JPH0750211B2 - Polarization-maintaining optical fiber coupler manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is capable of manufacturing a polarization maintaining optical fiber coupler with low crosstalk by preventing misalignment of the polarization main axis during fusion. The present invention relates to a wave holding optical fiber coupler manufacturing apparatus.

[Prior Art] A polarization-maintaining optical fiber coupler created by using a linear polarization-maintaining optical fiber having a function of maintaining polarization, in order to maintain polarization in the coupler, two linear polarization-maintaining optical fibers are used. It is necessary to perform fusion splicing and stretching with the polarization main axes of the fibers aligned in parallel. As an example of the linear polarization maintaining optical fiber, FIG. 3 shows a stress applying polarization maintaining optical fiber having a stress applying portion and maintaining polarization by stress birefringence. In the figure, 31 is a core, 32 is a stress applying portion, and 33 is a clad. This fiber has two principal axes of polarization that are orthogonal to each other as shown in FIG. Therefore, the polarization main axes of the two fibers can be aligned in parallel by detecting the position of the stress applying portion. Conventionally, in order to perform smooth drawing without applying unreasonable tension to the optical fiber that is fused and drawn,
An optical fiber coupler manufacturing apparatus provided with a drawing table that floats by gas pressure has been proposed (Japanese Patent Laid-Open No. 60-232515). However, the conventional apparatus has only one heating burner for fusing the optical fiber, and thus heating is performed only from one direction of the optical fiber. FIGS. 4 (A) to 4 (C) show a conventional heating method and a fusion state of optical fibers by the conventional method. That is, as shown in FIG. 4 (A), the two optical fibers 42A and 42B before fusion are bonded.
Even if the polarization main axes of are aligned in parallel, the burner 41 has only one flame outlet, and the heating is asymmetrical.
As shown in FIG. 3, the polarization-maintaining optical fibers 42A and 42B start to melt from the portion near the burner 41, and the polarization main axes of the two optical fibers deviate from the parallel state. As a result, as shown in FIG. 4 (C), in the state 43 after fusion, the polarization main axis deviation θ = θ ₁ + θ ₂ remains.

The crosstalk (CT), which indicates the polarization-maintaining ability of the polarization-maintaining optical fiber coupler, is approximately expressed as CT = 10log [tan ² θ] (1) with respect to the deviation θ of the polarization main axis. FIG. 5 shows the result of calculating the θ dependence of crosstalk by the equation (1). Crosstalk to -20
θ ≦ 5 ° and crosstalk −30 dB to keep dB below
In order to be below, θ ≦ 1.8 ° is required.

In the conventional device, as shown in FIG. 4, it is difficult to suppress the axial displacement due to fusion to 2 ° or less, and the crosstalk-30
It was not possible to make a polarization-maintaining optical fiber coupler with dB or less with good reproducibility.

[Problems to be Solved by the Invention] An object of the present invention is to solve the problem of misalignment of the polarization main axis during fusion and to manufacture a polarization maintaining optical fiber coupler with low crosstalk. It is to provide a coupler manufacturing apparatus.

[Means for Solving the Problems] In order to achieve such an object, the optical fiber coupler manufacturing apparatus of the present invention is configured so that 22 polarization-maintaining optical fibers are partially fused and stretched in the longitudinal direction. In an apparatus for producing an optical fiber coupler, a line perpendicular to a plane including cores of the two polarization-maintaining optical fibers aligned close to each other in parallel and passing substantially through a point to be fused It is characterized in that it is equipped with burners from which flames for fusion are emitted from two opposite directions.

[Operation] In the present invention, the fusion heating is performed symmetrically, and the deviation of the polarization main axis during fusion is small, so that a polarization maintaining optical fiber coupler with low crosstalk can be produced.

EXAMPLES The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic view of an embodiment of the present invention.

1A and 1B are burners for fusion, 2 is a burner support, 3A and 3B are polarization maintaining optical fibers, and 4A and 4B are optical fiber fixing devices. Five
A and 5B are made to float by the gas pressure on the drawing table.

2A and 2B show the steps of disposing and fusing a pair of optical fibers and burners. As shown in FIG. 2, the fusion burners 1A and 1B are perpendicular to the plane including the cores 6A and 6B of the two polarization-maintaining optical fibers 3A and 3B, and the two polarization-maintaining optical fibers 3A. , 3B are arranged so as to face each other substantially along a straight line 8 passing through the adjacent portions.

By heating and melting the adjacent parts of the polarization maintaining optical fibers 3A and 3B by the oxygen / propane flames from the burners 1A and 1B, a symmetrical heating state can be realized. Therefore, as shown in FIG. The state in which 7A and 7B are aligned in parallel and before fusion is maintained as it is, and fusion is performed as shown in FIG. 2 (B). The axis deviation during fusion bonding in this example could be suppressed within 1 °.

After the fusion bonding, heating and stretching are performed while applying a constant tension to the polarization maintaining optical fibers 3A and 3B by the stretching tables 5A and 5B that are floated by gas pressure, and the stretching is finished at a desired coupling ratio. The polarization-maintaining optical fiber coupler produced in this way had a reproducible crosstalk of 30-dB or less, and a polarization-maintaining optical fiber coupler with low crosstalk was realized.

In the present embodiment, it is needless to say that an optical fiber coupler which is less likely to be twisted or bent at the time of fusion can be produced even when a normal optical fiber coupler is produced.

[Effects of the Invention] As described above, in the present invention, fusion heating is performed symmetrically, and the polarization main axis shift during fusion is small, so a polarization-maintaining optical fiber coupler with low crosstalk is produced. There is an advantage that you can.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, FIGS. 2 (A) and 2 (B) are views showing a process of fusing a polarization maintaining optical fiber according to an embodiment of the present invention, and FIG. Sectional views of the wave-holding optical fiber, FIGS. 4 (A), (B), and (C) are diagrams showing a fusion process by a conventional manufacturing apparatus, and FIG. 5 is a crosstalk dependence on an axis deviation θ. FIG. 1A, 1B …… Burner for fusion, 2 …… Burner support for fusion, 3A, 3B, 42A, 42B …… Polarization-maintaining optical fiber, 4A, 4B …… Fiber fixing base, 5A, 5B …… Extending stand , 6A, 6B, 31 …… Core, 7A, 7B, 32 …… Stressing part, 8 …… Straight line, 21,43 …… Fused part, 33 …… Clad, 41 …… Burner.

Claims (1)

[Claims] 1. A core, a clad surrounding the core and having a refractive index lower than that of the core, and a thermal expansion coefficient different from the thermal expansion coefficient of the clad disposed on opposite sides of the core in the clad. An apparatus for producing an optical fiber coupler by using two polarization-maintaining optical fibers each of which has a stress imparting section, and fusion-bonding and extending a part of the two polarization-maintaining optical fibers in the longitudinal direction. A burner in which flames for fusion are emitted from two opposing directions which are perpendicular to a plane including cores of the two polarization-maintaining optical fibers closely aligned and substantially along a straight line passing through a point to be fused. A polarization-maintaining optical fiber coupler manufacturing apparatus comprising: