JPS61165609A - Measuring strain of optical transmission line - Google Patents

Abstract

PURPOSE:To measure strain at on-line and with an excellent precision by using a wave length multiplex transmission of a strain measuring signal composed of a different wave length than that of an information transmitting signal utilizing an optical wave mixer and an optical wave divider. CONSTITUTION:An optical wave mixer 8 combines an information transmitting pulse signal overlapped on a carrier optical wave with a wave length lambda1 and a strain measuring sine wave signal overlapped on a carrier optical wave with a wave length lambda2 and inputs to an optical fiber 3. An optical wave divider 9 divides the mixed optical signal to wave lengths lambda1 and lambda2 and the sine wave signal coming from a transmitter 10 is transmitted to a receiver 11. The strain epsilonof the optical fiber 3 or a multiple conductor optical fiber 7 can be calculated from a phase shift DELTAtheta in the strain measuring sine wave signal received by the receiver 11 applying an equation I. In the equation, l: length of optical fiber 3, f: modulated frequency, K: a constant (in case of nylon coated fiber conductor, approx. 7.1X10<5>).

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to a method for measuring distortion of an optical transmission line, and particularly relates to an optical multiplexer/
An optical transmission line in which a distortion measurement signal of a wavelength different from that of the information transmission signal is inserted and separated into an optical fiber via an optical demultiplexer, and the distortion of the optical transmission line is measured from the change in the phase. Concerning strain measurement method.

[Conventional technology]

Designing residual strain in optical fibers in optical cables, or measuring elongation strain in optical fibers due to changes in wind and weather conditions after optical cable installation, can prevent optical fiber breakage and improve optical communication systems. This is important in knowing the reliability of the system. Conventionally, in order to measure these strains, there has been a proposal to provide a strain resistance wire in an optical cable.

[Problems to be Solved by the Invention] However, in strain measurement using a strain resistance wire, an expensive strain resistance wire must be separately provided on the optical cable.

Furthermore, strain resistance wires are not suitable for accurately measuring strain over long distances in optical cables after installation.

For this reason, measurement of strain on optical cables after installation is rarely carried out at present.

[Object of the Invention] The present invention has been devised to solve the above-mentioned problems of the prior art, and the purpose of the present invention is to precisely and easily measure the distortion of an optical transmission line such as an optical cable online. An object of the present invention is to provide a method for measuring distortion of an optical transmission line.

[Summary of the Invention] In order to achieve the above object, the present invention inserts a distortion measurement signal of a wavelength different from that of an information transmission signal into an optical fiber via an optical multiplexer, and inserts the distortion measurement signal into the optical fiber at a predetermined wavelength. After propagating over a distance, the signals are separated via an optical demultiplexer, and the distortion is measured from the change in phase of the separated distortion measurement signals. Distortion measurement signals of different wavelengths are input, and the distortion of the optical transmission line can be constantly monitored without any effect on the information transmission signal.

[Example] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

First, prior to explaining the embodiments, the principle of strain measurement according to the method of the present invention will be explained based on the measuring apparatus shown in FIG.

In FIG. 2, 1 is an oscillator, 2 is an electric/optical converter that converts the modulation electric signal from the oscillator 1 into an optical signal for strain measurement, 3 is an optical fiber whose strain is measured, and 4 is an optical fiber 3. An optical/molar converter 5 converts the optical signal for strain measurement emitted from the optical signal into an electrical signal, and 5 amplifies the electrical signal from the optical/molar converter 4 and inputs it to a phase meter (vector voltmeter) 6. It's an amplifier. The electrical signal from the oscillator 1 and the electrical signals that have passed through the electrical/optical converter 2, the optical fiber 3, the optical/exchanger 4, and the amplifier 5 are input to the phase meter 6, respectively. The phase meter 6 detects the phase difference between these electrical signals.

When an optical signal is input into the optical fiber 3, the phase change of the output light is proportional to the length of the optical fiber 3.

Therefore, by measuring the change in the phase difference between the incident light and the output light using the phase meter 6, it is possible to measure the change in the length of the optical fiber 3, that is, the strain in the optical fiber 3.

The following relationship exists between the strain ε of the optical fiber 3 and the phase difference Δθ.

Here, β is the length of the optical fiber 3, f is the modulation frequency, and K is a constant, which is 7.1×10 5 in the case of a nylon-coated fiber core.

Next, FIG. 1 shows an example in which the above strain measurement principle is applied to a multi-core optical fiber cable.

In FIG. 1, 7 is a multi-core optical fiber cable,
An optical multiplexer 8 is provided at one end of the single optical fiber 3 of the multi-core optical fiber cable 7, and an optical demultiplexer 9 is provided at the other end. The optical multiplexer 8 multiplexes the information transmission pulse signal carried on the carrier of the light source with the wavelength λ1 and the sine wave signal for distortion measurement carried on the carrier of the light source with the wavelength λ2, and inputs the combined signal to the optical fiber 3. Further, the optical demultiplexer 9 separates these multiplexed optical signals into wavelengths λ'' and λ2. The sine wave signal for distortion measurement is transmitted from the transmitter 10 to the optical multiplexer 8, and the sine wave signal for distortion measurement separated by the optical demultiplexer 9 is sent to the receiver 1.
1.

