OPTICAL COMMUNICATION SYSTEM, CONTROL APPARATUS AND OPTICAL COMMUNICATION METHOD

An optical switch having a plurality of ports outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that another one of the plurality of ports according to a transmission path of an optical signal. An optical branching part branches an optical signal which has been output from a second port in accordance with a branching ratio. A measurement part measures a round trip time by transmitting and receiving an optical signal to and from an optical communication device through an optical switch, and calculates a transmission distance of the optical signal on the basis of the measured round trip time. An instruction part instructs, the optical branching part, of the branching ratio determined on the basis of the calculated transmission distance.

TECHNICAL FIELD

The present invention relates to an optical communication system, a control apparatus and an optical communication method.

BACKGROUND ART

The International Telecommunication Union Telecommunication (ITU-T) Standardization sector G.989.2 recommendations define Point to Point (PtP) Wavelength Division Multiplexing (WDM)-Passive Optical Network (PON) (refer to, for example, NPL 1). In the PtP WDM-PON system, communication is performed using different optical wavelengths for each ONU in the upstream direction and the downstream direction. The upstream direction is the direction from the ONU to the OLT. The downstream direction is the direction from the OLT to the ONU.

As described in NPL 1, in the PtP WDM-PON system, it is stipulated that a management control signal called Auxiliary Management and Control Channel (AMCC) is used as a signal for management and control used between the OLT and ONU. An AMCC signal is a signal which is superimposed on a main signal and transmitted after information to be transmitted is modulated in a predetermined manner. When the AMCC signal is superimposed on the main signal and transmitted, the OLT and the ONU can transmit a signal for management and control within the wavelength band of the optical wavelength used for the main signal. That is to say, management and control are realized without using a dedicated optical wavelength band for management and control. A wavelength determination process in which upstream and downstream optical wavelengths are determined is performed using the AMCC signal.

FIG.10is a diagram showing a configuration example of a PtP WDM-PON system.FIG.10shows a configuration relating to superimposition of an AMCC signal. An OLT and an ONU include a management control part. The AMCC signals are superimposed in the optical stage and separated in the electrical stage.FIG.11shows an example of an optical signal transmitted from an ONU or an OLT. The transmitted optical signal is the main signal on which the management control signal is superimposed. When the management control signal is superimposed on the optical signal, intensity modulation is added to the envelope of the main signal as shown inFIG.11. The main signal is a high-speed signal with a data rate on the order of gigabits per second (Gb/s). On the other hand, the management control signal is expected to be a low-speed signal with a data rate on the order of kilobits per second (kb/s) (for example, NPL 2).

On the other hand, the All-Photonics Network (APN) is an innovative network based on photonics technology. In the APN, optical nodes relay optical backbone networks and optical access networks to provide end-to-end optical paths for each service. For example, the optical node is assumed to be an optical Switch (SW) or the like.

FIG.12is a diagram showing a configuration of an optical communication system in APN (refer to, for example, NPL 3). The optical communication system shown inFIG.12has a user terminal92, an optical GW (optical gateway)93, and an APN controller96. The two optical GWs93are described as optical GWs93-1and93-2. Three user terminals92connected to an optical GW93-n(n=1, 2) are respectively described as user terminals92-n-1to92-n-3. The user terminal92includes an optical transceiver (TRx). The optical GW93-nhas an optical SW94-nand a wavelength multiplexing/demultiplexing part95-n. The optical GW93-1and the optical GW93-2are connected using an optical transmission line97via a wavelength multiplexing/demultiplexing part95-1and a wavelength multiplexing/demultiplexing part95-2.

The optical SW94-noutputs light input from a first port941from a second port942and outputs light input from a second port942from a first port941. Each second port942of the optical SW94-nis connected to the wavelength multiplexing/demultiplexing part95-n, but may be connected to another second port942. An Arrayed Waveguide Grating (AWG) is, for example, used for the wavelength multiplexing/demultiplexing part95-n. The wavelength multiplexing/demultiplexing part95-nmultiplexes optical signals of a plurality of wavelengths input from each second port942of the optical SW94-nand outputs the multiplexed signal to the optical transmission line97. Also, the wavelength multiplexing/demultiplexing part95-nreceives an optical signal from the optical transmission line97, demultiplexes the input optical signal, and outputs the demultiplexed signals to the optical SW94-n.

It is possible to select the transmission path through which the optical signal is transmitted by setting the connection relationship between the first ports941and the second ports942of each of the optical SW94-1and the optical SW94-2. The APN controller96determines the transmission/reception wavelength of each user terminal92and the port connection relationship between the first ports941and the second ports942of each of the optical SWs94-1and94-2. The APN controller96instructs the user terminals92on transmission/reception wavelengths in accordance with these determinations and instructs the optical SW94-1and optical SW94-2on the port connection relationship. InFIG.12, a user terminal92-1-1and a user terminal92-1-2communicate and a user terminal92-1-3and a user terminal92-2-3communicate. Different wavelengths are used for these communications.

CITATION LIST

Non Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the APN, management control information is superimposed on the main signal by superimposing the AMCC signal which is slower than the main signal. Therefore, in order for the APN controller to acquire the management control information from the user terminal, it is assumed that the AMCC signal is extracted in the middle of the transmission path between the user terminals. However, in many cases, the transmission distance from each user terminal to the optical GW is different. For this reason, if light is extracted from the transmission paths of different user terminals at the same branching ratio, there are cases in which the APN controller branches off extra light that exceeds the minimum photosensitivity at which the AMCC signal can be received. When extra light is branched off, the light energy used for transmitting the main signal to the end user becomes inefficient. For this reason, there is a possibility that the transmission distance of the main signal will not be able to be maximized. It is expected that the transmission distance of the main signal will be made longer by minimizing the power of the branched light within the range in which the APN controller can receive the AMCC signal.

