JP5366229B2 - Quantum cryptography communication method - Google Patents

Description

  The present invention particularly relates to a quantum cryptography communication method, and in particular, quantum cryptography communication suitable for a case where the relative position between a transmitter and a receiver that perform quantum cryptography communication changes as in mobile communication on a satellite or the like. Regarding the method.

  In quantum cryptography communication, a method has been proposed in which a synchronization signal for return is generated and transmitted between a transmitter and a receiver for synchronization between the transmitter and the receiver (Patent Document 1, Patent Document). 2).

  Further, in quantum cryptography communication, a method of exchanging synchronization pulses between QKD stations and locking the phase has been proposed in order to reliably detect weak quantum signals (see Patent Document 3).

  Furthermore, in quantum cryptography communication, a method has been proposed in which an optical clock is detected by a photodetector and the detection output is input to a synthesizer via a narrowband filter to generate timing (see Patent Document 4).

JP 2005-260911 A JP 2005-117512 A JP-T-2006-513678 JP 2004-356996 A

  According to Patent Document 1 and Patent Document 2, it is necessary to always achieve phase synchronization on the transmitter side based on a synchronization signal for folding, and for this purpose, a classical communication path such as an optical fiber is used. A loopback transmission line is essential. Therefore, for communication in which the relative position between the transmitter and the receiver changes, that is, the angle of arrival of light changes (hereinafter referred to as mobile communication), as in mobile communication on a satellite or the like, quantum cryptography communication is used. Could not be applied.

  Further, according to Patent Document 3, it is necessary to always lock the phase based on the synchronization pulse, and for this reason, the above-described classical communication path, which is a folded transmission path, is essential. Therefore, as in the case described above, quantum cryptography communication cannot be applied to mobile communication.

  Further, according to Patent Document 4, it is necessary to receive the same optical clock signal in the transmitter and the receiver, and it is impossible to cope with the case where the clock signal is a data signal.

  In addition to the above, according to the study by the present inventor, when applying quantum cryptography communication to mobile communication, the polarization basis axis used for quantum cryptography is determined between the mobile bodies performing mobile communication on the receiving side. A new problem arises that it cannot be detected. Therefore, if the polarization base axis used for quantum cryptography can be detected on the receiving side, it is considered that quantum cryptography communication can be applied to mobile communication.

  Further, according to the study of the present inventor, when quantum cryptography communication is applied to mobile communication, when measuring the arrival time of photons (photon pulses) in quantum key distribution, the transmission system and the reception system are accurate. A new problem arises in that it is necessary to have a clock that measures the time of day and measure it, and it is difficult to set the time of both. Therefore, it is considered that quantum cryptography communication can be applied to mobile communication if both times can be accurately set in the transmission system and the reception system (or a means equivalent to this can be obtained).

  An object of the present invention is to provide a quantum cryptography communication method capable of synchronizing signals between a transmitter and a receiver between a transmitter and a receiver that perform quantum cryptography communication.

In the quantum cryptography communication method of the present invention, a transmitter generates a first quantum key, superimposes the first quantum key on first data, transmits the first quantum key to a first station using laser light, and The first station receives and holds the first data and the first quantum key, and the transmitter generates a second quantum key, and converts the second quantum key into second data. Superimposing and transmitting to the second station using laser light, the second station receiving and holding the second data and the second quantum key, and the transmitter receiving the first quantum A third quantum key is generated by exclusive OR of the key and the second quantum key, and is transmitted to the first station and the second station, and the first station holds the first quantum key held by itself. The second quantum key is generated by an exclusive OR of the quantum key and the third quantum key, and the second station holds the second quantum key held by itself and the third quantum key. The exclusive OR of the quantum key, the first A quantum cryptography communication method for generating a quantum key, first communication means provided in the said transmitter first station and the second station is Pulse light that is a binary optical signal including an on period and an off period between the transmitter and the first station and the second station, and whose intensity is relatively stronger than that of the quantum cryptography signal. A second communication means provided in the transmitter, the first station, and the second station for transmitting and receiving a communication signal comprising the communication between the transmitter, the first station, and the second station; During transmission / reception of a signal and when the communication signal is in the OFF period, a quantum cryptography signal composed of pulsed light that is a binary optical signal and relatively weak in comparison with the communication signal is transmitted and received, The first and second communication means are superimposed on the communication signal and the communication signal. Send and receive the child encrypted signal with the same optical axis.

  Preferably, in the quantum cryptography communication method according to the present invention, the second communication means generates the quantum cryptography signal in synchronization with a falling edge of the communication signal in a period in which the communication signal is off. Transmission / reception is performed after a predetermined delay time elapses from the downstream.

  Preferably, in the quantum cryptography communication method of the present invention, the first or second communication means is incremented corresponding to the transmission speed of the communication signal and reset at a cycle longer than a propagation delay of the communication signal. And a relative time delay is detected using the counter.

