JPH0998156A - System and equipment for optical multiplex communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the discrimination of interference between codes by increasing transmission information quantity by using both optical frequency divided multiplexing(FDM) and optical encoded multiplexing (CDM). SOLUTION: The bundle of optical channels is provided with M pieces of optical FDM and N pieces of optical CDM. When the optical channel bundle to use both the optical FDM and the optical CDM is used, the total number of channels becomes MXN and the optical signals of these channels are transmitted through an optical fiber transmission line while being synthesized and multiplexed. Then, these signals are demultiplexed to respective channels at a reception part. Thus, since information is transmitted by respectively performing optical code division to the beams of respective optical frequencies, the throughput capacitance per optical fiber can be extended to a maximum without being limited in the number of multiplexers by the gain band width of an optical fiber amplifier. Further, an infinite S/N is secured and large capacitance information can be transmitted without fail.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for transmitting information in optical multiplex communication.

[0002]

2. Description of the Related Art Conventionally, various multiplex communication techniques have been developed as means for increasing the amount of information transmission. Multiplex communication is a technique for expanding the communication capacity by effectively utilizing the transmission band of the transmission path by sharing the same transmission path by a plurality of communication channels.

FIG. 8 is a block diagram of a multiplex communication system.
Reference numeral 81 is a multiplexer, 82 is a transmission line, and 83 is a demultiplexer. Here, the time division multiplexing (hereinafter abbreviated as TDM) is to allocate time slots to different channels, and frequency division multiplexing (hereinafter abbreviated as FDM).
Is a communication method in which different signals are simultaneously transmitted to the same transmission line by allocating channels to different frequencies, and the receiver receives by detecting a signal of a predetermined time slot or optical frequency.

At this time, since the TDM requires a multiplexer (MUX) and a demultiplexer (DEMUX) which are faster than the bit rate of information by the multiplex number, the multiplex number is restricted by the speed of the electronic circuit. . On the other hand, the optical FDM is the gain bandwidth of the optical fiber amplifier (EDFA) in the 1.55 μm band where the optical fiber has an extremely low loss, and the actual number of multiplexing is limited.

[0005]

In the conventional method for increasing the capacity of optical communication, a signal in which a TDM signal is further multiplexed by optical FDM is transmitted by one optical fiber. It was considered that the upper limit of the throughput capacity per book was (TDM multiplex number) × (optical FDM multiplex number).

[0006]

The present invention has been proposed in view of the above, and is an optical multiplex communication system for setting a plurality of channels on one optical transmission line and transmitting information using the plurality of channels at the same time. Thus, an optical multiplex communication system for transmitting information by dividing the light divided for each optical frequency by an optical code is provided.

The present invention is also an optical multiplex communication apparatus for setting a plurality of channels on one optical transmission line and transmitting information by using a plurality of channels at the same time. A transmitter having an optical encoder for code division;
An optical transmission unit that transmits the light output from the transmission unit, an optical frequency filter that divides the light transmitted through the optical transmission unit for each optical frequency, and the light of each optical frequency that is divided by the optical frequency filter is decoded. The present invention provides an optical multiplex communication device configured with a receiving unit including an optical decoder that converts the signal into a digital signal.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as an information transmission dimension for performing multiplexing, as shown in FIG. 1, an optical code is newly introduced to perform code multiplexing (hereinafter abbreviated as CDM), By carrying out so-called multi-dimensional multiplex optical communication in which a plurality of multiplexing dimensions including time and optical frequency are used together, it is intended to break the limit of the throughput capacity per conventional optical fiber.

FIG. 2 shows an optical CDM and an optical FD according to the present invention.
Optical path multiplexed with M (communication channel bundle)
It is a conceptual diagram which shows. This is a multiplexed network using M optical frequencies and N codes, and the optical path is # 11.
It consists of NM channels from # to #NM. Optical coded multiplexing will be described later.

FIG. 3 is a block diagram of an optical code multiplex communication system which is an embodiment of the present invention. N optical encoders 1, multiplexers 2, optical fiber transmission lines 3, demultiplexers 4, And N optical decoders 5. Further, FIG. 4 shows an optical decoder 5
FIG. 3 is a configuration diagram of No. 5, which includes an optical correlator 5a, an OE converter 5b, a threshold element 5c, and a pulse regenerator 5d.

