JPH0439047B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for aligning a panda-type polarization constant optical fiber, and more particularly to a method for aligning a polarization axis before fusing.

[Prior Art] As shown in FIG. 9, the optical panda type fiber 10 is
It is composed of a core 12, a cladding 14, and a stress applying section 16. The core 12 has different refractive indexes in two directions, X and Y, due to the stress applied by the stress applying section 16, and has two polarization axes 18X and Y.

When connecting constant polarization fibers, it is important to match the polarization axes of the two optical fibers to be connected.

One proposed method for this is to capture the light transmitted through the optical fiber with an image sensor (for example, a TV camera), and align the polarization axes so that the brightness distribution of the fiber image captured by the image sensor is the same for the left and right fibers. has been done. (Special request 1986
-Refer to No. 307193).

[Problems to be Solved by the Invention] However, since the above method aims at coarse alignment of the polarization axes of two optical fibers, it is possible to use other methods (for example, far-end monitoring method) for more precise fine alignment.
This must be done according to the following.

[Means for Solving the Problems] The present invention is based on a new recognition of the relationship between slight rotation of an optical fiber and changes in brightness distribution, and is based on a new understanding of the relationship between a slight rotation of an optical fiber and a change in brightness distribution. The feature is that the left and right fibers to be connected are rotated so that the value of the difference between the distances A and B to the line of maximum brightness that appears in the figure -A-B- becomes 0 (zero).

Below, we will first explain the principle (the relationship between the slight rotation of the optical fiber and changes in the brightness distribution),
Next, the actual alignment method will be explained.

[Principle] The optical fiber image obtained on the TV camera by the light transmitted through the optical fiber was simulated by a computer.

Figure 1a shows the results.

The outer diameter of the optical fiber 10 is 125 μm, and the stress applying part 1
6 had a diameter of 30 μm, the refractive index of the cladding 14 was 1.45, and the refractive index of the stress applying portion 16 was 1.44.

Parallel light ray 19 incident from the left enters optical fiber 1
It is refracted at the boundary with 0. The light is applied to the stress applying section 16
It is refracted again at the boundary. The angle of refraction was calculated using Fresnel's law.

Figure 1a k Figure 1b shows the light intensity distribution at the focal plane 20 of the TV camera. As you can see from the figure,
It is characterized by two bright lines (points of high light intensity).

That is, prominent bright lines 24, 26 can be seen on either side of the line 22 passing through the center of the fiber.

FIG. 2a shows a simulation result when the optical fiber 10 is slightly rotated, and FIG. 2b shows the light intensity distribution at the focal plane 20 of the TV camera.

Again, prominent bright lines 24, 26 can be seen on either side of the line 22 passing through the center of the fiber. However, the positions of the bright lines 24 and 26 are
It is different from the case shown in the figure.

Therefore, as shown in FIGS. 1b and 2b, the distance A from the center line 22 to the bright lines 24, 26,
Focusing on B, the value of -A-B- and the optical fiber 10
The relationship between the rotation angle θ and the rotation angle θ is shown in a graph based on the simulation results in FIG.

Note that θ=0 degrees is a case where the stress applying portion 16 is parallel to the observation surface (perpendicular to the light ray 19) as shown in FIG.

The change in -A-B- is large near θ=90 degrees,
At θ=90 degrees, -A-B- becomes zero.

Therefore, when aligning the polarization axis, it is sufficient to rotate the optical fiber 10 so that -A-B- becomes zero around 90 degrees. Since the change with respect to the rotation angle of -A-B- is large, alignment can be performed with high precision.

By doing the same thing for both of the two optical fibers 10 to be connected, it is possible to align the polarization axes with high precision.

Also, in the range of about 90 degrees ± 20 degrees, -A-B-
is changing linearly. Therefore, by checking the values of -A-B- of the left and right optical fibers 10 at the connection point after connection, it is possible to calculate the deviation of the polarization axis at the connection point.

[Actual alignment method] [1] Configuration A schematic diagram is shown in FIG. 5 (see Japanese Patent Application No. 307193/1983).

Reference numeral 28 denotes a z-axis table, which is swingable in the direction of arrow 30.

Mount the bracket 32 on the z-axis stand 28.
A bracket 32 rotatably supports a cylindrical member 34, and a dial 35 is directly connected to the cylindrical member 34.

An arm 36 protrudes from the cylindrical member 34, and a θ clamp 38 is provided at its tip. The θ clamp 38 clamps the covering portion 11 of the optical fiber 10. 3
For example, when the optical fiber 10 is rotated manually, the optical fiber 10
rotates.

40 is a V-groove stand, and 42 is a fiber clamp.

44 is a TV camera, 46 is its control device, 4
8 is a TV monitor, and 50 is an optical fiber image.

