Noise analysis device, noise analysis method, and program

Abstract

In a quantum signal light receiving means for acquiring a detection signal obtained by converting, into an electric signal, quantum signal light received through coherent detection of wavelength-multiplexed signal light in which normal transmission light and quantum signal light are wavelength-multiplexed, an optical power calculation means calculates the power of local oscillator light, normal transmission light, spontaneous emission light generated through amplification of the normal transmission light, and spontaneous Raman scattering light generated in an optical transmission path, all of which are included in the quantum signal light. A noise power calculation means calculates noise power included in the detection signal on the basis of the noise power caused by the local oscillator light, the noise power caused by the quantum signal light receiving means, the noise power due to the interaction between the local oscillator light and the spontaneous emission light, the noise power due to the interaction between the local oscillator light and the spontaneous Raman scattered light, and the noise power caused by the normal transmission light, all of which are calculated on the basis of the calculated power. An excess noise calculation means calculates excess noise included in the detection signal on the basis of the noise power included in the detection signal and the noise power caused by the local oscillator light.

Description

Noise analysis device, noise analysis method and program

[0001] The present disclosure relates to a noise analysis device, a noise analysis method, and a program.

[0002] To improve the confidentiality of communications, the use of communication systems that employ quantum key distribution (QKD) techniques is being considered. A known QKD technique is continuous-variable quantum key distribution (CV-QKD), which superimposes a weak quantum signal onto a wavelength division multiplexing (WDM) optical signal, as described in, for example, Patent Document 1.

[0003] Japanese Patent Application Laid-Open No. 2014-225865

[0004] To maximize the final key generation rate in CV-QKD, it is necessary to minimize the excess noise measured at the receiver of the quantum signal light. However, in a WDM transmission system that wavelength-multiplexes the quantum signal light and normal transmission light in CV-QKD, there is no analytical model to estimate the effect of the WDM transmission system on the excess noise measured at the receiver.

[0005] Excess noise is determined by many parameters that characterize the system and receiver. Therefore, to determine the optimal and required values ​​for device parameters such as the power of the local oscillator used in coherent detection of quantum signal light and the common-mode rejection ratio during coherent detection, it was necessary to repeatedly measure the excess noise while changing the combination of all parameters through experiments. As a result, designing a quantum signal light receiver for CV-QKD required an enormous amount of time through trial and error.

[0006] The noise analysis device according to the present disclosure is a quantum signal light receiving means for receiving, via an optical transmission line, wavelength-multiplexed signal light in which quantum signal light and normal transmission light in which signal light of a plurality of wavelengths are wavelength-multiplexed are wavelength-multiplexed, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the quantum signal light receiving means comprising: optical power calculation means for calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; a noise power calculation means for calculating noise power included in the detection signal based on a noise power corresponding to the first power due to the interaction between the local light and the spontaneous emission light, a noise power due to the quantum signal light receiving means, a noise power corresponding to the first and third powers due to the interaction between the local light and the spontaneous Raman scattered light, a noise power corresponding to the first and fourth powers due to the interaction between the local light and the spontaneous Raman scattered light, and a noise power corresponding to the second power due to the normally transmitted light; and an excess noise calculation means for calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power due to the local light.

[0007] The noise analysis method according to the present disclosure includes a quantum signal light receiving means for receiving, via an optical transmission line, wavelength-multiplexed signal light obtained by wavelength-multiplexing quantum signal light and normal transmission light obtained by wavelength-multiplexing signal light of a plurality of wavelengths, and for receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and for acquiring a detection signal obtained by converting the quantum signal light into an electrical signal, the quantum signal light receiving means calculating a first power that is the power of the local light, a second power that is the power of the normal transmission light, a third power that is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power that is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light. the noise power included in the detection signal is calculated based on a noise power corresponding to the first power caused by the local light, a noise power caused by the quantum signal light receiving means, a noise power corresponding to the first and third powers due to an interaction between the local light and the spontaneous emission light, a noise power corresponding to the first and fourth powers due to an interaction between the local light and the spontaneous Raman scattered light, and a noise power corresponding to the second power caused by the normal transmission light; and the excess noise included in the detection signal is calculated based on the noise power included in the detection signal and the noise power corresponding to the first power caused by the local light.

[0008] A program according to the present disclosure is a quantum signal light receiving means for receiving wavelength-multiplexed signal light, in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed, via an optical transmission line, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the program comprising: a process for calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; the noise power due to the quantum signal light receiving means, the noise power due to the first and third powers due to the interaction between the local light and the spontaneously emitted light, the noise power due to the first and fourth powers due to the interaction between the local light and the spontaneous Raman scattered light, and the noise power due to the second power due to the normally transmitted light; and the noise power due to the noise power due to the local light and the fourth powers due to the interaction between the local light and the spontaneous Raman scattered light.

[0009] According to the present disclosure, it is possible to estimate excess noise in a receiver of quantum signal light.

[0010] FIG. 1 is a diagram schematically showing the configuration of a quantum communication system. FIG. 1 is a diagram schematically showing the configuration of a quantum signal optical receiver. FIG. 2 is a block diagram schematically showing the configuration of a noise analysis system according to an embodiment. FIG. 3 is a block diagram schematically showing the configuration of a noise analysis device according to an embodiment. FIG. 4 is a block diagram schematically showing another configuration of a noise analysis device according to an embodiment. FIG. 5 is a flowchart showing excess noise calculation processing of a noise analysis device according to an embodiment. FIG. 6 is a block diagram schematically showing the configuration of a noise analysis device according to an embodiment. FIG. 7 is a flowchart showing minimum excess noise calculation processing in a noise analysis device according to an embodiment. FIG. 8 is a block diagram schematically showing the configuration of a noise analysis device according to an embodiment. FIG. 9 is a flowchart showing parameter requirement value calculation processing in a noise analysis device according to an embodiment. FIG. 10 is a diagram showing an example configuration of a computer for realizing a noise analysis device according to an embodiment.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same elements are designated by the same reference numerals, and redundant explanations will be omitted as necessary.

[0012] When referring to one embodiment below, it means that the present invention can be applied to any one of the embodiments described below or a combination of two or more embodiments, and is not limited to a specific embodiment.

[0013] First Embodiment A quantum communication system according to a first embodiment will be described below. The quantum communication system is configured as a system that performs quantum key distribution using a continuous-variable quantum key distribution (CV-QKD) method.

