JPS58151732A - Optical repeater - Google Patents

Abstract

PURPOSE:To detect accurately a period when no signal exists, by detecting whether the signal is included in the light after converting the light into electric signals, and amplifying them, and actuating automatic gain control. CONSTITUTION:The optical signal given from an optical transmission line is coverted into an electric signal by an avalanche photodiode APD module 14. This electric signal is amplified by a preamplifier 1, and the gain of the signal is supplied to a variable amplifier 2. Then the signal which is equalized and amplified is reproduced and converted again into an optical signal to be relayed. A part of the output signals of the amplifier 1 is applied to a detecting circuit 17. The circuit 17 checks whether the received signal has a prescribed level. When no optical signal is received any more, the gain of an AGC amplifying circuit 2 is set constant. The gain of a receiving circuit is lowered in a period when no signal exists in order to prevent the deterioration of S/N for both a discriminating circuit and a timing reproducing circuit within a relaying circuit.

Description

[Detailed description of the invention] ( The present invention relates to an optical repeater used in optical communication systems.

Conventionally, in optical communication systems, the modulation method is brightness modulation (Inte
nsity Modulation) The light receiving circuit is a photodiode. The optical signal is directly detected using a jUAPD (avalanche photodiode).

FIG. 1 is a block diagram showing a conventional O'yt repeater circuit.

Optical fiber 16? The original signal transmitted via APD
The module 14 converts it into an electrical signal. This army's Qi signal has a prefix width of 61. AGC (automatic gain control) amplifier 2
and is amplified and shaped by the equalization amplifier 3. Reference number 4
This is an id voltage detection circuit, which detects the peak value so that the signal voltage given to the DC regeneration circuit 7 and the identification circuit 8 is constant, and controls the AGC amplification width by the AGC control circuit 5. together with a DC/DC converter (DC-
DC converter) 60 Control input voltage to convert APD module 1-
The signal wave height fl[t-
Make it constant. Also, the same number 10 is a timing extraction circuit,
The same number 11 is a limiter circuit. The output signal from the identification circuit 8 is given to an LD (laser diode) drive circuit 9, which drives a laser diode module 15, etc., performs electrical-to-optical conversion, and then connects it to an optical fiber. 16e. Numeral 12 is an APC (automatic gain control) circuit provided for stabilizing multiple optical outputs, and a monitoring circuit i3 monitors the repeater circuit.

In the optical signal receiving circuit, there is no noise other than the thermal noise of the preamplifier 1 [AP
There is shot noise associated with optical-to-electrical conversion in the D module 14 and dark current of the APD.

In the conventional regenerative repeater circuit, in order to control the AGC control circuit 5 so that the output of the equalization amplifier 3 is one step,
When there is no signal, the AGC gain and the APD multiplication factor are maximum. As a result, the signal given to the identification circuit 8 exceeds the identification level, so the identification circuit 8 judges it as @1. If a monitoring method is used in which the signal is looped back, the noise generated in the downlink may deteriorate the RI rate, making monitoring impossible.

In order to deal with these problems, conventional circuits detect no signal at the data output terminal or timing extraction section, and thereby change the level of the DC regeneration circuit 7 to prevent erroneous judgments in the identification circuit 8. It consists of but,
As mentioned above, since the AGC gain and the multiplication factor of APD increase, 87N (
The disadvantage is that the signal-to-noise ratio (signal-to-noise ratio) deteriorates, and it cannot detect no signal when there is no signal, so it does not operate normally.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical repeater that eliminates the above-mentioned drawbacks.

