JP2733120B2 - Two-way optical communication system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a bidirectional optical communication system using an optical wavelength multiplexing system capable of large-capacity communication in which light of different wavelengths is transmitted by the same optical fiber. It is.

(Prior Art) Conventionally, techniques in such a field include PROCEEDINGS OF I
THE IEEE) 75 [11] (1987-11) P. 1512-1523.

As described in this document, in a bidirectional optical communication system using a conventional optical wavelength multiplexing system, for example, one switching center and one end connected to the switching center via an optical multiplexer are provided. An optical fiber for optical communication is provided, and a plurality of subscriber terminals are branched and connected to the other end of the optical fiber via an optical multiplexer. In this bidirectional optical communication system,
One wavelength is assigned to each subscriber terminal, and light of different wavelengths output from the exchange is multiplexed by an optical multiplexer and sent to one end of an optical fiber, and light sent from the other end of the optical fiber Is split into light of different wavelengths by an optical demultiplexer, and each subscriber terminal receives light of a corresponding wavelength.

(Problems to be Solved by the Invention) However, in the system having the above configuration, one wavelength is allocated to one subscriber terminal, so even when communication is not performed between the exchange and the subscriber terminal, The wavelength was monopolized and the efficiency of use of the wavelength was poor, thereby hindering the improvement of broadband communication.

An object of the present invention is to provide a bidirectional optical communication system which solves the problem of the prior art that the wavelength use efficiency is low.

(Means for Solving the Problems) In order to solve the above problems, a first aspect of the present invention provides an optical signal source for transmitting an optical signal of an arbitrary specific wavelength and receiving an optical signal of an specific wavelength. Bidirectional optical communication comprising: an exchange having reception means; and a subscriber terminal having a wavelength reception means for selecting and receiving an arbitrary wavelength and a variable wavelength transmission means for selecting and transmitting an arbitrary wavelength. In the system, when performing a call setup, the switching center transmits a specific wavelength not used by the optical signal source to the subscriber terminal by transmitting an optical signal, and the subscriber terminal transmits the optical signal to the subscriber terminal. The unused wavelength transmitted from the switching center is received by the wavelength receiving means, and the wavelength-variable transmitting means tunes and transmits an optical signal to the unused wavelength.

According to a second aspect, in the first aspect, when the call setup is performed from the subscriber terminal, the subscriber terminal tunes and transmits an optical signal to an arbitrary specific wavelength, and the exchange includes: After receiving the tuned optical signal transmitted from the subscriber terminal by the receiving means, an unused wavelength is transmitted to the subscriber terminal by transmitting the optical signal to the subscriber terminal.

In a third aspect based on the first or second aspect, the wavelength tunable transmission means tunes the optical signal to the unused specific wavelength using a wavelength tunable filter.

In a fourth aspect based on the third aspect, the tunable filter is used commonly with the wavelength receiving means.

(Operation) According to the present invention, since the two-way optical communication system is configured as described above, when performing a call setup, the switching center transmits a specific wavelength not used by the optical signal source to the subscriber terminal. By transmitting an optical signal to In the subscriber terminal, the specific wavelength transmitted from the switching center is received by the wavelength receiving means, and the optical signal is tuned to the specific wavelength by the wavelength variable transmitting means and transmitted. Therefore, it is not necessary to assign a specific wavelength to each subscriber terminal, and bidirectional optical communication can be performed using a different wavelength for each call setup from the exchange to the subscriber terminal or from the subscriber terminal to the exchange.

(Embodiment) FIG. 1 is a schematic configuration diagram of a bidirectional optical communication system using an optical wavelength multiplexing system according to a first embodiment of the present invention.

This bidirectional optical communication system uses a coherent optical communication technology, and includes one switching center 10 and a plurality of subscriber terminals 20a to 20m, and the switching center 10 includes a downstream optical fiber 30 and an upstream One end of the optical fiber 31 is connected, and the other end of the two optical fibers 30, 31 is connected to the subscriber terminals 20a to 20m via the splitters 32, 33, respectively. Switchgear 32,3
Numeral 3 is for distributing light in a plurality of directions, and is composed of, for example, a star coupler or the like which is concentrated by passive branching (branching of light without applying a voltage).

The exchange 10 includes a plurality of light sources 11a to 11n locked to different specific wavelengths λa to λn, respectively, and the light sources 11a to 11n.
And a plurality of light modulators 12a to 12n connected to the light source 11a.
Multiple coherent receivers 13a-13n connected to ~ 11n
And The optical modulators 12a to 12n are connected to a splitter 14 via an optical fiber, and the receivers 13a to 13n are connected to a splitter 15 via an optical fiber. Where the light source
11a to 11n are constituted by semiconductor lasers and the like, and optical modulators 12a to 1n
Together with 2n, they constitute an optical signal source fixed at a different specific wavelength. The receivers 13a to 13n are composed of, for example, polarization diversity receivers, and together with the local oscillation light sources 11a to 11n, constitute specific wavelength receiving means for receiving optical signals of different specific wavelengths.

