Optical communication system, control device, and optical communication method

Abstract

In the present invention, an optical switch having a plurality of ports outputs an optical signal inputted from a first port, which is a port connected to an optical communication device, from a second port, which is another port corresponding to the transmission path of the optical signal. A splitting unit splits the optical signal outputted from the second port in accordance with a splitting ratio. A measurement unit measures a round trip time by transmitting and receiving the optical signal 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. An instruction unit issues an instruction to an optical splitting unit with regard to a determined splitting ratio on the basis of the calculated transmission distance.

Description

[Technical Field]

[0001] The present invention relates to an optical communication system, a control device, and an optical communication method. [Background technology]

[0002] The ITU-T (International Telecommunication Union Telecommunication Standardization sector) G.989.2 recommendation specifies PtP (Point to Point) WDM (Wavelength Division Multiplexing)-PON (Passive Optical Network) (see, for example, Non-Patent Document 1). In a PtP WDM-PON system, communication is performed using different optical wavelengths for each ONU in the upstream and downstream directions. The upstream direction is from the ONU to the OLT. The downstream direction is from the OLT to the ONU.

[0003] As described in Non-Patent Document 1, a PtP WDM-PON system specifies the use of a management and control signal called an Auxiliary Management and Control Channel (AMCC) as a management and control signal used between an OLT and an ONU. The AMCC signal is a signal in which information to be transmitted is modulated using a predetermined method and then superimposed on a main signal for transmission. By superimposing the AMCC signal on the main signal for transmission, the OLT and ONU can transmit management and control signals within the wavelength range of the optical wavelength used for the main signal. In other words, management and control are achieved without using a dedicated optical wavelength range for management and control. The wavelength determination process in which the upstream optical wavelength and downstream optical wavelength are determined is performed using the AMCC signal.

[0004] FIG. 10 is a diagram showing an example of the configuration of a PtP WDM-PON system. The diagram shows a configuration related to the superposition of an AMCC signal. The OLT and ONU each include a management and control unit. The AMCC signal is superimposed in the optical stage and separated in the electrical stage. FIG. 11 shows an example of an optical signal transmitted from an ONU or OLT. The transmitted optical signal is a main signal on which a management and control signal is superimposed. By superimposing the management and control signal on the optical signal, intensity modulation is applied to the envelope of the main signal, as shown in FIG. 11. The main signal is a high-speed signal with a data rate on the order of Gb / s (gigabits per second). On the other hand, the management and control signal is expected to be a low-speed signal with a data rate on the order of kb / s (kilobits per second) (for example, Non-Patent Document 2).

[0005] On the other hand, the All-Photonics Network (APN) is an innovative network based on photonics technology. In an APN, optical nodes relay optical backbone networks and optical access networks to provide end-to-end optical paths for each service. For example, optical nodes are expected to be optical switches (SWs).

[0006] FIG. 12 is a diagram illustrating the configuration of an optical communication system in an APN (see, for example, Non-Patent Document 3). The optical communication system illustrated in FIG. 12 includes a user device 92, an optical gateway (GW) 93, and an APN controller 96. The two optical GWs 93 are referred to as optical GWs 93-1 and 93-2. The three user devices 92 connected to an optical GW 93-n (n=1, 2) are referred to as user devices 92-n-1 to 92-n-3, respectively. The user device 92 includes an optical transceiver (TRx). The optical GW 93-n includes an optical SW 94-n and a wavelength multiplexing / demultiplexing unit 95-n. The optical GWs 93-1 and 93-2 are connected by an optical transmission line 97 via wavelength multiplexing / demultiplexing units 95-1 and 95-2.

[0007] The optical SW 94-n outputs light input from a first port 941 from a second port 942, and outputs light input from the second port 942 from the first port 941. The second port 942 of the optical SW 94-n is connected to a wavelength multiplexing / demultiplexing unit 95-n, but may be connected to another second port 942. The wavelength multiplexing / demultiplexing unit 95-n, for example, uses an AWG (Arrayed Waveguide Grating). The wavelength multiplexing / demultiplexing unit 95-n multiplexes optical signals of multiple wavelengths input from each second port 942 of the optical SW 94-n, and outputs the multiplexed optical signals to the optical transmission line 97. The wavelength multiplexing / demultiplexing unit 95-n also receives an optical signal from the optical transmission line 97, demultiplexes the input optical signal, and outputs the demultiplexed optical signal to the optical SW 94-n.

[0008] By setting the connection relationship between the first port 941 and the second port 942 of each of the optical SWs 94-1 and 94-2, a transmission path along which an optical signal travels can be selected. The APN controller 96 determines the transmitting and receiving wavelengths of each user equipment 92 and the port connection relationship between the first port 941 and the second port 942 of each of the optical SWs 94-1 and 94-2. Based on these determinations, the APN controller 96 instructs the user equipment 92 on the transmitting and receiving wavelengths and instructs the optical SWs 94-1 and 94-2 on the port connection relationship. In FIG. 12, the user equipment 92-1-1 and the user equipment 92-1-2 communicate with each other, and the user equipment 92-1-3 and the user equipment 92-2-3 communicate with each other. Different wavelengths are used for these communications. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] "ITU-T G.989.2, 40-Gigabit-capable passive optical networks 2 (NG PON2): Physical media dependent (PMD) layer specification," Feb. 2019. [Non-patent document 2] Yuanqiu Luo, Hal Roberts, Klaus Grobe, Maurizio Valvo, Derek Nesset, Kota Asaka, Harald Rohde, Joe Smith, Jun Shan Wey, and Frank Effenberger, "Physical Layer Aspects of NG-PON2 Standards-Part 2: System Design and Technology Feasibility [Invited]," Journal of Optical Communications and Networking, Vol.8, No.1, pp.43-52, Jan. 2016. [Non-patent document 3] Takuya Kanai, Kazuaki Honda, Yasunari Tanaka, Makoto Kaneko, Kazutaka Hara, Junichi Kani, Tomoaki Yoshida, "Photonic Gateway Supporting All-Photonics Networks," Institute of Electronics, Information and Communication Engineers General Conference, Proceedings of the IEICE Communications Conference, Vol. 2, B-8-20, p. 141, March 2021 Summary of the Invention [Problem to be solved by the invention]

[0010] In an APN, management and control information is superimposed on the main signal by superimposing an AMCC signal, which has a lower speed than the main signal. Therefore, it is assumed that the APN controller extracts the AMCC signal along the transmission path between user devices to obtain management and control information from the user devices. However, in many cases, the transmission distance from each user device to the optical gateway varies. Therefore, if light is extracted from the transmission path of each user device using the same branching ratio, the APN controller may branch excess light that exceeds the minimum optical sensitivity required to receive the AMCC signal. Branching excess light results in inefficient optical energy transmission of the main signal to the end user. As a result, it may not be possible to maximize the transmission distance of the main signal. It is expected that the transmission distance of the main signal can be extended by minimizing the power of the branched light within the range where the APN controller can receive the AMCC signal.

