JP2930150B2 - Optical communication network - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical LA using optical communication.
The present invention relates to an optical communication network such as N (local area network).

[0002]

2. Description of the Related Art In a communication network, optical fibers derived from a plurality of terminal devices are respectively coupled via couplers, and communication is performed between the terminals via the optical fibers and couplers.

There are various types of couplers, one of which is called a star coupler. An optical LAN using the star coupler is described in E.P. G. FIG. Rawso
n, "Fibernet: Multimode Opt
ical Fibers for Local Com
puter Networks ”, IEEE Tran
actions on Communication
s, Vol. COM-26, NO. 7, JULY 19
78.

FIG. 8 shows light L using the star coupler.
2 shows a configuration example of an AN. A signal from each node 51 is converted into an optical signal by each light emitting element 52a and supplied to a star coupler 54 via each input optical fiber 53a. These optical signals are all mixed once by the star coupler 54, then distributed to each light receiving element 52b via each output optical fiber 53b and converted again into electric signals, and these electric signals are supplied to each node 51. Is done. As a result, a signal transmitted from one node can be transmitted to all nodes (broadcasting), and a normal LAN using a coaxial cable can be provided.
A communication network similar to can be constructed.

On the other hand, it has been proposed to configure a so-called multi-channel LAN by connecting each node with two or more communication paths. For example, in Japanese Patent Application Laid-Open No. 2-69999, filed by the present applicant, a CSMA / CD (carrier sense multi-channel) is used to transmit audio signals and image signals that require real-time characteristics over a LAN.
ple access / collision detection) and other contention buses, as well as TDMA (time division multiple acces
s) and other time-division buses are provided, and the bus to be used is selected according to the nature of the data to be transmitted.

[0006]

When this multi-channel LAN is realized using optical communication, for example,
As shown in FIG. 9, a bus (first channel) of the contention system from the bus controller 55 and a bus of the time division system (second channel)
Channel) via two star couplers 56 and 57 to each node 58 for detection.

[0007] As shown in FIG.
It is necessary to provide a light emitting element 59a, 59b for transmission and a light receiving element 60a, 60b for reception for each channel.

[0008] The number of star couplers required in this multi-channel LAN increases as the number of buses, that is, the number of channels increases. For this reason, there has been a problem that the configuration of the LAN is complicated and the construction cost of the LAN is increased.

An object of the present invention is to minimize an increase in the number of star couplers in a multi-channel optical communication network.

[0010]

In order to achieve the above object, an optical communication network according to the present invention derives a pair of optical fibers from each of a plurality of nodes and connects the pair of optical fibers to both ends of a star coupler. In each of the plurality of nodes, a transmission path and a reception path are provided for two systems, and a signal from a transmission path of one system is supplied to one of the pair of optical fibers and the one of the pair of optical fibers A first optical multiplexer / demultiplexer that supplies a reception signal from the other system to a reception path to the other system, and supplies a signal from the transmission path of the other system to the other of the pair of optical fibers, and And a second optical multiplexer / demultiplexer for supplying a reception signal from the optical fiber to the reception path to the one system.

[0011]

In the optical communication network according to the present invention, a signal from one transmission path is supplied to one end of a star coupler via a first optical multiplexer / demultiplexer and an optical fiber. The output from the other end of the star coupler is supplied to one of the receiving paths via the optical fiber and the second optical multiplexer / demultiplexer. This makes it possible to simultaneously transmit to all nodes connected to the star coupler.
Also, when transmitting from the other system, the star coupler is transmitted in the same direction as the transmission of one system, but in the opposite direction to the transmission of the one system, and the reception path of the other system is transmitted. Supplied to In this way, by reversing the direction of the light passing through the star coupler in each system, it is possible to transmit the signals of the two systems independently while using a common star coupler.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be specifically described below based on embodiments with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the optical communication network according to the present invention.