For example, in the case ofFIG.12, the transmission distance from user terminal92-1-1to the optical GW93-1is longer than the transmission distance from the user terminal92-1-3to the optical GW93-1. Splitters98are provided in the optical transmission lines between the optical SW94-1and the wavelength multiplexing/demultiplexing part95-1. The splitter98which branches the optical signal transmitted by the user terminal92-1-1uses a branching ratio in which the APN controller96is able to receive the optical signal from the user terminal92-1-1. This branching ratio is also applied to the splitter98which branches the optical signal transmitted by the user terminal92-1-3. Thus, excess light is extracted from the optical signal transmitted by the user terminal92-1-3, which may result in inefficiency in energy efficiency.

In view of the above circumstances, an object of the present invention is to provide an optical communication system, a control apparatus and an optical communication method capable of branching an optical signal having the power necessary for light reception while minimizing reduction in the power of an optical signal transmitted through a transmission path.

Solution to Problem

An optical communication system according to an aspect of the present invention includes: an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to a transmission path of the optical signal; an optical branching part which branches the optical signal which has been output from the second port in accordance with a branching ratio; a measurement part which measures a round trip time by transmitting and receiving an optical signal to and from the optical communication device through the optical switch and calculates a transmission distance of the optical signal on the basis of the measured round trip time; and an instruction part which instructs, the optical branching part, of a branching ratio determined on the basis of the calculated transmission distance.

An optical communication system according to an aspect of the present invention includes: an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to a transmission path of the optical signal; an optical branching part which branches the optical signal which has been output from the second port in accordance with a branching ratio; a measurement part which measures an optical intensity of the branched optical signal; and an instruction part which instructs the optical branching part to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

A control apparatus according to an aspect of the present invention includes: a measurement part which measures a round trip time by transmitting and receiving optical signals to and from the optical communication device through an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to the transmission path of the optical signal, and calculates a transmission distance of an optical signal on the basis of the measured round trip time; and an instruction part which instructs, an optical branching part which branches the optical signal which has been output from the second port in accordance with the branching ratio, of the branching ratio determined on the basis of the calculated transmission distance.

A control apparatus according to an aspect of the present invention includes: a measurement part which measures an optical intensity of an optical signal branched at an optical branching part which branches, in accordance with a branching ratio, an optical signal which has been output from a second port of an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from the second port that is another one of the plurality of ports according to a transmission path of the optical signal; and an instruction part which instructs the optical branching part to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

An optical communication method according to an aspect of the present invention includes: a switching step of outputting, by an optical switch having a plurality of ports, an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to a transmission path of the optical signal; a branching step of branching, by an optical branching part, the optical signal which has been output from the second port in accordance with a branching ratio; a measuring step of measuring, by a measurement part, a round trip time by transmitting and receiving an optical signal to and from the optical communication device through the optical switch and calculating a transmission distance of an optical signal on the basis of the measured round trip time; and an instruction step of instructing, the optical branching part, of the branching ratio determined on the basis of the calculated transmission distance.

An optical communication method according to an aspect of the present invention includes: a switching step of outputting, by an optical switch having a plurality of ports, an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to a transmission path of the optical signal; a branching step of branching, by an optical branching part, the optical signal which has been output from the second port in accordance with a branching ratio; a measuring step of measuring, by a measurement part, an optical intensity of the branched optical signal; and an instruction step of instructing, by an instruction part, the optical branching part to change the branching ratio so that the measured light intensity approaches a predetermined light intensity.

An optical communication method according to an aspect of the present invention includes: a measuring step in which measuring a round trip time by transmitting and receiving optical signals to and from the optical communication device through an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to the transmission path of the optical signal, and a transmission distance of an optical signal is calculated on the basis of the measured round trip time; and an instruction step of instructing, an optical branching part which branches the optical signal which has been output from the second port in accordance with the branching ratio, of the branching ratio determined on the basis of the calculated transmission distance.

An optical communication method according to an aspect of the present invention includes: a measuring step in which measures an optical intensity of an optical signal branched at an optical branching part which branches, in accordance with a branching ratio, an optical signal which has been output from a second port of an optical switch which has a plurality of ports and outputs an optical signal received from a first port that is one of the plurality of ports connected to an optical communication device from the second port that is another one of the plurality of ports according to a transmission path of the optical signal is measured; and an instruction step of instructing the optical branching part to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

Advantageous Effects of Invention

According to the present invention, it is possible to branch an optical signal having a power necessary for light reception while minimizing reduction in the power of the optical signal transmitted through the transmission path.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that the same constituent elements in a plurality of drawings will be denoted by the same reference and description thereof will be omitted.

This embodiment is applicable to, for example, an optical communication system which superimposes a management control signal of an AMCC signal on a high-speed main signal and transmits the superimposed signal. Such an optical communication system has a splitter for branching an optical signal on an optical transmission line for transmitting the optical signal between user terminals to extract the AMCC signal. The optical communication system of this embodiment makes the branching ratio of the optical signal in the splitter variable in accordance with the transmission distance between the user terminal and the optical GW. That is to say, the control apparatus of the optical communication system sets the branching ratio of the splitter to achieve the minimum light sensitivity at which the AMCC signal can be received. Thus, the deterioration of the power of the optical signal is suppressed as much as possible and the transmission distance of the main signal is maximized.

First Embodiment

FIG.1is a diagram showing a configuration of an optical communication system1according to a first embodiment. The optical communication system1has user terminals2, an optical GW3, and a control apparatus7. The number of user terminals2included in the optical communication system1is arbitrary. InFIG.1, two user terminals2are described as user terminals2-1and2-2. The optical GW3is connected to an optical network (not shown) via an optical transmission line P10. For example, an optical network is connected to a device with which the user terminal2communicates or an optical network is connected to a network which accommodates a device with which the user terminal2communicates. The direction from the user terminal2to the optical GW3is described as upstream and the direction from the optical GW3to the user terminal2is described as a downstream.