[0014] 1 is a diagram showing a schematic configuration of a quantum communication system 1000. The quantum communication system 1000 includes a transmitting device 1100, a receiving device 1200, and an optical transmission line 1300.

[0015] The transmitting device 1100 transmits normal transmission light, in which quantum signal light and multiple signal lights for data communication are wavelength-multiplexed, to the receiving device 1200 via an optical transmission path 1300 configured as a secret communication path. The transmitting device 1100 and the receiving device 1200 may also transmit and receive signals including, for example, basis information, test bits, error correction information, etc., via a public communication path not shown.

[0016] In this embodiment, the transmitting device 1100 transmits 1-bit key information to the receiving device 1200 using the QV-QKD method, superimposing it on the phase difference between weak quantum signal light and normal transmission light. Therefore, the receiving device 1200 can receive quantum key information by utilizing its reception function for receiving normal transmission light. Furthermore, normal transmission light and quantum signal light can coexist on the optical transmission path 1300 that transmits the normal transmission light. Therefore, unlike quantum key distribution using the BB84 protocol, there is no need to provide a dedicated optical transmission path, and quantum key distribution can be realized more easily and inexpensively. Note that various known methods may be applied to quantum key distribution using the QV-QKD method.

[0017] In CV-QKD, quantum signal light is selectively received by performing coherent detection in a quantum signal optical receiver provided in receiving device 1200. In this case, to maximize the final key generation rate, it is necessary to minimize the excess noise measured by the quantum signal optical receiver.

[0018] The transmitting device 1100 includes a quantum signal optical transmitter 1110, a multiplexer 1120, an erbium-doped fiber amplifier (EDFA) 1130, a multiplexer 1140, and optical transceivers TA1 to TAM. １ ~λ ＭThe optical signal is wavelength-multiplexed by a multiplexer 1120 to become normal transmission light SN. Here, M is an integer equal to or greater than 2. The normal transmission light SN output from the multiplexer 1120 is amplified by an EDFA 1130 and then input to a multiplexer 1140. The EDFA 1130 also outputs amplified spontaneous emission (ASE) light L generated when amplifying the normal transmission light SN. ＡＳＥ is input to the multiplexer 1140 via the transmission path of the normal transmission light SN.

[0019] The quantum signal optical transmitter 1110 transmits a weak light having a wavelength λ 1 that is different from the wavelength of the normal transmission light SN. Ｑ The quantum signal light Q is output to the multiplexer 1140 .

[0020] The multiplexer 1140 wavelength-multiplexes the normal transmission light SN amplified by the EDFA 1130 and the quantum signal light Q, and outputs the multiplexed signal light S. The wavelength-multiplexed signal light S is transmitted to the receiving device 1200 via the optical transmission path 1300. The quantum signal light Q is transmitted together with the normal transmission light SN. Therefore, while transmitting through the optical transmission path 1300, the quantum signal light Q is at a wavelength λ included in the normal transmission light SN. １ ~λ Ｍ The spontaneous Raman scattering light L caused by each of the signal lights ＲＡＭ is amplified by

[0021] The receiving device 1200 is provided with a quantum signal optical receiver 1210, demultiplexers 1220 and 1230, and optical transceivers TB1 to TBM. The wavelength-multiplexed signal light S transmitted from the transmitting device 1100 via the optical transmission line 1300 is distributed by the demultiplexer 1220 to the quantum signal optical receiver 1210 and the demultiplexer 1230. The wavelength-multiplexed signal light S input to the demultiplexer 1230 is distributed by the demultiplexer 1230 to the optical transceivers TB1 to TBM. The optical transceivers TB1 to TBM receive the wavelength-multiplexed signal light S having a wavelength λ １ ~λ Ｍ The signal light is received by the respective

[0022] The quantum signal optical receiver 1210 receives the quantum signal light Q included in the wavelength-multiplexed signal light S. Fig. 2 is a diagram showing a schematic configuration of the quantum signal optical receiver. The quantum signal optical receiver 1210 includes a 90° hybrid 1211, a local light source 1212, balanced photodiodes PD1 and PD2, transimpedance amplifiers A1 and A2, and a signal processing unit 1213.

[0023] One input port of the 90° hybrid 1211 is connected to the demultiplexer 1220, and receives the wavelength-multiplexed signal light S. The other input port of the 90° hybrid 1211 is connected to the local light source 1212, and receives the wavelength λ Ｑ A local light LO is input to the 90° hybrid 1211. One output port pair of the 90° hybrid 1211 is connected to a balanced photodiode PD1. The other output port pair of the 90° hybrid 1211 is connected to a balanced photodiode PD2.

[0024] The balanced photodiodes PD1 and PD2 output current signals i1 and i2, which are detection signals of the received light, to the transimpedance amplifiers A1 and A2, respectively. The transimpedance amplifiers A1 and A2 convert the current signals i1 and i2 into detection signals D1 and D2, which are voltage signals, respectively. The transimpedance amplifiers A1 and A2 then output the detection signals D1 and D2, respectively, to the signal processing unit 1213. The signal processing unit 1213 determines the bit indicated by the quantum signal light Q in accordance with the detection signals D1 and D2.

[0025] Next, we will briefly explain the transmission and reception of quantum signal light Q in quantum communication system 1000. In quantum communication system 1000, a phase difference of 2 / π or −2 / π is applied to normal transmission light SN amplified by EDFA 1130, and quantum signal light Q is wavelength-multiplexed. This allows 1-bit quantum signal light Q to be superimposed on normal transmission light SN by multiplexer 1140 and transmitted as wavelength-multiplexed signal light S to receiving device 1200.

[0026] In the receiving device 1200, the wavelength-multiplexed signal light S is made to interfere with the local light LO by the 90-degree hybrid 1211, thereby performing coherent detection. As a result, for example, when the bit of the quantum signal light Q is "1," the balanced photodiode PD1 detects a photon. Also, when the bit of the quantum signal light Q is "0," the balanced photodiode PD2 detects a photon. In other words, depending on the bit of the quantum signal light Q, either the balanced photodiodes PD1 or PD2 detects a photon. When the balanced photodiodes PD1 and PD2 detect a photon, they output current signals i1 and i2, respectively. As a result, the signal processing unit 1213 can determine the bit of the quantum signal light Q by observing whether a level change appears in either the detection signals D1 and D2 converted from the current signals i1 and i2.

[0027] The noise analysis device according to this embodiment is configured as a device that analytically calculates excess noise appearing in the detection signals D1 and D2. Note that, hereinafter, the light detected by the balanced photodiodes PD1 and PD2 will be referred to as received light.

