Patent ID: 12231172

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that in a plurality of drawings, like component are denoted by like reference numerals, and therefore explanations thereof are omitted.

First Embodiment

FIG.1is a diagram illustrating the configuration of an optical communication system1000according to a first embodiment. The optical communication system1000includes a user terminal1100, a control signal superimposition unit (superimposer)1200, and a management and control functional unit1300. The user terminal1100is connected to the control signal superimposition unit1200by an optical fiber1500.

As the user terminal1100, an optical communication apparatus configured to transmit/receive an optical signal according to the conventional technique can be used. The user terminal1100includes a signal mixer1110, an optical transceiver (TRx)1120, and a signal divider1130. The signal mixer1110outputs, to the TRx1120, a transmission signal in which a main signal and a control signal that are both electrical signals have been superimposed on one another. The control signal has a lower frequency than the frequency of the main signal. For example, as the control signal, the AMCC is used. The TRx1120converts the transmission signal from an electrical signal to an optical signal, and outputs the optical signal to the optical fiber1500. The TRx1120receives an input of an optical signal transmitted through the optical fiber1500, and converts the input optical signal to an electrical signal to output the electrical signal. The signal divider1130separates the electrical signal output by the TRx1120into the main signal and the control signal based on their respective frequencies.

Hereinafter, two units of user terminals1100, each of which is a counterpart of the other, are described as “user terminal1100-1” and “user terminal1100-2,” and the signal mixer1110, the TRx1120, and the signal divider1130included in a user terminal1100-i(i=1, 2) are described as “signal mixer1110-i,” “TRx1120-i,” and “signal divider1130-i,” respectively. The optical fiber1500between the user terminal1100-iand the control signal superimposition unit1200is described as “optical fiber1500-i.” The main signal and the control signal to be transmitted by the user terminal1100-iare described as “main signal Mi” and “control signal Ci,” respectively. Similarly to the conventional technique, the control signal Ci is, for example, an alive monitoring signal, a signal including state information (the wavelength, power, temperature, or the like of the TRx1120-i), a wavelength control signal, control signals other than the wavelength control signal, or the like.

The control signal superimposition unit1200includes transmission-reception separation devices1210-1and1210-2, optical amplifiers1220-1and1220-2, and optical modulators1230-1and1230-2. The transmission-reception separation devices1210-1and1210-2are connected by optical fibers1240-1and1240-2. On an optical fiber1240-i(i=1, 2), an optical amplifier1220-iand an optical modulator1230-iare provided.

The transmission-reception separation device1210-i(i=1, 2) receives an input of an optical signal output by the user terminal1100-ifrom the optical fiber1500-i, and outputs the optical signal to the optical amplifier1220-i. The transmission-reception separation device1210-ireceives an input of an optical signal output by the optical modulator1230-j(j=1, 2 and j≠i), and outputs the optical signal to the optical fiber1500-i.

Each of the optical amplifiers1220-1and1220-2has the characteristics of high-pass filter, and removes a low-frequency signal. Each of the optical amplifiers1220-1and1220-2is, for example, a semiconductor optical amplifier (SOA). The optical amplifier1220-i(i=1, 2) receives an input of an optical signal output by the transmission-reception separation device1210-i. The optical amplifier1220-iremoves a control signal superimposed on the low-frequency side of the input optical signal, and outputs the optical signal with the control signal removed to the optical modulator1230-i. Note that according to the transmittance characteristics of the optical amplifier1220-iserving as a high-pass filter, a frequency that can be sufficiently attenuated in the optical amplifier1220-iis selected as a carrier frequency of the control signal. The transmittance characteristics of the optical amplifier1220-iserving as a high-pass filter will be described later with reference toFIG.5.

Each of the optical modulators1230-1and1230-2is a lithium-niobate (LiNbO3(LN)) modulator, an electro-absorption (EA) modulator, or other types of modulators. The optical modulator1230-i(i=1, 2) receives an input of an optical signal as the main signal from the optical amplifier1220-i, and superimposes a control signal on the low-frequency side of the input optical signal. The optical modulator1230-ioutputs the optical signal with the control signal superimposed thereon to the transmission-reception separation device1210-j(j=1, 2 and j≠i).

The management and control functional unit1300manages and controls the optical communication system1000. The management and control functional unit1300outputs a control signal to be superimposed on a main signal to the control signal superimposition unit1200. A control signal to be superimposed on the main signal Mi (i=1, 2) is described as “control signal C3-i.”

FIG.2is a diagram for explaining the processing in the control signal superimposition unit1200. A signal mixer1110-1in the user terminal1100-1illustrated inFIG.1outputs the electrical signal E1in which the main signal M1and the control signal C1in the form of an electrical signal have been superimposed on one another. A TRx1120-1converts the electrical signal E1to an optical signal G11, and outputs the optical signal G11to an optical fiber1500-1.

The transmission-reception separation device1210-1receives an input of the optical signal G11transmitted through the optical fiber1500-1, and outputs the optical signal G11to the optical amplifier1220-1. The optical amplifier1220-1generates an optical signal G12with the control signal C1on the low-frequency side removed from the input optical signal G11, and outputs the optical signal G12to the optical modulator1230-1. The optical modulator1230-1superimposes the control signal C3-1, input from the management and control functional unit1300, on the low-frequency side of the optical signal G12to generate an optical signal G13, and outputs the optical signal G13to the transmission-reception separation device1210-2. The transmission-reception separation device1210-2outputs the optical signal G13to an optical fiber1500-2. A TRx1120-2in the user terminal1100-2illustrated inFIG.1receives an input of the optical signal G13transmitted through the optical fiber1500-2, and converts the optical signal G13to an electrical signal E1′. A signal divider1130-2separates the converted electrical signal E1′ into the main signal M1and the control signal C3-1.

A signal mixer1110-2in the user terminal1100-2illustrated inFIG.1outputs an electrical signal E2in which a main signal M2and a control signal C2in the form of an electrical signal have been superimposed on one another. The TRx1120-2converts the superimposed electrical signal E2to an optical signal G21, and outputs the optical signal G21to the optical fiber1500-2.

The transmission-reception separation device1210-2receives an input of the optical signal G21transmitted through the optical fiber1500-2, and outputs the optical signal G21to the optical amplifier1220-2. The optical amplifier1220-2generates an optical signal G22with the control signal C2on the low-frequency side removed from the input optical signal G21, and outputs the optical signal G22to the optical modulator1230-2. The optical modulator1230-2superimposes a control signal C3-2, input from the management and control functional unit1300, on the low-frequency side of the optical signal G22to generate an optical signal G23, and outputs the optical signal G23to the transmission-reception separation device1210-1. The transmission-reception separation device1210-1outputs the optical signal G23to the optical fiber1500-1. The TRx1120-1in the user terminal1100-1illustrated inFIG.1receives an input of the optical signal G23transmitted through the optical fiber1500-1, and converts the optical signal G23to an electrical signal E2′. A signal divider1130-1separates the converted electrical signal E2′ into the main signal M2and the control signal C3-2.

Note that a signal to be superimposed in the control signal superimposition unit1200uses the same frequency as a control signal to be transmitted by the user terminal1100. At this time, a pilot tone with a frequency different from, and within a lower frequency range than, the frequency of the main signal may be used as a carrier, or a control signal remaining as a baseband signal may be superimposed. It is allowable that a control signal to be superimposed in the control signal superimposition unit1200uses a pilot tone within a higher frequency range than the frequency of the main signal as a carrier, provided that the control signal is separable from the main signal in the user terminal1100.

If the management and control functional unit1300does not superimpose a control signal on an optical signal transmitted from the user terminal1100-1and addressed to the user terminal1100-2, then the control signal superimposition unit1200may not be provided with the optical amplifier1220-1and the optical modulator1230-1. If the management and control functional unit1300does not superimpose a control signal on an optical signal transmitted from the user terminal1100-2and addressed to the user terminal1100-1, then the control signal superimposition unit1200may not be provided with the optical amplifier1220-2and the optical modulator1230-2.

The optical communication system1000may be provided with a control signal superimposition unit1200aillustrated inFIG.3or a control signal superimposition unit1200billustrated inFIG.4, instead of the control signal superimposition unit1200illustrated inFIG.1.

FIG.3is a diagram illustrating the configuration of the control signal superimposition unit1200a. The control signal superimposition unit1200aincludes transmission-reception separation devices1210a-1and1210a-2, optical switches (SW)1250-1and1250-2, the optical amplifiers1220-1and1220-2, and the optical modulators1230-1and1230-2.

The transmission-reception separation device1210a-1and the optical SW1250-1are connected by an optical fiber1260-1. The transmission-reception separation device1210a-1and the optical SW1250-2are connected by optical fibers1270-2and1280-2. The transmission-reception separation device1210a-2and the optical SW1250-2are connected by an optical fiber1260-2. The transmission-reception separation device1210a-2and the optical SW1250-1are connected by optical fibers1270-1and1280-1. Each of the optical fibers1270-1and1270-2is a line on which a control signal is superimposed. Each of the optical fibers1280-1and1280-2is a line on which a control signal is not superimposed. On the optical fiber1270-i(i=1, 2), the optical amplifier1220-iand the optical modulator1230-iare provided.

The transmission-reception separation device1210a-i(i=1, 2) receives an input of an optical signal transmitted through the optical fiber1500-i, and outputs the input optical signal to an optical SW1250-i. The transmission-reception separation device1210a-ireceives an input of an optical signal transmitted through an optical fiber1270-j(j=1, 2 and j≠i) or through an optical fiber1280-j, and outputs the input optical signal to the optical fiber1500-i.

The optical SW1250-i(i=1, 2) includes one input port and two output ports. The input port of the optical SW1250-iis connected to an optical fiber1260-i. The two output ports are connected individually to the optical fibers1270-iand1280-i. The optical SW1250-ioutputs an optical signal input from the input port to either of the output ports.