[0011] For example, in the case of FIG. 12, the transmission distance from the user device 92-1-1 to the optical gateway 93-1 is longer than the transmission distance from the user device 92-1-3 to the optical gateway 93-1. A splitter 98 is provided in the optical transmission path between the optical SW 94-1 and the wavelength multiplexing / demultiplexing unit 95-1. The splitter 98, which splits the optical signal transmitted by the user device 92-1-1, has a branching ratio that allows the APN controller 96 to receive the optical signal from the user device 92-1-1. This branching ratio is also applied to the splitter 98, which splits the optical signal transmitted by the user device 92-1-3. As a result, excess light is extracted from the optical signal transmitted by the user device 92-1-3, which may result in energy inefficiency.

[0012] In view of the above circumstances, the present invention aims to provide an optical communication system, a control device, and an optical communication method that are capable of branching an optical signal of the power required for receiving while minimizing reduction in the power of the optical signal transmitted through the transmission path. [Means for solving the problem]

[0013] An optical communication system according to one embodiment of the present invention comprises an optical switch having a plurality of ports, which outputs an optical signal input from a first port that is the port connected to an optical communication device from a second port that is another port corresponding to the transmission path of the optical signal; an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio; a measurement unit that measures a round trip time by transmitting and receiving an optical signal to and from the optical communication device via the optical switch and calculates the transmission distance of the optical signal based on the measured round trip time; and an instruction unit that instructs the optical branching unit on a branching ratio determined based on the calculated transmission distance.

[0014] An optical communication system according to one embodiment of the present invention comprises an optical switch having a plurality of ports, which outputs an optical signal input from a first port that is the port connected to an optical communication device, from a second port that is another port corresponding to the transmission path of the optical signal, an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio, a measuring unit that measures the optical intensity of the branched optical signal, and an instruction unit that instructs the optical branching unit to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

[0015] A control device of one embodiment of the present invention has a plurality of ports, and is equipped with a measurement unit that measures a round trip time by transmitting and receiving an optical signal to and from an optical communication device via an optical switch that outputs an optical signal input from a first port, which is the port connected to an optical communication device, from another port, which is a second port, according to the transmission path of the optical signal, and calculates the transmission distance of the optical signal based on the measured round trip time, and an instruction unit that instructs an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio, the branching ratio being determined based on the calculated transmission distance.

[0016] A control device according to one embodiment of the present invention has a plurality of ports, and is equipped with a measurement unit that measures the optical intensity of an optical signal branched in an optical branching unit that branches an optical signal input from a first port, which is the port connected to an optical communication device, and outputs the optical signal from a second port, which is another port corresponding to the transmission path of the optical signal, in accordance with a branching ratio by an optical switch, and an instruction unit that instructs the optical branching unit to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

[0017] An optical communication method of one embodiment of the present invention includes a switching step in which an optical switch having a plurality of ports outputs an optical signal input from a first port, which is the port connected to an optical communication device, from a second port, which is another port corresponding to the transmission path of the optical signal; a branching step in which an optical branching unit branches the optical signal output from the second port in accordance with a branching ratio; a measurement step in which a measurement unit measures a round trip time by transmitting and receiving an optical signal to and from the optical communication device via the optical switch and calculates the transmission distance of the optical signal based on the measured round trip time; and an instruction step in which a branching ratio determined based on the calculated transmission distance is instructed to the optical branching unit.

[0018] An optical communication method of one aspect of the present invention includes a switching step in which an optical switch having a plurality of ports outputs an optical signal input from a first port, which is the port connected to an optical communication device, from a second port, which is another port corresponding to the transmission path of the optical signal; a branching step in which an optical branching unit branches the optical signal output from the second port in accordance with a branching ratio; a measurement step in which a measurement unit measures the optical intensity of the branched optical signal; and an instruction step in which an instruction unit instructs the optical branching unit to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity.

[0019] An optical communication method according to one aspect of the present invention includes a measurement step of measuring a round trip time by transmitting and receiving an optical signal to and from an optical communication device via an optical switch that has a plurality of ports and outputs the optical signal from a second port, which is another port according to a transmission path of the optical signal, and calculating a transmission distance of the optical signal based on the measured round trip time; and an instruction step of instructing an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio, the branching ratio being determined based on the calculated transmission distance.

[0020] An optical communication method according to one aspect of the present invention includes a measurement step of measuring the optical intensity of an optical signal branched in an optical branching unit that has a plurality of ports and outputs an optical signal input from a first port, which is the port connected to an optical communication device, from a second port, which is another port corresponding to a transmission path of the optical signal, and branches the optical signal output from the second port according to a branching ratio, and an instruction step of instructing the optical branching unit to change the branching ratio so that the measured optical intensity approaches a predetermined optical intensity. [Effects of the Invention]

[0021] According to the present invention, it is possible to split an optical signal with a power required for light reception while minimizing reduction in the power of the optical signal transmitted through the transmission path. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment of the present invention. [Figure 2] 2A and 2B are diagrams illustrating a configuration of a variable branching ratio coupler used as an optical branching switch according to the embodiment. [Figure 3] 2 is a diagram showing the configuration of a PLC (Planar Lightwave Circuit) used as an optical branching switch according to the embodiment. FIG. [Figure 4] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a second embodiment. [Figure 5] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a third embodiment. [Figure 6] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a fourth embodiment. [Figure 7] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a fifth embodiment. [Figure 8] FIG. 10 is a diagram illustrating a configuration of an optical communication system according to a sixth embodiment. [Figure 9] FIG. 2 is a diagram illustrating a hardware configuration of a control device according to the first to sixth embodiments. [Figure 10]1 is a diagram illustrating the configuration of a conventional PtP WDM-PON system. [Figure 11] 1 illustrates a prior art optical signal; [Figure 12] FIG. 1 is a diagram illustrating a configuration of a conventional optical communication system. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the same parts in the drawings are designated by the same reference numerals, and the description thereof will be omitted.

[0024] This embodiment is applicable, for example, to an optical communication system that transmits an AMCC management control signal superimposed on a high-speed main signal. Such an optical communication system has a splitter that splits an optical signal on an optical transmission path that transmits the optical signal between user equipment devices in order to extract the AMCC signal. The optical communication system of this embodiment varies the splitting ratio of the optical signal in the splitter depending on the transmission distance between the user equipment device and the optical gateway. That is, the control device of the optical communication system sets the splitter splitting ratio so as to achieve the minimum optical receiving sensitivity capable of receiving the AMCC signal. This minimizes degradation of the optical signal power and maximizes the transmission distance of the main signal.

[0025] (First embodiment) FIG. 1 is a diagram illustrating the configuration of an optical communication system 1 according to a first embodiment. The optical communication system 1 includes a user device 2, an optical gateway 3, and a control device 7. The optical communication system 1 may include any number of user devices 2. In FIG. 1, two user devices 2 are depicted as user devices 2-1 and 2-2. The optical gateway 3 is connected to an optical network (not shown) via an optical transmission path P10. For example, a device with which the user device 2 communicates is connected to the optical network, or the optical network is connected to a network accommodating a device with which the user device 2 communicates. The direction from the user device 2 to the optical gateway 3 is described as upstream, and the direction from the optical gateway 3 to the user device 2 is described as downstream.