A plurality of nodes 1 to 3 are mutually connected via a star coupler 4. The star coupler 4 is a general passive type star coupler having the same configuration as the star coupler shown in FIG. The structure of the star coupler itself is described in the above-mentioned reference E. G. FIG. Ra
wson, “Fibernet: MultimodeO
optical Fibers for Local C
Computer Networks ", IEEE Tr
actions on Communicati
ons, Vol. COM-26, NO. 7, JULY
1978, so a detailed description is omitted here.

From each of the nodes 1 to 3, a pair of optical fibers 5-6, 7-8, and 9-10 are led out, and one of the optical fibers 5, 7, and 9 is connected to one joint terminal 4a of the star coupler 4. The other optical fibers 6, 8, and 10 are connected to the other joining terminal 4 b of the star coupler 4.

Next, the configuration of each node will be described.
Since the nodes 1 to 3 have the same configuration, the node 1 will be described as an example.

The node 1 includes a node body 13 having output signal paths 11a and 11b and input signal paths 12a and 12b for the first and second channels, respectively.
It comprises a unidirectional / bidirectional interface (hereinafter simply referred to as an interface) 14 for making a connection between the node body 13 and the star coupler 4.

In the interface 14, the transmitting device 15a and the light emitting device 16a correspond to the output signal path 11a of the first channel of the node body 13, and the receiving device 17a and light receiving device 18 correspond to the input signal path 12a of the first channel.
a, a transmitting device 15b and a light emitting device 16b are provided for the output signal path 11b of the second channel, and a receiving device 17b and a light receiving device 18b are provided for the input signal path 12b of the second channel.

The output terminal of the light emitting device 16a for the first channel and the input terminal of the light receiving device 18b for the second channel are:
The optical multiplexer / demultiplexer 19 is connected to each branch end, and the common end of the optical multiplexer / demultiplexer 19 is connected to one of the joining terminals 4 a of the star coupler 4. Similarly, the output terminal of the light-emitting device 16b for the second channel and the input terminal of the light-receiving device 18a for the first channel are connected to the second optical multiplexing device.
The common end of the optical multiplexer / demultiplexer 20 is connected to each branch end of the splitter 20 and the other joint terminal 4 of the star coupler 4.
b.

Next, the operation of the above-described optical communication network will be described.

Now, consider the case where the first channel is transmitted from the node 1.
An output signal from 1a is supplied to the transmitting device 15a, and a signal light is output from the light emitting device 16a. This output signal light is supplied to one joining terminal 4 a of the star coupler 4 via the first optical demultiplexer / combiner 19 and the optical fiber 5.
Therefore, the output signal light from the node 1 is distributed and appears at the other joining terminal 4 b of the star coupler 4. The distributed signal light is supplied to the nodes 1 to 3 via the optical fibers 6, 8, and 10.

Next, considering the receiving operation in the node 1, the signal light from the optical fiber 6 is split by the second optical multiplexer / demultiplexer 20, and the light receiving device 18a and the receiving device 17a
And the signal light is converted into an electric signal. This electric signal is supplied to the input end of the first channel of the node body 13 via the input signal path 12a. Here, for convenience of explanation, transmission from node 1 and reception at node 1 have been described, but similar reception operations are performed at other nodes 2 and 3 as well. That is, the signal of the first channel transmitted from a certain node is transmitted to the first channel in all the other nodes.
It will be received as a channel signal.
That is, the broadcast property is secured.

Next, consider a case where the second channel is transmitted from the node 1. In this case, the transmitting device 15b and the light emitting device 16b for the second channel are activated, and the light from the light emitting device 16b is transmitted to the star coupler 4 via the second optical demultiplexer / combiner 20 and the optical fiber 6. Is supplied to the other joining terminal 4b. The signal light obtained from one of the connection terminals 4a after passing through the star coupler 4 passes through the optical fiber 5, is branched by the first optical multiplexer / demultiplexer 19, and supplied to the light receiving device 18b and the receiving device 17b. The signal light is converted into an electric signal. This electric signal is supplied to the input end of the second channel of the node body 13 via the input signal path 12b.

As described above, in this embodiment, when the first channel is transmitted from the node 1, the optical fiber 5 becomes a transmission line and the optical fiber 6 becomes a reception line.
On the other hand, when transmitting the second channel from the node 1, the optical fiber 6 becomes the transmission line and the optical fiber 5 becomes the reception line.