  Preferably, in the quantum cryptography communication method according to the present invention, the first communication means performs polarization of the communication signal in accordance with a polarization basis of a photon pulse of the quantum cryptography signal transmitted and received by the second communication means. Modulate.

  According to the quantum cryptography communication method of the present invention, the transmitter superimposes the first quantum key on the first data and transmits the first quantum key to the first station using the laser light, and transmits the second quantum key to the second data. The third quantum key generated by the exclusive OR of the first quantum key and the second quantum key is transmitted to the second station using laser light superimposed on the data, and the first and second stations Send to. As a result, the first station generates the second quantum key by the exclusive OR of the first quantum key held by itself and the third quantum key, and the second station holds the second quantum key held by itself. The first quantum key can be generated by exclusive OR of the key and the third quantum key, and the first station and the second station can share the quantum key.

  Further, according to the quantum cryptography communication method of the present invention, the first communication means transmits and receives a communication signal composed of relatively strong pulsed light, and the second communication means transmits a relatively weak quantum cryptography signal during a period in which the communication signal is off. Send and receive. Thereby, a classic communication path, for example, a transmission path made of an optical fiber can be made unnecessary, and quantum cryptography communication can be applied to mobile communication in a satellite or the like. Also, since the type of communication signal is not limited, quantum cryptography communication can be applied even if the communication signal is a data signal. Moreover, according to the quantum cryptography communication method of the present invention, the communication signal and the quantum cryptography signal superimposed on the communication signal are transmitted and received on the same optical axis. As a result, only one optical axis needs to be adjusted, so that the optical axis can be easily aligned between the transmitter and the receiver.

  Further, according to the quantum cryptography communication method of the present invention, the quantum cryptography signal is transmitted / received after the elapse of a predetermined delay time from the falling edge in synchronization with the falling edge of the communication signal in a period in which the communication signal is off. The Thereby, a relatively weak (actually very weak) quantum cryptography signal can be transmitted and received without being disturbed by a communication signal composed of relatively strong pulsed light.

  According to the quantum cryptography communication method of the present invention, the relative time delay is detected using a counter that is incremented corresponding to the transmission speed of the communication signal and is reset with a period longer than the propagation delay of the communication signal. As a result, when measuring the arrival time of a photon in quantum key distribution, it is possible to eliminate the need to have a clock that accurately clocks the transmission system and the reception system, and to eliminate the need to synchronize the time of both.

  Further, according to the quantum cryptography communication method of the present invention, the polarization modulation of the communication signal is performed in accordance with the polarization basis of the photon pulse of the transmitted / received quantum cryptography signal. Thereby, the polarization base axis used for the quantum cryptography can be detected on the receiving side between the mobile bodies performing mobile communication.

It is a block diagram of the quantum cryptography communication apparatus of this invention. It is a block diagram of the transmitter of the quantum cryptography communication apparatus of this invention. It is a block diagram of the receiver of the quantum cryptography communication apparatus of this invention. It is explanatory drawing of the quantum cryptography communication of this invention. It is another block diagram of the quantum cryptography communication apparatus of this invention. It is a figure which shows the example of application of the quantum cryptography communication of this invention.

  FIG. 1 is a configuration diagram of the quantum cryptography communication device of the present invention, and shows an example of the configuration of the quantum cryptography communication device of the present invention.

  The quantum cryptography communication device includes a transmitter 101 and a receiver 102, and performs quantum cryptography communication using an optical signal (laser light) between them. The transmitter 101 includes a communication satellite 101, for example. That is, it is a moving body. The receiver 102 includes a ground station (base station) 102, for example. That is, it is a fixed station.

  The quantum cryptography communication device includes first communication means 103 and second communication means 104. The 1st communication means 103 is provided in the transmitter 101 and the receiver 102, and transmits / receives the communication signal which consists of comparatively strong pulse light among these. The communication signal is composed of, for example, a data signal (for example, a moving image). The 2nd communication means 104 is provided in the transmitter 101 and the receiver 102, and transmits / receives a comparatively weak (very weak) quantum cryptography signal between these in the period when a communication signal is OFF.

  As can be seen from FIG. 1, there is one optical path 107 between the transmitter 101 and the receiver 102. In other words, the optical path (transmission path or communication path) by the first communication unit 103 and the optical path by the second communication unit 104 coincide with each other. That is, the same optical axis 107 is used. For this purpose, the transmitter 101 is provided with a superimposing unit 105 that superimposes and outputs the optical signal from the first communication unit 103 and the optical signal from the second communication unit 104. The receiver 102 is provided with a separating means 106 that receives and separates the optical signal output in a superimposed manner.

  2 and 3 are configuration diagrams of the transmitter 101 and the receiver 102 of the quantum cryptography communication apparatus of the present invention, respectively. 2 and 3, a thick line indicates an optical signal, and a thin line indicates an electric signal. FIG. 4 is an explanatory diagram of the quantum cryptography communication of the present invention, and particularly shows the superposition of the quantum cryptography signal on the communication signal and the identification of the time of the quantum cryptography signal.

