QKD system, monitoring device, multiplexing device and program

Abstract

To improve the transmission speed of an encryption key by optical wavelength multiplexing with a limited number of optical fibers, and to continue the transmission of an encryption key even when a problem such as disconnection occurs in the optical fiber.SOLUTION: In a QKD system according to an embodiment, a plurality of transmission devices transmit a plurality of quantum signals and a plurality of classical signals. A monitoring device monitors the transmission status of a plurality of optical fibers. The plurality of optical fibers include a first optical fiber in which the plurality of quantum signals are wavelength-multiplexed, and a second optical fiber in which the classical signals are wavelength-multiplexed. The monitoring device includes a monitoring unit and a control unit. The monitoring unit monitors the transmission state of the plurality of quantum signals flowing through the first optical fiber and the transmission state of the plurality of classical signals flowing through the second optical fiber. Depending on the monitoring results by the monitoring unit, the control unit instructs at least one of a first multiplexer and a second multiplexer to switch the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The embodiments of the present invention relate to a QKD system, a monitoring device, a multiplexing device, and a program. [Background technology]

[0002] Quantum Key Distribution (QKD) is a technology that securely shares an encryption key between a transmitter that continuously transmits single photons and a receiver that receives the single photons, connected via optical fiber. The encryption key shared by QKD is guaranteed to be resistant to eavesdropping based on the principles of quantum mechanics. Data encrypted using the shared encryption key and an encryption method known as a one-time pad is guaranteed by information theory to be undecipherable by any knowledgeable eavesdropper. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4784202 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with conventional technology, it was difficult to improve the encryption key transmission speed using optical wavelength multiplexing with a limited number of optical fibers, while continuing to transmit the encryption key even when a malfunction such as a break in the optical fiber occurred. [Means for solving the problem]

[0005] The QKD system of one embodiment includes a plurality of transmitting devices, a plurality of receiving devices, a first multiplexing device, a second multiplexing device, a plurality of optical fibers, and a monitoring device. The plurality of transmitting devices transmit a plurality of quantum signals including cryptographic key information shared by QKD (Quantum Key Distribution) and a plurality of classical signals including control information for the QKD. The plurality of receiving devices receive the plurality of quantum signals and the plurality of classical signals. The first multiplexing device is connected to the plurality of transmitting devices. The second multiplexing device is connected to the plurality of receiving devices. A plurality of optical fibers connect the first multiplexing device and the second multiplexing device. The monitoring device monitors the transmission status of the plurality of optical fibers. The plurality of optical fibers include a first optical fiber into which the plurality of quantum signals are wavelength-multiplexed and a second optical fiber into which the classical signals are wavelength-multiplexed. The monitoring device includes a monitoring unit and a control unit. The monitoring unit monitors the transmission status of the plurality of quantum signals flowing through the first optical fiber and the transmission status of the plurality of classical signals flowing through the second optical fiber. The control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers, depending on the monitoring result by the monitoring unit. [Brief explanation of the drawings]

[0006] [Figure 1] A diagram showing an example of the configuration of a typical QKD system. [Figure 2] FIG. 1 is a diagram showing an example of the configuration of a QKD system using multiple QKD devices. [Figure 3] FIG. 1 shows Example 1 of the case where optical wavelength multiplexing technology is used. [Figure 4] FIG. 10 is a diagram showing Example 2 when optical wavelength multiplexing technology is used. [Figure 5] FIG. 1 is a diagram showing an example of the device configuration of a QKD system according to a first embodiment. [Figure 6] FIG. 2 is a diagram showing an example of the functional configuration of a multiplexing device according to the first embodiment. [Figure 7] FIG. 2 is a diagram for explaining an example of optical fiber switching control according to the first embodiment. [Figure 8] FIG. 2 is a diagram for explaining an example of multiplexing control according to the first embodiment. [Figure 9] FIG. 3 is a diagram for explaining an example of quality degradation investigation control according to the first embodiment. [Figure 10] FIG. 10 is a diagram for explaining an example of synchronization parameter initialization control according to the second embodiment. [Figure 11] FIG. 10 is a diagram for explaining an example of light source wavelength switching control according to the third embodiment. [Figure 12] FIG. 2 is a diagram showing an example of the hardware configuration of a multiplexing device and a monitoring device according to the first to third embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments of a QKD system, a monitoring device, a multiplexing device, and a program will be described in detail with reference to the accompanying drawings.

[0008] Hereinafter, an encryption key exchange device that uses QKD (Quantum Key Distribution) technology will be referred to as a QKD device. Also, an encryption key exchange system configured with multiple QKD devices will be referred to as a QKD system. First, an example of a general QKD system will be described.

