JP3010897B2 - 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 monitoring and control of an optical amplifying repeater used in, for example, an optical communication system.

[0002]

2. Description of the Related Art Conventionally, there has been an apparatus of this kind as shown in FIG. FIG. 1 shows a configuration diagram of a conventional optical amplification repeater disclosed in Japanese Patent Application Laid-Open No. 3-214936.

In the conventional optical amplification repeater, when the main signal light c on which the monitor signal a is superimposed is input from the main signal light input terminal 1, the main signal light c is branched by the optical branch coupler 4.
A part of the branched main signal light c is input to the monitoring signal processing circuit 20. The monitoring signal processing circuit 20 performs a process based on the monitoring signal a. The monitor signal generating circuit 13 generates a monitor signal b based on the monitor signal a, drives the pump light source 9 by the pump light source driving circuit 8, modulates the intensity of the main signal light c by the rare earth doped optical fiber 2, and The main signal light d on which the monitor signal b is superimposed is transmitted to the next-stage repeater. At this time, the monitor signal b is superimposed with a different frequency from the monitor signal a.

FIG. 8 shows a conventional apparatus of this type. FIG.
1 shows a conventional optical amplifying repeater disclosed in Japanese Patent Application Laid-Open Publication No. H10-260,000.
In a conventional optical amplification repeater, an optical signal to be relayed and transmitted is normally split by an optical splitter 4, and one of the split signals is
The light is input to the optical multiplexer 3 in the optical fiber amplifier 21, amplified by the excitation light source 9, and transmitted. The other optical signal split by the optical splitting coupler 4 is input to the optical receiver 5, converted into an electric signal, and input to the no-signal detector 19. Now, assuming that the transmitted optical signal is interrupted, the no-signal detector 19 detects that no signal is present, and
2 to output a control signal. The transmitter 22 receives the control signal from the no-signal detector 19, oscillates at the frequency assigned to the repeater, and
Modulates the bias current of the excitation light source 9 in the inside. as a result,
The optical fiber amplifier 21 sends out spontaneous emission light modulated at the frequency assigned to the repeater. The modulated spontaneous emission light signal is observed at the terminal station, and a relay section in which a failure has occurred can be determined.

[0005]

Since the conventional optical repeater is configured as described above, it is necessary to set the monitor signal by the monitor signal processing circuit to a different frequency for each optical repeater.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. When a main signal light on which a first monitoring signal is superimposed is received from a preceding stage, the level fluctuation of the main signal light is used. It is an object of the present invention to provide an optical repeater having a function of demodulating and extracting a first monitoring signal and further superimposing a second monitoring signal on main signal light or spontaneous emission light for transmission.

[0007]

An optical repeater according to the present invention is, for example, a two-stage cascade-connected optical amplifier for superimposing and transmitting a second supervisory signal in an optical amplifier repeater. Has the following elements. (A) An optical signal on which a first monitoring signal is superimposed is input, a difference from a predetermined reference value is generated as an error signal, and the input optical signal is set to a constant level based on the error signal. Level means, (b) monitoring signal processing means for detecting and processing the first monitoring signal based on the error signal generated by the constant level means, (c) second monitoring signal processing means for detecting the first monitoring signal based on the processing of the monitoring signal processing means. Monitoring signal superimposing means for generating a second monitoring signal and superimposing the second monitoring signal on the optical signal whose level has been made constant by the constant level means;

In the optical repeater according to the present invention, the monitor signal is transmitted by being superimposed on the spontaneous emission light.

[0009]

In the optical repeater according to the present invention, for example, optical amplifiers are connected in cascade in two stages, and the constant level means operates so as to eliminate the first monitor signal of the main signal light by using the optical amplifier in the preceding stage. At the same time, the first monitoring signal is extracted. Then, the monitoring signal superimposing means superimposes the second monitoring signal generated based on the processing by the monitoring signal processing means on the main signal light having a constant level by the constant level means, using an optical amplifier at a subsequent stage. Therefore, it becomes possible to superimpose the second monitoring signal having an arbitrary frequency that does not depend on the carrier frequency of the first monitoring signal of the main signal light on the main signal light and transmit the superimposed signal.

