JPS63304731A - Optical communication method - Google Patents

Abstract

PURPOSE:To eliminate the need for addressing a transmission signal by using an optical multiplexer/demultiplexer as an optical branching/inserting device and assigning at least one optical frequency specific to each node. CONSTITUTION:Optical inserting devices 41-4n are optical multiplexers/ demultiplexers whose transmission frequency is fixed and optical inserting devices 51-5n are optical multiplexers/demultiplexers whose transmission frequency is variable. One frequency each (fi, fj, fk) is assigned to nodes 61-6n and the transmission frequency of the optical multiplexer/demultiplexer used as a branching device belonging to the node is fixed to its value. For example, in accessing the node 61 from the node 62, the transmission frequency of the optical multiplexer/demultiplexer 52 of the node 62 is tuned to the frequency fi at first, the light source frequency of the node 61 is set as the frequency fj and the optical multiplexer/demultiplexer 41 of the node 61 is set in advance to transmit only the frequency fi. Thus, the signal having the frequency fi sent from the node 62 is received selectively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical communication system in which a plurality of nodes communicate between nodes using a common optical fiber transmission path, and in particular, The present invention relates to an optical bus type communication system that can conventionally connect a large number of uplink nodes to the same transmission path.

[Conventional technology]

A bus-type communication system using optical fibers is useful as a method for realizing a wideband user/network interface that allows users to access wideband signals such as moving images and high-speed data.

FIG. 1 is a diagram showing an example of the configuration of a conventional optical bus type communication network, in which 1 is an optical fiber transmission line, 2 is an optical directional coupler,
3 represents a node.

As shown in the figure, in such a conventional configuration,
Since the optical directional coupler 2 is used as an optical drop/adder, the optical drop/adder has an identification 8 for the destination of the signal.
! Therefore, by adding the 7 address of the destination to the beginning of the time-divided transmission signal, the receiving side could distinguish whether the signal was needed or not.

[Problem that the invention seeks to solve]

In the conventional optical bus type communication network as described above, there is a control problem of having to add the destination address to the beginning of the transmitted signal, and furthermore, there is a need to add a destination address to the beginning of the transmitted signal. There were some drawbacks.

Therefore, the number of meters that can be connected to this bus-type communication network is limited, and the optical bus-type communication method that has been put into practical use
The number of nodes was about 10 at most.

In view of the shortcomings of the conventional systems, the present invention provides an optical bus type communication system that is not limited in the number of nodes due to losses in optical drop/droppers or does not require addresses to be attached to transmission signals. The purpose is to

[Means for solving problems]

According to the invention, the above-mentioned object is achieved by the means specified in the claims.

That is, the present invention optically frequency multiplexes each signal and uses an optical multiplexer/demultiplexer as an optical drop/adder at each node, and the optical drop/dropper is lossless in principle.
This method differs from the conventional technology in terms of α, such as the fact that there is no need to add a destination address to the transmitted signal.

〔Example〕

FIG. 12 is a diagram showing the configuration of an optical bus type communication network according to an embodiment of the present invention, in which 1 represents an optical fiber transmission line as in the case of FIG. 1, and 41 to 4n represent optical fiber transmission lines. Optical multiplexer/demultiplexers used as splitters, 5□ to 5n represent optical multiplexer/demultiplexers used as optical adders, and 6, to 60 represent nodes.

In the figure, optical splitters 4□-4n are optical multiplexers/demultiplexers with fixed transmission frequencies, and optical adders 51-5n are optical multiplexers/demultiplexers with variable transmission frequencies.

In this embodiment, each node has one frequency (“il B
l fk ), and the transmission frequency of the optical multiplexer/demultiplexer used as a splitter belonging to that mate is fixed to that value. Access between the mats is possible by tuning the transmitting side light source frequency and the transmission frequency of the optical multiplexer/demultiplexer used as the inserter.

For example, in order to access node 61 from node 62, first, the transmission frequency of optical multiplexer/demultiplexer 52 of node 62 is tuned to fi, and the light source frequency of /-doro 1 is set to fj and transmitted. The optical multiplexer/demultiplexer 41 of the node 61 is set in advance to transmit only fi, and the frequency f transmitted from the node 62
i signals can be selectively received.

When a semiconductor laser is used as a light source, tuning of the light source frequency is possible by changing the temperature and bias current.6 Figure 3 shows the double ring resonance of an optical waveguide used as an optical multiplexer/demultiplexer for an optical branch/adder. It is a diagram showing an example of the configuration of a vessel-shaped channel splitter, in which 7 is an optical waveguide, 81 and 8□ are ring-shaped optical waveguides, 9 is a thermal electrode, 10 is a lead wire, and 11 is an optical directional coupler. It represents.