[0009] 1 is a diagram showing an example of the configuration of a general QKD system 1. The general QKD system 100 includes a transmitting device 1, a receiving device 2, and two optical fibers 101 and 102.

[0010] The transmitting device 1 is a QKD device on the transmitting side. The transmitting device 1 generates photons, encodes cryptographic key information representing bit information of 0 or 1 into the photons, and transmits the photons with the encoded cryptographic key information to the receiving device 2.

[0011] The receiver 2 is a QKD device on the receiving side. The receiver 2 receives the photons sent from the transmitter 1 and decodes the encryption key information.

[0012] The optical fiber 101 is used as a quantum communication path for transmitting a quantum signal in which cryptographic key information is encoded.

[0013] The optical fiber 102 is used as a classical communication channel for transmitting a classical signal including control information for QKD. For example, the classical communication channel is used for transmitting an optical signal such as a synchronization signal between a photon transmitter used in the transmitting device 1 and a photon receiver used in the receiving device 2, or for transmitting data communication signals.

[0014] Because the quantum signal in the quantum communication channel is much weaker than the optical signal in the classical communication channel, physically separate optical fibers 101 and 102 are usually used for the quantum communication channel and the classical communication channel. Furthermore, in order to transmit signals dedicated to the QKD device, optical fiber 101 for the quantum communication channel and optical fiber 102 for the classical communication channel must be dark fibers.

[0015] FIG. 2 is a diagram showing an example configuration of a QKD system 100-2 using multiple QKD devices. In QKD system 100-2, in order to improve the transmission speed of the shared encryption key, the number of QKD devices is increased, thereby improving the transmission speed of the encryption key throughout QKD system 100-2. As shown in FIG. 2, for example, the transmission speed of the encryption key when three QKD systems are used is three times faster than when one QKD system 100 (FIG. 1) is used. However, in this case, the number of optical fibers required increases. Increasing the number of optical fibers required to implement a QKD system in society is not practical.

[0016] Therefore, there is a method of using optical wavelength multiplexing technology to realize a quantum communication channel and a classical communication channel on a single optical fiber (Patent Document 1). By shifting the wavelength of the optical signal for the quantum communication channel and the optical signal for the classical communication channel, it becomes possible to transmit encryption keys by QKD without mutual interference even when transmitted through the same optical fiber. With this technology, only one optical fiber is required for one QKD system.

[0017] Figure 3 is a diagram showing Example 1 of the case where optical wavelength multiplexing technology is used. In the QKD system 100-3 of Figure 3, in addition to a normal QKD device (transmitter 1 and receiver 2), optical fiber 101 used as a quantum communication channel, and optical fiber 102 used as a classical communication channel, multiplexers 3a and 3b that wavelength-multiplex optical signals and optical fiber 103 are used.

[0018] The transmitter 1 and multiplexer 3a, and the receiver 2 and multiplexer 3b are placed in the same rack, for example, and are connected by a short optical fiber. The multiplexers 3a and 3b are connected by an optical fiber 103 corresponding to the communication distance, just like a normal QKD device.

[0019] However, in Example 1 of Fig. 3, it is necessary to wavelength-multiplex optical signals with different intensities, which is technically difficult. Therefore, as shown in Fig. 4, a method can be considered in which optical fibers 101a to 101c of the quantum communication channels are wavelength-multiplexed into one optical fiber 101d, and optical fibers 102a to 102c of the classical communication channels are wavelength-multiplexed into one optical fiber 102d.

[0020] Fig. 4 is a diagram showing Example 2 of the case where optical wavelength multiplexing technology is used. In QKD system 100-4 in Fig. 4, multiplexers 4a and 4b perform wavelength multiplexing of optical signals from optical fibers 101a to 101c used for quantum communication paths, and multiplexers 4c and 4d perform wavelength multiplexing of optical signals from optical fibers 102a to 102c used for classical communication paths.

[0021] It is easier to wavelength-multiplex optical signals of the same intensity, as in the QKD system 100-4 of FIG. 4, than to wavelength-multiplex optical signals of different intensities, as in the QKD system 100-3 of FIG. 3. In the wavelength-multiplexing scheme shown in FIG. 3, if the number of QKD devices used is increased to improve the transmission speed of the encryption key, the number of optical fibers 103 required increases in proportion to the number of devices. On the other hand, with the wavelength-multiplexing scheme shown in FIG. 4, even if the number of QKD devices that perform wavelength multiplexing increases, the number of optical fibers required remains at two, thereby reducing implementation costs. A disadvantage of the wavelength-multiplexing scheme shown in FIG. 4 is that if one optical fiber is broken, all of the multiple QKD devices will stop operating. In other words, if even one optical fiber between the multiplexing devices is broken, transmission of the encryption key by the QKD devices will stop.

