JPH0650841B2 - Optical loop transmission system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a subscriber loop transmission system using optical fibers.

[Prior Art] As one of the methods for transmitting a signal to a subscriber using an optical fiber, the optical fiber is transmitted from a transmitting station to the first, second ...
There is an optical loop system in which subscribers (n is a positive integer) are sequentially connected and the end of the optical fiber is returned to the transmitting station again.

[Problems to be solved by the invention]

In such a loop system, if there is a fiber cut in the loop, the subscriber after the cut point cannot receive the signal. In order to eliminate such a defect, conventionally,
An optical signal having a wavelength different from that of the optical signal in the first direction is transmitted in the opposite direction by wavelength multiplexing or the like so that it can be received from either direction. However, such a conventional method has a drawback that two optical receivers are required to receive signals of respective wavelengths.

The present invention eliminates such drawbacks in the conventional method, and provides an optical loop transmission system capable of receiving signals flowing in both directions by one receiver.

[Means for solving problems]

According to the present invention, a plurality of subscriber units are connected to one transmitting unit in a loop with an optical fiber, and the transmitting station encodes the transmission signals by the first and second transmission line codes having a small correlation with each other. At the same time, the first and second optical signals are converted, and the first optical signal is supplied to one direction of the optical loop fiber through the optical directional coupler, and the second optical signal is supplied to the optical direction. It is characterized in that it is supplied to the other direction of the optical loop fiber through the sex coupler and transmitted.

〔Example〕

FIG. 1 shows an embodiment according to the present invention. The transmitted signal applied to the transmission signal input terminal 101 is the first encoder 102.
Is encoded by the first electro-optical converter 103, converted into an optical signal by the first electro-optical converter 103, and supplied to the first input terminal T1 of the optical directional coupler 104. The signal applied to the input terminal 101 is also applied to the second encoder 105 to be encoded, and then converted into an optical signal by the second electro-optical converter 106 to generate the optical directional coupler 104. Of the second input terminal T2.

The optical directional coupler 104 outputs the optical signal of the first input terminal T1 to the first output terminal T3 and outputs the optical signal of the second input terminal T2 to the second output terminal T4. The output terminal T3 of the optical directional coupler 104 is connected to one end of the loop fiber 107, and the output terminal T4 is connected to the other end of the loop fiber 107. As a result, the optical signal encoded by the first encoder 102 flows through the loop fiber 107 in the direction C1 in the figure, and the optical signal encoded by the second encoder 105 in the direction C2 in the figure. Flowing. On the loop fiber 107, optical signals in both C1 and C2 directions are superimposed and flow.

When the loop fiber 107 has no fault, each of the subscriber units 108 to 112 receives the optical signals superposed in both C1 and C2 directions.

Now assume that the loop fiber is cut at point 113 between subscriber units 109 and 110. At this time, the subscriber device 1
The optical signals in the C2 direction reach 08 and 109, and the optical signals in the C1 direction reach the subscriber units 110 to 112. The optical signals in the C1 direction and the C2 direction are encoded with signals having a small correlation with each other, and when receiving an optical signal in which the C1 direction and the C2 direction are superimposed, it is not necessary to separate them in the state of the optical signal, and one optical signal -Convert it into an electrical signal with an electrical converter,
After that, it is possible to separate the two signals by a correlation detector. When the loop fiber is normal, either one of the two detected signals is used as the output signal. When there is a failure in the loop fiber, each subscriber unit uses the received signal in the C1 or C2 direction.

2 (a) and 2 (b) show an example of the configuration of the first and second encoders 102 and 105 used when the input signal is a digital signal. These are self-synchronous three-stage and four-stage pseudo-random encoders, which generate codes having a small correlation with each other and encode the input signal. One bit of the input digital signal is converted into an N-bit (N is an integer) code by this encoder.

FIGS. 3 (a) and 3 (b) show a self-synchronous decoder used as a correlation detector of a receiver in a subscriber unit.
This corresponds to the encoder in Figures (a) and (b). Since it is a self-synchronous type, a synchronizing circuit is not particularly required, and the outputs of the reduction wave LPF are separated and output in the C1 direction and the C2 direction, respectively.

〔The invention's effect〕

As described above, according to the present invention, by transmitting signals encoded with small interphase codes in opposite directions to each other in the transmission path, even if the optical fiber is cut between the subscribers, It provides a means for receiving signals in the respective directions, and as a result that the signals in each direction are separated by the code, there is an effect that they can be received by one optical-electrical converter. This is extremely effective in reducing the price of the optical subscriber system.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the present invention, FIG. 2 is a diagram showing an example of an encoder, and FIG. 3 is a diagram showing an example of a decoder. In the figure, 101 ... Transmission signal input terminal, 104 ... Optical directional coupler, 107 ... Loop fiber, 108-11
2 ... Subscriber device, 113 ... Fiber cut point.

Claims (1)

[Claims] 1. In an optical loop subscriber system in which a plurality of subscriber devices are connected to one transmitter by an optical fiber in a loop, transmission signals are transmitted by first and second transmission line codes having a small mutual correlation. Each one is encoded and
Converting into a second optical signal, supplying the first optical signal through an optical directional coupler in one direction of an optical loop fiber, and supplying the second optical signal through the optical directional coupler. The optical loop transmission system is characterized in that the optical fiber is supplied to the other direction of the loop fiber.