JP2954238B2 - Two-way optical communication system - Google Patents

Description

The present invention relates to a 1: n bidirectional optical communication system.

In particular, the present invention relates to a two-way optical communication system that ensures the secrecy of two-way optical communication.

[Conventional technology]

FIG. 8 is a block diagram showing a configuration example of a conventional 1: n bidirectional optical communication system.

In the figure, an optical fiber 91 is connected between a transmitting / receiving end of one station device 80 and a transmitting / receiving end of a plurality of n terminal devices 85 _{1 to} 85 _n.
An optical communication network composed of optical couplers ₀ to _n and an optical star coupler 93 is set. Bidirectional optical communication is performed by wavelength division multiplexing of optical signals of wavelength λ _{1 on} the downstream line and wavelength λ _{2 on} the upstream line from the station device 80. Done.

Station apparatus 80, the processing circuit 81 which performs the process of transmitting and receiving signals, the light source 82 transmits the wavelength lambda ₁ of the optical signal intensity-modulated in accordance with the transmission signal information inputted from the processing circuit 81, the optical signal of the wavelength lambda ₂ detection circuit 83 which receives and outputs the received signal information to processing circuit 81, and the wavelength multiplexing circuit 84 performs wavelength demultiplexing of the optical signals of wavelengths lambda ₁ and lambda _2.

Each of the terminal devices 85 _{1 to} 85 _n transmits processing signals 86 1 to _n for performing signal transmission / reception processing, and transmits an optical signal of a wavelength λ ₂ whose intensity is modulated according to transmission signal information input from the processing circuits 86 1 _to 86 _n. light sources 87 _{1 to n,} the detection circuit 88 _{1 to n} for outputting the received signal information by receiving the optical signal of the wavelength lambda ₁ to the processing circuit 86 _{1 to n,}
Constituted by the wavelength multiplexing circuit 89 _{1 to n} which performs wavelength demultiplexing of the optical signals of wavelengths lambda ₁ and lambda _2.

The optical star coupler 93 has a function of branching the optical signal of the wavelength λ ₁ from the station device 80 into a plurality n for the downlink and a wavelength λ from each of the terminal devices 85 _{1 to} 85 _n for the uplink. It has a function of combining _two optical signals into one.

The identification of the terminal devices corresponding optical signals, in the station device 80 and each of the terminal devices 85 ₁ to 85 _n, the identification code added to the position, or the signal on the time axis assigned to each terminal device Detect and go.

[Problems to be solved by the invention]

By the way, such a conventional optical star coupler 93 transmits the wavelength λ ₂ from each of the terminal devices 85 _{1 to} 85 _n to the uplink.
Although the optical signal is combined into one, the mutual coupling can be reduced (for example, 40 dB) on the incident side depending on the directionality, so that one terminal device transmits the optical signal transmitted by the other terminal device. Interception is difficult and confidentiality is maintained.

However, the downstream optical signal (wavelength λ ₁ ) from the station device 80 is transmitted via the optical star coupler 93 to each of the terminal devices 85 ₁ to 85 _1.
Received by all of the 5 _n . That is, each of the terminal devices 85 ₁ to 8
5 Since each terminal device extracts a signal addressed to its own device from signals addressed to all terminal devices received by _n ,
It was virtually difficult to ensure the secrecy of communications.

An object of the present invention is to provide a two-way optical communication system capable of easily realizing two-way optical communication with excellent secrecy.

[Means for solving the problem]

FIG. 1 is a block diagram showing the principle configuration of the system of the present invention.

