阅读说明：本技术 改进的1550低损耗光纤制造设备及操作方法 (Improved 1550 low loss optical fiber manufacturing apparatus and method of operation ) 是由 龚成 王秋萍 刘成 赵禹 于 2019-12-10 设计创作，主要内容包括：本发明公开了一种改进的1550低损耗光纤制造设备及操作方法,在拉丝炉装置内,控制预制棒锥头成型的拉丝升速过程的温度,光纤经延伸管进入保温炉装置,将光纤再一次加热,使光纤的内外温度差降低；并在陶瓷管内对光纤进行保温退火,光纤经拉伸后进入涂覆模座；在拉丝过程当涂覆压力大于0.05MPa则单向阀开启,涂料进入模座,完成光纤的涂覆。本发明能够使预制棒锥头熔融区温度梯度缓慢变化,减小了预制棒横向内应力,降低了因预制棒熔融区锥头倾斜带来剪切力导致的附加衰减,避免了因改变折射率剖面结构而带来的瑞利散射,减少了光纤涂覆过程的微弯损耗。(The invention discloses an improved 1550 low-loss optical fiber manufacturing device and an operation method.A temperature of a fiber drawing acceleration process for forming a conical head of a preform rod is controlled in a fiber drawing furnace device, the optical fiber enters a heat preservation furnace device through an extension pipe, and the optical fiber is heated again, so that the temperature difference between the inside and the outside of the optical fiber is reduced; performing heat preservation annealing on the optical fiber in the ceramic tube, and stretching the optical fiber to enter a coating die holder; and in the wire drawing process, when the coating pressure is greater than 0.05MPa, the check valve is opened, and the coating enters the die holder to finish the coating of the optical fiber. The method can slowly change the temperature gradient of the melting zone of the cone head of the prefabricated rod, reduce the transverse internal stress of the prefabricated rod, reduce the additional attenuation caused by the shearing force due to the inclination of the cone head of the melting zone of the prefabricated rod, avoid the Rayleigh scattering caused by changing the section structure of the refractive index, and reduce the microbending loss in the optical fiber coating process.)

1. An improved 1550 low-loss optical fiber manufacturing device comprises a wire drawing furnace device, a heat preservation furnace device and a coating system, and is characterized in that a rod hanging table is arranged above the wire drawing furnace device, a prefabricated rod is hung below the rod hanging table, a wire drawing support is mounted in a wire drawing metal body in the wire drawing furnace device, a wire drawing coil lead frame is arranged on the periphery of the wire drawing support, a wire drawing graphite piece is mounted in the wire drawing support, a wire drawing copper coil is arranged on the periphery of the wire drawing graphite piece, the wire drawing copper coil is arranged in a parallel annular mode, the length of the wire drawing copper coil is 0.8-1.2M, and the number of turns of the wire drawing copper coil is 7-; a wire drawing gas cavity is arranged on the periphery of the wire drawing graphite piece, a cone head melting area is arranged at the lower end of the prefabricated rod, and the cone head melting area is positioned in the wire drawing gas cavity;

a heat preservation support with a heat preservation coil lead frame at the periphery is arranged in a heat preservation metal body of the heat preservation furnace device, a heat preservation graphite piece is arranged in the heat preservation support, heat preservation copper coils are arranged at the periphery of the heat preservation graphite piece, the heat preservation copper coils are arranged in a parallel ring shape, the length of the heat preservation copper coils is 0.6-1.0M, and the number of turns of the heat preservation copper coils is 4-7 turns; the middle of the heat-preservation graphite piece is a heat-preservation air cavity, and a ceramic tube is arranged below the heat-preservation graphite piece;

the lower end of the wire drawing air cavity is connected with the upper end of the heat insulation air cavity through an extension pipe;

the coating system is characterized in that a coating tank, a cache tank and a filter are sequentially connected through pipelines, and the filter is connected with a coating die holder pipeline through a filter screen and a one-way valve in sequence;

the lower part of the ceramic tube is connected with the coating die holder through a cooling tube, and a tension meter is arranged between the cooling tube and the coating die holder; a curing lamp is arranged at an outlet below the coating die holder, and a traction wheel is arranged between the curing lamp and the take-up reel; and the optical fiber at the outlet of the cone head melting area sequentially passes through the extension tube, the heat preservation air cavity, the ceramic tube, the cooling tube, the tensiometer, the coating die holder, the curing lamp and the traction wheel to the take-up reel.

