Multiplexing device, QKD system, QKD device, multiplexing method and adjustment method

Abstract

To suppress decrease in a key generation speed of a QKD device during wavelength division multiplexing schemes.SOLUTION: A multiplexer of an embodiment includes a combining section, a branching section, a light receiving section, and a control section. The combining section performs optical wavelength multiplexing on quantum signals transmitted from a plurality of QKD (Quantum Key Distribution) devices. The branching section splits the optical wavelength-multiplexed quantum signals into quantum signals to be measured and quantum signals to be output externally at a predetermined splitting ratio. The light receiving section measures intensity of the quantum signals to be measured and obtains a measurement result. The control unit adjusts the intensity of the quantum signals output from the plurality of respective QKD devices on the basis of the measurement result and the predetermined splitting ratio.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] Embodiments of the present invention relate to a multiplexing apparatus, a QKD system, a QKD apparatus, a multiplexing method, and an adjustment method.

Background Art

[0002] Quantum key distribution technology (Quantum Key Distribution, hereinafter QKD) is a technology for securely sharing an encryption key between a transmission device that continuously transmits single photons connected by an optical fiber and a reception device that receives single photons. The encryption key shared by QKD is guaranteed to be unlistened to based on the principles of quantum mechanics. Information theory guarantees that data encrypted and communicated using an encryption communication method called a one-time pad using the shared encryption key cannot be decrypted by any eavesdropper with any knowledge.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, conventional technology had a problem in that the key generation speed of the QKD device decreased when using wavelength division multiplexing. [Means for solving the problem]

[0006] The multiplexing device of this embodiment comprises a wave multiplexing unit, a splitter unit, a light receiving unit, and a control unit. The wave multiplexing unit optically wavelength-multiplexes quantum signals transmitted from a plurality of QKD (Quantum Key Distribution) devices. The splitter unit splits the optically wavelength-multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output externally, at a predetermined splitting ratio. The light receiving unit measures the intensity of the quantum signal to be measured and obtains the measurement result. The control unit adjusts the intensity of the quantum signals output from each of the plurality of QKD devices based on the measurement result and the predetermined splitting ratio. [Brief explanation of the drawing]

[0007] [Figure 1] A diagram showing an example configuration of a typical QKD system. [Figure 2] A diagram showing an example configuration of a QKD system using multiple QKD devices. [Figure 3] This figure shows an example of using optical wavelength division multiplexing technology. [Figure 4] This figure shows an example 2 of using optical wavelength division multiplexing technology. [Figure 5] A diagram showing an example of the device configuration of the QKD system according to the first embodiment. [Figure 6] A diagram showing an example of the functional configuration of the multiplexing device of the first embodiment. [Figure 7] A diagram illustrating an example of the multiplexing method of the first embodiment. [Figure 8] A diagram showing an example of the functional configuration of the multiplexing device of the second embodiment. [Figure 9] A diagram showing an example of the functional configuration of the multiplexing device and transmitting device of the third embodiment. [Figure 10] A diagram showing an example of the functional configuration of a multiplexing device and a transmitting device in a modified example of the third embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the multiplexing device, QKD system, QKD device, multiplexing method, and adjustment method will be described in detail below with reference to the attached drawings.

[0009] Hereafter, a cryptographic key exchange device that utilizes QKD (Quantum Key Distribution) technology will be referred to as a QKD device. Furthermore, a cryptographic key exchange system composed of multiple QKD devices will be referred to as a QKD system. First, we will explain an example of a typical QKD system.

[0010] Figure 1 shows an example configuration of a typical QKD system. A typical QKD system 100 includes a transmitter 1, a receiver 2, and two optical fibers 101 and 102.

[0011] Transmitter 1 is a QKD device on the transmitting side. Transmitter 1 generates a photon, encodes encryption key information representing bit information of 0 or 1 into the photon, and transmits the photon with the encoded encryption key information to receiver 2.

[0012] Receiving device 2 is the receiving QKD device. Receiving device 2 receives photons sent from transmitting device 1 and decodes the encryption key information.

