JPH088534B2 - Optical communication system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a multi-drop type optical communication system, and particularly to an optical communication system whose scale is expanded.

“Prior Art” Conventionally, in a multi-drop type optical communication system, a master station and each slave station communicate with each other by optical signals of the same wavelength. Further, as an optical coupler for connecting each slave station and a transmission line (optical fiber), the one having the same branching ratio (for example, 10: 1) is used.

FIG. 5 is a schematic configuration diagram showing the above-described conventional optical communication system. As shown in FIG. 5, both ends of the transmission line 2 are drawn into the master station 1 and one end of the transmission line 2 is electrically / optically (E / E). O) converter 3 and the other end is an optical / electrical / (O / E) converter 4
It is connected to the. Each of the slave stations 5 ₁ , 5 ₂ ... 5 _n-1 , 5 _n is connected to the transmission line 2 through an optical coupler 6, 6, ..., and these slave stations 5 ₁ , 5 ₂ ... 5 _{n- An} E / O converter 3 and an O / E converter 4 are also provided at ₁ and 5 _n . The arrow in the figure indicates the direction in which the optical signal flows.

"Problems to be Solved by the Invention" In the above-described conventional optical communication system, in the direction in which an optical signal flows through a transmission path,
The optical loss existing between the master station 1 and the remote station located farthest from the master station 1, that is, in the direction of flow from the master station 1 to the slave station, the light loss between the master station 1 and the slave station 5 _n Loss In the direction of the flow from the slave station to the master station 1, the optical loss between the slave station 5 ₁ and the master station 1 is in any case, the master station 1 and each slave station 5 ₁ , 5 ₂ ...
The performance of the 5 _n-1 , 5 _n E / O conversion circuit 3 and the O / E conversion circuit 4 must be below the dynamic range of light. Therefore, the distance of the transmission path 2 and the number of slave stations are limited.

Here, looking at the breakdown of the optical loss described above, the master station 1
Between the mobile station and the slave station 5 _n , {(n−1) × (passage loss of the optical coupler 6) + (2n−1) × (connection loss of the optical coupler 6 and the transmission line 2) + branch of the optical coupler 6 Loss + loss of transmission line 2}. Quantitatively looking at these, the passage loss of the optical coupler 6 is 0.5 dB, the connection loss between the optical coupler 6 and the transmission line 2 is 0.2 dB, the branch loss of the optical coupler 6 is 10 dB, the transmission line 2
Loss is 0.5 dB / km (λ = 1.3 μm). in this case,
The increased slave station _{5 1, 5 2 ...... 5 n} -1, 5 n the number and distance of the transmission path 2, while the transmission loss and the loss of the transmission path 2 of the optical coupler 6 is increased, branching optical coupler 6 The loss is as large as 10 dB regardless of them.

As described above, in the conventional optical communication system, the optical loss between the master station 1 and the remote station at the farthest position in the direction in which the optical signal flows is reduced by the E / O conversion circuit 3 and the O / E conversion circuit. Since it needs to be less than the dynamic range of 4,
There has been a limit to the system scale, such as a longer transmission line 2 and an increase in the number of slave stations.

By the way, it is possible to expand the system scale by inserting a repeater in the middle of the transmission line and regenerating and amplifying the optical signal. In this case, however, there is no transmission line which is a major feature of the multi-drop type optical communication system. There is a problem that the power supply is lost.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an optical communication system capable of solving the above-mentioned problems and expanding the system scale.

"Means for Solving the Problem" The present invention comprises one master station and a plurality of slave stations connected to a transmission path in the order in which optical signals output from this master station are received in the nearest position. In the optical communication system, the Nth slave station that receives the optical signal output from the master station at the farthest position and outputs the optical signal having the same wavelength as the optical signal from the master station, and the master station A first slave station for receiving the optical signal of the closest optical signal and outputting an optical signal of the same wavelength as the optical signal output from each of the remaining slave stations except the Nth slave station; A first optical multiplexer / demultiplexer that connects the slave station to a transmission line and outputs most of the optical signals from the master station and most of the optical signals from the first slave station to the transmission line; The N-th slave station is connected to the transmission line to supply most of the optical signals from the master station to the N-th slave station, and the N-th slave station. A second optical multiplexer / demultiplexer that outputs most of the optical signals from all the slave stations except the station to the transmission path, all the slave stations except the first and Nth slave stations, and the transmission path And a broadband wavelength coupler having the same characteristics for each of the optical signals of the two different wavelengths.

[Operation] According to the above configuration, the optical signal from the master station is supplied to the transmission path, that is, another slave station without being greatly attenuated by the first optical multiplexer / demultiplexer. The optical signal from the first slave station is also output to the transmission line without being greatly attenuated by the first optical multiplexer / demultiplexer.

