JPS60122744A - Manufacture of simple-mode fiber - Google Patents

Abstract

PURPOSE:To manufacture easily a simple-mode fiber having a large thickness ratio of the clad to the core by inserting a core rod attached with a clad into a quartz tube having an innner lining layer of a material identical to the clad, heating, and wiredrawing in manufacturing a parent material for the simple- mode fiber. CONSTITUTION:A core rod attached with a clad having 4-5 deposition ratio of the core to the clad is manufactured as a parent material for a simple-mode fiber. The clad core rod 3a attached with a clad layer 2a having the thickness about 1-2 times the radius of a core 1 on the outer circumference of the core 1 is inserted into a quartz tube 4a whose inner wall is lined with a rigid glass 8 consisting of phosphorus oxide silica or fluorine oxide silica and having the same composition as the clad 2a. The thickness is regulated to >=2 times the radius of the core 1. The whole body is heated by a heater 5, and the clad layer 2a and the glass 8 are fused into a body which is wiredrawn. A simple-mode fiber 6a having a large thickness ratio of the clad layer to the core can be easily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background and Objects of the Invention] The present invention relates to a method of manufacturing a single mode fiber (hereinafter referred to as 3M fiber).

The vapor phase attachment method (VAD method) is well known as a manufacturing method for reforming SM fibers. Conventionally, the core and crat glass materials and carrier gas were supplied from different burners, and the core and crat were supplied from different burners. The ratio of the thickness of the deposited layer to that of the cladding was also set to about 4 to 5 times. Therefore, when attempting to increase the effective thickness of the core layer to increase its length, the outer diameter of the soot would become large, making the transparent vitrification process difficult. The reform was drawn using the rod-in-tube (RT) method to produce 3M fiber.

That is, as shown in FIG. 1, a quartz tube 4 for size adjustment is jacketed around a thick-walled core rod 3 with a cladding in which the ratio of the thickness of the deposited layer between the core l and the crat 2 is 4 to 5 times, The clad core rod 3 and the quartz tube 4 were heated and welded together in a carbon furnace 5 and drawn to a predetermined diameter to produce a fiber 6.

In the case of this conventional manufacturing method, quartz glass is usually used as the material for the thick cladding 2, and the use of a large amount of glass that is effective in lowering the melting point, such as fused glass, is important for example in the shape of the soot. It was difficult because of problems such as deformation, cracking, and volatilization. Furthermore, since the composition of the conventional fiber 6 is close to quartz, it is necessary to draw the fiber at a sufficiently high temperature in order to obtain appropriate fiber strength, which causes the problem of OH groups, which are hydroxyl groups, diffusing from the quartz tube 4 to the core 1. there were.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a method for manufacturing a single mode fiber that facilitates the manufacture of a cladding (=I cocoad).

[Summary of the invention]

That is, in the present invention, a cladding core rod is produced by providing a cladding on the outer peripheral side of the core, and then this cladding core rod is inserted into a quartz tube, and the core rod is heated and welded together while being drawn to a predetermined diameter. In the method for manufacturing a mode fiber, the cladding is provided on the outer periphery of the core and has a thickness of about 1 to 2 times the radius of the core.
For each ζJ, an inner layer of synthetic glass having approximately the same refractive index as the cladding layer is deposited on the inner surface of the quartz tube to a depth at least twice the radius of the core by a chemical vapor deposition method. As a result, the cladding provided on the outer circumferential side of the core is formed separately on the outer circumference of the core and the inner surface of the quartz tube.

〔Example〕

The present invention will be explained below based on the illustrated embodiments. FIG. 2 shows an embodiment of the present invention. Note that parts that are the same as those in the conventional system are given the same reference numerals, and therefore their explanations will be omitted. In this embodiment, the clad 7 is a clad N2a provided around the outer periphery of the core 1 and whose thickness is approximately 1 to 2 times the radius of the core 1;
On the inner surface of the quartz tube 4a, a synthetic glass having approximately the same refractive index as the cladding F12a is deposited using a chemical vapor deposition method to form an inner burr layer 8 that is at least twice the radius of the core I.
It was formed with. By doing this, the cladding 7 provided on the outer circumferential side of the core l is connected to the outer circumference of the core 1 and the quartz tube 4a.
It is possible to obtain a manufacturing method of the 5M fiber 6a in which the cladded core rod 3a can be easily manufactured.

