JPH0488734A - Two-way optical fiber transmission system - Google Patents

Abstract

PURPOSE:To reduce number of required optical directional couplers by providing an optical directional coupler for coherent light to each end of one optical fiber transmission line so as to attain 2-way communication. CONSTITUTION:A transmission signal at an incoming transmission input terminal W1 is converted into a drive signal for a light emitting element 133 by an incoming signal interface section 132 to drive the light emitting element 133, by which the signal is converted into an optical signal and it is fed to a 2nd port P2 of an optical directional coupler 15. The incoming optical signal is sent to an optical fiber transmission line 3 from a 1st port P1. Moreover, a local oscillation light source control circuit 116 controls the oscillating frequency of a local oscillation light source 111, and the controlled local oscillation light is inputted to a 4th port P4 of the optical coupler 15. Thus, the optical signal inputted from a 3rd port P3 is inputted to a photodetector 112 and fed to a preamplifier 113. The signal amplified by the amplifier 113 is outputted from an output terminal W0. Furthermore, part of the output signal from a main amplifier 114 controls the circuit 116.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a bidirectional optical fiber transmission system, and more particularly to a bidirectional optical fiber transmission system obtained by improving the receiving side optical circuit in a coherent optical communication system.

[Conventional technology]

Conventionally, a bidirectional optical fiber transmission system is known as one that performs bidirectional optical communication using two optical fiber transmission lines. In such a bidirectional optical fiber transmission system, when performing coherent optical communication, two optical directional couplers connected in series are connected to each end of the optical fiber transmission line, and these optical directional couplings are performed. One of the vessels is used for optical coupling with the local oscillation light source, and the other is used for optical coupling for reverse direction transmission (transmission).

Such an optical directional coupler has a first port, a second port, and a third port, and guides light from the first port to the third port and from the second port to the first port.

In the above-mentioned conventional bidirectional optical fiber transmission system, two directional couplers are connected to each end of the two optical fiber transmission lines, and a total of four optical directional couplers are used to perform bidirectional transmission. doing.

[Problem to be solved by the invention]

However, this conventional bidirectional optical fiber transmission system requires twice as many parts as the bidirectional transmission systems using other optical intensity modulation methods, which use a total of two optical directional couplers. It has the disadvantage of becoming.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above-mentioned drawbacks and to provide a bidirectional optical fiber transmission system with fewer optical directional couplers.

[A trick to solve problems]

The bidirectional optical fiber transmission system of the present invention is a bidirectional optical fiber transmission system in which an optical transmitter and an optical receiver are coupled to both ends of an optical fiber transmission line, and optical signals are transmitted bidirectionally through the optical fiber transmission line. In optical fiber transmission systems,
An optical directional coupler that optically mixes the received light from the fiber transmission line and the local light from the local oscillation light source and guides it to an optical receiver, and sends the transmitted light from the optical transmitter to the optical fiber transmission line. It is characterized in that it is disposed between the optical transceiver and the fiber transmission line.

The present invention basically utilizes an optical directional coupler that optically couples the received light with the local light from the local oscillation light source, which is essential on the receiving side of coherent optical communication. By providing a port and coupling the output of a light source for reverse direction transmission to an optical fiber transmission line, the number of optical directional couplers required is reduced.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the bidirectional optical communication system of the present invention. FIG. 2 is an explanatory diagram showing an optical directional coupler used in the optical communication system of the present invention.

The bidirectional optical fiber transmission system shown in FIG. 1 is constructed by connecting an optical fiber transmission line 3 between a first optical transmitter/receiver 1a and a second optical transmitter/receiver 1b. Since the first optical transmitting/receiving device 1a and the second optical transmitting/receiving device 1b have the same configuration, only the configuration of one will be explained, and the other configuration will be given the same reference numerals and a detailed explanation will be omitted.

The optical transmitter/receiver 1 includes an optical receiver 11, an optical transmitter 13,
The optical directional coupler 15 is also provided.

As shown in FIG. 2, this optical directional coupler 15 is provided with a first port P + , a second boat P2, a third boat P3, and a fourth boat P4. The optical signal input from P, to the fourth port) P4,
The human-powered optical signal from the second boat P2 is transmitted to the first boat P.
, so as to guide the human-powered light from the fourth bow) P4 to the third bow) P+, respectively.

