JP2826457B2 - Optical repeater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical repeater, and more particularly, to transmission of monitoring information between optical repeaters.

[0002]

2. Description of the Related Art Generally, in the optical repeater, when an abnormality such as a failure occurs in its own repeater, a process for transmitting the fact to a subsequent stage is performed. In such a case, monitoring information indicating the occurrence of the abnormality is superimposed on the digital optical main signal, which is information that should be transmitted, and transmitted to the subsequent stage, and the subsequent stage repeater performs processing for extracting the monitoring information.

[0003] In addition to the fact that an abnormality such as a failure has occurred, communication between repeaters is similarly performed by superimposing it on the optical main signal and transmitting it.

[0004] The conventional repeater will be described with reference to FIG.

In the figure, a conventional repeater is an optical branching coupler 2 for branching an output optical main signal transmitted from an earlier stage through an optical fiber transmission line 1a into two, and directly amplifies one of the branched ones. An optical direct amplifier (EDFA) 3 is included.

Further, the conventional repeater 100 includes a light receiving element (PD) 12 for converting the other branched by the optical branch coupler 2 into an electric signal in order to extract monitoring information, and a current for the converted electric signal. A current-voltage conversion circuit (I / V) 13 for performing voltage conversion, and a demodulation circuit (DECO) for code-demodulating the converted output and sending it to a signal processing circuit (not shown)
D) 14 and a modulation circuit (COD) 15 for code-modulating the output of a signal processing circuit (not shown).

The optical direct amplifier 3 comprises an erbium-doped fiber (EDF) 4 and a laser drive circuit LD for driving an excitation semiconductor laser (LD) 11 in accordance with the output of a modulation circuit 15.
D10 and a wavelength division multiplexer (WDM) 5 for wavelength-division multiplexing the optical main signal in accordance with the output of the semiconductor laser 11 and transmitting it to the subsequent stage via the optical fiber transmission line 1b.

The repeaters having such a configuration are used by continuously connecting a large number of them, thereby constituting an optical fiber repeater transmission system. That is, in the conventional repeater, the main signal light is received from the preceding stage and transmitted to the subsequent stage, and the monitoring information is extracted from the output optical main signal from the preceding stage, and the monitoring information of the own repeater is superimposed on the main signal light. It is sent to the subsequent stage.

In this case, the monitoring information of the optical repeater is pre-modulated into a signal having a frequency component lower than the main signal bit rate to generate a monitoring signal, and the monitoring signal is used as a pumping light source for the semiconductor laser 11 of the optical direct amplifier 3. Control the injection current into the
The monitoring information is transmitted downstream of the optical fiber transmission line 1b by modulating the light intensity of the main signal light by the gain modulation of the optical direct amplifier 3.

[0010]

In order to construct a long-distance optical fiber communication system using the above-mentioned conventional optical repeaters, consider a case where optical repeaters are connected in multiple stages. Then
In order to directly amplify the main signal light on which the monitoring signal propagated from the upstream optical repeater located upstream of the optical fiber transmission line is superimposed in the own optical repeater and superimpose the monitor signal of the own repeater, When monitoring information is extracted by a downstream optical repeater located downstream, there is a drawback that interference occurs between monitoring signals of different optical repeaters.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional disadvantages, and has as its object to solve the problem such as the failure of a repeater.
An object of the present invention is to provide an optical repeater capable of avoiding interference of monitoring information indicating an abnormality .

[0012]

Means for Solving the Problems An optical repeater of the present invention, light
Monitoring information having a main signal and a lower frequency than this optical main signal
An optical signal input section for receiving an optical signal on which
The main signal is optically amplified and the amplified optical main signal is output and monitored.
It has a cutoff frequency higher than the frequency of
The optical direct amplifier to cut and the output side of the optical direct amplifier
After superimposing the monitoring information of the repeater on the amplified main signal
And a monitoring information superimposing unit for sending to a stage.
And Here, the monitoring information superimposing unit supervises the own relay device.
Superimposed by optical intensity modulation of amplified optical main signal with visual information
And an external light intensity modulation section. Also, direct light amplification
The feeder controls the light intensity of the amplified optical main signal to be constant.
Has a back loop.

[0013]

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

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical repeater according to the present invention, and portions equivalent to those in FIG. 4 are denoted by the same reference numerals. In the figure, the optical repeater 100 of this embodiment is different from the conventional one in that a feedback loop for keeping the optical intensity of the main signal constant is provided in the optical direct amplifier 3 and the output of the amplifier 3 is monitored. An external modulator (EA) 7 for superimposing information and an external modulator driving circuit 16 are provided.

The feedback loop in the optical direct amplifier 3 includes a branch coupler 6 for branching the optical main signal.
A light receiving element 8 for converting one of the branched outputs into an electric signal; an output light power constant circuit (ALC) 9 for keeping the power level of the converted electric signal constant; Driving laser drive circuit (LD
D) 10).

In such a configuration, the optical fiber transmission line 1
The optical main signal propagating through a is light intensity modulated with a sine wave signal having a frequency lower than the main signal bit rate frequency. This sine wave signal is monitoring information in the preceding-stage repeater. This monitoring information can be extracted by splitting a part of the input optical signal by the splitting coupler 2, performing photoelectric conversion in the light receiving element 12 and the current-voltage conversion circuit 13, and demodulating the signal by the demodulation circuit 14. This is the same as the conventional repeater (FIG. 3).