[2] Alignment For example, as shown in Fig. 6a, when observed with the TV camera 44 from the direction of θ = 90 degrees, an optical fiber image 50 as shown in Fig. 6b is obtained, and its brightness distribution is as shown in Fig. 6c. It becomes like this.

The brightness distribution in FIG. 6c corresponds to the light intensity distribution in FIG. 1b above.

However, the center line 52 does not exist.

However, in FIG. 6c, a and b are optical fibers 10
It hits both ends of. Therefore, if the positions of a and b are found on the screen, the line passing through the center is the center line 52. Furthermore, even if the centers of c and d are found instead of a and b, the center line 52 will be obtained in the same way.

The center line 52 and the highest brightness lines 5 appearing on both sides of the center line 52
-A-B- is determined from the distances A and B from 4 and 56.

Then, as described above, the optical fiber 10 is rotated so that -A-B-=0 near θ=90 degrees.

If this is done for the left and right optical fibers 10 that connect, the polarization axes can be matched with high precision.

In addition to aligning the polarization axes at 90 degrees (7th
b) or 45 degrees (Fig. 7c).

In such a case, first align the polarization axes as shown in Figure 7a, and then connect one optical fiber 10.
Just rotate it exactly 90 degrees or 45 degrees.

In this method, as described above, the point where -A-B- becomes zero is found, so the stress applying part 16 is connected to the left and right fibers with different distances from the fiber center (see Fig. 8a). ) or fibers with different outer diameters (Fig. 8b), the sizes of A and B are different for the left and right fibers, but the point where -A-B- is zero is the same for all fibers, so The same applies.

[Effect of the invention] When observing a panda-shaped optical fiber from the direction of θ = 90 degrees (direction passing through the stress-applying part and the center of the core), in the brightness distribution of the fiber image, the maximum that appears on both sides from the center line of the fiber image A hitherto unknown method for the phenomenon that the difference between the distances A and B to the brightness line -A-B- becomes zero, and the change in -A-B- is very large near θ = 90 degrees. Based on this recognition, the left and right fibers to be connected are rotated so that -A-B- respectively become zero. (1) The polarization axis of the constant polarization fiber can be aligned with high precision. I can do it. In fact, I was able to align it with a deviation of less than 1 degree.

(2) After connection, the deviation of the polarization axis at the connection point can be measured.

(3) As described above, the present invention can be similarly applied to cases where the stress applying portions 16 have different distances from the fiber center or fibers with different outer diameters.

[Brief explanation of drawings]

Figures 1a to 8b relate to the present invention,
Figure 1a is a computer simulation diagram of ray tracing at θ = 90 degrees, and Figure 1b is
Figure 2a is a computer-generated simulation diagram of ray tracing at different angles of θ, and Figure 2b is a diagram of the light intensity distribution at the focal plane of the TV camera.
A diagram of the light intensity distribution at the focus plane of the TV camera. Figure 3 is a diagram showing the relationship between the rotation angle θ of the fiber and -A-B-. Figure 4 is an explanatory diagram of the rotation angle θ. Figure 5 is the polarization diagram. A schematic illustration of the axis alignment device, FIG. 6a is an illustration of the observation direction by the control device 46, FIG. 6b is an illustration of the fiber image, FIG. 6c is an illustration of the brightness distribution, and FIGS. 7a and 7b. Figures 7c and 7c are explanatory diagrams of connection modes of constant polarization fibers, Figures 8a and 8b are explanatory diagrams of types of fibers to which the present invention can be applied, and Figure 9 is a general explanatory diagram of polarization constant optical fibers. . 11... Covered portion, 10... Optical fiber, 12
... Core, 14 ... Clad, 16 ... Stress applying part, 18 X, Y ... Polarization axis, 19 ... Light ray, 20
...Focus plane of the TV camera, 22...Line passing through the center of the fiber, 24, 26...Bright line, 28...
...Z-axis stand, 32...Bracket, 34...Cylindrical member, 36...Arm, 38...θ clamp, 40
...V groove stand, 42...Fiber clamp, 44...
...TV camera, 46...control device, 48...TV
Monitor, 50... Optical fiber image, 52... Center line, 54, 56... Line of maximum brightness.

Claims (1)

[Claims] 1. Capturing the transmitted light of the optical fiber with an image sensor, and adjusting the polarization axis based on the characteristics of the brightness distribution of the fiber image captured by the image sensor.
In the alignment method of a constant polarization optical fiber, the difference in the distance AB from the center line of the fiber image to the highest brightness line appearing on both sides of the fiber image in the brightness distribution of the fiber image of the panda type constant polarization optical fiber |A-B| A method for aligning polarization-constant optical fibers, which includes rotating the left and right fibers to be connected so that the polarization is zero.