JP2007324954A - Wavelength multiplexing repeater and optical communication system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength multiplexing repeater with one bidirectional optical amplifier and without causing the reflection/wraparound of a signal. <P>SOLUTION: The wavelength multiplexing repeater has: the bidirectional optical amplifier 31; a wavelength circulation optical multiplexer/demultiplexer having eight input ports A-H and the same number of output ports (a)-h and which multiplexes one input port at each optical wavelength to make it conductive to an output port and a circulator, wherein a downlink optical signal containing light with an M (M≥2;M<N) wavelength is inputted in a first port of the circulator, the other input port E of the wavelength circulation optical multiplexer/demultiplexer is connected to a third port of the circulator and when the optical signal containing the light with M wavelength enters the other input port E, the wavelength circulation optical multiplexer/demultiplexer 33 discards the optical signal in an output port to which the optical signal is outputted. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wavelength division multiplexing repeater applicable to an optical communication system that performs bidirectional communication using light of a plurality of wavelengths and an optical communication system using the same.

  In a system that performs bidirectional communication between a centralized station and a plurality of in-home devices using an optical data communication network, a network configuration that connects the centralized station and each in-home device radially with a single optical fiber is provided. It has been put into practical use (Single Star). This network configuration simplifies the system and equipment configuration, but one in-house device occupies one optical fiber (if the number of in-home devices is N, N optical fibers are required). It is difficult to reduce the price.

  Therefore, a PON (Passive Optical Network) system (also referred to as PDS (Passive Double Star)) in which one optical fiber is shared by a plurality of in-home devices has been proposed. In this optical communication system, a central station and a remote station having an optical branching coupler (optical coupler) are connected by a trunk optical fiber, and a plurality of branch optical fibers are respectively connected between the remote station and a plurality of in-home devices. Connected.

Recently, there has also been proposed an optical communication system that allows a plurality of lights wavelength-multiplexed to a trunk optical fiber. In order to efficiently increase the transmission capacity of the transmission line, a method of multiplexing and transmitting a plurality of optical signals having different wavelengths on one optical fiber is called wavelength multiplexing transmission or WDM transmission (Wavelength Division Multiplexing).
FIG. 15 shows a single-line optical fiber between a station-side device (optical transmission line termination devices OLT1 to OLT1-4) placed in the centralized station 1 and four in-home devices (ONU1 to 4) placed in each subscriber's house. 1 shows a wavelength division multiplexing transmission system that performs four-wavelength multiplexing two-way communication using the.

In the wavelength multiplexing transmission system, since light of a plurality of wavelengths is transmitted through a single optical fiber, it is necessary to multiplex optical signals of a plurality of wavelengths on the transmission side, and to multiplex on the reception side. A function for demultiplexing the optical signal into different wavelengths is required. A device having a function of multiplexing and demultiplexing is called an optical multiplexer / demultiplexer.
AWG (Arrayed-Waveguide Grating) is one of optical multiplexers / demultiplexers, and is an optical component having a structure for realizing the optical multiplexing / demultiplexing function using a planar optical circuit (PLC). Most widely used in WDM transmission systems.

In order to compensate for attenuation of light transmitted through a long-distance optical fiber, a wavelength division multiplexing optical communication system in which an optical amplifier circuit is provided in the remote station is also used.
FIG. 16 is a diagram showing a wavelength division multiplexing optical communication system in which the remote station 3 is provided with a bidirectional optical amplifier circuit using two optical amplifiers (EDFA, Raman fiber amplifier, SOA, etc.).
As an example of the bidirectional optical amplifier circuit, in the following Patent Document 1, an optical signal input from one end of an optical cable is used in a bidirectional communication system using optical fibers using wavelengths of 1.3 μm band and 1.5 μm band. The 1.5μm band component is demultiplexed and amplified by the corresponding optical amplifier, and the output is coupled to the other end of the optical cable via another optical multiplexer / demultiplexer. Similarly, it is input from the opposite side of the optical cable. A configuration in which a 1.3 μm band optical signal is amplified in the reverse direction by another optical amplifier and output to the other end of the optical cable is disclosed (see FIG. 4 of Patent Document 1).
JP-A-5-315691 JP 2005-12278

In the configuration of FIG. 16, an optical isolator is originally added to an optical amplifier having a bidirectional amplification function to provide a unidirectional amplification function, and two sets of the optical amplifier and the optical isolator are used.
Using an optical isolator, the operation becomes unstable by repeating the positive feedback that the output of the optical amplifier returns by reflection and wraparound, is again amplified by the optical amplifier, and then returns by reflection and wraparound. This is to prevent this.

