JP2591146B2 - Monitoring method for Hikari Low Cable System - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring system for an optical submarine cable system, and more particularly, to an in-service monitoring of an optical submarine repeater (hereinafter, referred to as a repeater) constituting an optical submarine cable system. The present invention relates to a method and a return monitoring method for monitoring a repeater and a submarine cable by returning a signal with the repeater.

[Conventional technology]

In the conventional in-service monitoring system for optical submarine cable systems, the repeater is provided with the monitoring function, and the terminal station sends a command signal for each repeater in in-service to measure the bit error rate. The bias current of the laser diode was measured by replacing the frame format with.

Further, in the conventional loop monitoring method, the signal transmission is stopped, a command signal composed of a pulse train of the line transmission measurement is transmitted from the terminal station to each repeater, and a loop circuit is formed by the repeater to monitor the loop. Was. The return monitoring method includes an electric-stage return method in which a return circuit is formed between identification circuits in upstream and downstream regenerative amplifiers constituting a repeater, and a part of output light of a light-emitting element between regenerative amplifiers is received by a light-receiving element. There is an optical wrapping method in which the input is turned back (for example, Journal of Lightwave Technology, Vol.Lt-2, No.
6, DEC.1894).

[Problems to be solved by the invention]

However, in the above-described conventional in-service monitoring method, it is necessary to send a command signal from the terminal station to the repeater, and the command signal is multiplexed at the same speed as the transmission signal, which may adversely affect the transmission signal. In addition, a repeater must accurately extract a command signal from a randomly transmitted transmission signal, which requires advanced technology,
A complicated and large-scale monitoring circuit must be provided, which is uneconomical. Furthermore, the monitoring and control device is similarly large at the terminal station, which is uneconomical, and requires a skilled operator to control the device.

Further, the conventional loopback monitoring method has the following disadvantages. That is, in the conventional electric-stage folding method, the monitoring circuit is complicated and large-scale, and when performing the folding monitoring, the measurement of the bit error rate cannot be performed. on the other hand,
In the light-stage folding method, an optical signal is branched at an optical output point,
Further, since it is necessary to couple the optical signal at the optical input point, the optical loss in the relay section is increased, and the cost is increased due to the necessity of installing an optical switch.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and eliminate the need to send a command signal from a terminal station for monitoring a repeater, and furthermore, a monitoring method for an optical submarine cable system using a simple and small monitoring circuit. Is to provide.

[Means for solving the problem]

The present invention relates to a monitoring system for an optical submarine cable system, comprising: an oscillator that generates a monitor signal having a frequency unique to the regenerative amplifier, for each of an upstream and a downstream regenerative amplifier constituting an optical submarine repeater of the system; A modulator that modulates the monitoring signal output by a signal representing the state of the repeater, a unit that separates only all frequency bands of the monitoring signal from an input signal, and amplifies the signal. Optical signal sending means for adding the monitor signal and the monitor signal modulated by the modulator to convert the monitor signal into the optical signal; receiving a command signal having the same frequency as the monitor signal, When the level becomes equal to or higher than a certain level, a folding circuit for forming a folding circuit for providing one output signal to the other input between the upstream and downstream regeneration amplifiers. Forming means; a terminal connected to the repeater; monitoring means for monitoring the repeater based on a monitor signal from the repeater; and a signal for sending the predetermined command signal to the repeater. Transmission means is provided.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an optical submarine cable system using a monitoring system according to the present invention. This system includes a repeater 3 and a terminal device 6, which are connected by a submarine cable 1 constituted by an optical fiber. The repeater 3 includes an upstream and downstream regenerative amplifier 4
And the regenerative amplifier 4 has a regenerative amplifier circuit as a main component.
10 and a monitoring circuit 20 for sending a monitoring signal to the terminal device 6.

The terminal device 6 includes a light emitting element driving circuit (LDD) 6 on the transmitting side.
1. Equipped with a light emitting element (LD) 62, and a transmitter 63 for setting a loopback circuit, and a light receiving circuit (APD) 64, a frequency separation filter (L / H) 65, and a monitoring device 66 on the receiving side. . Then, the light emitting element driving circuit (LDD) 61 drives the light emitting element (LD) 62 by the PCM signal from the input terminal _Sd or _Su, and as a result, the light emitting element 62 transmits the optical signal to the optical fiber 2.
Through to the regenerative amplifier 4. The transmitter 63 outputs a command signal when the regenerative amplifier 4 forms a loopback circuit. The light emitting element driving circuit 61 drives the light emitting element 62 by the signal, and the light emitting element 61 converts the command signal into an optical signal. The signal is sent to the reproduction amplifier 4 as a signal. On the other hand, a light receiving circuit (APD) 64 receives an optical signal through the optical fiber 2, converts it into an electric signal, and outputs it. Frequency separation filter 65 separates the electrical signal into a monitoring signal group from the PCM signal and the repeater 3, the output for PCM signals subjected to the service terminal R _u
Or output to R _d . On the other hand, the monitoring signal group is provided to the monitoring device 66, where the regenerative amplifier is identified by the frequency and the modulation degree of each monitoring signal, and the operation state of each regenerative amplifier 4 is monitored.