Operation of the control signal superimposition unit1200ais described below. The transmission-reception separation device1210a-1receives an input of the optical signal G11with the main signal M1and the control signal C1superimposed on one another from the optical fiber1500-1, and outputs the optical signal G11to the optical SW1250-1. The optical SW1250-1outputs the optical signal G11, which is a target from which a control signal is removed, to the optical amplifier1220-1, or outputs the optical signal G11, from which a control signal is not removed, to the transmission-reception separation device1210a-2.

The optical amplifier1220-1receives an input of the optical signal G11from the optical SW1250-1, and outputs the optical signal G12with the control signal C1on the low-frequency side removed from the optical signal G11. The optical modulator1230-1outputs the optical signal G13in which the control signal C3-1input from the management and control functional unit1300has been superimposed on the low-frequency side of the optical signal G12. The transmission-reception separation device1210-2outputs an optical signal G14, which is the optical signal G13input from the optical modulator1230-1or the optical signal G11input from the optical SW1250-1, to the optical fiber1500-2. The TRx1120-2in the user terminal1100-2illustrated inFIG.1converts the optical signal G14to an electrical signal, and the signal divider1130-2separates the converted electrical signal into the main signal M1and the control signal C1or the control signal C3-1.

The transmission-reception separation device1210a-2receives an input of the optical signal G21with the main signal M2and the control signal C2superimposed on one another from the optical fiber1500-2, and outputs the optical signal G21to the optical SW1250-2. The optical SW1250-2outputs the optical signal G21, which is a target from which a control signal is removed, to the optical amplifier1220-2, or outputs the optical signal G21, from which a control signal is not removed, to the transmission-reception separation device1210a-1.

The optical amplifier1220-2receives an input of the optical signal G21from the optical SW1250-2, and outputs the optical signal G22with the control signal C2on the low-frequency side removed from the optical signal G21. The optical modulator1230-2outputs the optical signal G23in which the control signal C3-2input from the management and control functional unit1300has been superimposed on the low-frequency side of the optical signal G22. The transmission-reception separation device1210a-1outputs an optical signal G24, which is the optical signal G23input from the optical modulator1230-2or the optical signal G21input from the optical SW1250-2, to the optical fiber1500-1. The TRx1120-1in the user terminal1100-1illustrated inFIG.1converts the optical signal G24to an electrical signal, and the signal divider1130-2separates the converted electrical signal into the main signal M1and the control signal C2or the control signal C3-2.

FIG.4is a diagram illustrating the configuration of the control signal superimposition unit1200b. The control signal superimposition unit1200bis different from the control signal superimposition unit1200aillustrated inFIG.3in that the transmission-reception separation devices1210-1and1210-2illustrated inFIG.1are provided instead of the transmission-reception separation devices1210a-1and1210a-2, and further optical SWs1290-1and1290-2are provided.

An optical SW1290-i(i=1, 2) includes two input ports and one output port. The optical SW1290-iis connected to the optical modulator1230-iby the optical fiber1270-i, connected to the optical SW1250-iby the optical fiber1280-i, and connected to the transmission-reception separation device1210-j(j=1, 2 and j≠i) by an optical fiber1295-i.

The optical SW1290-1outputs the optical signal G13transmitted through the optical fiber1270-1, or the optical signal G11transmitted through the optical fiber1280-1to an optical fiber1295-1as the optical signal G14. The transmission-reception separation device1210-2receives an input of the optical signal G14transmitted through the optical fiber1295-1, and outputs the input optical signal G14to the optical fiber1500-2. The optical SW1290-2outputs the optical signal G24, which is the optical signal G23transmitted through the optical fiber1270-2or the optical signal G21transmitted through the optical fiber1280-2to an optical fiber1295-2. The transmission-reception separation device1210-1receives an input of the optical signal G24transmitted through the optical fiber1295-2, and outputs the input optical signal G24to the optical fiber1500-1. Note that in the control signal superimposition unit1200b, each of the optical SWs1290-1and1290-2may be replaced with an optical coupler.

FIG.5is a graph illustrating response characteristics of the optical amplifiers1220-1and1220-2.FIG.5illustrates the response characteristics of the optical amplifiers1220-1and1220-2when they are SOAs. The optical amplifiers1220-1and1220-2exhibit adequate response characteristics to a signal with a sufficiently high frequency equal to or higher than 10 GHz. In contrast, the response characteristics of the optical amplifiers1220-1and1220-2significantly deteriorate within the low frequency range equal or lower than several GHz. By taking advantage of these response characteristics, it is possible to remove a low-frequency signal. For example, a frequency Fa is set to the main signal, while a frequency Fb is set to the control signal, and this makes it possible to remove the control signal from an optical signal having passed through the optical amplifiers1220-1and1220-2.

Note that since the differences in response characteristics depend on the gain of the SOA, the length of the SOA is increased, or the SOAs are connected in multiple stages, so that this makes it possible to increase the differences in response characteristics. Also, the differences in response characteristics depend on input power to the SOA. It is possible to increase the differences in response characteristics by increasing the output power of the TRx1120installed in the user terminal1100such that the input power to the SOA is increased. Note that the details and other information on the SOA characteristics are described in, for example, Reference Literature 1 “K. Sato et al., “Reduction of Mode Partition Noise by Using Semiconductor Optical Amplifiers,” IEEE Journal of Selected Topics in Quantum Electronics, vol. 7, No. 2, pp. 328-333, 2001.”

According to the present embodiment, the optical communication system includes the control signal superimposition unit1200,1200a, or1200b, unlike the conventional optical communication system, so that even after connection between the user terminals1100has completed, the management and control functional unit1300can still transmit a control signal such as a wavelength management and control signal to the user terminals1100.

Second Embodiment

An optical communication system according to the present embodiment superimposes a control signal that provides instructions about wavelength switching somewhere along a communication path between subscriber terminal, and switches the wavelength for the subscriber terminal to a different wavelength.

FIG.6is a diagram illustrating the configuration of an optical communication system2000according to a second embodiment. The optical communication system2000includes a subscriber terminal2100, an optical gateway (GW)2200, a management and control functional unit2300, an optical SW control functional unit2400, and an optical GW2500. The subscriber terminal2100is an optical communication apparatus according to the conventional technique. For example, the subscriber terminal2100is the user terminal1100of the first embodiment.

The optical GW2200includes an optical SW2210and one or more control signal superimposition units2220. The optical SW2210includes N (N is an integer equal to or larger than 1) first ports2211, and M (M is an integer equal to or larger than 2) second ports2212. The N first ports2211are described as “first ports2211-1to2211-N,” respectively. The M second ports2212are described as “second ports2212-1to2212-M,” respectively.

The first port2211is connected to the subscriber terminal2100through an optical transmission path2600. Hereinafter, the optical transmission path2600connected to a first port2211-n(n is an integer equal to or larger than 1, and equal to or smaller than N) is described as “optical transmission path2600-n.” The subscriber terminal2100connected to the optical transmission path2600-nis described as “subscriber terminal2100a-n.” Subscriber terminals2100a-1to2100a-N are collectively referred to as “subscriber terminal2100a,” or are described as “subscriber terminal2100a” when any of the subscriber terminals2100a-1to2100a-N is not specified.

The second port2212is connected to an optical transmission path2700. Hereinafter, the optical transmission path2700connected to a second port2212-k(k is an integer equal to or larger than 1, and equal to or smaller than M) is described as “optical transmission path2700-k.” Some of the second ports2212are connected to the management and control functional unit2300, while the other second ports2212are connected to an additional optical communication apparatus. In the present embodiment, the second port2212-1is connected to the management and control functional unit2300through an optical transmission path2700-1, while the second port2212-m(m is an integer equal to or larger than 2, and equal to or smaller than M) is connected to an additional optical communication apparatus such as an optical SW through an optical transmission path2700-m.

The optical SW2210outputs an optical signal, input from any of the first ports2211, through the second port2212corresponding to the destination of this optical signal. The optical SW2210outputs an optical signal, input from any of the second ports2212, through the first port2211corresponding to the subscriber terminal2100aas the destination of this optical signal.

The control signal superimposition unit2220is provided on the optical transmission path2700-m(m is an integer equal to or larger than 2, and equal to or smaller than M). On some of the optical transmission paths2700-2to2700-M, the control signal superimposition unit2220may not be provided. The control signal superimposition unit2220superimposes a control signal, output by the management and control functional unit2300, on one or both of an optical signal whose transmission source is the subscriber terminal2100aand an optical signal addressed to the subscriber terminal2100a.

As the control signal superimposition unit2220, the control signal superimposition unit1200of the first embodiment illustrated inFIGS.1and2is used. In the control signal superimposition unit2220, the transmission-reception separation device1210-1(FIGS.1and2) is connected to the optical transmission path2700between the transmission-reception separation device1210-1and the optical SW2210, instead of being connected to the optical fiber1500-1, while the transmission-reception separation device1210-2(FIGS.1and2) is connected to the optical transmission path2700between the transmission-reception separation device1210-2and an optical SW different from the optical SW2210, instead of being connected to the optical fiber1500-2. If the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100a, then the control signal superimposition unit1200that does not include the optical amplifier1220-1and the optical modulator1230-1may be used as the control signal superimposition unit2220. If the management and control functional unit2300does not superimpose a control signal on an optical signal addressed to the subscriber terminal2100a, then the control signal superimposition unit1200that does not include the optical amplifier1220-2and the optical modulator1230-2may be used as the control signal superimposition unit2220. Alternatively, as the control signal superimposition unit2220, the control signal superimposition unit1200aillustrated inFIG.3or the control signal superimposition unit1200billustrated inFIG.4may be used.

