JPS62159005A - Measuring method for length of optical fiber - Google Patents

Abstract

PURPOSE:To execute a measurement with a high accuracy by a simple device in a short time by measuring a phase difference in case of an optical fiber to be measured of a long size, and a phase difference in case of this fiber of a short size, which has been cut short by fixing an electro-optical converting side, and deriving its difference. CONSTITUTION:An electro-optical converter 2, and an optical-electric converter 3 are provided on one end of an optical fiber 1, and the other end, respectively. The converter 2 converts a sine wave electric signal for modulation from an oscillator 4 to a sine wave optical signal, and converts a sine wave optical signal emitted from its other end to a sine wave electric signal. This sine wave electrical signal is inputted to a phase meter 5, also, the sine wave electric signal which has been generated in the oscillator 4 is also inputted to the phase meter 5, and a phase difference of the sine wave electrical signal of a phase phi1 from the oscillator and the sine wave electrical signal of a phase phi2 from the converter 3 is detected by the phase meter 5. By the way, length of a fiber to be measured can be derived by measuring a phase difference in case of the optical fiber to be measured 1 of a long size, and a phase difference of the optical fiber 1 of a short size, which has been cut short by fixing the converter side 2, and deriving its difference.

Description

BACKGROUND AND OBJECTIVES OF THE INVENTION The present invention relates to an optical fiber length measuring method, and more particularly to an optical fiber length measuring method that measures the phase difference of a sine wave signal.

Conventionally, various methods such as mechanical or optical methods are known for measuring the length of an optical fiber. By the way, the mechanical method measures the number of rotations of a roller when the optical fiber is wound onto another bobbin again, and has the drawbacks of requiring a long time and poor measurement accuracy. was there.

On the other hand, the optical method involves injecting pulsed light into an optical fiber.
The length of the optical fiber is measured from the elongation time at the output end, and although the measurement accuracy is good, there is a problem in that the device is large-scale.

The present invention has been made in view of the above, and its purpose is to provide an optical fiber length measuring method that can measure optical fiber length with high accuracy in a short time and with a simple device. be.

[Summary of the Invention] The present invention is characterized by the phase of the sine wave optical signal at the output end of the optical fiber to be measured when the sine wave optical signal is input to one end of the optical fiber to be measured, and the phase of the sine wave optical signal at the output end of the optical fiber to be measured, when the optical fiber to be measured is input to the light source side. The length of the optical fiber to be measured is measured by measuring the difference between the phase of the sinusoidal optical signal at the output end when the optical fiber is fixed and cut short.

[Example] Hereinafter, an example of the method of the present invention will be described in detail with reference to FIG.

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber length measuring device for explaining an embodiment of the optical fiber length measuring method of the present invention. In FIG. 1, reference numeral 1 denotes an optical fiber to be measured, and one end of the optical fiber 1 is provided with an electric-to-optical converter 2, and the other end is provided with an optical-to-electrical converter 3. The electrical-to-optical converter 2 converts the sinusoidal electrical signal for modulation from the oscillator 4 into a sinusoidal optical signal, and transmits this to the optical fiber under test 1.
incident from one end. The optical-to-electrical converter 3 converts a sine wave optical signal propagating through the optical fiber 1 to be measured and emitted from the other end into a sine wave electrical signal. This converted sine wave electric signal is input to the phase meter 5, and the sine wave electric signal generated by the oscillator 4 is also input to the phase meter 5. Sine wave electrical signal and light
A phase difference θ (=ψ1−ψ2) with the sinusoidal electric signal of phase ψ2 from the electrical converter 3 is detected.

By the way, when measuring the length of the optical fiber 1 to be measured, the phase difference θl when the optical fiber 1 to be measured is long and the optical fiber 1 to be measured is fixed to the electro-optic converter 2 side and cut short. If the phase difference θ2 for a short optical fiber is measured and the difference is calculated by 〇(-〇1-θ2), the length of the optical fiber 1 to be measured is given by the following equation.

CΔθ L = -X - N-f 360 ... (1) Here, C; speed of light N; group refractive index f of optical fiber 1 to be measured; frequency of sine wave electric signal (or sine wave light No. 13) , the length of the optical fiber to be measured can be determined from equation (1) by measuring the change in phase difference when the fiber is long or short.

According to the embodiments of the present invention described above, (1) The measuring device may be simple, and the optical fiber length can be easily measured in a short time.

('2J) The measurement accuracy is determined by the frequency of the sinusoidal electrical signal from the transmitter 3, so by controlling this frequency, the optical fiber length can be measured with the required accuracy.

There is an advantage.

Note that by measuring the change in output ΔP at the same time as the change in phase difference Δθ due to cutback, it is possible to measure the length of an optical fiber whose optical fiber length is unknown and the loss value per unit length.

[Effects of the Invention] As explained above, according to the present invention, the optical fiber length can be measured with high accuracy over a long period of time using a simple device.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber length measuring device for explaining an embodiment of the optical fiber length measuring method of the present invention. 1... Optical fiber to be measured. 2...Electric-optical converter. 3... Optical-electrical converter. 4... Oscillator. 5...Phase meter.

Claims (1)

[Claims] (1) The phase of the sine wave optical signal at the output end of the optical fiber to be measured when a sine wave optical signal is input to one end of the optical fiber to be measured, and the output when the optical fiber to be measured is fixed to the light source side and cut short. 1. An optical fiber length measuring method, characterized in that the length of the optical fiber to be measured is measured by measuring the difference between the phase of a sinusoidal optical signal at an end of the optical fiber.