JPH0897776A - Optical repeater - Google Patents

Abstract

PURPOSE: To prevent a monitor information signal of each optical repeater superimposed onto a main signal light amplified directly and optically at each optical repeater from being in crosstalk among the optical repeaters in the optical fiber relay transmission system comprising optical repeaters in multi- stage connection via the optical fiber transmission line. CONSTITUTION: Each optical repeater 100 is provided with an optical direct amplifier 3 applying optical direct amplification to a main signal light obtained by superimposing the monitor information on the digital main signal light sent from an optical repeater at a pre-stage, and an external modulator 7 applying optical intensity modulation to monitor information of its own repeater to the signal light at a frequency different from that for other repeaters. Then the signal is superimposed at a frequency different and specified to each optical repeater 100 through external modulation. Thus, a different frequency is assigned from each optical repeater 100 for the frequency used to superimpose the monitor signal onto the main signal light, then even when the optical relay transmission system is formed through multi-stage connection, the monitor information is propagated without interference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of each optical repeater in an optical fiber repeater transmission system in which optical repeaters using an optical direct amplifier are connected in multiple stages via optical fiber transmission lines, and more particularly, to an optical repeater. The present invention relates to a configuration for transmitting monitoring information of each optical repeater between devices.

[0002]

2. Description of the Related Art Generally, in an optical repeater, when an abnormality such as a failure occurs in the own optical repeater, a process of transmitting the fact to the subsequent stage is performed. In this case, the monitoring information that indicates the occurrence of the abnormality is superimposed on the digital main signal light that is the information signal to be originally transmitted, and is sent to the optical repeater in the subsequent stage. Is being detected.

FIG. 4 shows the configuration of the above-mentioned conventional optical repeater.
Will be described with reference to.

In FIG. 4, a conventional optical repeater comprises an optical branching coupler 2 for branching into two main signal lights transmitted from an optical repeater in the preceding stage through an optical fiber transmission line 1a, and a branched main signal. An optical direct amplifier 3 that directly amplifies one of the lights is provided. As the optical direct amplifier 3, an optical fiber amplifier using an erbium-doped optical fiber is generally used.

In the conventional optical repeater 100, the light receiving element (PD) 12 for converting the other main signal light branched by the optical branching coupler 2 to extract the monitoring information into an electric signal.
And a current-voltage conversion circuit (I / V) 13 that performs current-voltage conversion on the converted electric signal, and a demodulation circuit (DEC) that performs code demodulation of the converted output and sends it to the signal processing circuit.
OD) 14 and a modulation circuit (COD) 15 that code-modulates the output of the signal processing circuit.

The optical fiber amplifier 3 includes an erbium-doped optical fiber 4 and a laser driving circuit (LD) for driving a pumping semiconductor laser (LD) 11 in accordance with the output of the modulation circuit 15.
D) 10 and a wavelength division multiplexer (WDM) 5 for wavelength-division-multiplexing the main signal light according to the outputs of the pumping semiconductor laser 11 and sending it to the optical repeater in the subsequent stage through the optical fiber transmission line 1b.
It has and.

The optical repeater having the above-mentioned structure is several tens of kilometers.
To 100 km, the optical fiber repeater transmission system is configured by connecting in multiple stages with a predetermined distance. In conventional optical repeaters,
The main signal light is received from the optical repeater in the previous stage and sent to the optical repeater in the subsequent stage, and the monitoring information signal is extracted from the signal light from the optical repeater in the previous stage, and the monitoring information of the own repeater is used as the main signal. It is superposed on the light and sent to the optical repeater in the subsequent stage.

In this case, the supervisory information signal is generated by pre-modulating the supervisory information of the optical repeater into a signal having a frequency component lower than the main signal bit rate. Then, the injection information to the pumping semiconductor laser 11 which is the pumping light source of the optical fiber amplifier 3 is modulated by the monitoring information signal, the gain modulation of the optical fiber amplifier 3 is performed, and the main signal light is modulated in optical intensity. Is transmitted toward the optical repeater side in the subsequent stage of the optical fiber transmission line 1b.