[0022] (First embodiment) Below, we will explain an embodiment of a QKD system that can improve the transmission speed of encryption keys using optical wavelength multiplexing with a limited number of optical fibers, while continuing to transmit encryption keys even when a malfunction such as a break occurs in the optical fiber.

[0023] [Example of equipment configuration] 5 is a diagram showing an example of the device configuration of a QKD system 200 of the first embodiment. The QKD system 200 of the first embodiment includes transmitting devices 1a to 1c, receiving devices 2a to 2c, multiplexing devices 5a and 5b, and a monitoring device 6. The numbers of transmitting devices 1a to 1c and receiving devices 2a to 2c are not limited to three each and may be any. The multiplexing devices 5a and 5b are connected by three optical fibers 103a to 103c. Hereinafter, when there is no need to distinguish between the optical fibers 103a to 103c, they will simply be referred to as optical fiber 103.

[0024] The multiplexing device 5a is installed on the transmitting side and is connected to the quantum communication channels and classical communication channels of the multiple transmitting devices 1a to 1c. The multiplexing device 5b is installed on the receiving side and is connected to the quantum communication channels and classical communication channels of the multiple receiving devices 2a to 2c. The multiplexing devices 5a and 5b multiplex the multiple quantum communication channels onto a single optical fiber 103 and the multiple classical communication channels onto a single optical fiber 103.

[0025] The multiplexers 5a and 5b are connected by three or more optical fibers 103 (optical fibers 103a to 103c in the example of FIG. 5), and have a function of switching which optical fiber 103 to use for transmitting encryption keys by QKD. That is, the multiplexers 5a and 5b have the function of switching between the optical fibers 103a to 103c to be used as the quantum communication channel and the classical communication channel, in addition to the function of optical wavelength multiplexing. The multiplexers 5a and 5b switch between the multiple optical fibers 103a to 103c between the multiplexers 5a and 5b to determine the optical fiber 103 to be used as the quantum communication channel and the optical fiber 103 to be used as the classical communication channel.

[0026] Normally, when transmitting an encryption key by QKD using two optical fibers 103 and also securing an unused optical fiber 103 as a spare, the number of optical fibers 103 between the multiplexers 5a and 5b must be more than two. For example, in the example of Fig. 5, the optical fiber 103a is used as the quantum communication path, the optical fiber 103b is used as the classical communication path, and the optical fiber 103c is secured as a spare.

[0027] The monitoring device 6 includes a monitoring unit 61 and a control unit 62 .

[0028] The monitoring unit 61 monitors the transmission status of the encryption keys of each QKD device (transmitting devices 1a to 1c and receiving devices 2a to 2c). For example, the monitoring unit 61 monitors the transmission status of the multiple quantum signals flowing through the optical fiber 103a by receiving at least one of the encryption key generation speed based on the quantum signals and the error rate of the quantum signals from the multiple receiving devices 2a to 2c. For example, if the monitoring unit 61 detects that transmission of the encryption keys in each QKD device has stopped due to a break in the optical fiber 103a, it notifies the control unit 62 of the stoppage of transmission of the encryption keys.

[0029] The control unit 62 switches the optical fiber 103 used by the multiplexing devices 5a and 5b depending on the transmission status of the encryption keys of each QKD device monitored by the monitoring unit 61. For example, when the control unit 62 receives a notification from the monitoring unit 61 that the transmission of the encryption keys has been stopped, it transmits an instruction to the multiplexing devices 5a and 5b to switch the optical fiber 103a, which has been used as the quantum communication path, to the optical fiber 103c.

[0030] Although the example of FIG. 5 shows a configuration in which three QKD systems are multiplexed using optical wavelengths, the number of QKD systems to be multiplexed may be two or more.

[0031] Hereinafter, when there is no need to distinguish between the multiplexing devices 5a and 5b, they will simply be referred to as the multiplexing device 5.

[0032] [Example of functional configuration of multiplexing device] 6 is a diagram showing an example of the functional configuration of the multiplexing device 5 of the first embodiment. The multiplexing device 5 of the first embodiment includes a multiplexing unit 51 and a switching control unit 52.

[0033] The multiplexing unit 51 receives a plurality of quantum signals including cryptographic key information shared by QKD and a plurality of classical signals including control information for QKD from a plurality of QKD devices (transmitting devices 1a to 1c). The multiplexing unit 51 then wavelength-multiplexes the plurality of quantum signals using an optical fiber 103a (first optical fiber) selected from the plurality of optical fibers 103, and wavelength-multiplexes the plurality of quantum signals using an optical fiber 103b (second optical fiber) selected from the plurality of optical fibers 103.