[0028] When focusing on the transmission of quantum signal light Q that is wavelength-multiplexed with normal transmission light, the noise power included in the detection signal is expressed as σ ｔｏｔａｌ ２ The noise power σ ｔｏｔａｌ ２ is generally expressed by the following formula: In the above equation, σ ｓｈｏｔ ２ is the noise power of the shot due to the local light LO. ＲＩＮ ２ is the power of RIN (Relative Intensity Noise) superimposed on the local light LO. ｔｈ ２ is the thermal noise of the transimpedance amplifiers A1 and A2 of 1213. ＬＯ－ＡＳＥ ２ ASE Hikari L ＡＳＥ is the beat noise power between the local oscillator LO and the ＳｐＲＳ ２ is the spontaneous Raman scattered light L ＲＡＭand the beat noise power between the local oscillator LO.

[0029] In contrast, in CV-QKD, the quantum signal light Q is transmitted through the optical transmission path 1300 together with the normal transmission light SN. Therefore, noise due to the normal transmission light SN occurs. Therefore, in order to estimate the noise power of the detection signal, it is necessary to take into account the noise due to the normal transmission light SN. Therefore, in the noise analysis device according to this embodiment, the noise power σ of the detection signal is ｔｏｔａｌ ２ is expressed by the following formula: In the above equation, σ ｓｈｏｔ，ＷＤＭ ２ is the shot noise power that usually arises from the transmitted light SN. ｓｅｌｆ，ＷＤＭ ２ is the self-beat noise power that usually arises from the transmitted optical signal.

[0030] Here, e is the Napier's constant. R is the sensitivity of the balanced photodiodes PD1 and PD2. Δf is the reception baseband bandwidth (however, one-sided bandwidth). CMRR is the common mode rejection ratio at the 90° hybrid. RIN is the relative intensity noise of the local light LO. i ＴＩＡ is the input-equivalent noise current density of the transimpedance amplifiers A1 and A2. M is the number of wavelengths of the signal light contained in the normal transmission light SN. γ ＷＤＭ is the scaling factor.

[0031] P Ｃ is the power of the normally transmitted light SN at the input of the balanced photodiodes PD1 and PD2, i.e., at position B in FIG. ＡＳＥ ASE light L at position B ＡＳＥ (However, the power is a single polarized wave.) ＳｐＳＲ is the spontaneous Raman scattered light L at position B. ＲＡＭ (However, the power is a single polarized wave.) Ｌ Let be the power of the local light LO at position B.

[0032] Here, the insertion loss of the multiplexer 1140 is η Ｍ , isolation is ξＭ The ASE light L output from the EDFA 1130 is ＡＳＥ The power of p ＡＳＥ The optical noise bandwidth (both sides bandwidth) is Δλ. The power of the normal transmission light SN output from the multiplexer 1140 is p ｃ Let's say.

[0033] The transmission loss in the optical transmission line 1300 is expressed as η Ｆ The distance of the optical transmission line 1300 is L. The spontaneous Raman scattering light L generated in the optical transmission line 1300 ＲＡＭ The power of p ＳｐＳＲ Let's say.

[0034] The insertion loss of the duplexer 1220 is η Ｄ , isolation is ξ Ｄ The fundamental loss of the 90° hybrid 1211 is η ｉｎｔ , the excess loss is η ｅｘ In this case, the loss η at the time of reception in the quantum signal optical receiver 1210 is Ｂを , η ｉｎｔ η ｅｘ The power of the local light LO output from the local light source 1212 is expressed as p Ｌ Let's say.

[0035] Under the above definition, the power P of the normal transmission light SN at position B ｃ is expressed by the following formula:

[0036] Power P of the local light LO at position B Ｌ is expressed by the following formula:

[0037] ASE light L at position B ＡＳＥ Power P ＡＳＥ is expressed by the following formula: The power p of the ASE light from the EDAF 1130 in the above formula ＡＳＥ is defined by the following formula: In addition, n ｓｐ is the noise figure of the EDFA 1130. G is the gain of the EDFA 1130. h is Planck's constant. c is the speed of light in a vacuum.

[0038] Spontaneous Raman scattered light L at position BＲＡＭ Power P ＳｐＳＲ is expressed by the following formula: In the above formula, the spontaneous Raman scattered light L generated in the optical transmission line 1300 ＲＡＭ Power of p ＳｐＳＲ is defined by the following formula: In addition, γ Ｒ (λ Ｑ , λ ｉ ) is the wavelength λ contained in the normal transmission light SN １ ~λ Ｍ The wavelength λ is the spontaneous Raman scattering light caused by the i-th signal light among the signal lights Ｑ is the Raman gain coefficient of the quantum signal light Q. α is the loss coefficient of the optical transmission line.

[0039] Next, the terms on the right side of equation [2] will be explained. Shot noise power σ ｓｈｏｔ ２ is expressed by the following formula:

[0040] The power σ of RIN superimposed on the local light LO ＲＩＮ ２ is expressed by the following formula:

[0041] The thermal noise power σ of the transimpedance amplifiers A1 and A2 ｔｈ ２ is expressed by the following formula:

[0042] ASE light L ＡＳＥ and the beat noise power σ ＬＯ－ＡＳＥ ２ is expressed by the following formula:

[0043] Spontaneous Raman scattering light L ＲＡＭ and the beat noise power σ ＬＯ－ＳｐＲＳ ２ is expressed by the following formula:

[0044] Shot noise power σ generated from normal transmitted light SN ｓｈｏｔ，ＷＤＭ ２ is expressed by the following formula:

[0045] Self-beat noise power σ generated from normal transmitted light ｓｅｌｆ，ＷＤＭ ２ is expressed by the following formula:

[0046] Under the above definitions, the excess noise ε of the detection signals D1 and D2 is expressed by the following equation.

[0047] Next, a noise analysis device 10 according to this embodiment will be described. Fig. 3 is a block diagram showing a schematic configuration of a noise analysis system according to one embodiment. The noise analysis system 100 includes the noise analysis device 10 and a storage unit 50.

[0048] The memory unit 50 stores in advance parameters used to calculate the excess noise ε. Specifically, the memory unit 50 stores the sensitivity R of the balanced photodiode, the reception baseband bandwidth Δf, the common mode rejection ratio CMRR, the relative intensity noise RIN of the local oscillator LO, the input equivalent noise current density i ＴＩＡ , the number of wavelengths of signal light included in the normal transmission light SN, M, and the scaling factor γ ＷＤＭ In addition to the above parameters, the storage unit 50 also stores parameters included in parameter sets PS1 and PS2, which will be described later.