2. The improved 1550 low loss optical fiber manufacturing equipment according to claim 1, wherein the ceramic tube has a length of 0.7-1.3M.

3. The improved 1550 low loss optical fiber manufacturing equipment according to claim 1, wherein the filter holes of the filter are 2-4 um.

4. The improved 1550 low loss optical fiber manufacturing equipment according to claim 1, wherein the filter holes of the filter screen are 1-2 um.

5. A method of operating an optical fiber manufacturing apparatus according to claim 1, characterized by the steps of:

step 1: in a wire drawing furnace device, controlling the temperature of a wire drawing acceleration process of the preform taper head forming to be 1970-2200 ℃, smoothly increasing the speed to 2000-2200 m/min in steps of 3 ℃, and after wire drawing, enabling the optical fiber to enter a heat preservation furnace device through an extension pipe;

step 2: heating the optical fiber to 1300-1400 ℃ again in a heat preservation furnace device to reduce the temperature difference between the inside and the outside of the optical fiber, carrying out heat preservation annealing on the optical fiber in a ceramic tube to slowly reduce the temperature of the optical fiber to 800-1000 ℃, and stretching the optical fiber through a traction wheel, wherein a tensiometer controls the tension of the optical fiber to be 80-100 g by regulating and controlling the rod feeding speed of a preform rod and the temperature of a wire drawing furnace device; the optical fiber enters a coating die holder after being stretched;

and step 3: in the cooling pipe, performing heat exchange treatment on the optical fiber through helium in the cooling pipe to reduce the temperature of the optical fiber to 50-60 ℃, and feeding the cooled optical fiber into a coating system;

and 4, step 4: in a coating system, the opening pressure of a one-way valve is set to be 0.05MPa, and coating enters a die holder to finish the coating of the optical fiber; the one-way valve is used for preventing the coating in the coating die holder and the pipeline thereof from flowing back to the filter to form bubbles;

and 5: the coated optical fiber in the coating system enters a curing lamp for ultraviolet curing of the coated resin.

6. The method of claim 5, wherein the rod-feeding speed of the preform with a diameter of 150mm is 2mm/min and the step-up time is 55-65 min.

7. The operating method according to claim 5, wherein the rod feeding speed of the preform with the diameter of 200mm in the drawing and accelerating process is 1mm/min, and the step accelerating time is 85-95 min.

Technical Field

The present invention relates to optical fibers and optical fiber production equipment, and more particularly to an improved 1550 low loss optical fiber manufacturing apparatus and method of operation.

Technical Field

With the rapid development of optical communication information technology, the demand for optical fibers is increasing. The drawing speed is improved on the original basis, and the attenuation of the optical fiber is increased in the intangible production of the large-diameter prefabricated rod. The attenuation of an optical fiber is one of the key indicators for measuring the performance of an optical fiber. It determines the maximum unrepeatered transmission distance and the quality of the signal that can be achieved by the optical fiber communication system. Reducing the attenuation of the transmission fiber has obviously become a major concern for every fiber manufacturer. Although the existing optical fiber drawing technology is mature, the requirements of high-yield production of modern optical fiber manufacturers and the use requirements of low attenuation and other optical fibers with good performance of customers are met, obviously, the attenuation of the optical fibers is influenced by the non-uniform temperature field caused by the inclination of the generated magnetic induction line of the induction coil of the traditional spiral drawing furnace, the scattering loss caused by the internal stress generated by the optical fibers cannot be fully eliminated due to simple heat preservation and annealing of the extension tube, and the microbending loss caused by bubbles/impurities cannot be fully eliminated due to the fact that a simple coating and feeding device cannot fully eliminate the microbending loss, so that the requirements of high-quality optical fiber production cannot be met.

In the process of forming the prefabricated rod, the nonuniformity of density distribution caused by the defect of molecular structure caused by the tensile stress of quartz molecules is avoided as much as possible in the process from the prefabricated rod to the optical fiber; and prevent the optical fiber coating from being uneven to cause the micro-bending loss generated by the strain of the surface layer of the optical fiber. The loss of the optical fiber in the 1550nm waveband is mainly the scattering loss caused by Rayleigh scattering, and for the G652D optical fiber, the Rayleigh scattering loss of the optical fiber is reduced to ensure the uniformity of the density distribution of quartz molecules.

