Free space local oscillator continuous variable quantum key distribution method and system

Abstract

The present invention provides a free-space local local oscillator continuous variable quantum key distribution method and system, including: step S1: generating pulse light, using a beam splitter to divide the pulse signal into a pilot signal and a quantum signal and modulate the quantum signal; step S2: polarization multiplexing of the pilot signal and the quantum signal; step S3: monitoring the signal and separating the pilot signal from the quantum signal; step S4: using a laser of the same frequency at the receiving end to generate local oscillator light, and performing coherent detection with the pilot signal and the quantum signal respectively; step S5: correcting the polarization of the pilot and quantum signals, and compensating the phase of the quantum signal. The present invention proposes a polarization compensation and phase compensation scheme suitable for free-space local local oscillator, which can accurately recover the polarization and phase from the data end, and has the advantages of not requiring the use of a polarization controller and reducing phase noise.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication technology, and in particular to a free-space local oscillator continuous variable quantum key distribution method and system, and more particularly to a free-space local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing. Background Art

[0002] Information security is becoming increasingly important with the rapid development of computer and communication technologies. Among them, quantum key distribution technology with unconditional security has been born, supported by the basic principles of quantum mechanics such as the uncertainty principle. Quantum key distribution technology can be generally divided into two categories: discrete variable quantum key distribution and continuous variable quantum key distribution. Among them, continuous variable quantum key distribution has attracted many scholars at home and abroad to conduct in-depth research on its theory and application because of its high code rate and low cost. For continuous variable quantum key distribution, it can be divided into optical fiber channel and free space channel in terms of channel; there are local oscillator schemes and local local oscillator schemes in terms of implementation schemes. Then the free space local local oscillator continuous variable quantum key distribution scheme is also an important scheme in this field.

[0003] The free-space local oscillator continuous variable quantum key distribution scheme is very meaningful, but there are also corresponding problems. First of all, in the local local oscillator continuous variable quantum key distribution scheme, the local oscillator light is generated by the receiving end, which will cause a large phase noise of the quantum signal. Therefore, it is necessary to send a pilot carrying reference phase information to compensate for the phase offset of the quantum signal. Secondly, if the pilot and quantum signal are polarization-multiplexed, it is necessary to perform polarization demultiplexing at the receiving end. Polarization demultiplexing usually uses a polarization controller to adjust the polarization state of the light to match the polarization beam splitter, but in the free-space channel, the transmittance of the channel is non-constant, which makes it impossible for us to directly obtain an effective feedback value to adjust the polarization controller. Therefore, it is very meaningful to perform polarization demultiplexing at the data end instead of using a polarization controller.

[0004] Patent document CN107566120B (application number: CN201710899926.2) discloses a local oscillator continuous variable quantum key distribution method and system, including the following processes: coherent pulse light source generation, local oscillator light and signal light separation, pulse signal light transmission, dual-phase modulated pulse signal light, pulse signal light return, noise-free linear amplifier processing, and measurement and detection. However, the invention has limited phase noise control. Summary of the invention

[0005] In view of the defects in the prior art, the object of the present invention is to provide a free-space local oscillator continuous variable quantum key distribution method and system.

[0006] A free-space local oscillator continuous variable quantum key distribution method provided by the present invention includes:

[0007] Step S1: Generate pulse light, use a beam splitter to split the pulse signal into a pilot signal and a quantum signal, and modulate the quantum signal;

[0008] Step S2: polarization multiplexing of the pilot signal and the quantum signal;

[0009] Step S3: monitor the signal and separate the pilot signal and the quantum signal;

[0010] Step S4: using a laser of the same frequency to generate local oscillator light at the receiving end, and performing coherent detection with the pilot signal and the quantum signal respectively;

[0011] Step S5: Correct the polarization of the pilot and quantum signal, and compensate the phase of the quantum signal.

[0012] Preferably, in step S1:

[0013] After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator;

[0014] The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator;

[0015] The pilot signal is generated simultaneously with the quantum signal.

[0016] Preferably, in step S2:

[0017] The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

[0018] Preferably, in step S3:

[0019] The beam splitter is used to separate the light in a preset range for signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

[0020] Preferably, in step S5:

[0021] The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

[0022] A free-space local oscillator continuous variable quantum key distribution system provided by the present invention includes:

[0023] Module M1: Generates pulsed light, uses a beam splitter to separate the pulse signal into a pilot signal and a quantum signal, and modulates the quantum signal;

[0024] Module M2: pilot signal and quantum signal polarization multiplexing;

[0025] Module M3: monitors the signal and separates the pilot signal from the quantum signal;

[0026] Module M4: A laser with the same frequency is used at the receiving end to generate local oscillator light, and coherent detection is performed with the pilot signal and quantum signal respectively;

[0027] Module M5: Corrects the polarization of the pilot and quantum signal, and compensates the phase of the quantum signal.