In particular, the line conditions between the remote station 3 and the in-house device ONU are poor, and a connection method such as a mechanical splice having a large reflection is often adopted. Therefore, it is important to suppress reflection from this section. There is also reflection between the remote station 3 and the optical transmission line termination device OLT.
However, optical isolators are expensive, and there is a need to reduce system construction costs so that two sets need not be used.

Further, the wavelength distinction characteristics required for optical multiplexers / demultiplexers are strictly required, which is one of the factors for increasing the system construction cost.
SUMMARY OF THE INVENTION An object of the present invention is to provide a wavelength multiplexing repeater that solves the problem of signal reflection and wraparound and an optical communication system using the same.

  The wavelength multiplexing repeater of the present invention has N (N ≧ 2) first group ports and the same number N second group ports, and one first group port is connected to the optical A wavelength revolving optical multiplexer / demultiplexer that demultiplexes each wavelength and conducts bidirectionally to each of the second group of ports, and outputs an optical signal input to the first port to the second port, And a circulator for outputting an optical signal input from the third port to the first port, and M one-way (M ≧ 2; M An optical signal including light having a wavelength of <N) is input to the first port of the circulator, and the second port of the circulator is connected to the N input ports of the wavelength-circulating optical multiplexer / demultiplexer. One of the first group of ports is connected to the third port of the circulator. The other first group of ports of the optical multiplexer / demultiplexer is connected, and the wavelength-circulating optical multiplexer / demultiplexer is configured such that an optical signal including light of the M wavelengths is transmitted to the other first group of ports. In the case of entering, the optical signal is discarded at the port from which the optical signal is output in the second group of ports.

  Here, “wavelength circulation” means an optical signal having the same wavelength input from different ports in an optical multiplexer / demultiplexer having a plurality of (N) first group ports and a plurality (N) second group ports. Means optical multiplexing / demultiplexing characteristics that are always output from different ports of the second group without excess or deficiency. That is, in the wavelength revolving optical multiplexer / demultiplexer, the input side port and wavelength are connected one-to-one with the output side port and wavelength according to a certain rule.

According to the structure of the present invention, an output signal that is input to one of the first group of ports of the wavelength-circulating optical multiplexer / demultiplexer and output from the second group of ports of the wavelength-circular optical multiplexer / demultiplexer is reflected. Assuming that the signal is returned, the signal passes through the third port of the circulator and enters the “one other first group of ports” of the wavelength-circulating optical multiplexer / demultiplexer by wraparound. Come.
This signal can be sent out to the port from which the optical signal is output (second group port not in use) out of the second group of ports, and can be discarded due to the wavelength recurring property.

As described above, by using the wavelength-circulating optical multiplexer / demultiplexer for multiplexing / demultiplexing of transmission / reception signals, it is possible to suppress the reflection / wrapping of the optical signal unavoidable for bidirectional transmission.
If the number N of ports of the wavelength-circulating optical multiplexer / demultiplexer and the number M of wavelengths used for one-way optical signals have a relationship of M ≦ (N / 2), the number of ports in the second group for discarding Is preferable because M can be secured at least.

In particular, if there is a relationship of M <(N / 2), when N wavelengths that can pass through the wavelength-circulating optical multiplexer / demultiplexer are arranged at equal intervals, the M wavelengths used Wavelengths that are not used can be interrupted. For this reason, it is possible to relax the wavelength distinct characteristic specification required for the optical multiplexer / demultiplexer.
In addition, the wavelength of one port of the first group that is bi-directionally connected to the port of the second group and the other one port of the first group that is bi-directionally connected to the same port of the second group The wavelength difference from the wavelength is preferably M or more and (N−M) or less when the adjacent wavelength interval is 1.

 If it is less than M, the reflected / sneak signal returned to the wavelength-circulating optical multiplexer / demultiplexer may be output to the same second group of ports as the signal to be relayed. If (N−M) is exceeded, the reflected / wrapped signal that has returned to the wavelength-circulating optical multiplexer / demultiplexer is output to the same second group of ports as the signal to be relayed. This is because there is a risk of it.