[0009]

Consider a case in which optical repeaters are connected in multiple stages in order to form a long-distance optical fiber communication system by using the optical repeaters having the above-described conventional configuration. The main signal light, which is superposed with the monitoring information signal propagating from the optical repeater at the previous stage located on the signal source side of the optical fiber transmission line, is directly amplified by the own optical repeater and the monitoring information of the own optical repeater. Since the signals are superimposed, there is a problem that interference occurs between the monitoring information signals of different optical repeaters when the monitoring information is extracted by the optical repeater in the subsequent stage located far from the optical signal source.

In view of the above-mentioned drawbacks of the above-described conventional optical repeater, the present invention does not interfere with the monitor information signal from each optical repeater, and the optical repeater which receives the monitor information signal receives the monitor information signal. An object of the present invention is to provide an optical repeater that can specify an optical repeater that is an oscillation source.

[0011]

In order to eliminate the above-mentioned drawbacks, an optical repeater according to the present invention has an optical repeater connected in multiple stages via an optical fiber transmission line, and in the optical repeater in the preceding stage, the main signal is transmitted to the main signal. Monitoring information detecting means for detecting the monitoring information from the signal light on which the monitoring information signal is superposed, optical amplifying means for optically amplifying the main signal and transmitting the amplified main signal, and monitoring information in the optical repeater for the amplified main signal. And a signal light sending means for sending the signal light to the optical repeater in the subsequent stage by superimposing the above.

In particular, the signal light transmitting means is characterized by superposing the monitoring information on the amplified main signal light by modulating the intensity of the amplified main signal light. Here, the light intensity modulation is characterized in that the amplified main signal is performed using an external modulation means.

Further, the external modulation means is a semiconductor light intensity modulator that changes the extinction ratio of light by changing the current value according to the monitoring information signal, or the optical modulator by changing the voltage value according to the monitoring information signal. That changes the extinction ratio of LiNbO
It is characterized by being a three-waveguide type optical intensity modulator.

Further, the optical amplification means is characterized by having a gain control means for controlling the optical amplification gain of the main signal light constant.

Further, the superimposition of the supervisory information signal in the signal light transmitting means is characterized in that the supervisory information signal is converted into a frequency shift keying modulated optical signal.

The frequency shift keying modulation is
A different frequency band is used for each of the optical repeaters connected in multiple stages.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an optical repeater of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the optical repeater of the present invention, and the same portions as those in FIG. 4 are designated by the same reference numerals. In FIG. 1, the optical repeater 100 of the present embodiment is different from the conventional one, in that the optical fiber amplifier 3 is provided with a feedback loop for keeping the amplification gain of the optical intensity of the main signal light constant, The external modulator 7 for superimposing the monitoring information on the output of the optical fiber amplifier 3, the external modulator driving circuit 16, and the monitoring information superimposed on the main signal light from the optical fiber transmission line 1a are separated and detected. Band pass filter (BPF) 1 for
7 is provided.

The feedback loop in the optical fiber amplifier 3 includes a branch coupler 6 for branching the main signal light, a light receiving element 8 for converting one of the branch outputs into an electric signal, and the converted electric signal. Output power constant control circuit (AGC) 9 that keeps the amplification gain constant from the power level of the input optical power and the power level of the optical input, which will be described later, and a pumping semiconductor laser (LD) by the output of the constant output optical power gain control circuit 9. Laser drive circuit (LDD) for driving 11
10 is provided.

In the configuration described above, the main signal light propagating through the optical fiber transmission line 1a is light intensity modulated with a signal having a frequency lower than the main signal bit rate frequency.
This signal becomes the monitoring information in the optical repeater in the preceding stage.
As for the monitoring information, a part of the input optical signal is branched by the branching coupler 2, photoelectrically converted by the light receiving element 12 and the current-voltage conversion circuit 13, and a sine wave signal of a required frequency is selected from a plurality of monitoring information. Band pass filter 17
By demodulating from the signal filtered by the demodulation circuit (DECOD) 14, the signals can be separated and detected.