The user terminal2transmits and receives optical signals. A user terminal in the related art can be used as the user terminal2. The user terminal2shown inFIG.1is a two-core optical transmission/reception device. The user terminal2is connected to the optical GW3via an optical transmission line P1and an optical transmission line P2. The optical transmission line P1and the optical transmission line P2are, for example, two optical fibers in one two-core optical fiber cable. The user terminal2has an optical transceiver (TRx)21.

The optical transmission/reception part21is a wavelength variable optical transmitter/receiver. For example, the optical transmission/reception part21is an optical transceiver which mutually converts an optical signal and an electrical signal. The user terminal2can select a wavelength according to a transmission/reception destination and set it in the optical transmission/reception part21. For example, the user terminal2sets the wavelengths to be used for the upstream optical signal and the downstream optical signal in the optical transmission/reception part21in accordance with the instruction received from the control apparatus7. The optical transmission/reception part21transmits/receives an optical signal in which a management control signal of an AMCC signal is superimposed on a main signal. Specifically, the optical transmission/reception part21converts a transmission signal in which a main signal of an electric signal and a management control signal of a lower frequency electric signal than the main signal are superimposed into an optical signal to generate an upstream optical signal and outputs the generated upstream optical signal to the optical transmission line P1. Furthermore, the optical transmission/reception part21receives a downstream optical signal from the optical transmission line P2and converts the received downstream optical signal into an electrical signal. The optical transmission/reception part21separates the main signal and the management control signal of the AMCC signal from the signal converted into the electrical signal.

Note that the user terminal2may be a single-core optical transmission/reception device. In this case, the optical transmission/reception part21is connected to the optical GW3through one optical transmission line.

The optical GW3has a separation part31, a separation part32, an optical SW4, an optical branching part5, and a wavelength multiplexing/demultiplexing part6. The optical GW3has one or more separation parts31, one or more optical branching parts5, and one or more wavelength multiplexing/demultiplexing parts6.

The separation part31and the separation part32separate upstream optical signals and downstream optical signals. The separation part31and the separation part32can be implemented by, for example, a circulator or an upper/lower separation filter.

The separation part31is connected to the user terminal2using the optical transmission lines P1and P2and is connected to the optical SW4using the optical transmission line P3. The separation part31outputs the upstream optical signal input from the optical transmission line P1to the optical transmission line P3and outputs the downstream optical signal input from the optical transmission line P3to the optical transmission line P2.

The separation part32is connected to the optical SW4using the optical transmission line P4and is connected to the optical transmission/reception part (TRx)71of the control apparatus7using the optical transmission lines P5and P6. The separation part32outputs the upstream optical signal input from the optical transmission line P4to the optical transmission line P5and outputs the downstream optical signal input from the optical transmission line P6to the optical transmission line P4.

The optical SW4has a plurality of first ports41and a plurality of second ports42. The optical SW4outputs an optical signal of a predetermined wavelength input from the first port41to the second port42according to the transmission path to the destination of the optical signal. Also, the optical SW4outputs an optical signal of a predetermined wavelength input from the second port42to the first port41according to the transmission path to the destination of the optical signal. The optical SW4can change the connection between the first ports41and the second ports42. The connection relationship between the first ports41and the second ports42is referred to as a port connection relationship. For example, the optical SW4changes the port connection relationship in accordance with instructions from the control apparatus7. The one or more first ports41are connected to the user terminal2via the optical transmission lines P1, P2, and P3and the separation part31. The one or more second ports42are connected to the optical transmission/reception part71of the control apparatus7via the optical transmission lines P4, P5, and P6and the separation part32and other one or more second ports42are connected to the wavelength multiplexing/demultiplexing part6via an optical transmission line P4. A second port42connected to the optical transmission/reception part71of the control apparatus7is referred to as a second setting port42.

The optical branching part5is provided on the optical transmission line P4between the optical SW4and the wavelength multiplexing/demultiplexing part6. There may be an optical transmission line P4in which the optical branching part5is not provided. The optical branching part5has a separation part51, an optical branching switch52, and a separation part53. The separation part51and the separation part53are connected using an optical transmission line P7and an optical transmission line P8. The optical branching switch52is provided on the optical transmission line P7.

The separation part51separates the upstream optical signal and the downstream optical signal. The separation part51can be implemented by, for example, a circulator or an upper/lower separation filter. The separation part51receives the upstream optical signal output from the second port42of the optical SW4through the optical transmission line P4and outputs the received upstream optical signal to the optical transmission line P7. Furthermore, the separation part51receives the downstream optical signal output from the separation part53via the optical transmission line P8and outputs the received downstream optical signal to the optical transmission line P4.

The optical branching switch52branches the upstream optical signal transmitted through the optical transmission line P7in accordance with the set branching ratio. The branching ratio is instructed from the control apparatus7. Any optical branching device can be used for the optical branching switch52as long as the optical branching ratio can be varied. For example, the optical branching switch52may be an evanescent coupling type optical coupler, a fusion drawing type coupler whose length can be changed in a longitudinal direction, a planar lightwave circuit (PLC), or the like. The optical branching switch52outputs the branched optical signal to the control apparatus7via the optical transmission line P9. The upstream optical signal which is not branched using the optical branching switch52is transmitted through the optical transmission line P7and input to the separation part53.

The separation part53separates the upstream optical signal and the downstream optical signal. The separation part53can be realized using a circulator, an upper/lower separation filter, or the like, similarly to the separation part51. The separation part53receives the upstream optical signal from the optical transmission line P7and outputs the received upstream optical signal to the optical transmission line P4between the separation part53and the wavelength multiplexing/demultiplexing part6. Also, the separation part53receives the downstream optical signal output from the wavelength multiplexing/demultiplexing part6from the optical transmission line P4and outputs the received downstream optical signal to the optical transmission line P8.