Further, as the structure to be discarded, it is possible to employ a light energy absorber to terminate a port that is not a signal transmission path of the wavelength revolving optical multiplexer / demultiplexer.
The wavelength division multiplexing repeater of the present invention may have a bidirectional optical amplifier. According to this wavelength multiplexing repeater, stable operation can be ensured even if the amplification degree of the bidirectional optical amplifier is increased.

  The optical communication system of the present invention is a bidirectional optical communication system in which a central station and a remote station are connected by a fiber, and a remote station and a plurality of in-home devices are connected by optical fibers. The station is equipped with the wavelength multiplexing repeater of the present invention.

  As described above, according to the present invention, when wavelength-division bidirectional communication is relayed, instead of a complicated and large-scale optical branching coupler, a wavelength-circulating optical multiplexer / demultiplexer is used to perform bidirectional transmission. The wraparound can be suppressed.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a diagram showing an overall configuration of a wavelength division multiplexing optical communication system (hereinafter referred to as “optical communication system”). An optical communication system component in the station is called a centralized station 1 ′, and an optical communication system component in the subscriber's house is called an indoor station 5. The optical communication system includes a central station 1 ', a plurality of home stations 5, and a remote station 3' (also referred to as a remote node), and a single-line repeater optical fiber 2 is used between the central station 1 'and the remote station 3'. The remote station 3 'and the in-home station 5 are connected by a single branch optical fiber 4 respectively. The relay optical fiber 2 and the branch optical fiber 4 are collectively referred to as “optical fiber”.

The central station 1 ′ includes an optical transmission line termination device OLT (Optical Line Terminals) serving as a connection end with the relay optical fiber 2.
The home station 5 includes a home device ONU (Optical Network Unit) that transmits and receives a broadband optical signal of a personal computer installed in the home to the optical network.
The operation of the optical communication system will be briefly described. A downstream optical signal that enters the central station 1 'from a higher-level network is transmitted to the repeater optical fiber 2 through the optical transmission line termination device OLT in the central station 1'. Since WDM is used, the wavelength of the optical signal to be transmitted is different for each in-home device at the transmission destination. The optical signal transmitted to the repeater optical fiber 2 is branched by the remote station 3 'and received by the destination home station 5, and the home station 5 decodes and decodes the optical signal.

On the other hand, the upstream optical signal transmitted from the home station 5 is received by the central station 1 'via the remote station 3'. In the central station 1 ′, the data is transmitted from here to the upper network via a broadband access router or the like.
FIG. 2 is a diagram illustrating a connection state of the centralized station device 1, the remote station device 3 using the wavelength circulating AWG (cAWG), and the in-home devices ONU1 to 4 and the configuration of the main parts thereof in the optical communication system. .

The central station apparatus 1 is installed in the central station 1 ′ and is connected to the repeater optical fiber 2 so as to separate the light according to the traveling direction of the optical signal, the AWG 12 that demultiplexes the optical signal for each wavelength of light, It includes four optical transmission line termination devices OLT1 to OLT4 that perform conversion between signals and electrical signals.
Each of the in-home devices ONU1 to 4 performs conversion between an optical signal and an electrical signal.

The remote station device 3 is installed in the remote station 3 ′ and optically relays between the four optical transmission line termination devices OLT1 to OLT4 and the four in-home devices ONU1 to 4.
The wavelengths of the downstream optical signals entering the remote station device 3 from the optical transmission line termination devices OLT1 to OLT4 through the repeater optical fiber 2 are λ1, λ2, λ3, and λ4, respectively. The wavelengths of the upstream optical signals entering 3 are λ5, λ6, λ7, and λ8, respectively. For example, it is assumed that there is a relationship of λ1 <λ2 <λ3 <λ4 <λ5 <λ6 <λ7 <λ8.