  First, transmission of a communication signal by the first communication means 103 in the transmitter 101 will be described with reference to FIG. The first communication means 103 in the transmitter 101 basically includes an input data recorder 3, a falling trigger pulse generation circuit (hereinafter referred to as trigger generation circuit) 8, and a communication laser 16. The beam splitter 17 is the superimposing means 105.

  Prior to transmission of input data, a PN signal (pseudo noise signal or pseudo random signal) is input to the trigger generation circuit 8 via the switch SW. Therefore, at this time, the switch SW connects the PN generator 2 and the trigger generation circuit 8 in accordance with a switch control signal described later. The PN generator 2 generates and outputs a PN signal having a predetermined data pattern in synchronization with, for example, a 10 MHz clock (generator) 1. As the clock 1, for example, a GPS clock is used. The PN signal is input to the trigger generation circuit 8 and the coincidence detection circuit 7. Instead of the clock 1, a clock with the same high frequency may be used (the same applies to other circuits below).

  The trigger generation circuit 8 detects the falling edge based on the PN signal, generates a falling trigger pulse in synchronization with the falling edge, and inputs the PN signal to the communication laser 16 (laser light source). . The detected fall (and fall trigger pulse) is indicated by an arrow in the modulation waveform (a) of FIG.

  The falling trigger pulse is input to the data controller 5 and the first and second delay pulse generators 9 and 10 (described later). The communication laser 16 generates and outputs a communication signal (binary optical signal) composed of relatively strong pulsed light based on the PN signal (electrical signal). The communication signal is shown in the modulation waveform (a) of FIG. In the communication laser 16, the wavelength λ1 is empirically determined in advance, and the intensity (intensity of the pulsed light) is determined in advance. The output light of the communication laser 16 is input to the beam splitter 17.

  The beam splitter 17 superimposes an optical signal having a wavelength λ 1 from the communication laser 16 and an optical signal having a wavelength λ 2 (described later) from the polarization beam splitter 13, and outputs the superimposed signal along the same optical axis 107. The beam splitter 17 is set so as to reflect light (communication signal) of wavelength λ1 (almost) as it is and to transmit light of wavelength λ2 (quantum encryption signal) as it is.

  The aforementioned PN signal is output from the communication laser 16 prior to the input data. Thereby, the PN signal of the predetermined data pattern is transmitted to the receiver 102. This PN signal is output from the communication laser 16 in the same manner as the input data.

  On the other hand, the PN signal output from the PN generator 2 is input to the coincidence detection circuit 7. The coincidence detection circuit 7 compares the PN signal with a data pattern (not shown) provided in advance in synchronization with the clock 1 (not shown), and if the two coincide, forms a reset signal and outputs it. To do.

  A reset signal from the coincidence detection circuit 7 is input to the counter 6. The counter 6 is reset by the reset signal and counts the clock 1. The counting of the clock 1 will be described later. The count output (count value) of the counter 6 is input to the data controller 5. The data controller 5 forms and outputs a switch control signal in response to the input of the first count value from the counter 6.

  The switch control signal is applied to the switch SW. Thus, the switch SW is switched so as to connect the input data recorder 3 and the trigger generation circuit 8. As a result, the input data (binary signal) held in the input data recorder 3 is input to the trigger generation circuit 8 via the switch SW. For this purpose, data (input data) to be transmitted as a communication signal is prepared in advance in the input data recorder 3 (for example, held in a memory or as real-time stream data or the like). The input data is arbitrary data, and after quantum key sharing is performed, is data (for example, a moving image) encrypted by quantum cryptography (key data). Although not shown, the input data recorder 3 starts sending data by a switch control signal and sends input data in synchronization with the clock 1.

  Accordingly, the communication laser 16 generates and outputs a communication signal (binary optical signal) based on the input data (data to be originally transmitted) in the same manner as the PN signal described above, and outputs the quantum cryptography signal. Are superimposed and output from the beam splitter 17.

  Thus, transmission / reception of data to be originally transmitted is started by transmission (and reception) of a PN signal having a predetermined data pattern. Therefore, the PN signal having a predetermined data pattern is a data communication start signal. Instead of using the PN generator 2 as a start signal, pseudo data having a predetermined data pattern similar to the start signal may be added to the head of the input data.

  Next, transmission of the quantum cryptography signal by the second communication unit 104 in the transmitter 101 will be described with reference to FIG. The second communication means 104 in the transmitter 101 basically includes a random generator 4, a data controller 5, first and second delay pulse generators 9 and 10, first and second quantum lasers 11 and 12, It comprises a polarizing beam splitter 13, an attenuator 14 and a modulator 15. Elements other than those constituting the first and second communication means 103 and 104 may be considered as elements common to the first and second communication means 103 and 104 (the same applies to the receiver 102).