[0034] In response to a switching instruction from the monitoring device 6, the switching control unit 52 switches the optical fiber 103a (first optical fiber) or the optical fiber 103b (second optical fiber) to another optical fiber selected from the plurality of optical fibers 103 (optical fiber 103c in the example of Figure 5).

[0035] 7 is a diagram for explaining an example of switching control of the optical fibers 103a to 103c in the first embodiment. It is assumed that the quantum communication paths (optical fibers 101a to 101c) of three QKD systems are multiplexed onto the optical fiber 103a, the classical communication paths (optical fibers 102a to 102c) are multiplexed onto the optical fiber 103b, and the optical fiber 103c is unused.

[0036] Suppose that for some reason optical fiber 103a is broken or eavesdropped on, and transmission of the encryption key cannot be continued (step S1). Then, monitoring unit 61 detects that the transmission status of the encryption key of each QKD device (transmitting devices 1a to 1c and receiving devices 2a to 2c) has stopped (step S2), and notifies control unit 62 of the detection result.

[0037] At this time, the monitoring unit 61 may notify not only the encryption key transmission suspension state but also operation information of the QKD device related to the detection result. For example, the operation information of the QKD device may be the number of detected photons, QBER (Quantum Bit Error Rate), and encryption key transmission speed (also called encryption key sharing speed or encryption key generation speed). The relationship between QBER (quantum bit error rate) and encryption key transmission speed is such that as QBER increases, the encryption key transmission speed decreases.

[0038] Based on the notification from the monitor 61, the control unit 62 issues an instruction to at least one of the multiplexers 5a and 5b to switch the quantum communication path from the optical fiber 103a to the unused optical fiber 103c (step S3).

[0039] Upon receiving the instruction from the control unit 62, the switching control units 52 of the multiplexers 5a and 5b switch the quantum communication path to the unused optical fiber 103c instead of the optical fiber 103a, thereby continuing the transmission of the encryption key (step S4).

[0040] The control unit 62 can also issue an instruction to switch the classical communication channel in the same manner as in the case of the quantum communication channel described above, and the multiplexing devices 5a and 5b can also switch the classical communication channel in the same manner as in the case of the quantum communication channel described above.

[0041] 7, the transmission of the encryption key can be continued even when a problem occurs in the optical fiber 103, thereby improving redundancy. The number of optical fibers 103 may be three or more, and may include at least one unused optical fiber 103.

[0042] 8 is a diagram for explaining an example of multiplexing control in the first embodiment. By wavelength-multiplexing quantum signals with the same optical intensity, it is possible to suppress the deterioration of the quantum signal error rate (QBER) and the deterioration of the encryption key transmission speed. However, the optical wavelength multiplexing may still cause a deterioration in the encryption key transmission speed. This deterioration can be suppressed by reducing the number of wavelengths multiplexed.

[0043] Assume that the quantum communication channels (optical fibers 101a to 101c) of three QKD systems are multiplexed onto optical fiber 103a, the classical communication channels (optical fibers 102a to 102c) are multiplexed onto optical fiber 103b, and optical fiber 103c is unused.

[0044] The monitoring unit 61 monitors the states of the optical fibers 103a to 103c (for example, transmission states and states of use or non-use) and the transmission states of the encryption keys (step S11).

[0045] If the transmission rate of the encryption key monitored by the monitoring unit 61 is normal and there is an unused optical fiber 103 (optical fiber 103c in the example of FIG. 8), the control unit 62 performs multiplexing control based on the operating status of each QKD device (transmitting devices 1a to 1c and receiving devices 2a to 2c) from the monitoring unit 61. Specifically, if the transmission status of the optical fibers 103a to 103c is normal, the control unit 62 issues an instruction to at least one of the multiplexing devices 5a and 5b to demultiplex some of the wavelength-multiplexed multiple quantum signals and switch the transmission of the demultiplexed quantum signals to the unused optical fiber 103. In the example of FIG. 8, the control unit 62 issues an instruction to at least one of the multiplexing devices 5a and 5b to demultiplex some of the wavelength-multiplexed optical fiber 103a, assign the optical fiber 101c to the optical fiber 103c, and assign the optical fibers 101a and 101b to be wavelength-multiplexed on the optical fiber 103a (step S12).