The number M of wavelengths per one-way signal is 4.
As shown in FIG. 2, the remote station device 3 includes a bidirectional optical amplifier 31, a wavelength revolving AWG 33, and an optical circulator 32 that functions as a 3-port optical path separator.
The bidirectional optical amplifier 31 has a function of bidirectionally amplifying light in a band including wavelengths λ1 to λ8. As the bidirectional optical amplifier 31, a semiconductor optical amplifier (SOA), an erbium-doped optical fiber amplifier, or the like is used. A semiconductor optical amplifier (SOA) amplifies light using a semiconductor laser under conditions before an oscillation threshold. The erbium-doped optical fiber amplifier performs optical amplification by using stimulated emission between energy levels of erbium ions. Both are inherently bidirectional due to their structure.

As shown in FIG. 3, the optical circulator 32 has three ports (1), (2), and (3). The optical signal input to the port (1) is output to the port (2), and the port (3 ) Is output to port (1), and the optical signal input to port (2) is output to port (3).
The light transmitted from the optical transmission line termination devices OLT1 to OLT4 and amplified by the bidirectional optical amplifier 31 is output from the port (1) to the wavelength circulating AWG 33 through the port (2), and the in-home devices ONU1 to ONU4. The light that has propagated through and passed through the wavelength-circulating AWG 33 is output from the port (3) to the bidirectional optical amplifier 31 through the port (1). The optical signal reflected from the in-home devices ONU 1 to 4 and returned to the remote station device 3 goes from the port (2) of the optical circulator 32 to the port (3), and is input again to the wavelength-circulating AWG 33. Further, the optical signal reflected by the optical transmission line termination devices OLT1 to OLT4 and returned to the remote station device 3 passes from the port (1) of the optical circulator 32 to the port (2), and is input again to the wavelength-circulating AWG 33. The

The optical circulator 32 can be made, for example, by combining an optical isolator using a Faraday rotation effect of a magnetic field and a two-branch star type optical coupler. A TE / TM mode conversion effect on the waveguide may be used instead of the Faraday rotation effect.
As shown in FIG. 5 and FIG. 6, the wavelength revolving AWG 33 includes eight input ports A to H serving as a first group of ports and eight output ports a to h serving as a second group of ports. In addition, wavelength pass filters respectively corresponding to the wavelengths λ1 to λ8 are incorporated. The number of ports N is 8.

The wavelength-circulating AWG 33 functions to distribute the wavelength-multiplexed optical signals entering the input ports A to H to the different output ports a to h according to the wavelength while keeping the light. The optical signal of which wavelength is distributed to which output port is determined for each input port, and an optical signal of the same wavelength is not sent from one input port to another output port.
In the embodiment of the present invention, as shown in FIG. 4, the wavelength circulating AWG 33 connects the port A and the port E to the optical circulator 32, and connects the four output ports a to d to the in-home devices ONU 1 to 4. Connected to.

The optical signal of wavelength λ1 is connected between port A and port a, the optical signal of wavelength λ2 is connected between port A and port b, and the optical signal of wavelength λ3 is connected between port A and port c. The optical signal of wavelength λ4 is connected between port A and port d.
Also, due to the circularity, the optical signal of wavelength λ5 of port A is connected to port e, the optical signal of wavelength λ6 is connected to port f, the optical signal of wavelength λ7 is connected to port g, and the optical signal of wavelength λ8 is connected to port h (See FIG. 5).

On the other hand, the optical signal of wavelength λ5 is connected between port E and port a, the optical signal of wavelength λ6 is connected between port E and port b, and the optical signal of wavelength λ7 is connected between port E and port c. The optical signal of wavelength λ8 is connected between port E and port d (see FIG. 6).
Also, due to the circularity, the optical signal of wavelength λ1 of port E is connected to port e, the optical signal of wavelength λ2 is connected to port f, the optical signal of wavelength λ3 is connected to port g, and the optical signal of wavelength λ4 is connected to port h (see FIG. 6).

The wavelength reciprocating AWG 33 absorbs light energy from the ports e to h from which optical signals of wavelengths λ5 to λ8 inputted from the port A are outputted and optical signals of wavelengths λ1 to λ4 inputted from the port E are outputted. The structure is terminated at the body, so that the output light does not return.
Next, an optical signal transmission mode will be described.
The wavelength revolving AWG 33 uses the light of wavelengths λ1, λ2, λ3, and λ4 that has entered the wavelength revolving AWG 33 according to the respective wavelengths, the port a for the in-home device ONU1, the port b for the in-home device ONU2, and the in-home device. This is distributed to the port c for the ONU 3 and the port d for the in-home device ONU 4.