[0013] Optical fiber 101 is used as a quantum communication channel to transmit quantum signals in which encryption key information is encoded.

[0014] The optical fiber 102 is used as a classical communication channel to transmit classical signals containing QKD control information. For example, the classical communication channel is used to transmit synchronization signals between the photon transmitter used in transmitting device 1 and the photon receiver 2 used in receiving device 2, as well as optical signals such as data communication.

[0015] Since quantum signals in a quantum communication channel are extremely weak compared to optical signals in a classical communication channel (at the level of 1 photon per pulse), physically separate optical fibers 101 and 102 are usually used for the quantum communication channel and the classical communication channel. Also, in order to transmit signals dedicated to the QKD device, the optical fiber 101 of the quantum communication channel and the optical fiber 102 of the classical communication channel need to be dark fibers.

[0016] Figure 2 is a diagram showing a configuration example of a QKD system 100-2 by a plurality of QKD devices. In the QKD system 100-2, in order to improve the transmission speed of the shared encryption key, the number of QKD devices is increased to improve the transmission speed of the encryption key in the entire QKD system 100-2. As shown in Figure 2, for example, when using a 3-form QKD system, the transmission speed of the encryption key is three times that when using the 1-form QKD system 100 (Figure 1). However, in this case, the number of required optical fibers increases. An increase in the number of optical fibers required for the social implementation of the QKD system is not practical.

[0017] Therefore, there is a method of realizing the quantum communication channel and the classical communication channel with one optical fiber using the optical wavelength multiplexing technology (Patent Document 1). By shifting the wavelength of the optical signal of the quantum communication channel and the wavelength of the optical signal of the classical communication channel, even when transmitted through the same optical fiber, the transmission of the encryption key by QKD is possible without mutual interference. With this technology, the number of optical fibers required for one form of the QKD system becomes one.

[0018] Figure 3 is a diagram showing Example 1 when using the optical wavelength multiplexing technology. In the QKD system 100-3 of Figure 3, in addition to the normal QKD devices (transmitter 1 and receiver 2), the optical fiber 101 used as the quantum communication channel, and the optical fiber 102 used as the classical communication channel, multiplexing devices 3a and 3b for wavelength multiplexing the optical signals and an optical fiber 103 are used.

[0019] The transmitting device 1 and the multiplexing device 3a, and the receiving device 2 and the multiplexing device 3b are arranged, for example, in the same rack and connected by short optical fibers. The multiplexing devices 3a and 3b are connected by optical fibers 103 corresponding to the communication distance, similar to a typical QKD device.

[0020] However, in Example 1 of Figure 3, wavelength multiplexing of optical signals of different intensities is required, which is technically difficult. Therefore, as shown in Figure 4, a method can be considered in which the optical fibers 101a to 101c of the quantum communication channel are wavelength multiplexed into a single optical fiber 101d, and the optical fibers 102a to 102c of the classical communication channel are wavelength multiplexed into a single optical fiber 102d.

[0021] Figure 4 shows Example 2 of using optical wavelength division multiplexing technology. In the QKD system 100-4 of Figure 4, wavelength division multiplexing of optical signals from optical fibers 101a to 101c used in the quantum communication channel is performed by multiplexers 4a and 4b, and wavelength division multiplexing of optical signals from optical fibers 102a to 102c used in the classical communication channel is performed by multiplexers 4c and 4d.

[0022] Wavelength division multiplexing of optical signals of the same intensity, as in QKD system 100-4 in Figure 4, is easier than wavelength division multiplexing of optical signals of different intensities, as in QKD system 100-3 in Figure 3. In the wavelength division multiplexing scheme shown in Figure 3, increasing the number of QKD devices used to improve the transmission speed of the encryption key increases the number of optical fibers 103 required in proportion to the number of devices. On the other hand, with the wavelength division multiplexing scheme shown in Figure 4, even if the number of QKD devices performing wavelength division multiplexing increases, the number of optical fibers required remains at two, thus reducing implementation costs.

