子体增强化学气相沉积（PCVD )车床上 进行掺杂沉积， 在反应气体四氯化硅 ( SiCl4 )和氧气（02 ) 中， 通入四氯 化锗（GeCl4 ) 以引入锗（Ge )掺杂， 通过微波使衬管内的反应气体离子化 变成等离子体， 并最终以玻璃的形式沉积在衬管内壁； 根据图 2所示光纤波 导结构的掺杂要求， 通过改变混合气体中掺杂气体的流量， 沉积芯层； 沉积 完成后， 用电加热炉将沉积管熔缩成实心芯棒； 然后采用氢氟酸（HF )对 芯棒进行腐蚀，把芯棒外部的衬管层部分腐蚀掉后， 以合成的掺氟石英玻璃 为套管采用 RIT工艺制得光纤预制棒。将光纤预制棒置于拉丝塔以 0.4牛顿 光纤芯层不掺氟。
表 4: 普通"双包层型"光纤剖面参数及光纤动态疲劳参数 nd测试结果
Figure imgf000016_0001
把表 2、 3、 4中的结果进行对比，可以看出： 在其它条件相同的情况下, 本发明的材料组成和剖面结构设计大大提高了光纤的动态疲劳参数 nd。

Claims

权 利 要 求 书
1、 一种抗弯曲多模光纤， 包括有芯层和包层， 其特征在于： 芯层半径 R1为 24 ~ 26 米， 芯层折射率剖面呈抛物线， 最大相对折射率差 Δ1为 0.9 - 1.1% , 芯层外的包层由三部分组成， 从内到外依次为： 内包层半径 R2为芯层半径 R1的 1.04 ~ 1.6倍， 相对折射率差 Δ2为 -0.01 ~ 0.01%, 中 间包层为折射率渐变包层， 中间包层半径 R3为芯层半径 R1 的 1.06 ~ 1.8 倍， 相对折射率差由 Δ2递减渐变至 Δ4, 外包层半径 R4为芯层半径 R1的 2.38 ~ 2.63倍， 相对折射率差 Δ4为 -0.20% ~ -0.40%。
2、 按权利要求 1所述的抗弯曲多模光纤， 其特征在于： 所述的内包层 半径 R2为芯层半径 R1的 1.04 ~ 1.25倍。
3、 按权利要求 1或 2所述的抗弯曲多模光纤， 其特征在于： 所述的外 包层相对折射率差 Δ4 沿径向为恒定的， 或者为渐变的， 渐变包括从内向 外递增渐变或从内向外递减渐变。
4、 按权利要求 3所述的抗弯曲多模光纤， 其特征在于： 所述的外包层 相对折射率差 Δ4从内向外递增渐变，从 -0.40 %递增为 -0.25 % ,或者从 -0.35 %递增为 -0.15 %。
5、 按权利要求 3所述的抗弯曲多模光纤， 其特征在于： 所述的外包层 相对折射率差 Δ4从内向外递减渐变，从 -0.15 %递减为 -0.35 % ,或者从 -0.10 %递减为 -0.30 %。
6、 按权利要求 1或 2所述的抗弯曲多模光纤， 其特征在于： 各层的材 料组成为： 芯层由掺锗和氟的石英玻璃组成， 氟的贡献量 AF 为 -0.03±0.02%； 所述的内包层由掺错和氟的石英玻璃组成， 从内包层外界面 ( 32 )至内界面（21 ), 掺氟和掺错逐渐连续增加， 呈梯度变化； 所述的中 间包层由掺氟的石英玻璃组成， 由中间包层内界面 （32 )至外界面 （43 ) 掺氟逐渐连续增加； 所述的外包层由掺氟的石英玻璃组成。
7、 按权利要求 6所述的抗弯曲多模光纤， 其特征在于： 所述的掺错和 氟石英玻璃的材料组分为 Si02-Ge02-F-Cl; 所述的掺氟石英玻璃的材料组 分为 Si02-F-Cl。
8、 一种按权利要求 1所述的抗弯曲多模光纤的制造方法， 其特征在于： 将纯石英玻璃衬管固定在等离子体增强化学气相沉积车床上进行掺杂沉 积， 在反应气体四氯化硅和氧气中， 通入含氟的气体， 引进氟掺杂， 通入 四氯化锗以引入锗掺杂， 通过微波使衬管内的反应气体离子化变成等离子 体， 并最终以玻璃的形式沉积在衬管内壁； 根据所述光纤波导结构的掺杂 要求， 通过改变混合气体中掺杂气体的流量， 依次沉积中间包层、 内包层 和芯层； 沉积完成后， 用电加热炉将沉积管熔缩成实心芯棒； 然后采用氢 氟酸对芯棒进行腐蚀， 把芯棒外部的衬管层腐蚀掉后， 以合成的掺氟石英 玻璃为套管采用 RIT工艺制得光纤预制棒， 或采用 OVD或 VAD外包沉积 工艺在芯棒外沉积外包层制得光纤预制棒； 将光纤预制棒置于拉丝塔以 0.2 ~ 0.4牛顿的低张力拉成光纤，在光纤表面涂覆内外两层紫外固化的聚丙 稀酸树脂即成。
9、 按权利要求 8所述的抗弯曲多模光纤的制造方法， 其特征在于： 各 层的材料组成为： 芯层由掺锗和氟的石英玻璃组成， 氟的贡献量 AF 为 -0.03±0.02%； 所述的内包层由掺错和氟的石英玻璃组成， 从内包层外界面
( 32 )至内界面（21 ), 掺氟和掺错逐渐连续增加， 呈梯度变化； 所述的中 间包层由掺氟的石英玻璃组成， 由中间包层内界面 （32 )至外界面 （43 ) 掺氟逐渐连续增加； 所述的外包层由掺氟的石英玻璃组成。
10、 一种按权利要求 8所述的制造方法对预制棒折射率分布进行修正和 补偿的方法， 其特征在于： 包括下列步骤：
( 1 )根据光纤折射率分布， 初步设计光纤预制棒折射率分布；
(2)精确调节制备目标预制棒所用气体混合物的组成和供给速率， 使其 与步骤（ 1 ) 决定的折射率分布相符合；
(3)根据上一步骤确定的条件， 将反应气体混合物引入衬管并在其内进 行反应， 完成衬管内部形成玻璃的氧化物的沉积， 制成光纤预制棒；
(4)对步骤（3) 沉积工艺得到的预制棒进行精确折射率分布的测量， 并把该预制棒拉成光纤；
(5)对步骤（4)得到的光纤进行精确折射率分布的测量；
(6)根据光纤的测试结果优化设计待制造光纤所要求的折射率分布， 并 与步骤（5)测量的光纤折射率分布进行对比， 如果对比差别超过规定公差 范围， 则根据对比结果对预制棒折射率分布设计进行修正；
(7)在后续沉积工艺中， 改变反应气体混合物的组成与时间的关系来实 现步骤（6)对预制棒折射率分布设计的修正；
(8) 重复步骤（3) ~ (7), 直至步骤（6) 的对比差别在可接受的规定 公差内。
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