[0026] The user device 2 transmits and receives optical signals. A user device of the prior art can be used as the user device 2. The user device 2 shown in FIG. 1 is a dual-core optical transceiver. The user device 2 is connected to the optical GW 3 via optical transmission paths P1 and P2. The optical transmission paths P1 and P2 are, for example, two optical fibers in a single dual-core optical fiber cable. The user device 2 has an optical transceiver unit (TRx) 21.

[0027] The optical transmitter / receiver 21 is a wavelength-tunable optical transmitter / receiver. For example, the optical transmitter / receiver 21 is an optical transceiver that converts optical signals into electrical signals and vice versa. The user device 2 can select a wavelength according to the transmission / reception destination and set it in the optical transmitter / receiver 21. For example, the user device 2 sets the wavelengths to be used for the upstream optical signal and the downstream optical signal in the optical transmitter / receiver 21 according to instructions received from the control device 7. The optical transmitter / receiver 21 transmits and receives an optical signal in which an AMCC management control signal is superimposed on a main signal. Specifically, the optical transmitter / receiver 21 converts a transmission signal in which an electrical main signal and an electrical management control signal having a lower frequency 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 path P1. The optical transmitter / receiver 21 also inputs a downstream optical signal from the optical transmission path P2 and converts the input downstream optical signal into an electrical signal. The optical transmitter / receiver 21 separates the main signal and the AMCC management control signal from the converted electrical signal.

[0028] The user device 2 may be a single-core optical transmitter / receiver. In this case, the optical transmitter / receiver 21 is connected to the optical GW 3 by a single optical transmission line.

[0029] The optical GW 3 includes a demultiplexer 31, a demultiplexer 32, an optical SW4, an optical branching unit 5, and a wavelength multiplexer / demultiplexer 6. The optical GW 3 includes one or more demultiplexers 31, one or more optical branching units 5, and one or more wavelength multiplexer / demultiplexer units 6.

[0030] The separators 31 and 32 separate the upstream optical signal from the downstream optical signal. The separators 31 and 32 can be realized by, for example, a circulator or an upstream / downstream separation filter.

[0031] The demultiplexer 31 is connected to the user device 2 via optical transmission lines P1 and P2, and to the optical SW4 via optical transmission line P3. The demultiplexer 31 outputs an upstream optical signal input from the optical transmission line P1 to the optical transmission line P3, and outputs a downstream optical signal input from the optical transmission line P3 to the optical transmission line P2.

[0032] The demultiplexer 32 is connected to the optical SW4 via an optical transmission path P4, and is connected to the optical transceiver (TRx) 71 of the control device 7 via optical transmission paths P5 and P6. The demultiplexer 32 outputs an upstream optical signal input from the optical transmission path P4 to the optical transmission path P5, and outputs a downstream optical signal input from the optical transmission path P6 to the optical transmission path P4.

[0033] The optical SW4 has a plurality of first ports 41 and a plurality of second ports 42. The optical SW4 outputs an optical signal of a predetermined wavelength input from the first port 41 to a second port 42 corresponding to the transmission path to the destination of the optical signal. The optical SW4 also outputs an optical signal of a predetermined wavelength input from the second port 42 to the first port 41 corresponding to the transmission path to the destination of the optical signal. The optical SW4 can change the connection between the first port 41 and the second port 42. The connection relationship between the first port 41 and the second port 42 is referred to as the port connection relationship. For example, the optical SW4 changes the port connection relationship in accordance with an instruction from the control device 7. One or more first ports 41 are connected to the user device 2 via optical transmission lines P1, P2, and P3 and the demultiplexer 31. One or more second ports 42 are connected to the optical transceiver 71 of the control device 7 via optical transmission lines P4, P5, and P6 and the demultiplexer 32, and the other one or more second ports 42 are connected to the wavelength multiplexer / demultiplexer 6 via the optical transmission line P4. The second port 42 connected to the optical transceiver 71 of the control device 7 will be referred to as the second setting port 42 .

[0034] The optical branching unit 5 is provided on the optical transmission path P4 between the optical SW4 and the wavelength multiplexing / demultiplexing unit 6. There may be an optical transmission path P4 on which the optical branching unit 5 is not provided. The optical branching unit 5 has a separation unit 51, an optical branching switch 52, and a separation unit 53. The separation unit 51 and the separation unit 53 are connected by the optical transmission path P7 and the optical transmission path P8. The optical branching switch 52 is provided on the optical transmission path P7.

[0035] The separator 51 separates the upstream optical signal from the downstream optical signal. The separator 51 can be realized, for example, by a circulator or an upstream / downstream separation filter. The separator 51 receives the upstream optical signal output from the second port 42 of the optical SW4 via the optical transmission path P4, and outputs the received upstream optical signal to the optical transmission path P7. The separator 51 also receives the downstream optical signal output from the separator 53 via the optical transmission path P8, and outputs the received downstream optical signal to the optical transmission path P4.

[0036] The optical branching switch 52 branches the upstream optical signal transmitted through the optical transmission line P7 according to a set branching ratio. The branching ratio is instructed by the control device 7. Any optical branching device can be used for the optical branching switch 52 as long as it can vary the optical branching ratio. For example, the optical branching switch 52 can be an evanescent coupling type optical coupler, a fused / stretched type coupler whose longitudinal length is variable, or a planar lightwave circuit (PLC). The optical branching switch 52 outputs the branched optical signal to the control device 7 via the optical transmission line P9. The upstream optical signal not branched by the optical branching switch 52 is transmitted through the optical transmission line P7 and input to the separator 53.

[0037] The separator 53 separates the upstream optical signal from the downstream optical signal. Like the separator 51, the separator 53 can be realized by a circulator, an upstream / downstream separation filter, or the like. The separator 53 receives the upstream optical signal from the optical transmission path P7, and outputs the received upstream optical signal to the optical transmission path P4 between the separator 53 and the wavelength multiplexing / demultiplexing unit 6. The separator 53 also receives the downstream optical signal output by the wavelength multiplexing / demultiplexing unit 6 from the optical transmission path P4, and outputs the received downstream optical signal to the optical transmission path P8.

[0038] The wavelength multiplexing / demultiplexing unit 6 has multiple first ports (not shown) and one second port (not shown). The multiple first ports of the wavelength multiplexing / demultiplexing unit 6 correspond to different wavelengths. The first ports of the wavelength multiplexing / demultiplexing unit 6 are connected to different second ports 42 of the optical SW4 via the optical transmission line P4. The second port of the wavelength multiplexing / demultiplexing unit 6 is connected to the optical transmission line P10. The wavelength multiplexing / demultiplexing unit 6 multiplexes upstream optical signals of different wavelengths input from the optical SW4 via the multiple first ports and outputs the multiplexed optical signal from the second port. The wavelength multiplexing / demultiplexing unit 6 also inputs downstream optical signals transmitted through the optical transmission line P10 via the second port and demultiplexes the input downstream optical signals into optical signals of different wavelengths. The wavelength multiplexing / demultiplexing unit 6 outputs the demultiplexed downstream optical signals from separate first ports. For example, the wavelength multiplexing / demultiplexing unit 6 is an arrayed waveguide grating (AWG).

