JPH0353628A - Optical communication system - Google Patents

Abstract

PURPOSE:To reduce the system cost and to improve the multiplexity by applying FM modulation to a signal in the stage of an electric signal to differentiate the band of each frequency-modulated signal, applying electrooptic conversion to the FM modulation signal and making the wavelength of each optical signal identical. CONSTITUTION:After a communication electric signal is modulated so that the frequency band of modulated signals is differentiated from each other in each of multi-points (201-20N), electrooptic conversion is applied to optical signals of the save wavelength and the resulting signal is sent to an optical transmission line 25. Then an electric signal obtained through optoelectric conversion at a center 26 is subject to band-split into each modulated signal and each modulated signal is demodulated to obtain a communication electric signal at the multi- points (201-20N). Thus, optical signals outputted from the multi-points (201-20N) have the same wavelength. Thus, the system cost is reduced to a low cost and the multiplexity is improved.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical communication system that performs optical communication between multiple points and a center, the purpose of this invention is to keep the price of the system low and greatly improve the degree of multiplicity. In an optical communication system that performs optical communication using a single optical transmission path between a point and a center, after modulating the electrical signal for communication so that the frequency band of each modulated signal is different at each of the multiple points. , performs electrical/optical conversion on optical signals of the same wavelength and sends them to the optical transmission line, performs optical/electrical conversion at the center, separates the resulting electrical signals into each modulated signal, and separates the band of each modulated signal. It is configured to demodulate the signal and obtain electrical signals of communication signals at each of the multiple points.

[Industrial Application Field] The present invention relates to an optical communication system, and more particularly, to an optical communication system for performing optical communication between multiple points and a center.

In recent years, systems have been developed that connect a plurality of subscribers and a center using optical cables to perform bidirectional optical communications.

In such a system, communication from the center to each subscriber can be accomplished by simply distributing optical signals output from the center to each subscriber using an optical coupler.

However, communication from each subscriber to the center must be optically coupled to prevent interference between the optical signals output by each subscriber.

[Conventional technology]

FIG. 2 shows a block diagram of an example of a conventional method.

Here, only communication from each subscriber to the center is shown.

In the figure, each subscriber 10+ to 10N has a terminal 111.
The electric signals coming from each of ~11N are sent to an electric/optical converter (
E/O) 11+ to IIN are converted into optical signals, respectively. Each of the electrical/optical converters 11+ to 11N outputs a wavelength λ of light.
1 to λN are made different from each other, and these output lights are wavelength-multiplexed by a multiplexer 13 and then transmitted to a center 15 by an optical fiber 14.

At the center 15, the wavelength-multiplexed optical signal transmitted through the optical fiber 14 is separated into wavelengths λ1 to λN by a demultiplexer 16, and the separated optical signals of each wavelength λ1 to λN are sent to an optical/N air converter (0/N). E) Each of 17+ to 17N is converted into an electric signal and output from terminals 181 to 18N, respectively.

[Problem to be solved by the invention]

Since the conventional method performs wavelength multiplexing, it requires a multiplexer 13 that multiplexes optical signals of different wavelengths λ1 to λN, and a demultiplexer 16 that has a noilter for each wavelength λ1 to λN. The duplexer 13 and the duplexer 16 are expensive, and
There is a problem in that the multiplicity N is limited to about 3 to 4 due to the limitation of the wavelength band of the light to be transmitted.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an optical communication system that can keep the cost of the system low and greatly improves the multiplicity.

(Means for Solving the Problems) The optical communication system of the present invention is an optical communication system that performs optical communication between multiple points and a center using a single optical transmission path. After modulating the electrical signals for communication so that the signal frequency bands differ from each other, electrical/optical conversion is performed to optical signals of the same wavelength, which are sent out to the optical transmission line, and the electricity obtained by optical/electrical conversion at the center. Each signal is changed w
The band is separated into four signals, and each modulated signal is demodulated to obtain the electrical signal of the communication signal at each multipoint.