[0049] The configuration of the noise analysis device 10 will be described. Fig. 4 is a block diagram showing a schematic configuration of the noise analysis device according to one embodiment. The noise analysis device 10 includes an optical power calculation unit 2, a noise power calculation unit 3, and an excess noise calculation unit 4.

[0050] The noise analysis device 10 may also have a function of appropriately reading out parameters from the storage unit 50. Fig. 5 is a block diagram schematically showing another configuration of a noise analysis device according to an embodiment. The noise analysis device 10 may further have a parameter reading unit 1.

[0051] Next, a description will be given of the calculation process of excess noise by the noise analysis device 10. Fig. 6 is a flowchart showing the calculation process of excess noise by the noise analysis device according to one embodiment.

[0052] Step S1: The parameter reading unit 1 reads the power P of the normal transmission light SN at the position B. ｃ , ASE light L at position B ＡＳＥ Power P ＡＳＥ , spontaneous Raman scattered light L at position B ＲＡＭ Power P ＳｐＳＲ , and the power P of the local light LO at position B Ｌ The parameter reading unit 1 reads a parameter set PS1 consisting of parameters used to calculate the parameter set PS1 from the storage unit 50. The parameter reading unit 1 then transfers the read parameter set PS1 to the optical power calculation unit 2.

[0053] The parameter set PS1 includes the following parameters: [Parameters included in the parameter set PS1] Power p of the normal transmission light SN output from the multiplexer 1140 ｃ Spontaneous emission light L from EDAF 1130 ＡＳＥ Power of p ＡＳＥ Spontaneous Raman scattered light L generated in the optical transmission line 1300 ＲＡＭ Power of p ＳｐＳＲ The power p of the local light LO output from the local light source 1212 Ｌ Insertion loss η of the multiplexer 1140 Ｍ Isolation ξ of the multiplexer 1140 Ｍ Transmission loss η in the optical transmission line 1300 Ｆ Insertion loss η of the demultiplexer 1220 Ｄ The isolation of the duplexer 1220 is ξ Ｄ Loss η in 90° hybrid 1211 Ｂ Noise figure n of EDFA 1130 ｓｐ Gain G of EDFA 1130 Wavelength λ of quantum signal light Q Ｑ The optical noise bandwidth Δλ is the distance L of the optical transmission line 1300. The number M of wavelengths of the signal light included in the normal transmission light SN is the Raman gain γ of the quantum signal light Q due to the spontaneous Raman scattering light caused by the 1st to Mth optical signals. Ｒ (λ Ｑ , λ １ ) ~γ Ｒ (λ Ｑ , λ Ｍ )

[0054] The parameter reading unit 1 also reads the noise power σ ｔｏｔａｌ ２ and the shot noise power σ due to the local light LO ｓｈｏｔ ２ The parameter set PS2 consisting of parameters for calculating the noise power is read from the storage unit 50. The parameter reading unit 1 then transfers the read parameter set PS2 to the noise power calculation unit 3.

[0055] The parameter set PS2 includes the following parameters: [Parameters included in the parameter set PS2] Sensitivity R of the balanced photodiodes PD1 and PD2 Reception baseband bandwidth Δf Common mode rejection ratio CMRR at the 90° hybrid Relative intensity noise RIN of the local light LO Input equivalent noise current density i of the transimpedance amplifiers A1 and A2 ＴＩＡ Scaling factor γ ＷＤＭ

[0056] Step S2: The optical power calculation unit 2 applies the parameter set PS1 received from the data reading unit 1 to the above-mentioned equations [3] to [8] to calculate the power P of the normal transmission light SN at the position B. ｃ , ASE light L at position B ＡＳＥ Power P ＡＳＥ , spontaneous Raman scattered light L at position B ＲＡＭ Power P ＳｐＳＲ , and the power P of the local light LO at position B Ｌ Calculate.

[0057] Step S3: The noise power calculation unit 3 applies the parameter set PS2 received from the data reading unit 1 and the four power values ​​at position B calculated by the optical power calculation unit 2 to equations [2], [9] to

[15] to obtain the noise power σ in the detection signals D1 and D2. ｔｏｔａｌ ２ and the shot noise power σ due to the local light LO ｓｈｏｔ ２ Calculate.

[0058] Step S4: The excess noise calculation unit 4 calculates the noise power σ in the detection signals D1 and D2 calculated by the noise power calculation unit 3. ｔｏｔａｌ ２and the shot noise power σ due to the local light LO ｓｈｏｔ ２ is applied to equation

[16] to calculate the excess noise ε.

[0059] Thus, according to this configuration, in CV-QKD in which a quantum signal is transmitted together with normal light, the excess noise in the received quantum signal can be analytically calculated.

[0060] This makes it possible to efficiently estimate excess noise, which could previously only be understood through trial and error experiments, using the model expressed by the above formula, thereby significantly reducing the time spent on designing quantum communication systems and quantum signal optical receivers.

[0061] Second Embodiment In the first embodiment, a noise analysis device that calculates the excess noise ε has been described. In the present embodiment, a noise analysis device that further calculates the minimum value of the excess noise from the calculated excess noise ε will be described.

[0062] 7 is a block diagram showing a schematic configuration of a noise analysis device according to one embodiment. The noise analysis device 20 has a configuration in which a minimum excess noise calculation unit 5 is added to the noise analysis device 10. The other configuration of the noise analysis device 20 is the same as that of the noise analysis device 10, so redundant explanations will be omitted.

[0063] The minimum excess noise calculation unit 5 calculates the minimum value ε of the excess noise ε. ｍｉｎ is calculated based on the principles explained below.

[0064] The excess noise ε shown in equation

[16] is the power P of the local light LO at position B. Ｌ In this case, the second derivative of the excess noise ε is positive, so the excess noise ε is a downward convex function. Therefore, the first derivative of the excess noise ε in equation

[16] , dε / dP Ｌ When becomes 0, the excess noise ε becomes the minimum value.

[0065] In this case, the optimum local light power P at position B when the excess noise ε is at its minimum value is Ｌ，ｏｐｔ can be calculated using the following formula:

[0066] The optimum local light power P calculated by equation

[16] Ｌ，ｏｐｔ By applying ｍｉｎ is expressed by the following formula:

[0067] Next, the minimum excess noise ε in the noise analysis unit 20 ｍｉｎ 8 is a flowchart showing the calculation process of the minimum excess noise in the noise analysis device according to one embodiment.