In this double ring type channel splitter, the diameters of the ring waveguides are different from each other, and the resonant frequency interval is the least common multiple of the resonant frequency intervals of each ring.

In addition, the period of the resonant frequency can be changed by changing the propagation constant (equivalent refractive index) of the waveguide, and in reality, as shown in Figure 3, thermal modulation or modulation due to electro-optic effect is applied to the waveguide. This can be achieved by setting electrodes for this purpose.

FIG. 4 schematically shows the frequency dependence of the transmission loss of the double ring resonator type channel demultiplexer shown in FIG.

The transmission loss repeatedly becomes zero at constant frequency intervals ΔF.

Therefore, the maximum frequency band available for frequency multiplexing is ΔF.

Further, if the width of the low transmission loss region is Δf, the number N of channels that can be frequency multiplexed is N=ΔF/Δf.

FIG. 5 shows an example of calculating the frequency dependence of the transmission loss of a double ring resonator channel duplexer designed with ΔF=40 GHz.

In this calculation example, a silica-based optical waveguide with a refractive index of 1.46 is assumed, and the radius of the ring waveguide is 5736.8 μm and 6556.3 μm, respectively, and the power coupling between each ring waveguide and input/output optical waveguide is The coefficient 1 is 0.12, and the power coupling coefficient between the ring waveguides 2 is 0.006.

In this calculation example, the worst value of crosstalk is -14 dB, and it is considered that almost no deterioration due to crosstalk occurs.

Also, the 3dB transmission bandwidth Δf is 190MHz,
The number of channels that can be frequency multiplexed is 210.

This indicates that the number of nodes is 20 times or more compared to the conventional optical bus system.

In addition, there is essentially no increase in loss due to the optical drop/adder, and it does not become a limiting factor for the number of /- codes.

On the other hand, a tunable optical multiplexer/demultiplexer can use a movable diffraction grating as a wavelength separation quadruplet, or can be configured with a double ring resonator. However, in optical multiplexers/demultiplexers using diffraction gratings, the number of channels is limited by the coupling loss between the optical fiber and the diffraction grating, and the ones realized to date have a maximum of 2 channels.
There are approximately 0 channels.

In addition, in order to fabricate a double ring resonator with the same ΔF as the double ring resonator described above, the radius of the ring must be approximately halved, and radiation loss due to bending of the waveguide will be reduced. There is a possibility that it will increase significantly. Therefore, it is difficult to increase the number of channels even in the case of a double ring resonator.

Therefore, it is desirable that the optical multiplexer/demultiplexer for a drop/adder according to the present invention uses an optical waveguide double ring resonator as shown in FIG.

〔Effect of the invention〕

As explained above, in this method, since the address of the node corresponds to the optical frequency, there is no need to add the 7 addresses of the destination to the i signal. By using the optical fiber as an optical fiber, it is possible in principle to selectively transmit a large number of optical frequencies arranged at narrow wave number intervals without loss, and there are advantages such as being able to connect a large number of nodes.

[Brief explanation of the drawing]

Figure m1 is a diagram showing an example of the configuration of a conventional optical bus type communication network, Figure 2 is a diagram showing the configuration of an optical bus type communication network according to an embodiment of the present invention, and Figure 3 is a double ring resonant type communication network. A diagram showing an example of the configuration of a channel duplexer, Figure 4 is a schematic diagram of the transmission characteristics of a double ring resonant spoken channel duplexer, and Figure 15 is a schematic diagram of the transmission characteristics of a double ring resonant spoken channel duplexer. It is a figure showing a calculation result. 1...Optical 7 fiber transmission line, 2.11.
...Optical directional coupler, 3.61~6n ・
・・・・・・ Node, 41~4n・・・・・・
Optical splitter, 5, ~5 ++... Optical adder,
7... Optical waveguide, 8... Ring-shaped optical waveguide, 9... Thermal electrode,
10 ・・・・・・Lead line agent Patent attorney
Takashi Honma Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) A plurality of nodes equipped with an optical fiber transmission line, an optical branch/adder for taking in an optical signal on the optical fiber transmission line or sending out an optical signal, and a plurality of light sources whose oscillation optical frequency is variable. In a bus-type communication network that communicates between nodes, an optical multiplexer/demultiplexer is used as an optical branch/adder, and at least one unique optical frequency is assigned to each node. Optical communication method. (2) Claim No. 1 which uses a double ring resonator type channel demultiplexer as an optical multiplexer/demultiplexer for an optical branch/adder.
Optical communication method described in ).