[0046] The multiplexing units 51 of the multiplexing devices 5a and 5b switch the allocation of quantum communication paths based on instructions from the control unit 62 (step S13). This reduces the number of optical wavelength multiplexes in the optical fiber 103a, making it possible to suppress deterioration in the encryption key transmission speed of the optical fibers 101a and 101b. Furthermore, since the optical fiber 103c is used only for the optical fiber 101c and optical wavelength multiplexing is not performed in the optical fiber 101c, deterioration in the encryption key transmission speed of the optical fiber 101c is also suppressed. By canceling a portion of the optical wavelength multiplexing in this way, the encryption key transmission speed of the entire QKD system 200 is improved.

[0047] Fig. 9 is a diagram for explaining an example of quality degradation investigation control according to the first embodiment. In the example of Fig. 9, control when investigating the cause of performance degradation will be explained.

[0048] Assume that the quantum communication channels (optical fibers 101a to 101c) of three QKD systems are multiplexed onto optical fiber 103a, the classical communication channels (optical fibers 102a to 102c) are multiplexed onto optical fiber 103b, and optical fiber 103c is unused.

[0049] First, the monitoring unit 61 detects a deterioration in the encryption key generation speed (step S21) and notifies the control unit 62 of the detection result indicating the deterioration in the encryption key generation speed. For example, if the encryption key generation speed is lower than a generation threshold, the monitoring unit 61 notifies the control unit 62 of the detection result indicating the deterioration in the encryption key generation speed. Note that if the error rate of the quantum signal is higher than an error rate threshold, the monitoring unit 61 may also notify the control unit 62 of the detection result indicating the deterioration in the error rate of the quantum signal.

[0050] When the control unit 62 receives the notification from the monitoring unit 61, it issues an instruction to at least one of the multiplexers 5a and 5b to switch the optical fibers 103a to 103c (step S22). For example, the control unit 62 issues an instruction to at least one of the multiplexers 5a and 5b to switch the quantum communication paths (optical fibers 101a to 101c) wavelength-multiplexed onto the optical fiber 103a and the classical communication paths (optical fibers 102a to 102c) wavelength-multiplexed onto the optical fiber 103b.

[0051] In accordance with instructions from the control unit 62, the switching control units 52 of the multiplexing devices 5a and 5b switch the quantum communication paths (optical fibers 101a to 101c) that were wavelength-multiplexed onto the optical fiber 103a to the optical fiber 103b, and switch the classical communication paths (optical fibers 102a to 102c) that were wavelength-multiplexed onto the optical fiber 103b to the optical fiber 103a (step S23).

[0052] The monitoring unit 61 receives the encryption key transmission speed measured after the replacement and compares the encryption key transmission speeds before and after the replacement (step S24). If the encryption key transmission speed has improved, the monitoring unit 61 identifies the quality degradation of the optical fiber 103 in which a degradation in the encryption key generation speed was detected in step S21.

[0053] As described above, in the QKD system 200 of the first embodiment, multiple transmission devices 1a to 1c transmit multiple quantum signals including cryptographic key information shared by QKD and multiple classical signals including QKD control information. Multiple reception devices 2a to 2c receive the multiple quantum signals and multiple classical signals. A multiplexing device 5a (first multiplexing device) is connected to the multiple transmission devices 1a to 1c. A multiplexing device 5b (second multiplexing device) is connected to the multiple reception devices (2a to 2c). Multiple optical fibers 103a to 103c connect the first multiplexing device and the second multiplexing device. A monitoring device 6 monitors the transmission states of the multiple optical fibers 103a to 103c. The multiple optical fibers 103 include an optical fiber 103a (first optical fiber) into which multiple quantum signals are wavelength-multiplexed and an optical fiber 103b (second optical fiber) into which classical signals are wavelength-multiplexed. The monitoring unit 61 monitors the transmission states of the multiple quantum signals flowing through the first optical fiber and the transmission states of the multiple classical signals flowing through the second optical fiber. The control unit 62 issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to another optical fiber selected from the multiple optical fibers 103, depending on the monitoring result by the monitoring unit 61.

[0054] As a result, according to the first embodiment of the QKD system 200, it is possible to improve the transmission speed of the encryption key by optical wavelength multiplexing with a limited number of optical fibers 103, while continuing to transmit the encryption key even when a malfunction such as a break occurs in the optical fiber 103.

[0055] (Second embodiment) Next, a second embodiment will be described. In the description of the second embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described. In the second embodiment, an example will be described in which the monitoring device 6 performs synchronization parameter initialization control.

[0056] 10 is a diagram for explaining an example of synchronization parameter initialization control in the second embodiment. When the optical fiber 103 used between the multiplexing devices 5a and 5b is switched, if the characteristics of the optical fiber 103, such as its length, change before and after the switch, it may be necessary to initialize the synchronization parameters used to synchronize transmission and reception between the transmitting device 1 and the receiving device 2.