The present invention relates to a bidirectional optical communication system for performing bidirectional optical communication between opposing 1: n (n is an integer of 2 or more) transmission / reception devices via an optical communication network including a 1: n optical star coupler. In one transmission / reception apparatus, a wavelength tunable light source capable of generating optical signals of a plurality of n wavelengths, and a wavelength for performing wavelength control corresponding to each of the plurality of n transmission / reception apparatuses opposed to the wavelength tunable light source And a control means, wherein the 1: n optical star coupler selectively splits an optical signal of a plurality of n wavelengths of a downlink transmitted from one transmission / reception apparatus for each wavelength and a plurality of n
, Respectively, and combines optical signals of predetermined wavelengths of the uplink transmitted from the plurality of n transceivers into one and sends them to one transceiver.

(Operation)

Optical signals having different wavelengths are transmitted from one transmission / reception device (station device) to the downlink through time-division control for each of a plurality of n transmission / reception devices (terminal devices) as transmission destinations. on the other hand,
The 1: n optical star coupler has a function of selectively branching a downstream optical signal for each wavelength, and an optical signal of a corresponding wavelength is distributed to each of a plurality of n transmitting / receiving apparatuses. Therefore, each of the plurality of n transmitting / receiving apparatuses receives only the optical signal addressed to the own apparatus, and cannot intercept the optical signals addressed to other apparatuses.

In addition, an optical signal of a predetermined wavelength is transmitted to the uplink line from the plurality of n transmitting / receiving apparatuses to one transmitting / receiving apparatus under time division control between the transmitting / receiving apparatuses. On the other hand, a 1: n optical star coupler combines each optical signal of the uplink into one,
It is easy to reduce mutual coupling depending on the direction, and it is impossible to intercept an optical signal transmitted from another transmitting / receiving apparatus to the uplink.

In this way, in the downlink, the wavelength is set for each transmitting / receiving device, and the 1: n optical star coupler is provided with wavelength selectivity, thereby facilitating the secrecy in the 1: n bidirectional optical communication system. Can be secured.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of a 1: n bidirectional optical communication system according to the present invention.

In the figure, between the terminal apparatus 30 ₁ to 30 _n receive end of the transmission and reception end and a plurality n of one station unit 20, configured fibers 40
_An optical communication network composed of ₀ to 40 _n and a wavelength-selective optical star coupler 50 is set, and the downlink from the station device 20 has a wavelength λ.
_{11, λ 12, ..., λ} 1n, uplink is configured to bi-directional optical communication is performed by wavelength multiplexing of the optical signals of the wavelength lambda _2.

Station apparatus 20, processing circuit 21 that performs transmission and reception processing of the signal, processing circuit 21 variable wavelength light source 22 for transmitting an optical signal intensity-modulated in accordance with the transmission signal information inputted at a predetermined wavelength lambda ₁₁ to [lambda] _1n from receives the transmission destination information from the processing circuit 21, the corresponding wavelength control circuit 23 for controlling time division wavelength setting, the received signal information by receiving the optical signal of the wavelength lambda ₂ to the processing circuit 21 to the wavelength-variable light source 22 Output detection circuit 24, wavelengths λ _{11 to} λ _1n
And constituted by a wavelength multiplexing circuit 25 which performs wavelength demultiplexing of the optical signals of wavelength lambda _2.

Each terminal device 30 ₁ to 30 _n includes a light source 32 for transmitting an optical signal having a wavelength lambda ₂ in response to the transmission signal information inputted from the processing circuit 31 _{1 to n,} the processing circuit 31 _{1 to n} for transmitting and receiving processing of the signal
_{1 to n} , wavelengths λ ₁₁ to λ assigned to each terminal device
Detection circuit 33 _{1 to n} which receives a single optical signal having a wavelength of _1n outputs the received signal information to processing circuit 31 _{1 to n,} the wavelength lambda ₁₁ ~
constituted by the wavelength multiplexing circuit 34 _{1 to n} which performs wavelength demultiplexing of the corresponding wavelength and the optical signal of the wavelength lambda ₂ of lambda _1n.