The wavelength multiplexing/demultiplexing part6has a plurality of first ports (not shown) and one second port (not shown). A plurality of first ports of the wavelength multiplexing/demultiplexing part6correspond to different wavelengths. The first ports of the wavelength multiplexing/demultiplexing part6are respectively connected to the different second ports42of the optical SW4via the optical transmission line P4. A second port of the wavelength multiplexing/demultiplexing part6is connected to the optical transmission line P10. The wavelength multiplexing/demultiplexing part6multiplexes upstream optical signals of different wavelengths input from the optical SW4through a plurality of first ports and outputs the multiplexed optical signal from the second port. Furthermore, the wavelength multiplexing/demultiplexing part6receives the downstream optical signal transmitted through the optical transmission line P10from the second port and demultiplexes the received downstream optical signal into optical signals of different wavelengths. The wavelength multiplexing/demultiplexing part6outputs the demultiplexed downstream optical signals from different first ports. For example, the wavelength multiplexing/demultiplexing part6is an arrayed waveguide grating (AWG).

The control apparatus7is, for example, an APN controller. The control apparatus7includes an optical transmission/reception part (TRx)71, an optical reception part (Rx)72, and a control part73. One or both of the optical transmission/reception part71and the optical reception part72may be provided outside the control apparatus7and may be provided in, for example, the optical GW3. Furthermore, the control apparatus7may include a plurality of optical transmission/reception parts71and a plurality of optical reception parts72, respectively. When the control apparatus7includes a plurality of optical transmission/reception parts71, the optical transmission/reception parts71are connected to different second setting ports42. When the control apparatus7includes the plurality of optical reception parts72, the optical reception parts72is connected to different optical branching parts5.

The optical transmission/reception parts71transmits and receives optical signals. The optical transmission/reception parts71may be a wavelength variable optical transmitter/receiver or a fixed wavelength optical transmitter/receiver. The functions of the optical transmission/reception part71are the same as those of the optical transmission/reception part21of the user terminal2. The optical transmission/reception part71is connected to the second setting port42of the optical SW4via the optical transmission lines P4, P5, and P6and the separation part32. The optical transmission/reception part71outputs an optical signal addressed to the user terminal2to the optical SW4. Furthermore, the optical transmission/reception part71receives an optical signal transmitted from the user terminal2and output from the second setting port42of the optical SW4. The optical signal transmitted/received by the optical transmission/reception part71is a management control signal of the AMCC signal.

The optical reception part72receives an optical signal. The optical reception part72may be a wavelength variable optical receiver or a fixed wavelength optical receiver. An optical transceiver such as an optical transmitter/receiver may be used as the optical reception part72. The optical reception part72receives the optical signal branched by the optical branching part5from the optical transmission line P9and converts the received downstream optical signal into an electrical signal. The optical reception part72separates the management control signal of the AMCC signal from the signal which has been converted into the electrical signal.

The control part73includes a measurement part74, a path control part75, and an instruction part76. The path control part75determines allocation resources such as transmission paths and transmission/reception wavelengths used by each user terminal2. The path control part75instructs the user terminal2on the transmission/reception wavelength on the basis of the determined allocated resource. Furthermore, the path control part75instructs the optical SW4regarding the port connection relationship between the first port41and the second port42of the optical SW4on the basis of the determined allocated resources.

The measurement part74transmits an AMCC management control signal from the optical transmission/reception part71to the user terminal2and receives, from the user terminal2, a response signal of the transmitted management control signal. The measurement part74measures the transmission distance between the control apparatus7and the user terminal2on the basis of the difference between the transmission time of the management control signal and the reception time of the response signal. The transmission distance between the optical SW4and the control apparatus7is very short compared to the transmission distance between the control apparatus7and the user terminal2. For this reason, the measured transmission distance between the control apparatus7and the user terminal2is regarded as the transmission distance between the user terminal2and the optical SW4. Also, since the transmission distance between the optical SW4and the optical branching part5is short, the transmission distance between the user terminal2and the optical SW4is regarded as the transmission distance between the user terminal2and the optical branching part5. Note that, when the transmission distance between the optical SW4and the control apparatus7is known, the measurement part74may subtract the transmission distance between the optical SW4and the control apparatus7from the measured transmission distance between the control apparatus7and the user terminal2and calculate the transmission distance between the user terminal2and the optical SW4. Thus, even when the transmission distance between the optical SW4and the control apparatus7is long, the transmission distance between the user terminal2and the optical SW4can be calculated more accurately. For example, an amount of attenuation of the light power when the light output from the optical SW4is received by the optical transmission/reception part71of the control apparatus7is measured in advance. The transmission distance between the optical SW4and the control apparatus7can be calculated on the basis of the measured attenuation.

The instruction part76calculates the branching ratio to be set in the optical branching switch52on the basis of the transmission distance measured by the measurement part74. The instruction part76instructs the calculated branching ratio to the optical branching part5on the optical transmission line P4which transmits the optical signal from the user terminal2whose transmission distance has been measured.

Subsequently, an example of the optical branching switch52will be described.

FIG.2is a diagram showing a configuration of a branching ratio variable coupler501. The branching ratio variable coupler501is used as the optical branching switch52. The branching ratio variable coupler501has a base512including a fiber511and a base514including a fiber513. The fiber511is used as a part of the optical transmission line P7or is connected to the optical transmission line P7on the separation part51side and the optical transmission line P7on the separation part53side. The fiber511is used as a part of the optical transmission line P9or connected to the optical transmission line P9.

If the core of the fiber511and the core of the fiber513approach each other, the light propagating through the fiber511can be joined to the adjacent fiber513. Thus, the light can be branched. The branching ratio can be adjusted by changing the distance between the core of the fiber511and the core of the fiber513. The distance between the core of the fiber511and the core of the fiber513can be adjusted by moving the base514with the motor so that the distance corresponds to the branching ratio instructed by the control apparatus7. InFIG.2, an upper surface of a base512including the fiber511lies on an xz plane and optical signals are transmitted along an x-axis. Although the base514is moved in a y-axis direction to change the branching ratio inFIG.2, the base514may be moved in a z-axis direction.