The optical repeater of the present invention is an optical repeater that converts an optical signal from an optical transmission line into an electrical signal, equalizes and amplifies this electrical signal, performs identification and regeneration, and then converts it back into an optical signal and sends it out to the optical transmission line. , a conversion means for converting the optical signal into the electric signal, a preamplification means for amplifying the output of the conversion means, and an equalization amplification means provided after the preamplification means and having a variable gain amplification section. , a detecting means for detecting a no-signal state based on the output of the pre-multiplying means; and when the detecting means detects a no-signal state, the gain gcN! and a control section t which operates to control the gain of the variable gain section so as to perform automatic gain control in response to the output of the preamplifier when the gain of h is constant and is not detected.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing a simple embodiment of the present invention.

In the figure, the same valley numbers as in Figure 1 indicate the same structure JI.
! In this embodiment, a no-signal detection circuit 17t- is provided to detect a state in which there is no element +a, that is, a no-signal state, and this detection circuit 17, as shown in FIG. A branch circuit 17-1 having an emitter follower or a two-way grounded transistor, and this branch circuit 17
It is comprised of a rectifier circuit 17-2 that rectifies the output of -1, a DC amplifier circuit 17-3, and a comparison circuit 17-4 that compares the output of this amplifier circuit 17-3 with a reference level.

The reference level of the comparator circuit 17-4 is a!, which is about 6 (dB) lower than the specified minimum light reception level. It is sufficient to set the voltage to the reference voltage E1 of 1.

Further, as shown in the AGC control circuit 5'fl, 31!3, an amplifier 5'-2 for amplifying the DC level of the peak value detection circuit 4 applied via the terminal af, and an amplifier 5'
An analog switch 5'-Hr for selecting whether to apply the DC level of the peak value detection circuit 40 or the second reference voltage E1t to the peak value detection circuit 40 and the output of the amplifier 5'-2 is connected to the terminal C1-2. It is applied to the AGC amplifier circuit 2 to control the gain.

Next, the operation will be explained.

First, when receiving all optical signals, the preamplifier l
The voltage after branching, rectifying and amplifying the output of is the first Er
Because of the higher voltage, the analog switch 5'-1 is connected to the terminal at.
- selected and normal automatic gain control is performed.

Next, when the optical signal is no longer received for some reason, the voltage applied to the comparator circuit 17-4 changes to the first reference voltage E+.
y) Low no signal detection circuit 17 is analog switch 5
'-1? The second reference voltage E is switched to the amplifier 5'-2.
■Let them be supplied. As a result, the gain of the AGC amplifier circuit 2 becomes constant, and this state continues until the optical signal is received.

In this way, the reference voltage & for making the gain of the AGC amplifier circuit 2 constant and the reference voltage E1 for detecting a no-signal state can be set independently.

As described above, in the present invention, by lowering the gain of the receiving circuit when there is no signal, the S/O in the identification circuit and the timing recovery circuit is
This has the effect of preventing N deterioration and ensuring reliable monitoring.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional optical repeater, FIG. 2 is a block diagram showing an emergency embodiment of the present invention, and FIG. 3 is a circuit diagram showing a no-signal detection circuit and an AGC control circuit. 1... Pre-amplifier circuit, 2... AGC amplification circuit, 3... Equalization amplification circuit, 4... Peak detection circuit, 5... ...AGO control circuit, 6...
・・・・D C/D C Konno (-Evening, 7・・・・・・
First-rate regeneration circuit, 8...Identification circuit, 9...
・LD drive circuit, 10...timing extraction circuit, 11... iv circuit, 12...A
PC circuit, 13...Monitoring circuit, 14...
・APD module, -115...LD module, -16...Fino (-cable, 5'...
...AGC control circuit, 17...No signal detection circuit.

Claims (1)

[Claims] An optical repeater converts the original signal from the optical transmission line into an electrical signal, equalizes and amplifies it, performs identification and regeneration, and then converts it back into an optical signal and sends it out to the optical transmission line. a converting means for converting into a signal; a preamplifying means for amplifying the output tube of the converting means; an equalizing amplifying means provided after the preamplifying means and having a variable gain amplifier; An optical repeater characterized in that it comprises: a detection means for detecting a no-signal state based on an output; and a control means operable to control gain.