[0023] In the multiplexing device 4 shown in Figures 3 and 4, the optical signal is attenuated. Generally, the optical signal is attenuated by about 1 dB per device. As mentioned above, since the quantum signal is very weak, the 2 dB attenuation from the two devices (transmitter and receiver) significantly affects the performance (key generation speed) of the QKD device. The reduction in key generation speed due to a 2 dB attenuation is 40%.

[0024] (First Embodiment) The following describes an embodiment of a QKD system that can suppress the reduction in key generation speed of the QKD device when using wavelength division multiplexing.

[0025] [Example of device configuration] Figure 5 shows an example of the device configuration of the QKD system 200 of the first embodiment. The QKD system 200 of the first embodiment comprises transmitting devices 1a to 1b, receiving devices 2a to 2b, and multiplexing devices 5a and 5b. Note that the number of transmitting devices 1a to 1b and receiving devices 2a to 2b is not limited to two, but can be any number. The multiplexing devices 5a and 5b are connected by two optical fibers 103a to 103b. Hereinafter, when optical fibers 103a to 103b are not distinguished, they will simply be referred to as optical fiber 103.

[0026] Multiplexer 5a is installed on the transmitting side and is connected to the quantum and classical communication channels of multiple transmitting devices 1a to 1b. Multiplexer 5b is installed on the receiving side and is connected to the quantum and classical communication channels of multiple receiving devices 2a to 2b. Multiplexer 5a multiplexes the optical fibers 101a to 101b of multiple quantum communication channels into a single optical fiber 103a. Multiplexer 5b multiplexes the optical fibers 102a to 102b of multiple classical communication channels into a single optical fiber 103b.

[0027] Hereafter, when multiplexing devices 5a and 5b are not distinguished, they will simply be referred to as multiplexing device 5.

[0028] To solve the aforementioned problems, in the QKD system 200 of the first embodiment, the output strength of the quantum signal from the transmitter 1 is increased by the amount of attenuation in the multiplexer 5. For example, for a 2 dB attenuation (40% reduction) between two units, increasing the output strength of the quantum signal from the transmitter 1 by 40% will make the intensity of the quantum signal received by the receiver 2 the same as when the multiplexer 5 is not used. On the other hand, in that case, the quantum signal strength from the transmitter 1 will rise above the level of one photon per pulse. That is, the probability of multiple photons being included in one pulse will increase, and the theoretical security of quantum cryptography cannot be guaranteed (for example, Non-Patent Literature 1).

[0029] The problem with increasing the intensity of the quantum signal output from transmitter 1 is that the intensity of the quantum signal will exceed the 1-photon level within the range accessible to an eavesdropper. Therefore, as shown in Figure 5, transmitter 1 and multiplexer 5 are installed in a physically protected area (e.g., a server room) that is inaccessible to eavesdroppers, and the output intensity of the quantum signal from transmitter 1 is increased so that the intensity of the quantum signal at the time of output from multiplexer 5 is at the 1-photon level. In this way, within the range accessible to an eavesdropper (outside the physically protected area), the intensity of the quantum signals transmitted by each transmitter 1 will be at the 1-photon level, and the theoretical security of quantum cryptography will be maintained.

[0030] However, in the example shown in Figure 5, the intensity of the quantum signal from the transmitting device 1 can only be increased by the 1dB attenuation of one multiplexer 5, and the signal is still affected by the attenuation of the receiving multiplexer 5. In this case, the reduction in key generation speed due to the 1dB attenuation of one multiplexer 5 is 20%, which is less than the reduction in key generation speed when there are two multiplexers 5 with a 2dB attenuation.

[0031] [Example of functional configuration] Figure 6 shows an example of the functional configuration of the multiplexing device 5a of the first embodiment. The multiplexing device 5a of the first embodiment includes a wave multiplexing unit 51, a branching unit 52, a light receiving unit 53, and a control unit 54.

[0032] The multiplexing unit 51 optically multiplexes quantum signals transmitted from multiple transmitting devices 1. The multiplexing unit 51 is implemented by a WDM (Wavelength Division Multiplexing) module, such as a DWDM (Dense Wavelength Division Multiplexing) optical add-drop module.

