JPH0354290B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extinction ratio measurement system for a polarization-maintaining optical fiber used in optical communications, and more particularly to a method for injecting light into the polarization axis of a polarization-maintaining optical fiber.

FIG. 1 is a system diagram of a conventional extinction ratio measurement system for a polarization-maintaining optical fiber. The light emitted from the light source 1 passes through a polarizing plate 2a and a λ/2 plate 3, and then is condensed by a lens 4a and enters a polarization preserving optical fiber 5.
The light emitted from this polarization-maintaining optical fiber is converted into a substantially parallel beam by a lens 4b, passes through a polarizing plate 2b, and is detected by a photoelectric detector 6.

To measure the extinction ratio, first adjust the rotation angles of the polarizing plate 2a and the λ/2 plate 3, and when the detected power becomes the minimum, fix the λ/2 plate 3 and rotate the polarizing plate 2b. Then, read the maximum value dBmax. and minimum value dBmin. of the signal power with the detector, and find the difference between them. In this state where the polarization preserving optical fiber 5 is stationary, the light source 1
coherence lens length and polarization preserving optical fiber 5
Due to the relationship with the coupling length of the polarization preserving optical fiber, the detected power may become minimum even when the light is not incident on the intrinsic polarization axis, or the detected power may fluctuate over time. The problem was that it was extremely difficult to match the beams and make them incident.

It is an object of the present invention to provide a method for injecting light into a polarization axis of a polarization-maintaining optical fiber, which eliminates the drawbacks of the above-mentioned prior art and allows the extinction ratio to be measured by accurately injecting polarized light into the polarization axis in a short time. The purpose and feature of this system is to provide a disturbance section that changes the state of a part of the polarization-maintaining optical fiber.
After the plate is rotated and fixed so that the detected power of the photoelectric detector is minimized, the second polarizing plate is rotated and set so that the maximum and minimum values of the detected power are maximized.

FIG. 2 is a system diagram of an extinction ratio measurement system for a polarization-maintaining optical fiber according to an embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. In this case, a vibration applying section 7 is provided in a part of the polarization maintaining optical fiber 5. To measure the extinction ratio, as described above, the rotation angle of the polarizing plate 2a and the λ/2 plate 3 is adjusted to minimize the detected power, and the λ/2 plate 3 is fixed. Next, rotate the polarizing plate 2b to obtain the maximum detected power.
dBmax. and the minimum value dBmin. are read by the detector 6, and the extinction ratio is determined from the difference between them.

Here, the λ/2 plate is rotated so that the detected power is minimized, and when it is fixed, an arbitrary part of the polarization-maintaining optical fiber is subjected to arbitrary vibration using, for example, a motor or a speaker. On the other hand, when external disturbances such as vibrations are applied to the polarization preserving optical fiber 5, when the polarized light that matches the unique polarization axis is incident on the polarization preserving optical fiber 5, it is disturbed by the vibration. It has the property that the polarization direction of the transmitted light does not change without changing the polarization direction of the transmitted light. Therefore, when rotating and fixing the λ/2 plate so that the detected power is minimized while giving vibration to the polarization-maintaining optical fiber 5 to be tested, this is the optimal light input method. .

The fact that it is now possible to inject light in a state suitable for a specific polarization axis by simply applying arbitrary vibration to a part of a polarization-maintaining optical fiber makes it easy to measure the extinction ratio. This shows that it can be streamlined. In other words, this method can be said to be a dynamic extinction ratio measurement system.

The light input method of this embodiment vibrates a part of the polarization-maintaining optical fiber and adjusts the rotation angle of the first polarizing plate and the λ/2 plate to minimize the power detected by the photoelectric detector. Then, by rotating the second polarizing plate and setting it so that the difference between the maximum and minimum detected power becomes the maximum, it is possible to easily and accurately determine the extinction ratio.

In the above embodiment, measurement is performed by applying vibration to the polarization-maintaining optical fiber, but instead of vibration, an appropriate physical external disturbance is applied, such as elongation to a portion of the polarization-maintaining optical fiber. Good too. However, this elongation must be made random over time. Note that this elongation may be caused by blowing hot air locally using a dryer or the like to change the temperature.

The method of injecting light into the polarization axis of a polarization-maintaining optical fiber according to the present invention allows polarized light to be incident in a short time and easily while matching the intrinsic polarization axis, and adds a slight disturbance to the conventional measurement system. This becomes possible simply by simply doing this, and the effect of accurately measuring the extinction ratio can be obtained.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a conventional extinction ratio measurement system for a polarization-maintaining optical fiber, and FIG. 2 is a system diagram of an extinction ratio measurement system for a polarization-maintaining optical fiber, which is an embodiment of the present invention. 1... Light source, 2... Polarizing plate, 3... λ/2 plate, 4... Lens, 5... Polarization preserving optical fiber, 6... Detector, 7
...Vibration applying section.

Claims (1)

[Scope of Claims] 1. Light emitted from a light source passes through a first polarizing plate and a λ/2 plate, and then is condensed and input into a polarization-maintaining optical fiber, and the light is emitted from the polarization-maintaining optical fiber. In the extinction ratio measurement system for the polarization preserving optical fiber configured such that the emitted light is condensed and passed through a second polarizing plate and detected by a photoelectric detector, a change in state is detected in a part of the polarization preserving optical fiber. After rotating the λ/2 plate while giving a disturbance to a part of the polarization-maintaining optical fiber by providing a disturbance section to give a disturbance, and fixing it so that the detected power of the photoelectric detector is minimized,
A method for introducing light into a polarization axis of a polarization-maintaining optical fiber, characterized in that the second polarizing plate is rotated to set the maximum and minimum values of the detected power to be maximum. 2. The method of injecting light into a polarization axis of a polarization-maintaining optical fiber according to claim 1, wherein the disturbance section is a vibration application section.