JPH02198233A - Optical repeater - Google Patents

Abstract

PURPOSE:To easily confirm a system margin by providing a monitor circuit or the like comprising a decoder and a voltage controlled oscillator and applying ASK(Amplitude Shift Keying) modulation to a sent optical signal while modulation is able to be varied. CONSTITUTION:An optical signal 11 is inputted to a decoder 24 in a monitor circuit 23 via an optic/electric transducer 13 and a reproduced repeater circuit 14 or the like, decoded and a decoder output signal 28 is applied to a voltage controlled oscillator 29. The signal 28 varies the output of the oscillator 29, superimposed on a drive signal 19 via an LPF 33 to apply ASK modulation. That is, the oscillator 29 is subject to frequency varying by the signal 28 and since the resulting signal passes through an LPF 33, the amplitude of a low frequency superimposing signal 34 superimposed on the signal 19 is changed to change the modulation degree of the ASK modulation of the optical signal 36. Thus, accurate system margin is confirmed even after the establishment of the system by measuring in advance the relation between the frequency of the variable frequency signal 31 and the code error of an optical repeater or the like of the next stage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical repeater equipped with a monitoring circuit for checking a system margin.

[Conventional technology]

Optical fiber is non-inductive and has a signal-to-noise ratio (signal to noise ratio) in the transmission cable.
It is widely used for optical information communication because of its low deterioration, low loss, and wide band characteristics.

In an optical fiber communication system, an optical signal converted from an electrical signal at a terminal equipment is transmitted to another terminal equipment through an optical fiber cable, and the terminal equipment that receives the optical signal converts the optical signal into the original electrical signal. It is something that converts.

However, when performing long-distance transmission, an optical signal propagated over a long distance through an optical fiber is subjected to waveform distortion due to attenuation and dispersion due to scattering or absorption during the propagation process. Therefore, when performing long-distance transmission, repeaters are often installed at fixed distances to compensate for deterioration in transmission quality due to such attenuation and waveform distortion. A regenerative repeater works to regenerate a distorted electrical signal into a digital signal that matches the one on the transmitting side.

Conventionally, optical repeaters have had an optical repeater human output monitoring function in order to check the system margin after the installation work of this optical repeater system.

[Problem to be solved by the invention]

However, in the conventional monitoring function, only electric power was monitored because modulation from an electrical signal to an optical signal uses intensity modulation that changes the intensity (power) of light according to the electrical signal. Therefore, deterioration of the SN ratio in the -1 amplitude direction can be monitored, but the SN ratio in the time direction can be monitored.
It was not possible to monitor the deterioration of the ratio. Therefore, in systems where the information transmission speed is high and the influence of dispersion due to the spectrum of the laser diode (LD) cannot be ignored, or in systems where the addition of jitter affects long-distance systems, there is a clear system margin. could not be confirmed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical repeater that allows easy confirmation of the system margin.

[Means to solve the problem]

The optical repeater of the present invention includes (i) opto-electrical conversion means for receiving an optical signal including a monitoring signal for checking system margin from an optical fiber and converting it into an electrical signal; and (11) using this opto-electrical conversion means. a regenerative repeater that performs equivalent amplification, retiming, and identification reproduction of the converted electrical signal and outputs a regenerated signal, and (iii) converts the regenerated signal regenerated by the regenerative repeater into an optical signal and supplies it to an optical fiber. (iv) a supervisory signal demodulator that demodulates the supervisory signal included in the reproduced signal; and (v) a signal with an oscillation frequency that corresponds to the voltage value of the supervisory signal demodulated by the supervisory signal demodulator. and (vi) superimposition means for superimposing the output signal of the oscillation means on the reproduced signal.

That is, the optical repeater of the present invention has a low frequency ΔS K (Amplitude 5hift Key
The eye pattern (Bye
The system margin is ensured by observing the deterioration of code errors in the next-stage optical repeater that receives this optical signal.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 shows a circuit diagram of an optical repeater in one embodiment of the present invention.

The optical repeater of this embodiment includes a photoelectric conversion element 13 that converts an optical signal 11 supplied from an optical fiber (not shown) into an electrical signal 12. The photoelectric conversion element 13 is, for example, a photodiode or an avalanche photodiode (
APD> is used. The electrical signal 12 converted by the photoelectric conversion element 13 is supplied to a regenerative repeater circuit 14. The regenerative relay circuit 14 receives the supplied electrical signal 12
equivalent amplification (Reshaping), retiming (R
etiming) and identification regeneration (Regenerat).
ing) and output as the original pulse-shaped reproduction signal 16 without distortion or the like. The reproduced signal 16 output from the regenerative repeater circuit 14 is supplied to the light source drive circuit 17. The light source drive circuit 17 outputs a drive signal 19 having a current value for driving the electro-optical conversion element 18 in accordance with the reproduction signal 16. As the electro-optical conversion element 18, for example, a light emitting diode (LE
D) and a laser diode (LD) are used. The drive signal 19 is converted into an optical signal by the electro-optical conversion element 18, and the optical signal is supplied to an optical fiber (not shown).