The other of the main signal lights branched by the branch coupler 2 is directly amplified in the erbium-doped optical fiber 4 by the pumping light having a wavelength effective for the amplification characteristic of the erbium-doped optical fiber 4. The light intensity of the pumping semiconductor laser 11 is feedback-loop controlled so that a part of the amplified signal light transmitted from the erbium-doped optical fiber 3 is branched by the branch coupler 6 and the branched signal light has a constant gain. .

Regarding the above feedback loop control,
This will be described in detail with reference to FIGS. 2 and 3. In Figure 2,
When the feedback loop control is performed so that the amplification gain of the input / output signal light of the erbium-doped optical fiber 4 becomes constant, the sine wave signal of the frequency of the sine wave signal whose light intensity is modulated to the input main signal light is changed. The frequency characteristics of the amplitude ratio before and after the optical direct amplification are shown.

From FIG. 2, when the frequency f at which the optical intensity of the input signal light is modulated is higher than 10 kHz, the gain of the sine wave signal superimposed on the main signal light is 0 dB even if the feedback loop control is performed. , EDF input / output does not change the amplitude ratio of the light intensity modulation. on the other hand,
It can be seen that the amplitude of the sine wave signal is attenuated when the frequency f is lower than 10 kHz.

Reference will now be made to FIG. 3 for a more specific description. FIG. 3 shows monitoring information superimposed on the digital signal light input to the optical fiber amplifier 3. Consider the case where the frequencies of the signals superimposed on the A portion and the B portion are 1 kHz and 10 kHz, respectively. Due to the frequency characteristics in FIG. 2 described above, the input / output amplitude ratio of the portion A is −3.
Since it is higher than dB, the output amplitude is attenuated and becomes a flat digital main signal light. On the other hand, it can be seen that the supervisory signal component is output in the portion B without being attenuated. Therefore,
It can be seen that if the monitoring information is transmitted using the frequency band in which the amplitude modulated by the light intensity is not attenuated, the monitoring signal from the optical repeater in the preceding stage can be transmitted to the subsequent stage as it is.

Returning to FIG. 1, the main signal light from the optical repeater in the preceding stage is directly amplified by the optical fiber amplifier 3 (here, the monitoring information from the preceding stage is also output at the same time), and then the external modulator 7 Entered in. The monitoring information of the optical repeater to be superimposed on the main signal light is converted into a monitoring signal having a frequency component lower than the frequency of the main signal in the modulation circuit 15. The frequency used for conversion is a frequency unique to each optical repeater, and different frequencies are used.
The external modulator driving circuit 16 drives the external modulator 7 in response to the monitoring information signal, so that the monitoring information signal is superimposed on the main signal. As the external modulator 7, a semiconductor external modulator that changes the extinction ratio of light by a current-modulated signal according to the monitoring information signal may be used, or the extinction ratio of light may be changed by changing the voltage value. A LiNbO3 optical waveguide type external modulator may be used.

Further, in order to obtain the monitoring information in which the intensity of the main signal light is modulated, the optical main signal light input from the optical fiber transmission line 1a is converted into an electrical signal by the receiving circuit 12 and the current-voltage conversion circuit 13 described above. After being converted into, the frequency component of interest is separated and detected by the band pass filter 17 capable of setting the required frequency, and then the demodulation circuit (DECO
D) 14 can demodulate the monitoring information.

As described above, since the frequency component of the sine wave signal of the monitor signal which is desirable to be superimposed on the main signal light is 10 kHz or more, two different frequencies (for example, f1 = 19 kHz and f2 = 20 kHz) are used. FS to have
K (Frepuency Shift Keying)
It is effective to carry out modulation in advance to convert the monitoring information into an electric signal. Needless to say, other modulation methods are also effective.