[0033] The branching unit 52 splits the input optical signal (quantum signal) into two optical signals at a predetermined branching ratio (e.g., 50:50). One optical signal is output to the light receiving unit 53, and the other optical signal is output to the outside (the optical fiber 103a of the quantum communication channel). The branching unit 52 is implemented by, for example, a beam splitter.

[0034] While the predetermined branching ratio can be arbitrary, setting it to 50:50 generally helps prevent manufacturing errors during the installation process of the branching section 52 (for example, the mistake of installing it in the opposite ratio).

[0035] The light-receiving unit 53 measures the intensity of the input optical signal and transmits the measurement result to the control unit 54. The light-receiving unit 53 is implemented, for example, by a photodiode.

[0036] The control unit 54 estimates the intensity of the quantum signal output to the outside (the optical fiber 103a of the quantum communication channel) from the measurement results of the light receiving unit 53 and the branching ratio of the branching unit 52. Then, the control unit 54 instructs each of the multiple transmitters 1 to adjust the output intensity of their quantum signals so that the quantum signals of each transmitter 1 output to the outside of the multiplexer 5a are at the 1-photon level (1 photon per pulse). The control unit 54 is implemented by, for example, a microprocessor.

[0037] Each transmitter 1 adjusts the output intensity of the quantum signal based on instructions received from the control unit 54. This allows the intensity of the quantum signal from each transmitter 1 to be automatically adjusted so that the quantum signal output from the multiplexer 5 is at the single-photon level. In other words, with the configuration shown in Figure 6, the attenuation rate of the transmitting multiplexer 5a is automatically taken into consideration, and the output intensity of the quantum signal from each transmitter 1 can be automatically adjusted. For example, even if there is variation in the attenuation rate depending on the wavelength of the quantum signal from each transmitter 1, the intensity of the quantum signal from each transmitter 1 can be automatically adjusted.

[0038] [Examples of redundancy methods] Figure 7 is a diagram illustrating an example of the multiplexing method of the first embodiment. The example in Figure 7 shows an example of optical wavelength multiplexing with two transmitting devices 1. The configuration of the multiplexing device 5 is the same as in Figure 6, and the function of each component is as described above.

[0039] First, the transmitter 1b receives an instruction from the control unit 54 to turn off the output of the quantum signal of the transmitter 1 other than the one being adjusted (in the example of Figure 7, transmitter 1a), and turns off the output (step S1).

[0040] Next, the transmitter 1a outputs a quantum signal of normal intensity (1-photon level) (step S2).

[0041] Next, the multiplexer 51 optically wavelength-multiplexes the quantum signals transmitted from the transmitters 1a and 1b (step S3). However, in the example shown in Figure 7, since the output of transmitter 1b (outputs other than those being adjusted) is turned off in step S1, the quantum signal from transmitter 1b is not included in the optically wavelength-multiplexed quantum signal.

[0042] Next, the branching unit 52 branches the quantum signal to the light receiving unit 53 and the external output (optical fiber 103a of the quantum communication channel) at a predetermined branching ratio (for example, 50:50) (step S4). For example, if a 1-photon level quantum signal is a 0.8-photon level quantum signal (8 photons per 10 pulses) at the time of input to the branching unit 52, then with a branching ratio of 50:50, a 0.4-photon level quantum signal is branched to the light receiving unit 53, and a 0.4-photon level quantum signal is branched to the external output.

[0043] Next, the light-receiving unit 53 measures the intensity of the branched quantum signal and transmits the measurement result to the control unit 54 (step S5).

[0044] Next, the control unit 54 estimates the intensity of the external output quantum signal from the measurement result of the light receiving unit 53 and the branching ratio of the branching unit 52 (50:50 in this case), and issues an instruction to the transmitting device 1a to adjust the intensity so that the external output quantum signal reaches a predetermined intensity (for example, a 1-photon level) (step S6). For example, if the measurement result of the light receiving unit 53 is 0.4 photons, then with a branching ratio of 50:50, the intensity of the external output quantum signal is estimated to be 0.4 photons. When the control unit 54 adjusts the intensity so that the external output quantum signal reaches a 1-photon level, it issues an instruction to the transmitting device 1a to increase its output by 2.5 times (to a 2.5-photon level).