The regenerative amplifier 4 has a function of performing analog relay amplification in the frequency band of the monitor signal and a function of modulating a low frequency single spectrum monitor signal having a frequency assigned to each regenerative amplifier with a signal representing the operating state of the regenerative amplifier. Things PC
It has a function of being superimposed on the M signal and sending it to the optical fiber as an optical signal, and a function of forming a loop-back circuit by a command signal from the terminal device 6.

Next, the regenerative amplifier 4 will be described in detail with reference to the block diagram of FIG. The repeater 3 includes the upstream and downstream regenerative amplifiers 4 as described above. Each regenerative amplifier 4 includes a light receiving circuit (APD) 11,
It includes an equalizing amplifier circuit (EQL) 12, a timing circuit (TIM) 13, an identification circuit (DEC) 14, a light emitting element drive circuit (LDD) 15, and a light emitting element (LD) 16. Oscillator (OSC) 21, Modulators (MOD) 22, 23, Frequency separation filter (H / L) 24, Amplifier (AMP) 25, Combiner (HYB) 2
6. It has a detector (DET) 27 and a folding circuit (SW) 28.

The light receiving circuit 11 of each regenerative amplifier 4 is
And converts the signal into an electric signal and outputs it to the frequency separation filter 24. The optical signal received by the light receiving circuit 11 from the optical fiber 2 is a high-speed PCM transmitted from the terminal device 6.
The signal is superimposed with a monitoring signal group of a single low-frequency spectrum generated by a repeater (usually plural) at the preceding stage. The frequency separation filter 24 receives the electric signal from the light receiving circuit 11 and receives a PCM signal. The signal and the monitoring signal group are separated, and the former is output to the equalizing amplifier circuit 12, and the latter is output to the amplifier 25.

The PCM signal supplied to the equalizing amplifier circuit 12 is reproduced and amplified by the equalizing amplifier circuit 12, the identification circuit 14 and the timing circuit 13 connected thereto, and output to the light emitting element drive circuit 15. The monitoring signal group supplied to the amplifier 25 is amplified there to compensate for the optical fiber loss in the relay section, and is output to the coupler 26.

On the other hand, the monitoring oscillator 21 generates a monitoring signal of a low frequency single spectrum having a frequency unique to the regenerative amplifier and outputs the signal to the modulator 22. The monitoring signal output to the modulator 22 is primary-modulated by the modulator 22 by a signal indicating the operation state of the light receiving circuit 11,
Further, the signal is secondarily modulated by the modulator 23 with a signal indicating the operation state of the light emitting element 16. The secondary modulation is performed by a modulation method different from the primary modulation. The modulated monitor signal is superimposed on the monitor signal group from the amplifier 25 by the coupler 26. One output of the coupler 26 is superimposed on the reproduced PCM signal from the identification circuit 14 in the light emitting element driving circuit 15, drives the light emitting element 16 and sends it to the next relay section as an optical signal.

As for the other output of the coupler 26, the frequency component of the monitor signal of the regenerative amplifier is detected by the detector 27, and its level is determined. As a result, when the signal level is equal to or higher than a certain level, the detector 27 controls the folding circuit 28 so that the light-emitting element 16 of one regenerative amplifier 4 is switched to the other regenerative amplifier 4.
A circuit for turning back to the output of the light receiving circuit 11 is formed. Then, the back photocurrent of the light emitting element 16 is supplied to the light receiving circuit 11 of the other regenerative amplifier via the equalizer and the switch, and the signal is folded. When the regenerative amplifier 4 forms a loopback circuit, the transmitter 63 of the terminal device 6 generates a signal having the same frequency as the frequency of the monitor signal of the regenerative amplifier and sends it out as a command signal. As a result, when the command signal is transmitted, the level of the monitoring signal frequency component of the regenerative amplifier input to the detector 27 becomes high, and a folding circuit is formed.

FIG. 3 shows such a system, in which the signal received by the terminal device 6 is represented by a spectrum. The spectrum of the frequency f _s1 represents the monitor signal transmitted from the first repeater, and the spectrum of the frequency f _sn The spectrum represents a monitor signal transmitted from the n-th repeater. The spectrum at the frequency f ₀ is that of the fundamental frequency component of the PCM signal at the line transmission speed, and the spectra at the frequencies 2f ₀ and 3f ₀ are the spectra of the second and third harmonics. In addition,
The monitoring device 66 of the terminal device 6 includes a plurality of narrow band filters, and each of the filters extracts a monitoring signal of each frequency f _{s1 to} f _sn .