  The random generator 4 generates a random signal (binary signal) taking a random value in synchronization with the clock 1 and inputs the random signal to the data controller 5 and the modulator 15. This random signal is a quantum key (encryption key or key data). The data controller 5 forms and outputs an output signal based on the random signal. The output signal is input to the first and second delay pulse generators 9 and 10. The output signal is a control signal for outputting a delay pulse to either one of the first or second delay pulse generators 9 and 10 (alternatively) according to a random signal (that is, randomly). At this time, the data controller 5 forms an output signal in synchronization with the clock 1, for example, and outputs the signal in synchronization with the falling trigger pulse (see the modulation waveform (a) in FIG. 4) output from the trigger generation circuit 8. Is output. Therefore, the output signal is output only when the falling trigger pulse is input, and only one of the first or second delay pulse generators 9 and 10 outputs the delay pulse.

  The output signal of the data controller 5 is input to one input terminal of the first and second delay pulse generators 9 and 10. A falling trigger pulse output from the trigger generation circuit 8 is input to the other input terminals of the first and second delay pulse generators 9 and 10.

  Only when the output signal of the data controller 5 is input, the first delay pulse generator 9 generates a delay pulse after a delay time D based on the falling trigger pulse. Quantum cryptography) is input to the laser 11. The delayed pulse is shown in photon transmission timing (b) of FIG. The delay time D is predetermined empirically. The first quantum laser 11 generates and outputs a quantum encryption signal (binary optical signal) composed of pulse light that is not very strong, based on the delayed pulse. The intensity of the quantum cryptography signal (pulse light) is determined in advance and is weaker than the communication signal. The wavelength λ2 of the quantum cryptography signal is determined empirically in advance. The output of the first quantum laser 11 is input to the polarization beam splitter 13. The same applies to the second delay pulse generator 10 and the second quantum laser 12.

  The delay time D is sufficiently shorter than one cycle of transmission / reception of communication signals (and hence one cycle of clock 1). Therefore, in the second communication means 104, the quantum cryptography signal is synchronized with the falling edge of the communication signal (with reference to the falling edge) in a period in which the communication signal is off, and a delay time D determined in advance from the falling edge. Sent and received after elapse of.

  Here, the output of the first quantum laser 11 is, for example, that the polarization is H (or V), that is, the polarization direction is 0 degree (or the polarization direction is 90 degrees). This corresponds to 0 (or 1) of the binary signal, for example. The output of the second quantum laser 12 is, for example, that the polarization is V (or H), that is, the polarization direction is 90 degrees (or the polarization direction is 0 degrees). This corresponds to 1 (or 0) of the binary signal, for example.

  The polarization beam splitter 13 superimposes and outputs the outputs of the first and second quantum lasers 11 and 12. The polarization beam splitter 13 is set to transmit the output (polarized light H) of the first quantum laser 11 as it is and reflect the output (polarized light V) of the second quantum laser 12 as it is. Actually, only one of the first and second quantum lasers 11 and 12 outputs an optical signal, and therefore outputs either one of both outputs. As described above, the polarization beam splitter 13 outputs polarized light H or V (photons) based on the quantum key data.

  The optical output of the polarization beam splitter 13 is input to the modulator 15 via the attenuator 14. The light output of the polarization beam splitter 13 is attenuated by the attenuator 14 in consideration of the propagation loss until it becomes 1 photon or less per pulse in the receiver 102. Thereby, the quantum cryptography signal (pulse light) is a binary optical signal composed of relatively weak (very weak) pulse light. The strength of the quantum cryptography signal is determined in advance and is weak compared to the communication signal.

  A random signal from the random generator 4 is input to the modulator 15 as the modulation signal. The modulator 15 modulates the polarization direction of the light output of the polarization beam splitter 13 based on the modulation signal, and then inputs the light to the beam splitter 17. That is, the modulator 15 randomly changes (modulates) the polarization direction of the light output from the polarization beam splitter 13 having the polarization H (0 degree) or V (90 degrees) by 45 degrees. Therefore, the polarization direction of the light output from the modulator 15 (polarization of the quantum cryptography signal) is as shown in FIG.

  As described above, the light (communication signal) from the communication laser 16 and the light (quantum encryption signal) from the modulator 15 are superimposed and output in a predetermined direction. That is, the first and second communication means 104 transmit and receive the communication signal and the quantum cryptography signal on the same optical axis 107. This may be considered as a signal obtained by superimposing the modulation waveform (a) and the photon transmission timing (b) in FIG. Therefore, in accordance with the key data, a weak optical signal (quantum cipher signal) having H or V polarization from the first and second quantum lasers 11 and 12 is constant from the falling edge of the output of the communication laser 16. After the delay time D, the polarization is modulated and transmitted together with the communication laser 16.