[0039] The control device 7 is, for example, an APN controller. The control device 7 includes an optical transceiver (TRx) 71, an optical receiver (Rx) 72, and a control unit 73. One or both of the optical transceiver 71 and the optical receiver 72 may be provided outside the control device 7, for example, in the optical GW 3. The control device 7 may also include a plurality of optical transceivers 71 and a plurality of optical receivers 72. When the control device 7 includes a plurality of optical transceivers 71, each optical transceiver 71 is connected to a different second setting port 42. When the control device 7 includes a plurality of optical receivers 72, each optical receiver 72 is connected to a different optical branching unit 5.

[0040] The optical transceiver 71 transmits and receives optical signals. The optical transceiver 71 may be a wavelength-tunable optical transceiver or a fixed-wavelength optical transceiver. The function of the optical transceiver 71 is similar to that of the optical transceiver 21 of the user device 2. The optical transceiver 71 is connected to the second setting port 42 of the optical SW4 via optical transmission paths P4, P5, and P6 and the separator 32. The optical transceiver 71 outputs an optical signal addressed to the user device 2 to the optical SW4. The optical transceiver 71 also receives an optical signal transmitted from the user device 2 and output from the second setting port 42 of the optical SW4. The optical signal transmitted and received by the optical transceiver 71 is an AMCC management control signal.

[0041] The optical receiving unit 72 receives an optical signal. The optical receiving unit 72 may be a wavelength-tunable optical receiver or a fixed-wavelength optical receiver. An optical transmitter / receiver such as an optical transceiver may be used as the optical receiving unit 72. The optical receiving unit 72 receives the optical signal branched by the optical branching unit 5 from the optical transmission path P9 and converts the input downstream optical signal into an electrical signal. The optical receiving unit 72 separates the management and control signal (AMCC) signal from the signal converted into an electrical signal.

[0042] The control unit 73 includes a measurement unit 74, a route control unit 75, and an instruction unit 76. The route control unit 75 determines the transmission route and allocation resources, such as transmission and reception wavelengths, to be used by each user device 2. The route control unit 75 instructs the user device 2 on the transmission and reception wavelengths based on the determined allocation resources. Furthermore, the route control unit 75 instructs the optical SW4 on the port connection relationship between the first port 41 and the second port 42 of the optical SW4 based on the determined allocation resources.

[0043] The measurement unit 74 transmits an AMCC management control signal from the optical transceiver 71 to the user equipment 2 and receives a response signal to the transmitted management control signal from the user equipment 2. The measurement unit 74 measures the transmission distance between the control device 7 and the user equipment 2 based on 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 SW4 and the control device 7 is much shorter than the transmission distance between the control device 7 and the user equipment 2. Therefore, the measured transmission distance between the control device 7 and the user equipment 2 is considered to be the transmission distance between the user equipment 2 and the optical SW4. Furthermore, since the transmission distance between the optical SW4 and the optical branching unit 5 is also short, the transmission distance between the user equipment 2 and the optical SW4 is considered to be the transmission distance between the user equipment 2 and the optical branching unit 5. If the transmission distance between the optical SW4 and the control device 7 is known, the measurement unit 74 may calculate the transmission distance between the user equipment 2 and the optical SW4 by subtracting the transmission distance between the optical SW4 and the control device 7 from the measured transmission distance between the control device 7 and the user equipment 2. This makes it possible to more accurately calculate the transmission distance between the user device 2 and the optical SW4 even when the transmission distance between the optical SW4 and the control device 7 is long. For example, the amount of attenuation of the optical power when the light output from the optical SW4 is received by the optical transceiver 71 of the control device 7 is measured in advance. Based on the measured amount of attenuation, the transmission distance between the optical SW4 and the control device 7 can be calculated.

[0044] The instructing unit 76 calculates the branching ratio to be set in the optical branching switch 52 based on the transmission distance measured by the measuring unit 74. The instructing unit 76 instructs the calculated branching ratio to the optical branching unit 5 on the optical transmission path P4 that transmits the optical signal from the user device 2 whose transmission distance has been measured.

[0045] Next, an example of the optical branch switch 52 will be described. 2 is a diagram showing the configuration of a variable branching ratio coupler 501. The variable branching ratio coupler 501 is used as an optical branching switch 52. The variable branching ratio coupler 501 has a base 512 having a fiber 511 and a base 514 having a fiber 513. The fiber 511 is used as part of the optical transmission path P7, or is connected to the optical transmission path P7 on the separation unit 51 side and the optical transmission path P7 on the separation unit 53 side. The fiber 511 is used as part of the optical transmission path P9, or is connected to the optical transmission path P9.

[0046] When the core of fiber 511 and the core of fiber 513 approach each other, light propagating through fiber 511 can be coupled to the adjacent fiber 513, thereby enabling light branching. The branching ratio can be adjusted by changing the distance between the core of fiber 511 and the core of fiber 513. This can be adjusted by moving base 514 with a motor so that the distance between the core of fiber 511 and the core of fiber 513 corresponds to the branching ratio specified by control device 7. In FIG. 2, the top surface of base 512 on which fiber 511 is mounted is on the xz plane, and the optical signal is transmitted in the direction along the x-axis. In FIG. 2, base 514 is moved in the y-axis direction to change the branching ratio, but it may also be moved in the z-axis direction.

[0047] 3 is a diagram showing the configuration of the PLC 505. The PLC 505 can be used as the optical branch switch 52. The PLC 505 has a waveguide 551 and a waveguide 552, a power supply 554, and a thin-film heater 555. The waveguide 551 is used as part of the optical transmission line P7, or is connected to the optical transmission line P7 on the separation unit 51 side and the optical transmission line P7 on the separation unit 53 side. The waveguide 552 is used as part of the optical transmission line P9, or is connected to the optical transmission line P9.

[0048] A coupler 553 is formed in a part of the waveguide 551 and the waveguide 552. In the coupler 553, a part of the light transmitted through the waveguide 551 is coupled to the waveguide 552. A power supply 554 changes the power supplied to a thin-film heater 555 that heats the coupler 553, thereby changing the amount of heat generated by the thin-film heater 555, and therefore the branching ratio can be changed. The PLC 505 controls the power supply 554 so that the power supplied to the thin-film heater 555 corresponds to the branching ratio instructed by the control device 7.

[0049] Next, the operation of the optical communication system 1 shown in Fig. 1 will be described. Here, the case where the user device 2-1 is communicating will be described as an example. A path Q1 is set in the optical SW4 between the first port 41 connected to the user device 2-1 and the second setting port 42.