The management and control functional unit2300sets the wavelength to the subscriber terminal2100connected to the management and control functional unit2300through the optical SW2210. The management and control functional unit2300switches the path for the subscriber terminal2100ato a different path in the optical SW2210, and thereafter outputs a control signal to be superimposed on an optical signal to the control signal superimposition unit2220. Examples of the control signal include a wavelength control signal, an on/off control signal for a TRx, and a bit-rate control signal. The wavelength control signal is a signal that provides instructions about the initial settings of the wavelength, wavelength offset calibration, wavelength switching, or the like. Note that the control signal is not limited to those signals described above. The optical SW control functional unit2400sets a path between the first port2211and the second port2212of the optical SW2210.

The optical GW2500includes an optical SW2510. The optical SW2510includes one or more first ports2511, and one or more second ports2512. The optical SW2510outputs an optical signal, input from any of the first ports2511, through the second port2512corresponding to the destination of this optical signal. The optical SW2510outputs an optical signal, input from any of the second ports2512, through the first port2511corresponding to the destination of this optical signal. The second port2512is connected to the subscriber terminal2100or an additional optical SW. The subscriber terminal2100connected to the optical GW2500is described as “subscriber terminal2100b.” The subscriber terminal2100bmay be located inside the optical GW2500, or may be located outside the optical GW2500. In addition, the optical GW2500may be of an identical configuration to the optical GW2200.

Operation of the optical communication system2000at the time of newly connecting the subscriber terminal2100a-1to a network is described below. First, the subscriber terminal2100a-1is connected to the management and control functional unit2300by a path P0through the optical SW2210. For example, the subscriber terminal2100a-1uses a wavelength λ11for transmission, while using a wavelength λ12for reception. The management and control functional unit2300transmits a control signal to the subscriber terminal2100a-1to instruct the subscriber terminal2100a-1to set the wavelength corresponding to a communication destination. For example, the communication destination is represented as a service to be utilized, or as a user at the communication destination. In this example, the communication destination for the subscriber terminal2100a-1is the subscriber terminal2100b, and the subscriber terminal2100a-1sets a wavelength λ21for transmission, while setting a wavelength λ22for reception. In accordance with the timing of wavelength switching operation performed by the subscriber terminal2100a-1, the optical SW control functional unit2400switches the path P0between the first port2211-1and the second port2212-1in the optical SW2210to a path P1between the first port2211-1and the second port2212-2. Upon this switching, the subscriber terminal2100a-1starts communicating with the subscriber terminal2100bthat is a desired connection destination for the subscriber terminal2100a-1.

When the subscriber terminal2100a-1connects to an additional connection destination during communication with the subscriber terminal2100b, it is necessary to set a wavelength to be used for the subscriber terminal2100a-1. Thus, the management and control functional unit2300outputs a control signal that instructs the subscriber terminal2100a-1to change the wavelength to a different wavelength to the control signal superimposition unit2220on the optical transmission path2700-2. The control signal superimposition unit2220removes a control signal from an optical signal transmitted from the subscriber terminal2100band addressed to the subscriber terminal2100a-1, and superimposes the control signal, output by the management and control functional unit2300, on the optical signal. According to the control signal superimposed on the received optical signal, the subscriber terminal2100a-1sets a wavelength λ31for transmission, while setting a wavelength λ32for reception.

The management and control functional unit2300outputs a control signal that instructs the subscriber terminal2100bto change the wavelength or stop transmission at this wavelength, to the control signal superimposition unit2220on the optical transmission path2700-2. The control signal superimposition unit2220removes a control signal from an optical signal transmitted from the subscriber terminal2100a-1and addressed to the subscriber terminal2100b, and superimposes the control signal, output by the management and control functional unit2300, on the optical signal. According to the control signal superimposed on the received optical signal, the subscriber terminal2100bchanges the wavelength or stops transmission at this wavelength.

In accordance with the timing of wavelength switching operation performed by the subscriber terminal2100a-1, the optical SW control functional unit2400switches the path P1to a path P2between the first port2211-1and the second port2212-3in the optical SW2210. Upon this switching, the subscriber terminal2100a-1starts communicating with a new communication destination. The control signal superimposition unit2220that superimposes a control signal on an optical signal to be transmitted/received by the subscriber terminal2100a-1switches from the control signal superimposition unit2220on the optical transmission path2700-2to the control signal superimposition unit2220on the optical transmission path2700-3.

Note that a splitter may be provided in the control signal superimposition unit1200, which is used as the control signal superimposition unit2220, between the transmission-reception separation device1210-1and the optical amplifier1220-1and between the transmission-reception separation device1210-2and the optical amplifier1220-2, or a splitter may be provided in the control signal superimposition unit1200a, which is used as the control signal superimposition unit2220, between the transmission-reception separation device1210a-1and the optical SW1250-1and between the transmission-reception separation device1210a-2and the optical SW1250-2, or a splitter may be provided in the control signal superimposition unit1200b, which is used as the control signal superimposition unit2220, between the transmission-reception separation device1210-1and the optical SW1250-1and between the transmission-reception separation device1210-2and the optical SW1250-2, such that the splitter may be used to split a part of an optical signal, and output it to the management and control functional unit2300. The management and control functional unit2300monitors a control signal set in the part of the split optical signal.

In a case where the subscriber terminal2100is connected by using a passive optical network (PON), even when the communication destination is changed, the same path and the same wavelength may still be used continuously, or different wavelengths may be used on the same path. In the above descriptions, the control signal provides instructions about wavelength switching, however, the control signal is not limited thereto.

In the present embodiment, the control signal superimposition unit2220is provided, so that even after the subscriber terminal2100has completed connection with its desired connection destination, the management and control functional unit2300can still transmit a wavelength management and control signal.

Note that an optical SW may use different ports for transmission to and for reception from a single unit of subscriber terminal2100a.FIG.7is a diagram illustrating the configuration of an optical communication system2000awhen an optical SW uses different ports for transmission to and for reception from a single unit of subscriber terminal2100a. The optical communication system2000aillustrated inFIG.7is different from the optical communication system2000illustrated inFIG.6in that an optical GW2200ais provided instead of the optical GW2200, and the subscriber terminal2100ais connected to an optical transmission path2650instead of the optical transmission path2600. WhileFIG.7only illustrates a single unit of subscriber terminal2100a, a plurality of units of subscriber terminals2100acan possibly be connected to the optical GW2200a.

The optical GW2200aincludes a transmission-reception separation device2230, the optical SW2210, and a control signal superimposition unit2220a. WhileFIG.7illustrates only a single control signal superimposition unit2220a, the optical GW2200acan possibly include a plurality of control signal superimposition units2220a. The transmission-reception separation device2230is connected to the optical transmission path2650, and also connected to an optical transmission path2600-n1(n1is an integer equal to or larger than 1, and equal to or smaller than N), and an optical transmission path2600-n2(n2≠n1, and n2is an integer equal to or larger than 2, and equal to or smaller than N). The transmission-reception separation device2230receives an input of an optical signal transmitted by the subscriber terminal2100afrom the optical transmission path2650, and outputs the input optical signal to the first port2211-n1of the optical SW2210. The transmission-reception separation device2230outputs the optical signal, output from the first port2211-n2of the optical SW2210, to the optical transmission path2650.

The optical SW2210receives an input of an optical signal, whose transmission source is the subscriber terminal2100a, from the first port2211-n1, and outputs the input optical signal from the second port2212-m1(m1is an integer equal to or larger than 3, and equal to or smaller than M). The optical SW2210receives an input of an optical signal addressed to the subscriber terminal2100afrom the second port2212-m2(m2≠m1, and m2is an integer equal to or larger than 3, and equal to or smaller than M), and outputs the input optical signal from the first port2211-n2. Note that although not illustrated inFIG.7, the second ports2212-1and2212-2of the optical SW2210are connected to the management and control functional unit2300. The second port2212-1outputs a signal addressed to the management and control functional unit2300from the subscriber terminal2100a. The second port2212-2receives an input of a signal transmitted from the management and control functional unit2300and addressed to the subscriber terminal2100a.

The control signal superimposition unit2220ais connected to the second port2212-m1of the optical SW2210by the optical transmission path2700-m1, while being connected to the second port2212-m2of the optical SW2210by the optical transmission path2700-m2. The control signal superimposition unit2220aincludes splitters2221-1and2221-2, the optical amplifiers1220-1and1220-2, the optical modulators1230-1and1230-2, and a transmission-reception separation device2222. The splitter2221-1, the optical amplifier1220-1, and the optical modulator1230-1are provided on the optical transmission path2700-m1. The splitter2221-2, the optical amplifier1220-2, and the optical modulator1230-2are provided on the optical transmission path2700-m2. The transmission-reception separation device2222is connected to the optical transmission paths2700-m1and2700-m2, and also connected to an optical fiber between the transmission-reception separation device2222and an additional optical SW.

The splitter2221-1receives an input of an optical signal output by the optical SW2210, and splits the input optical signal into parts. The splitter2221-1outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-1. The splitter2221-2splits an optical signal input from the transmission-reception separation device2222into parts. The splitter2221-2outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-2. The transmission-reception separation device2222outputs a signal input from the optical transmission path2700-m1to an optical fiber connected to an additional optical SW, and outputs a signal input from the optical fiber connected to the additional optical SW to the optical transmission path2700-m2.

Operation of the optical communication system2000ais described below. The transmission-reception separation device2230receives an input of an optical signal transmitted by the subscriber terminal2100a, and outputs the input optical signal to the first port2211-n1of the optical SW2210. The optical SW2210outputs an optical signal, input from the first port2211-n1, through the second port2212-m1corresponding to the subscriber terminal2100bas a destination of this optical signal. The splitter2221-1in the control signal superimposition unit2220asplits an optical signal output from the second port2212-m1into parts. The splitter2221-1outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-1. The management and control functional unit2300monitors a control signal set in the part of the optical signal split by the splitter2221-1.