First, from the transmitting side, a total of M.times.N pieces of input information are optically coded and multiplexed by the optical encoder 1 on N optical frequencies, each of which differs by M, and multiplexed by the multiplexer 2. Then, it is transmitted as an optical signal through the optical fiber transmission line 3. On the other hand, on the receiving side, the demultiplexer 4 demultiplexes into N optical frequencies, and the optical correlator 5a of the optical decoder 5 performs optical correlation calculation between the key coding pattern and the received waveform. , OE converter 5b converts it into an electric signal, and the output is further converted into a threshold element 5c.
Information is reproduced only when the output of the OE converter 5b exceeds a certain threshold, and otherwise, "0" is reproduced and decoded by the pulse regenerator 5d. By reproducing the information, the throughput capacity per one optical fiber is utilized to the maximum.

Next, optical code multiplex communication in the present invention will be described. 5A is a conceptual diagram showing the principle of optical coded multiplexing, FIG. 5B is a conceptual diagram showing the principle of conventional optical FDM, and FIG. 5C is a conceptual diagram showing the principle of TDM. Is.

Here, as can be seen from FIG. 5 (a),
Optical coded multiplexing expresses 1-bit information with a specific time waveform, and even if different codes exist on the same transmission line at the same time, they can be distinguished on the receiving side by the difference in code patterns. By being able to do so, multiplexing becomes possible.

In optical coding and multiplexing, coding methods are roughly classified into coherent coding and incoherent coding. Since coherent coding with small inter-code interference is considered to be promising in the future, The explanation will focus on this. FIG. 6 is a diagram showing a specific configuration of the coherent optical code multiplex communication system, and FIG. 7 is a diagram showing configurations of an optical encoder and an optical decoder. In the figure, 6 is a light source, 7 is an optical encoder, 8 is an optical decoder, 9 is an optical delay line, 1
0 is a phase shifter, 11 is an optical switch, 12 is a 3 dB coupler, 13 is an OE converter, 14 is a threshold element, and 15 is a pulse regenerator.

As shown in FIG. 6, the optical encoder 7 is 3 dB.
The coupler 14 is composed of the optical delay line 9-3 dB coupler 14 connected in multiple stages, and the delay time of the i-th optical delay line 9 satisfies the relationship of τi = 2τi−1. Further, as shown in FIG. 7, the optical decoder 8 is obtained by inverting the left and right (input terminal and output terminal) of the optical encoder 7, and the constituent elements are the same as those of the optical encoder 7. Further, a phase shifter 10 is inserted in the optical delay line 9, and the phase shift amounts of the i-th optical delay line 9 of the optical encoder 7 and the optical decoder 8 are respectively set to φe.
i and φdi.

[0016]

[Table 1]

Table 1 shows (111) of the optical encoder 7 having a two-stage configuration.
The phase of the code pattern of 1) is set to time slots t1 to t4
The impulse responses of the output terminal 23 and the output terminal 24 with respect to the input of the terminal 21 are shown in the upper and lower rows, respectively. When the input amplitude is 4, all the amplitudes are 1.

[0018]

[Table 2]

Tables 2 (a) and 2 (b) show the above 2
Input terminal 2 of the optical decoder 8 for the optical encoder 7 having a stage configuration
1'-output terminal 23 'and input terminal 22'-output terminal 2
4C shows a decoded waveform of FIG. 4C, where the input is terminal 2
It is the decoded waveform of the output when it is present simultaneously in 1'and 22 '. The shift amount of the phase shifter 10 is φe1 = φe2 = 0 and φd1 = φd2 = π in the two-stage configuration.

The code pattern is changed by selecting the phase 0 or π of the phase shifter 10 or the optical switch 11 of the optical delay line 9.
Can be performed by either ON / OFF of.
The characteristic of the coherent code to be noted in Table 2 is that in the case of (c), the amplitude of the side lobe becomes 0 with respect to the peak power value 64 in the autocorrelation, and an infinite SN ratio can be secured. is there.

Next, intersymbol interference will be described. When the output of the cross-correlation calculation when inputting to the optical decoder 8 having keys with different reception patterns is 0, the codes are said to be orthogonal, and in this case, ideal reception without intersymbol interference occurs. it can.