Disclosure of Invention

It is an object of the present invention to provide an improved 1550 low loss optical fibre fabrication apparatus and method. In the optical fiber drawing process, in the process from the prefabricated rod to the optical fiber forming, the uniformity of the molecular structure density distribution of quartz molecules under tensile stress is ensured, and the uniformity of an optical fiber coating is ensured, so that the microbending loss generated by the optical fiber surface strain caused by the optical fiber coating is reduced.

In order to achieve the purpose, the invention adopts the following technical scheme.

An improved 1550 low-loss optical fiber manufacturing device comprises a drawing furnace device, a holding furnace device and a coating system, wherein a rod hanging table is arranged above the drawing furnace device, a prefabricated rod is hung below the rod hanging table, a drawing support is arranged in a drawing metal body in the drawing furnace device, a drawing coil lead frame is arranged on the periphery of the drawing support, a drawing graphite piece is arranged in the drawing support, a drawing copper coil is arranged on the periphery of the drawing graphite piece, the drawing copper coils are arranged in a parallel annular mode, the length of each drawing copper coil is 0.8-1.2M, and the number of turns of each drawing copper coil is 7-9 turns; a wire drawing gas cavity is arranged on the periphery of the wire drawing graphite piece, a cone head melting area is arranged at the lower end of the prefabricated rod, and the cone head melting area is positioned in the wire drawing gas cavity;

a heat preservation support with a heat preservation coil lead frame at the periphery is arranged in a heat preservation metal body of the heat preservation furnace device, a heat preservation graphite piece is arranged in the heat preservation support, heat preservation copper coils are arranged at the periphery of the heat preservation graphite piece, the heat preservation copper coils are arranged in a parallel ring shape, the length of the heat preservation copper coils is 0.6-1.0M, and the number of turns of the heat preservation copper coils is 4-7 turns; the middle of the heat-preservation graphite piece is a heat-preservation air cavity, and a ceramic tube is arranged below the heat-preservation graphite piece;

the lower end of the wire drawing air cavity is connected with the upper end of the heat insulation air cavity through an extension pipe;

the coating system is characterized in that a coating tank, a cache tank and a filter are sequentially connected through pipelines, and the filter is connected with a coating die holder pipeline through a filter screen and a one-way valve in sequence;

the lower part of the ceramic tube is connected with the coating die holder through a cooling tube, and a tension meter is arranged between the cooling tube and the coating die holder; a curing lamp is arranged at an outlet below the coating die holder, and a traction wheel is arranged between the curing lamp and the take-up reel; and the optical fiber at the outlet of the cone head melting area sequentially passes through the extension tube, the heat preservation air cavity, the ceramic tube, the cooling tube, the tensiometer, the coating die holder, the curing lamp and the traction wheel to the take-up reel.

Further, the length of the ceramic tube is 0.7-1.3M.

Further, the filtration pore of filter is 2~4 um.

Further, the filtration pore of filter screen is 1~2 um.

An improved 1550 method for operating a low-loss optical fibre manufacturing apparatus, comprising the steps of:

step 1: in a wire drawing furnace device, controlling the temperature of a wire drawing acceleration process of the preform taper head forming to be 1970-2200 ℃, smoothly increasing the speed to 2000-2200 m/min in steps of 3 ℃, and after wire drawing, enabling the optical fiber to enter a heat preservation furnace device through an extension pipe;

step 2: heating the optical fiber to 1300-1400 ℃ again in a heat preservation furnace device to reduce the temperature difference between the inside and the outside of the optical fiber, carrying out heat preservation annealing on the optical fiber in a ceramic tube to slowly reduce the temperature of the optical fiber to 800-1000 ℃, and stretching the optical fiber through a traction wheel, wherein a tensiometer controls the tension of the optical fiber to be 80-100 g by regulating and controlling the rod feeding speed of a preform rod and the temperature of a wire drawing furnace device; the optical fiber enters a coating die holder after being stretched;

and step 3: in the cooling pipe, performing heat exchange treatment on the optical fiber through helium in the cooling pipe to reduce the temperature of the optical fiber to 50-60 ℃, and feeding the cooled optical fiber into a coating system;

and 4, step 4: in a coating system, the opening pressure of a one-way valve is set to be 0.05MPa, and coating enters a die holder to finish the coating of the optical fiber; the one-way valve is used for preventing the coating in the coating die holder and the pipeline thereof from flowing back to the filter to form bubbles;

and 5: the coated optical fiber in the coating system enters a curing lamp for ultraviolet curing of the coated resin.