[0045] Next, the transmitting device 1a adjusts the intensity of the quantum signal according to instructions from the control unit 54 (step S7).

[0046] The adjustment of the quantum signal of the transmitter 1a is completed by the processing in steps S1 to S7. The QKD system 200 of the first embodiment also adjusts the transmitter 1b in a similar manner.

[0047] As described above, in the multiplexing device 5a of the first embodiment, the multiplexing unit 51 multiplexes quantum signals transmitted from multiple QKD devices (transmitters 1a and 1b in the example of Figure 6) using optical wavelength multiplexing. The branching unit 52 branches the optically wavelength multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output externally, at a predetermined branching ratio. The light receiving unit 53 measures the intensity of the quantum signal to be measured and acquires the measurement result. Then, the control unit 54 adjusts the intensity of the quantum signals output from each of the multiple QKD devices based on the measurement result and the predetermined branching ratio.

[0048] As a result, with the multiplexing device 5a of the first embodiment, in the case of wavelength division multiplexing, the key generation speed of the QKD device can be prevented from decreasing due to attenuation by the multiplexing device 5a. Specifically, in a configuration in which quantum signals transmitted from multiple QKD devices are optically wavelength multiplexed by the multiplexing device 5a, it is possible to prevent a decrease in the key generation speed due to the presence of the multiplexing device 5a while ensuring the theoretical security of quantum cryptography.

[0049] (Second Embodiment) Next, a second embodiment will be described. In the description of the second embodiment, explanations similar to those of the first embodiment will be omitted, and the differences from the first embodiment will be described.

[0050] In the first embodiment described above, in order to adjust the output intensity of the quantum signal of each transmitting device 1, it was necessary to turn off the output of transmitting device 1 other than the one to be adjusted. This is because the intensity of the quantum signal measured by the light receiving unit 53 becomes the sum of the quantum signals of multiple transmitting devices 1, making it impossible to measure the intensity of the quantum signal of a single transmitting device 1. In the first embodiment described above, the more transmitting devices 1 there are, the more times the on / off control of the output of each transmitting device 1 needs to be performed.

[0051] Therefore, in the second embodiment, a configuration will be described that allows the intensity of the quantum signal of the transmitter 1 to be adjusted to be adjusted while the output of the quantum signals of transmitters 1 other than the one to be adjusted remains turned on.

[0052] [Example of functional configuration] Figure 8 shows an example of the functional configuration of the multiplexer 5a-2 of the second embodiment. The multiplexer 5a-2 of the first embodiment includes a multiplexer 51, a branching unit 52, a light receiving unit 53, a control unit 54, and a filter unit 55. In the second embodiment, the filter unit 55 is added at the position shown in Figure 8.

[0053] The filter unit 55 is a filter that allows only quantum signals of a specific wavelength to pass through, and the wavelength it allows to pass through is variable. The wavelengths of the quantum signals transmitted from multiple transmitters 1 are different from each other. The filter unit 55 is equipped with a variable filter that allows quantum signals of the wavelength to be adjusted to pass through, and does not allow quantum signals of wavelengths other than the wavelength to pass through. For example, the filter unit 55 changes the wavelength that passes through it based on instructions from the control unit 54.

[0054] The filter unit 55 allows the light receiving unit 53 to measure only the intensity of the quantum signal from the transmitter 1 being adjusted. This eliminates the need to turn off the output of transmitters 1 other than the one being adjusted, and by changing the wavelength of the filter unit 55, the output intensity of the quantum signal from each transmitter 1 can be adjusted.

[0055] (Third embodiment) Next, the third embodiment will be described. In the description of the third embodiment, explanations similar to those of the first embodiment will be omitted, and the differences from the first embodiment will be described.