Wavelength selective optical star coupler 50 has the function of selecting branches the optical signal of the wavelength lambda ₁₁ to [lambda] _1n from station device 20 to the optical fiber 40 ₁ to 40 _n corresponding to each terminal apparatus is applied to downlink, for uplink has the potential to be combined into one optical signal having a wavelength lambda ₂ from each of the terminal devices 30 ₁ to 30 _n.

FIG. 3 is a diagram showing an example of wavelength allocation of optical signals transmitted bidirectionally in the configuration of the embodiment.

In the figure, the wavelength λ ₂ of the optical signal in the uplink is, for example,
It is arranged in the 1.3 μm band (1300 nm). Incidentally, in this case, the wavelength of the light source 32 _{1 to n} of each of the terminal devices 30 ₁ to 30 _n may be set exactly to the same wavelength, or within a predetermined range 1.3μm band (e.g. 1300nm~1320nm ) May be different. The predetermined range is set according to the characteristics of the wavelength-selective optical star coupler 50 and the detection circuit 24 of the station device 20.

The wavelengths λ _{11 to} λ _1n of the optical signal on the downlink are, for example,
It is arranged in the 1.5 μm band (1500 nm). Note that this wavelength λ
_{11 to} λ _1n are within the wavelength tunable range of the wavelength tunable light source 22,
Usually, | λ _{11 to} λ _1n | ≒ several nm. Therefore, each wavelength λ ₁₁ , λ ₁₂ ,.
For example, they are 1500 nm, 1501 nm, respectively. The wavelength tunable light source 22 includes, for example, a known distributed feedback type (DFB) semiconductor laser or a distributed Bragg reflection type (DBR).
A semiconductor laser is used. Such a semiconductor laser has an injection current (processing circuit) applied to its intensity control electrode.
21), and the wavelength of the output light is controlled according to the injection current applied to the wavelength control electrode (wavelength control information from the wavelength control circuit 23). Configuration.

The station device 20 transmits an optical signal having a different wavelength for each destination terminal device in a time-division manner based on the wavelength allocation example shown in FIG.

Figure 4 is a time chart of the optical signal transmitted in the downlink optical fiber 40 ₀ to 40 _n.

FIG. 4 (a) shows an optical fiber output from the station device 20 and an optical fiber.
Shows an optical signal incident on the wavelength selective optical star coupler 50 through 40 _0, sequentially transmitted as a burst signal having a wavelength lambda ₁₁ to [lambda] _1n to each terminal device corresponding. Each burst signal is a pulse signal intensity-modulated at a corresponding wavelength according to a predetermined modulation code.

Figure 4 (b) shows the optical signals emitted from the wavelength-selective optical star coupler 50, is selected for each wavelength is branched into the optical fiber 40 ₁ to 40 _n of the terminal devices corresponding. Therefore,
In each terminal device 30 ₁ to 30 _n , the corresponding optical fiber 40 ₁ to 40 _n
, Only the burst signal addressed to the terminal itself is received, and the burst signal addressed to other terminal devices cannot be received, and secrecy can be ensured.

Figure 5 is a time chart of the optical signal transmitted in the uplink line of the optical fiber 40 _0.

The wavelength-selective optical star coupler 50 has an upstream wavelength λ ₂
Does not have wavelength selectivity. Accordingly, the optical signal of wavelength lambda ₂ from each of the terminal devices 30 ₁ to 30 _n is transmitted in a time division manner in response to a predetermined communication rules are coupled by the wavelength selective optical star coupler 50, via the optical fiber 40 ₀ Station device 20
Is transmitted to The station device 20 performs a receiving process by detecting a code for identifying the transmitting terminal device from each burst signal.

The optical signal transmitted to the station apparatus 20 from each of the terminal devices 30 ₁ to 30 _n is the direction of the wavelength selective optical star coupler 50, it is possible to reduce (e.g., 40 dB) the mutual coupling with the incident side However, it is difficult for one terminal device to intercept the optical signal transmitted by the other terminal device, and secrecy is ensured.