The subscriber terminals 20a to 20m include, for example, coherent receivers 21a to 21m composed of polarization diversity receivers, tunable light sources 22a to 22m composed of semiconductor lasers and the like, and an optical modulator 23a.
~ 23 m, which are splitters 32,
33 respectively. The tunable light sources 22a to 22m are also local oscillation light sources of the coherent receivers 21a to 21m, and constitute tunable receiving means for freely selecting and receiving a wavelength. The tunable light sources 22a to 22m and the optical modulators 23a to 23m constitute tunable transmission means capable of freely selecting a wavelength and carrying a signal.

 The arrows in FIG. 1 indicate the traveling directions of light.

 Next, the operation will be described.

For example, when a call is set up from the subscriber terminal 20a to the exchange 10, one wavelength, for example, λa is used for a call request. In the subscriber terminal 20a, after tuning (tuning) the wavelength of the wavelength variable light source 22a to λa, confirming that the wavelength λa is not used by the receiver 21a, the modulation operation of the optical modulator 23a A call request signal is put on the output light of the variable light source 22a. This call request signal is transmitted to the branching device 33, the optical fiber
The signal is received by the receiver 13a on the switching center 10 side via the switch 31 and the branching device 15.

The exchange 10 selects a wavelength that is not used, for example, λn, and superimposes information that the wavelength λn is to be used on the light of the wavelength λa for the call request by the optical modulator 12a.
4. The signal is sent to the subscriber terminal 20a via the optical fiber 30 and the branching device 32. In the subscriber terminal 20a, the information superimposed on the call request wavelength λa is read by the receiver 21a. In the subscriber terminal 20a, the wavelength tunable light source 22a and the optical modulator 23a
, A call setting confirmation signal is transmitted at the wavelength λa, and then the wavelength of the wavelength tunable light source 22a is tuned to λn,
Start communication with.

When performing communication between the subscriber terminal 20a and the exchange 10, the subscriber terminal 20a uses the wavelength λ output from the wavelength-variable light source 22a.
The light modulator 23a puts information on the light of n and sends it to the exchange 10 via the splitter 33 and the optical fiber 31. Then exchange 10
Then, the signal of the wavelength λn input through the splitter 15 is
The signal is received by the receiver 13n. The output light of the light source 11n is applied to the optical modulator 12
The signal is put on n, and the splitter 14, the optical fiber 30, and the splitter 32
Through the subscriber terminal 20a. In the subscriber terminal 20a, the transmitted signal is received by the receiver 21a.
In the case of terminating the communication, if the switching station 10 or the subscriber terminal 20a sends a signal indicating the end of the communication at the wavelength λn, the other party receives the signal and the communication is terminated.

On the other hand, when performing a call setup from the exchange 10 to, for example, the subscriber terminal 20a, the exchange 10 uses the optical modulator 12a to
The call request signal is placed on the wavelength λa,
And to the subscriber terminal 20 via the branching device 32. In the subscriber terminal 20a, the information of the wavelength λa is read by the receiver 21a, and thereafter communication is performed in the same procedure as described above.

In the first embodiment, since bidirectional optical communication is performed using different wavelengths for each call setting, it is not necessary to match the number of subscriber terminals with the number of wavelengths λa to λn. Bidirectional optical communication with many subscriber terminals 20a to 20m can be performed, and wavelength use efficiency is improved. Furthermore, in this two-way optical communication system, since the coherent optical communication technology is used, high-precision optical circuits are required for the system, but wavelength use efficiency is remarkably improved and low loss is achieved. And high-precision broadband communication becomes possible.

FIG. 2 is a schematic configuration diagram of a bidirectional optical communication system showing a second embodiment of the present invention, and the same reference numerals are given to the elements common to the elements in FIG.

This bidirectional optical communication system is configured using a demultiplexing element, and includes one switching center 40 and a plurality of subscriber terminals 50a to 50a.
0m, the transmission side of the exchange 40 is connected to the subscriber terminals 50a to 50m via the downstream optical fiber 30 and the branch unit 32, and the reception side is the upstream optical fiber 31 and the branch unit.
33 are connected to the subscriber terminals 50a to 50m.

