JPH02287504A - Method of aligning constant polarization optical fiber - Google Patents

Abstract

PURPOSE:To align the double refractive axes of the optical fibers which are larger in the refractive index of the stress imparting parts than the double refractive axes by irradiating the optical fibers with light, determining the luminance distribution of the fiber images and aligning the fibers in such a manner that the peaks of the luminance in the central part exist in the same position with respect to the right and left optical fibers. CONSTITUTION:The bow tie type constant polarization optical fibers 12 having the refractive index in the stress imparting parts 14 larger than the refractive index of clads 17 are irradiate with the light 21 from a direction (x) in the case of connecting the optical fibers 12. The light transmitted through the fibers is then observed with a TV camera, etc., and the luminance distribution of the fiber images is determined. The peak (c) of the extreme luminance is observed on a center line 24 when the double refractive axes 18 coincide with the direction (x). The double refractive axes 18 can, therefore, be aligned by rotationally adjusting the optical fibers 12 in such a manner that the peaks (c) of the luminance exist in the same position with respect to the right and left fibers 12 to be connected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application J] This invention relates to a method for aligning a birefringence axis in a polarization-constant optical fiber.

[Prior Art] In FIG. 5a, 12 is the entire optical fiber, 13 is a stress applying portion, 16 is a core, and 17 is a cladding. Also 1
8 is the stress applying part! This is the birefringence axis passing through the center of 3.

The light source 20 irradiates the optical fiber 12 with light 21 from the X direction (see arrows 19 for the x and y directions), and the light transmitted through the optical fiber 12 is observed with an image sensor such as a TV camera 22.

Then, a fiber image as shown in Fig. 5b is obtained, and its luminance distribution becomes as shown in Fig. 5c.

As can be seen from Figures 5b and 5c, two luminance peaks a
,b can be seen.

When aligning for splicing, 1 for 2 fibers.
If the brightness peaks of a and b appear at the same position in both, the birefringence axes 18 will coincide (Japanese Patent Application No. 1112-
30? (See Publication No. 193).

[Issues to be Solved by the Invention j & 11 The above method utilizes the characteristics of a PANDA type polarization constant optical fiber in which the stress applying portion has a lower refractive index than the cladding.

However, in the case of a bowtie-type polarized optical fiber in which the stress applying part 14 has a higher refractive index than the cladding 17 as shown in FIG. 6, even if the fiber is rotated once,
As described above, two luminance peaks do not appear.

In other words, the above method cannot be used for a Poutie type polarization constant optical fiber.

[Means for Solving the Problem] When aligning the optical fiber 12, such as a bowtie type, in which the refractive index of the stress applying portion 14 is larger than the birefringence axis 1B, the first
As shown in Figure a-1c, (1) The same as the above case is used in that the optical fiber 12 is irradiated with light and the transmitted light is observed with a TV right camera to determine the brightness distribution of the fiber image. (2) In the case of a bow-tie type, etc., focus on the point where the brightness peak C appears at the center of the brightness distribution, and (3) regarding the left and right optical fibers 12,
The brightness peak C should be at the same position.

[Explanation 1 The following is the principle of the present invention (phenomena utilized by the invention).

The evaluation method after alignment and connection will be explained using a Poutie type polarization constant optical fiber as an example.

[1F Principle (1) As shown in FIG. 1a, light 21 is irradiated onto the optical fiber 12 from the X direction, and an appropriate focal plane is observed using an image sensor such as the TV right camera.

When the birefringence axis 18 coincides with the X direction, the fiber image becomes as shown in FIG. 1b, and the brightness distribution becomes as shown in FIG. 1C.

That is, a remarkable peak C of brightness is seen on the center line 24.

Note that the center line 24 is calculated from the intersection points d, e (or f, g) of the arbitrary brightness level 26 and the brightness profile,
The center corresponds to the center of the optical fiber 12.

(2) Next, as shown in FIG. 2a, when the optical fiber 12 is rotated by θ, the peak C in the brightness distribution moves by δ from the center line 24, as shown in FIG. 2b.