[0022]

[Table 3]

[0023]

[Table 4]

Tables 3 and 4 are (1010) and (1101) for the optical encoder 7 having (1111) as a key, respectively.
Shows the cross-correlation waveform when the pattern is input to the optical decoder 8. (a) and (b) of Tables 3 and 4 show the optical decoding for the optical encoder 7 having the above two-stage configuration, respectively. Input terminal 21'-output terminal 23 'and input terminal 22'-
The decoded waveform at the output terminal 24 'is shown, and (c) is the decoded waveform at the output when the inputs are simultaneously present at the terminals 21' and 22 '. The shift amount of the phase shifter 10 is φe1 = φe2 = 0 and φd1 = φd2 = π in the two-stage configuration.

Comparing the results of Tables 3 and 4 with the results of Table 2, the peak power values are 36/64 and 16/64, respectively.
It can be seen that the output value decreases to 0 and the output value is not 0 other than the peak value. Considering that 36 is the maximum value of the cross-correlation peak from the examination results of other patterns, the input pattern and the key of the optical decoder 8 are matched by setting the threshold level of the threshold element 14 higher than 36. , Can discriminate disagreement. This is the principle of multiplex communication itself.

The present invention has been described above based on the embodiments, but the present invention is not limited to the above-mentioned embodiments, and can be carried out in any manner as long as the configuration described in the claims is not changed. .

[0027]

As described above, in the present invention,
In an optical multiplex communication system in which a plurality of channels are set on one optical transmission line and information is transmitted using the plurality of channels, information of each optical frequency is transmitted by optical code division. The throughput capacity per optical fiber can be expanded to the maximum without being limited by the number of multiplexes due to the gain bandwidth of the fiber amplifier element.

Further, according to the present invention, an optical multiplex communication apparatus for setting a plurality of channels on one optical transmission line and transmitting information using the plurality of channels is used for optical code division of light for each optical frequency. By the optical frequency filter and the optical frequency filter that divides the light transmitted by the optical transmission unit for each optical frequency, the optical transmission unit configured to transmit the light output from the transmission unit, Since it is composed of a receiving section consisting of an optical decoder for decoding the light of each optical frequency that has been divided, an infinite SN ratio can be secured, interference between codes can be easily distinguished, and a large amount of information can be stored. Can be transmitted without error, which is a great effect.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the introduction of a coding dimension as an information transmission dimension in the present invention.

FIG. 2 is a conceptual diagram showing an optical path in which an optical CDM and an optical FDM are used together and multiplexed in the present invention.

FIG. 3 is a configuration diagram of an optical code multiplex communication system according to an embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical decoder according to an embodiment of the present invention.

5A is a conceptual diagram showing the principle of optical coding and multiplexing in one embodiment of the present invention, FIG. 5B is a conceptual diagram showing the principle of conventional optical FDM, and FIG. 5C is a diagram showing the principle of TDM. It is a conceptual diagram.

FIG. 6 is a configuration diagram of a coherent optical code multiplexing system which is another embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical encoder and an optical decoder.

FIG. 8 is a conceptual diagram showing a configuration of a conventional multiplex communication system.

[Explanation of symbols]

 1, 7 optical encoder 2 multiplexer 3 optical fiber transmission line 4 demultiplexer 5, 8 optical decoder 5a optical correlator 5b, 13 OE converter 5c, 14 threshold element 5d, 15 pulse regenerator 6 light source 9 light Delay line 10 phase shifter 11 optical switch 12 3 dB coupler 21, 22 optical encoder input terminal 23, 24 optical encoder output terminal 21 ', 22' optical decoder input terminal 23 ', 24' optical decoder Output terminal

Claims (2)

[Claims] 1. An optical multiplex communication system in which a plurality of channels are set on one optical transmission line and information is transmitted using the plurality of channels, wherein light of each optical frequency is divided by optical codes. An optical multiplex communication system characterized by transmitting information. 2. An optical multiplex communication apparatus for setting a plurality of channels on one optical transmission line and transmitting information by using the plurality of channels at the same time, wherein the light of each optical frequency is optical code-divided. A transmission section having an encoder, an optical transmission section for transmitting the light output from the transmission section, an optical frequency filter for dividing the light transmitted through the optical transmission section for each optical frequency, and the optical frequency filter An optical multiplex communication device comprising: a receiving unit including an optical decoder that decodes light of each optical frequency.