[Effect]

In the method of the present invention, since the optical signals output from each of the multiple points have the same wavelength, they can be mixed using an inexpensive optical coupler without using an expensive multiplexer, and without using an expensive demultiplexer at the center. Optical/electrical conversion can be performed as is, and the cost of the system can be kept low. Further, the multiplicity can be increased simply by changing the carrier wave frequency used for modulation at each multipoint.

〔Example〕

FIG. 1 shows a block diagram of an embodiment of the method of the present invention. Here, only communication from each subscriber to the center is shown.

In FIG. 1, in each of the access terminals 201 to 20N, electrical signals coming from terminals 211 to 21N are supplied to FM modulators 221 to 22N, respectively, for frequency modulation. FM
The modulators (FM) 22+ to 22N have different carrier frequencies f1 to fN, and the output signals of these
The frequency bands of the M modulation signals are different.

FM to be output from each of the above FM modulators 221 to 22N
The modulation signals are transmitted through electrical/optical converters (E/O) 231 to 23, respectively.
N signals are converted into optical signals.

The wavelengths of the lights output from each of the electrical/optical converters 23+ to 23N are the same, and after being mixed by the optical coupler 24, the output lights are transmitted to the center 26 by the optical fiber 25.

At the center 26, the optical signal transmitted through the optical fiber 25 is supplied to an optical/electrical converter (0/E) 27, where it is converted into an electrical signal. The obtained electrical signal is passed through a bandpass filter 281
~28N respectively.

The center frequencies of the passbands of the bandpass filters 281 to 28N are set to frequencies f1 to fN, respectively, and the FM modulated signals for each subscriber are separated. Bandpass filter 28+~
The EM modulated signals separated by 28N are demodulated into original electrical signals by FMIQ modulators (DFM) 29+ to 29N, and output from terminals 30 to 30N, respectively.

In this way, by performing FM modulation at the electrical signal stage, the bands of each FM modulated signal are made different, and in order to perform electrical/optical conversion, each optical signal has the same wavelength and is mixed using an inexpensive optical coupler. be able to. Furthermore, there is no need to separate the transmitted optical signal using an expensive demultiplexer.

Furthermore, the electrical/optical converters 231 to 23N can have the same configuration, which also reduces the cost.

Furthermore, since the wavelength of the optical signal to be transmitted remains the same by simply changing the carrier frequency of each FM modulator, the degree of multiplexing, that is, the number of subscribers, increases significantly.

Note that although frequency modulation and demodulation are performed in the above embodiments, this may also be amplitude modulation and demodulation, angle modulation and demodulation, etc., as long as the bands of each modulated signal are different.

〔Effect of the invention〕

As described above, according to the optical communication system of the present invention, expensive multiplexers and demultiplexers are unnecessary and inexpensive optical couplers can be used, and the cost of the system can be kept low. The number can be greatly increased, which is extremely useful in practice.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the method of the present invention, and FIG. 2 is a block diagram of an example of the conventional method. In the figure, 20+ to 2ON are subscribers, 22+ to 22N are FM modulators, 231 to 23N are electrical/optical converters, 24 is an optical coupler, 25 is an optical fiber 27 is an optical/electrical converter, and 281 to 28N are bandpass filters. , 291-29N indicate "M demodulator.

Claims (1)

[Claims] In an optical communication system that performs optical communication between multiple points (20_1 to 20_N) and a center (26) using a single optical transmission path (25), the multipoints (20_1 to 20_N) ) After modulating an electrical signal for communication so that the frequency bands of each modulated signal are different from each other, electrical/optical conversion is performed to an optical signal of the same wavelength, which is sent to the optical transmission line (25). The electrical signal obtained by optical/electrical conversion at the center (26) is band-separated into each modulated signal, and each modulated signal is demodulated and transmitted to the multiple points (20_1 to 20_1).
0_N) An optical communication system characterized by obtaining electrical signals for each communication signal.