[0056] In the first embodiment described above, each transmitting device 1 adjusts the output strength of the quantum signal in response to instructions from an external control unit 54. However, the ability to freely adjust the output strength of the quantum signal of the transmitting device 1 from the outside has some security drawbacks.

[0057] Therefore, in the third embodiment, a configuration will be described that allows the intensity of the quantum signal of the transmitter 1 to be adjusted to be adjusted while maintaining security.

[0058] [Example of functional configuration] Figure 9 shows an example of the functional configuration of the multiplexer 5a-3 and transmitter 1a-2 of the third embodiment. The multiplexer 5a-3 of the third embodiment includes a multiplexer 51, a branching unit 52, and a light receiving unit 53. The transmitter 1a-2 of the third embodiment includes a control unit 11 and a light source 12. In the third embodiment, the multiplexer 5a-3 does not have a control unit 54, and the transmitter 1a-2 has an additional control unit 11. The functional configuration of the transmitter 1b-2 is the same as that of the transmitter 1a-2.

[0059] The control unit 11 adjusts the intensity of the quantum signal to be measured, which is branched at a predetermined branching ratio from the quantum signal obtained by optical wavelength multiplexing of the quantum signal transmitted from another QKD device connected to the multiplexer 5a-3 (transmitter 1b-2 in the example of Figure 9) and the quantum signal transmitted from the light source 12, based on the predetermined branching ratio.

[0060] In the configuration of the third embodiment, the multiplexer 5a-3 measures the intensity of the quantum signal using the light receiving unit 53. The measurement results are transmitted to the control units 54 of each transmitting device 1a-2 and 1b-2. When the control units 54 of each transmitting device 1a-2 and 1b-2 receive the measurement results of the quantum signal intensity to be measured from the multiplexer 5a-3, they adjust the intensity of the quantum signal transmitted from the light source 12 based on the measurement results and a predetermined branching ratio. This makes it possible to adjust the intensity of the quantum signal of the transmitting device 1 to be adjusted while maintaining security.

[0061] (Modified version of the third embodiment) Next, a modified example of the third embodiment will be described. In describing the modified example, explanations similar to those for the third embodiment will be omitted, and only the differences from the third embodiment will be described.

[0062] [Example of functional configuration] Figure 10 shows an example of the functional configuration of a modified multiplexer 5a-4 and a transmitter 1a-3 of the third embodiment. The modified multiplexer 5a-4 includes a multiplexing unit 51 and a branching unit 52. The modified transmitter 1a-3 includes a control unit 11, a light source 12 and a light receiving unit 13. In the modified version, the multiplexer 5a-3 lacks a light receiving unit 53, and the transmitter 1a-3 has an additional light receiving unit 13. The functional configuration of the transmitter 1b-3 is the same as that of the transmitter 1a-3.

[0063] In the modified example, the multiplexing unit 51 multiplexes the quantum signals from each transmitting device 1a-3 and 1b-3 using optical wavelength multiplexing. The branching unit 52 then branches the multiplexed quantum signals at a predetermined branching ratio and transmits the branched quantum signals to be measured to each transmitting device 1a-3 and 1b-3.

[0064] In each transmitting device 1a-3 and 1b-3, the light receiving unit 13 measures the intensity of the quantum signal to be measured, which has been branched at a predetermined branching ratio, and inputs the measurement result to the control unit 11. The control unit 11 adjusts the intensity of the quantum signal based on the measurement result and the branching ratio of the branching unit 52.

[0065] One of the advantages of this modified configuration is that it simplifies the configuration of the multiplexer 5a-4.

[0066] The second advantage of this modified configuration is that it allows for the effective use of the mechanisms of each transmitting device 1a-3 and 1b-3. Normally, transmitting device 1 has a mechanism that measures the intensity of the quantum signal for the control of the light source 12 and feeds the result back into the light source control, and in this modified configuration, this already existing mechanism can be effectively utilized.

[0067] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0068] (Note) Furthermore, the above embodiments can be summarized in the following technical proposal.