  On the other hand, data serving as a source of a quantum key (key data) transmitted as a quantum encryption signal is held in the data controller 5. For this purpose, the data controller 5 includes a memory (not shown).

  As described above, the reset signal from the coincidence detection circuit 7 is input to the counter 6. The counter 6 counts clock 1. Since the input data is transmitted in synchronization with the clock 1, the counter 6 is incremented corresponding to the transmission speed (ie, transmission clock) of the communication signal. The increment of the counter 6 is shown in the counter value (c) of FIG. The counter 6 is reset by a reset signal, and specifically, is reset with a period longer than the propagation delay of the communication signal. This is indicated by the counter value (d) in FIG. The propagation delay of the communication signal can be known in advance through experience. As indicated by a dotted line in FIG. 4, the counter value (c) shows a part of one period of the counter value (d) in an enlarged manner in terms of time.

  For the reset, the PN generator 2 forms and outputs a PN signal having a predetermined data pattern with a period longer than the propagation delay of the communication signal. Therefore, the counter 6 is reset with a period longer than the propagation delay of the communication signal. As a result, the counter value of the counter 6 has a sawtooth shape as indicated by the counter value (d). The reset timing (cycle) is shown in reset timing (e) of FIG. The same applies to the counter 30 described later. Thus, using the counter 6 (and 30), it is possible to detect a relative time delay in transmission / reception of a communication signal and a quantum cryptography signal even without a clock indicating an absolute time.

  In practice, the PN generator 2 continuously outputs a PN signal having a predetermined data pattern until quantum key sharing is performed. When quantum key sharing is performed, the switch SW is switched to the input data recorder 3 side. Thereafter, the data pattern is transmitted from the communication laser 16 to the receiver 102. In the transmitter 101, while the switch SW is switched to the input data recorder 3 side and input data is being transmitted from the input data recorder 3, key sharing can be performed in near real time.

  The count output (count value) of the counter 6 is input to the data controller 5. Although not shown, the data controller 5 generates key data (data that is the source of the encryption key). The data controller 5 holds (records) the key data signal and the random signal from the random generator 4 together with (corresponding to) the count value from the counter 6 at that time. That is, the key data in each count value of the counter 6 and the randomly polarized data are recorded. Thereby, it is possible to record at which timing (what number clock) the transmission of the communication signal is started, and which polarization of the optical signal of H or V is formed. That is, the encryption key in the transmitter 101 can be known.

  In the transmitter 101, the modulator 15 may be omitted and four quantum lasers may be provided. That is, in addition to the first and second quantum lasers 11 and 12 for H and V, a quantum laser that outputs light having a polarization of H + 45 degrees and a quantum laser that outputs light having a polarization of V + 45 degrees And may be provided. Further, in the transmitter 101, the modulator 15 may be omitted, and two quantum lasers having non-orthogonal binary polarization (H, H + 45 degrees) may be provided.

  Further, in the transmitter 101, only one quantum laser may be provided, and the modulator 15 may modulate the output from the quantum laser with four values (H, V, H + 45 degrees, V + 45 degrees). . Further, in the transmitter 101, only one quantum laser may be provided, and the modulator 15 may modulate the output from the quantum laser with non-orthogonal binary values (H, H + 45 degrees).

  Next, reception of a communication signal by the first communication unit 103 in the receiver 102 will be described with reference to FIG. The beam splitter 20 is the separating means 106. The first communication means 103 in the receiver 102 basically includes a communication receiver 21, a clock extraction circuit 22, and a communication data recorder 23.

  As described above, the communication signal from the communication laser 16 and the quantum encryption signal from the modulator 15 are superimposed on the optical signal from the transmitter 101. This is received by the beam splitter 20. The optical signal from the transmitter 101 is distributed by the beam splitter 20 and input to the communication receiver 21 and the modulator 24. The beam splitter 20 is set to transmit light (communication signal) having a wavelength λ1 as it is and reflect light (quantum encryption signal) having a wavelength λ2 as it is. Accordingly, the communication signal is input to the communication receiver 21 and the quantum cryptography signal is input to the modulator 24.

  The communication receiver 21 converts the input optical signal (communication signal) into an electrical signal and outputs the electrical signal. The output of the communication receiver 21 is input to the clock extraction circuit 22 and the delay pulse generator 28. The clock extraction circuit 22 extracts a clock from the input communication signal by a known clock extraction means, and outputs a communication signal (hereinafter referred to as data) and the clock. The data and clock are input to the communication data recorder 23 and held (recorded). This is arbitrary data obtained as a transmission result, and after the quantum key sharing is performed, it is a communication signal encrypted by quantum cryptography (key data), that is, data (for example, a moving image or the like).

  As described above, as a communication signal, a PN signal having a predetermined data pattern is transmitted prior to input data. Accordingly, the held data includes a PN signal having a predetermined data pattern at the head thereof. However, since the data pattern of the PN signal is a predetermined one, it is easy to remove it from the stored data, and thus original data can be obtained.