The optical amplifier1220-1removes the control signal on the low-frequency side from the input optical signal, and outputs the optical signal to the optical modulator1230-1. The optical modulator1230-1superimposes a control signal, input from the management and control functional unit2300, on the optical signal input from the optical amplifier1220-1, and outputs the superimposed signal to the transmission-reception separation device2222. The transmission-reception separation device2222outputs a signal input from the optical modulator1230-1to an additional optical SW connected to the subscriber terminal2100b.

The transmission-reception separation device2222receives an input of an optical signal transmitted by the subscriber terminal2100bfrom the additional optical SW, and outputs the input optical signal to the optical transmission path2700-m2. The splitter2221-2receives an input of the optical signal output by the transmission-reception separation device2222, and splits the input optical signal into parts. The splitter2221-2outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-2. The management and control functional unit2300monitors a control signal set in the part of the optical signal split by the splitter2221-2.

The optical amplifier1220-2removes the control signal on the low-frequency side from the input optical signal, and outputs the optical signal to the optical modulator1230-2. The optical modulator1230-2superimposes a control signal, input from the management and control functional unit2300, on the optical signal input from the optical amplifier1220-2, and inputs the superimposed signal to the second port2212-m2of the optical SW2210. The optical SW2210outputs the optical signal, input from the second port2212-m2, through the first port2211-n2corresponding to the subscriber terminal2100aas a destination of this optical signal. The transmission-reception separation device2230receives an input of the optical signal output from the first port2211-n2, and outputs the input optical signal to the optical transmission path2650between the transmission-reception separation device2230and the subscriber terminal2100a.

Note that if the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100aand addressed to the subscriber terminal2100b, then the control signal superimposition unit2220amay not be provided with the optical amplifier1220-1and the optical modulator1230-1. If the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100band addressed to the subscriber terminal2100a, then the control signal superimposition unit2220amay not be provided with the optical amplifier1220-2and the optical modulator1230-2.

There is a case where the subscriber terminal2100bis connected to an optical GW2200a(described as “optical GW2200a-2”) different from the optical GW2200a(described as “optical GW2200a-1”) connected to the subscriber terminal2100a. In that case, the control signal superimposition unit2220ain the optical GW2200a-1may not be provided with the optical amplifier1220-2and the optical modulator1230-2, and simultaneously, the control signal superimposition unit2220ain the optical GW2200a-2may not be provided with the optical amplifier1220-2and the optical modulator1230-2. In this case, the control signal superimposition unit2220ain the optical GW2200a-1superimposes a control signal for the subscriber terminal2100bon an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100b. In addition, the control signal superimposition unit2220ain the optical GW2200a-2superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100bto the subscriber terminal2100a.

Alternatively, the control signal superimposition unit2220ain the optical GW2200a-1may not be provided with the optical amplifier1220-1and the optical modulator1230-1, and simultaneously, the control signal superimposition unit2220ain the optical GW2200a-2may not be provided with the optical amplifier1220-1and the optical modulator1230-1. In this case, the control signal superimposition unit2220ain the optical GW2200a-2superimposes a control signal for the subscriber terminal2100bon an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100b. In addition, the control signal superimposition unit2220ain the optical GW2200a-1superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100bto the subscriber terminal2100a.

According to the present embodiment, the optical communication system includes the control signal superimposition unit2220or2220a, so that even after connection between the subscriber terminals2100has completed, the management and control functional unit2300can still transmit, to the subscriber terminals2100, a control signal for controlling an item included in the state information, such as a wavelength management and control signal.

Third Embodiment

In the second embodiment, a control signal is superimposed at the subsequent stage to an optical SW. In the present embodiment, a control signal is superimposed at the previous stage to an optical SW.

FIG.8illustrates the configuration of an optical communication system3000of the present embodiment. The optical communication system3000is different from the optical communication system2000of the second embodiment illustrated inFIG.6in that an optical GW3200is provided instead of the optical GW2200.

The optical GW3200includes a control signal superimposition unit3210and the optical SW2210. The control signal superimposition unit3210is provided on the optical transmission path2600-nbetween the subscriber terminal2100a-nand the optical SW2210. The control signal superimposition unit3210superimposes a control signal, output by the management and control functional unit2300, on one or both of an optical signal transmitted by the subscriber terminal2100a-nand an optical signal transmitted to the subscriber terminal2100a-n.

As the control signal superimposition unit3210, the control signal superimposition unit1200of the first embodiment illustrated inFIGS.1and2is used. In the control signal superimposition unit3210, the transmission-reception separation device1210-1(FIGS.1and2) is connected to the optical transmission path2600between the transmission-reception separation device1210-1and the subscriber terminal2100a, instead of being connected to the optical fiber1500-1, while the transmission-reception separation device1210-2(FIGS.1and2) is connected to the optical transmission path2600between the transmission-reception separation device1210-2and the optical SW2210. If the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100a, then the control signal superimposition unit1200that does not include the optical amplifier1220-1and the optical modulator1230-1may be used as the control signal superimposition unit3210. If the management and control functional unit2300does not superimpose a control signal on an optical signal addressed to the subscriber terminal2100a, then the control signal superimposition unit1200that does not include the optical amplifier1220-2and the optical modulator1230-2may be used as the control signal superimposition unit3210. Alternatively, as the control signal superimposition unit3210, the control signal superimposition unit1200aof the first embodiment illustrated inFIG.3or the control signal superimposition unit1200bof the first embodiment illustrated inFIG.4may be used.

The optical communication system3000operates in the same manner as in the second embodiment at the time of performing the initial settings and wavelength switching on the subscriber terminal2100a-1to be newly connected to the network. That is, the subscriber terminal2100a-1is connected to the management and control functional unit2300by the path P0between the first port2211-1and the second port2212-1through the optical SW2210. The management and control functional unit2300outputs a control signal for the initial settings to the optical SW2210to instruct the optical SW2210to set the wavelength and other information corresponding to a communication destination. The optical SW2210transmits the control signal output by the management and control functional unit2300to the subscriber terminal2100a-1through the path P0. In accordance with the timing of wavelength switching operation performed by the subscriber terminal2100a-1, the optical SW control functional unit2400switches the path P0to the path P1between the first port2211-1and the second port2212-2. The subscriber terminal2100a-1performs the initial settings such as wavelength switching according to the received control signal, and thereafter starts communicating with its desired connection destination through the path P1.

When the subscriber terminal2100a-1connects to an additional connection destination during the communication using the path P1in the optical SW2210, the management and control functional unit2300outputs a control signal that instructs the control signal superimposition unit3210on the optical transmission path2600-1to change the wavelength to a different wavelength. The control signal superimposition unit3210removes a control signal from an optical signal output by the optical SW2210and addressed to the subscriber terminal2100a-1, and superimposes the control signal, output by the management and control functional unit2300, on the optical signal. According to the control signal superimposed on the received optical signal, the subscriber terminal2100a-1sets the wavelength to be used for transmission, and the wavelength to be used for reception.

The management and control functional unit2300outputs, to the control signal superimposition unit3210on the optical transmission path2600-1, a control signal that instructs the subscriber terminal2100(not illustrated) as a communication destination for the subscriber terminal2100a-1to change the wavelength or stop transmission at this wavelength. The control signal superimposition unit3210removes a control signal from an optical signal transmitted from the subscriber terminal2100a-1and addressed to the subscriber terminal2100as a communication destination, and superimposes the control signal, output by the management and control functional unit2300, on the optical signal. In accordance with the timing of wavelength switching operation performed by the subscriber terminal2100a-1, the optical SW control functional unit2400switches the path P1to the path P2in the optical SW2210. Upon this switching, the subscriber terminal2100a-1starts communicating with a new communication destination.

Note that in the optical communication system3000, the control signal superimposition unit3210may superimpose a control signal for performing the initial settings on the subscriber terminal2100a-1to be newly connected to the network, and transmit the superimposed control signal. The subscriber terminal2100a-1is connected to the management and control functional unit2300by the path P0through the optical SW2210. The management and control functional unit2300outputs unmodulated light (or modulated light) to the optical SW2210. The optical SW2210outputs the light output by the management and control functional unit2300through the path P0. Further, the management and control functional unit2300outputs, to the control signal superimposition unit3210on the optical transmission path2600-1, a control signal for the initial settings to be transmitted to the subscriber terminal2100a-1. The control signal superimposition unit3210on the optical transmission path2600-1superimposes the control signal input from the management and control functional unit2300on the light input from the optical SW2210. The control signal superimposition unit3210outputs the optical signal with the control signal superimposed on the light. The subscriber terminal2100a-1receives the optical signal transmitted through the optical transmission path2600-1, and performs the initial settings according to the control signal set in the received optical signal.

Note that a splitter may be provided in the control signal superimposition unit1200, which is used as the control signal superimposition unit3210, between the transmission-reception separation device1210-1and the optical amplifier1220-1and between the transmission-reception separation device1210-2and the optical amplifier1220-2, or a splitter may be provided in the control signal superimposition unit1200a, which is used as the control signal superimposition unit3210, between the transmission-reception separation device1210a-1and the optical SW1250-1and between the transmission-reception separation device1210a-2and the optical SW1250-2, or a splitter may be provided in the control signal superimposition unit1200b, which is used as the control signal superimposition unit3210, between the transmission-reception separation device1210-1and the optical SW1250-1and between the transmission-reception separation device1210-2and the optical SW1250-2, such that the splitter may be used to split a part of an optical signal, and output it to the management and control functional unit2300. The management and control functional unit2300monitors a control signal set in the part of the split optical signal.