FIG.3is a diagram showing a configuration of a PLC505. The PLC505can be used as the optical branching switch52. The PLC505has waveguides551and552, a power supply554, and a thin film heater555. The waveguide551is used as a part of the optical transmission line P7or is connected to the optical transmission line P7on the separation part51side and the optical transmission line P7on the separation part53side. The waveguide552is used as a part of the optical transmission line P9or connected to the optical transmission line P9.

A combiner553is formed in a part of the waveguide551and the waveguide552. In the combiner553, a part of the light transmitted through waveguide551is joined to the waveguide552. The amount of heat generated by the thin film heater555is changed by changing the power supplied from the power supply554to the thin film heater555which heats the combiner553so that the branching ratio can be changed. The PLC505controls the power supply554so that the power supplied to the thin film heater555corresponds to the branching ratio instructed by the control apparatus7.

Subsequently, the operation of the optical communication system1shown inFIG.1will be described. Here, a case in which the user terminal2-1communicates will be described as an example. A path Q1between the first port41connected to the user terminal2-1and the second setting port42is set in the optical SW4.

(Processing 1) If the user terminal2-1performs initialization, connection between the user terminal2-1and the control apparatus7is started. Thus, the optical SW4receives the optical signal transmitted by the optical transmission/reception part21of the user terminal2-1from the first port41and outputs the received optical signal from the second setting port42. The optical transmission/reception part71of the control apparatus7receives the optical signal output from the second setting port42by the optical SW4, acquires the management control signal of the AMCC signal from the received optical signal, and outputs it to the control part73. Furthermore, the control part73transmits, from the optical transmission/reception part71, an AMCC signal management control signal addressed to the user terminal2-1. The optical SW4outputs the management control signal input from the second setting port42from the first port41to which the user terminal2-1is connected. The optical transmission/reception part21of the user terminal2-1receives the optical signal output from the first port41by the optical SW4and acquires the management control signal of the AMCC signal from the received optical signal.

(Processing 2) The measurement part74of the control apparatus7transmits a message M1in which a time stamp indicating the current time t1is set from the optical transmission/reception part71to measure the transmission distance between the user terminal2-1and the optical GW3. The message M1is a management control signal of AMCC signal. The optical SW4outputs the message M1input from the second setting port42from the first port41to which the user terminal2-1is connected.

(Processing 3) The optical transmission/reception part21of the user terminal2-1receives the message M1. The user terminal2-1transmits, from the optical transmission/reception part21, a message M2in which the time stamp obtained from the message M1is set. The message M2is a management control signal of AMCC signal. The optical SW4outputs the message M2input from the first port41from the second setting port42. The optical transmission/reception part71of the control apparatus7outputs the received message M2to the measurement part74.

(Processing 4) The measurement part74of the control apparatus7calculates Round Trip Time (RTT) which is the frame round trip propagation time on the basis of time t1indicated by the time stamp set in the message M2and time t2when the message M2was received. The measurement part74multiplies the RTT by the refractive index [m/μs] in the fiber to calculate the transmission distance between the user terminal2-1and the optical SW4. Alternatively, the measurement part74subtracts the transmission distance between the optical SW4and the control apparatus7from the transmission distance obtained by multiplying the RTT by the refractive index in the fiber, thereby obtaining the distance between the user terminal2-1and the optical SW4.

(Processing 5) The path control part75of the control apparatus7determines the wavelength of upstream communication, the wavelength of downstream communication, and the transmission path to be assigned to the user terminal2-1in accordance with the communication destination of the user terminal2-1. The path control part75transmits, from the optical transmission/reception part71, a message M3in which the wavelength to be assigned to the user terminal2-1is set. The message M3is a management control signal of AMCC signal. The optical SW4outputs the message M3input from the second setting port42from the first port41to which the user terminal2-1is connected. The user terminal2-1sets the wavelength assigned by the message M3to the optical transmission/reception part21. Furthermore, the path control part75of the control apparatus7sets the port connection relationship of the path Q2to the optical SW4. Thus, the path Q1of the optical SW4is switched to the path Q2between the first port41connected to the user terminal2-1and the second port42connected to the wavelength multiplexing/demultiplexing part6.

(Processing 6) The instruction part76calculates the intensity of light when the light transmitted from the optical transmission/reception part21of the user terminal2reaches the optical GW3on the basis of the transmission distance calculated by the measurement part74in Processing 4. For example, the instruction part76stores in advance a relational expression representing the relationship between the transmission distance and the light intensity and substitutes the value of the transmission distance between the user terminal2-1and the optical GW3into the relational expression to determine the intensity. The relational expression may be a relational expression according to the characteristics of the optical transmission line P1between the user terminal2-1and the optical GW3. Alternatively, the relational expression may be a relational expression using the characteristics of the optical transmission line P1between the user terminal2-1and the optical GW3as parameters in addition to the transmission distance. In this case, the instruction part76stores in advance a value representing the characteristics of the optical transmission line P1. The instruction part76calculates, from the light having the calculated intensity, a branching ratio for branching light having an intensity at which the optical reception part72can receive the AMCC signal with the minimum light receiving sensitivity. The instruction part76instructs the calculated branching ratio to the optical branching part5on the transmission path set in Processing 5. The optical branching part5controls the optical branching switch52to branch at the branching ratio instructed by the instruction part76.