[0068] Steps S1 to S4 are the same as those in FIG. 6, so redundant explanations will be omitted.

[0069] Step S5: The minimum excess noise calculation unit 5 calculates the optimum local light power P Ｌ，ｏｐｔ is calculated by equation

[17] .

[0070] Furthermore, the minimum excess noise calculation unit 5 calculates the optimum local light power P Ｌ，ｏｐｔ Applying

[16] to equation

[16] , the minimum excess noise ε ｍｉｎ Calculate.

[0071] Therefore, with this configuration, it is possible to analytically estimate the minimum value of excess noise that can be achieved in a quantum signal receiver, which has been difficult to grasp using general methods.

[0072] This allows us to efficiently estimate the minimum value of excess noise using the model expressed by the above formula without conducting experiments, which in turn makes it possible to design quantum communication systems and quantum signal optical receivers more efficient and in a shorter time.

[0073] Third Embodiment In this embodiment, a noise analysis device capable of calculating required values ​​of parameters that determine excessive noise from the calculated excessive noise ε will be described. Fig. 9 is a block diagram schematically showing the configuration of a noise analysis device according to one embodiment. The noise analysis device 30 has a configuration in which a required parameter value calculation unit 6 is added to the noise analysis device 20. The other configuration of the noise analysis device 30 is the same as that of the noise analysis device 20, so duplicated explanations will be omitted.

[0074] The parameter request value calculation unit 6 calculates the parameter request value PMTreq under certain conditions based on the principle explained below.

[0075] When designing a quantum signal optical receiver, a method for determining parameters will be considered. Here, an example of determining the CMRR will be described. When designing a quantum signal optical receiver, the excess noise ε is set to the allowable excess noise ε, which is an operationally allowable value. ｎｕｌｌ It is required to suppress the allowable excess noise ε ｎｕｌｌ is the minimum excess noise ε ｍｉｎ The above values.

[0076] In this case, from equation

[16] , the optimum local light power P Ｌ，ｏｐｔ In this case, the allowable excess noise ε ｎｕｌｌ To satisfy the CMRR requirement, ｒｅｑ can be expressed by the following formula:

[0077] Here, in order to simplify the calculation, the following substitutions are made:

[0078] Applying equations

[20] to

[24] to equation

[19] , equation

[19] is converted to the required value CMRR ｒｅｑ Solving for, we get the following equation:

[0079] Thus, the allowable excess noise ε ｎｕｌｌ By solving equation

[19] for the parameters to be designed, it is possible to obtain the required value PMTreq of the parameters to be designed.

[0080] Next, a description will be given of the calculation process of the required parameter values ​​in the noise analysis device 30. Fig. 10 is a flowchart showing the calculation process of the required parameter values ​​according to one embodiment.

[0081] Steps S1 to S5 are the same as those in FIG. 8, so redundant explanations will be omitted.

[0082] Step S6: The parameter requirement value calculation unit 6 receives the allowable excess noise ε given as a setting value from the outside. ｎｕｌｌ and parameter specification information INF that specifies the parameter for which the required value is to be calculated, the required value PMTreq of the target parameter is calculated.

[0083] Parameter specification information INF and allowable excess noise ε ｎｕｌｌ may be stored in advance in the storage unit 50 by the user of the noise analysis device 30. At the start of step S6, the parameter reading unit 1 reads the parameter specification information INF and the allowable excess noise ε from the storage unit 50. ｎｕｌｌ Then, the parameter reading unit 1 may read out the read parameter specification information INF and the allowable excess noise ε ｎｕｌｌ may be transferred to the parameter request value calculation unit 6.

[0084] The parameter requirement calculation unit 6 calculates the allowable excess noise ε ｎｕｌｌ and solving for the target parameter to calculate the required value PMTreq.

[0085] By following the above procedure, it becomes possible to analytically determine the required values ​​of the parameters of the design object.

[0086] Therefore, this configuration makes it possible to analytically estimate the device parameters in a quantum communication system and a quantum signal optical receiver that affect excess noise, which is not possible with conventional methods, and thereby enables the design of a quantum signal receiver to be completed more efficiently and in a shorter time.

[0087] Other Embodiments The present disclosure has been described above with reference to the embodiments, but the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0088] Although the quantum signal optical receiver that performs coherent detection using a 90° hybrid has been described above, this is merely an example. For example, a quantum signal optical receiver having a detector with another configuration, such as a homodyne detector that does not use a 90° hybrid, may also be used.

[0089] In the above-described embodiment, the noise analysis device according to the present disclosure has been described primarily as a hardware configuration, but this is not limited thereto. It is also possible to realize the noise analysis device according to the present disclosure by having a computer execute a computer program to perform any desired processing. These processes may be realized by having a computer including at least one processor (e.g., a microprocessor, a CPU, a GPU, an MPU, or a DSP (Digital Signal Processor)) execute the program. Specifically, one or more programs including instructions for causing a computer to perform these algorithms related to transmission signal processing or reception signal processing may be created, and the programs may be supplied to the computer.

[0090] A computer program can be stored and provided to a computer using various types of non-transitory computer-readable media. Non-transitory computer-readable media include various types of tangible storage media. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (e.g., magneto-optical disks), CD-ROMs (Read Only Memory), CD-Rs, CD-R / Ws, and semiconductor memories (e.g., mask ROMs, PROMs (Programmable ROMs), EPROMs (Erasable PROMs), flash ROMs, and RAMs (Random Access Memory)). The program may be provided to the computer by various types of transient computer-readable media. Examples of transient computer-readable media include electrical signals, optical signals, and electromagnetic waves. The transient computer-readable media can provide the program to the computer via a wired communication path such as an electrical wire or optical fiber, or via a wireless communication path.

[0091] An example of the configuration of a computer for realizing a noise analysis device is shown below. FIG. 11 is a diagram showing an example of the configuration of a computer for realizing a noise analysis device according to one embodiment. The noise analysis device can be realized by a computer 9000, such as a dedicated computer or a personal computer (PC). However, the computer does not need to be physically single; multiple computers may be used when performing distributed processing. As shown in FIG. 11 , the computer 9000 includes, for example, a processor 9001, a ROM (Read Only Memory) 9002, a RAM (Random Access Memory) 9003, a storage unit 9004, a communication interface 9005, and a user interface 9006.