Note that the position where the birefringence axis 18 coincides with the X direction is defined as 0 degrees, and the clockwise direction is defined as 10 degrees, and the counterclockwise direction is defined as 10 degrees.

When the optical fiber 12 is rotated back and forth around the 0 degree position above, the relationship between the rotation angle θ and the amount of movement δ (number of lines) is shown in a graph as shown in Figure 3. Become.

[2] Alignment method The above phenomenon is used to align the mind.

In other words, in the case of connection, if the fibers are rotated in the 0 direction so that the brightness distribution profile of both the left and right fibers becomes as shown in Figure 1C (the brightness peak C coincides with the center line 24), the The refraction axes 18 coincide.

In addition, in the case of connection, in addition to the case where the birefringence axes 18 are made to coincide, the birefringence axes 18 may be made to differ by 90 degrees or 45 degrees. In that case, as described above, once the birefringent axes 18 are aligned, one fiber may be rotated accurately by 80 degrees or 45 degrees.

The alignment accuracy can be calculated by determining the slope of the graph in FIG. 3, and the result is approximately 2.46 per line.

For reference, the case of θ=90 degrees is shown in 4a and 4b.
Shown in the figure. In this case, no brightness peak appears.

[3] Evaluation after connection As shown in FIG. 3, in the range of ±30 degrees from 0, the relationship between θ and the amount of movement δ has linearity.

Utilizing this fact, the displacement of the birefringence axis 18 can be measured by measuring the amount of movement δ for each fiber after connection.

[4] How to find the brightness peak position and focus plane (1) The brightness peak position can be determined simply by finding the maximum value of the brightness profile, or by finding a value slightly lower than the peak value as shown in Figure 1C. The threshold 28 may be determined and calculated from the intersection points J and k with the profile.

(2) There is no problem with the focus position when capturing the brightness distribution profile if the length of f2g in FIG. 1c is always kept constant.

[Effect of the invention 1] The natural phenomenon described below, namely, Light is emitted from the T and the transmitted light is
When the brightness distribution of the fiber image is determined by observation with a V-camera or the like, a brightness peak C appears at the center of the brightness distribution. It is based on a new Wla for the phenomenon that there is a certain relationship between the angle θ of the birefringence axis 18 with respect to the y direction.

(1) Like a bowtie type optical fiber, the refractive index of the stress applying portion 14 is larger than that of the cladding portion 17, and the optical fiber can be accurately aligned.

(2) As described above, the deviation of the birefringence axis at the connection point can be measured after connection.

[Brief explanation of the drawing]

Figures 1a-4b relate to the present invention. FIG. 1a is an explanatory diagram of a state in which light is irradiated from a 0 degree direction, and FIG. 1b is an explanatory diagram of a fiber image in that case. FIG. 1C is an explanatory diagram of a brightness distribution profile. FIG. 2a is an explanatory diagram of a state where the fiber is rotated by θ and light is irradiated, and FIG. 2b is an explanatory diagram of the brightness distribution profile in that case. Figure 3 shows the rotation angle θ of the fiber and the movement amount δ of the brightness peak.
Figure 4a is an explanatory diagram of a state in which the fiber is rotated by 90 degrees and light is irradiated, and Figure 4b is an explanatory diagram of the brightness distribution profile in that case. Figure 5a and subsequent figures relate to the prior art; Figure 5a is an explanatory diagram of a state in which a fiber is irradiated with light and observed with a TV camera, and Figure 5b is an explanatory diagram of a fiber image in that case. FIG. 5c is an explanatory diagram of a brightness distribution profile. FIG. 6 is an explanatory diagram of a bowtie type polarization constant optical fiber. : Optical fiber: Core: Birefringent axis Light source: Light: Center line 13.14: Stress applying section 17: Clad 20: Light source 22: TV camera

Claims (1)

[Claims] When aligning an optical fiber in which the refractive index of the stress applying part is larger than the birefringence axis, the optical fiber is irradiated with light, the transmitted light is observed with a TV camera, and the brightness distribution of the fiber image is determined. A method for aligning a constant polarization optical fiber, in which the brightness peak appearing at the center of the brightness distribution is located at the same position for the left and right optical fibers.