JP2015174796A - Method for manufacturing optical fiber and optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber small in Rayleigh scattering loss and connection loss with a common optical fiber although having a relative index difference between a core and clad required in order to maintain an optical waveguide structure and low in cost as compared with a pure quartz core optical fiber, and to provide the optical fiber.SOLUTION: The method for manufacturing an optical fiber includes drawing an optical fiber preform 103, having 0.32% or less of a relative refractive index difference between a core part 101 consisting of a quartz glass in which germanium is added and a clad part 102 formed in the periphery of the core part 101 and consisting of a pure quartz glass, by a drawing tension of 3.5 N or more to manufacture an optical fiber 105. The optical fiber 105 is obtained by the method for manufacturing an optical fiber and has a transmission loss of 0.18 dB/km or less when light having a wavelength of 1550 nm is transmitted.

Description

  The present invention relates to an optical fiber manufacturing method and an optical fiber including a core made of quartz glass to which germanium is added.

  The optical fiber has an optical waveguide structure in which the refractive index of the core is relatively higher than the refractive index of the cladding, and the light is confined and transmitted using the total reflection at the interface between the core and the cladding.

  The most popular general optical fiber has a core made of quartz glass doped with germanium for increasing the refractive index so that the refractive index of the core is higher than that of the cladding, and the periphery of the core. And a clad made of pure quartz glass.

  The refractive index of the core depends on the germanium concentration. When the germanium concentration increases, the refractive index of the core also increases, and the relative refractive index difference between the core and the cladding increases. In order to satisfy practical bending characteristics and maintain the optical waveguide structure, a certain degree of relative refractive index difference is required. In general optical fibers, the optical waveguide structure can be increased by increasing the germanium concentration. The relative refractive index difference necessary for maintaining the above is ensured.

  However, the Rayleigh scattering loss, which accounts for about 80% to 90% of the transmission loss caused by the optical fiber, depends on the fluctuation of the glass composition. Therefore, the higher the concentration of germanium, the easier the fluctuation occurs. Loss will increase.

  In order to reduce Rayleigh scattering loss while maintaining the optical waveguide structure, a core made of pure quartz glass and a clad made of quartz glass formed around the core and added with fluorine for lowering the refractive index Have been proposed (for example, see Patent Document 1).

  This pure silica core optical fiber is made of pure silica glass, so there is no principle of Rayleigh scattering loss due to fluctuations in the glass composition, and long-distance transmission applications such as submarine cables that connect remote islands without relaying. It is suitable for.

JP 2010-64915 A JP-A-2-133333 JP-A-7-198978

  However, when producing a pure silica core optical fiber, it is difficult to soot combine the core portion and the clad portion of the optical fiber preform at the same time as when producing a general optical fiber, It is necessary to manufacture the core part and the clad part in separate processes and integrate them by the rod-in-tube method. Also, the drawing conditions are complicated and the drawing speed is slow, and the size of the optical fiber preform is increased. However, there is a problem that the cost is high. Furthermore, the need for a large amount of fluorine in order to maintain the optical waveguide structure by adjusting only the refractive index of the cladding is also a cause of high cost.

  As described above, a pure silica core optical fiber has a core made of pure silica glass, whereas a general optical fiber has a core made of quartz glass to which germanium is added. When optically connecting a pure silica core optical fiber and a general optical fiber, there is a problem that Fresnel reflection occurs at the connection interface due to the difference in the refractive index of the core in the two, resulting in an increase in connection loss. is there.

  Therefore, an object of the present invention is to reduce the Rayleigh scattering loss and the connection loss with a general optical fiber while having a relative refractive index difference between the core and the clad necessary for maintaining the optical waveguide structure, and to obtain pure quartz. An object of the present invention is to provide an optical fiber manufacturing method and an optical fiber which are low in cost compared to a core optical fiber.

  Invented to achieve this object, the present invention has a relative refractive index difference between a core portion made of quartz glass to which germanium is added and a clad portion made of pure quartz glass and formed around the core portion. This is an optical fiber manufacturing method in which an optical fiber is manufactured by drawing an optical fiber preform of 0.30% or more and 0.32% or less with a drawing tension of 3.5N or more.

  Annealing treatment may be performed after drawing the optical fiber preform.

  The drawing speed is preferably 100 m / min or more.

  In addition, the present invention is an optical fiber obtained through these optical fiber manufacturing methods and having a transmission loss of 0.18 dB / km or less when light having a wavelength of 1550 nm is transmitted.