Further, in the optical repeater according to the present invention, when the main signal light cannot be used as a carrier due to a line disconnection or the like, the monitor signal can be transferred to a subsequent stage by using the spontaneous emission light as the carrier.

[0011]

[Embodiment 1] An embodiment of the present invention will be described below with reference to the drawings. FIG.
1 is a configuration diagram showing an optical amplification repeater according to the present invention.
In the figure, 1 is a main signal light input terminal, 2 and 17 are rare earth doped optical fibers, 3 and 16 are wavelength division multiplexing optical couplers,
Is an optical branching coupler, 5 is a light receiver, 6 is a differential amplifier, 7 is a reference potential generating circuit, 8 and 14 are excitation light source driving circuits, 9 and 1
5 is an excitation light source, 10 is a demodulation circuit, 11 is a separation circuit, 12
Is a multiplexing circuit, 13 is a monitor signal generation circuit, 18 is a main signal light output terminal, a is a first monitor signal, b is a second monitor signal,
c is a main signal light on which the first monitor signal a is superimposed, d is a main signal light on which the second monitor signal b is superimposed, e and f are pump lights,
g is a level error signal, and h is amplified light.

An optical signal 30 receives the optical signal on which the first monitor signal is superimposed, generates a predetermined reference value and an error signal, and sets the input optical signal to a constant level based on the error signal. A constant level means, 40 is a monitoring signal processing means for detecting and processing the first monitoring signal based on the error signal generated by the constant level means, and 50 is a second monitoring signal processing means, based on the processing of the monitoring signal processing means. Is a monitoring signal superimposing means for generating the monitoring signal of the above and superimposing the second monitoring signal on the optical signal.

Next, the operation will be described with reference to FIG. The main signal light input terminal 1 inputs the main signal light c on which the first monitor signal a, which is a low frequency signal, is superimposed from the optical amplification repeater at the preceding stage. The optical branching coupler 4 branches a part of the main signal light c on which the first monitoring signal a from the main signal light input terminal 1 is superimposed,
One of the branched output sides is connected to the rare-earth-doped optical fiber 17, and the other is connected to the light receiver 5 that receives a part of the main signal light c. When the light level of the main signal light c on which the first monitoring signal a is superimposed is constant, the light output of the pump light source 9 is controlled by the pump light source driving circuit 8 so as to be a predetermined constant value. For example, when the main signal light c is intensity-modulated by the first monitoring signal a which is a low frequency signal, the light level of the main signal light c does not become constant. In this case, the constant level amplifier 30 operates so that the light level becomes constant. When the light level changes, the light level received by the light receiver 5 changes. The light receiver 5 converts the level fluctuation into light / electricity. The differential amplifier 6 compares the light level with the level of the reference potential generating circuit 7, takes the difference, and outputs it as a level error signal g caused by the superimposed first monitoring signal a.

An excitation light source driving circuit 8 controls the output level of the excitation light e of the excitation light source 9 based on the level error signal g,
The light enters the rare earth-doped optical fiber 2 from the wavelength multiplexing optical multiplexer 3. The rare-earth doped optical fiber 2 is, for example, a single-mode fiber having a length of several meters to several tens of meters doped with erbium, which is a rare-earth element, and pumps the pump light e of the pump light source 9 backward from the wavelength division multiplexing optical multiplexer 3. by doing,
The rare-earth doped optical fiber 2 is in an inverted distribution state, and the main signal light c from the main signal light input terminal 1 is amplified by the stimulated emission action. Therefore, the pumping light source driving circuit 8 of the constant level amplifying means 30 controls the first monitoring signal a and the level error signal g so that they are in opposite phases, and the rare-earth doped optical fiber 2
When the pumping light e is excited, the amplified light h whose light level is stabilized is obtained.