As described above, the signal light is input from one joint terminal 4a of the star coupler 4 when transmitting the first channel, and the signal light is input from the other joint terminal 4b when transmitting the second channel. By using the bidirectionality of light, the same star coupler 4 can be used to separate the first channel signal light and the second channel signal light.

Next, an example in which communication between nodes is performed based on different protocols using the above-described multi-channel optical communication network will be described.

For example, the first channel is a channel according to a contention protocol, and the second channel is a channel according to a time division protocol.
Further, one of the nodes is made to function as a bus control device called a slot generator, and has a function of time division control of the second channel.

From the node functioning as a bus control device, as shown in FIG.
The bus control signal S1 and the node signal S2 are output. The bus control signal S1 includes a message designating a specific node. All nodes receive the bus control signal S1, and only the node specified in the message is permitted to transmit in the time slot T. The signal transmitted from the node based on this permission is the node signal S2.

The procedure for starting the time-division communication will be described below.

When a node wants to transmit using a time division bus, that is, the second channel, it transmits the request to the bus controller using the contention bus, that is, the first channel. Upon receiving the transmission request, the bus control device generates a bus control signal S1 including a message permitting transmission of the requested node. Thus, the node that has requested transmission can transmit the node signal S2 at a predetermined short cycle using the second channel. Therefore, real-time performance when transmitting an audio signal, a moving image signal, or the like is ensured.

In the above embodiment, two communication paths are formed by using one star coupler.
If four star couplers are used, four communication paths can be formed, and if three star couplers are used, six communication paths can be formed. That is, by adding star couplers, the number of transmission paths can be increased by two channels per star coupler.

Further, in the above-described embodiment, the case where different protocols are used has been described as an example of multi-channel. However, the present invention is not limited to this, and a plurality of communication channels are used. The present invention can be applied to any optical communication network.

Further, in the above-mentioned optical communication network, instead of a normal star coupler, it is necessary to connect to the same node as described in Japanese Patent Application No. 2-98370 filed by the present applicant. It is also possible to use a passive star coupler (hereinafter referred to as an interconnectable star coupler) in which the transmission coefficient of a signal between a pair of input terminal and output terminal is 0.

When the above-mentioned interconnectable star couplers are used, the network can be expanded by connecting the star couplers even when the number of nodes increases. Further, as described in the above-mentioned Japanese Patent Application No. 2-98370, a network formed by connecting mutually connectable star couplers has bidirectionality. It is possible to maintain confidentiality and increase communication capacity.

FIGS. 3 and 5 show configuration examples of interconnectable passive star couplers which can be used in place of the star coupler 4 of the optical communication network shown in FIG.

FIG. 3 shows an example of the configuration of a three-terminal interconnectable passive star coupler. Here, an interconnectable passive star coupler is constructed by using six 1 × 2 optical branch paths 21. The 1 × 2 optical branching path 21
As shown in FIG. 4, there is one optical path 21a and two optical paths 21b and 21c on the other end, and optical input / output signals to each terminal are respectively _ua1 , _u2a , _u3a and _va1. , V _a2 , v
_{If a3} is set, the transfer characteristic of the 1 × 2 optical branch path 21 is expressed by the following equation.

[0037]

(Equation 1)

The transfer characteristic of this star coupler is expressed by the following equation.

[0039]

(Equation 2)

FIG. 5 shows an example of the configuration of a five-terminal interconnectable passive star coupler. Here, 10 1 × 2 optical branch paths 21 and 5 2 × 2 optical branch paths 22 are combined. As shown in FIG. 6, the 2 × 2 optical branching path 22 has two optical paths 22a and 22b and two optical paths 22c and 22d on the other end, and transmits an optical input / output signal to each terminal. _ub1 , _ub2 , _ub3 , _ub4 , _vb1 , _vb2 , _vb3 ,
_Assuming that v _b4 , the transfer characteristic of the 2 × 2 optical branch path 22 is expressed by the following equation.

