JPS61127238A - Optical transmission system - Google Patents

Abstract

PURPOSE:To reduce the intra-station equipment cost of a center station remarkably by adopting the wavelength multiplex system and connecting the center station and all subscriber terminal devices via an optical fiber transmission line in a loop to allow all the subscriber terminal devices to share an optical transceiver and an optical multiplexing and demultiplexing circuit in the center station. CONSTITUTION:An optical transmitter 11 in a center station 10 converts outgoing data at an input terminal 16 to an optical signal of wavelength lambda1 and applies the result to an optical multiplexer 14. A photodetector 21 converts the optical signal of wavelength lambda1 fed from an optical demultiplexer 24 into an electric signal, from which the outgoing data signal addressed to the own subscriber terminal is extracted and given to an output terminal 27 and the outgoing data signal addressed to other subscriber terminal devices is fed to an optical transmitter 22. The optical transmitter 22 combines the outgoing data signal addressed to the other subscriber terminal devices fed from the optical transmitter 21 and an incoming data signal addressed to the center station from the own subscriber terminal device applied from an input terminal 29, converts the result into the optical signal of wavelength lambda1 and the signal is fed to an optical multiplexer 26.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention Industrial Field of Application The present invention relates to the distribution of video signals from a center station to subscriber terminals via an optical fiber transmission line, and the distribution of video signals between the center station and subscriber terminals. The present invention relates to an optical transmission system that performs data transmission.

Conventional Technology The end portion of a communication network that provides services to general subscribers, such as a public telecommunications network, consists of one central office, such as a subscriber exchange, and a large number of subscriber terminals accommodated in this central office. .

As traditional narrowband metallic subscriber lines are replaced by broadband fiber-optic transmission lines, the most basic services provided by such networks will be unidirectional video distribution services similar to broadcasting and low transmission speeds. Number K b /
It is considered to be a bidirectional digital data communication service with a speed of approximately 10 Kb/s to several 10 Kb/s.

In such an optical fiber transmission line, analog transmission is suitable for transmitting video signals from the viewpoint of economy, and wavelength multiplexing is suitable for multiplexing this and digital data signals.

If we maintain the basic configuration of the conventional subscriber line and perform video distribution and bidirectional digital communication between one center station and a large number of subscriber terminals using the wavelength multiplexing method, the system as shown in Figure 4 will be used. Become something.

That is, the center station 1 and each subscriber terminal 2-1 to 2-n
The subscriber terminals 2-1 to 2-n are connected in a star shape by optical fiber transmission lines 3-1 to 3-n, and each subscriber terminal 2-1 to 2-n is provided with an optical transmitter a and an optical receiver for data communication.

In addition to installing an optical receiver C for receiving video signals and an optical multiplexer/demultiplexer d, a subscriber terminal corresponding section 1-1 in the center station 1 is installed.
~1-n includes an optical transmitter A and an optical receiver B for data communication.
The configuration includes an optical transmitter C for transmitting video signals, and an optical multiplexer/demultiplexer. Bidirectional data communication and unidirectional video distribution are performed using wavelengths λ1. This is carried out using light of λ2 as a carrier wave.

Problems to be Solved by the Invention The configuration shown in FIG. 4 above has the advantage of expanding services while maintaining the existing basic network configuration. There is a problem in that terminal handling units must be installed in the center office in equal numbers to the number of subscriber terminals, and the equipment in the center office becomes extremely expensive.

Structure of the Invention The optical transmission system of the present invention that solves the problems of the prior art described above employs a wavelength multiplexing method.

By connecting the center station and all subscriber terminals in a loop via optical fiber transmission lines, and having all subscriber terminals share the optical transceiver and optical multiplexing/demultiplexing circuit in the center station,
It is configured to significantly reduce the cost of equipment within the center station.

The effects of the present invention will be explained in detail by way of three examples below.

Embodiment FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In FIG. 1, 10 is a center station, 2o-1, 20-2-
. . . 20-n is the subscriber 4# terminal, and 40 is a loop-shaped optical fiber transmission line that connects the center station and all subscriber terminals in a circular manner.

In the center station 10, 11.13 is an optical transmitter, 12
14 is an optical multiplexer, 15 is a light source waver, 16. is an optical receiver;
Reference numerals 17 and 18 are output terminals connected to local equipment such as a switching device (not shown).

In the subscriber terminal 20-1, 21.23 is an optical receiver;
22 is an optical transmitter, 24 is an optical demultiplexer, 25 is an optical branch circuit,
26 is an optical multiplexer, 27, 28 and 29 are output terminals connected to other devices in the subscriber terminal (not shown) 6 In the center station 10, the optical transmitter 11 is connected to the input terminal 1.
The downlink data signal on 6 is converted into an optical signal of wavelength λl and supplied to optical multiplexer 14. Further, the optical transmitter 13 converts the downstream video signal on the input terminal 18 into an optical signal of wavelength λ2, and supplies the optical signal to the optical multiplexer 14. The optical multiplexer 14 combines the optical signal with the wavelength λ1 and the optical signal with the wavelength λ2 to form the optical fiber transmission line 4.
Send to one end of 0. On the other hand, the light source transducer 15 extracts an optical signal of wavelength λ1 from the other end of the optical fiber transmission line 40 and supplies it to the optical receiver 12. The optical receiver 12 is.

An optical signal with a wavelength λ1 is converted into an electrical signal, and an upstream data signal from each subscriber terminal is extracted from the electrical signal and supplied to the output terminal 17.

