JPH08136402A - Measuring method of maintained polarization plane surface of polarization plane maintaining optical fiber - Google Patents

Abstract

PURPOSE: To provide a measuring method of the maintained polarization plane of a polarization plane maintaining optical fiber in which a maintained polarization plane can be obtained easily and precisely. CONSTITUTION: A one-end surface 1a of a polarization plane maintaining optical fiber 1 is picked up from the frontal surface by means of a CCD camera 4, a picked up image is image-processed by means of an image processing unit 5, the maintained wave polarization plane of the polarization plane maintaing optical fiber can be thereby measured. It is desirable to make while light incident from a one-end surface picked up by means of the polarization plane maintaing optical fiber and the other end surface on the opposite side and to take an image processing method in which the inertial main axis of a binarized image of a core is obtained and the obtained inertial main axis is obtained as a maintained polarization plane in order to measure the maintained polarization plane precisely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring method for obtaining a polarization maintaining surface of a polarization maintaining optical fiber.

[0002]

2. Description of the Related Art Conventionally, polarization-maintaining optical fibers have been used for measurement of optical fiber gyroscopes, waveguides of optical fiber interferometers, or for coherent communication or transmission lines of optical integrated circuits. . FIG. 3 is a diagram showing a cross section of an example of a polarization-maintaining optical fiber. In FIG. 3, the polarization-maintaining optical fiber 21 is composed of an elliptical core 22 in the center and a clad 23 around the core, and the polarization-maintaining optical fiber 21 is polarized along the major and minor axes of the elliptical shape of the core 22. There is a surface 24. When polarized light is incident on the polarization maintaining surface 24, the polarized light is retained.

Since this polarization-maintaining optical fiber 21 has a polarization-maintaining surface 24 determined by its sectional structure, when the polarization-maintaining optical fiber 21 is connected, for example,
It is necessary to match the polarization maintaining surfaces 24 in both cross sections of the polarization maintaining optical fiber 21 to be connected. Therefore, when the polarization-maintaining optical fiber 21 is to be connected by an optical connector, the polarization-maintaining surface 24 when the polarization-maintaining optical fiber 21 is set in the optical connector is set to match a predetermined reference plane. Therefore, it is necessary to measure the polarization plane 24.

FIG. 4 is a diagram for explaining an example of a method for measuring the polarization maintaining surface of a conventional polarization maintaining optical fiber. In FIG. 4, 31 is a light source, 32 is a polarizer, 33 is a polarization-maintaining optical fiber to be measured, 34 is an analyzer, and 35
Is an optical sensor, and 36 is an optical power meter. In the device having the above-described configuration, the analyzer 34 is rotated to output the optical power meter 37 while the polarized light having passed through the polarizer 32 is incident on the polarized light maintaining surface of the polarization maintaining optical fiber 33. The position at which is the maximum is found as the polarization-preserving surface. In the case of assembling as an optical connector, the end face of the polarization-maintaining optical fiber 33 is rotated and fixed so that the obtained polarization-maintaining surface coincides with a reference surface, for example, a horizontal plane.

[0005]

However, in the above-described conventional polarization-maintaining surface measuring method, the optical axis adjustment and detection for making the light emitted from the polarizer 32 incident on the core of the polarization-maintaining optical fiber 33 are performed. There is a problem that operations such as rotation of photons are required, and it takes time and labor to measure the polarization maintaining surface. Further, a method of measuring a polarization-maintaining surface by capturing an image from the side surface of the polarization-maintaining optical fiber and performing image processing without using the large-scale device as described above is also considered. Since it is difficult to make a determination, there was a problem that the accuracy for measuring the polarization-maintaining surface deteriorates.

The object of the present invention is to solve the above problems,
An object of the present invention is to provide a method for measuring a polarization-maintaining surface of a polarization-maintaining optical fiber that can easily and accurately determine the polarization-maintaining surface.

[0007]

A method for measuring a polarization-maintaining surface of a polarization-maintaining optical fiber according to the present invention is a method in which one end surface of a polarization-maintaining optical fiber is imaged by a CCD camera from the front and the imaged image is processed. By doing so, the polarization maintaining surface of the polarization maintaining optical fiber is measured.
Here, the polarization-maintaining surface is a surface that is determined by the cross-sectional structure of the polarization-maintaining optical fiber, and is a surface that preserves the polarization until the exit end when linearly polarized light that matches the surface is incident. is there.

[0008]

In the above structure, the end face of a normal polarization-maintaining optical fiber has an elliptical core at the center, and the polarization-maintaining face exists along the major and minor axes of this elliptical shape. Therefore, if the elliptical shape of the core is extracted from the captured image of the end face and the extracted elliptical image of the core is image-processed to find its principal axis of inertia, the obtained principal axis of polarization is the plane of polarization. It becomes the polarization-preserving surface of the storage optical fiber, and it is easy to judge the image, and the polarization-preserving surface can be measured easily and accurately.