[0050] (Process 1) When the user device 2-1 performs initial configuration, a connection between the user device 2-1 and the control device 7 is initiated. As a result, the optical SW4 receives the optical signal transmitted by the optical transceiver 21 of the user device 2-1 from the first port 41 and outputs the received optical signal from the second configuration port 42. The optical transceiver 71 of the control device 7 receives the optical signal transmitted by the optical SW4 from the second configuration port 42, acquires an AMCC management control signal from the received optical signal, and outputs the acquired signal to the control unit 73. The control unit 73 also transmits an AMCC management control signal addressed to the user device 2-1 from the optical transceiver 71. The optical SW4 outputs the management control signal received from the second configuration port 42 from the first port 41 to which the user device 2-1 is connected. The optical transceiver 21 of the user device 2-1 receives the optical signal transmitted by the optical SW4 from the first port 41 and acquires the AMCC management control signal from the received optical signal.

[0051] (Process 2) In order to measure the transmission distance between the user device 2-1 and the optical GW 3, the measurement unit 74 of the control device 7 transmits a message M1, which includes a timestamp indicating the current time t1, from the optical transceiver 71. The message M1 is an AMCC management control signal. The optical SW4 outputs the message M1, which is input from the second setting port 42, from the first port 41 to which the user device 2-1 is connected.

[0052] (Process 3) The optical transceiver 21 of the user device 2-1 receives the message M1. The user device 2-1 then transmits a message M2 from the optical transceiver 21, which contains the timestamp acquired from the message M1. The message M2 is an AMCC management control signal. The optical SW4 outputs the message M2 input from the first port 41 from the second setting port 42. The optical transceiver 71 of the control device 7 outputs the received message M2 to the measurement unit 74.

[0053] (Process 4) The measurement unit 74 of the control device 7 calculates the round trip time (RTT), which is the frame round trip time, based on the time t1 indicated by the timestamp set in the message M2 and the time t2 at which the message M2 is received. The measurement unit 74 multiplies the RTT by the refractive index [m / μs] in the fiber to calculate the transmission distance between the user device 2-1 and the optical SW4. Alternatively, the measurement unit 74 may calculate the transmission distance between the user device 2-1 and the optical SW4 by subtracting the transmission distance between the optical SW4 and the control device 7 from the transmission distance obtained by multiplying the RTT by the refractive index in the fiber.

[0054] (Process 5) The route control unit 75 of the control device 7 determines the wavelengths for upstream and downstream communications to be assigned to the user device 2-1 and the transmission routes, depending on the communication destination of the user device 2-1. The route control unit 75 transmits a message M3, which sets the wavelengths to be assigned to the user device 2-1, from the optical transceiver 71. The message M3 is an AMCC management and control signal. The optical SW4 receives the message M3 from the second setting port 42 and outputs it from the first port 41 to which the user device 2-1 is connected. The user device 2-1 sets the wavelength assigned by the message M3 in the optical transceiver 21. Furthermore, the route control unit 75 of the control device 7 sets the port connection relationship of the path Q2 to the optical SW4. As a result, the path Q1 of the optical SW4 is switched to the path Q2 between the first port 41 connected to the user device 2-1 and the second port 42 connected to the wavelength multiplexing and demultiplexing unit 6.

[0055] (Process 6) Based on the transmission distance calculated by the measurement unit 74 in Process 4, the instructing unit 76 calculates the intensity of light transmitted from the optical transceiver 21 of the user device 2 when it reaches the optical GW3. For example, the instructing unit 76 stores in advance a relational expression representing the relationship between the transmission distance and the optical intensity, and calculates the intensity by substituting the value of the transmission distance between the user device 2-1 and the optical GW3 into the relational expression. The relational expression may be a relational expression based on the characteristics of the optical transmission path P1 between the user device 2-1 and the optical GW3. Alternatively, the relational expression may be a relational expression that uses the characteristics of the optical transmission path P1 between the user device 2-1 and the optical GW3 as a parameter in addition to the transmission distance. In this case, the instructing unit 76 stores in advance a value representing the characteristics of the optical transmission path P1. The instructing unit 76 calculates a branching ratio for branching light with an intensity that allows the optical receiver 72 to receive an AMCC signal with the minimum optical receiving sensitivity from the calculated intensity of light. The instruction unit 76 instructs the calculated branching ratio to the optical branching unit 5 on the transmission path set in the process 5. The optical branching unit 5 controls the optical branching switch 52 so as to perform branching at the branching ratio instructed by the instruction unit 76.

[0056] (Process 7) The optical transceiver 21 of the user device 2-1 converts the electrical signal, in which the AMCC control signal is superimposed on the main signal, into an optical signal of the wavelength set in process 5 and transmits it. The optical SW4 outputs the optical signal input from the first port 41 from the second port 42 set in path Q2. The optical branching switch 52 of the optical branching unit 5 inputs the optical signal output from the second port 42 and outputs the optical signal branched from the input optical signal at the branching ratio set in process 6 to the optical receiving unit 72 of the control device 7. The optical receiving unit 72 of the control device 7 obtains the AMCC control signal from the received optical signal and outputs it to the control unit 73. The optical signal not branched by the optical branching switch 52 of the optical branching unit 5 is output to the optical transmission line P10 via the wavelength multiplexing / demultiplexing unit 6.

[0057] Through the above-described processing, the optical communication system 1 adjusts the branching ratio of the optical branching switch 52 according to the transmission distance between each user device 2 and the optical GW 3. This allows the branching ratio of the optical branching switch 52 to be set to an optimal value, thereby maximizing the transmission distance of the main signal.

[0058] (Second embodiment) In the first embodiment, the control device determines the branching ratio based on the transmission distance between the optical gateway and the user device. In this embodiment, the control device determines the branching ratio based on the reception power of the light branched by the optical branching unit. This embodiment will be described focusing on the differences from the first embodiment.

[0059] Fig. 4 is a diagram showing the configuration of an optical communication system 12 according to the second embodiment. In Fig. 4, the same components as those in the optical communication system 1 according to the first embodiment shown in Fig. 1 are denoted by the same reference numerals, and their description will be omitted. The optical communication system 12 differs from the optical communication system 1 of the first embodiment in that it includes a control device 8 instead of the control device 7.

[0060] The control device 8 includes an optical transceiver 71, an optical receiver 72, and a control unit 83. The control unit 83 includes a route control unit 75, a measurement unit 84, and an instruction unit 86. The measurement unit 84 may be provided outside the control unit 83 or outside the control device 8.

[0061] The measuring unit 84 is a power monitor. The measuring unit 84 measures the reception power of the light received by the optical receiving unit 72 and outputs the result to the instructing unit 86. The instructing unit 86 changes the branching ratio of the optical branching unit 5 based on the reception power so that the optical receiving unit 72 approaches the minimum light-receiving sensitivity at which it can receive an AMCC signal. That is, when the reception power is greater than the minimum light-receiving sensitivity, the instructing unit 86 instructs the optical branching unit 5 to change the branching ratio by a predetermined amount or by an amount corresponding to the deviation of the reception power from the minimum light-receiving sensitivity so as to reduce the power of the light branched to the optical receiving unit 72. On the other hand, when the reception power is less than the minimum light-receiving sensitivity, the instructing unit 86 instructs the optical branching unit 5 to change the branching ratio by a predetermined amount or by an amount corresponding to the deviation of the reception power from the minimum light-receiving sensitivity so as to increase the power of the light branched to the optical receiving unit 72.