On the other hand, the optical signals from all the slave stations except the Nth slave station are supplied to the master station without being greatly attenuated by the second optical multiplexer / demultiplexer. The optical signal from the Nth slave station is also supplied to the master station without being greatly attenuated by the second optical multiplexer / demultiplexer.

Therefore, since the first and second optical multiplexer / demultiplexers having branching losses smaller than those of the conventional optical coupler are used, it is possible to increase the number of transmission lines and the number of slave stations.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a multi-drop type optical communication system which is an embodiment of the present invention.

This embodiment differs from the conventional optical communication system (FIG. 5) in the following points.

The wavelength of the optical signal output from each of the master station 1A and the slave station 5A _n is set to λ = 1.55 μm. Other slave stations 5A ₁ , 5
A ₂ ...... 5A _n-1 The wavelength of the optical signal output from each is λ = 1.3
It is set to μm.

The optical multiplexer / demultiplexer 7 is used to connect the slave station 5A ₁ and the transmission line 2, and the optical multiplexer / demultiplexer 8 is used to connect the slave station 5A _n and the transmission line 2. Hereinafter, details of each of the optical multiplexers / demultiplexers 7 and 8 will be described.

FIG. 2 is a diagram showing the optical multiplexer / demultiplexer 7. The optical multiplexer / demultiplexer 7 acts as an optical coupler with a wavelength separation of 10 dB (branch loss of 0.5 dB), and has a wavelength λ = 1.55 μ at the terminal a.
When the optical signal of m is supplied, 90% of it is output from the terminal b, and the remaining 10% is output from the terminal d. When an optical signal with wavelength λ = 1.3 μm is supplied to terminal c,
% Is output from the terminal b, and the remaining 10% is output from the terminal d. On the other hand, when an optical signal of wavelength λ = 1.3 μm is supplied to the terminal a, 90% of it is output from the terminal d, and the remaining 10
% Is output from the terminal b.

FIG. 3 is a diagram showing the optical multiplexer / demultiplexer 8. This optical multiplexer / demultiplexer 8 has a wavelength separation of 20 dB or more (branch loss of 0.05 dB or less).
When an optical signal having a wavelength λ = 1.55 μm is supplied to the terminal a, 99% thereof is output from the terminal d and the remaining 1% is output from the terminal b.
When an optical signal having a wavelength λ = 1.3 μm is supplied to the terminal c, 99% of it is output from the terminal d, and the remaining 1% is output from the terminal b. On the other hand, when an optical signal having a wavelength λ = 1.3 μm is supplied to the terminal a, 99% of it is output from the terminal b, and the remaining 1% is output from the terminal d. Also, terminal c
When an optical signal with wavelength λ = 1.55 μm is supplied to
Is output from the terminal b, and the remaining 1% is output from the terminal d.

The optical multiplexers / demultiplexers 7 and 8 described above are each connected to the transmission line 2 as shown in FIG. That is, the optical multiplexer / demultiplexer 7 has its terminal a connected to the E / O conversion circuit 3B of the master station 1A via the transmission line 2 and its terminal b connected to the optical coupler 6A via the transmission line 2. Also connected to the E / O conversion circuit 3A terminal c child station 5A _1, terminal d is connected to the O / E conversion circuit 4A of Doko station 5A _1. On the other hand, the terminal a of the optical multiplexer / demultiplexer 8 is connected to the transmission line 2, and the terminal b is connected to the O / E conversion circuit 4B of the master station 1A via the transmission line 2. Also connected to the E / O conversion circuit 3B of the terminal c child station 5A _n, is connected to the O / E converter 4B of terminals d child station 5A _n.

An optical coupler 6A connecting each of the slave stations 5A _{2 to} 5A _n-1 and the transmission line 2 has a branching ratio of 10: 1 and a wavelength λ = 1.3 μm, 1.5
A broadband wavelength coupler is used that has the same characteristics for both 5 μm optical signals.

In the optical communication system configured as described above, the master station
90% of the output of an optical signal with a wavelength of 1.55 μm from 1A
Is output from terminal b to transmission line 2 and the remaining 10
% Is supplied to the slave station 5A ₁ from the terminal d. Where slave station 5A ₁
Is received, 10% of the optical signal output from the master station 1A is supplied. Further, the optical signal output to the transmission path 2 is supplied to the slave station in the receiving state. In this case, if the slave station 5A _n is in the receiving state, 99% of the optical signal reaching the optical multiplexer / demultiplexer 8 is supplied to this slave station 5A _n . On the other hand, the wavelength λ output from the slave station 5A _{1 is} 1.3 μm.
90% of the optical signal is output from the terminal b to the transmission line 2. Further, 99% of the optical signal of wavelength λ = 1.55 μm output from the slave station 5A _n is supplied from the terminal b to the master station 1A.

