JPS6130782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber transmission system, and more particularly to a fault search method for locating a transmission line fault caused by a break in an optical fiber at both end stations.

The relay interval L of the optical fiber cable transmission method is
It is well known that the relay spacing can be significantly increased compared to conventional wired transmission systems using balanced pair cables or coaxial cables. The effect of increasing the repeater spacing is to significantly reduce the number of repeaters required for the line length when designing terrestrial optical fiber cable transmission systems or submarine optical fiber cable transmission systems, and from the system design perspective. Various transmission methods that are highly economical and reliable can be realized. On the other hand, even with optical fiber cable transmission systems that have such excellent features, especially in submarine optical fiber cable transmission systems, once a submarine repeater failure, optical fiber breakage, or cable failure occurs, the failure will occur. A series of fault repair work, including detecting the location, scale, and content of the fault, dispatching a repair ship, locating the fault point, and completely restoring the transmission line fault, requires a long repair period, a large amount of money, and the use of a large number of personnel. shall be. As mentioned above, applying optical fiber to submarine cable transmission systems has the great advantage of expanding the repeater interval, but on the other hand, once a submarine optical cable transmission line failure like the one described above occurs, it is difficult to locate the failure point and determine the nature of the failure. It is inevitable that this will be extremely difficult. For this reason, in realizing a submarine optical fiber transmission system, maintenance personnel need to develop a monitoring system for submarine optical fiber transmission lines that can quickly and accurately detect the location of faults, accurately determine the scale of the fault, etc. It has to be realized.

From this point of view, the present invention mainly relates to optical fiber breakage failures in submarine optical cables, and monitors optical fiber breakage failures by focusing on the cable connection point of the manufacturing unit length (loKm) or arbitrary cable length (lxKm) of the optical cable. This is what we are trying to do. In other words, since the manufacturing unit length (loKm) of an optical fiber cable is usually shorter than the relay interval (LKm), a plurality of manufacturing unit lengths (loKm) of n pieces are connected in series to form an optical transmission line with the relay interval (LKm). It consists of Fiber optic connection points are generally housed within a connection housing. In particular, submarine optical cables are placed on the ocean floor and are subject to large water pressure.To prevent the optical fiber connection points from becoming damaged due to the pressure, the optical fiber connection points are placed inside a pressure-resistant and water-resistant connection box. is housed in. For example, four to nine connection boxes are provided in one relay section. The present invention aims to facilitate troubleshooting by utilizing the connection box.

This invention focuses on connecting boxes for submarine optical cables and optical wavelength division multiplexing transmission technology. built-in, and always receives a single frequency signal from the oscillator.
Directly modulated by a light emitting element with good linearity such as an LED, and transmitted to both terminal stations using different optical wavelengths λ ₂ and λ ₃ , which are different from the optical wavelength λ 1 that carries _the main transmission signal,
The receiving end station monitors the above-mentioned specific fault detection current to determine whether or not there is a break in the optical fiber in the optical fiber transmission line.
This is an attempt to determine the location.

FIG. 1 shows an embodiment of the invention. 1 is a submarine optical digital terminal station (transmitting side), 2 is an optical fiber cable connection box, 3 is a submarine optical repeater, 4 is a submarine optical digital terminal station (receiving side), and 5 is a digital regenerator in the repeater 3. , 6 is an optical digital transmitter of the terminal station 1, 7 is an optical digital receiver of the terminal station 4, 8 to 1
3 is an optical demultiplexer/combiner, 14 to 19 are optical modulators, 2
0 to 25 are optical demodulators, 26 to 29 are fault detection current oscillators, 30 to 35 are amplifiers, 36 and 37 are fault detection current level measuring devices provided at terminal stations 1 and 4, respectively, and 38 to 41 are power couplings. 42 is a submarine optical fiber cable.

Next, the operation of this invention will be explained. It is now assumed that the optical transmission line is composed of one optical fiber transmission line from terminal station 1 to terminal station 4 in FIG. Set the frequency of the fault search current oscillator to terminal station 1, cable connection box 2
(One set is shown in the figure, but in general there are multiple sets) f ₁ ,...fi,
fj, . At the terminal 1, the fault detection current fo of the fault detection current oscillator 26 is applied to the optical modulator 14 and converted into light of wavelength λ ₂ . This wavelength λ ₂
The light from the transmitter 6 and the light having a wavelength λ ₁ that carried the digital information of the main signal from the transmitter 6 are combined by a demultiplexer/combiner 8, and the terminal station 4 connects the reproducing digital repeater 3 and the cable connection box 2. The light of λ ₃ that has carried the fault search current is demultiplexed by a demultiplexer/multiplexer 8 . The lights of λ ₁ and λ ₂ combined by the demultiplexer/multiplexer 8 are sent to the submarine optical cable transmission line 42 . The light of wavelength λ ₃ demultiplexed by the demultiplexer/multiplexer 8 is returned to a baseband signal by the demodulator 20 using a PIN diode, etc., and its output is amplified to a predetermined level by the amplifier 30 and then converted to the fault detection current level. Applying it to the measuring device 36,
The fault search currents f ₁ ,...fi are received, and it is detected whether there is any fault search current that has not yet reached.