The other of the main optical signals branched by the branch coupler 2 is directly amplified in the fiber 4 by pumping light having a wavelength effective for the amplification characteristics of the erbium-doped fiber 4. Here, the light intensity of the pumping semiconductor laser 11 is controlled by a feedback loop such that a part of the output optical signal of the amplifier 3 is branched by the branch coupler 6 and the branched signal light has a constant light intensity. is there.

The feedback loop control will be described with reference to FIGS. FIG. 2 shows frequency characteristics of light intensity modulation of an input optical signal in a direct optical amplifier that has performed feedback loop control so that the output signal light intensity is constant.

As shown in the figure, even when feedback loop control is performed so that the output signal light intensity becomes constant when the frequency f at which the optical intensity of the input signal light is modulated is higher than 10 KHz, the input signal light is not changed. The amplitude ratio of the light intensity modulation between the output and the output does not change and is 0 dB. On the other hand, if the frequency f is 10
When the frequency is lower than KHz, the amplitude ratio changes and becomes -3 dB at 3 KHz.

Here, reference is made to FIG. FIG. 3 shows a waveform of an output optical signal when a digital optical signal in which the frequency of the signal superimposed on the portion A is 1 kHz and the frequency of the signal superimposed on the portion B is 10 kHz is input to the optical direct amplifier 3. It is shown. According to the frequency characteristics of FIG. 2 described above, the portion A has a flat output because the input / output amplitude ratio is -3 dB or more. On the other hand, the portion B is output without becoming flat. That is, by the feedback loop control, the amplifier 3 functions as a high-pass filter that cuts a frequency band lower than 3 KHz.

Therefore, if the monitoring information is transmitted using the cut frequency band, the monitoring signal from the preceding stage will not be transmitted to the subsequent stage as it is, so that the monitoring signals will not interfere with each other. In the case of the amplifier having the frequency characteristic shown in FIG. 2, the effective frequency as the monitoring signal superimposed on the main optical signal is the main signal bit rate frequency (about 1 MHz or more, for example, 10 GHz).
z, 2.4 GHz, 600 MHz), which is at most 2-3 KHz.

As described above, since the frequency of the sine wave signal of the monitor signal desirably superimposed on the main optical signal is 2 to 3 KHz, two different frequencies (for example, f1) are used.
= 1 KHz, f2 = 2 KHz)
It is effective to convert the monitoring information into an electric signal by performing modulation (uity shift keying) in advance. Needless to say, other modulation schemes may be used.

Returning to FIG. 1, the main optical signal from the preceding stage is input to the external modulator 7 after the light intensity becomes constant by the feedback control of the amplifier 3. The monitoring information of the repeater to be superimposed on the main optical signal is converted by the modulation circuit 15 into a monitoring signal having a frequency component lower than the main signal bit rate frequency. In response to this monitoring signal, the external modulator driving circuit 16
Drives the external modulator 7 so that the monitoring signal is superimposed on the main optical signal. The main optical signal on which the monitor signal is superimposed is transmitted to the subsequent repeater, and processed in the same manner as described above.

In short, the monitoring information from the preceding stage is cut in the optical direct amplifier 3 functioning as a filter, and the monitoring information of the own repeater is superimposed on the filtered main signal after the cut and transmitted to the subsequent stage. As a result, the monitoring information does not interfere with each other.

[0025]

As described above, according to the present invention, the monitoring information is cut from the output optical main signal transmitted from the preceding stage and superimposed with the monitoring information on the digital main signal, and the signal after the cut is self-repeated. By superimposing the monitoring information of the device and sending it to the subsequent stage, there is an effect that the monitoring information can be propagated without interference even when an optical repeater is connected in multiple stages to form an optical repeater transmission system.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical repeater according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating frequency characteristics of light intensity modulation in an optical direct amplifier.

FIG. 3 is a conceptual diagram illustrating an operation of the optical direct amplifier.

FIG. 4 is a block diagram showing a configuration of a conventional optical repeater.

[Explanation of symbols]

 1a, 1b Optical fiber transmitter 2, 6 Optical branching coupler 3 Optical direct amplifier 4 Erbium-doped fiber 5 Wavelength division multiplexer 7 External modulator 8, 12, Light receiving element 9 Output light power constant circuit 10 Laser drive circuit 11 Pump semiconductor laser 13 Current-voltage conversion circuit 14 Demodulation circuit 15 Modulation circuit 16 External modulator drive circuit

Claims (5)

(57) [Claims] (1)An optical main signal and a lower frequency than the optical main signal.
Light to which an optical signal on which monitoring information having a number is superimposed is input
Signal input means; The optical main signal is optically amplified to output an amplified optical main signal.
In particular, it has a cut-off frequency higher than the frequency of the monitoring information.
An optical direct amplifier for cutting the monitoring information;  The amplifier is disposed on the output side of the optical direct amplifier, and
Monitoring that superimposes the monitoring information of the repeater on the signal and sends it to the subsequent stage
Information superimposition meansHaveOptical relay characterized by the following:
vessel. 2. The monitoring information superimposing means includes an external light intensity modulating means for superimposing the amplified optical main signal by modulating the light intensity with the monitoring information of the own repeater.
Optical repeater according to claim 1, this and features are. 3. The optical repeater according to claim 2, wherein the optical direct amplifier has a feedback loop for controlling the light intensity of the amplified optical main signal to be constant. 4. The monitoring information superimposing means: a converting means for converting the monitoring information of the self-repeater into an optical signal; and a modulation for modulating the amplified optical main signal with the converted optical signal and sending it to a subsequent stage. The optical repeater according to claim 1 or 2, further comprising: 5. An FS for converting the monitoring information into an FSK-modulated optical signal.
The optical repeater according to claim 4, further comprising K modulation means .