Using the optical coupler 7 to the connection with the slave station 5A ₁ and transmission path 2 as described above, since the use demultiplexer 8 for connection to the transmission line 2 and the slave station 5A _n, conventionally, the child The branch loss is smaller than the optical coupler used for the stations 5A ₁ and 5A _n (10 dB of the conventional optical coupler, 0.5 dB for the optical multiplexer / demultiplexer 7 and 0.05 dB for the optical multiplexer / demultiplexer 8). Is). Therefore, since the branch loss is small, the transmission distance and the number of slave stations can be increased, so that the system scale can be expanded. In this case, when expanding the system scale with the conventional configuration,
It becomes necessary to insert a repeater in the middle of the optical transmission line 2 to regenerate and amplify the optical signal, but this impairs the non-power supply of the transmission line, which is a major feature of the multi-drop type optical communication system. It is a disadvantage. However, in contrast, the present proposal does not require the repeater even in the system scale that requires the repeater in the conventional technology. Therefore, the power supply of the transmission line can be eliminated, and the characteristics of the multi-drop type optical communication system can be greatly brought out.

Although the optical multiplexer / demultiplexer 7 has a wavelength demultiplexing degree of 10 dB in the above embodiment, it may have a wavelength demultiplexing degree of 20 dB or more like the optical multiplexer / demultiplexer 8.

Further, in the above embodiment, the optical multiplexers / demultiplexers 7 and 8 are used only for the slave stations 5A ₁ and 5A _n, but the optical multiplexers / demultiplexers may be used for the remaining slave stations.

[Advantages of the Invention] As described above, according to the optical communication system of the present invention, the first optical multiplexer / demultiplexer is used to connect the first slave station located closest to the master station to the transmission path. Then, the connection between the transmission line of the first optical multiplexer / demultiplexer and the first slave station is
Most of the optical signals from the master station and the first slave station are output to the transmission path, and the connection between the Nth slave station farthest from the master station and the transmission path is performed. While using the second optical multiplexer / demultiplexer, the emission wavelength of the Nth slave station is made the same as that of the master station, and the connection between the transmission path of the second optical multiplexer / demultiplexer and the Nth slave station is Most of the optical signals from the master station are the Nth
Since the optical signals from all the slave stations except the Nth slave station are supplied to the master station, it is conventionally used for the first and Nth slave stations. Branch loss is smaller than that of optical couplers. Therefore, since the branching loss is small, the transmission distance and the number of slave stations can be increased, so that the system scale can be expanded. Further, in the conventional technology, even if the system scale requires a repeater, since the repeater is not required in the present invention, the power supply of the transmission line can be eliminated, and the features of the multi-drop type optical communication system can be achieved. You can draw out a lot.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a multi-drop type optical communication system according to an embodiment of the present invention, FIGS. 2 and 3 are diagrams showing an optical multiplexer / demultiplexer applied to the embodiment, and FIG. Is a diagram showing a connection state of each optical multiplexer / demultiplexer to a transmission line, and FIG. 5 is a schematic configuration diagram showing a conventional multi-drop type optical communication system. 1A ... Master station, 2 ... Transmission path (optical fiber), 3A, 3B ...
… Electrical / optical conversion circuit, 4A, 4B …… Optical / electrical conversion circuit, 5A ₁
~ 5A _n ...... Slave station (5A ₁ is the first slave station, 5A _n is the Nth slave station), 6A ...... Broadband wavelength coupler, 7 ...... Optical multiplexer / demultiplexer (First optical multiplexer / demultiplexer) , 8 ... Optical multiplexer / demultiplexer (second optical multiplexer / demultiplexer).

Claims (1)

[Claims] 1. An optical communication system comprising a master station and a plurality of slave stations connected to a transmission line in the order of receiving an optical signal output from the master station in the nearest direction, wherein the master station An Nth Nth optical signal output from a station is received at the farthest distance and an optical signal having the same wavelength as the optical signal from the master station is output.
Of the slave station and an optical signal of the same wavelength as the optical signal output from each of the remaining slave stations except the N-th slave station. Connecting the first slave station and the transmission line, and outputting most of the optical signals from the master station and most of the optical signals from the first slave station to the transmission line. 1 optical multiplexer / demultiplexer, connects the Nth slave station and the transmission line, supplies most of the optical signal from the master station to the Nth slave station, and A second optical multiplexer / demultiplexer that outputs most of the optical signals from all the slave stations except the slave station to the transmission path, and all the slave stations except the first and Nth slave stations and the transmission And a broadband wavelength coupler having the same characteristics for each of the optical signals of the two different wavelengths.