  According to the present invention, while having the relative refractive index difference between the core and the clad necessary for maintaining the optical waveguide structure, the Rayleigh scattering loss and the connection loss with a general optical fiber are small, and the pure silica core light It is possible to provide an optical fiber manufacturing method and an optical fiber that are low in cost compared to a fiber.

It is a figure explaining the manufacturing method of the optical fiber which concerns on embodiment of this invention. It is a figure explaining the reason for numerical limitation of a relative refractive index difference. It is a figure explaining the reason for the numerical limitation of a drawing tension. It is a figure which shows the relationship between the transmission loss and drawing speed of the optical fiber obtained through the manufacturing method of the optical fiber of FIG.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.

  As shown in FIG. 1, the optical fiber manufacturing method according to the present embodiment includes a core portion 101 made of quartz glass to which germanium is added, and a clad portion made of pure silica glass that is formed around the core portion 101. An optical fiber preform 103 having a relative refractive index difference with respect to 102 of 0.30% or more and 0.32% or less is introduced into the drawing furnace 104, and the heating temperature in the drawing furnace 104 is adjusted, whereby 3.5N or more. The optical fiber 105 is manufactured by drawing with the drawing tension.

  The core portion 101 is a portion that becomes the core of the optical fiber 105, and the cladding portion 102 is a portion that becomes the cladding of the optical fiber 105. The core part 101 and the clad part 102 are produced in a single process by soot synthesis at the same time as the optical fiber preform 103 is produced.

  Here, the reason for limiting each numerical value will be described.

  The reason for manufacturing the optical fiber 105 by drawing the optical fiber preform 103 having a relative refractive index difference of 0.30% or more and 0.32% or less is that the relative refractive index difference is 0.30% as shown in FIG. When an optical fiber 105 is manufactured by drawing less than the optical fiber preform 103, the bending loss of the optical fiber 105 obtained through the optical fiber manufacturing method is defined in ITU-T G.652 which is an international standard. This is because the optical fiber 105 having a relative refractive index difference between the core and the clad necessary for maintaining the optical waveguide structure cannot be obtained.

  Satisfying the upper limit defined in the international standard ITU-T G.652 means that an optical fiber bent in a loop shape with a bending radius of 37.5 mm has a wavelength of 16XX nm (in FIG. 2). , 1650 nm), the bending loss per 100 turns is 0.5 dB or less.

  Further, when the optical fiber 105 is manufactured by drawing the optical fiber preform 103 having a relative refractive index difference exceeding 0.32%, the Rayleigh scattering loss due to the fluctuation of the glass composition increases. . This is because, in order to increase the relative refractive index difference, it is necessary to increase the concentration of germanium, so that the dispersion of germanium in the quartz glass becomes non-uniform and the glass composition tends to fluctuate easily. Yes.

  The reason for manufacturing the optical fiber 105 by drawing the optical fiber preform 103 with a drawing tension of 3.5 N or more is that the optical fiber preform 103 is drawn with a drawing tension of less than 3.5 N, as shown in FIG. In the case where the optical fiber 105 is manufactured, germanium added to the core portion 101 is easily diffused into the clad portion 102 when the optical fiber 105 is manufactured by drawing the optical fiber preform 103, and as a result. This is because the change in the refractive index distribution, that is, the decrease in the relative refractive index difference becomes significant, and the bending loss of the optical fiber 105 obtained through the optical fiber manufacturing method is greatly reduced.

  The optical fiber 105 obtained through the optical fiber manufacturing method according to the present embodiment described so far has its bending loss satisfying the upper limit value defined in ITU-T G.652 which is an international standard. Therefore, it can be said that there is a relative refractive index difference between the core and the clad necessary for maintaining the optical waveguide structure.

  Further, according to the method of manufacturing an optical fiber according to the present embodiment, when the optical fiber 105 is manufactured by drawing the optical fiber preform 103, a decrease in the relative refractive index difference can be suppressed. An optical fiber 105 having a relative refractive index difference between the core and the clad necessary for maintaining the optical waveguide structure is obtained even if the concentration of germanium is lowered in order to reduce the Rayleigh scattering loss due to the fluctuation of the composition. be able to.

  As a result of these, the transmission loss when transmitting light having a wavelength of 1550 nm through the optical fiber 105 obtained through the optical fiber manufacturing method according to the present embodiment is very small, 0.18 dB / km or less. Is possible.