[0069] Technical proposal 1 A multiplexer that optically multiplexes quantum signals transmitted from multiple QKD (Quantum Key Distribution) devices, A branching unit that splits a wavelength-multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output externally, at a predetermined branching ratio. A light receiving unit that measures the intensity of the quantum signal to be measured and acquires the measurement result, A control unit that adjusts the intensity of the quantum signals output from each of the plurality of QKD devices based on the measurement results and the predetermined branching ratio, A multiplexing device equipped with the following features.

[0070] Technical proposal 2 The control unit adjusts the intensity of the quantum signals output from each of the plurality of QKD devices so that the quantum signals from each of the plurality of QKD devices output to the outside of the multiplexer are one photon per pulse. The multiplexing device described in Technical Proposal 1.

[0071] Technical proposal 3 The wavelengths of the quantum signals transmitted from the aforementioned multiple QKD devices are different from each other. A filter section equipped with a variable filter that allows quantum signals of the wavelength to be adjusted to pass through, but blocks quantum signals of wavelengths other than the wavelength to be adjusted. A multiplexing device according to technical proposal 1 or 2, further comprising the above.

[0072] Technical proposal 4 A multiplexing device described in any one of Technical Proposals 1 to 3, The aforementioned multiple QKD devices, A QKD system equipped with this feature.

[0073] Technical proposal 5 A QKD (Quantum Key Distribution) device connected to a multiplexer, A light source that transmits quantum signals, A control unit adjusts the intensity of the quantum signal to be measured, which is branched at a predetermined branching ratio from a quantum signal obtained by optical wavelength multiplexing of a quantum signal transmitted from another QKD device connected to the multiplexing device and a quantum signal transmitted from the light source, based on the predetermined branching ratio, and the intensity of the quantum signal transmitted from the light source. A QKD device equipped with this feature.

[0074] Technical proposal 6 The control unit receives the measurement result of the intensity of the quantum signal to be measured from the multiplexer, and adjusts the intensity of the quantum signal transmitted from the light source based on the measurement result and the predetermined branching ratio. The QKD device described in Technical Proposal 5.

[0075] Technical proposal 7 The system further includes a light-receiving unit that measures the quantum signal to be measured, which is branched from the aforementioned wavelength-multiplexed quantum signal at a predetermined branching ratio, and acquires the measurement result. The control unit adjusts the intensity of the quantum signal transmitted from the light source based on the measurement result and the predetermined branching ratio. The QKD device described in Technical Proposal 5.

[0076] Technical proposal 8 The multiplexing device performs optical wavelength multiplexing of quantum signals transmitted from multiple QKD (Quantum Key Distribution) devices, The multiplexing device performs the step of splitting the optical wavelength multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output to the outside, at a predetermined branching ratio. The multiplexing device measures the intensity of the quantum signal to be measured and obtains the measurement result. The multiplexing device adjusts the intensity of the quantum signals output from each of the plurality of QKD devices based on the measurement results and the predetermined branching ratio. Multiplexing methods including

[0077] Technical proposal 9 A method for adjusting a QKD (Quantum Key Distribution) device connected to a multiplexer, The light source transmits a quantum signal, The control unit adjusts the intensity of the quantum signal to be measured, which is branched at a predetermined branching ratio from a quantum signal obtained by optical wavelength multiplexing of a quantum signal transmitted from another QKD device connected to the multiplexing device and a quantum signal transmitted from the light source, based on the predetermined branching ratio. Adjustment methods including those mentioned. [Explanation of Symbols]

[0078] 1. Transmitter 2. Receiving device 3 Multiplexer 4 Multiplexer 5 Multiplexer 11 Control Unit 12 light source 13 Light receiving part 51 Wave section 52 Branching point 53 Light receiving section 54 Control Unit 55 Filter section 100 QKD System 101 Optical Fiber 102 Optical Fiber 103 Optical Fiber

Claims

1. A multiplexer that optically multiplexes quantum signals transmitted from multiple QKD (Quantum Key Distribution) devices, A branching unit that splits a wavelength-multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output externally, at a predetermined branching ratio. A light receiving unit that measures the intensity of the quantum signal to be measured and acquires the measurement result, A multiplexing device comprising: a control unit that adjusts the intensity of quantum signals output from each of the plurality of QKD devices based on the measurement results and the predetermined branching ratio, The control unit adjusts the intensity of the quantum signal output from each of the multiple QKD devices to the branching point to be greater than one photon per pulse, thereby increasing the intensity of the quantum signal between the multiple QKD devices and the branching point to be greater than one photon per pulse, and adjusting the intensity of the quantum signal output from the branching point to the outside to be one photon per pulse. Multiplexer.