An optical SW may use different ports for transmission to and for reception from a single unit of subscriber terminal2100a.FIG.9is a diagram illustrating the configuration of an optical communication system3000awhen an optical SW uses different ports for transmission to and for reception from a single unit of subscriber terminal2100a. The optical communication system3000aillustrated inFIG.9is different from the optical communication system3000illustrated inFIG.8in that an optical GW3200ais provided instead of the optical GW3200, and the subscriber terminal2100ais connected to the optical transmission path2650instead of the optical transmission path2600. WhileFIG.9only illustrates a single unit of subscriber terminal2100a, a plurality of units of subscriber terminals2100acan possibly be connected to the optical GW3200a.

The optical GW3200aincludes a control signal superimposition unit3210aand the optical SW2210. WhileFIG.9illustrates only a single control signal superimposition unit3210a, the optical GW3200acan possibly include a plurality of control signal superimposition units3210a. The control signal superimposition unit3210aincludes a transmission-reception separation device3211, the splitters2221-1and2221-2, the optical amplifiers1220-1and1220-2, and the optical modulators1230-1and1230-2. The splitter2221-1, the optical amplifier1220-1, and the optical modulator1230-1are provided on the optical transmission path2600-n1between the transmission-reception separation device3211and the first port2211-n1of the optical SW2210. The splitter2221-2, the optical amplifier1220-2, and the optical modulator1230-2are provided on the optical transmission path2600-n2between the transmission-reception separation device3211and the first port2211-n2of the optical SW2210. The transmission-reception separation device3211is connected to the optical transmission path2650, and to the optical transmission paths2600-n1and2600-n2.

The transmission-reception separation device3211receives an input of an optical signal transmitted by the subscriber terminal2100afrom the optical transmission path2650, and outputs the input optical signal to the optical transmission path2600-n1. The splitter2221-1receives an input of the optical signal output by the transmission-reception separation device3211, and splits the input optical signal into parts. The splitter2221-1outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-1. The optical amplifier1220-1removes the control signal on the low-frequency side from the input optical signal, and outputs the optical signal to the optical modulator1230-1. The optical modulator1230-1superimposes a control signal, input from the management and control functional unit2300, on the optical signal input from the optical amplifier1220-1, and outputs the superimposed signal to the optical transmission path2600-n1.

The splitter2221-2receives an input of an optical signal addressed to the subscriber terminal2100afrom the optical SW2210, and splits the input optical signal into parts. The splitter2221-2outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the optical amplifier1220-2. The optical amplifier1220-2removes the control signal on the low-frequency side from the input optical signal, and outputs the optical signal to the optical modulator1230-2. The optical modulator1230-2superimposes a control signal, input from the management and control functional unit2300, on the optical signal input from the optical amplifier1220-2, and outputs the superimposed signal to the transmission-reception separation device3211. The transmission-reception separation device3211outputs the optical signal input from the optical modulator1230-2to the optical transmission path2650between the transmission-reception separation device3211and the subscriber terminal2100a.

If the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100a, then the control signal superimposition unit3210amay not be provided with the optical amplifier1220-1and the optical modulator1230-1. If the management and control functional unit2300does not superimpose a control signal on an optical signal addressed to the subscriber terminal2100a, then the control signal superimposition unit3210amay not be provided with the optical amplifier1220-2and the optical modulator1230-2.

There is a case where the subscriber terminal2100as a communication destination for the subscriber terminal2100ais connected to an optical GW3200a(described as “optical GW3200a-2”) different from the optical GW3200a(described as “optical GW3200a-1”) connected to the subscriber terminal2100a. In that case, the control signal superimposition unit3210ain the optical GW3200a-1may not be provided with the optical amplifier1220-2and the optical modulator1230-2, and simultaneously, the control signal superimposition unit3210ain the optical GW3200a-2may not be provided with the optical amplifier1220-2and the optical modulator1230-2. In this case, the control signal superimposition unit3210ain the optical GW3200a-1superimposes a control signal for the subscriber terminal2100as a communication destination on an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100as the communication destination. In addition, the control signal superimposition unit3210ain the optical GW3200a-2superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100as the communication destination to the subscriber terminal2100a.

Alternatively, the control signal superimposition unit3210ain the optical GW3200a-1may not be provided with the optical amplifier1220-1and the optical modulator1230-1, and simultaneously, the control signal superimposition unit3210ain the optical GW3200a-2may not be provided with the optical amplifier1220-1and the optical modulator1230-1. In this case, the control signal superimposition unit3210ain the optical GW3200a-2superimposes a control signal for the subscriber terminal2100as the communication destination on an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100as the communication destination. The control signal superimposition unit3210ain the optical GW3200a-1superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100as the communication destination to the subscriber terminal2100a.

According to the present embodiment, the optical communication system includes the control signal superimposition unit3210or3210a, so that even after the subscriber terminal2100has completed connection with its desired connection destination, the management and control functional unit2300can still transmit a control signal, such as a wavelength management and control signal, to the subscriber terminal2100. In addition, since each control signal superimposition unit3210or3210ais dedicated for each individual subscriber terminal2100, the management and control is more simplified compared to the second embodiment.

Fourth Embodiment

In the above embodiments, a control signal superimposed on an optical signal transmitted by a user terminal is eliminated by a filter somewhere along a communication path, and then an additional control signal is superimposed on the optical signal. In the present embodiment, a control signal superimposed on an optical signal transmitted by a user terminal is removed somewhere along a communication path by an inverted control signal, and then an additional control signal is superimposed on the optical signal.

FIG.10is a diagram illustrating the configuration of an optical communication system4000according to a fourth embodiment. The optical communication system4000includes a user terminal4100, a control signal superimposition unit4200, the management and control functional unit1300, and a user terminal4300. The user terminal4100and the user terminal4300are connected by an optical fiber4400. The control signal superimposition unit4200is provided on the optical fiber4400.

As the user terminal4100, an optical communication apparatus configured to transmit an optical signal according to the conventional technique can be used. The user terminal4100includes a signal mixer4110and an optical transmitter (Tx)4120. The signal mixer4110outputs the electrical signal E1to the Tx4120. In the electrical signal E1, the main signal M1and the control signal C1that are electrical signals with different frequencies have been superimposed on one another. The frequency of the control signal C1is lower than the frequency of the main signal M1. For example, as the control signal C1, the AMCC is used. The Tx4120converts the electrical signal E1to the optical signal G11, and outputs the optical signal G11to the optical fiber4400.

The control signal superimposition unit4200includes a splitter4210, a photo diode (PD)4220, a signal processing unit4230, an optical modulator4240, and an optical modulator4250. The splitter4210, the optical modulator4240, and the optical modulator4250are provided on the optical fiber4400.

The splitter4210receives an input of the optical signal G11output by the user terminal4100from the optical fiber4400. The splitter4210splits the input optical signal G11into parts, and outputs a part of the split optical signal G11to the PD4220, while outputting the remaining part of the split optical signal G11to the optical modulator4240.

The PD4220converts the part of the optical signal G11split by the splitter4210to an electrical signal E11, and outputs the converted electrical signal E11to the signal processing unit4230.

The signal processing unit4230reads the control signal C1from the electrical signal E11output by the PD4220, and generates an inverted signal E12that is the inverted control signal C1. The inverted signal E12is a signal with its phase inverted from the original control signal C1. Since the control signal C1falls within the low frequency range, it is possible for the signal processing unit4230to generate the inverted signal E12without performing costly signal processing. The signal processing unit4230outputs the generated inverted signal E12to the optical modulator4240.

The optical modulator4240is an LN modulator, an EA modulator, an SOA, or the like. The optical modulator4240modulates the optical signal G11input from the splitter4210again based on the inverted signal E12input from the signal processing unit4230, and removes the control signal C1from the optical signal G11. The main signal M1is set in the optical signal G12with the control signal C1removed. The optical modulator4240outputs the optical signal G12to the optical modulator4250.

The optical modulator4250superimposes the control signal C3, input from the management and control functional unit1300, on the low-frequency side of the optical signal G12to generate an optical signal G13, and outputs the optical signal G13to the user terminal4300. As the optical modulator4250, the optical modulator1230-1in the first embodiment illustrated inFIGS.1and2can be used.

As the user terminal4300, an optical communication apparatus configured to receive an optical signal according to the conventional technique can be used. The user terminal4300includes an optical receiver (Rx)4310and a signal divider4320. The Rx4310receives the optical signal G13, output by the control signal superimposition unit4200, from the optical fiber4400, converts the received optical signal G13to an electrical signal E13, and outputs the electrical signal E13. The signal divider4320separates the electrical signal E13, output by the Rx4310, into the main signal M1and the control signal C3based on their respective frequencies.

Note that some or all of the functional units in the control signal superimposition unit4200may be included in the management and control functional unit1300. According to the present embodiment, the optical communication system includes the control signal superimposition unit4200, so that even after connection between the user terminal4100and the user terminal4300has completed, the management and control functional unit1300can still transmit a control signal to the user terminal4300.

Although not illustrated inFIG.10, the PD4220or the signal processing unit4230may be connected to the management and control functional unit1300. The PD4220or the signal processing unit4230transmits information in a control signal superimposed in the user terminal4100to the management and control functional unit1300. This allows the management and control functional unit1300to monitor information in a control signal transmitted between user terminals.

Note that if the control signal superimposition unit4200does not superimpose a control signal, then the control signal superimposition unit4200allows a signal transmitted from the user terminal4100to directly pass through the transmission path without applying a signal to the optical modulator4240and the optical modulator4250. In this case, an SOA cannot be used in principle.

Fifth Embodiment

In the fourth embodiment, a control signal superimposed on an optical signal transmitted by a user terminal is removed somewhere along a communication path by an inverted control signal, and then an additional control signal is superimposed on the optical signal. In the present embodiment, an optical signal is modulated somewhere along a communication path by using a signal in which an inverted control signal and an additional control signal have been superimposed on one another. The present embodiment is described below, mainly focusing on the differences from the fourth embodiment.