The wavelength recurring AWG 33 includes wavelengths a, λ5, λ6, λ7, and λ8 input from the port a for the in-home device ONU1, the port b for the in-home device ONU2, the port c for the in-home device ONU3, and the port d for the in-home device ONU4. An upstream optical signal is output from port E.
Therefore, the downstream optical signals of wavelengths λ1, λ2, λ3, and λ4 input from the optical circulator 32 are demultiplexed by the wavelength reciprocating AWG 33 and delivered to the in-home devices ONU1 to 4, and also input from the in-home devices ONU1 to 4. The upstream optical signals having the wavelengths λ 5, λ 6, λ 7, and λ 8 are combined and passed to the optical circulator 32. As described above, the combined light is input to the bidirectional optical amplifier 31 and emitted toward the optical transmission line termination devices OLT1 to OLT4.

If there is a reflection between the remote station device 3 and the in-home device ONU, the reflected signals of the wavelengths λ1, λ2, λ3, and λ4 pass through the ports a to d of the wavelength reciprocating AWG 33 again to the port A. However, the circulator 32 does not return to the optical amplifier, but is guided to the port E of the wavelength-circulating AWG 33 and enters the wavelength-circulating AWG 33 again from here.
The reflected signal that enters the wavelength circulating AWG 33 from the port E is output to the ports e to h as shown in FIG. Since the ports e to h are terminated with a terminal incorporating a light energy absorber (for example, a black film), even if these reflected signals appear at the ports e to h, they disappear here.

Next, it is assumed that there is a reflection between the remote station device 3 and the central station device 1. The wavelength recurring AWG 33 includes wavelengths a, λ5, λ6, λ7, and λ8 input from the port a for the in-home device ONU1, the port b for the in-home device ONU2, the port c for the in-home device ONU3, and the port d for the in-home device ONU4. An upstream optical signal is output from port E.
If there is a reflection between the remote station device 3 and the centralized station device 1, the reflected signals of wavelengths λ 5, λ 6, λ 7, and λ 8 appear again at port A by the circulator 32. Then, as shown in FIG. 5, the light is guided to the port E of the wavelength revolving AWG 33 and discarded here.

As described above, according to the configuration of the embodiment of the present invention, it is possible to prevent the upstream and downstream signals from wrapping around without an isolator.
Further, since no isolator is provided, it is possible to simultaneously perform upstream and downstream signal amplification with a single optical amplifier, thereby reducing the number of optical amplifiers and reducing costs. In addition, even if the amplification factor of the optical amplifier is increased, the occurrence of positive feedback due to reflected light can be suppressed, and stable operation is possible.

Next, another embodiment will be described.
Previously, the principle was explained using a minimum number of 8 ports as the wavelength reciprocating AWG 33 for the number of wavelengths 4 used.
However, by providing a margin for the number of ports of the wavelength reciprocating AWG 33, the wavelength interval of the upstream and downstream signals is widened, and the distinction characteristics of the wavelength filters in the optical transmission line termination devices OLT1 to OLT1 and the in-home devices ONU1 to 4 are alleviated. Configuration is also possible.

FIG. 7 is a diagram illustrating a connection state of the central station device 1, the remote station device 3, and the in-home devices ONU1 to ONU1 and their main components in the optical communication system.
The difference between this system and the system of FIG. 2 is that the wavelength configuration of the upstream and downstream optical signals is different.
This wavelength configuration is shown in FIG.

According to FIG. 8, the wavelengths of the downstream optical signals entering the remote station device 3 from the optical transmission line termination devices OLT1 to OLT4 are λ1, λ2, λ3, and λ4 as in FIG. The wavelengths of the upstream optical signals entering the remote station device 3 from λ9, λ10, λ11, and λ12 are separated from λ1, λ2, λ3, and λ4.
The wavelength of the downstream optical signal of the in-home device ONU1 is λ1, the wavelength of the upstream optical signal is λ9, the wavelength of the downstream optical signal of the home device ONU2 is λ2, the wavelength of the upstream optical signal is λ10, and the downstream light of the home device ONU3 The wavelength of the signal is λ3, the wavelength of the upstream optical signal is λ11, the wavelength of the downstream optical signal of the in-home apparatus ONU4 is λ4, and the wavelength of the upstream optical signal is λ12. The intervals between the wavelengths are equal, and there is a relationship of λ1 <λ2 <λ3 <λ4 <λ5 <λ6 <λ7 <λ8 <λ9 <λ10 <λ11 <λ12. Wavelengths λ5, λ6, λ7, and λ8 are not used.