The monitoring signal processing means 40 demodulates the level error signal g of the differential amplifier 6 by the demodulation circuit 10, separates the level error signal g by the separation circuit 11, and processes the same by the monitoring signal processing circuit 20, whereby the first The relay device can be controlled by the monitoring signal a. The multiplexing circuit 12 receives the signal from the demultiplexing circuit 11, receives the first monitoring signal a, receives the signal from the monitoring signal processing circuit 20, and multiplexes the signal from the optical repeater. .

The supervisory signal superimposing means 50 generates a second supervisory signal b from the repeater from the supervisory signal generation circuit 13, controls the excitation light source 15 by the excitation light source drive circuit 14, and transmits the second excitation signal b to the rare earth doped optical fiber 17. By pumping the pumping light f of the pumping light source 15 backward from the wavelength multiplexing optical multiplexer 16, the second monitor signal is added to the first amplified light h stabilized to a constant level in the fiber by the same operation as described above. It becomes possible to output the main signal light d on which b is superimposed.

As described above, in this embodiment, in the optical amplification repeater provided with the optical amplifier, the main signal light on which the first monitor signal is superimposed is input, and the first amplified light is output.
A first optical fiber doped with a medium that amplifies light, a first pumping light source that generates a first pumping light that pumps the first optical fiber, and connected to the first optical fiber,
A first wavelength multiplexing optical coupler for wavelength multiplexing, a first pumping light source driving circuit for driving the first pumping light source, an optical branching coupler for branching the first amplified light, and branching of the optical branching coupler A photodetector for performing optical / electrical conversion of output light, a reference potential generating circuit for setting a reference potential for comparing an electric signal output from the photodetector with a predetermined reference value, and the photodetector and the reference potential A differential amplifier which receives an output signal of a generating circuit as an input, compares the two, and outputs a level error signal, and a demodulator which receives a level error signal of the differential amplifier, that is, an extracted first monitoring signal, and demodulates the same. A circuit, the first amplified light is input, the second amplified light is output, a second optical fiber doped with a medium for amplifying the light, and a second pump for pumping the second optical fiber A second excitation light source for generating light, A second wavelength multiplexing optical coupler that is connected to the second optical fiber and wavelength-multiplexes the second pump light and the first amplified light, and a second pump light source that drives the second pump light source An optical repeater amplifying device comprising: a drive circuit; and a monitor signal generation circuit connected to a second pump light source drive circuit for superimposing a second monitor signal on the second pump light source. did. In this case, the carrier frequencies of the first monitor signal a and the second monitor signal b may be the same.

As the first monitoring signal a and the second monitoring signal b, as shown in FIG. 2A, the carrier is monitored information (in this case, 1, 0, 1, 0, 1,...) What is modulated by ASK may be used. As a means for demodulating the monitoring signal, the main signal on which the monitoring signal is superimposed is received by the photodetector, optically / electrically converted, and passed through a band-pass filter that passes only the modulation frequency of the monitoring signal. The modulated signal shown in b) is extracted. If the modulated signal is square-law detected or synchronously detected, the corresponding optical repeater / amplifier can obtain monitoring information. It goes without saying that other modulation schemes (for example, FSK, PSK, etc.) may be used.

FIG. 3A shows a case where the monitoring information is directly converted into a PCM signal without a carrier wave. The corresponding optical repeater / amplifier can obtain monitoring information in the same manner as in the example of the ASK modulation.

As described above, according to this embodiment, since the second optical amplifier for modulation is provided in the optical repeater apparatus, the monitor signal b output from the monitor signal generating circuit 13 is replaced with the monitor signal a of the preceding stage. Irrespective of the degree of modulation, the excitation light source 15 can be controlled.