[0092] The processor 9001, ROM 9002, RAM 9003, storage unit 9004, communication interface 9005, and user interface 9006 are connected to each other so as to be able to communicate with each other via a bus 9007. Note that although explanation of the OS software for operating the computer is omitted, it is also installed in the computer 9000 as appropriate.

[0093] The ROM 9002 is configured by, for example, a nonvolatile semiconductor memory device, etc. The ROM 9002 stores information such as various programs used by the computer 9000.

[0094] The storage unit 9004 is configured with various storage devices such as a hard disk, a solid state disk, etc. Furthermore, the storage unit 9004 is not limited to a storage device installed in the computer 9000, but may be a storage device external to the computer 9000. The external storage device may be a cloud storage device connected to the computer 9000 via various communication means, for example, a network. The storage unit 9004 stores information such as various programs and data used by the computer 9000.

[0095] The RAM 9003 is configured by a volatile semiconductor memory device, etc. Programs, data, and other information used by the processor 9001 are loaded into the RAM 9003 from one or both of the ROM 9002 and the storage unit 9004 as appropriate.

[0096] The processor 9001 may be configured with, for example, a CPU (Central Processing Unit). Furthermore, the processor 9001 may include not only a CPU but also a GPU (Graphics Processing Unit). A GPU is suitable for performing routine processing in parallel, and by applying it to neural network processing, for example, it is possible to improve processing speed compared to a CPU. The processor 9001 executes various processes based on various programs stored in the ROM 9002 or various programs and data held in the RAM 9003, as appropriate. Furthermore, the processor 9001 may store data generated by the processing in the RAM 9003 or the storage unit 9004, as appropriate.

[0097] The communication interface 9005 is an interface that connects the computer 9000 to a communication network such as the Internet or an intranet via various wired communication means or wireless communication means, etc. This allows the computer 9000 to communicate with other devices, systems, sensors, etc. that are connected to the communication network.

[0098] The user interface 9006 includes, for example, a display unit that provides information so that the user can recognize it using a display device or the like, and an audio output unit that outputs audio. The user interface 9006 also includes an input unit that allows the user to input information to the computer 9000 by operating it, such as a keyboard, a mouse, or a touch panel. The user interface 9006 may also include devices such as sensors that obtain information useful to the user.

[0099] Although the computer 9000 has been described as a single device here, this is merely an example. The computer 9000 may be composed of multiple physically separated devices. Some of the multiple devices may be portable devices, and the other devices may be stationary devices.

[0100] Each drawing is merely an example for describing one or more embodiments. Each drawing may not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessary to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

[0101] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes.

[0102] (Supplementary Note 1) In quantum signal light receiving means, wavelength-multiplexed signal light in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed is transmitted over an optical transmission line, the quantum signal light is received from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and a detection signal in which the quantum signal light is converted into an electrical signal is obtained, the quantum signal light receiving means comprises optical power calculation means for calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; a noise power calculation means for calculating noise power included in the detection signal based on noise power corresponding to the first power, noise power caused by the quantum signal light receiving means, noise power corresponding to the first and third powers due to interaction between the local light and the spontaneous emission light, noise power corresponding to the first and fourth powers due to interaction between the local light and the spontaneous Raman scattered light, and noise power corresponding to the second power caused by the normally transmitted light; and an excess noise calculation means for calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power caused by the local light.

[0103] (Supplementary Note 2) The noise analysis device according to Supplementary Note 1, wherein the noise power calculation means calculates a first noise power which is the power of shot noise generated by the local light according to the first power, a second noise power which is the power of relative intensity noise of the local light according to the first power, a third noise power which is the power of noise generated when the quantum signal light is converted into the electrical signal, a fourth noise power which is the power of beat noise between the spontaneous emission light and the local light according to the first and third powers, a fifth noise power which is the power of beat noise between the spontaneous Raman scattering light and the local light according to the first and fourth powers, a sixth noise power which is the power of shot noise generated by the normally transmitted light according to the second power, and a seventh noise power which is the power of self-beat noise generated by the normally transmitted light, and calculates the noise power included in the detection signal by adding up the calculated first to seventh noise powers.

[0104] (Supplementary Note 3) The noise power calculation means calculates the first noise power σ ｓｈｏｔ ２ is calculated by the following formula: The second noise power σ ＲＩＮ ２ is calculated by the following formula: The third noise power σ ｔｈ ２ is calculated by the following formula: The fourth noise power σ ＬＯ－ＡＳＥ ２ is calculated by the following formula: The fifth noise power σ ＬＯ－ＳｐＲＳ ２ is calculated by the following formula: The sixth noise power σ ｓｈｏｔ，ＷＤＭ ２ is calculated by the following formula: The seventh noise power σ ｓｅｌｆ，ＷＤＭ ２ is calculated by the following formula: In the above equation, e is Napier's number, P Ｌ is the first power, P ｃ is the second power, P ＡＳＥ is the third power, PＳｐＳＲ is the fourth power, R is the sensitivity of a detection element in the quantum signal light receiving means that receives the quantum signal light and outputs a current signal, Δf is a reception baseband bandwidth, CMRR is a common mode rejection ratio in an optical circuit that detects the quantum signal light by causing interference between the wavelength-multiplexed signal light and the local light, RIN is the relative intensity noise of the local light, i ＴＩＡ is the input equivalent noise current density of a transimpedance amplifier that converts the current signal output by the detection element into a voltage signal, M is the number of wavelengths of the signal light of the plurality of wavelengths wavelength-multiplexed into the normal transmission light, γ ＷＤＭ is a scaling factor, and the noise power calculation means calculates the noise power included in the detection signal by the following formula: 3. The noise analysis apparatus of claim 2.

[0105] (Supplementary Note 4) The excess noise calculation means calculates the excess noise ε by the following formula: 4. The noise analysis apparatus of claim 3.

