JPH0692665A - Production of fluoride glass optical waveguide - Google Patents

Abstract

PURPOSE:To decrease the eccentricity of a core of a fluoride glass optical waveguide produced by inserting a fluoride glass rod into a fluoride glass pipe and integrating the components by selecting the maximum outer diameter and the minimum outer diameter of the rod and the inner diameter of the pipe to satisfy a specific relationship. CONSTITUTION:A fluoride glass having a composition of ZrF4-BaF2-LaF3-AlF3- NaF, etc., and doped with specific amounts of compounds containing rare earth elements such as Pr (e.g. PrF3) and PbF2 is melted and cast into a mold to form a core rod having prescribed maximum outer diameter d1 and minimum outer diameter d2. Separately, a pipe for clad having a prescribed inner diameter D is produced from a ZrF4-BaF2-LaF3-AlF3-NaF fluoride glass doped with a specific amount of HfF4, etc. The rod for core is inserted into the pipe for clad in such a manner as to satisfy the relationships of 0<=(D-d1)<=0.2mm, d1>=d2>=(d1)/2 and a core eccentricity of <=0.2%. The assembly is integrated by heating in an inert gas such as Ar and drawn to obtain the objective fluoride glass optical waveguide for light amplification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplification optical waveguide (including an optical fiber) used mainly in a repeater section of an optical communication system.

[0002]

2. Description of the Related Art An optical communication system comprises a light emitting section, a relay section and a light receiving section, and an optical waveguide is connected between them. The relay section compensates for transmission loss and pulse spread when the transmitted signal light propagates through the optical waveguide. Conventionally, the configuration is such that the signal light is once converted into an electric signal and compensated, and then converted into a signal light using a semiconductor laser. However, this method has a drawback in that it is expensive because the structure of the apparatus is extremely complicated. Therefore, recently, it has been attempted to fabricate an optical waveguide with a core glass doped with a rare earth element as a core portion and directly amplify the signal light having a wavelength of 1.3 μm or 1.55 μm by this optical waveguide.

Of these rare earth elements, ZBLAN (ZrF ₄ -BaF ₂ ) having a core portion doped with praseodymium (Pr) is particularly preferable.
Single-mode optical waveguides made of -LaF ₃ -AlF ₃ -NaF) -based fluoride glass have attracted attention because they efficiently amplify signal light with a wavelength of 1.3 μm. As a method of manufacturing a base material for a fluoride glass optical waveguide, rods and pipes are manufactured by melting raw materials and casting them into a mold, and heating these materials.
A method in which, after being integrated, the film is stretched to a predetermined outer diameter is common.

[0004]

The diameter of the core portion of the optical waveguide for optical amplification is determined by the density of incident light, which determines the gain of amplification.
Compared with other optical waveguides, it is about 2 to 4 μm smaller (for example, the core diameter of the optical waveguide for optical communication is about 10 μm).
It is not easy to connect the optical amplification optical waveguides.
Further, even if connection is possible, since the core part diameter is small and it is difficult to butt, the connection loss tends to be large.
However, in practical use, an optical waveguide having a connection loss as small as possible is desirable.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical amplification optical waveguide having a small connection loss and a wavelength of amplified light in the 1.3 μm band. According to the present invention, in the method for producing a fluoride glass optical waveguide, when the rod made of fluoride glass is inserted into a pipe made of fluoride glass and integrated, the maximum outer diameter of the rod is d1, the minimum. Assuming that the outer diameter is d2 and the inner diameter of the pipe is D, d1, d2 and D are 0 ≦ (D-d1) ≦ 0.2mm and d1 ≧ d2.
There is provided a method for manufacturing a fluoride glass optical waveguide, which is characterized by satisfying a relation of ≧ (d1) / 2.

[0006]

[Function] In order to provide a 1.3 μm band optical amplification optical waveguide with a small connection loss, as a result of an examination of a conventional method for producing a base material for an optical waveguide, the main factor is the eccentricity of the core portion with respect to the clad portion (hereinafter Simply called core eccentricity) was considered. Further, the cause of core eccentricity is presumed as follows. That is, in the conventional manufacturing method, when the core rod and the cladding pipe are heated and integrated, the thermal contraction rates of the two differ, so the center of the cladding and the center of the core of the obtained optical waveguide preform are misaligned. It was thought that there was something to do with it. Originally, it may be necessary to find the composition of the rod for the core part and the pipe for the clad part with a small difference in heat shrinkage, but the composition of both currently used is not suitable for performance due to problems such as stability. I can't find anything else to change, so I have to use it as it is.