FIG.11is a diagram illustrating the configuration of an optical communication system4000aof the present embodiment. The optical communication system4000aillustrated inFIG.11is different from the optical communication system4000of the fourth embodiment illustrated inFIG.10in that a control signal superimposition unit4200ais provided instead of the control signal superimposition unit4200.

The control signal superimposition unit4200aincludes the splitter4210, the PD4220, the signal processing unit4230, a superimposition unit4260, and an optical modulator4270. The superimposition unit4260outputs a superimposed signal E14to the optical modulator4270. The superimposed signal E14is an electrical signal obtained by superimposing the inverted signal E12input from the signal processing unit4230, and the control signal C3input from the management and control functional unit1300on one another. The optical modulator4270modulates the optical signal G11input from the splitter4210again based on the superimposed signal E14input from the superimposition unit4260, and generates the optical signal G13with the control signal C1removed and with the control signal C3superimposed on the main signal M1. The optical modulator4270outputs the generated optical signal G13to the user terminal4300.

Note that some or all of the functional units in the control signal superimposition unit4200amay be included in the management and control functional unit1300. According to the present embodiment, the number of optical modulators to be used in a control signal superimposition unit can be reduced, compared to the fourth embodiment.

In the same manner as in the fourth embodiment, the PD4220or the signal processing unit4230may be connected to the management and control functional unit1300. The PD4220or the signal processing unit4230transmits information in a control signal superimposed in the user terminal4100to the management and control functional unit1300. This allows the management and control functional unit1300to monitor information in a control signal transmitted between user terminals. Note that if the control signal superimposition unit4200adoes not superimpose a control signal, then the control signal superimposition unit4200aallows a signal transmitted from the user terminal4100to directly pass through the transmission path without applying a signal to the optical modulator4270.

Sixth Embodiment

In the present embodiment, an optical communication system that switches the wavelength to a different wavelength during communication between user terminals uses the control signal superimposition unit of the fifth embodiment or a sixth embodiment to superimpose a control signal somewhere along a communication path. The present embodiment is described below, mainly focusing on the differences from the above embodiments.

FIG.12is a diagram illustrating the configuration of an optical communication system5000according to the sixth embodiment. The optical communication system5000is different from the optical communication system2000of the second embodiment illustrated inFIG.6in that an optical GW5200is provided instead of the optical GW2200. The optical GW5200is different from the optical GW2200illustrated inFIG.6in that a control signal superimposition unit5220is provided instead of the control signal superimposition unit2220. In the optical GW5200, the control signal superimposition unit5220is provided on the optical transmission path2700-m(m is an integer equal to or larger than 2, and equal to or smaller than M), whileFIG.12illustrates only a single control signal superimposition unit5220. On some of the optical transmission paths2700-2to2700-M, the control signal superimposition unit5220may not be provided.

The control signal superimposition unit5220includes transmission-reception separation devices5221-1and5221-2, and superimposition units5222-1and5222-2. The transmission-reception separation device5221-1outputs an optical signal, output by the optical SW2210, to the superimposition unit5222-1, and outputs an optical signal, output by the superimposition unit5222-2, to the optical SW2210. The transmission-reception separation device5221-2outputs an optical signal, output by the superimposition unit5222-1, to an additional optical SW such as the optical SW2510, and outputs an optical signal, input from an additional optical SW such as the optical SW2510, to the superimposition unit5222-2.

The superimposition units5222-1and5222-2are either the control signal superimposition unit4200of the fourth embodiment illustrated inFIG.10or the control signal superimposition unit4200aof the fifth embodiment illustrated inFIG.11. The superimposition unit5222-1removes a control signal set by the subscriber terminal2100afrom an optical signal transmitted by the subscriber terminal2100a, and superimposes a control signal, output by the management and control functional unit2300, on the optical signal. In the superimposition unit5222-1, the splitter4210(FIGS.10and11) splits the optical signal input from the transmission-reception separation device5221-1into parts, while the optical modulator4250(FIG.10) or the optical modulator4270(FIG.11) outputs the optical signal to the transmission-reception separation device5221-2. The superimposition unit5222-2removes a control signal set by a transmission source of an optical signal addressed to the subscriber terminal2100afrom the optical signal, and superimposes a control signal, output by the management and control functional unit2300, on the optical signal. In the superimposition unit5222-2, the splitter4210(FIGS.10and11) splits the optical signal input from the transmission-reception separation device5221-2into parts, while the optical modulator4250(FIG.10) or the optical modulator4270(FIG.11) outputs the optical signal to the transmission-reception separation device5221-1.

Note that an optical SW may use different ports for transmission to and for reception from a single unit of subscriber terminal2100a.FIG.13is a diagram illustrating the configuration of an optical communication system5000awhen an optical SW uses different ports for transmission to and for reception from a single unit of subscriber terminal2100a. The optical communication system5000aillustrated inFIG.13is different from the optical communication system2000aillustrated inFIG.7in that an optical GW5200ais provided instead of the optical GW2200a. WhileFIG.13only illustrates a single unit of subscriber terminal2100a, a plurality of units of subscriber terminals2100acan possibly be connected to the optical GW5200a.

The optical GW5200aincludes the transmission-reception separation device2230, the optical SW2210, and a control signal superimposition unit5220a. WhileFIG.13illustrates only a single control signal superimposition unit5220a, the optical GW5200acan possibly include a plurality of control signal superimposition units5220a. The control signal superimposition unit5220ais different from the control signal superimposition unit2220aillustrated inFIG.7in that the superimposition unit5222-1is provided instead of the optical amplifier1220-1and the optical modulator1230-1, and the superimposition unit5222-2is provided instead of the optical amplifier1220-2and the optical modulator1230-2.

Operation of the optical communication system5000ais described below. An optical signal transmitted by the subscriber terminal2100ais output from the second port2212-m1of the optical SW2210in the same manner as the optical communication system2000aillustrated inFIG.7. The splitter2221-1in the control signal superimposition unit5220asplits the optical signal, output from the second port2212-m1by the optical SW2210, into parts. The splitter2221-1outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the superimposition unit5222-1. The management and control functional unit2300monitors a control signal set in the part of the optical signal split by the splitter2221-2.

The superimposition unit5222-1removes a control signal set by the subscriber terminal2100afrom the optical signal transmitted by the subscriber terminal2100a, and superimposes an additional control signal, output by the management and control functional unit2300, on the optical signal. The superimposition unit5222-1outputs the optical signal with the control signal removed and with the additional control signal superimposed to the transmission-reception separation device2222. The transmission-reception separation device2222outputs the signal, input from the superimposition unit5222-1, to an additional optical SW connected to the subscriber terminal2100b.

The transmission-reception separation device2222receives an input of an optical signal, transmitted by the subscriber terminal2100band addressed to the subscriber terminal2100a, from an additional optical SW, and outputs the input optical signal to the optical transmission path2700-m2. The splitter2221-2splits the optical signal input from the transmission-reception separation device2222into parts. The splitter2221-2outputs a part of the split optical signal to the management and control functional unit2300, while outputting the remaining part of the split optical signal to the superimposition unit5222-2. The management and control functional unit2300monitors a control signal set in the part of the optical signal split by the splitter2221-2.

The superimposition unit5222-2removes a control signal set by a counterpart subscriber terminal2100bfrom an optical signal addressed to the subscriber terminal2100a, and superimposes an additional control signal, output by the management and control functional unit2300, on the optical signal. The superimposition unit5222-2inputs the optical signal with the control signal removed and with the additional control signal superimposed to the second port2212-m2of the optical SW2210. The optical SW2210outputs the optical signal, input from the second port2212-m2, through the first port2211-n2corresponding to the subscriber terminal2100aas a destination of this optical signal. The transmission-reception separation device2230outputs the optical signal output from the first port2211-n2to the optical transmission path2650.

Note that if the management and control functional unit2300does not superimpose a control signal on an optical signal transmitted from the subscriber terminal2100a, then each of the control signal superimposition units5220and5220amay not be provided with the superimposition unit5222-1. If the management and control functional unit2300does not superimpose a control signal on an optical signal addressed to the subscriber terminal2100a, then each of the control signal superimposition units5220and5220amay not be provided with the superimposition unit5222-2.

There is a case where the subscriber terminal2100as a communication destination for the subscriber terminal2100ais connected to an optical GW5200or5200adifferent from the optical GW5200or5200aconnected to the subscriber terminal2100a. In that case, the superimposition unit5222-2may not be provided in the control signal superimposition unit5220or5220ain the optical GW5200or5200ato which the subscriber terminal2100ais connected, and simultaneously, the superimposition unit5222-2may not be provided in the control signal superimposition unit5220or5220ain the optical GW5200or5200ato which the subscriber terminal2100as a communication destination is connected. In this case, the control signal superimposition unit5220or5220ain the optical GW5200or5200a, to which the subscriber terminal2100ais connected, superimposes a control signal for the subscriber terminal2100as a communication destination on an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100as a communication destination. In addition, the control signal superimposition unit5220or5220ain the optical GW5200or5200a, to which the subscriber terminal2100as a communication destination is connected, superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100as a communication destination to the subscriber terminal2100a.

Likewise, there is a case where the subscriber terminal2100as a communication destination for the subscriber terminal2100ais connected to an optical GW5200or5200adifferent from the optical GW5200or5200aconnected to the subscriber terminal2100a. In that case, the superimposition unit5222-1may not be provided in the control signal superimposition unit5220or5220ain the optical GW5200or5200ato which the subscriber terminal2100ais connected, and simultaneously, the superimposition unit5222-1may not be provided in the control signal superimposition unit5220or5220ain the optical GW5200or5200ato which the subscriber terminal2100as a communication destination is connected. In this case, the control signal superimposition unit5220or5220ain the optical GW5200or5200a, to which the subscriber terminal2100as a communication destination is connected, superimposes a control signal for the subscriber terminal2100as a communication destination on an optical signal to be transmitted from the subscriber terminal2100ato the subscriber terminal2100b. In addition, the control signal superimposition unit5220or5220ain the optical GW5200or5200a, to which the subscriber terminal2100ais connected, superimposes a control signal for the subscriber terminal2100aon an optical signal to be transmitted from the subscriber terminal2100as a communication destination to the subscriber terminal2100a.

