JP2546498B2 - WDM optical communication system - 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 communication system, and more particularly to a wavelength division multiplexing optical communication system for collectively transmitting a plurality of optical signals having different wavelengths.

[0002]

2. Description of the Related Art An optical communication system for collectively transmitting a plurality of optical signals having different wavelengths is disclosed in Japanese Patent Laid-Open No. 63-16140.
As typified by JP-B-6, a wavelength division multiplexing optical communication system for multiplexing these optical signals is widely used. In such a wavelength division multiplexing optical communication system, for example, 0.8 μm
Band and 1.3μm band, or 1.3μm band and 1.55μ
Different wavelength bands such as m band were used. Recently, there has been proposed a wavelength division multiplexing optical communication system that performs wavelength division multiplexing using a plurality of wavelengths in the same wavelength band such as the 1.55 μm band.

Particularly, in the latter wavelength division multiplexing optical communication system for multiplexing optical signals in the same wavelength band, when separating an optical signal after transmission into respective wavelengths, an optical bandpass filter having only a corresponding wavelength as a pass band. Alternatively, a wavelength separation coupler is used.

[0004]

By the way, in the case of collectively transmitting a plurality of optical signals having different wavelengths in the same wavelength band as described above, one of the optical transmitters for outputting the respective optical signals is used. There was a problem that a normal communication system could not be maintained when the optical output was cut off. In order to explain this easily, the case where optical signals of two wavelengths are collectively transmitted will be described. One optical transmission board is the first optical transmission board, and the other optical transmission board is the second optical transmission board. An optical receiving board that receives an optical signal in the original state from the first optical transmitting board is referred to as a first optical receiving board, and
The second optical receiving board is an optical receiving board that receives an optical signal in the original state from the optical transmitting board.

When the optical output of the first optical transmitting board is cut off, the first optical receiving board which should receive the optical signal from now has to issue an alarm such as optical receiving cutoff. However, in this case, 2
Since the wavelengths of two optical signals are close to each other, if the amount of attenuation in the stopband of the optical bandpass filter or wavelength demultiplexing coupler cannot be sufficiently secured, or if the received optical power is large depending on the transmission distance, The optical receiving board receives the optical signal from the second optical transmitting board which is normally transmitting the optical signal. Moreover, when the frequencies of the optical signals of the two wavelengths are close to each other, the clock signal for sampling becomes similar. As a result, the first optical receiving board does not enter the state of interruption of optical reception and does not enter the state of issuing an alarm for notifying this. This makes it impossible to maintain a normal communication system.

On the other hand, for example, in Japanese Unexamined Patent Publication No. 61-196634, a failure detection / alarm circuit detects a disconnection of a transmission signal and inserts an alarm signal from the transmission side instead of the original transmission signal. Then, it is sent to the transmission line. However, with this method
Since the alarm circuit is arranged, it is not possible to cope with the case where the transmission line is disconnected.

Therefore, an object of the present invention is to transmit one optical transmission board or an optical signal before multiplexing even when a plurality of optical signals having different wavelengths in the same wavelength band are collectively transmitted. An object of the present invention is to provide a wavelength division multiplexing optical communication system in which a corresponding optical receiving board can detect this condition and reliably issue an alarm even if the road is disconnected.

Another object of the present invention is to provide a wavelength division multiplexing optical communication system having a simple structure of an optical receiving board and capable of accurately detecting a state of optical output interruption of a specific optical transmitting board. .

[0008]

According to a first aspect of the present invention, (a) an optical digital signal train having a specific optical wavelength belonging to the same wavelength band is subjected to optical intensity modulation of a specific signal wave. A plurality of optical transmitters that send out signals, (b) an optical multiplexer that multiplexes the optical signals output from these optical transmitters and sends them out from the transmission end of the transmission line, and (c) from the receiving end of this transmission line. An optical distributor that distributes the obtained multiplexed optical signals by the number of optical transmission boards that are the targets of optical signal transmission,
(D) A plurality of optical bandpass filters for inputting the distributed output signals of the optical distributor and extracting optical signals of wavelengths in the corresponding pass bands of the optical transmission board, and (e) these optical bandpass filters. The electrical signal after photoelectric conversion of the optical signal extracted by the filter is increased to a predetermined amplitude level.
And the equivalent amplification means (f)
Clock based on the electrical signal after being amplified
Timing extraction means to create a signal, and
Each clock created by the ming extraction means
Electricity after being amplified by the equivalent amplification means using the signal
A data signal that samples the signal and reproduces the data signal.
Created by issue identification means and (h) timing extraction means
Has been their <br/> then respectively input along with the data signal identification means of the clock signal, a plurality of electrical signals bandpass filter for extracting a specific signal wave light intensity modulated by the corresponding light transmitting plate, (Li ) A wavelength multiplexing optical communication system is provided with an alarm issuing means for issuing an alarm when an output of any one of these electric signal bandpass filters is cut off as an input disconnection of an optical signal from a corresponding optical transmission board.