Therefore, a method of reducing the core eccentricity without changing the compositions of the core rod and the cladding pipe was considered. As a concrete value, it is known that the core eccentricity is preferably 0.2% or less. As a result of various studies to achieve this value, when the core rod is inserted into the cladding pipe, the core rod should be fixed so that the center of the core rod and the center of the cladding pipe match as much as possible. I understood it. Specifically, if the gap between the core portion rod and the clad portion pipe is made smaller in the maximum outer diameter portion, the core portion rod becomes difficult to move in the clad portion pipe. That is, if the center of the core rod and the center of the clad pipe are made to coincide with each other, the center of the core and the center of the clad can be easily coincided with each other even in the minimum outer diameter portion of the rod for the core.

Further, when a rod is usually manufactured, a portion having a uniform outer diameter and a tapered portion are formed in a step of stretching or mechanically polishing a thick rod. Therefore, if this tapered portion can also be used, it is more economical. Therefore, in the case of the tapered rod, the range of the minimum outer diameter with respect to the maximum outer diameter was examined as well as the practical use as well as the uniform outer diameter.

[0009]

EXAMPLES Hereinafter, experimental examples of the present invention will be described in detail. 20
A ZBLAN-based fluoride glass doped with 00 ppm Pr, specifically PrF ₃ and 8 mol% PbF ₂ was prepared, and the ZBLAN-based fluoride glass was melted and cast into a mold to have an outer diameter of
A 10 mm core rod was produced. The core rod was stretched in an inert gas, specifically, argon gas to prepare eight types of core rods having different shapes. Also 40m
ZBLAN-based fluoride glass doped with ol% HfF ₄ was produced, melted and cast into a rotating mold to produce an outer diameter of 10 m.
16 m pipe with inner diameter 3.5 mm and length 140 mm
This was made. The core rods with different shapes are inserted into the clad pipe, and these are heated to about 300 ° C in an inert gas, specifically, argon gas to be integrated, and then further stretched to form a clad portion. A rod for core part with a core was prepared. In order to secure the thickness of the clad part, the rod for the core part with the clad part and the rest of the pipe for the clad part are integrated and stretched in the same manner as the first time, and eight ZBLA
A base material for N-based fluoride glass optical waveguide was prepared. The ZB
A base material for a LAN-based fluoride glass optical waveguide was drawn to obtain an optical waveguide having a clad diameter of 125 μm and a core diameter of 2 to 5 μm. The optical waveguide was cut, and the eccentricity of the core portion was measured with a microscope.

As shown in Table 1, in the process of manufacturing an optical waveguide, when a rod made of a tapered fluoride glass is integrated with a pipe by using a pipe, the maximum outer diameter of the rod is d1 and the minimum outer diameter is It was found that the core eccentricity can be 0.2% or less when d2 and D are the inner diameter of the pipe and they satisfy the relations of 0 ≦ (D-d1) ≦ 0.2 mm and d1 ≧ d2 ≧ (d1) / 2. If the eccentricity of the core part is 0.2% or less, the connection loss is sufficiently small and no problem occurs in practical use.
In the above experiment, the cladding pipe was inserted twice, but it goes without saying that if the cladding pipe is made thicker, it can be performed in one step.

[0011]

[Table 1] * 1 The outer diameter (D) of the pipe is 10.0 mm and the inner diameter is 3.5 mm. In the table
d1 is the maximum diameter of the rod, d2 is the minimum diameter, and 1 formula is 0 ≦ (D-d1)
≦ 0.2 (mm), Formula 2 is d1 ≧ d2 ≧ (d1) / 2. * 2 Numbers 1, 5 and 6 are examples of the present invention, and others are comparative examples.

[0012]

According to the present invention, when the rod made of fluoride glass and the pipe are heated and integrated in the process of manufacturing the optical waveguide, the maximum outer diameter of the taper type rod is set.
Let d1, minimum outer diameter be d2, pipe inner diameter be D,
0 ≦ (D-d1) ≦ 0.2 mm and d1 ≧ d2 ≧ (d1) / 2 are satisfied by the manufacturing method of the fluoride glass optical waveguide, the eccentricity of the core is small, that is, the connection loss is small. A fluoride glass optical waveguide for optical amplification can be obtained.

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G02B 6/00 376 B 7036-2K 6/12 N 9018-2K 6/16 7036-2K

Claims (1)

[Claims] 1. A method for producing a fluoride glass optical waveguide, wherein when a rod made of fluoride glass is inserted into a pipe made of fluoride glass and integrated, a maximum outer diameter of the rod is d1 and a minimum outer diameter is If the diameter is d2 and the inner diameter of the pipe is D, then d1, d2 and D are 0 ≦ (D-d1) ≦ 0.2 mm and
A method of manufacturing a fluoride glass optical waveguide, characterized by satisfying a relationship of d1 ≧ d2 ≧ (d1) / 2.