The optical repeater receives the reproduced signal 16 regenerated in the reproducing path 14.
A band-pass filter 22 is provided for demodulating a monitoring signal 21 in a specific band from the . The monitoring signal 21 demodulated by the bandpass filter 22 is manually input to the monitoring circuit 23. In the monitoring circuit 23 , the input monitoring signal 21 is decoded by a decoder 24 and supplied to an AND gate 27 as a decoder output signal 26 . The decoder output signal 28 of the decoder 24 is also applied to a voltage controlled oscillator (VCO) 29.

The voltage controlled oscillator 29 outputs a variable frequency signal 31 whose frequency changes depending on the applied voltage value. Variable frequency signal 31 is supplied to AND gate 27 . The AND gate 27 performs a logical product of the manually input decoder output signal 26 and the variable frequency signal 31, resulting in an output signal 32 of the monitoring circuit 23. The output signal 32 of the monitoring circuit 23 passes through a low frequency pass filter 33 and is superimposed on the drive signal 9 as a low frequency superimposed signal 34.

The operation of an embodiment of the optical repeater configured as described above will be described below.

An optical signal 11 supplied to the optical repeater from an optical fiber (not shown) is converted into an electrical signal 12 by a photoelectric conversion element 13. Since the converted electrical signal 12 is distorted during the transmission process through the optical fiber, the regenerative repeater circuit 14 performs equivalent amplification, retiming, and identification regeneration to generate the original pulse-shaped regenerated signal 16 without any distortion. Output. The reproduction signal 16 is supplied to a light source drive circuit 17, and a drive signal 19 corresponding to the signal value is output. The drive signal 19 is converted into an optical signal again by the electro-optical conversion element 18, and is transmitted to the next optical repeater, also not shown, through an optical fiber, not shown.

On the other hand, when a monitoring signal is added to the optical signal 11 and the reproduced signal 16 to monitor whether communication between terminal devices (not shown) through an optical fiber or an optical repeater is normal or not. There is. Since this monitoring signal has a specific band, the portion of the reproduced signal 16 is input to the band pass filter 22 to demodulate the monitoring signal 21. The monitoring signal 21 separated from the reproduced signal is input to a monitoring circuit 23, and a decoder 24 discriminates the command of the monitoring signal 21 and performs various monitoring.

A decoder output signal 26 decoded by the decoder 24 is supplied to an AND gate 27, while a decoder output signal 28 is applied to a voltage controlled oscillator (VCO) 29. The voltage controlled oscillator 29 outputs a variable frequency signal 31 whose frequency corresponds to the applied voltage value, and supplies it to the AND gate 27 .

The AND gate 27 logically ANDs the decoder output signal 26 and the variable frequency signal 3I, and outputs the monitoring circuit 23 output signal 3I.
Outputs 2. The output signal 32 of the monitoring circuit 23 passes through a low frequency pass filter 33 and is superimposed on the drive signal 19 as a low frequency superimposed signal 34.

In this embodiment, the voltage controlled oscillator 2 is controlled by the decoder output signal 28.
9 is changed and superimposed on the drive signal 19 through a low frequency pass filter 33 to perform ASK modulation. Since the voltage controlled oscillator 29 is frequency-variable by the decoder output signal 28 and passes through the low frequency pass filter 32, the drive signal 1
The amplitude of the low frequency superimposed signal 34 superimposed on the signal 9 changes.

That is, the modulation degree of ASK modulation of the optical signal 36 can be changed. Therefore, by measuring in advance the relationship between the degree of modulation, that is, the frequency of the variable frequency signal 310 output by the voltage controlled oscillator 29, and the code error of the next stage optical repeater or terminal equipment, it is possible to This function makes it possible to check the system margin.

〔Effect of the invention〕

As described above, according to the present invention, since the transmitted optical signal is subjected to ASK modulation that can change the degree of modulation, it becomes possible to confirm an accurate system margin.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention. 13...Photoelectric conversion element, 14...Regenerative relay circuit, 17...Light source drive circuit, 18...Electro-optical conversion element, 22... ... band pass filter, 23 ... monitoring circuit, 24 ... decoder,
29... Voltage controlled oscillator.

Claims (1)

[Claims] A photoelectric conversion means for receiving an optical signal including a monitoring signal for checking a system margin from an optical fiber and converting it into an electric signal; and an equivalent value of the electric signal converted by the photoelectric conversion means. a regenerative repeater that performs amplification, retiming, and identification reproduction and outputs a regenerated signal; an electro-optic converter that converts the regenerated signal regenerated by the regenerative repeater into an optical signal and supplies it to an optical fiber; and the regenerated signal. a supervisory signal demodulating means for demodulating the supervisory signal included in the supervisory signal; an oscillating means for outputting a signal with an oscillation frequency corresponding to a voltage value of the supervisory signal demodulated by the supervisory signal demodulating means; and an output signal of the oscillating means. and a superimposing means for superimposing the reproduced signal on the reproduced signal.