Embodiment 2 FIG. The first embodiment is an example in which the main signal light c is always input to the optical amplifying repeater. However, if the fiber is cut upstream of the optical amplifying repeater or the upstream optical amplifying repeater fails. In this case, a situation occurs in which the main signal light c is not input to the optical amplification repeater. In this case, if the excitation light source 15 is modulated by the second monitoring signal b with the same device configuration as in the first embodiment, and the second monitoring signal b is transferred using the spontaneous emission light as a carrier wave, even if the main signal light c is not present. The monitoring signal can be transferred downstream.

FIG. 4A shows a spontaneous emission light spectrum of the optical amplifier when the main signal light c is not input. Also,
FIG. 4B shows a spontaneous emission light spectrum of the optical amplifier when the main signal light c is input. When there is the main signal light c, the level of the spontaneous emission light is low because the energy of the optical amplifier is used for amplifying the main signal light c. However, if the main signal light c is not input, the stimulated emission stops, and the level of the spontaneous emission light increases. When the main signal light c is cut off, the second monitoring signal b may be transferred using this high-level spontaneous emission light as a carrier wave.

Embodiment 3 FIG. In the first embodiment, the configuration in which the rare-earth-doped optical fibers 2 and 17 are pumped backward is shown. However, as shown in FIG. 5, even in the case of forward pumping, the same effect as in the above-described embodiment can be expected. 1
9 is a band pass filter.

Embodiment 4 FIG. In the first embodiment, the configuration in which two wavelength multiplexing couplers are used has been described. However, as shown in FIG. 6, the same effect as in the above embodiment can be expected in the case of one wavelength multiplexing coupler.

[0025]

As described above, according to the present invention, it is not necessary to change the frequency of the supervisory signal for each optical repeater, and when the optical repeaters are connected in multiple stages, the supervisory signal is provided for each optical repeater. This has the effect of saving the trouble of setting the frequency of.

[Brief description of the drawings]

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

FIG. 2 is a signal diagram showing an operation of the optical amplification repeater according to the present invention (when a monitor signal is ASK-modulated).

FIG. 3 is a signal diagram showing the operation of the optical amplification repeater according to the present invention (when the monitor signal is a baseband PCM signal).

FIG. 4 is a diagram showing an absorption spectrum of a rare earth-doped optical fiber.

FIG. 5 is a configuration diagram illustrating an optical amplification repeater according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram illustrating an optical amplification repeater according to a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a conventional optical amplification repeater.

FIG. 8 is a configuration diagram showing a conventional optical amplification repeater.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Main signal light input terminal 2, 17 Rare earth doped optical fiber 3, 16 Wavelength multiplexing optical coupler 4 Optical branching coupler 5 Optical receiver 6 Differential amplifier 7 Reference potential generation circuit 8, 14 Pump light source drive circuit 9, 15 Pump light source 10 Demodulation Circuit 11 Separation circuit 12 Multiplexer 13 Monitor signal generation circuit 18 Main signal light output terminal a First monitor signal b Second monitor signal c Main signal light on which first monitor signal a is superimposed d Second monitor signal main signal light b superimposed e first pump light f second pump light g level error signal h first amplified light 30 constant level amplifying means 40 supervisory signal processing means 50 supervisory signal superimposing means

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-270520 (JP, A) JP-A-3-252231 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 10/00-10/28

Claims (2)

(57) [Claims] 1. A enter the optical signal optical repeater (a) a first monitoring signal is superimposed with the following elements, light
A signal that is out of phase with the first supervisory signal superimposed on the signal
It was generated as an error signal No., superimposing the optical signals and the error signal
Constant level means that a constant level of optical signals inputted by, (b) the based on the generated error signal by the constant level device to detect and process the first monitoring signal monitoring signal processing means, ( c) Monitoring signal superimposing means for generating a second monitoring signal based on the processing of the monitoring signal processing means and superimposing the second monitoring signal on the optical signal which has been set to a constant level by the constant level means. 2. A light switching device of claim 1, the light
An optical repeater, comprising: an optical amplifier for amplifying an optical signal, wherein a spontaneous emission light output from the optical amplifier is used as an optical carrier for transmitting a supervisory signal.