Further, the rod feeding speed of the phi 150mm preform in the wire drawing speed-up process is 2mm/min, and the step speed-up time is 55-65 min.

Further, the rod feeding speed of the phi 200mm preform in the wire drawing speed-up process is 1mm/min, and the step speed-up time is 85-95 min.

The method can slowly change the temperature gradient of the melting zone of the cone head of the prefabricated rod, reduce the transverse internal stress of the prefabricated rod, reduce the additional attenuation caused by the shearing force caused by the inclination of the cone head of the melting zone of the prefabricated rod and avoid Rayleigh scattering caused by changing the section structure of the refractive index. The breakage of molecular bonds in the optical fiber structure is reduced, the structural defects are reduced, and the loss caused by Rayleigh scattering is greatly reduced. Effectively prevents the microcrack phenomenon caused by the internal stress concentration caused by the quenching of the optical fiber and reduces the microbending loss in the coating process of the optical fiber.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a schematic diagram showing a parallel ring arrangement structure of a wire-drawing copper coil 6 and a heat-insulating copper coil 13 according to the present invention;

FIG. 3 is a graph of 1550 attenuation for an optical fiber according to the invention compared to 1550 attenuation for a conventional technical fiber.

In the figure: 1-rod hanging table, 2-prefabricated rod, 3-wiredrawing metal body, 4-wiredrawing graphite piece, 5-wiredrawing coil lead frame, 6-wiredrawing copper coil, 7-wiredrawing support, 8-cone head melting zone, 9-wiredrawing air cavity, 10-extension tube, 11-heat preservation metal body, 12-heat preservation coil lead frame, 13-heat preservation copper coil, 14-heat preservation support, 15-heat preservation graphite piece, 16-heat preservation air cavity, 17-ceramic tube, 18-cooling tube, 19-tensiometer, 20-coating die holder, 21-one-way valve, 22-filter screen, 23-filter, 24-cache tank, 25-coating tank, 26-curing lamp, 27-traction wheel, 28-take-up reel and 29-optical fiber; 001-wire drawing furnace device, 002-heat preservation furnace device and 003-coating system.

Detailed Description

The invention is further described below with reference to the figures and examples. Referring to fig. 1 and 2, a cone head melting zone 8 of a preform 2 hung below a rod hanging table 1 is located in a wire drawing gas cavity 9 of a wire drawing furnace 001, wherein the wire drawing furnace 001 comprises a wire drawing metal body 3, a wire drawing coil lead frame 5, a wire drawing copper coil 6, a wire drawing support 7 and a wire drawing graphite piece 4. The eddy current generated by the wire-drawing copper coil 6 acts on the wire-drawing graphite piece 4 to generate heat, the conical head melting area 8 is heated, then annealing treatment is carried out through the extension pipe 10, the optical fiber needs to pass through the holding furnace device 002 for better annealing treatment of the optical fiber due to the fact that the wire-drawing speed is too high, wherein the upper half part of the holding furnace device 002 is composed of a heat-insulating metal body 11, a heat-insulating coil lead frame 12, a heat-insulating copper coil 13, a heat-insulating support 14 and a heat-insulating graphite piece 15. The lower half of the optical fiber holding furnace device 002 is composed of a ceramic tube 17. The heat preservation furnace device 002 has an internal optical fiber channel formed by a heat preservation air cavity 16. The micro-crack phenomenon caused by the internal stress concentration caused by the rapid cooling of the optical fiber can be effectively prevented through the processes. The optical fiber from the holding furnace device 002 is coated after passing through the cooling tube 18, wherein the tension meter 19 is mainly used for detecting the tension of the optical fiber and adjusting and controlling the rod feeding speed of the preform 2 and the furnace temperature of the drawing furnace device 001. The coating used by the optical fiber 29 before entering the coating die holder 20 passes through the coating system 003, the coating system 003 having a coating tank 25, a buffer tank 24 for buffering the coating, a filter 23 for filtering air bubbles/impurities, a check valve 21 for preventing the backflow of the coating, and a filter screen 22 for filtering the coating again. After passing through the coating die holder 20, the optical fiber 29 is cured by the curing lamp 26. Finally the fiber 29 passes through the traction wheel 27 into the take-up reel 28.