In the case of the optical direct amplifier having the frequency characteristic shown in FIG. 2, the frequency effective as the supervisory signal to be superimposed on the main signal light is considerably lower than the frequency component of the main signal and is at most about 10 to 500 kHz. Is.

In this way, the main signal light on which the supervisory signal is superimposed is transmitted to the repeater in the subsequent stage, and by assigning different frequency bands to each repeater, it is possible to prevent interference between the supervisory information. It will be possible.

[0029]

As described above, in the optical repeater of the present invention, the monitoring information of the own optical repeater is added to the main signal light transmitted from the preceding optical repeater and having the monitoring information superimposed on the digital main signal light. Even if an optical repeater transmission system is configured by connecting optical repeaters in multiple stages by superimposing each of them on different frequency bands and sending them to the optical repeater in the subsequent stage, the monitoring information from each optical repeater is not interfered. Can be sent and received.

[Brief description of drawings]

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

FIG. 2 shows frequency characteristics of light intensity modulation in an optical direct amplifier.

FIG. 3 shows the concept of operation of an optical direct amplifier.

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

[Explanation of symbols]

 1a, 1b Optical fiber transmission line 2 Optical branching coupler 3 Optical direct amplifier (EDFA) 4 Erbium-doped optical fiber (EDF) 5 Wavelength division multiplexer (WDM) 6 Optical branching coupler 7 External modulator (EA) 8 Photodetector (PD) ) 9 constant gain circuit of optical power (AGC) 10 pumping semiconductor laser drive circuit (LDD) 11 pumping semiconductor laser (LD) 12 photodetector (PD) 13 current-voltage conversion circuit (I / V) 14 demodulation circuit (code conversion) (DECOD) 15 Modulation circuit (code conversion) (COD) 16 External modulator drive circuit 17 Band pass filter (BPF)

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Claims (11)

[Claims] 1. An optical repeater connected in multiple stages via an optical fiber transmission line, in a preceding optical repeater, monitoring information detecting means for detecting monitoring information from signal light in which a monitoring information signal is superimposed on a main signal. An optical amplifying unit that optically amplifies the main signal and sends the amplified main signal; and superimposes monitoring information in the own optical repeater on the amplified main signal, and sends the signal light to a subsequent optical repeater. An optical repeater comprising a signal light transmitting means. 2. The light according to claim 1, wherein the signal light transmitting means superimposes the monitoring information on the amplified main signal light by performing optical intensity modulation on the amplified main signal light. Repeater. 3. The light intensity modulation is performed by using an external modulation means for the amplified main signal.
An optical repeater as described. 4. The semiconductor optical intensity modulator for changing the extinction ratio of light by changing the current value according to the monitoring information signal, wherein the external modulator is a semiconductor optical intensity modulator.
An optical repeater as described. 5. The external modulation means changes the extinction ratio of light by changing the voltage value according to the monitoring information signal.
The optical repeater according to claim 3, which is an iNbO3 waveguide type optical intensity modulator. 6. The optical repeater according to claim 3, wherein the optical amplifying unit has a gain control unit that controls the optical amplification gain of the main signal light to be constant. 7. The optical repeater according to claim 6, wherein the optical amplifying means is an optical fiber amplifier using an erbium-doped optical fiber. 8. The optical repeater according to claim 1, wherein the superposition of the supervisory information signal in the signal light transmitting means converts the supervisory information signal into a frequency shift keying modulated optical signal. . 9. The optical repeater according to claim 3, wherein the superposition of the supervisory information signal in the signal light transmitting means converts the supervisory information signal into a frequency shift keying-modulated optical signal. . 10. The frequency shift keying modulation comprises:
9. The optical repeater according to claim 8, wherein a different frequency band is used for each of the optical repeaters connected in multiple stages. 11. The frequency shift keying modulation comprises:
The optical repeater according to claim 9, wherein a different frequency band is used for each of the optical repeaters connected in multiple stages.