In the uplink shown in FIG. 5, the guard time G is set so that the burst signals do not overlap.
Similarly, a guard time may be set in the downlink. This downlink guard time is effective when the signal speed is particularly fast and the transition time required for wavelength switching of the wavelength tunable light source 22 cannot be ignored.

FIG. 6 is a flowchart for explaining the operation of the wavelength control circuit 23 of the station device 20. The wavelength control circuit 23 includes a microprocessor that processes transmission destination information from the processing circuit 21 and a DC current generation circuit that generates a corresponding control current. FIG. 6A shows the case of the synchronous transfer mode, and FIG. 6B shows the case of the asynchronous transfer mode.

In FIG. 6A, a control signal for starting transmission is input from the processing circuit 21, and "1" is set in the counter.
The injection current I = I (N) is set according to the value N of the counter, and is applied to the wavelength control electrode of the variable wavelength light source 22. Note that the injection current I (N) according to the counter value N has a predetermined relationship between a predetermined time position and a destination terminal device, and is set with reference to the relationship (STM mode).

When the application time of the injection current I = I (N) exceeds a predetermined time, the counter is incremented, and the injection current is sequentially updated until the counter value N exceeds the number n of the terminal devices, and the optical signal of the corresponding wavelength is updated. Are transmitted in a time-division manner. When the value N of the counter exceeds the number n of the terminal devices, the counter is reset and the same processing is repeated.

In FIG. 6B, the destination terminal device is determined from the transmission destination information (coded label) input from the processing circuit 21. Subsequently, the injection current I is set according to the wavelength corresponding to the destination terminal device, and is applied to the wavelength control electrode of the variable wavelength light source 22.

FIG. 7 is a diagram showing a configuration of an embodiment of a wavelength-selective optical star coupler used in the method of the present invention. Here, the configuration of a basic unit that performs one-to-two branching is shown.

In the figure, the basic unit is an optical waveguide connected to the input / output port 71.
Interference filter 75 connected via 73 and input / output port
77, 79 are connected via optical waveguides 81, 83 to a Mach-Zehnder interferometer 85, an interference filter 75 and a Mach-Zehnder interferometer 85.
And two optical waveguides 87 and 89 connecting the input and output units.

The Mach-Zehnder interferometer 85 includes a directional coupler 91 connected to input / output ports 77 and 79 via optical waveguides 81 and 83, and a directional coupler 91 connected to an interference filter 75 via optical waveguides 87 and 89. The directional coupler 93 includes two optical waveguides 95 and 97 connecting the directional couplers 91 and 93. In the Mach-Zehnder interferometer 85, predetermined wavelength selectivity is realized by appropriately setting the optical path length difference between the two optical waveguides 95 and 97 connecting the directional couplers 91 and 93.

Further, interference filter 75 is totally reflected light signal with a wavelength lambda ₁₁ and lambda _12, a configuration having a 50% transmission characteristic with respect to wavelength lambda ₂ of the optical signal.

Here, λ ₁₁ (for example, 1500 nm) and λ ₁₂ (for example, 15 nm)
01 nm) is input from the input / output port 71, and the wavelength λ
It is assumed that an optical signal of ₂ (for example, 1300 nm) is input from the input / output ports 77 and 79, respectively.

Optical signals of wavelengths λ ₁₁ and λ ₁₂ incident from the input / output port 71 are totally reflected by the interference filter 75 and are incident on the Mach-Zehnder interferometer 85 via the optical waveguide 87. In Mahatsuenda interferometer 85, to separate the optical signal of the wavelength lambda ₁₁ and lambda ₁₂ in accordance with a predetermined wavelength selectivity, output respectively ports 77, 79
Emitted from

Further, the optical signal of the wavelength λ ₂ input from the input / output port 77 is output to both or one of the optical waveguides 87 and 89 via the Mach-Zehnder interferometer 85. That is, Mahatsuenda interferometer 85, because it is set that wavelength selection characteristics with respect to optical signals of wavelengths lambda ₁₁ and lambda _12, the wavelength lambda ₂
The output destination differs depending on the numerical value. In any case, optical signals that have passed through both or one of the optical waveguides 87 and 89 are coupled by the interference filter 75 and output from the input / output port 71. Note that the optical signal of wavelength λ ₂ is ideally free from coupling loss in the interference filter 75,
Input / output port 71 with half the light intensity (3dB) of 77 incident light intensity
Is emitted from.