[0062] The instructing unit 86 may also change the branching ratio of the optical branching unit 5 so that the branching ratio approaches a target range, which is a predetermined range of optical sensitivity within which the optical receiving unit 72 can receive an AMCC signal. The target range can be any range of optical sensitivity equal to or greater than the minimum optical sensitivity. When the received power is greater than the predetermined target range, the instructing unit 86 instructs the optical branching unit 5 to change the branching ratio by a predetermined amount or by an amount corresponding to the deviation of the received power from the target range so as to reduce the power of the light branched to the optical receiving unit 72. When the received power is less than the target range, the instructing unit 86 instructs the optical branching unit 5 to change the branching ratio by a predetermined amount or by an amount corresponding to the deviation of the received power from the target range so as to increase the power of the light branched to the optical receiving unit 72.

[0063] After issuing an instruction to change the branching ratio, the instruction unit 86 receives the measured value of the received power received by the optical receiving unit 72 from the measurement unit 84. When the instruction unit 86 receives feedback of the received power, it repeats the process of changing the branching ratio of the optical branching unit 5 again so that the received 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 light-receiving sensitivity, the instruction unit 86 may not instruct to change the branching ratio if the deviation between the received power and the minimum light-receiving sensitivity is equal to or smaller than a predetermined value.

[0064] (Third embodiment) In the first and second embodiments, the wavelength multiplexing / demultiplexing unit has a single-core configuration. In this embodiment, the wavelength multiplexing / demultiplexing unit has a two-core configuration. This embodiment will be described, focusing on the differences from the first embodiment.

[0065] Fig. 5 is a diagram showing the configuration of an optical communication system 13 according to a third embodiment. In Fig. 5, the same components as those in the optical communication system 1 according to the first embodiment shown in Fig. 1 are denoted by the same reference numerals, and their description will be omitted. The optical communication system 13 differs from the optical communication system 1 of the first embodiment in that it includes an optical GW 3a instead of the optical GW 3. The optical GW 3a differs from the optical GW 3 of the first embodiment in that it includes an optical branching unit 5a and a wavelength multiplexing / demultiplexing unit 6a instead of the optical branching unit 5 and wavelength multiplexing / demultiplexing unit 6.

[0066] The optical branching unit 5a is connected to the optical SW4 by an optical transmission line P4, and is connected to the wavelength multiplexing / demultiplexing unit 6a by optical transmission lines P7 and P8. The optical branching unit 5a includes a separation unit 51a and an optical branching switch 52. The separation unit 51a receives an upstream optical signal output from the second port 42 of the optical SW4 via the optical transmission line P4, and outputs the received upstream optical signal to the optical transmission line P7. The separation unit 51a also receives a downstream optical signal output from the wavelength multiplexing / demultiplexing unit 6a via the optical transmission line P8, and outputs the received downstream optical signal to the optical transmission line P4.

[0067] The wavelength multiplexing / demultiplexing unit 6a is a two-core AWG. Each of the multiple first ports of the wavelength multiplexing / demultiplexing unit 6a is connected to the optical transmission line P7 or the optical transmission line P8. The wavelength multiplexing / demultiplexing unit 6a receives upstream optical signals of different wavelengths output by the optical SW4 from the multiple first ports connected to the optical transmission line P7, multiplexes the received optical signals, and outputs the multiplexed signals from the second port to the optical transmission line P10. The wavelength multiplexing / demultiplexing unit 6a also receives downstream optical signals transmitted through the optical transmission line P10 from the second port, and demultiplexes the received downstream optical signals into optical signals of different wavelengths. The wavelength multiplexing / demultiplexing unit 6a outputs the demultiplexed downstream optical signals from separate first ports to the optical transmission line P8.

[0068] The difference between the third embodiment and the first embodiment described above may be applied to the second embodiment. That is, the optical communication system 12 of the second embodiment shown in Fig. 4 may include the optical GW3a of the third embodiment instead of the optical GW3.

[0069] (Fourth embodiment) The optical communication system of this embodiment has a plurality of optical GWs that are connected to each other. This embodiment will be described focusing on the differences from the first embodiment. Note that the differences between the fourth embodiment and the first embodiment may also be applied to the second embodiment.

[0070] Fig. 6 is a diagram showing the configuration of an optical communication system 14 according to a fourth embodiment. In Fig. 6, the same components as those in the optical communication system 1 according to the first embodiment shown in Fig. 1 are denoted by the same reference numerals, and their description will be omitted. The optical communication system 14 differs from the optical communication system 1 of the first embodiment in that the optical GW3 is connected to an optical GW3 at another site by an optical transmission path P10. In Fig. 6, the optical communication system 14 has two optical GW3, but may have three or more optical GW3.

[0071] The control device 7 has a plurality of optical transmitters / receivers 71 and optical receivers 72. Each of the optical transmitters / receivers 71 is connected to an optical SW4 of a different optical GW3. Each of the optical receivers 72 is connected to an optical branching unit 5 of a different optical GW3. A route controller 75 of the control device 7 can determine transmission routes between user devices 2 connected to different optical GW3. The route controller 75 determines transmission and reception wavelengths to be assigned to the user devices 2 and port connection relationships in the optical SW4 of each optical GW3 so that the user devices 2 transmit and receive optical signals using the determined transmission routes. The route controller 75 notifies each user device 2 of the transmission and reception wavelengths and instructs the optical SW4 of each optical GW3 of the port connection relationships, as in the first embodiment. A measurement unit 74 and an instruction unit 76 of the control device 7 perform the same processes as in the first embodiment for the user devices 2 connected to each optical GW3 and the optical branching units 5 of each optical GW3.

[0072] According to this embodiment, even when an optical GW is located in a different location, the optical communication system can calculate the transmission distance between the user device and the optical GW and set an appropriate branching ratio in the optical branching unit based on the calculated transmission distance, as in the first to third embodiments. Furthermore, by providing an optical branching unit on the transmission side path and setting the branching ratio in the optical branching unit as in the first embodiment, it is possible to maximize the transmission distance.

[0073] (Fifth embodiment) The optical gateway of the fourth embodiment has a single-core wavelength multiplexing / demultiplexing unit. The optical gateway of this embodiment has a two-core wavelength multiplexing / demultiplexing unit. This embodiment will be described focusing on the differences from the above-mentioned embodiments.

[0074] FIG. 7 is a diagram showing the configuration of an optical communication system 15 according to a fifth embodiment. In FIG. 7, the same components as those in the optical communication system 14 according to the fourth embodiment shown in FIG. 6 are denoted by the same reference numerals, and their description will be omitted. The optical communication system 15 differs from the optical communication system 14 according to the fourth embodiment in that the optical GW 3a according to the third embodiment shown in FIG. 5 is provided instead of the optical GW 3. The optical transmitters and receivers 71 of the control device 7 are each connected to the optical SW4 of a different optical GW 3a, and the optical receivers 72 are each connected to the optical branching units 5 of the different optical GW 3a. The operation of the optical communication system 15 is the same as that of the optical communication system 14 according to the fourth embodiment. As described above, the configuration connected to the AWG may be a single-core configuration or a two-core configuration.