The exchange 40 includes a plurality of transmitters 41a to 41n locked to different specific wavelengths λa to λn, respectively.
To 41n, a branching device 42 composed of a star coupler or the like for connecting the downstream optical fiber 30 to a different specific wavelength λa
A plurality of receivers 43a to 43l each receiving an optical signal of λl
And a wavelength demultiplexing element 44 for connecting the upstream optical fiber 31 to the receivers 43a to 43l. Transmitter 41
a to 41n are each configured by an optical signal source including a light source and an optical modulator, for example. The wavelength demultiplexing element 44 separates signals of different wavelengths λa to λl, and together with the receivers 43a to 431 connected thereto, a specific wavelength receiving means for receiving optical signals of different specific wavelengths λa to λl. Make up.

Unlike the subscriber terminals 50a to 50m shown in FIG. 1, the subscriber terminals 50a to 50m do not have a light source and transmit using light from the exchange 40. That is, each of the subscriber terminals 50a to 50m is
Branching devices 51a to 51m connected to the
1m, the receiver 53a via the tunable filters 52a to 52m
~ 53m are connected and the wavelength tunable filters 54a ~ 54m
The optical modulators 55a to 55m are connected via the. The tunable filters 52a to 52m and 54a to 54m have a function of freely selecting a wavelength, and one of the tunable filters 52a to 52m and the receiver
53a to 53m constitute wavelength variable receiving means for freely selecting and receiving wavelengths. The other tunable filters 54a to 54m, together with the optical modulators 55a to 55m, constitute tunable transmission means capable of freely selecting a wavelength and carrying a signal.

 Next, the operation will be described.

For example, when setting up a call from the subscriber terminal 50a to the exchange 40, wavelengths, for example, λa and λb, are used for the call setting. In the subscriber terminal 50a, the light having the wavelength λa from the transmitter 41a on the exchange 40 side is split into the splitter 42, the optical fiber 30, and the splitters 32 and 51.
a, and is received by the receiver 53a via the tunable filter 52a. Then, at the receiver 53a, after confirming that the light of the wavelength λa is not used, the light of the wavelength λa from the transmitter 41a is selected by the wavelength tunable filter 54a, and the signal of the communication request is placed by the optical modulator 55a, The signal is sent to the exchange 40 via the branching device 33 and the optical fiber 31.

In the exchange 40, the signal of the wavelength λa is separated by the wavelength demultiplexing element 44 and then received by the receiver 43a of the wavelength λa. In the transmitter 41a of the wavelength λa, the wavelength used for communication,
For example, the information of λn, λn-1 is placed on the wavelength λb,
2. Send the signal to the subscriber terminal 50a via the optical fiber 30 and the branching device 32.

In the subscriber terminal 50a, the wavelength λb
Is selected and received by the receiver 53a. After the reception, the optical modulator 55a sends a confirmation signal to the exchange 40 using the light of the wavelength λa, and then the wavelength tunable filters 52a and 54a.
To the wavelengths λn and λn-1, respectively,
Communicate with 40. The end of communication is performed by notifying the other party using light of wavelengths λn and λn-1. The wavelength tunable filter 52a and the receiver 53a always receive the light of the wavelength λb to avoid interference, and monitor whether the wavelength λa is used and whether there is a transmission request from the exchange 40. ing.

On the other hand, the call setting from the exchange 40 to, for example, the subscriber terminal 50a is performed using light of the wavelength λb. The optical exchange 55a on the side of the subscriber terminal 50a uses the light of the wavelength λa to
After sending the confirmation signal to the side, communication is performed in the same manner as described above.

In the second embodiment, since the coherent technique is not used unlike the first embodiment, the number of wavelengths is required to be about twice as large as that of the first embodiment, and the use efficiency of the wavelength is reduced. However, since the coherent technique is not used, it is not necessary to configure a high-sensitivity optical circuit, and the configuration of each optical circuit is simplified. In addition, since the subscriber terminals 50a to 50m use light from the exchange 40 without providing a light source, the circuit configuration is simpler than that of FIG.

In the first and second embodiments, since the plurality of subscriber terminals 20a to 20m and 50a to 50m are connected using the branching devices 32 and 33, secret information is leaked from the branching devices 32 and 33. There is a possibility that. To secure such confidentiality, different signals are encrypted for each of the subscriber terminals 20a to 20m and 50a to 50m. That is, when information is sent from the exchange 40 to, for example, the subscriber terminal 50a, the encrypted information is subscribed from the exchange 40 using the encryption of information determined in advance with the subscriber terminal 50a. If it is sent to the user terminal 50a, secrecy can be ensured.

FIG. 3 is a schematic configuration diagram of a subscriber terminal according to a third embodiment of the present invention.

This subscriber terminal 20a-1 is a modified example of the subscriber terminal 20a of FIG. 1, and performs almost the same operation as the subscriber terminal 20a of FIG. 1 without using the coherent technology. Things.

