JPH0336825A - Optical relay system - Google Patents

Abstract

PURPOSE:To attain the effective use of a semiconductor laser and to reduce number of light sources by utilizing part of the power of an optical output of a local oscillation semiconductor laser as a light source for light intensity modulation system. CONSTITUTION:An optical signal inputted to an optical input terminal T1 is coupled with an output light of a local oscillation semiconductor laser 2 at an optical directional coupler 1 and inputted to a photodetector 3, in which the signal is converted into an electric signal and the original signal is reproduced by a demodulation circuit 4 for coherent optical communication. On the other hand, a half the power of the output light of the semiconductor laser 2 is coupled with a received light at the coupler 1 and outputted to an optical external modulator 6. The original signal reproduced by the demodulation circuit 4 as the optical modulation signal is inputted to the modulator 6 via the external modulation drive circuit 5, the modulator 6 modulates the intensity of the light and an optical distributer 7 outputs the light while distributing it into plural intensity modulation light signals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the configuration of an optical relay system, and particularly to the effective use of semiconductor lasers.

[Conventional technology]

Conventionally, in this type of optical relay system, a data signal is converted into an electrical signal by an optical receiver, is applied to a separately prepared light source, is converted back into an optical signal, and is sent to the next optical receiver. is sent out.

[The problem that the invention attempts to solve]

In the conventional optical relay system described above, for example, when the trunk route is optically relayed using the coherent optical communication method, and the branch line after the optical receiver is optically relayed using the conventional optical intensity modulation method, the relay In terms of dexterity, it is necessary to equip a local oscillation semiconductor laser for coherent optical demodulation and a semiconductor laser as a light source for retransmission, but from the point of view of effective use of semiconductor lasers, the disadvantage is that it is a wasteful configuration. was there.

[Means to solve the problem]

In order to eliminate such drawbacks, the present invention provides an optical relay system that demodulates an optical signal transmitted using a coherent optical communication method and transmits it again using an optical intensity modulation method.
An optical directional coupler that combines the optical output of a local oscillation semiconductor laser with received light and outputs it as an optical signal for demodulation and an optical signal for retransmission, and retransmits the optical signal for retransmission output from this optical directional coupler. A transmitting means used as a light source for intensity modulation is provided.

[Effect]

In the optical relay system according to the present invention, a part of the optical output of the local oscillation semiconductor laser, which is essential for the coherent optical communication system, is used as a light source for the optical intensity modulation system.

〔Example〕

The figure is a system diagram showing an embodiment of the optical relay system according to the present invention. In the figure, l is an optical directional coupler, 2 is a local oscillation semiconductor laser, 3 is a light receiving element, 4 is a demodulation circuit,
5 is an external modulator drive circuit, 6 is an optical external modulator as a transmitting means, 7 is an optical frequency divider, TI is an optical input terminal, TOl
``TOn is an optical output terminal.

The illustrated embodiment shows a case where a long-distance transmission section is optically relayed using a coherent optical communication method, and a short-distance distribution transmission system is constructed using an optical intensity modulation method on the receiving side.

Next, the operation will be explained. An optical signal for coherent optical communication transmitted over a long distance is input to the optical input terminal TI.

The input optical signal is combined with the output light of the local oscillation semiconductor laser 2 by the optical directional coupler l, inputted to the light receiving element 3, converted into an electrical signal by the light receiving element 13, and used for coherent optical communication. The original signal is reproduced in the demodulation circuit 4.

On the other hand, in the optical directional coupler 1, the local oscillation semiconductor laser 2
1/2 of the power of the output light is combined with the received light and output to the optical external modulator 6 side. In principle, this output light maintains a constant level that does not change over time. To the optical external modulator 6, as an optical modulation signal,
The original signal reproduced by the demodulation circuit 4 is sent to the external modulator drive circuit 5.
It is input after passing through. The intensity of the light is modulated by the optical external modulator 6, further divided into 0 intensity-modulated lights by the optical distributor 7, and outputted from 0 light output terminals TOI to TOn.

That is, in this embodiment, the output light of the local oscillation semiconductor laser 2 is used for demodulating the original purpose optical signal, and at the same time,
It is also used as a light source for intensity modulation for relay transmission.

〔Effect of the invention〕

As explained above, the present invention makes it possible to reduce the number of light sources in an optical relay system by using a part of the optical output power of a local oscillation semiconductor laser as a light source for an optical intensity modulation method. This has the effect of making it easier, more economical, and more compact.

[Brief explanation of drawings]

The figure is a system diagram showing an embodiment of the optical relay system according to the present invention. l... Optical directional coupler, 2... Local oscillation semiconductor laser, 3... Light receiving element, 4... Demodulation circuit, 5... External modulator drive circuit, 6... Optical external modulation 7... Optical divider, TI... Optical input terminal, TO1=TOn...
Optical output terminal.

Claims (1)

[Claims] In an optical relay system that demodulates an optical signal transmitted using a coherent optical communication method and transmits it again using an optical intensity modulation method, the optical output of a local oscillation semiconductor laser is combined with the received light to generate an optical signal for demodulation and an optical signal for retransmission. an optical directional coupler that outputs an optical directional coupler, and a transmitter that uses a retransmission optical signal output from the optical directional coupler as an intensity modulation light source for retransmission. Relay system.