[0106] (Supplementary Note 5) The optical power calculation means calculates the first power P Ｌ is calculated by the following formula: The second power P ｃ is calculated by the following formula: The third power P ＡＳＥ is calculated by the following formula: The fourth power P ＳｐＳＲ is calculated by the following formula: In the above equation, η Ｍ is the insertion loss of a multiplexer that multiplexes the normal transmission light amplified by the fiber optical amplifier with the quantum signal light, and ξ Ｍ is the isolation of the multiplexer, η Ｄ is the insertion loss of a demultiplexer that branches the wavelength-multiplexed signal light transmitted through the optical transmission line to the quantum signal light receiving means, and ξ Ｄ is the isolation of the duplexer, η Ｆ is the loss of the optical transmission line, η Ｂ is the loss due to the optical circuit, L is the distance of the optical transmission line, p ｃis the power of the wavelength-multiplexed signal light output from the multiplexer, p ＡＳＥ is the power of the spontaneous emission light input to the multiplexer, p ＳｐＳＲ is the power of spontaneous Raman scattered light generated in the optical transmission line, p Ｌ is the power of the local light input to the optical circuit.

[0107] (Note 6) The optical power calculation means calculates the power p of the spontaneous emission light input to the multiplexer. ＡＳＥ is calculated by the following formula: The power p of the spontaneous Raman scattered light generated in the optical transmission line ＳｐＳＲ is calculated by the following formula: In the above formula, n ｓｐ is the noise figure of the fiber optical amplifier, G is the gain of the fiber optical amplifier, h is Planck's constant, c is the speed of light in a vacuum, λ Ｑ is the wavelength of the quantum signal light, Δλ is the optical noise bandwidth, γ Ｒ (λ Ｑ 6. The noise analysis device according to claim 5, wherein λi) is the Raman gain of the quantum signal light due to the i-th optical signal among M signal lights included in the normal transmission light.

[0108] (Supplementary Note 7) The quantum signal light receiving means includes a 90° hybrid to one input of which the wavelength-multiplexed signal light is input and to the other input of which the local light is input, the two detection elements connected to two outputs of the 90° hybrid, respectively, the transimpedance amplifier that converts the two current signals output by the two detection elements into two voltage signals, and a signal processing unit that detects a bit indicated by the quantum signal light based on the two voltage signals, and the quantum signal light is output from the 90° hybrid to one of the two detection elements depending on the bit indicated by the quantum signal light.

[0109] (Supplementary Note 8) The noise analysis device calculates the excess noise ε by multiplying the power P of the local light input to the quantum signal optical receiving means, which is the fourth power. Ｌ is a quadratic function of , and is a downward convex function, and is expressed by the following formula: Calculating the optimum local light power, which is the first power when the excess noise ε is at its minimum value, by the following formula: The minimum value of the excess noise ε is calculated by the following formula: 8. The noise analysis device according to claim 4, further comprising a minimum excess noise calculation means.

[0110] (Supplementary Note 9) A permissible excess noise ε greater than the minimum value of the excess noise ｎｕｌｌ The excess noise ε ｎｕｌｌ 9. The noise analysis apparatus according to claim 8, further comprising a parameter requirement value calculation means for calculating a requirement value of the specific parameter corresponding to:

[0111] (Supplementary Note 10) In quantum signal light receiving means for receiving wavelength-multiplexed signal light, in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed, via an optical transmission line, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the quantum signal light receiving means calculates a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, which are contained in the extracted quantum signal light, a noise power included in the detection signal based on a noise power corresponding to the first power due to light emission, a noise power due to the quantum signal light receiving means, a noise power corresponding to the first and third powers due to an interaction between the local light and the spontaneous emission light, a noise power corresponding to the first and fourth powers due to an interaction between the local light and the spontaneous Raman scattered light, and a noise power corresponding to the second power due to the normally transmitted light, and an excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power due to the local light.

[0112] (Supplementary Note 11) In quantum signal light receiving means, wavelength-multiplexed signal light in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed is transmitted over an optical transmission line, the quantum signal light is received from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and a detection signal in which the quantum signal light is converted into an electrical signal is obtained, the quantum signal light receiving means includes a process of calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; a process of calculating noise power included in the detection signal based on noise power corresponding to the first power, noise power caused by the quantum signal light receiving means, noise power corresponding to the first and third powers due to an interaction between the local light and the spontaneous emission light, noise power corresponding to the first and fourth powers due to an interaction between the local light and the spontaneous Raman scattered light, and noise power corresponding to the second power due to the normally transmitted light; and a process of calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power due to the local light.

[0113] REFERENCE SIGNS LIST 1 Parameter reading unit 2 Optical power calculation unit 3 Noise power calculation unit 4 Excess noise calculation unit 5 Minimum excess noise calculation unit 6 Parameter requirement value calculation unit 10 Noise analysis device 20 Noise analysis device 30 Noise analysis device 50 Storage unit 100 Noise analysis system 200 Noise analysis system 1100 Transmitting device 1110 Quantum signal optical transmitter 1120 Multiplexer 1130 EDFA 1140 Multiplexer 1200 Receiving device 1210 Quantum signal optical receiver 1211 90° hybrid 1212 Local oscillator light source 1213 Signal processing unit 1220 Demultiplexer 1230 Demultiplexer 1300 Optical transmission path 9000 Computer 9001 Processor 9002 ROM 9003 RAM 9004 Storage unit 9005 Communication interface 9006 User interface 9007 Bus A1 Transimpedance amplifier A2 Transimpedance amplifier PD1 BPD PD2 BPD Q Quantum signal light SN Normal transmission light S Wavelength multiplexed signal light

Claims

1. A quantum signal light receiving means for receiving wavelength-multiplexed signal light, in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed, transmitted over an optical transmission line, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the quantum signal light receiving means comprising: optical power calculation means for calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; a noise power calculation means for calculating noise power included in the detection signal based on noise power corresponding to the first power due to the local light, noise power due to the quantum signal light receiving means, noise power corresponding to the first and third powers due to interaction between the local light and the spontaneous emission light, noise power corresponding to the first and fourth powers due to interaction between the local light and the spontaneous Raman scattered light, and noise power corresponding to the second power due to the normal transmission light; and an excess noise calculation means for calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power due to the local light.

2. The noise analysis device according to claim 1, wherein the noise power calculation means calculates: a first noise power which is the power of shot noise generated by the local light and corresponds to the first power; a second noise power which is the power of relative intensity noise of the local light and corresponds to the first power; a third noise power which is the power of noise generated when the quantum signal light is converted into the electrical signal; a fourth noise power which is the power of beat noise between the spontaneous emission light and the local light and corresponds to the first and third powers; a fifth noise power which is the power of beat noise between the spontaneous Raman scattering light and the local light and corresponds to the first and fourth powers; a sixth noise power which is the power of shot noise generated by the normally transmitted light and corresponds to the second power; and a seventh noise power which is the power of self-beat noise generated by the normally transmitted light, and calculates the noise power contained in the detection signal by adding up the calculated first to seventh noise powers.