(Processing 7) The optical transmission/reception part21of the user terminal2-1converts the electrical signal in which the AMCC control signal is superimposed on the main signal into an optical signal with the wavelength set in Processing 5 and transmits the optical signal. The optical SW4outputs the optical signal input from the first port41from the second port42set using the path Q2. The optical branching switch52of the optical branching part5receives the optical signal output from the second port42and the optical signal branched from the input optical signal at the branching ratio set in Processing 6 is output to the optical reception part72of the control apparatus7. The optical reception part72of the control apparatus7acquires the AMCC control signal from the received optical signal and outputs it to the control part73. The optical signal which is not branched in the optical branching switch52of the optical branching part5is output to the optical transmission line P10via the wavelength multiplexing/demultiplexing part6.

Through the above-described processing, the optical communication system1adjusts the branching ratio of the optical branching switch52in accordance with the transmission distance between each user terminal2and the optical GW3. Thus, since the branching ratio of the optical branching switch52can be optimized, the transmission distance of the main signal can be maximized.

Second Embodiment

In the first embodiment, the control apparatus determines the branching ratio on the basis of the transmission distance between the optical GW and the user terminal. In this embodiment, the control apparatus determines the branching ratio on the basis of the received power of the light branched by the optical branching part. This embodiment will be described with a focus on differences from the first embodiment.

FIG.4is a diagram showing a configuration of an optical communication system12according to a second embodiment. Constituent elements inFIG.4that are the same as those of the optical communication system1according to the first embodiment shown inFIG.1will be denoted by the same reference numerals and description thereof will be omitted. The optical communication system12differs from the optical communication system1of the first embodiment in that it includes a control apparatus8instead of the control apparatus7.

The control apparatus8includes an optical transmission/reception part71, an optical reception part72, and a control part83. The control part83includes a path control part75, a measurement part84, and an instruction part86. The measurement part84may be provided outside the control part83or may be provided outside the control apparatus8.

The measurement part84is a power monitor. The measurement part84measures the reception power of the light received by the optical reception part72and outputs the measured reception power to the instruction part86. The instruction part86changes the branching ratio of the optical branching part5on the basis of the reception power so that a reception power at the optical reception part72approaches the minimum light receiving sensitivity at which the optical reception part72can receive the AMCC signal. That is to say, when the received power is greater than the minimum photosensitivity, in order to reduce the power of the light branched to the optical reception part72side, the instruction part86instructs the optical branching part5to change the branching ratio by a predetermined change amount or by a change amount corresponding to the deviation of the received power from the minimum light receiving sensitivity. Furthermore, when the received power is smaller than the minimum photosensitivity, in order to increase the power of the light branched to the optical reception part72side, the instruction part86instructs the optical branching part5to change the branching ratio by a predetermined change amount or by a change amount corresponding to the deviation of the received power from the minimum light receiving sensitivity.

Furthermore, the instruction part86may change the branching ratio of the optical branching part5so that a reception power at the optical reception part72approaches a target range that is a predetermined light receiving sensitivity range in which the optical reception part72can receive the AMCC signal. The target range can be any range of photosensitivity of the minimum photosensitivity or more. When the received power is greater than the specified target range, in order to reduce the power of the light branched to the optical reception part72side, the instruction part86instructs the optical branching part5to change the branching ratio by a predetermined change amount or by a change amount according to the deviation of the received power from the target range. Furthermore, when the received power is less than the target range, in order to increase the power of the light branched to the optical reception part72side, the instruction part86instructs the optical branching part5to change the branching ratio by a predetermined change amount or by a change amount according to the deviation of the received power from the target range.

After instructing to change the branching ratio, the instruction part86receives, from the measurement part84, the measured value of the reception power received by the optical reception part72. Upon receiving feedback of the reception power, the instruction part86repeatedly performs the process of changing the branching ratio of the optical branching part5again so that the reception power approaches the minimum light receiving sensitivity or the target range. Note that, when changing the branching ratio so that the received power approaches the minimum photosensitivity, the instruction part86may not instruct to change the branching ratio when the deviation between the received power and the minimum photosensitivity is a predetermined value or more.

Third Embodiment

In the first embodiment and the second embodiment, the wavelength multiplexing/demultiplexing part has a single core configuration. In this embodiment, the wavelength multiplexing/demultiplexing part has a two-core configuration. This embodiment will be described with a focus on differences from the first embodiment.

FIG.5is a diagram showing a configuration of an optical communication system13of the third embodiment. Constituent elements inFIG.5that are the same as those of the optical communication system1according to the first embodiment shown inFIG.1will be denoted by the same reference numerals and description thereof will be omitted. The optical communication system13differs from the optical communication system1of the first embodiment in that it includes an optical GW3ainstead of the optical GW3. The optical GW3adiffers from the optical GW3of the first embodiment in that it includes an optical branching part5aand a wavelength multiplexing/demultiplexing part6ainstead of the optical branching part5and the wavelength multiplexing/demultiplexing part6.

The optical branching part5ais connected to the optical SW4through an optical transmission line P4and is connected to the wavelength multiplexing/demultiplexing part6athrough an optical transmission line P7and an optical transmission line P8. The optical branching part5aincludes a separation part51aand an optical branching switch52. The separation part51areceives the upstream optical signal output from the second port42of the optical SW4through the optical transmission line P4and outputs the received upstream optical signal to the optical transmission line P7. Furthermore, the separation part51areceives the downstream optical signal output from the optical transmission line P8by the wavelength multiplexing/demultiplexing part6aand outputs the input downstream optical signal to the optical transmission line P4.

A wavelength multiplexing/demultiplexing part6ais a two-core AWG. A plurality of first ports of the wavelength multiplexing/demultiplexing part6aare respectively connected to the optical transmission lines P7or the optical transmission lines P8. The wavelength multiplexing/demultiplexing part6areceives upstream optical signals of different wavelengths output by the optical SW4from a plurality of first ports connected to the optical transmission lines P7and multiplexes the received optical signals and outputs it from the second port to the optical transmission line P10. Furthermore, the wavelength multiplexing/demultiplexing part6ainputs the downstream optical signal transmitted through the optical transmission line P10from the second port and demultiplexes the input downstream optical signal into optical signals of different wavelengths. The wavelength multiplexing/demultiplexing part6aoutputs the demultiplexed downstream optical signals from separate first ports to the optical transmission lines P8.