In the subscriber terminal 20-1, the optical demultiplexer 24 extracts the optical signal of wavelength λ1 from the input end of the optical fiber transmission line and supplies it to the optical receiver 21, and also outputs the optical signal of wavelength λ2 to the optical branching circuit 25. supply to. The optical branching circuit 25 branches the optical signal of wavelength λ2 and supplies one to the optical receiver 23 and supplies the other to the optical multiplexer 26. The optical multiplexer 26 combines the optical signal of wavelength λ2 supplied from the optical branching circuit 25 with the optical transmitter 22.
The optical signals of wavelength λ1 supplied from the optical fibers are combined and sent to the output end of the optical fiber transmission line 40.

The optical receiver 21 receives the wavelength λ1 supplied from the optical demultiplexer 24.
Converts the optical signal of
supply to. The optical transmitter 22 receives the downlink data signal addressed to other subscriber terminals supplied from the optical receiver 21 and the input terminal 29.
The uplink data signals addressed to the center station from own subscriber terminals supplied from the subscriber terminals are combined, converted into an optical signal of wavelength λ1, and supplied to the optical multiplexer 26.

On the other hand, the optical receiver 23 converts the optical signal of wavelength λ2 supplied from the optical branching circuit 25 into an electrical signal, reproduces the downlink video signal from the center station, and sends it to the output terminal 2.
Supply to 8.

The downlink video signal from the center station is a frequency division multiplexed analog video signal consisting of m channels CHI to CNm with a carrier of ClxCm, as illustrated in FIG. 2(A). On the other hand, the bidirectional data signal is
) as exemplified.

This is a time division multiplexed digital signal in which one frame consists of k time slots (channels) #1 to #k. For each time slot, the center office 10 or the subscriber terminal captures an empty time slot when a call arrives at the subscriber terminal or a call originates from the subscriber terminal.

Alternatively, it may be used in an appropriate manner, such as by being fixedly assigned to subscriber terminals in advance.

As shown in FIG. 1, an optical signal with a wavelength λ1 carrying a data signal is once converted into an electrical signal by the optical receiver 21 of each subscriber terminal, and then converted again into an optical signal with a wavelength λl, and each Sent from the subscriber terminal. Therefore, for the optical signal of wavelength λl, the transmission loss in the optical fiber transmission line and the optical separation loss in each subscriber terminal are compensated for.

Once the optical signal of wavelength λ2 carries the electrical signal.

Transmission losses in the optical fiber transmission line and optical demultiplexing and branching losses at each subscriber terminal accumulate and gradually attenuate.

Therefore, if the cumulative attenuation is large due to reasons such as accommodating a large number of subscriber terminals, wavelength A slave station 30 may be inserted to compensate for the attenuation of the optical signal of λ2.

The slave station 30 is one, for example, as shown in FIG.

an optical demultiplexer 31 that demultiplexes an optical signal with a wavelength λ2 from one end of an optical fiber transmission line; an optical receiver 33 that converts the optical signal with a wavelength λ2 supplied from the optical demultiplexer 31 into a video signal;
The video signal supplied from this optical receiver 33 is retransmitted with wavelength λ
an optical transmitter 34 that converts the optical signal into an optical signal of 2, and this optical transmitter 3;
The optical multiplexer 32 combines the optical signal of the wavelength λ2 supplied from the optical demultiplexer 31 with the optical signal of the wavelength λ1 supplied from the optical demultiplexer 31 and sends the combined signal to the other end of the optical fiber transmission line.

Effects of the Invention As explained in detail above, the optical transmission system of the present invention adopts the wavelength multiplexing method, and connects the center station and all subscriber terminals in a loop via an optical fiber transmission line. Because the subscriber terminals in the center station share the optical transceiver and optical multiplexing/demultiplexing circuit, the in-office equipment at the center station is 1/(
The number of subscriber terminals) will be doubled, resulting in a significant reduction in the cost of equipment within the nine stations.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical transmission system according to an embodiment of the present invention, and FIG. 2 is a conceptual diagram showing an example of the configuration of a video signal and bidirectional data signal transmitted by the optical transmission system of FIG. 1. 3 is a block diagram illustrating the configuration of a slave station inserted as necessary in the system of FIG. 1, and FIG.
The figure is a block diagram showing the configuration of a conventional system. 10...Center station, 20-1.20-2...20
-n: subscriber terminal, 30: slave station inserted as necessary, 40: optical fiber transmission line; in the center station 10, 11.13: optical transmitter, 12: optical receiver, 1
4. Optical multiplexer; 15. Light source waver; subscriber terminal 20-
In 1. 21.23... Optical receiver, 22... Optical transmitter, 24...
Optical demultiplexer, 25... Optical branch circuit, 26... Optical multiplexer. Patent source: NEC Corporation Representative: Patent attorney: Toshihiko Enoki Figure 1

Claims (1)

[Scope of Claims] A center station and a subscriber terminal are connected in a loop via an optical fiber transmission line, and the center station transmits a downlink data signal using light of a first wavelength as a carrier wave and a second
an optical circuit that sends a downstream video signal having a carrier wave of light having a wavelength of 1 to one end of an optical fiber transmission line, and an optical circuit that receives an upstream data signal having a carrier wave of light of the first wavelength from the other end of the optical fiber transmission line. each subscriber terminal comprises: an optical circuit that receives light of the first and second wavelengths from one end of the optical fiber transmission line; and a circuit that converts the received light of the first wavelength into an electrical signal. an optical/electrical circuit that extracts a downlink data signal destined for its own subscriber terminal, adds an uplink data signal from its own subscriber terminal to a downlink data signal destined for other subscriber terminals, and converts it into light of a first wavelength. and an optical circuit that extracts a part of the energy from the light of the second wavelength received from one end of the optical fiber transmission line, and a part of the energy of the light of the first wavelength outputted from the optical/electrical circuit. 1. An optical transmission system comprising: means for transmitting a portion of the extracted light having a second wavelength to the other end of an optical fiber transmission line.