The received light transmitted through the optical fiber transmission line 3 is input to the first port P of the optical directional coupler 15, optically mixed with the local light from the optical receiver 11, and then sent to the optical receiver 11. is input. The optical receiver 11 converts this input optical signal into an electrical signal and sends it to eight terminals W. This is how it is output from.

The transmission signal input from the input terminal WI is sent to the optical transmitter 13.
The optical directional coupler 15 converts the optical signal into an optical signal.
The signal is transmitted from the second port P2 to the optical fiber transmission line 3 via the first port P.

FIG. 3 is a block diagram showing the configuration of one transmitting/receiving device of the bidirectional optical fiber transmission system of the present invention.

As shown in FIG. 3, the predecessor force signal transmitted through the optical fiber transmission line 3 is input to the first port P+ of the optical directional coupler 15. The optical directional coupling 15 is
After optically coupling the received light input from the first port P+ with the local light from the local oscillation light source 111 input from the fourth port P, the light is transmitted to the light receiving element 112 via the third port P3. It is designed to lead to. Light receiving element 11
2 converts the manually input optical signal into an electrical signal and then supplies it to the preamplifier 113. This electrical signal is amplified by a preamplifier 113, and then amplified by a main amplifier 114 and sent to an output terminal W. is output from.

On the other hand, a part of the signal amplified by the main amplifier 114 is input to the local oscillation light source control circuit 116, which controls the oscillation frequency of the local oscillation light source 111 to produce a stable reproduction signal. It has gained.

Further, the transmission signal inputted from the transmission input terminal WI is amplified by the upstream signal interface section 132, and then the light emission is controlled by the light emitting element 133.

The operation of the embodiment having the above-mentioned configuration will be explained.

In the optical directional coupler 15, optical coupling loss occurs in principle, and this loss cannot be avoided in the conventional system. In order to effectively utilize this loss, a bidirectional optical communication system is configured in this example. The upstream transmission signal input from the upstream transmission input terminal W is converted into a drive signal for the light emitting element 133 by the upstream signal interface section 132 . This drive signal is converted into an optical signal by driving the light emitting element 133, and is supplied to the second baud P2 of the optical directional coupler 15. This upstream optical signal is inputted to the second port P2 of the optical directional coupler 15, and the optical signal is sent from the first port P to the optical fiber transmission line 3.

Further, the local oscillation light source control circuit 116 controls the local oscillation light source 1
11, and inputs the controlled local light to the fourth port P4 of the optical directional coupler 15. As a result, the optical signal input from the third port Ps is optically mixed with the local light in the optical directional coupler 15, and is input as an output optical signal to the light receiving element 112 from the third port Ps. This optical signal is converted into an electrical signal by the light receiving element 112 and supplied to the preamplifier 113. The signal amplified by the preamplifier 113 is further amplified by the main amplifier 114 and output to the output terminal W. is output from.

Note that a part of the 8-power signal from the main amplifier 114 controls the local oscillation light source control circuit 116.

In this way, a bidirectional optical fiber transmission system can be constructed by simply providing one optical directional coupler 15 for coherent optical communication at each end of the optical fiber transmission line 3, thereby reducing the number of required parts. be able to.

〔Effect of the invention〕

As explained above, the present invention enables two-way communication by simply providing one optical directional coupler for coherent light at one end of each optical fiber transmission line. This has the effect of reducing the required number of.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the optical communication system of the present invention, Fig. 2 is a diagram showing an optical directional coupler used in the embodiment, and Fig. 3 shows a part of the embodiment in detail. FIG. 1a... First transmitting/receiving device, 1b... Second transmitting/receiving device, 3... Optical fiber transmission line, 11... Optical receiver, 1
3... Optical transmitter, 15... Optical directional coupler, Pl...
・First boat, P2...second boat, P3...third boat, P4...fourth boat.

Claims (1)

[Claims] In a bidirectional optical fiber transmission system in which an optical transmitter and an optical receiver are coupled to both ends of a single optical fiber transmission line, and optical signals are transmitted bidirectionally through the optical fiber transmission line. , an optical directional coupler that optically mixes the received light from the fiber transmission line and the local light from the local oscillation light source and guides it to the optical receiver, and sends the transmitted light from the optical transmitter to the optical fiber transmission line. A bidirectional optical fiber transmission system, characterized in that a bidirectional optical fiber transmission system is provided between the optical transceiver and the fiber transmission line.