As described above, the modulators 22 and 23 of the regenerative amplifier 4 modulate the monitoring signal with the signals indicating the operating states of the light receiving circuit 11 and the light emitting element 16, and there are various methods of the modulation. FIGS. 4 and 5 show examples in which different modulation methods are adopted, and specifically show the waveforms of the monitoring signals extracted by the monitoring device 66. FIG. FIG. 4 shows a monitor signal when the monitor signal of the frequency _fsn is frequency-modulated by a signal representing the operation state of the light receiving circuit 11 and amplitude-modulated by a signal representing the operation state of the light emitting element 16. In the monitoring device 66, the operating state of the light emitting element 16 can be known from the amplitude of the monitoring signal.
Can be known. FIG. 5 shows a monitor signal when the monitor signal of the frequency _fsn is frequency-modulated by a signal indicating the operation state of the light receiving circuit 11 and phase-modulated by a signal indicating the operation state of the light emitting element 16. In the figure, t ₁ , t ₂ , and t ₃ indicate the period of the phase inversion of the monitoring signal that changes depending on the operation state of the light emitting element 16. In the monitoring device 66, the operating state of the light emitting circuit 11 can be known from the frequency of the monitoring signal, and the operating state of the light emitting element 16 can be known from the phase inversion cycle.

When a monitoring signal modulated with a signal indicating the operation state of the light receiving circuit 11 and the light emitting element 16 is superimposed on the PCM signal, the monitoring signal is superimposed as an analog signal. The following low level can be set, and the S / N ratio of the PCM signal can be increased. Further, by superimposing the monitoring signal on the PCM signal through the limiter, the influence on the PCM signal can be suppressed more reliably, and the reliability can be improved.

〔The invention's effect〕

As described above, the optical rotating cable system according to the monitoring method of the present invention includes, in each of the upstream and downstream regenerative amplifiers constituting the optical submarine repeater of the system, an oscillator that generates a monitor signal having a frequency unique to the regenerative amplifier; A modulator that modulates the monitor signal output by the oscillator with a signal indicating the state of the repeater, and an optical signal transmitting unit that converts the monitor signal modulated by the modulator into an optical signal and transmits the optical signal to a cable; The terminal station connected to the repeater is provided with monitoring means for monitoring the repeater based on a monitoring signal from the repeater. Therefore, unlike the related art, there is no need to send a command signal for controlling the repeater from the terminal station device for performing in-service monitoring, and the command signal does not affect the transmission signal. In addition, since there is no need to extract a command signal, the monitoring circuit is simple and small, and is economical. Further, the terminal station can similarly reduce the size of the monitoring and control device, thereby improving the economic efficiency, and does not require a skilled operator to control the device.

Further, the optical submarine cable system according to the monitoring method of the present invention, when receiving a predetermined command signal, forms a loop between the upstream and downstream regenerative amplifiers to form a loop for applying one output signal to the other input. The terminal station connected to the repeater includes circuit forming means, and the terminal station connected to the repeater includes signal transmission means for transmitting the predetermined command signal to the repeater. Therefore, loopback monitoring can be performed by a simple and small-scale circuit, there is no problem such as an increase in optical loss in the relay section, and the measurement of the bit error rate can be performed at the same time.

Further, since the monitoring circuit of the repeater and the monitoring and regulating device of the terminal station are both simple and small in scale and easy to operate, maintenance becomes easy and the reliability of the system is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical submarine cable system using a monitoring method according to the present invention, FIG. 2 is a block diagram showing a regenerative amplifier of a repeater constituting the optical submarine cable of FIG. 1, FIG. 4 is a graph showing the spectrum of the monitor signal and the transmission signal, and FIGS. 4 and 5 are waveform diagrams showing the modulated monitor signal. DESCRIPTION OF SYMBOLS 1 ... Submarine cable 2 ... Optical fiber 3 ... Repeater 4 ... Regenerative amplifier 6 ... Terminal device 10 ... Regenerating amplifier circuit 11,64 ... Light receiving circuit 12 ... Equalizing amplifier circuit 13 ... Timing Circuit 14 Identification circuit 15,61 Light-emitting element drive circuit 16,62 Light-emitting element 20 Monitoring circuit 21 Monitoring oscillator 22,23 Modulator 24 Frequency separation filter 25 Amplifier 26 …… Coupler 27 …… Detector 28 …… Fold circuit 63 …… Oscillator 64 …… Monitor

Claims (1)

(57) [Claims] 1. A monitoring system for an optical submarine cable system, comprising: an oscillator for generating a monitor signal having a frequency unique to the regenerative amplifier, for each of an upstream and a downstream regenerative amplifier constituting an optical submarine repeater of the system; A modulator that modulates the monitor signal output from the oscillator with a signal indicating a state of the repeater; a unit that separates and amplifies only all frequency bands of the monitor signal from an input signal; Optical signal sending means for adding the monitored signal and the monitoring signal modulated by the modulator to convert the signal into the optical signal; receiving a command signal having the same frequency as the frequency of the monitoring signal; When the level of the signal becomes equal to or higher than a predetermined value, forms a folding circuit for providing one output signal to the other input between the upstream and downstream regeneration amplifiers. A path forming unit, a monitoring unit that monitors the relay unit based on a monitoring signal from the relay unit, to a terminal station connected to the relay unit, and sends the predetermined command signal to the relay unit. A monitoring system for an optical submarine cable system, comprising: a signal transmitting unit.