(1) Parallel ring coil induction wire drawing furnace with increased heating zone:

the structure is characterized in that 1 turn of the wire-drawing copper coil 6 in the wire-drawing furnace is added on the original basis, the wire-drawing copper coil 6 is transformed into a parallel annular form (as shown in figure 2) from the original spiral form, the temperature field in the wire-drawing furnace device 001 is prolonged by increasing the number of turns, the temperature gradient of the cone head melting zone 8 can be slowly changed, the length of the cone head melting zone 8 is prolonged, the diameter of the cone head melting zone 8 in each unit direction is slowly changed, and the transverse internal stress of the cone head melting zone 8 is reduced. The wire-drawing copper coil 6 is changed into a parallel annular arrangement form (as shown in figure 2) from an original spiral form, mainly because the perpendicularity of an electromagnetic field generated inside the parallel annular arrangement form coil is better, and the influence of intermolecular additional shearing force on the refractive index profile structure of the preform caused by nonuniform heating around the cone head melting area 8 due to the inclination of a temperature field can be avoided. This can reduce additional attenuation due to shear force caused by the inclination of the cone head melting region 8, and can prevent rayleigh scattering caused by changing the refractive index profile structure.

(2) Forming and controlling a conical head in the wire drawing speed-up process:

the wire drawing speed-up process is the forming process of the cone head melting area 8. The proper rod feeding speed, the proper temperature rise and the proper take-up speed gradient are the keys for controlling the forming and reducing the defects of molecular structures caused by the tensile stress of quartz molecules so as to cause the nonuniformity of density distribution. In order to reduce the defect of molecular structure caused by tensile stress of quartz molecules in the drawing process, the speed lag must be kept at a proper gradient, so that each point of the cross section of the cone head melting zone 8 is drawn along the axial direction at a speed gradient in proportion to the flow path of mass points during drawing, otherwise, the original refractive index profile distribution of the preform can generate distortion in the drawing process, thereby causing the defect of the quartz molecular structure and further causing the performance deterioration of the optical fiber. When the temperature of the drawing furnace device 001 is too high, the surface viscosity of the cone head melting area 8 is low. Since the silica glass is a poor thermal conductor, the heat conduction is delayed, and the center temperature of the preform 2 is lowered, resulting in an increase in the velocity delay. When the temperature of the drawing furnace apparatus 001 is too low, the slope of the change in the viscosity of the silica glass with the temperature increases, and the difference in the viscosity between the surface and the axis of the preform 2 increases, resulting in an increase in the speed lag. The velocity lag may also result in large stresses and strains within the optical fiber 29, which may cause molecular bonds in the structure of the optical fiber 29 to break, forming structural defects. According to practical experience, the speed of the prefabricated rod 2 with the diameter of 150mm is increased by about 60min at the rod feeding speed of 2mm/min, the prefabricated rod 2 is well formed, the stress of the necking section and the stretching section is fully released in the diameter changing process, and the attenuation of the drawn optical fiber is low. According to the practical experience, the preform 2 with the diameter of 200mm needs about 90min to be subjected to a speed raising process at a rod feeding speed of 1mm/min, the preform 2 is well formed, and the stress of the necking section and the stretching section is released most fully in the diameter changing process, so that the breakage of molecular bonds in the structure of the optical fiber 29 is reduced, the structural defects are reduced, and the loss caused by Rayleigh scattering is greatly reduced.

(3) Holding furnace device:

holding furnace device 002 characterized by: after the optical fiber 29 is formed in the drawing furnace device 001, the optical fiber enters the cooling tube 18 to be gradually cooled from high temperature (above 800 ℃) to 50-60 ℃ and then enters the coating system 003. Upon cooling in the cooling tube 18, the glass undergoes a change in viscosity from low to high. During this cooling process, the transition temperature T at which the glass of the optical fiber changes from the softened state to the solidified state is critical for the attenuation of the optical fiber. The magnitude of T represents the degree of annealing of the optical fiber 29 during cooling. The lower T, the more complete the stress relief in the glass, and the lower the coefficient of rayleigh scattering caused by density non-uniformity. Under normal conditions of a common wire drawing tower, the temperature of the optical fiber 29 formed in the wire drawing furnace is about 1800 ℃ and the temperature of the optical fiber after passing through an extension tube of 1.5-1.8 meters is about 800 ℃, and the defect of a molecular structure is caused because the internal stress cannot be fully released in the cooling process of the optical fiber 29 with a high wire drawing speed, so that the attenuation of the optical fiber with uneven density distribution is large. After the extension pipe 10 is transformed, the length is shortened to 0.8-1.2 m, and the temperature of the optical fiber 29 out of the extension pipe 10 is about 1200 ℃. Therefore, a heat preservation furnace device 002 is installed below the optimized shortened extension pipe 10, the upper half part of the heat preservation furnace device is heated by a heat preservation copper coil 13 for heating, the heat preservation copper coil 13 is arranged in a parallel ring shape (as shown in figure 2), the length of the heat preservation copper coil is 0.6-1.0 meter, and the number of turns is 4-7 turns; the optical fiber 29 is heated to 1300-1400 ℃ again, so that the temperature difference between the inside and the outside of the optical fiber 29 is reduced, the quartz crystal grains are refined, the crack extension is reduced, and the residual internal stress inside is fully released again. The lower half of the holding furnace device 002 is formed by the ceramic tube 17, the optical fiber 29 is subjected to heat preservation and annealing again, the length of the optical fiber is 0.7-1.3 m, and the temperature of the optical fiber 29 discharged from the ceramic tube 17 at the lower half of the holding furnace device 002 is slowly reduced to 800-900 ℃. Through the above process, the micro-crack phenomenon caused by the internal stress concentration due to the rapid cooling of the optical fiber 29 can be effectively prevented, and the scattering loss of the optical fiber can be finally reduced.

(4) Coating system bubble/impurity removal device:

the coating system 003 is characterized by: the buffer tank 24 is sufficiently static to remove air bubbles from the coating material, and ensures that air bubbles do not immediately enter the coating die holder 20 when the coating material tank 25 is empty. Since the coating material in the coating system 003 is likely to generate gel and impurities in the coating material due to heat curing during the long-time drawing process, the coating material is likely to enter the coating die holder 20, causing various coating defects to occur to affect the performance of the optical fiber 29. The filter screen 22 is capable of further disposing of air bubbles/impurities during the passage of the filter 23 to the coating die holder 20. The check valve 21 is opened at a pressure of 0.05MPa to prevent the generation of a backflow bubble when the coating material at the coating die holder 20 is returned to the filter 23 during the drawing completion process, and the optical fiber 29 is slightly bent and lost due to a gap between the coating layer and the optical fiber caused by the bubble during the drawing again. Through the treatment of the coating system 003, the coating entering the coating die holder 20 can be ensured to have no bubbles, no impurities and the like, and the coating problem is reduced, namely the microbending loss in the optical fiber coating process is reduced.

Through the equipment selection and modification and the process control, a front-and-back two-section wire drawing comparison experiment is carried out on the same rod, and the 1550 waveband attenuation value is selected to be compared with the 1550 attenuation of the conventional process wire drawing (as shown in figure 3). Through the improvement of the manufacturing method, the wire drawing copper coil 6 of the wire drawing furnace is replaced by a parallel annular type, the former spiral type and 7 turns are changed into 8 turns, the forming control of a cone head melting area in the wire drawing speed-up process, the extension pipe of the wire drawing furnace is shortened from 1.8 meters to 1.0 meter, a heat preservation furnace device is added below the extension pipe of the wire drawing furnace, and the influence of bubbles/impurities on the attenuation of the optical fiber 29 is reduced by utilizing a bubble/impurity removing device of the coating system 003 device. Production equipment aspect: a parallel coil induction wire drawing furnace device 001 with an increased heating zone, an optical fiber holding furnace device 002 and a coating system 003 bubble/impurity removal device. Five sleeve Rods (RIC) are respectively tested, and the attenuation data of the optical fiber 29 respectively drawn by the front section and the rear section of the same preform rod 2 at the 1550nm waveband are analyzed in a statistical mean manner from the former 0.184-0.196 dB/KM and the total mean value of 0.189dB/KM to the current 0.177-0.185 dB/KM and the total mean value of 0.182 dB/KM. The average value is reduced by 0.007dB/KM, so that the market demand can be better met.

In the forming process from the prefabricated rod 2 to the optical fiber 29, the invention ensures that quartz molecules do not draw tensile stress to cause the defect of molecular structure, thereby causing the nonuniformity of density distribution and simultaneously preventing the microbending loss caused by the strain of the surface layer of the optical fiber due to the nonuniform inner coating of the optical fiber.