Similarly, the wavelength lambda ₂ of the optical signal incident from the input port 79, and is emitted from the output port 71.

The wavelength of the optical signal incident from the input and output ports 77 and 79 is not necessarily the same wavelength lambda _2, as long as the wavelength band corresponding to 50% of the transmission characteristic in the interference filter 75, different wavelengths , The same operation is possible.

Further, a one-to-four wavelength-selective optical star coupler is realized by configuring the basic unit described above in two stages. That is, in the basic unit of the first stage, the optical signals of wavelengths λ ₁₁ and λ ₁₂ and the wavelength λ
_13, lambda ₁₄ branches the optical signal, a configuration that branches the optical signal of each wavelength, respectively the next stage of the basic unit, the wavelength lambda ₂ of the optical signal sequentially one input at a basic unit of each stage This is a configuration that is coupled to the output port.

In general, the same applies to a 1: n wavelength-selective optical star coupler.

〔The invention's effect〕

As described above, the present invention has excellent confidentiality by assigning a unique wavelength to each of transmission signals on the downlink for a plurality of n transmission / reception devices and branching the optical star coupler while waiting for wavelength selectivity. A 1: n bidirectional optical communication system can be constructed economically and easily.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle configuration of the present invention. FIG. 2 is a block diagram showing an embodiment of a 1: n bidirectional optical communication system according to the present invention. FIG. 3 is a diagram showing an example of wavelength arrangement of optical signals transmitted bidirectionally in the configuration of the embodiment. FIG. 4 is a time chart of an optical signal transmitted on the downlink. FIG. 5 is a time chart of an optical signal transmitted on the uplink. FIG. 6 is a flowchart for explaining the operation of the wavelength control circuit of the station device. FIG. 7 is a diagram showing a configuration of an embodiment of a wavelength-selective optical star coupler used in the system of the present invention. FIG. 8 is a block diagram showing a configuration example of a conventional 1: n bidirectional optical communication system. 20 station device, 21 processing circuit, 22 tunable light source,
23 wavelength control circuit, 24 detection circuit, 25 wavelength multiplexing circuit, 30 terminal equipment, 31 processing circuit, 32 light source, 33 detection circuit, 34 wavelength multiplexing Circuit, 40 optical fiber, 50 wavelength selective optical star coupler, 71, 77,
79 ... I / O ports, 73, 81, 83, 87, 89, 95, 97 ...
Optical waveguide, 75 ... Interference filter, 85 ... Mach-Zehnder interferometer, 91, 93 ... Directional coupler.

Claims (1)

(57) [Claims] 1. Bidirectional optical communication for performing bidirectional optical communication between opposing 1: n (n is an integer of 2 or more) transmitting / receiving apparatuses via an optical communication network including 1: n optical star couplers. In the method, one transmitting / receiving apparatus performs wavelength control corresponding to each of a plurality of n transmitting / receiving apparatuses capable of generating optical signals of a plurality of n wavelengths and a plurality of n transmitting / receiving apparatuses opposed to the variable wavelength light source. A 1: n optical star coupler, wherein the one-to-n optical star coupler selectively branches an optical signal having a plurality of n wavelengths of a downlink transmitted from one transceiver for each wavelength, and a plurality of n each of the transceivers. Bidirectional optical communication, wherein optical signals of predetermined wavelengths of the uplink transmitted from the plurality of n transmitting / receiving apparatuses are combined into one and transmitted to one transmitting / receiving apparatus. method.