When white light is made incident from the other end surface of the polarization-maintaining optical fiber opposite to the one end surface for imaging, the elliptical shape of the core can be obtained more accurately, and as a result, the polarization-maintaining surface can be obtained. It is preferable because the measurement can be performed accurately. Further, as a method of image processing, if the inertial principal axis of the binarized image of the core is obtained and the obtained inertial principal axis is obtained as the polarization-maintaining surface, the polarization-maintaining surface can be accurately measured. preferable.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a flow chart for explaining an example of a method for measuring the polarization maintaining surface of a polarization maintaining optical fiber according to the present invention. The present invention will be described with reference to FIG. 1. First, one end face of a polarization-maintaining optical fiber is imaged from the front with a CCD camera. At this time, the core portion of the polarization-maintaining optical fiber has a different shade from the other portions without using any illumination, so that the core portion can be extracted by subsequent image processing. However, it is preferable to allow white light to enter from the other end surface of the polarization-maintaining optical fiber because the difference in shade between the core portion and the other portions becomes larger. Further, as the CCD camera, a conventionally known one can be used.

Next, the imaged image is subjected to image processing to measure the polarization maintaining surface. As the image processing method, any conventionally known method can be used as long as the polarization maintaining surface can be measured. As an example thereof, a method of binarizing the core portion and then obtaining the principal axis of inertia is preferable because the polarization-maintaining surface can be easily and accurately obtained.
Here, in the binarization, for example, assuming that one pixel of a captured image has 1 byte, that is, 256 gradations, the gradation threshold is calculated according to the shading of the core part and other parts, and based on this threshold This can be performed by setting the side where the gradation of the core portion is present to 0, and setting the other portions to 1. Further, as a method of obtaining the principal axis of inertia, a method of obtaining the center of gravity of the figure of the core portion and then obtaining the direction of the principal axis can be adopted as is conventionally known.

FIG. 2 is a diagram showing the construction of an example of an apparatus for carrying out the method of measuring the polarization maintaining plane of the polarization maintaining optical fiber of the present invention. In the example shown in FIG. 2, 1 is a polarization-maintaining optical fiber to be measured, 2 is an objective lens, 3 is a lens barrel, and 4
Is a CCD camera, 5 is an image processing device, 6 is a monitor, and 7 is a white light source. In the apparatus having the above-described configuration, the other end surface 1a of the polarization-maintaining optical fiber 1 is connected to the objective lens 2 and the lens barrel while the white light emitted from the white light source 7 is incident from the one end surface 1b of the polarization-maintaining optical fiber 1. The image is enlarged through 3 and imaged by the CCD camera 4. The picked-up image is image-processed by the image processing apparatus 5, and the result is displayed on the core portion 11 and the obtained polarization maintaining surface 12 as shown in the monitor 6 of FIG.

Therefore, for example, when it is attempted to fix a polarization-maintaining optical fiber to an optical connector so that the polarization-maintaining surface coincides with a predetermined reference plane, for example, at the position of the polarization-maintaining optical fiber 1 described above, V that constitutes the optical connector
Set the polarization-maintaining optical fiber temporarily fixed on the groove substrate,
While observing the display on the monitor 6, the end face of the polarization-maintaining optical fiber 1 is rotated so that the polarization-maintaining face 12 is located at a predetermined reference plane position, and fixed at that position. Can be obtained.

In the above example, the core of the polarization-maintaining optical fiber has an elliptical shape, and the polarization-maintaining surface is obtained from the elliptical shape. By the way, in some actual polarization-maintaining optical fibers, the core has a circular shape, and even in such an example, a jacket having an elliptical shape corresponding to the polarization-maintaining surface or a polarization-maintaining surface is supported. Since there is a stress imparting portion, etc., and there is a difference in shade between that portion and the other portion on the image picked up according to the present invention, and binarization is possible, the same polarization can be obtained by applying the present invention described above. You can ask for a storage surface.

[0015]

As is apparent from the above description, according to the present invention, the end face is imaged, the elliptical shape of the core is extracted from the imaged image, and the extracted image of the elliptical shape of the core is subjected to image processing. When the principal axis of inertia of the polarization is obtained, the obtained principal axis of inertia becomes the polarization-maintaining surface of the polarization-maintaining optical fiber, so that the image can be easily determined and the polarization-maintaining surface can be measured easily and accurately.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining an example of a method of measuring a polarization maintaining surface of a polarization maintaining optical fiber of the present invention.

FIG. 2 is a diagram showing a configuration of an example of an apparatus for carrying out a method for measuring a polarization maintaining surface of a polarization maintaining optical fiber of the present invention.

FIG. 3 is a diagram showing a cross section of an example of a polarization-maintaining optical fiber.

FIG. 4 is a diagram for explaining an example of a method for measuring a polarization maintaining surface of a conventional polarization maintaining optical fiber.

[Explanation of symbols]

1 polarization-maintaining optical fiber, 1a, 1b end face, 2 objective lens, 3 lens barrel, 4CCD camera, 5 image processing device, 6 monitor, 7 white light source

Claims (3)

[Claims] 1. A polarization-maintaining surface of a polarization-maintaining optical fiber is measured by imaging one end of a polarization-maintaining optical fiber from the front with a CCD camera and processing the captured image. Polarization plane Measurement method of polarization maintaining plane of optical fiber. 2. The method for measuring a polarization maintaining surface of a polarization maintaining optical fiber according to claim 1, wherein white light is incident from the other end surface of the polarization maintaining optical fiber. 3. In the image processing, the principal axis of inertia of the binarized image of the core of the polarization-maintaining optical fiber in the captured image is obtained,
The method for measuring the polarization maintaining surface of a polarization maintaining optical fiber according to claim 1 or 2, which is performed by determining the obtained principal axis of inertia as a polarization maintaining surface.