  Data and clock are input to the coincidence detection circuit 29. The coincidence detection circuit 29 receives the PN signal that is the output of the PN generator 33. For this purpose, the PN generator 33 generates and outputs a PN signal having a predetermined data pattern in synchronization with the clock 32. As the clock 32, for example, a GPS clock is used. The coincidence detection circuit 29 compares the PN signal with the inputted data in synchronization with the inputted clock, and when both coincide with each other, forms and outputs a reset signal. Therefore, the reset signal is output when the PN signal of a predetermined data pattern transmitted prior to the input data is detected to coincide.

  For example, although not shown, the communication data recorder 23 may discard the data (PN signal) held until that time by the reset signal. Thereby, the communication data recorder 23 can record only the input data which is the original data except for the PN signal.

  Next, reception of the quantum cryptography signal by the second communication unit 104 in the receiver 102 will be described with reference to FIG. The second communication means 104 in the receiver 102 basically includes a modulator 24, a polarization beam splitter 25, first and second single photon receivers 26 and 27, a delay pulse generator 28, a data controller 31, and a random controller. It comprises a generator 34.

  The random generator 34 generates a random signal (binary signal) taking a random value in synchronization with the clock 32 and inputs the random signal to the modulator 24 and the data controller 31. The modulator 24 modulates the polarization direction of the light from the beam splitter 20 based on a random signal (modulation signal) from the random generator 34, and then inputs the light to the polarization beam splitter 25. That is, the modulator 24 randomly modulates the light whose polarization direction is polarization H (0 degree) or V (90 degrees) by 45 degrees randomly, and modulates the light by 45 degrees randomly. input. Therefore, the polarization direction of the optical output from the modulator 24 (polarization of the quantum cryptography signal) is as shown in FIG.

  The optical signal modulated by the modulator 24 is distributed by the polarization beam splitter 25 and input to the first and second single photon receivers 26 and 27. For example, the polarization beam splitter 25 is set to reflect the optical signal of polarization H (the output of the first quantum laser) as it is and transmit the optical signal of polarization V (the output of the second quantum laser) as it is. . Thereby, the optical signal of polarization H is input to the first single photon receiver 26, and the optical signal of polarization V is input to the second single photon receiver 27.

  The output of the communication receiver 21 is input to the delay pulse generator 28. The delay pulse generator 28 detects the fall based on the output of the communication receiver 21, forms a gate signal after a delay time D from this, and outputs the gate signal from the first and second single photon reception. Input to the machines 26 and 27 as control signals. The delay pulse generator 28 is a circuit common to the first and second single photon receivers 26 and 27, and includes a circuit corresponding to the trigger generation circuit 8.

  The first single photon receiver 26 opens its gate in accordance with the gate signal, receives light from the polarization beam splitter 25 only during the open period of the gate, converts it into an electrical signal, and outputs it. The output of the first single photon receiver 26 is input to the data controller 31. The same applies to the second single photon receiver 27.

  As described above, in synchronization with a relatively strong communication signal (bit) that is different from the weak quantum encryption signal, the quantum encryption signal (photon) is transmitted when the optical signal of the communication signal is off, and is synchronized with the communication signal. At this timing, the gate is opened and a weak photon pulse for quantum cryptography is detected. Thereby, background light noise can be suppressed and the optical communication path and the quantum communication path can be isolated. In particular, by taking a delay time D relatively from the communication signal (on period), a photon pulse can be detected using a gate, and the present invention can be used even in the presence of background light such as spatial transmission. Can be applied. In addition, this makes it possible to detect a weak photon pulse for quantum cryptography even if there is a transmission delay. Therefore, even if arbitrary content data is transmitted as a communication signal, the data signal and the quantum cryptography signal can coexist.

  The data controller 31 includes a memory (not shown), and holds (records) the outputs of the first and second single photon receivers 26 and 27 in synchronization with the clock 1.

  As described above, the reset signal from the coincidence detection circuit 29 is input to the counter 30. The counter 30 counts the clock from the clock extraction circuit 22. The counter 30 is reset by a reset signal. The count output (count value) of the counter 30 is input to the data controller 31.

  The data controller 31 holds the count output (count value) of the counter 30 at that time in association with the outputs of the first and second single photon receivers 26 and 27. This is the data that is the source of the encryption key obtained as a transmission result. For this purpose, the data controller 31 includes a memory (not shown). Thereby, it is possible to record at which timing (what number clock) the transmission of the communication signal is started, and which polarization of the optical signal of H or V is formed. That is, the data that is the source of the encryption key in the receiver 102 can be recorded. The quantum key can be obtained by processing data after confirming with random communication data that the randomly polarized data matches by transmission and reception. That is, the data controllers 5 and 31 perform the communication, and confirm that the data that is the basis of the quantum key recorded by each data matches.