According to the present embodiment, the optical communication system includes the control signal superimposition unit5220or5220a, so that even after connection between the subscriber terminals2100has completed, the management and control functional unit2300can still transmit a control signal, such as a wavelength management and control signal, to the subscriber terminals2100.

Seventh Embodiment

In the sixth embodiment, a control signal is superimposed at the subsequent stage to an optical SW. In the present embodiment, a control signal is superimposed at the previous stage to an optical SW. The present embodiment is described below, mainly focusing on the differences from the above embodiments.

FIG.14is a diagram illustrating the configuration of an optical communication system6000according to a seventh embodiment. The optical communication system6000is different from the optical communication system3000of the third embodiment illustrated inFIG.8in that an optical GW6200is provided instead of the optical GW3200. The optical GW6200is different from the optical GW3200illustrated inFIG.8in that the control signal superimposition unit5220according to the sixth embodiment illustrated inFIG.12is provided instead of the control signal superimposition unit3210.

Note that the management and control functional unit2300may transmit a control signal for performing the initial settings on the subscriber terminal2100athrough the optical SW2210in the same manner as in the third embodiment, or may transmit the control signal superimposed by the control signal superimposition unit5220. In a case where a control signal is superimposed and transmitted by the control signal superimposition unit5220, the management and control functional unit2300outputs unmodulated light (or modulated light) to the optical SW2210, and further outputs the control signal to the control signal superimposition unit5220. The optical SW2210outputs the light input from the management and control functional unit2300to the optical transmission path2600. The control signal superimposition unit5220superimposes the control signal, input from the management and control functional unit2300, on the light input from the optical SW2210, and outputs the optical signal with the control signal superimposed to the subscriber terminal2100a.

Note that an optical SW may use different ports for transmission to and for reception from a single unit of subscriber terminal2100a.FIG.15is a diagram illustrating the configuration of an optical communication system6000awhen an optical SW uses different ports for transmission to and for reception from a single unit of subscriber terminal2100a. The optical communication system6000aillustrated inFIG.15is different from the optical communication system3000aillustrated inFIG.9in that an optical GW6200ais provided instead of the optical GW3200a. WhileFIG.15only illustrates a single unit of subscriber terminal2100a, a plurality of units of subscriber terminals2100acan possibly be connected to the optical GW6200a.

The optical GW6200aincludes a control signal superimposition unit6210and the optical SW2210. WhileFIG.15illustrates only a single control signal superimposition unit6210, the optical GW6200acan possibly include a plurality of control signal superimposition units6210. The control signal superimposition unit6210is different from the control signal superimposition unit3210aillustrated inFIG.9in that the superimposition unit5222-1is provided instead of the optical amplifier1220-1and the optical modulator1230-1, and the superimposition unit5222-2is provided instead of the optical amplifier1220-2and the optical modulator1230-2.

The superimposition unit5222-1removes a control signal set by the subscriber terminal2100afrom an optical signal transmitted by the subscriber terminal2100a, and superimposes a control signal, output by the management and control functional unit2300, on the optical signal. In the superimposition unit5222-1, the splitter4210(FIGS.10and11) splits an optical signal input from the optical transmission path2650into parts, and the optical modulator4250(FIG.10) or the optical modulator4270(FIG.11) outputs the optical signal to the optical SW2210. The superimposition unit5222-2removes a control signal from an optical signal addressed to the subscriber terminal2100a, and superimposes a control signal, output by the management and control functional unit2300, on the optical signal. In the superimposition unit5222-2, the splitter4210(FIGS.10and11) splits an optical signal input from the optical SW2210into parts, and the optical modulator4250(FIG.10) or the optical modulator4270(FIG.11) outputs the optical signal to the optical transmission path2650.

According to the present embodiment, even after the subscriber terminal2100has completed connection with its desired connection destination, the management and control functional unit2300can still transmit a control signal, such as a wavelength management and control signal, to the subscriber terminal2100. In addition, since each control signal superimposition unit5220or6210is dedicated for each individual subscriber terminal2100, the management and control is more simplified compared to the sixth embodiment.

Eighth Embodiment

In the present embodiment, a user utilizes multiple services.FIG.16is a diagram illustrating the configuration of an optical communication system7000according to an eighth embodiment. The optical communication system7000includes a user terminal7100, a control signal superimposition unit7200, the management and control functional unit1300, a wavelength division multiplexer7300, a user terminal7400, and a user terminal7500. The user terminal7100and the control signal superimposition unit7200are connected by an optical fiber7610. The wavelength division multiplexer7300is connected to the control signal superimposition unit7200by an optical fiber7620, connected to the user terminal7400by an optical fiber7630, and connected to the user terminal7500by an optical fiber7640.

The user terminal7100utilizes two or more services. An example case is now described in which the user terminal7100utilizes a service #1provided by the user terminal7400, and a service #2provided by the user terminal7500. For example, the user terminal7400provides a data communication service, while the user terminal7500provides a video-related service of analog signals and other signals. Note that the multiple services to be utilized by the user terminal7100are not limited to those described above, but the user terminal7100can utilize any service. These services use optical signals with different wavelengths. Any of the multiple services uses a low-frequency control signal.

The user terminal7100includes the signal mixer1110, the TRx1120, the signal divider1130, a TRx7110, and a wavelength division multiplexer7120. The signal mixer1110outputs, to the TRx1120, a transmission signal for the service #1in which the main signal M1and the control signal C1that are both electrical signals have been superimposed on one another. The TRx1120converts the transmission signal from an electrical signal to an optical signal, and outputs the optical signal to the wavelength division multiplexer7120. The TRx1120converts the optical signal for the service #1, input from the wavelength division multiplexer7120, to an electrical signal, and outputs the electrical signal. The signal divider1130separates the electrical signal converted by the TRx1120into the main signal and the control signal based on their respective wavelengths. The TRx7110converts a transmission signal for the service #2from an electrical signal to an optical signal, and outputs the optical signal to the wavelength division multiplexer7120. The TRx7110converts the optical signal for the service #2, input from the wavelength division multiplexer7120, to an electrical signal, and outputs the electrical signal.

The wavelength division multiplexer7120multiplexes the optical signal output by the TRx1120and the optical signal output by the TRx7110together, and outputs the multiplexed optical signal to the optical fiber7610. The wavelength division multiplexer7120receives an input of the optical signal transmitted through the optical fiber7610, and divides the input optical signal into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The wavelength division multiplexer7120outputs the optical signal for the service #1to the TRx1120, while outputting the optical signal for the service #2to the TRx7110.

The control signal superimposition unit7200is either the control signal superimposition unit1200of the first embodiment illustrated inFIGS.1and2, the control signal superimposition unit1200aof the first embodiment illustrated inFIG.3, the control signal superimposition unit1200bof the first embodiment illustrated inFIG.4, the control signal superimposition unit4200of the fourth embodiment illustrated inFIG.10, the control signal superimposition unit4200aof the fifth embodiment illustrated inFIG.11, or the control signal superimposition unit5220of the sixth embodiment illustrated inFIG.12.

The wavelength division multiplexer7300receives an input of an optical signal transmitted through the optical fiber7620, and divides the input optical signal into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The wavelength division multiplexer7300outputs the optical signal for the service #1to the optical fiber7630, while outputting the optical signal for the service #2to the optical fiber7640. The wavelength division multiplexer7120multiplexes the optical signal for the service #1transmitted through the optical fiber7630, and the optical signal for the service #2transmitted through the optical fiber7640together, and outputs the multiplexed optical signal to the optical fiber7620.

The user terminal7400includes a TRx7410. The TRx7410converts the optical signal for the service #1transmitted through the optical fiber7630to an electrical signal, and converts the electrical signal for the service #1to an optical signal to output the optical signal to the optical fiber7630. As the user terminal7400, for example, the user terminal1100may be used.

The user terminal7500includes a TRx7510. The TRx7510converts the optical signal for the service #2transmitted through the optical fiber7640to an electrical signal, and converts the electrical signal for the service #2to an optical signal to output the optical signal to the optical fiber7640.

Operation of the optical communication system7000is described below. The user terminal7100outputs an optical signal obtained by multiplexing an optical signal for the service #1and an optical signal for the service #2together. In the optical signal for the service #1, the main signal M1and the control signal C1that are both electrical signals have been superimposed on one another. The control signal superimposition unit7200removes the control signal C1for the service #1from the optical signal transmitted by the user terminal7100, and superimposes the control signal C3-1, output by the management and control functional unit1300, on the optical signal to output the superimposed optical signal to the optical fiber7620.

The wavelength division multiplexer7300divides the optical signal output by the control signal superimposition unit7200into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The wavelength division multiplexer7300outputs the optical signal for the service #1to the optical fiber7630, while outputting the optical signal for the service #2to the optical fiber7640. The TRx7410in the user terminal7400receives the optical signal for the service #1to convert the optical signal to an electrical signal, and separates the electrical signal into the main signal M1and the control signal C3-1. The TRx7510in the user terminal7500converts an electrical signal for the service #2to an optical signal.