[0057] In the example of Fig. 10, the length of the optical fiber 103c is longer than the length of the optical fiber 103a. For example, suppose that the optical fiber 103a, which has been used for multiplexing the quantum communication paths (optical fibers 101a to 101c), is switched to the unused optical fiber 103c by the switching control described above with reference to Fig. 7 (step S31). In such a case, the control unit 62 issues an instruction to, for example, the transmitting devices 1a to 1c to initialize synchronization parameters (step S32).

[0058] The instruction in step S32 may be issued to the receiving devices 2a to 2c, or may be issued to both the transmitting devices 1a to 1c and the receiving devices 2a to 2c.

[0059] As described above, in the QKD system 200-2 of the second embodiment, if the characteristics of the optical fiber 103 before switching are different from the characteristics of the optical fiber 103 after switching, the control unit 62 issues an instruction to at least one of the multiple transmitting devices 1a to 1c and the multiple receiving devices 2a to 2c to initialize synchronization parameters used to synchronize transmission and reception between the multiple transmitting devices 1a to 1c and the multiple receiving devices 2a to 2c.

[0060] As a result, according to the QKD system 200-2 of the second embodiment, even if the characteristics such as the length of the optical fiber 103 change before and after switching, the same effects as those of the first embodiment can be obtained.

[0061] (Third embodiment) Next, a third embodiment will be described. In the description of the third embodiment, the same description as in the first embodiment will be omitted, and only the differences from the first embodiment will be described. In the third embodiment, an example will be described in which the monitoring device 6 controls switching of the light source wavelength.

[0062] Generally, there is only one wavelength for quantum signals and only one wavelength for classical signals. In order for the multiplexing devices 5a and 5b to multiplex quantum signals (signals flowing through quantum communication channels) and classical signals (signals flowing through classical communication channels) transmitted from multiple transmitting devices 1a to 1c, the devices must be designed and manufactured in advance so that the wavelengths of the signals from each of the transmitting devices 1a to 1c are different.

[0063] The transmitting devices 1a to 1c of the third embodiment are equipped with a plurality of quantum signal light sources that generate quantum signals with different wavelengths, and a plurality of classical signal light sources that generate classical signals with different wavelengths. Below, we will explain a control method for switching the wavelengths of the light sources depending on the transmitting devices 1a to 1c that are combined by multiplexing.

[0064] 11 is a diagram for explaining an example of light source wavelength switching control in the third embodiment. In order for multiplexing devices 5a and 5b to optically wavelength-multiplex the quantum communication paths and classical communication paths of each QKD device (transmitting devices 1a to 1c and receiving devices 2a to 2c), the quantum signals and classical signals generated by each transmitting device must have different wavelengths.

[0065] The transmitting device 1a of the third embodiment can generate three types of quantum signals (quantum 1-1 to 1-3) with different wavelengths and three types of classical signals (classical 1-1 to 1-3) with different wavelengths. Similarly, the transmitting device 1b can generate three types of quantum signals (quantum 2-1 to 2-3) with different wavelengths and three types of classical signals (classical 2-1 to 2-3) with different wavelengths. Similarly, the transmitting device 1c can generate three types of quantum signals (quantum 3-1 to 3-3) with different wavelengths and three types of classical signals (classical 3-1 to 3-3) with different wavelengths.

[0066] The monitoring unit 61 collects wavelength information of the light source of the quantum signal and wavelength information of the light source of the classical signal from each of the transmission devices 1a to 1c (step S41).

[0067] Based on the wavelength information collected in step S41, the control unit 62 instructs each of the transmitting devices 1a to 1c as to which wavelength of the light source to use (step S42).

[0068] Based on the instruction in step S42, each of the transmitting devices 1a to 1c selects a different quantum signal light source and a different classical signal light source, and starts encryption key transmission using the selected light sources.

[0069] As described above, in the QKD system 200-3 of the third embodiment, the control unit 62 instructs each of the transmitting devices 1a-1c to have different wavelengths for the quantum signals and classical signals of each of the transmitting devices 1a-1c. For example, by assigning a light source with a wavelength of 1550.12 nm to Quantum 1-1, a light source with a wavelength of 1550.92 nm to Quantum 2-2, and a light source with a wavelength of 1549.32 nm to Quantum 3-3, and using Quantum 1-1 in transmitting device 1a, Quantum 2-2 in transmitting device 1b, and Quantum 3-3 in transmitting device 1c, quantum signals with different wavelengths can be generated and wavelength multiplexing can be performed. As a result, according to the QKD system 200-3 of the third embodiment, wavelength multiplexing can be performed without any problems in the multiplexing devices 5a and 5b.