That is, according to the first aspect of the invention, each of the plurality of optical transmitters is adapted to perform optical intensity modulation of a unique signal wave with respect to an optical digital signal train having a unique optical wavelength. Therefore, by monitoring the presence or absence of the corresponding unique signal wave in each optical receiver, an alarm can be immediately issued when the reception of the signal wave is interrupted. Also, when the signal sent from its own optical transmission board is cut off for some reason, it can be reliably detected, so the signal sent from another optical transmission board may be mistaken for its own signal. As a result, it is possible to avoid the inconvenience of not receiving an alarm and not issuing an alarm.

[0010]

[0011]

FIG. 1 shows wavelength division multiplexing in one embodiment of the present invention.
2 illustrates a configuration of an optical communication system. here
To simplify the explanation, the same wave is generated by two optical transmitters.
A case where two types of long band optical signals are transmitted will be described. First
1 optical transmitter board 11₁Has a wavelength of λ₁First optical signal 12 of₁
Is sent. This first optical signal 12 ₁
Is the inherent low frequency f₁The sine wave of the optical digital main signal sequence
Is superimposed on the amplitude of. Second optical transmitter board 11₂Is
Wavelength is λ₂Second optical signal 12₂To send
ing. This second optical signal 12₂Is the inherent low frequency f₂
The sine wave of is superimposed on the amplitude of the optical digital main signal sequence.
ing.

FIG. 2 shows an example of the first optical signal output from the first optical transmission board. The vertical axis represents the intensity of the output optical signal, and the horizontal axis represents the passage of time. The first optical signal 12 ₁ is turned on / off as an optical digital signal train with a unique wavelength λ ₁ , and the light intensity at the time of on changes in a sinusoidal shape with a unique low frequency f ₁ . Similarly, FIG. 3 shows an example of the second optical signal output from the second optical transmission board. In this case, the light intensity when the _second optical signal 12 ₂ is on is the low frequency f ₂ peculiar to
It fluctuates like a sine wave.

These first and second optical signals 11 ₁ , 1
1 ₂ is input to the optical multiplexer 13 and is multiplexed and transmitted to the transmission line 14
Is transmitted from the transmitting end of.

On the other hand, it is received at the receiving end of the transmission line 14.
The optical signal 15 is input to the optical distributor 16 and divided into two.
You. One of the distributed optical signals is the first optical bandpass filter.
Ruta 17₁Entered in. First optical bandpass filter
17₁Is the first optical transmitter 11 ₁Corresponding to the wavelength λ
₁First optical signal 18 of₁To extract. First extracted
Optical signal 18₁Is the first optical receiver 19₁Entered in.
Similarly, the other optical signal distributed is the second optical bandpass signal.
Filter 17₂Entered in. Second optical bandpass filter
Ruta 17₂Is the second optical transmission board 11₂Is compatible with the waves
Long λ₂Second optical signal 18₂To extract. Extracted first
2 optical signal 18₂Is the second optical receiver 19₂Entered in
You.

FIG. 4 specifically shows the configuration of the first optical receiver board. The second optical receiving board 19 ₂ has the same configuration as the _first optical receiving board 19 _1, and therefore its explanation is omitted. The first optical receiving board 19 ₁ includes a photodiode 21 as a light receiving element that receives the _first optical signal 18 ₁ . The electric signal 22 obtained by the photodiode 21 is input to the equalization amplification circuit 23 and amplified to a predetermined amplitude level. The electric signal 24 output from the equalization amplification circuit 23 is supplied to the identification circuit 25, the bandpass filter 26, and the timing extraction circuit 27.

The timing extraction circuit 27 generates a clock signal 28 based on the input electric signal 24 and supplies it to the discrimination circuit 25. The identification circuit 25 uses the clock signal 28 to sample the electric signal 24 and reproduce the data signal. This is a circuit operation of a general optical receiving circuit.

On the other hand, the bandpass filter 26 is
1 optical receiver board 19₁First optical transmission provided corresponding to
Board 11₁Low frequency f superimposed on the main signal at₁Low frequency signal
Is extracted. Therefore, the second optical receiver 19₂Place
In the case of the second optical transmission board 11 ₂Low superimposed on the main signal with
Frequency f₂The low frequency signal of is extracted. band
The extraction result 29 output from the pass filter 26 is an alarm.
It is adapted to be input to the circuit 31. First optical reception
Board 19₁In this case, the alarm circuit 31 outputs a low value from this extraction result 29.
Frequency f₁Monitor when the low frequency signal of
At that time, the input disconnection alarm signal 32 is output to its output terminal 33.
I am trying to help.