On the other hand, the light signals λ ₁ and λ ₂ sent to the submarine optical cable transmission line 42 reach the cable connection box 2 and are processed by the demultiplexer/multiplexer 9 to convert the signals λ 1 and λ 2 including the digital signals.
₁ and a λ ₂ light carrying a fault searching current of frequency fo toward the receiving terminal station 4.
Light of λ ₃ carrying the fault searching current of fo...fj heading toward the transmitting terminal station 1 is combined. The demultiplexed light of λ ₁ passes through the fiber connection point and is applied to the demultiplexer/multiplexer 10 . Further, the light of λ ₂ is demodulated into the baseband by the optical demodulator 21 . The output of the oscillator 27 having the unique oscillation frequency f ₁ of the cable connection box 2 is coupled to the demodulated output via the hybrid circuit 39, and after being amplified to a specified level by the amplifier 32, the optical modulator 16 ₂ is directly modulated and applied to the demultiplexer/multiplexer 10. In the demultiplexer/multiplexer 10, λ
The wavelength λ ₃ light coming from the transmission line ₄₂ is demultiplexed and sent to the demodulator 22 _. The fault search current output of the oscillator 27 is combined with the signal demodulated to the baseband by the demodulator 22 via the hybrid 38. After the combined output is amplified to a specified level by the amplifier 31, the optical modulator 15 carries the fault search current in the light of λ ₃ , and sends it out to the transmitting terminal station 1 via the demultiplexer/multiplexer 9.

In the repeater 3, the demultiplexer/multiplexer 11 receives λ ₁
The only difference from the operation in the connecting box 2 is that the digital signal carried by the light of λ ₁ is regenerated and repeated by the regenerative repeater 5 after being split into light of λ ₂ and λ 2. The series of functions of demultiplexing, demodulation, insertion of fault-search current, amplification, modulation, and multiplexing are exactly the same. In the receiving terminal station 4, the light of λ ₁ modulated by the digital signal is demultiplexed by the demultiplexer/multiplexer 13 and supplied to the receiver 7, and the fault detection current demultiplexed by the demultiplexer/multiplexer 13 is carried. The demodulator 25 demodulates the light having a wavelength of λ ₂ , and its output is supplied to the level measuring device 37 via the amplifier 35 to detect each fo...fj component of each fault search current.

Suppose now that a cable failure occurs. In the case of undersea systems, even if the power supply line is cut, it is often exposed underwater and can be used to supply power. In other words, one of the paths of the power supply current is connected to the ground, and one terminal station supplies power between a positive potential and the ground, and the other terminal supplies power between a negative potential and the ground. Therefore, even if a fault occurs, the power supply state is maintained, and when both terminal stations 1 and 4 receive the fault search current, the connection boxes and repeaters near the fault point can receive the fault search current, but the connection boxes further from the fault point receive the fault detection current. , the fault detection current of the repeater cannot be received. If there is a section in which both the terminal stations 1 and 4 cannot receive the fault search current, it is possible to estimate the fault scale from that section. In other words, if there is only one fault location, the fault point can be estimated from only one terminal station, but if there are multiple fault locations, it is not possible to detect that the faults are occurring at multiple locations from only one terminal station.

As explained above, a fault-search current oscillator corresponding to each of the cable connection box of the submarine optical cable and the submarine optical repeater is built-in, and in addition to the light of wavelength λ ₁ of the main signal that carries the submarine optical transmission line, To precisely locate the point of failure of an optical fiber break by performing wavelength division multiplex transmission of only the information of the fault search current upstream and the respective lights of optical wavelengths λ ₂ and λ ₃ that are carried in each direction down. , as well as the scale of the failure, greatly contributing to the maintenance of submarine optical cable transmission lines by minimizing the time required to repair the failure, minimizing the replacement section of the failed cable, and improving the economic efficiency of repair methods. can do. In other words, the interval between repeaters becomes longer in the optical fiber transmission line, but
By providing fault-search current sources in each of a plurality of fiber connection boxes existing at intervals of one relay device, the location and scale of the fault can be easily detected.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention. 1: Submarine optical digital terminal station (transmission side), 2: Optical fiber cable connection box, 3: Submarine optical repeater,
4: submarine optical digital terminal station (receiving side), 5: digital regenerative repeater, 6: optical digital transmitter,
7: Optical digital receiver, 8-13: Optical demultiplexer/multiplexer, 14-19: Optical modulator, 20-25: Optical demodulator, 26-29: Fault-search current oscillator, 30-3
5: Amplifier, 36, 37: Fault detection current level measuring device, 38 to 41: Power coupler, 42: Submarine optical fiber cable.

Claims (1)

[Claims] 1. A cable connection box for an optical cable containing at least one optical fiber, and a fault-search current oscillator, a fault-search current amplifier, a first and second optical-to-electrical converter, a first, Second
An electro-optical converter, a first and a second demultiplexer/multiplexer for demultiplexing and multiplexing light with optical wavelengths λ ₁ , λ ₂ , and λ ₃ are built in, respectively. A light with a wavelength λ ₁ that carries a signal, and a light with a wavelength λ ₂ that carries information on all fault search currents in the downstream direction.
Wavelength division multiplexing is performed in the upstream direction with light having a wavelength of λ ₃ that carries information on all the fault detection currents, and the upstream and downstream incoming light is transmitted to the first demultiplexer/multiplexer by the cable connection box and the optical repeater. The λ ₂ light is converted into an electrical signal by the first optical-to-electrical converter, and _the electrical signal and _the output of the fault-search current oscillator are converted into the first optical-to-electrical converter. λ ₂ in electrical-optical conversion
The light of λ ₂ is multiplexed with the light of λ ₁ by the second demultiplexer/combiner and sent in the downstream direction, and the second light of λ ₃ splits the light of
Converting the light of λ ₃ into an electrical signal by the second optical-to-electrical converter, converting the electrical signal and the output of the fault-search current oscillator into light of λ ₃ by the second electrical-to-optical conversion, The light of λ ₃ is sent in the upstream direction through the first demultiplexer/multiplexer, and both end stations of the optical fiber transmission line receive all the fault detection currents, and a break in the optical fiber is detected based on the presence or absence of the fault detection current. A fault detection method for an optical fiber transmission system, comprising means for detecting a failure.