[0070] Finally, examples of the hardware configurations of the multiplexing device 5 and the monitoring device 6 according to the first to third embodiments will be described.

[0071] [Example of hardware configuration] 12 is a diagram showing an example of the hardware configuration of the multiplexing device 5 and the monitoring device 6 according to the first to third embodiments. The multiplexing device 5 and the monitoring device 6 according to the first to third embodiments include a processor 201, a main storage device 202, an auxiliary storage device 203, a display device 204, an input device 205, and a communication device 206. The processor 201, the main storage device 202, the auxiliary storage device 203, the display device 204, the input device 205, and the communication device 206 are connected via a bus 210.

[0072] It should be noted that the multiplexing device 5 and the monitoring device 6 may not be provided with some of the above configurations. For example, if the multiplexing device 5 and the monitoring device 6 can use the input function and display function of an external device, the multiplexing device 5 and the monitoring device 6 may not be provided with the display device 204 and the input device 205.

[0073] The processor 201 executes a program read from the auxiliary storage device 203 to the main storage device 202. The main storage device 202 is a memory such as a ROM and a RAM. The auxiliary storage device 203 is a hard disk drive (HDD), a memory card, or the like.

[0074] The display device 204 is, for example, a liquid crystal display. The input device 205 is an interface for operating the multiplexing device 5 and the monitoring device 6. The display device 204 and the input device 205 may be realized by a touch panel or the like having a display function and an input function. The communication device 206 is an interface for communicating with other devices.

[0075] For example, the programs executed by the multiplexing device 5 and the monitoring device 6 are provided as a computer program product in the form of an installable or executable file recorded on a computer-readable storage medium such as a memory card, hard disk, CD-RW, CD-ROM, CD-R, DVD-RAM, or DVD-R.

[0076] Furthermore, for example, the programs executed by the multiplexing device 5 and the monitoring device 6 may be stored on a computer connected to a network such as the Internet, and may be provided by being downloaded via the network.

[0077] Furthermore, for example, the programs executed by the multiplexing device 5 and the monitoring device 6 may be provided via a network such as the Internet without being downloaded. Specifically, for example, the control process of the multiplexing device 5 and the control process of the monitoring device 6 may be executed by a cloud service of an ASP (Application Service Provider) type.

[0078] Furthermore, for example, the programs for the multiplexing device 5 and the monitoring device 6 may be provided in a state where they are pre-installed in a ROM or the like.

[0079] The programs executed by the multiplexing device 5 and the monitoring device 6 have a modular configuration that includes functions that can be realized by programs among the above-mentioned functional configurations. As for each function, as actual hardware, the processor 201 reads the program from a storage medium and executes it, and the above-mentioned functional blocks are loaded onto the main memory device 202. In other words, the above-mentioned functional blocks are generated on the main memory device 202.

[0080] Note that some or all of the above-described functions may be realized by hardware such as an integrated circuit (IC) rather than by software.

[0081] Furthermore, each function may be realized using a plurality of processors 201, and in this case, each processor 201 may realize one of the functions, or may realize two or more of the functions.

[0082] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0083] 1. Transmitting device 2. Receiving device 3 Multiplexer 4 Multiplexer 5 Multiplexer 6 Monitoring equipment 51 Multiplexer 52 Switching control section 61 Monitoring Department 62 Control Unit 100 QKD Systems 101 Optical Fiber 102 Optical Fiber 103 Optical Fiber 201 processor 202 Main storage 203 Auxiliary storage device 204 Display device 205 Input Device 206 Communication Equipment 210 Bus

Claims

1. a plurality of transmitting devices that transmit a plurality of quantum signals including cryptographic key information shared by QKD (Quantum Key Distribution) and a plurality of classical signals including control information of the QKD; a plurality of receiving devices for receiving the plurality of quantum signals and the plurality of classical signals; a first multiplexing device connected to the plurality of transmitting devices; a second multiplexing device connected to the plurality of receiving devices; a plurality of optical fibers connecting the first multiplexer and the second multiplexer; a monitoring device that monitors the transmission status of the plurality of optical fibers, the plurality of optical fibers include a first optical fiber in which the plurality of quantum signals are wavelength-multiplexed and a second optical fiber in which the classical signals are wavelength-multiplexed; The monitoring device a monitoring unit that monitors a transmission state of a plurality of quantum signals flowing through the first optical fiber and a transmission state of a plurality of classical signals flowing through the second optical fiber; a control unit that issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit, the plurality of optical fibers is three or more and includes at least one unused optical fiber; the control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to an unused optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit. QKD system.