The differences between the third embodiment and the first embodiment described above may be applied to the second embodiment. That is to say, the optical communication system12in the second embodiment shown inFIG.4may have the optical GW3aof the third embodiment instead of the optical GW3.

Fourth Embodiment

The optical communication system in this embodiment has a plurality of mutually connected optical GWs. This embodiment will be described with a focus on differences from the first embodiment. Note that the difference between the fourth embodiment and the first embodiment may be applied to the second embodiment.

FIG.6is a diagram showing the configuration of the optical communication system14of the fourth embodiment. Constituent elements inFIG.6that are the same as those of the optical communication system1according to the first embodiment shown inFIG.1are denoted by the same reference numerals and descriptions thereof will be omitted. The optical communication system14differs from the optical communication system1of the first embodiment in that the optical GW3is connected to another optical GW3in another link end via an optical transmission line P10. InFIG.6, the optical communication system14has two optical GWs3, but may have three or more optical GWs3.

The control apparatus7has a plurality of optical transmission/reception parts71and a plurality of optical reception parts72, respectively. Each of the plurality of optical transmission/reception parts71is connected to an optical SW4of a different optical GW3. Each of the plurality of optical reception parts72is connected to the optical branching part5of a different optical GW3. The path control part75of the control apparatus7can determine transmission paths between user terminals2connected to different optical GWs3. The path control part75determines transmission/reception wavelengths to be assigned to the user terminals2and the port connection relationship in the optical SW4of each optical GW3so that the user terminals2transmit and receive optical signals using the determined transmission paths. The path control part75notifies each user terminal2of the transmission/reception wavelength and instructs the optical SW4of each optical GW3regarding the port connection relationship, as in the first embodiment. The measurement part74and the instruction part76of the control apparatus7perform the same processing as in the first embodiment on the user terminal2connected to each optical GW3and the optical branching part5of each optical GW3.

According to this embodiment, even when there is an optical GW on another link end, as in the first to third embodiments, the optical communication system can calculate the transmission distance between the user terminal and the optical GW and set an appropriate branching ratio for the optical branching part on the basis of the calculated transmission distance.

Furthermore, it is possible to maximize the transmission distance by providing an optical branching part in the path on the transmission side and setting the branching ratio in the optical branching part as in the first embodiment.

Fifth Embodiment

An optical GW in the fourth embodiment has a wavelength multiplexing/demultiplexing part with a single core. The optical GW in this embodiment has a wavelength multiplexing/demultiplexing parts with two cores. This embodiment will be described with a focus on differences from the above-described embodiment.

FIG.7is a diagram showing a configuration of an optical communication system15of the fifth embodiment. Constituent elements inFIG.7that are the same as those of the optical communication system14according to the fourth embodiment shown inFIG.6will be denoted by the same reference numerals and description thereof will be omitted. The optical communication system15differs from the optical communication system14of the fourth embodiment in that it includes optical GWs3aof the third embodiment shown inFIG.5instead of the optical GWs3. The plurality of optical transmission/reception parts71of the control apparatus7are respectively connected to the optical SW4of different optical GW3aand the plurality of optical reception parts72are respectively connected to the optical branching parts5of different optical GW3a. The operation of the optical communication system15is similar to that of the optical communication system14of the fourth embodiment. As described above, the configuration connected to the AWG may be a single-fiber configuration or a two-fiber configuration.

Sixth Embodiment

In a sixth embodiment, ports of an optical SW are divided into an upstream-only port and a downstream-only port. This embodiment will be described with a focus on differences from the above-described embodiment.

FIG.8is a diagram showing a configuration of an optical communication system16of the sixth embodiment. Constituent elements inFIG.8that are the same as those of the optical communication system14according to the fourth embodiment shown inFIG.6will be denoted by the same reference numerals and description thereof will be omitted. The optical communication system16differs from the optical communication system14of the fourth embodiment in that it includes an optical GWs3binstead of the optical GWs3.

The optical GW3bhas an optical SW4, an optical branching part5and a wavelength multiplexing/demultiplexing part6. A plurality of first ports41of the optical SW4respectively correspond to an upstream or a downstream. The first port41corresponding to an upstream is connected to the optical transmission/reception part21of the user terminal2via the optical transmission line P1and the first port41for a downstream is connected to the optical transmission/reception part21of the user terminal2via the optical transmission path P2. That is to say, the optical transmission/reception part21of the user terminal2is connected to the two first ports41of the optical SW4through the optical transmission line P1and the optical transmission line P2, respectively. Similarly, a plurality of second ports42of the optical SW4respectively correspond to an upstream or a downstream. One or more second ports42of the second ports42corresponding to an upstream are connected to the optical transmission/reception part71of the control apparatus7via the optical transmission line P6and the other one or more second ports42corresponding to an upstream are connected to the wavelength multiplexing/demultiplexing part6via an optical transmission line P4. One or more second ports42of the second ports42corresponding to a downstream are connected to the optical transmission/reception part71of the control apparatus7via the optical transmission line P5and the other one or more second ports42corresponding to a downstream are connected to the wavelength multiplexing/demultiplexing part6via an optical transmission line P11.

Each of the plurality of first ports (not shown) of the wavelength multiplexing/demultiplexing part6corresponds to an upstream or a downstream. The first port corresponding to an upstream of the wavelength multiplexing/demultiplexing part6is connected to the second port42corresponding to an upstream of the optical SW4via the optical transmission line P4and the first port corresponding to the downstream of the wavelength multiplexing/demultiplexing part6is connected to the second port42corresponding to the downstream of the optical SW4via the optical transmission line P11.

The procedure for setting the branching ratio to the optical branching part5in the optical communication system16is the same as in the above-described embodiment. Here, the optical communication system16performs an upstream communication and a downstream communication as follows.