The TRx7410in the user terminal7400converts the electrical signal for the service #1to an optical signal, and outputs the converted optical signal. The TRx7410may convert an electrical signal, in which the main signal M2and the control signal C2have been superimposed on one another, to an optical signal. The TRx7510in the user terminal7500converts the electrical signal for the service #2to an optical signal, and outputs the converted optical signal. The wavelength division multiplexer7300multiplexes the optical signal for the service #1output by the user terminal7400, and the optical signal for the service #2output by the user terminal7500together, and outputs the multiplexed optical signal to the optical fiber7620.

The control signal superimposition unit7200removes the control signal C2for the service #1from the optical signal output by the wavelength division multiplexer7300, and superimposes the control signal C3-2, output by the management and control functional unit1300, on the optical signal to output the superimposed optical signal to the optical fiber7610. The wavelength division multiplexer7120in the user terminal7100receives an input of the optical signal output by the control signal superimposition unit7200, and divides the input optical signal into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The TRx1120receives the optical signal for the service #1to convert the optical signal to an electrical signal. The signal divider1130separates the electrical signal converted by the TRx1120into the main signal M2and the control signal C3-2. The TRx7110converts an electrical signal for the service #2to an optical signal.

Ninth Embodiment

In the eighth embodiment, optical signals for multiple services are multiplexed into an optical signal to be input to the control signal superimposition unit. In the present embodiment, an optical signal for a control-signal rewriting service, which is one of the multiple services to be utilized by a user, is input to the control signal superimposition unit. In the present embodiment, the differences from the eighth embodiment are mainly described below.

FIG.17is a diagram illustrating the configuration of an optical communication system7000aaccording to a ninth embodiment. The optical communication system7000aincludes the user terminal7100, a wavelength division multiplexer7600, the control signal superimposition unit7200, the user terminal7400, and a service providing apparatus7700. The wavelength division multiplexer7600is connected to the user terminal7100by an optical fiber7810, connected to the control signal superimposition unit7200by an optical fiber7820, and connected to the service providing apparatus7700by an optical fiber7830. The user terminal7400is connected to the control signal superimposition unit7200by an optical fiber7840.

The wavelength division multiplexer7600receives an input of an optical signal transmitted through the optical fiber7810, and divides the input optical signal into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The wavelength division multiplexer7600outputs the optical signal for the service #1to the optical fiber7820, while outputting the optical signal for the service #2to the optical fiber7830. The wavelength division multiplexer7600multiplexes the optical signal for the service #1transmitted through the optical fiber7820, and the optical signal for the service #2transmitted through the optical fiber7830together, and outputs the multiplexed optical signal to the optical fiber7810.

The service providing apparatus7700provides the service #2. The service providing apparatus7700may be installed on the network such as in a communications station in the same manner as the control signal superimposition unit7200. The service providing apparatus7700includes a TRx7710. The TRx7710converts the optical signal for the service #2transmitted through the optical fiber7830to an electrical signal, and converts the electrical signal for the service #2to an optical signal to output the optical signal to the optical fiber7830.

Operation of the optical communication system7000ais described below. In the same manner as in the eighth embodiment, the user terminal7100outputs an optical signal obtained by multiplexing an optical signal for the service #1and an optical signal for the service #2together. In the optical signal for the service #1, the main signal M1and the control signal C1that are both electrical signals have been superimposed on one another. The wavelength division multiplexer7600divides the optical signal output by the user terminal7100into an optical signal for the service #1and an optical signal for the service #2based on their respective wavelengths. The wavelength division multiplexer7600outputs the optical signal for the service #1to the optical fiber7820, while outputting the optical signal for the service #2to the optical fiber7830. The TRx7710in the service providing apparatus7700converts an electrical signal for the service #2to an optical signal. The control signal superimposition unit7200removes the control signal C1from the optical signal for the service #1divided by the wavelength division multiplexer7600, and superimposes the control signal C3-1, output by the management and control functional unit1300, on the optical signal to output the superimposed optical signal to the optical fiber7840. The TRx7410in the user terminal7400receives the optical signal for the service #1to convert the optical signal to an electrical signal, and separates the electrical signal into the main signal M1and the control signal C3-1.

The TRx7410in the user terminal7400converts the electrical signal for the service #1to an optical signal, and outputs the converted optical signal. The TRx7410may convert an electrical signal, in which the main signal M2and the control signal C2have been superimposed on one another, to an optical signal. The control signal superimposition unit7200removes the control signal C2for the service #1from the optical signal output by the user terminal7400, and superimposes the control signal C3-2, output by the management and control functional unit1300, on the optical signal to output the superimposed optical signal to the optical fiber7820.

In contrast, the TRx7710in the service providing apparatus7700converts the electrical signal for the service #2to an optical signal, and outputs the optical signal. The wavelength division multiplexer7600multiplexes the optical signal for the service #1output by the control signal superimposition unit7200, and the optical signal for the service #2output by the service providing apparatus7700together, and outputs the multiplexed optical signal to the optical fiber7810. The user terminal7100receives an input of the optical signal output by the wavelength division multiplexer7600to perform the same processing as in the eighth embodiment.

Note that each of the control signal superimposition units1200,1200a,1200b,2220,2220a,3210,3210a,4200,4200a,5220,5220a,6210, and7200may be provided physically in a single unit of signal control apparatus, or may be virtually a single unit of signal control apparatus made up of physically distributed functional units.

A user terminal configured to perform optical communication according to the conventional technique superimposes a main signal and a control signal on one another in the form of an electrical signal, converts the superimposed electrical signal to an optical signal, and then transmits the optical signal. Due to this operation, the user terminal cannot extract only a control signal from the optical signal, cannot add another control signal, or cannot rewrite the control signal somewhere along a communication path. In order to change the optical wavelength to be used by a user terminal, it is necessary to make a change to the settings of the optical wavelength directly on the user terminal. This makes it difficult for telecommunications carriers and other providers who provide communication services to flexibly change the wavelength through the network. According to the embodiments described above, a control signal provided to a user terminal is removed from an optical signal somewhere along a communication path of the optical signal, and then another control signal is superimposed on the optical signal. In the manner as described above, it is possible to replace a portion of the signal superimposed on the optical signal with a different signal somewhere along the communication path. Thus, this makes it possible for telecommunications carriers and other providers to flexibly transmit a control signal that instructs a user terminal to make a change to the settings, and to allow the user terminal to change the wavelength and other settings.

According to the embodiments described above, an optical signal processing apparatus includes a removal unit and a superimposition unit. The removal unit receives, from a first optical transmission path, an optical signal converted from an electrical signal, in which a first signal and a second signal having different frequencies from each other have been superimposed, and removes the second signal from the optical signal which has been input. The superimposition unit superimposes a third signal having a frequency different from a frequency of the first signal in an electricity field on the optical signal in which the second signal removed by the removal unit, and outputs the optical signal in which the third signal has been superimposed to a second optical transmission path. For example, the superimposition unit is either of the optical modulators1230-1,1230-2,4250, and4270described in the above embodiments.

As the removal unit, an amplifier having lower response characteristics to a frequency of the second signal than response characteristics to a frequency of the first signal can be used. For example, the removal unit is either of the optical amplifiers1220-1and1220-2described in the above embodiments.

The removal unit may read the second signal from the optical signal which has been input from the first optical transmission path, modulate the optical signal by using an inverted signal obtained by inverting the second signal which has been read, and remove the second signal from the optical signal. For example, the removal unit is the PD4220, the signal processing unit4230, and the optical modulator4240described in the above embodiments.

The removal unit may read the second signal from the optical signal which has been input from the first optical transmission path, and generate an inverted signal by inverting the second signal which has been read. The superimposition unit modulates the optical signal which has been input from the first optical transmission path by using a signal, in which the inverted signal and the third signal have been superimposed, so as to remove the second signal from the optical signal and to superimpose the third signal on the optical signal. For example, the removal unit is the PD4220and the signal processing unit4230described in the above embodiments, while the superimposition unit is the superimposition unit4260and the optical modulator4270.

Each of the second signal and the third signal may have a frequency lower than or higher than a frequency of the first signal. The first signal may be a main signal, while the second signal and the third signal may be control signals.

The embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, but may also cover the design and the like without departing from the scope of the present invention.

REFERENCE SIGNS LIST

1000,2000,2000a,3000,3000a,4000,4000a,5000,5000a,6000,6000a,7000,7000aOptical communication system1100-1,1100-2,4100,4300,7100,7400,7500User terminal1110,1110-1,1110-2,4110Signal mixer1120,1120-1,1120-2,7110,7410,7510,7710Optical transceiver1130,1130-1,1130-2,4320Signal divider1200,1200a,1200b,2220,2220a,3210,3210a,4200,4200a,5220,5220a,6210,7200Control signal superimposition unit1210-1,1210-2,1210a-1,1210a-2,2222,2230,3211,5221-1,5221-2,6222-2Transmission-reception separation device1220-1,1220-2Optical amplifier1230-1,1230-2,4240,4250,4270Optical modulator1240-1,1240-2,1260-1,1260-2,1270-1,1270-2,1280-1,1280-2,1295-1,1295-2,1500-1,1500-2,4400,7610,7620,7630,7640,7810,7820,7830,7840Optical fiber1250-1,1250-2,1290-1,1290-2,2210,2510Optical switch1300,2300Management and control functional unit2100a,2100a-1to2100a-3,2100bSubscriber terminal2200,2200a,2500,3200,3200a,5200,5200a,6200,6200aOptical gateway2211-1to2211-N,2211-n1,2211-n2,2511First port2212-1to2212-M,2212-m1,2212-m2,2512Second port2221-1,2221-2Splitter2400Optical SW control functional unit2600-n1,2600-n2,2650,2700-1to2700-3,2700-m1,2700-m2Optical transmission path4120Optical transmitter4210Splitter4230Signal processing unit4260,5222-1,5222-2Superimposition unit4310Optical receiver7120,7300,7600Wavelength division multiplexer7700Service providing apparatus