3. The noise power calculation means calculates the first noise power σ ｓｈｏｔ ２ is calculated by the following formula: The second noise power σ ＲＩＮ ２ is calculated by the following formula: The third noise power σ ｔｈ ２ is calculated by the following formula: The fourth noise power σ ＬＯ－ＡＳＥ ２ is calculated by the following formula: The fifth noise power σ ＬＯ－ＳｐＲＳ ２ is calculated by the following formula: The sixth noise power σ ｓｈｏｔ，ＷＤＭ ２ is calculated by the following formula: The seventh noise power σ ｓｅｌｆ，ＷＤＭ ２ is calculated by the following formula: In the above equation, e is Napier's constant, P Ｌ is the first power, P ｃ is the second power, P ＡＳＥ is the third power, P ＳｐＳＲ is the fourth power, R is the sensitivity of a detection element in the quantum signal light receiving means that receives the quantum signal light and outputs a current signal, Δf is a reception baseband bandwidth, CMRR is a common mode rejection ratio in an optical circuit that detects the quantum signal light by causing interference between the wavelength-multiplexed signal light and the local light, RIN is the relative intensity noise of the local light, and i ＴＩＡ is the input equivalent noise current density of a transimpedance amplifier that converts the current signal output by the detection element into a voltage signal, M is the number of wavelengths of the signal light of the plurality of wavelengths wavelength-multiplexed into the normal transmission light, γ ＷＤＭ is a scaling factor, and the noise power calculation means calculates the noise power included in the detection signal by the following formula: The noise analysis device according to claim 2 .

4. The excess noise calculation means calculates the excess noise ε by the following formula: The noise analysis device according to claim 3 .

5. The optical power calculation means calculates the first power P Ｌ is calculated by the following formula: The second power P ｃ is calculated by the following formula: The third power P ＡＳＥ is calculated by the following formula: The fourth power P ＳｐＳＲ is calculated by the following formula: In the above equation, η Ｍ is the insertion loss of a multiplexer that multiplexes the normal transmission light amplified by the fiber optical amplifier with the quantum signal light, and ξ Ｍ is the isolation of the multiplexer, η Ｄ is the insertion loss of a demultiplexer that branches the wavelength-multiplexed signal light transmitted through the optical transmission line to the quantum signal light receiving means, and ξ Ｄ is the isolation of the duplexer, η Ｆ is the loss of the optical transmission line, η Ｂ is the loss due to the optical circuit, L is the distance of the optical transmission line, p ｃ is the power of the wavelength-multiplexed signal light output from the multiplexer, p ＡＳＥ is the power of the spontaneous emission light input to the multiplexer, p ＳｐＳＲ is the power of spontaneous Raman scattered light generated in the optical transmission line, p Ｌ The noise analysis device according to claim 4 , wherein τ is the power of the local light input to the optical circuit.

6. The optical power calculation means calculates the power p of the spontaneous emission light input to the multiplexer. ＡＳＥ is calculated by the following formula: The power p of the spontaneous Raman scattering light generated in the optical transmission line ＳｐＳＲ is calculated by the following formula: In the above formula, n ｓｐ is the noise figure of the fiber optical amplifier, G is the gain of the fiber optical amplifier, h is Planck's constant, c is the speed of light in a vacuum, λ Ｑ is the wavelength of the quantum signal light, Δλ is the optical noise bandwidth, γ Ｒ (λ Ｑ 6. The noise analysis device according to claim 5, wherein λi) is the Raman gain of the quantum signal light due to the ith optical signal among M signal lights included in the normal transmission light.

7. The noise analysis device according to claim 6, wherein the quantum signal light receiving means comprises: a 90° hybrid to one input of which the wavelength-multiplexed signal light is input and the other input of which the local light is input; two detection elements connected respectively to two outputs of the 90° hybrid; the transimpedance amplifier that converts the two current signals output by the two detection elements into two voltage signals; and a signal processing unit that detects a bit indicated by the quantum signal light based on the two voltage signals, and the quantum signal light is output from the 90° hybrid to one of the two detection elements depending on the bit indicated by the quantum signal light.

8. The noise analysis device calculates the excess noise ε based on the fourth power P of the local light input to the quantum signal optical receiving means. Ｌ is a quadratic function of , and is a downward convex function, and is expressed by the following formula: Calculating the optimum local light power, which is the first power when the excess noise ε is at its minimum value, by the following formula: The minimum value of the excess noise ε is calculated by the following formula: The noise analysis device according to claim 4 or 5, further comprising a minimum excess noise calculation means.

9. In a quantum signal light receiving means for receiving wavelength-multiplexed signal light, in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed, via an optical transmission line, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the quantum signal light receiving means calculates a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light, a noise power included in the detection signal based on a noise power corresponding to the first power caused by the local light, a noise power caused by the quantum signal light receiving means, a noise power corresponding to the first and third powers due to an interaction between the local light and the spontaneous emission light, a noise power corresponding to the first and fourth powers due to an interaction between the local light and the spontaneous Raman scattered light, and a noise power corresponding to the second power caused by the normally transmitted light; and a noise analysis method for calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power caused by the local light.

10. In a quantum signal light receiving means for receiving wavelength-multiplexed signal light, in which normal transmission light in which signal light of a plurality of wavelengths is wavelength-multiplexed and quantum signal light are wavelength-multiplexed, via an optical transmission line, receiving the quantum signal light from the transmitted wavelength-multiplexed signal light by coherent detection using local light, and acquiring a detection signal in which the quantum signal light is converted into an electrical signal, the quantum signal light receiving means includes a process for calculating a first power which is the power of the local light, a second power which is the power of the normal transmission light, a third power which is the power of spontaneous emission light generated by amplification of the normal transmission light, and a fourth power which is the power of spontaneous Raman scattering light generated in the optical transmission line, all of which are included in the extracted quantum signal light; a process of calculating noise power included in the detection signal based on noise power corresponding to the first power due to the local light, noise power due to the quantum signal light receiving means, noise power corresponding to the first and third powers due to interaction between the local light and the spontaneous emission light, noise power corresponding to the first and fourth powers due to interaction between the local light and the spontaneous Raman scattered light, and noise power corresponding to the second power due to the normal transmission light; and a process of calculating excess noise included in the detection signal based on the noise power included in the detection signal and the noise power corresponding to the first power due to the local light.

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