In the embodiment of the present invention, as shown in FIG. 9, the wavelength revolving AWG 33 connects the port A and the port E to the optical circulator 32, and the four output ports ad are connected to the in-home devices ONU1 to ONU1-4. Connected. The ports eh are terminated with a light energy absorber. Ports i, j, k, and l are not used.
FIG. 10 is a demultiplexing characteristic diagram of the wavelength revolving AWG 33. The wavelength revolving AWG 33 outputs the downstream optical signals having wavelengths λ1, λ2, λ3, and λ4 that have entered the input port A from the output ports a to d. The upstream optical signals λ9, λ10, λ11, and λ12 input from the output ports a to d are output from the input port E.

The optical signals of wavelengths λ1, λ2, λ3, and λ4 input from the E port are connected to ports e to h.
The wavelength reciprocating AWG 33 terminates ports e to h from which optical signals of wavelengths λ1, λ2, λ3, and λ4 input from the E port are output with an optical energy absorber, so that output light does not return. It has a structure.

Thus, when there is a reflection between the remote station device 3 and the in-home device ONU, the reflected signals of λ 1, λ 2, λ 3, λ 4 reach the wavelength circulatory AWG 33 and are circulated by the circulator 32. It is led to E port of AWG33.
Reflected signals of wavelengths λ1, λ2, λ3, and λ4 that enter the wavelength revolving AWG 33 from the E port are output to ports e to h as shown in FIG. Since the ports e to h are terminated with a light energy absorber, even if these reflected signals appear at the ports e to h, they disappear here.

The feature of this embodiment is that the wavelengths λ1, λ2, λ3, and λ4 and the wavelengths λ9, λ10, λ11, and λ12 are separated from each other. It is low. Therefore, the cutoff characteristics of the wavelength filters in the OLTs 1 to 4 and the ONUs 1 to 4 may be moderate, and a reduction in cost can be realized.
As yet another embodiment, an optical communication system that transmits a video signal or the like at a common wavelength to each in-home device ONU and implements a multiplexing service is also assumed.

FIG. 11 is a diagram illustrating a connection state of the centralized station device 1, the remote station device 3, and the in-home devices ONU1 to ONU1 in the optical communication system according to this embodiment, and a configuration of main parts thereof.
The difference between this system and the system of FIG. 7 is that the remote station apparatus 3 is provided with a multiplex transmission station 34 for transmitting video signals and the like at a common wavelength λ16.
FIG. 12 is a demultiplexing characteristic diagram of the wavelength revolving AWG 33. The wavelength revolving AWG 33 outputs the downstream optical signals of wavelengths λ1, λ2, λ3, and λ4 that have entered the input port A from the output ports a to d. The upstream optical signals λ9, λ10, λ11, and λ12 input from the output ports a to d are output from the input port E. Downstream optical signals of wavelength λ16 entering the ports M, N, O, and P are output from the output ports a to d, respectively.

In the embodiment of the present invention, as shown in FIG. 13, the wavelength reciprocating AWG 33 connects the port A and the port E to the optical circulator 32, and connects the four output ports ad to the in-home devices ONU1 to ONU4. is doing. Ports M, N, O, and P are connected to the multiple transmission station 34.
Further, the wavelength revolving AWG 33 has a structure in which the ports e to h from which the optical signal input from the E port is output are terminated with a light energy absorber so that the output light does not return.

As described above, when there is a reflection between the remote station device 3 and the in-home device ONU, the reflected signals of the wavelengths λ1, λ2, λ3, and λ4 are guided to the E port of the wavelength reciprocating AWG 33 through the circulator 32. Thus, these reflected signals can be discarded.
In addition, a video signal or the like can be transmitted at a common wavelength using the vacant wavelength λ16, and services can be multiplexed.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments. For example, the number of optical transmission line termination devices OLT and in-home devices ONU is not limited to four. Further, by making the AWG 12 shown in FIGS. 2, 7 and 11 have a wavelength recursive property, the wavelength multiplexing repeater of the present invention can be applied not only to a remote station apparatus but also to a central station apparatus. . In addition, various modifications can be made within the scope of the present invention.