The optical transmission/reception part21of the user terminal2outputs an optical signal to the optical transmission line P1. The optical SW4outputs, to the second port42corresponding to the transmission path to the destination of the optical signal among the second ports42corresponding to the upstream signal, the upstream optical signal of a predetermined wavelength in which the first port41has input from the optical transmission line P1. That is to say, the optical SW4outputs an upstream optical signal to the second setting port42connected to the optical transmission/reception part71of the control apparatus7via the optical transmission line P5or the second port42connected to the wavelength multiplexing/demultiplexing part6via the optical transmission line P4. The optical branching part5receives the optical signal output from the second port42corresponding to the upstream. The optical branching part5outputs the optical signal branched from the received upstream optical signal to the optical reception part72of the control apparatus7and outputs the optical signal not branched to the wavelength multiplexing/demultiplexing part6. The wavelength multiplexing/demultiplexing part6multiplexes the upstream optical signals which are output from the respective second ports42corresponding to the upstream of the optical SW4and are not branched using the optical branching part5and outputs the multiplexed optical signal to the optical transmission line P10.

Also, the wavelength multiplexing/demultiplexing part6receives the downstream optical signal transmitted through the optical transmission line P10and demultiplexes the received downstream optical signal into optical signals of different wavelengths. The wavelength multiplexing/demultiplexing part6outputs the demultiplexed downstream optical signals to different optical transmission lines P11. Furthermore, the optical transmission/reception part71of the control apparatus7outputs a downstream optical signal in which the control management signal of the AMCC signal is set to the optical transmission line P6. The optical SW4outputs a downstream optical signal of a predetermined wavelength input from the second port42corresponding to the downstream from the first port41corresponding to the transmission path to the destination of the optical signal among the first ports41corresponding to the downstream to the optical transmission line P2. The optical transmission/reception part21of the user terminal2receives the optical signal transmitted through the optical transmission line P2.

In the optical SW4, the first port41corresponding to an upstream and the first port41corresponding to a downstream may be alternately disposed and the first port41corresponding to the upstream and the first port41corresponding to the downstream may be disposed separately in an upper position and a lower position. When dividing into the upper position and the lower position, the first port41corresponding to upstream may be disposed in the upper position and the first port41corresponding to downstream may be disposed in the lower position, or the first port41corresponding to downstream may be disposed in the upper position and the first port41corresponding to upstream may be disposed in the upper position. Similarly, in the optical SW4, the second port42corresponding to the upstream and the second port42corresponding to the downstream may be disposed alternately and the second port42corresponding to the upstream and the second port42corresponding to the downstream may be disposed separately in an upper position and a lower position. When dividing into the upper position and the lower position, the second port42corresponding to upstream may be disposed in the upper position and the second port42corresponding to downstream may be disposed in the lower position, or the second port42corresponding to downstream may be disposed in the upper position and the second port42corresponding to upstream may be disposed in the lower position. Also, the optical SW4and the optical branching part5may be configured of one PLC.

A hardware configuration example of the control apparatus7and control apparatus8will be described.FIG.9is a device configuration diagram showing a hardware configuration example of the control apparatus7and control apparatus8. The control apparatus7and control apparatus8include a processor701, a storage part702, a communication interface703, and a user interface704.

The processor701is a central processing device which performs calculations and controls. The processor701is, for example, a CPU. The processor701implements the functions of a control part73and a control part83by reading the program from the storage part702and executing it. The storage part702further has a work area and the like used when the processor701executes various programs. The communication interface703is for communicably connecting to another device. The communication interface703is, for example, the optical reception part72. The user interface704is an input device such as a keyboard, a pointing device (mouse, tablet, or the like), buttons, a touch panel and a display device such as a display. The user interface704is used for inputting an artificial operation.

Note that all or some of the functions of the control part73may be implemented using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA).

According to the embodiment described above, it is possible to change the branching ratio of the optical separation part for extracting the AMCC signal superimposed on the main signal from the optical signal transmitted by the user terminal in accordance with the transmission distance between the user terminal and the optical GW. It is possible to maximize the transmission distance of the main signal by setting the branching ratio of the optical branching part so that the APN controller has the minimum light receiving sensitivity for receiving the AMCC signal.

According to the embodiments described above, the optical communication system has an optical switch, an optical branching part, a measurement part, and an instruction part. An optical switch has a plurality of ports and outputs an optical signal input from a first port that is one of the plurality of ports connected to an optical communication device from a second port that is another one of the plurality of ports according to the transmission path of the optical signal. The optical branching part branches the optical signal which has been output from the second port of the optical switch in accordance with the branching ratio. The measurement part measures the round trip time by transmitting and receiving optical signals to and from the optical communication device via the optical switch and calculates the transmission distance of the optical signal on the basis of the measured round trip time. The instruction part instructs the optical branching part of the branching ratio determined on the basis of the transmission distance measured by the measurement part. For example, the optical GW has an optical switch and an optical branching part, and the control apparatus has a measurement part and an instruction part.

The instruction part may calculate the optical intensity of the optical signal transmitted over the transmission distance calculated by the measurement part and instruct the optical branching part of a branching ratio for branching light of a predetermined light intensity from the light of the calculated light intensity.

Also, the measurement part may measure the optical intensity of the optical signal branched by the optical branching part. In this case, the instruction part instructs the optical branching part to change the branching ratio in accordance with the difference between the measured optical intensity of the optical signal and the predetermined optical intensity so that the light intensity of the optical signal measured by the measurement part approaches a predetermined light intensity.

The predetermined light intensity is an optical intensity which enables the optical receiving part which receives the optical signal branched by the optical branching part to obtain, from the received optical signal, the management control signal which is superimposed on the main signal and is slower than the main signal.

Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like within the scope of the present invention.

REFERENCE SIGNS LIST