  The optical fiber 105 obtained through the optical fiber manufacturing method according to the present embodiment includes a core made of quartz glass to which germanium is added, and the glass composition of the general optical fiber and the core is the same or similar. Therefore, when optically connecting to a general optical fiber, Fresnel reflection hardly occurs at the connection interface, and connection loss can be minimized.

  Furthermore, according to the method for manufacturing an optical fiber according to the present embodiment, it is possible to use the optical fiber preform 103 produced by simultaneously soot-synthesizing the core portion 101 and the clad portion 102, and draw conditions. Etc., the drawing speed is high, and the optical fiber preform 103 can be easily increased in size. Therefore, it is possible to manufacture the optical fiber 105 at a lower cost than a pure silica core optical fiber. .

  Up to this point, the Rayleigh scattering loss mainly caused by the fluctuation of the glass composition has been considered, but it is known that the Rayleigh scattering loss is caused not only by the fluctuation of the glass composition but also by the fluctuation of the glass density.

  Therefore, in the method of manufacturing an optical fiber according to the present embodiment, it is more preferable that the optical fiber base material 103 is drawn and then the optical fiber 105 is introduced into the annealing furnace 106 to perform an annealing treatment, and the drawing speed is further set to 100 m. / Min or more is desirable.

  By performing the annealing treatment, the fictive temperature of the glass can be lowered to reduce the glass density fluctuation, and the Rayleigh scattering loss due to the glass density fluctuation can be reduced.

  However, in the annealing treatment, since the fictive temperature of the glass can be further lowered by lengthening the treatment time, it is necessary to lengthen the treatment time in order to sufficiently reduce the fluctuation of the glass density.

  Therefore, when annealing treatment is applied to an optical fiber obtained through a general optical fiber manufacturing method, there is a limit to the improvement of the drawing speed, so that the drawing speed is 100 m / min or more. It is difficult to improve production efficiency, and further cost reduction cannot be achieved.

  On the other hand, according to the method of manufacturing an optical fiber according to the present embodiment, as shown in FIG. 4, the transmission loss when transmitting light having a wavelength of 1550 nm is zero even without annealing. Since the optical fiber 105 of .179 dB / km or less can be manufactured, the optical fiber 105 with sufficiently reduced transmission loss can be obtained without increasing the processing time.

  That is, in the optical fiber manufacturing method according to the present embodiment, the annealing process is an additional step, and the optical fiber 105 has a transmission loss of 0.18 dB / km or less when light having a wavelength of 1550 nm is transmitted. This is not an essential process.

  Therefore, when the optical fiber 105 obtained through the optical fiber manufacturing method according to the present embodiment is annealed, the transmission loss can be sufficiently reduced even if the drawing speed is 100 m / min or more. It becomes possible.

  Although the production efficiency is reduced, the transmission loss can be further improved by setting the drawing speed to 100 m / min or less.

  As shown in FIG. 1, the optical fiber 105 obtained through the optical fiber manufacturing method according to the present embodiment is introduced into the coating machine 107 after being annealed, and a coating layer is formed around it. After that, the optical fiber cable 108 is obtained by being wound by a winder (not shown).

  As described above, according to the present invention, while having a relative refractive index difference between a core and a clad necessary for maintaining an optical waveguide structure, a Rayleigh scattering loss and a connection loss with a general optical fiber are provided. Therefore, it is possible to provide an optical fiber manufacturing method and an optical fiber that are small in size and low in cost as compared with a pure silica core optical fiber.

DESCRIPTION OF SYMBOLS 101 Core part 102 Clad part 103 Optical fiber preform 104 Drawing furnace 105 Optical fiber 106 Annealing furnace 107 Coating machine 108 Optical fiber cable

Claims (4)

  An optical fiber mother having a relative refractive index difference of 0.30% or more and 0.32% or less between a core part made of quartz glass to which germanium is added and a clad part made of pure silica glass formed around the core part An optical fiber manufacturing method, wherein an optical fiber is manufactured by drawing a material with a drawing tension of 3.5 N or more.   The method of manufacturing an optical fiber according to claim 1, wherein an annealing treatment is performed after drawing the optical fiber preform.   The manufacturing method of the optical fiber of Claim 1 or 2 which makes a drawing speed 100 m / min or more.   It is obtained through the method for manufacturing an optical fiber according to any one of claims 1 to 3, and has a transmission loss of 0.18 dB / km or less when light having a wavelength of 1550 nm is transmitted. Optical fiber.

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