1 is a diagram illustrating an overall configuration of an optical communication system according to an embodiment of the present invention. It is a figure which shows the connection state of the central station apparatus 1, the remote station apparatus 3, and the in-home apparatus ONU1-4, and those principal part structures in the same optical communication system. FIG. 4 is a diagram showing an optical signal transmission direction between ports of the optical circulator 32. It is a connection diagram of the wavelength revolving AWG33. It is a figure which shows the wavelength related connection state between the ports of wavelength revolving AWG33. It is a figure which shows the wavelength related connection state between the ports of wavelength revolving AWG33. It is a figure which shows the connection state of the central station apparatus 1, the remote station apparatus 3, and the in-home apparatus ONU1-4 of an optical communication system, and those principal part structures in other embodiment of this invention. It is an arrangement | sequence diagram of the wavelength used for optical communication. It is a connection diagram of the wavelength revolving AWG33. It is a figure which shows the wavelength related connection state between the ports of wavelength revolving AWG33. It is a figure which shows the connection state of the centralized station apparatus 1, the remote station apparatus 3, and the in-home apparatus ONU1-4 of an optical communication system, and those principal part structures in other embodiment of this invention. It is a figure which shows the wavelength related connection state between the ports of wavelength revolving AWG33. It is a connection diagram of the wavelength revolving AWG33. It is an arrangement | sequence diagram of the wavelength used for optical communication. Wavelength multiplexing transmission system for performing four-wavelength multiplexing bidirectional communication using single-wire optical fiber between a station-side device placed in a centralized station and four in-home devices (ONU1 to 4) placed in each subscriber's house FIG. FIG. 2 is a diagram showing a wavelength division multiplexing optical communication system in which a remote optical apparatus (two-way optical amplifier circuit) using two optical amplifiers (EDFA, Raman fiber amplifier, SOA, etc.) is provided in the remote station device 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Centralized station apparatus 1 'Centralized station 2 Trunk line optical fiber 3 Remote station apparatus 3' Remote station 4 Branch line optical fiber 5 In-home apparatus 31 Bidirectional optical amplifier 32 Optical circulator 33 Wavelength circulating AWG

Claims (7)

A device that relays bidirectional optical communication,
There are N (N ≧ 2) first group ports and the same number N second group ports, and one second group port is demultiplexed for each wavelength of light and second A wavelength-circulating optical multiplexer / demultiplexer that conducts bidirectionally to each of the ports of the group;
The optical signal input to the first port is output to the second port, the optical signal input to the second port is output to the third port, and the optical signal input from the third port is output to the first port. A circulator that outputs to one port,
An optical signal including light of one-way M wavelengths (M ≧ 2; M <N) is input to the first port of the circulator,
A first group of one of the N input ports of the wavelength-circulating optical multiplexer / demultiplexer is connected to the second port of the circulator,
The third port of the circulator is connected to the other port of the first group of the wavelength-circulating optical multiplexer / demultiplexer,
The wavelength-circulating optical multiplexer / demultiplexer, when an optical signal including light of the M wavelengths enters the other one first group of ports, A wavelength division multiplexing repeater that is discarded at the port from which the optical signal is output. M ≦ (N / 2)
The wavelength multiplexing repeater according to claim 1, wherein: M <(N / 2)
The wavelength division multiplexing repeater according to claim 2, wherein:   The wavelength of one port of the first group that is bi-directionally connected to the second group of ports, and the wavelength of another port of the first group that is bi-directionally connected to the same second group of ports. 2. The wavelength division multiplexing repeater according to claim 1, wherein the wavelength difference between the first and second wavelengths is M or more and (N−M) or less when the adjacent wavelength interval is 1.   2. The wavelength multiplexing repeater according to claim 1, wherein the wavelength-circulating optical multiplexer / demultiplexer terminates a port from which the optical signal is output among the second group of ports with an optical energy absorber.   2. The wavelength multiplexing repeater according to claim 1, further comprising a bidirectional optical amplifier.   2. An optical communication system in which a central station and a plurality of in-home devices are connected via an optical fiber via a remote station, wherein the remote station is provided with the wavelength multiplexing repeater according to claim 1. system.

Images