  As described above, in the counter 30 (and 6) incremented at the data transmission rate, the number of bits of the counter 30 can be reduced by resetting in a cycle longer than the propagation delay. In mobile communication, Even if the propagation distance changes, the counter 30 can detect the relative time delay.

  That is, the receiver 102 can know the head of the data by resetting the counter 30 (and 6) at a constant cycle. In addition, the period is set to be longer than the propagation delay time from transmission to reception. Thereby, transmission / reception data can be identified by relative propagation delay. Therefore, even if the receiver 102 (and the transmitter 101) does not have an absolute time, the time of the weak quantum cryptography photon pulse can be identified, and the number of bits of the counter 30 can be reduced.

  As described above, the light (communication signal) from the communication laser 16 and the light (quantum cipher signal) from the modulator 15 are separated, the data and the clock are detected from the communication signal, and constant from the falling edge of the clock. After the delay time D, the gates of the single photon receivers 26 and 27 are opened, and a weak optical signal having H or V polarization is detected.

  In the receiver 102, the modulator 24 may be omitted and four single photon receivers may be provided. That is, a single photon receiver that receives light having polarizations of H, V, H + 45 degrees, and V + 45 degrees may be provided.

  FIG. 5 is another configuration diagram of the quantum cryptography communication device of the present invention. In this example, in particular, in the examples of FIGS. 1 to 4, the first communication unit 103 further adjusts the polarization of the communication signal in accordance with the polarization basis of the photon pulse of the quantum cryptographic signal transmitted and received by the second communication unit 104. This is an example of modulation.

  As shown in FIG. 5A, the transmitter 101 synchronizes with the data signal (for example, at the reset timing of the counter 6 described above), and adjusts the communication signal (optical signal) according to the polarization base of the quantum encryption signal. ) Polarization modulation. For example, the polarization direction is 0 degree (polarization H) and 90 degrees (polarization V).

  Assuming that the phase difference in the polarization direction is relatively shifted by Δθ in the receiver 102, the results are as shown in FIGS. That is, in the receiver 102, the half-wave plate or the like is adjusted at the subsequent stage of the polarizer (polarizing beam splitter) 20 so that the AC component of the received light is maximized, so that the selected polarization base axis of the transmitter 101 is adjusted. It is possible to match.

  For example, when the polarizer is installed at 0 degree (horizontal direction), if the phase difference Δθ is 0 degree, the polarity of the received signal is inverted as shown in FIG. The amplitude (intensity) of is not changed. If the phase difference Δθ is 0 to 45 degrees, the polarity of the received signal is reversed and the amplitude (intensity) of the signal is slightly reduced as shown in FIG. If the phase difference Δθ is between 45 degrees and 135 degrees, as shown in FIG. 5D, the polarity of the received signal is not reversed, but the amplitude (intensity) of the signal is slightly reduced. If the phase difference Δθ is between 135 degrees and 180 degrees, the polarity of the received signal is reversed and the amplitude (intensity) of the signal is slightly reduced as shown in FIG. Even when Δθ = 90 degrees, the AC component of the received signal is maximum, but since the phase is inverted by 180 degrees, it can be identified that the polarization direction is different by 90 degrees.

  As described above, in synchronization with the timing of the communication signal (data), the polarization modulation of the communication signal (optical signal) is performed in accordance with the polarization base of the quantum cryptography photon pulse. Even if the relation of the arrival angle changes, the half-wave plate etc. is adjusted so as to maximize the AC component of the optical signal after the polarizer, and the direction of the polarization axis is detected and selected on the transmission side. It can be aligned with the polarization base axis. In addition, the polarization direction of the weak quantum cryptography photon pulse can be detected. Thereby, it is possible to know the weak polarization base of the quantum cryptography photon pulse from the received signal of the communication signal. By applying polarization modulation to the communication signal, the polarization base of the weak quantum cryptography photon pulse can be detected.

  FIG. 6 is a diagram illustrating an application example of the quantum cryptography communication of the present invention.

  The satellite which is the transmitter 101 is located on the ground station A at time T1. At this time, the satellite generates a quantum key α (for example, 1001), superimposes it on the data A, and transmits it to the ground station A. The ground station A receives and holds the data A and the quantum key α.

  Thereafter, the satellite moves and is located on the ground station B at time T2. At this time, the satellite generates a quantum key β (for example, 1010), superimposes it on the data B, and transmits it to the ground station B. The ground station B receives and holds the data B and the quantum key β.

  Further, the satellite generates a quantum key γ (in this case, 0011) by the exclusive OR of the quantum keys α and β (γ = αXORβ), which is transmitted to the base stations A and B by a normal communication means, for example. Send. This may be eavesdropped.

