Optical fiber and method of making the same

Abstract

An optical fiber preform 2 having a viscosity ratio Reta=eta0 / etat of 2.5 or less between the core average viscosity eta0 and the total average viscosity etat is prepared, and is drawn by a drawing furnace 11 so as to yield an optical fiber 3, which is then heated to a temperature within a predetermined range so as to be annealed by a heating furnace 21 disposed downstream the drawing furnace 11. Here, upon annealing in the heating furnace 21, the fictive temperature Tf within the optical fiber lowers, thereby reducing the Rayleigh scattering loss. At the same time, the viscosity ratio condition of Reta<=2.5 restrains the stress from being concentrated into the core, thereby lowering the occurrence of structural asymmetry loss and the like. Hence, anoptical fiber which can reduce the transmission loss caused by the Rayleigh scattering loss and the like as a whole, and a method of making the same can be obtained.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to an optical fiber for transmitting light, and a method of making the same.[0003] 2. Related Background Art[0004] In the transmission of light using an optical fiber, the transmission loss (Rayleigh scattering loss) caused by Rayleigh scattering within the optical fiber becomes problematic. For this problem, an optical fiber which can reduce the Rayleigh scattering loss or a method of making the same has been proposed.[0005] For example, "Sakaguchi, the Transactions of the Institute of Electronics, Information and Communication Engineers, 2000 / 1, Vol. J83-C, No. 1, pp. 30-36", discloses that the Rayleigh scattering loss in an optical fiber can be reduced by annealing the optical fiber after drawing. Namely, the Rayleigh scattering intensity within glass is not constantly fixed by materials thereof, but depends on a fictive temperature Tf which is a virtual temperature indicative of the randomness in the state of a...

AI Technical Summary

Benefits of technology

[0031] While the optical fiber preform (optical fiber) has a configuration restraining the stress from being concentrated into the core, tension control is effected such that the tension at the time of drawing is held within a preferable tension value range of 0.05 to 0.20 N, whereby an optical fiber having reduced the transmission loss can be obtained reliably.

Problems solved by technology

In the transmission of light using an optical fiber, the transmission loss (Rayleigh scattering loss) caused by Rayleigh scattering within the optical fiber becomes problematic.

However, conventionally proposed manufacturing methods which are effective in lowering Rayleigh scattering loss, such as the above-mentioned manufacturing method having an annealing process using a heating furnace, and the like are not considered to fully realize the reduction of transmission loss in the optical fiber.

In particular, there has been a problem that even optical fibers prepared by the same manufacturing method yield a case where the transmission loss reducing effect is obtained and a case where the transmission loss is hardly reduced or increases to the contrary, whereby the transmission loss reducing effect cannot be obtained reliably.

Here, the dependence of transmission loss upon tension in thus obtained optical fiber becomes greater, thereby causing the transmission loss to increase.

In this case, however, a long heater is required to reheat the cooled optical fiber.

If the viscosity ratio R.eta. is large as such, a sufficient transmission loss reducing effect cannot be obtained even when the optical fiber is made by a manufacturing method having a Rayleigh scattering loss reducing effect such as the manufacturing method shown in FIG. 1 carrying out annealing by use of a heating furnace after drawing or the like.

Also, there is a possibility that the effect of reducing the Rayleigh scattering loss is not fully obtained due to the stress concentration and the like.

When the amount of addition of Ge or the like is too large within the core, by contrast, the optical fiber becomes inappropriate due to the increase in transmission loss caused by additives, and the like.

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