2. the monitoring unit monitors the transmission status of the plurality of quantum signals flowing through the first optical fiber by receiving at least one of a cryptographic key generation speed based on the quantum signals and an error rate of the quantum signals from the plurality of receiving devices. The QKD system of claim 1.

3. when the control unit detects that at least one of the encryption key generation speed is lower than a generation threshold and the error rate of the quantum signal is higher than an error rate threshold, the control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to swap the first optical fiber and the second optical fiber; the monitoring unit identifies quality degradation of the first optical fiber when the encryption key generation speed improves after the first optical fiber and the second optical fiber are swapped.

3. The QKD system of claim 2.

4. When the transmission states of the plurality of optical fibers are normal, the control unit demultiplexes a portion of the plurality of quantum signals wavelength-multiplexed onto the first optical fiber, and issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch transmission of the demultiplexed quantum signals to the unused optical fiber. A QKD system according to any one of claims 1 to 3.

5. when transmission of the plurality of quantum signals flowing through the first optical fiber is stopped, the control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber to another optical fiber selected from the plurality of optical fibers. A QKD system according to any one of claims 1 to 3.

6. When the characteristics of the optical fiber before the switching are different from the characteristics of the optical fiber after the switching, the control unit issues an instruction to at least one of the plurality of transmitting devices and the plurality of receiving devices to initialize synchronization parameters used for synchronization of transmission and reception between the plurality of transmitting devices and the plurality of receiving devices. A QKD system according to any one of claims 1 to 3.

7. the plurality of transmitting devices, a plurality of quantum signal light sources that generate quantum signals with different wavelengths; a plurality of classical signal light sources that generate classical signals with different wavelengths; the control unit issues instructions to the plurality of transmitting devices to use the quantum signal light source so that the wavelengths of the plurality of quantum signals waveform-multiplexed onto the first optical fiber are different, and issues instructions to the plurality of transmitting devices to use the classical signal light source so that the wavelengths of the plurality of classical signals waveform-multiplexed onto the second optical fiber are different. A QKD system according to any one of claims 1 to 3.

8. A monitoring device for monitoring transmission states of a plurality of optical fibers connecting a first multiplexing device connected to a plurality of transmitting devices and a second multiplexing device connected to a plurality of receiving devices, comprising: the plurality of optical fibers include a first optical fiber in which a plurality of quantum signals including cryptographic key information shared by QKD (Quantum Key Distribution) are wavelength-multiplexed, and a second optical fiber in which a plurality of classical signals including control information of the QKD are wavelength-multiplexed; a monitoring unit that monitors a transmission state of a plurality of quantum signals flowing through the first optical fiber and a transmission state of a plurality of classical signals flowing through the second optical fiber; a control unit that issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit, the plurality of optical fibers is three or more and includes at least one unused optical fiber; the control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to an unused optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit. Monitoring equipment.

9. A multiplexing device connected to an opposing multiplexing device by a plurality of optical fibers, a multiplexing unit that receives, from a plurality of QKD (Quantum Key Distribution) devices, a plurality of quantum signals each including cryptographic key information shared by QKD and a plurality of classical signals each including control information for the QKD, and wavelength-multiplexes the plurality of quantum signals using a first optical fiber selected from the plurality of optical fibers, and wavelength-multiplexes the plurality of quantum signals using a second optical fiber selected from the plurality of optical fibers; a switching control unit that switches the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers in response to a switching instruction from a monitoring device, the plurality of optical fibers is three or more and includes at least one unused optical fiber; the switching control unit switches the first optical fiber or the second optical fiber to an unused optical fiber selected from the plurality of optical fibers in response to a switching instruction from the monitoring device. Multiplexer.

10. A program for causing a monitoring device to function, the monitoring device monitoring the transmission status of a plurality of optical fibers connecting a first multiplexing device connected to a plurality of transmitting devices and a second multiplexing device connected to a plurality of receiving devices, the program comprising: the plurality of optical fibers include a first optical fiber in which a plurality of quantum signals including cryptographic key information shared by QKD (Quantum Key Distribution) are wavelength-multiplexed, and a second optical fiber in which a plurality of classical signals including control information of the QKD are wavelength-multiplexed; a monitoring unit that monitors a transmission state of a plurality of quantum signals flowing through the first optical fiber and a transmission state of a plurality of classical signals flowing through the second optical fiber; a control unit that issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to another optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit; the plurality of optical fibers is three or more and includes at least one unused optical fiber; the control unit issues an instruction to at least one of the first multiplexing device and the second multiplexing device to switch the first optical fiber or the second optical fiber to an unused optical fiber selected from the plurality of optical fibers according to a monitoring result by the monitoring unit. program.

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