That is, an inner burr N8 doped with fluorine and phosphorus is formed on the inner surface of the quartz tube 4a, and the cladded core rod 3a is inserted into the inner burr N8 and these are welded and integrated, and at the same time, a wire is drawn to a predetermined outer diameter. Since the cladding 7 on the outer circumferential side of the core 1 is formed of the cladding layer 2a provided on the outer periphery of the core 1 and the synthetic glass inner burr N8 provided on the inner surface of the quartz tube 4a,
There is no need to increase the thickness of the cladding N2a provided on the outer periphery of the core 1, making it easier to manufacture the cladded core rod 3a, and ensuring a sufficient substantial thickness of the core 1. T: I can. It has become possible to use a large amount of fluorinated glass, etc., and core 1. Cladding layer 2
a. By appropriately combining the glass compositions of the inner burr layer 8, 5M fibers 6a having various refractive index distributions can be obtained.

That is, the refractive index distribution of the 5M fiber 6a shown in FIG. 3 is a distribution of a germa-doped/silica-doped/fluorine-doped structure in the order of core 1/crut layer 2a/inner burr layer 8, and is shown in FIG. are similarly germanium/fluorine/silica or fluorine composition distributions, and those shown in Figure 5 are likewise silica/fluorine/fluorine/fluorine composition distributions.
Among these, the radiation resistance characteristics of the transmission loss of the 5M fiber 6a having the configuration shown in FIG. 5 were particularly good. Also these 8M fiber 6&
has sufficient strength even when the drawing temperature is approximately 50°C lower than conventional wires, and has low absorption loss due to OH groups, which are hydroxyl groups, which have a large effect on the transmission loss of the 1.3μ sheath band, resulting in low loss. there were.

As described above, according to this embodiment, the production of the cladding 7 provided on the outer peripheral side of the core 1 is simplified, and the yield is improved. Since the material of the cladding 7 can be selected freely to some extent, transmission loss and dispersion can be improved.

It has low loss performance due to low OH grouping.

〔Effect of the invention〕

As described above, the present invention provides a single mode fiber manufacturing method in which the cladding provided on the outer peripheral side of the core is made separately, making it easier to manufacture a cladded core rod. − can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a drawing state in a conventional single mode fiber manufacturing method, and FIG. 2 is a perspective view showing a drawing state in an embodiment of the single mode fiber manufacturing method of the present invention. , and FIGS. 3 to 5 are refractive index distribution diagrams of a single mode fiber according to an embodiment of the method for manufacturing a single mode fiber of the present invention. l: core, 2a: cladding layer. 3a: core rod with cladding, 4a: quartz tube. 5: Carbon furnace. 6a: Fiber (5M fiber), 7: Clad. 8: Inner burr layer.

Claims (1)

[Claims] 0) A cladded core rod is made by providing a cladding on the outer peripheral side of the core, and then this cladded core rod is inserted into a quartz tube, and the wire is heated and welded together to a predetermined diameter. In the method for manufacturing a single mode fiber, the cladding includes a cladding layer provided around the outer periphery of the core and having a thickness of about l to twice the radius of the core, and the cladding layer on the inner surface of the quartz tube. A single mode fiber characterized in that it is formed of a rigid glass having a refractive index that is approximately the same as that of the core, and a hollow layer that is deposited by chemical vapor deposition to a radius of at least twice the radius of the core. Production method. (2) The method for manufacturing a single mode fiber according to claim 1, wherein the rigid glass is phosphorous oxide silica or fluorine oxide optical silica.