That is, the subscriber terminal 20a-1 includes an optical modulator 23a, a laser diode 24a, a wavelength tunable filter 25a, and an external reflecting mirror 26a.
a and a light receiver 27a. Here, the wavelength variable filter 25a and the light receiver 27a constitute a wavelength variable receiving means for freely selecting and receiving a wavelength. further,
The laser diode 24a, the wavelength tunable filter 25a, and the external reflection mirror 26a constitute an external resonator laser capable of widening the variable wavelength range, and the external resonator laser and the optical modulator 23a freely select a wavelength to transmit a signal. The wavelength tunable transmission means that can be mounted is constituted.

In the subscriber terminal 20a-1, the light from the splitter 32 is received by the light receiver 27a via the wavelength tunable filter 25a. The wavelength of the signal received by the light receiver 27a is adjusted by the wavelength tunable filter 25a. It is supposed to. Moreover, using the wavelength tunable filter 25a, the laser diode 24a, the wavelength tunable filter 25a, and the external reflected light 26 have the same wavelength.
a) emits an external cavity laser composed of
At 3a, a signal is put and sent to the branching device 33 side. This allows
With a relatively simple circuit configuration, almost the same coherent optical communication as in the first embodiment can be performed.

It should be noted that the present invention is not limited to the illustrated embodiment.
The circuit configurations of 0, 40 and the subscriber terminals 20a to 20m, 20a-1, 50a to 50m can be modified to configurations other than those illustrated. For example, in the subscriber terminals 50a to 50m of FIG.
By omitting to 51 m and providing a new light source, it is possible to use only one wavelength such as λa for call setting.

Further, in the above embodiment, two optical fibers 30 and 31 are used. However, if an isolator or the like is used, it is possible to perform uplink and downlink communication with one optical fiber. In this case, the splitters 14 and 15 and 32 and 33 have the same configuration.

(Effects of the Invention) As described in detail above, according to the first, second, third and fourth inventions, both the exchange and the subscriber terminal use different wavelengths for each call setup. Since the optical communication is performed, it is not necessary to match the number of subscriber terminals with the number of wavelengths. Therefore, more subscriber terminals can be connected with a smaller number of wavelengths, and the use efficiency of wavelengths can be remarkably improved. As a result, high-precision and broadband optical wavelength multiplex communication can be performed.

In particular, the subscriber terminal tunes and transmits an optical signal to a specific wavelength not used by the wavelength tunable transmitting means. Communication can be performed. Therefore, even if the given wavelength interval is narrow, high-density wavelength multiplexing can be realized, and bidirectional optical communication with more terminals can be performed.

[Brief description of the drawings]

1 and 2 are schematic structural diagrams of a bidirectional optical communication system showing first and second embodiments of the present invention, and FIG. 3 is a diagram showing a subscriber terminal showing a third embodiment of the present invention. It is a schematic block diagram. 10,40 ... Exchange, 11a-11n ... Light source, 12a-12n, 23a-2
3m, 55a ~ 55m ... optical modulator, 13a ~ 13n, 21a ~ 21m, 43a ~ 43
l, 53a-53m ... receiver, 14,15,32,33,51a-51m ... dropout device, 20a-20m, 20a-1,50a-50m ... subscriber terminal, 22a-2
2m …… Tunable light source, 24a …… Laser diode, 25a, 5
2a to 52m, 54a to 54m: tunable filter, 26a: external reflecting mirror, 27a: photoreceiver, 30, 31: optical fiber, 41a to 4
1n: transmitter, 44: wavelength demultiplexing element.

Claims (4)

(57) [Claims] An exchange having an optical signal source for transmitting an optical signal of an arbitrary specific wavelength and a receiving means for receiving an optical signal of an specific wavelength, a wavelength receiving means for selecting and receiving an arbitrary wavelength, and an optional A subscriber terminal having wavelength tunable transmitting means for selecting and transmitting a wavelength of the optical signal, wherein the switching center is used by the optical signal source when performing call setup. A specific wavelength that has not been transmitted is transmitted by transmitting an optical signal to the subscriber terminal.The subscriber terminal receives the unused specific wavelength transmitted from the exchange by the wavelength receiving means, A bidirectional optical communication system, wherein a wavelength-variable transmitting unit tunes an optical signal to the unused wavelength and transmits the signal. 2. When the call setup is performed from the subscriber terminal, the subscriber terminal tunes and transmits an optical signal to an arbitrary specific wavelength, and the switching center transmits the optical signal from the subscriber terminal. 2. The two-way optical communication system according to claim 1, wherein after the tuned optical signal is received by the receiving means, an unused wavelength is transmitted by transmitting an optical signal to the subscriber terminal. 3. The bidirectional optical communication system according to claim 1, wherein the wavelength tunable transmission means tunes the optical signal to the unused wavelength using a wavelength tunable filter. 4. The bidirectional optical communication system according to claim 3, wherein said tunable filter is used in common with said wavelength receiving means.