[0075] (Sixth embodiment) In the sixth embodiment, the ports of the optical SW are divided into ports dedicated to upstream and ports dedicated to downstream. This embodiment will be described focusing on the differences from the above-described embodiments.

[0076] Fig. 8 is a diagram showing the configuration of an optical communication system 16 according to a sixth embodiment. In Fig. 8, the same components as those in the optical communication system 14 according to the fourth embodiment shown in Fig. 6 are denoted by the same reference numerals, and their description will be omitted. The optical communication system 16 differs from the optical communication system 14 according to the fourth embodiment in that it includes an optical GW3b instead of the optical GW3.

[0077] The optical GW 3b includes an optical SW4, an optical branching unit 5, and a wavelength multiplexing / demultiplexing unit 6. The first ports 41 of the optical SW4 correspond to either upstream or downstream signals. The first ports 41 corresponding to upstream signals are connected to the optical transceiver 21 of the user device 2 via an optical transmission line P1, and the first ports 41 corresponding to downstream signals are connected to the optical transceiver 21 of the user device 2 via an optical transmission line P2. That is, the optical transceiver 21 of the user device 2 is connected to the two first ports 41 of the optical SW4 via the optical transmission lines P1 and P2. Similarly, the second ports 42 of the optical SW4 correspond to either upstream or downstream signals. Of the second ports 42 corresponding to upstream signals, one or more second ports 42 are connected to the optical transceiver 71 of the control device 7 via the optical transmission line P6, and the other one or more second ports 42 are connected to the wavelength multiplexing / demultiplexing unit 6 via the optical transmission line P4. Of the second ports 42 corresponding to downstream, one or more second ports 42 are connected to the optical transceiver unit 71 of the control device 7 via optical transmission path P5, and the other one or more second ports 42 are connected to the wavelength multiplexing / demultiplexing unit 6 via optical transmission path P11.

[0078] Each of the plurality of first ports (not shown) of the wavelength multiplexing / demultiplexing unit 6 corresponds to an upstream or downstream. The first port corresponding to the upstream of the wavelength multiplexing / demultiplexing unit 6 is connected to the second port 42 corresponding to the upstream of the light SW4 via an optical transmission line P4, and the first port corresponding to the downstream of the wavelength multiplexing / demultiplexing unit 6 is connected to the second port 42 corresponding to the downstream of the light SW4 via an optical transmission line P11.

[0079] The procedure for setting the branching ratio for the optical branching unit 5 in the optical communication system 16 is the same as in the above-described embodiment, except that the optical communication system 16 performs upstream communication and downstream communication as follows.

[0080] The optical transceiver 21 of the user device 2 outputs an optical signal to the optical transmission path P1. The optical SW4 outputs an upstream optical signal of a predetermined wavelength input to the first port 41 from the optical transmission path P1 to one of the second ports 42 corresponding to the upstream signal, which corresponds to the transmission path to the destination of the optical signal. That is, the optical SW4 outputs the upstream optical signal to the second setting port 42 connected to the optical transceiver 71 of the control device 7 via the optical transmission path P5, or to the second port 42 connected to the wavelength multiplexing / demultiplexing unit 6 via the optical transmission path P4. The optical drop unit 5 inputs the optical signal output from the second port 42 corresponding to the upstream. The optical drop unit 5 outputs the optical signal dropped from the input upstream optical signal to the optical receiving unit 72 of the control device 7, and outputs the optical signal that was not dropped to the wavelength multiplexing / demultiplexing unit 6. The wavelength multiplexing / demultiplexing unit 6 multiplexes the upstream optical signals that are output from each second port 42 corresponding to the upstream of the optical SW4 and that were not branched off by the optical branching unit 5, and outputs the combined optical signal to the optical transmission path P10.

[0081] The wavelength multiplexer / demultiplexer 6 receives a downstream optical signal transmitted through the optical transmission path P10 and demultiplexes the received downstream optical signal into optical signals of different wavelengths. The wavelength multiplexer / demultiplexer 6 outputs the demultiplexed downstream optical signals to different optical transmission paths P11. The optical transceiver 71 of the control device 7 outputs a downstream optical signal, in which an AMCC control management signal is set, to the optical transmission path P6. The optical SW4 outputs the downstream optical signal of a predetermined wavelength received from the second port 42 corresponding to the downstream signal to the optical transmission path P2 from one of the first ports 41 corresponding to the downstream signal, which corresponds to the transmission path to the destination of the optical signal. The optical transceiver 21 of the user device 2 receives the optical signal transmitted through the optical transmission path P2.

[0082] In the optical SW4, the first ports 41 corresponding to the upstream and the first ports 41 corresponding to the downstream may be arranged alternately, or the first ports 41 corresponding to the upstream and the first ports 41 corresponding to the downstream may be arranged separately in an upper and a lower stage. When divided into the upper and lower stages, the first ports 41 corresponding to the upstream may be arranged in the upper stage and the first ports 41 corresponding to the downstream may be arranged in the lower stage, or the first ports 41 corresponding to the downstream may be arranged in the upper stage and the first ports 41 corresponding to the upstream may be arranged in the lower stage. Similarly, in the optical SW4, the second ports 42 corresponding to the upstream and the second ports 42 corresponding to the downstream may be arranged alternately, or the second ports 42 corresponding to the upstream and the second ports 42 corresponding to the downstream may be arranged separately in the upper and the lower stage. When divided into the upper and the lower stage, the second ports 42 corresponding to the upstream and the second ports 42 corresponding to the downstream may be arranged in the upper stage and the second ports 42 corresponding to the downstream may be arranged in the lower stage, or the second ports 42 corresponding to the downstream may be arranged in the upper stage and the second ports 42 corresponding to the upstream. Furthermore, the optical SW4 and the optical branching unit 5 may be configured as a single PLC.

[0083] Next, an example of the hardware configuration of the control devices 7 and 8 will be described. Fig. 9 is a diagram showing an example of the hardware configuration of the control devices 7 and 8. The control devices 7 and 8 include a processor 701, a storage unit 702, a communication interface 703, and a user interface 704.

[0084] The processor 701 is a central processing unit that performs calculations and control. The processor 701 is, for example, a CPU. The processor 701 realizes the functions of the control units 73 and 83 by reading and executing programs from the storage unit 702. The storage unit 702 further has a work area and the like when the processor 701 executes various programs. The communication interface 703 is connected to other devices so as to be able to communicate with them. The communication interface 703 is, for example, the optical receiving unit 72. The user interface 704 is an input device such as a keyboard, a pointing device (mouse, tablet, etc.), a button, a touch panel, or a display device such as a display. Human operations are input via the user interface 704.

[0085] All or part of the functions of the control unit 73 may be realized using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA).