  Thereafter, the ground station A uses the quantum key α and quantum key γ held by itself to generate the quantum key β of the counterpart ground station B by the exclusive OR (β = αXORγ). That is, for example, β = 1010 can be known. For example, data A is data from the ground station B, and its quantum key is β. Similarly, the base station B uses the quantum key β and the quantum key γ held by itself to generate the quantum key α of the counterpart ground station A by the exclusive OR (α = βXORγ). That is, for example, α = 1001 can be known. For example, data B is data from ground station A, and its quantum key is α. Thereby, the ground stations A and B can share the quantum key.

  As mentioned above, although this invention was demonstrated according to the embodiment, this invention can be variously deformed within the range of the main point.

  For example, the above description has been made on optical communication using the ground and a satellite. However, in the present invention, the transmitter 101 is not limited to a satellite. For example, any mobile body such as an airplane, a ship, an automobile, etc. that has a communication function and performs mobile body communication may be used. Further, not only the transmitter 101 side but also the receiver 102 side may be a moving body. That is, the present invention can be applied to optical communication between satellites. Furthermore, the transmitter 101 side is not limited to a mobile body, but may be a fixed ground station. That is, optical communication (terrestrial optical communication) between fixed stations on the ground may be used.

  The signals transmitted and received according to the present invention may be data signals in various fields such as the field of military, personal and commercial secret communications, or other signals.

  As described above, according to the present invention, in the quantum cryptography communication method, a classical communication path, for example, a transmission path made of an optical fiber can be eliminated, and the quantum cryptography communication is used for mobile communication in a satellite or the like. The quantum cryptography communication can be applied regardless of the type of communication signal.

1, 32 Clock 2, 33 PN generator 3 Input data recorder 4, 34 Random generator 5, 31 Data controller 6, 30 Counter 7, 29 Match detection circuit 8 Falling trigger pulse generation circuit (trigger generation circuit)
9, 10 Delay pulse generator 11, 12 Quantum laser 13, 25 Polarizing beam splitter 14 Attenuator 15, 24 Modulator 16 Communication laser 17, 20 Beam splitter 21 Communication receiver 22 Clock extraction circuit 23 Communication data recorder 26, 27 Single photon receiver 28 Delay pulse generator

Claims (7)

A transmitter generates a first quantum key, superimposes the first quantum key on first data and transmits the first quantum key to a first station using a laser beam;
The first station receives and holds the first data and the first quantum key;
The transmitter generates a second quantum key, superimposes the second quantum key on second data and transmits the second quantum key to a second station using a laser beam;
The second station receives and holds the second data and the second quantum key;
The transmitter generates a third quantum key by exclusive OR of the first quantum key and the second quantum key, and transmits the third quantum key to the first station and the second station;
The first station generates the second quantum key by an exclusive OR of the first quantum key held by itself and the third quantum key,
The quantum encryption communication method, wherein the second station generates the first quantum key by an exclusive OR of the second quantum key and the third quantum key held by the second station ,
The first communication means provided in the transmitter and the first station and the second station includes an on period and an off period between the transmitter and the first station and the second station. Send and receive communication signals consisting of pulsed light that is a binary optical signal that is relatively strong compared to the quantum cryptography signal,
Second communication means provided in the transmitter and the first station and the second station is during transmission and reception of the communication signal between the transmitter and the first station and the second station, and During a period when the communication signal is off, a quantum cryptography signal made up of pulsed light that is a binary optical signal and has a relatively weak intensity compared to the communication signal,
The first and second communication means transmit and receive the communication signal and the quantum cryptography signal superimposed on the communication signal on the same optical axis.
A quantum cryptography communication method characterized by the above. The transmitter is a satellite; the first station is a first ground station; and the second station is a second ground station;
A satellite as the transmitter is located on the first ground station at a first time, and transmits the first quantum key superimposed on the first data to the first ground station. ,
A satellite that is the transmitter is located on the second ground station at a second time after the first time, and the second quantum key is superimposed on the second data to overlap the second data. To the second ground station,
The quantum cryptography communication method according to claim 1, wherein a satellite that is the transmitter transmits the third quantum key to the first ground station and the second ground station. The quantum cryptography communication method according to claim 2, wherein the first data is data from the second ground station, and the second data is data from the first ground station. The second communication means transmits and receives the quantum cryptography signal after a predetermined delay time has elapsed from the falling edge in synchronization with the falling edge of the communication signal in the off period of the communication signal. The quantum cryptography communication method according to claim 1 . The first or second communication means includes a counter that is incremented corresponding to the transmission speed of the communication signal and is reset with a period longer than a propagation delay of the communication signal, and using the counter, delay of relative time The quantum cryptography communication method according to claim 1 , wherein the quantum cryptography communication method is detected. The first communication means, said second and is transmitted and received by the communication means fit polarization basis of photon pulses of the quantum cryptography signal, according to claim 1, wherein the quantum cryptography, characterized in that to perform polarization modulation of the communication signal Communication method. It said transmitter superimposing means provided in the quantum cryptography communication method according to claim 1, wherein the superimposing the quantum cryptography signal to the communication signal.

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