The transmitting section 10 has the above-mentioned oscillator 1 and the electric/optical converter 2, and the receiving section 11 has the optical/electrical converter 4, the amplifier 5, and the phase meter 6.

An information transmission pulse signal carried on a carrier with a wavelength λ1 is combined with a sine wave signal for distortion measurement carried on a carrier with a wavelength λ2 in an optical multiplexer 8, and the combined optical signal is a two-wavelength molecule. It is transmitted through the optical fiber 3. The wavelength-multiplexed optical signal is sent to an optical demultiplexer 9 to separate wavelengths λ1. λ2, the pulse signal for information transmission is transmitted to the receiving side, and the sine wave signal for distortion measurement is received by the receiving section 11. The distortion of the optical fiber 3 or multi-core optical fiber cable 7 is calculated from the phase change of the distortion measuring sine wave signal received by the receiving section 11 using the above equation (1).

As described above, in the method of the present invention, the distortion measurement signal having a wavelength different from that of the information transmission signal is wavelength-multiplexed and transmitted using the optical multiplexer 8 and the optical demultiplexer 9. The average strain over the entire length of the optical fiber 3 can be accurately measured online without affecting the information transmission signal in any way.

In addition, this method uses the optical fiber 3 for information transmission of the multi-core optical fiber cable 7 also for strain measurement, and compared to the strain resistance wire method, strain measurement can be performed more easily and at lower cost.

In the above example, λt -0, 85μ pot, λ2-0
．． Using a 79 μl light emitting diode, the length of the optical fiber 3 is R-1 km, and the frequency of the sine wave signal for strain measurement is f-IMH.
z, the transmission speed of pulse signals for information transmission is 6.3 Mb/s
When we conducted an experiment, we measured a phase change of 1 to 2 degrees in the sine wave signal for distortion measurement. This is the strain ε of optical fiber 3
This corresponds to 0.07 to 0.14%.

In the above embodiment, the multi-core optical fiber cable 7 was used, but other optical fiber-containing overhead ground wires and optical fiber/M
It can also be applied to optical transmission lines such as field line composite cables. Furthermore, the information transmission signal has not only a wavelength of λ1 but also a wavelength of λ2.
Of course, it may be multiplexed than waves. Also, on the transmitting side, a synchronization pulse placed on a carrier of wavelength λ3 is mixed in corresponding to a specific phase, for example, zero phase, of the sine wave signal for distortion measurement.
The synchronization pulse may be extracted on the receiving side, and the distortion of the optical fiber may be measured from the change in the phase difference between the synchronization pulse and the sine wave signal for measuring distortion.

[Effects of the Invention] In summary, the present invention exhibits the following excellent effects.

(1) Since the distortion measurement signal with a different wavelength from the information transmission signal is wavelength-multiplexed using an optical multiplexer and optical demultiplexer, information can be transmitted without affecting the information transmission signal in any way. At the same time, distortion can be measured online with high precision.

(Distortion in optical transmission lines such as optical cables can be monitored online with high accuracy, and the reliability of the entire optical communication system can be expected to improve.)

(3) Clear knowledge of the correspondence between distortion in the optical transmission line (optical cable) and weather conditions (wind, snow, etc.) can be obtained, making it possible to design and manufacture more reliable optical cables.

(4) Using optical fibers for information transmission and strain measurement
Unlike the strain resistance wire method, there is no need to separately provide a strain resistance wire, and strain measurement can be easily and inexpensively performed.

(5) If the present invention is applied to optical fiber/power line composite cables, high voltage preventive maintenance becomes possible.

[F]) If the present invention is applied to an optical fiber-containing overhead ground wire, it can be used in a power transmission line maintenance system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a measurement system for implementing the method of the present invention, and FIG. 2 is a block diagram of a system for explaining the measurement principle that is the basis of strain measurement of the present invention. In the figure, 1 is an oscillator, 2 is an electrical/optical converter, 3 is an optical fiber, 4 is an optical/electrical converter, 5 is an amplifier, 6 is a phase meter, and 7
is a multi-core optical fiber cable, 8 is an optical multiplexer, 9 is an optical demultiplexer, 10 is a transmitter, 11 is a receiver, λ is the wavelength of the carrier carrying the pulse signal for information transmission, and λ2 is for distortion measurement. This is the wavelength of the carrier carrying the sine wave signal. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 1 Figure 2

Claims (1)

[Claims] An optical multiplexer and an optical demultiplexer are installed in the optical fiber, and a distortion measurement signal with a wavelength different from that of the information transmission signal is inserted into the optical fiber via the optical multiplexer, and then separated via the optical demultiplexer. A method for measuring distortion in an optical transmission line, characterized in that the distortion is measured from a change in the phase of the separated distortion measurement signal.