[0086] According to the embodiment described above, it is possible to change the branching ratio of the optical branching unit for extracting the AMCC signal superimposed on the main signal from the optical signal transmitted by the user equipment according to the transmission distance between the user equipment and the optical gateway. By setting the branching ratio of the optical branching unit so that the APN controller has the minimum optical receiving sensitivity for receiving the AMCC signal, it is possible to maximize the transmission distance of the main signal.

[0087] According to the above-described embodiment, the optical communication system includes an optical switch, an optical branching unit, a measurement unit, and an instruction unit. The optical switch has multiple ports and outputs an optical signal input from a first port connected to an optical communication device from a second port corresponding to the transmission path of the optical signal. The optical branching unit branches the optical signal output from the second port of the optical switch in accordance with a branching ratio. The measurement unit measures the round trip time by transmitting and receiving an optical signal to and from the optical communication device via the optical switch, and calculates the transmission distance of the optical signal based on the measured round trip time. The instruction unit instructs the optical branching unit on the branching ratio determined based on the transmission distance measured by the measurement unit. For example, the optical gateway includes an optical switch and an optical branching unit, and the control device includes a measurement unit and an instruction unit.

[0088] The instruction unit may calculate the optical intensity of the optical signal transmitted over the transmission distance calculated by the measurement unit, and instruct the optical branching unit on a branching ratio for branching light of a predetermined optical intensity from light of the calculated optical intensity.

[0089] The measuring unit may measure the optical intensity of the optical signal branched by the optical branching unit. In this case, the instructing unit instructs the optical branching unit to change the branching ratio in accordance with the deviation between the optical intensity of the optical signal measured by the measuring unit and the predetermined optical intensity so that the optical intensity of the optical signal measured by the measuring unit approaches the predetermined optical intensity.

[0090] The specified optical intensity is an optical intensity at which the optical receiving unit, which receives the optical signal branched by the optical branching unit, can obtain from the received optical signal an OAM signal that is superimposed on a main signal and is slower than the main signal.

[0091] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the present invention that do not deviate from the gist of the present invention. [Explanation of symbols]

[0092] 1, 12, 13, 14, 15, 16...Optical communication systems, 2, 2-1, 2-2, 92-1-1 to 92-1-3, 92-2-1 to 92-2-3...user device, 3, 3a, 3b, 93-1, 93-2…Hikari GW, 4, 94-1, 94-2... Optical SW 5, 5a...optical branching section, 6, 6a, 95-1, 95-2...Wavelength multiplexing / demultiplexing section, 7, 8...Control device, 21...Optical transmitter / receiver unit, 31, 32...separation section, 41, 941...First Port, 42, 942...Second port, 51, 51a, 53...separation section, 52...Optical branch switch, 71...Optical transmitter / receiver unit, 72...optical receiving unit, 73, 83...Control section, 74, 84...measuring section, 75...Routing control section, 76, 86...instruction section, 96...APN controller, 97...Optical transmission line, 98…Splitter, 501... Variable branching ratio coupler, 511, 513...Fiber, 512, 514…units, 551, 552...waveguide, 553…combiner, 554…power supply, 555...Thin film heater, 701...processor, 702...Storage section, 703...Communication Interface, 704...User Interface, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11...Optical transmission line

Claims

1. an optical switch having a plurality of ports, the optical switch inputting an optical signal from a first port connected to an optical communication device, and outputting the optical signal from a second port corresponding to a transmission path of the optical signal; an optical branching unit that branches the optical signal output from the second port according to a branching ratio; a measurement unit that measures a round trip time by transmitting and receiving an optical signal to and from the optical communication device via the optical switch, and calculates a transmission distance of the optical signal based on the measured round trip time; an instruction unit that instructs the optical branching unit on a branching ratio determined based on the calculated transmission distance; An optical communication system comprising:

2. an optical switch having a plurality of ports, the optical switch inputting an optical signal from a first port connected to an optical communication device, and outputting the optical signal from a second port corresponding to a transmission path of the optical signal; an optical branching unit that branches the optical signal output from the second port according to a branching ratio; a measurement unit for measuring the optical intensity of the branched optical signal; an instruction unit that instructs the optical branching unit to change a branching ratio so that the measured light intensity approaches a predetermined light intensity; An optical communication system comprising:

3. a measurement unit having a plurality of ports, the measurement unit measuring a round trip time by transmitting and receiving an optical signal to and from the optical communication device via an optical switch that inputs an optical signal from a first port that is the port connected to the optical communication device and outputs the optical signal from a second port that is another port according to a transmission path of the optical signal, and calculating a transmission distance of the optical signal based on the measured round trip time; an instruction unit that instructs an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio, the branching ratio being determined based on the calculated transmission distance; A control device comprising:

4. an optical switch having a plurality of ports, the optical switch inputting an optical signal from a first port which is the port connected to an optical communication device and outputting the optical signal from a second port which is another port corresponding to a transmission path of the optical signal, the optical switch branching the optical signal output from the second port in accordance with a branching ratio; and a measuring unit for measuring the optical intensity of the branched optical signal. an instruction unit that instructs the optical branching unit to change a branching ratio so that the measured light intensity approaches a predetermined light intensity; A control device comprising:

5. a switching step in which an optical switch having a plurality of ports outputs an optical signal input from a first port, which is the port connected to an optical communication device, from a second port, which is another port corresponding to a transmission path of the optical signal; a branching step in which an optical branching unit branches the optical signal output from the second port according to a branching ratio; a measurement step in which a measurement unit measures a round trip time by transmitting and receiving an optical signal to and from the optical communication device via the optical switch, and calculates a transmission distance of the optical signal based on the measured round trip time; an instruction step of instructing the optical branching unit to determine a branching ratio based on the calculated transmission distance; An optical communication method comprising:

6. a switching step in which an optical switch having a plurality of ports outputs an optical signal input from a first port, which is the port connected to an optical communication device, from a second port, which is another port corresponding to a transmission path of the optical signal; a branching step in which an optical branching unit branches the optical signal output from the second port according to a branching ratio; a measuring step in which a measuring unit measures the optical intensity of the branched optical signal; an instruction step in which an instruction unit instructs the optical branching unit to change a branching ratio so that the measured light intensity approaches a predetermined light intensity; An optical communication method comprising:

7. a measuring step of measuring a round trip time by transmitting and receiving an optical signal to and from the optical communication device via an optical switch having a plurality of ports, the optical signal being input from a first port which is the port connected to the optical communication device and outputting the optical signal from a second port which is another port according to a transmission path of the optical signal, and calculating a transmission distance of the optical signal based on the measured round trip time; an instruction step of instructing an optical branching unit that branches the optical signal output from the second port in accordance with a branching ratio, the branching ratio being determined based on the calculated transmission distance; An optical communication method comprising:

8. an optical switch having a plurality of ports, which inputs an optical signal from a first port that is the port connected to an optical communication device and outputs the optical signal from a second port that is another port corresponding to a transmission path of the optical signal, and which branches the optical signal output from the second port in accordance with a branching ratio, and measures the optical intensity of the branched optical signal; an instruction step of instructing the optical branching unit to change a branching ratio so that the measured light intensity approaches a predetermined light intensity; An optical communication method comprising:

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