As described above, the wavelength division multiplexing optical communication system of this embodiment is
In the system, each optical receiver board 19 ₁, 19₂Is self
Extract the corresponding low frequency signal and it will not be extracted
When it becomes, it means that the signal that should be received was cut off.
Detected and issued an alarm. Therefore,
Unlike the conventional WDM optical communication system,
Signal will not be received by mistake, and a normal communication system
Will be able to maintain.

In the embodiment, the photodiode (PD) is used as the light receiving element for photoelectric conversion, but it goes without saying that other light receiving elements can be used.
Further, although the sine wave is superimposed on the main signal by the transmitting board in the embodiment, it is needless to say that it is not limited to the sine wave as long as its period and waveform can be identified on the receiving side such as a triangular wave. Absent.

[0021]

As described above, according to the first aspect of the present invention, the light intensity modulation is performed on the unique signal wave with respect to the optical digital signal train having the unique light wavelength output from each optical transmission board. Therefore, by monitoring the presence or absence of the corresponding unique signal wave in each optical receiver, an alarm can be immediately issued when the reception of the signal wave is interrupted. Therefore, it is possible to avoid the inconvenience that the optical receiving board erroneously receives a signal sent from another optical transmitting board as its own signal and does not issue an alarm.

According to the first aspect of the invention, the optical bandpass
After photoelectric conversion of the optical signal extracted by the filter
In addition, the equivalent amplification means is used to
This signal is amplified by the timing extraction means.
Create a clock signal based on each signal and
The data signal is identified by the data signal identification means using the lock signal.
Bandpass fill for electrical signals in parallel with performing identification
To check the disconnection of the output after passing the alarm
did. Therefore, from the optical distributor on the receiving side
There is some obstacle in the path to the optical bandpass filter
Even if there is a situation that occurs and other signals are mixed in,
The means for reporting is that after passing through a bandpass filter for electrical signals.
Since the output is checked, the optical signal from the corresponding optical transmitter board
If you can accurately check the input of the issue
There is an advantage to say. In addition, this may cause data to be mixed.
The possibility of error can also be detected immediately.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a configuration of a wavelength division multiplexing optical communication system according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of a signal waveform of an optical signal output from the first optical transmission board in the present embodiment.

FIG. 3 is a waveform diagram showing an example of a signal waveform of an optical signal output from a second optical transmission board in the present embodiment.

FIG. 4 is a block diagram showing a specific circuit configuration of a first optical receiver board according to the present embodiment.

[Explanation of symbols]

11 ₁ 1st optical transmission board 11 ₂ 2nd optical transmission board 12 ₁ , 18 ₁ 1st optical signal 12 ₂ , 18 ₂ 2nd optical signal 13 Optical multiplexer 14 Optical fiber (transmission path) 16 Optical distribution Device 17 ₁ First optical bandpass filter 17 ₂ Second optical bandpass filter 19 ₁ First optical receiver board 19 ₂ Second optical receiver board 26 Bandpass filter 31 Alarm circuit 32 Input disconnection alarm signal

Claims (1)

(57) [Claims] 1. A plurality of optical transmission boards for transmitting optical signals obtained by optical-intensity-modulating specific signal waves for optical digital signal trains each having a specific optical wavelength belonging to the same wavelength band, and these optical transmissions. An optical multiplexer that multiplexes the optical signals output from the board and sends it out from the transmission end of the transmission path, and the multiplexed optical signal obtained from the reception end of this transmission path as many as the number of optical transmission boards that are the targets of the optical signal transmission. An optical distributor for distributing, a plurality of optical bandpass filters for respectively receiving the output signals distributed by the optical distributor, and extracting optical signals of wavelengths in the corresponding pass bands of the optical transmission board, and these optical bandpass filters. The electrical signal after photoelectric conversion of the optical signal extracted by the bandpass filter is set to a predetermined amplitude level.
Based on the electric signal after being amplified by the equivalent amplifying means and the equivalent amplifying means.
Timing extraction to create clock signals for each
Means and each of the timing created by this timing extraction means
Amplified by the equivalent amplification means using a clock signal.
The electrical signal after being sampled to reproduce the data signal
And a clock signal generated by the timing extracting means.
Signal is input together with the data signal identification means, and a plurality of electric signal bandpass filters for extracting a unique signal wave whose optical intensity is modulated by the corresponding optical transmission board, and an output of one of these electric signal bandpass filters A wavelength-division-multiplexed optical communication system comprising: an alarm issuing means for issuing an alarm when an optical signal from a corresponding optical transmission board is disconnected when the disconnection occurs.