2. The wavelengths of the quantum signals transmitted from the aforementioned multiple QKD devices are different from each other. A filter section equipped with a variable filter that allows quantum signals of the wavelength to be adjusted to pass through, but blocks quantum signals of wavelengths other than the wavelength to be adjusted. The multiplexing device according to claim 1, further comprising:

3. A multiplexing device according to claim 1 or 2, The aforementioned multiple QKD devices, A QKD system equipped with this feature.

4. A QKD (Quantum Key Distribution) device connected to a multiplexer, A light source that transmits quantum signals, The system comprises a quantum signal obtained by wavelength multiplexing a quantum signal transmitted from another QKD device connected to the multiplexing device and a quantum signal transmitted from the light source, and a control unit that adjusts the intensity of the quantum signal to be measured, which is branched at a predetermined branching ratio by the branching section of the multiplexing device, and the intensity of the quantum signal transmitted from the light source, based on the predetermined branching ratio. The control unit increases the intensity of the quantum signal output from the light source to more than one photon per pulse, thereby increasing the intensity of the quantum signal between the QKD device and the branching section to more than one photon per pulse, and adjusts the intensity of the quantum signal output from the branching section to the outside to be one photon per pulse. QKD device.

5. The control unit receives the measurement result of the intensity of the quantum signal to be measured from the multiplexer, and adjusts the intensity of the quantum signal transmitted from the light source based on the measurement result and the predetermined branching ratio. The QKD apparatus according to claim 4.

6. The system further includes a light-receiving unit that measures the quantum signal to be measured, which is branched from the aforementioned wavelength-multiplexed quantum signal at a predetermined branching ratio, and acquires the measurement result. The control unit adjusts the intensity of the quantum signal transmitted from the light source based on the measurement result and the predetermined branching ratio. The QKD apparatus according to claim 4.

7. The multiplexing unit comprises the steps of optical wavelength multiplexing quantum signals transmitted from a plurality of QKD (Quantum Key Distribution) devices, The branching section splits the optical wavelength multiplexed quantum signal into a quantum signal to be measured and a quantum signal to be output externally, at a predetermined branching ratio. The light-receiving unit measures the intensity of the quantum signal to be measured and obtains the measurement result. The control unit includes the step of adjusting the intensity of the quantum signal output from each of the plurality of QKD devices based on the measurement result and the predetermined branching ratio, The adjustment step involves increasing the intensity of the quantum signal output from each of the multiple QKD devices to the branching point to more than one photon per pulse, thereby increasing the intensity of the quantum signal between the multiple QKD devices and the branching point to more than one photon per pulse, and adjusting the intensity of the quantum signal output from the branching point to the outside to one photon per pulse. Multiplexing method.

8. A method for adjusting a QKD (Quantum Key Distribution) device connected to a multiplexer, The light source transmits a quantum signal, The control unit includes the step of adjusting the intensity of the quantum signal to be measured, which is branched by the branching section of the multiplexing device at a predetermined branching ratio from a quantum signal obtained by optical wavelength multiplexing of a quantum signal transmitted from another QKD device connected to the multiplexing device and a quantum signal transmitted from the light source, based on the predetermined branching ratio, and the intensity of the quantum signal transmitted from the light source. The adjustment step involves increasing the intensity of the quantum signal output from the light source to more than one photon per pulse, thereby increasing the intensity of the quantum signal between the QKD device and the branching section to more than one photon per pulse, and adjusting the intensity of the quantum signal output from the branching section to the outside to one photon per pulse. Adjustment method.

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