[0041]

(Equation 3)

The transfer characteristic of the star coupler 23 is expressed by the following equation.

[0043]

(Equation 4)

FIG. 7 shows an example of the configuration of an optical communication network formed by combining the five-terminal interconnectable passive star coupler shown in FIG. 5 and a bidirectional optical amplifier. FIG.
In the figure, 23 is a five-terminal interconnectable passive star coupler of FIG. 5, 24 is a bidirectional optical amplifier, and 25 is a node having the interface 14 shown in FIG. Although the semiconductor laser amplifier is specifically used as the bidirectional optical amplifier 24, this may be a rare earth doped fiber amplifier. For the semiconductor laser amplifier, see Shimada and Nakagawa, "Research Status of Semiconductor Laser Amplifiers Used in Optical Communication Systems", O plus E, August 1989, pp. 106-111. For the rare earth doped fiber amplifier, see Horiguchi "Optical Fiber Amplifier", Optics, Vol. 19, No. 5, P276-P282.

According to the configuration of FIG. 7, two independent bidirectional communication channels can be formed by one star coupler, and a new interconnectable passive communication system can be provided in response to the increase in the number of nodes. The network can be expanded by adding a type star coupler.

[0046]

As described above, according to the present invention,
One star coupler can form two independent communication paths. Therefore, an increase in the number of star couplers required in a multi-channel optical communication network can be suppressed, and the configuration of the communication network can be simplified, and the cost of building the communication network can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical communication network of the present invention using a star coupler.

FIG. 2 is a diagram for explaining a time slot in the time division method.

FIG. 3 is a schematic diagram showing a circuit configuration of a three-terminal interconnectable passive star coupler applicable to the optical communication network shown in FIG. 1;

FIG. 4 is a schematic view of a 1 × 2 optical branch used in the star coupler shown in FIG. 3;

5 is a schematic diagram showing a circuit configuration of a five-terminal interconnectable passive star coupler applicable to the optical communication network shown in FIG. 1; .

6 is a schematic view of a 2 × 2 optical branch used in the star coupler shown in FIG. 5;

FIG. 7 is a schematic diagram showing a configuration of an optical communication network configured by combining a five-terminal interconnectable passive star coupler and a bidirectional optical amplifier.

FIG. 8 is a configuration diagram showing an embodiment of a conventional optical LAN using a star coupler.

FIG. 9 is a diagram illustrating a configuration example of a conventional multi-channel optical LAN using a star coupler.

FIG. 10 is an explanatory diagram showing transmission and reception units of each channel in a conventional multi-channel optical LAN.

[Explanation of symbols]

1 to 3 nodes, 4 star couplers, 4a, 4b connection terminals, 5 to 10 optical fibers, 11a, 11b output signal paths, 12a, 12b input signal paths, 13 node bodies, 14 interfaces, 15a, 15b transmission devices, 16a, 16b light emitting device, 17a, 17b receiving device, 18a, 18b light receiving device, 19, 20
Multiplexer, 211 × 2 optical branch, 222 × 2 optical branch, 235-terminal interconnectable passive star coupler, 24 bidirectional optical amplifier, 25 nodes with interface, 51 nodes, 52a light emitting element, 52
b light receiving element, 53a input optical fiber, 53b output optical fiber, 54 star coupler, 55 bus controller, 56,57 star coupler, 58 node, 59
a, 59b light emitting element, 60a, 60b light receiving element

Claims (1)

(57) [Claims] 1. A pair of optical fibers are derived from each of a plurality of nodes, and the pair of optical fibers are connected to both ends of a star coupler. Each of the plurality of nodes has two transmission paths and two reception paths. A first optical fiber for supplying a signal from the transmission path of one system to one of the pair of optical fibers and supplying a reception signal from the one optical fiber to a reception path to the other system. A wave / demultiplexer, and a signal from the transmission path of the other system is supplied to the other of the pair of optical fibers, and a reception signal from the other optical fiber is supplied to a reception path to the one system. Second
An optical communication network comprising: an optical multiplexer / demultiplexer.