[0028] Preferably, in the module M1:

[0029] After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator;

[0030] The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator;

[0031] The pilot signal is generated simultaneously with the quantum signal.

[0032] Preferably, in the module M2:

[0033] The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

[0034] Preferably, in the module M3:

[0035] The beam splitter is used to separate the light in a preset range as signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

[0036] Preferably, in the module M5:

[0037] The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. In an actual free-space quantum key distribution system, due to the characteristics of the free-space channel, it is difficult to obtain a stable feedback to adjust the polarization controller. The present invention can perform polarization recovery at the data end without adjusting the polarization controller;

[0040] 2. The signal light and the local oscillator light are not homologous light, and there is a large phase difference. The present invention generates a pilot signal while generating a quantum signal, so that the pilot signal will track the phase drift of the quantum signal. Finally, after polarization recovery, the pilot signal can be used for phase compensation;

[0041] 3. The present invention proposes a polarization compensation and phase compensation scheme suitable for free space local oscillator, which can accurately restore polarization and phase from the data end. Its advantages are that it does not require the use of a polarization controller and reduces phase noise. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0043] Figure 1 It is a free-space local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing. DETAILED DESCRIPTION

[0044] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0045] Embodiment 1:

[0046] The present invention relates to a polarization compensation and phase compensation method. The present invention provides a free space local local oscillator continuous variable quantum key distribution polarization compensation method based on pilot polarization multiplexing, which comprises the following steps: step one, generating a pulse signal; step two, using a beam splitter to divide the pulse signal into a pilot signal and a quantum signal; step three, modulating the quantum signal and performing polarization multiplexing on the pilot signal and the quantum signal; step four, separating the pilot signal from the quantum signal; step five, dual-path interference detection; and step six, polarization compensation and phase compensation.

[0047] According to a free space local oscillator continuous variable quantum key distribution method provided by the present invention, Figure 1 As shown, including:

[0048] Step S1: Generate pulse light, use a beam splitter to split the pulse signal into a pilot signal and a quantum signal, and modulate the quantum signal;

[0049] Specifically, in step S1:

[0050] After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator;

[0051] The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator;

[0052] Step S2: polarization multiplexing of the pilot signal and the quantum signal;

[0053] Specifically, in step S2:

[0054] The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

[0055] Step S3: monitor the signal and separate the pilot signal and the quantum signal;

[0056] Specifically, in step S3:

[0057] The beam splitter is used to separate the light in a preset range as signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

[0058] Step S4: using a laser of the same frequency to generate local oscillator light at the receiving end, and performing coherent detection with the pilot signal and the quantum signal respectively;

[0059] Step S5: Correct the polarization of the pilot and quantum signal, and compensate the phase of the quantum signal.

[0060] The pilot signal is generated simultaneously with the quantum signal.

[0061] Specifically, in step S5:

[0062] The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

[0063] Embodiment 2:

[0064] Embodiment 2 is a preferred example of Embodiment 1, and is used to illustrate the present invention in more detail.

[0065] Those skilled in the art may understand the free-space local local oscillator continuous variable quantum key distribution method provided by the present invention as a specific implementation of a free-space local local oscillator continuous variable quantum key distribution system, that is, the free-space local local oscillator continuous variable quantum key distribution system may be implemented by executing the step flow of the free-space local local oscillator continuous variable quantum key distribution method.

[0066] A free-space local oscillator continuous variable quantum key distribution system provided by the present invention includes:

[0067] Module M1: Generates pulsed light, uses a beam splitter to separate the pulse signal into a pilot signal and a quantum signal, and modulates the quantum signal;

[0068] Specifically, in the module M1:

[0069] After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator;

[0070] The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator;

[0071] The pilot signal is generated simultaneously with the quantum signal.

[0072] Module M2: pilot signal and quantum signal polarization multiplexing;

[0073] Specifically, in the module M2:

[0074] The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

[0075] Module M3: monitors the signal and separates the pilot signal from the quantum signal;

[0076] Specifically, in the module M3:

[0077] The beam splitter is used to separate the light in a preset range for signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

[0078] Module M4: A laser with the same frequency is used at the receiving end to generate local oscillator light, and coherent detection is performed with the pilot signal and quantum signal respectively;

[0079] Module M5: Corrects the polarization of the pilot and quantum signal, and compensates the phase of the quantum signal.

[0080] Specifically, in the module M5:

[0081] The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

[0082] Embodiment 3:

[0083] Embodiment 3 is a preferred example of Embodiment 1, and is used to illustrate the present invention in more detail.

[0084] First, due to the characteristics of the free space channel, it is difficult to obtain a stable feedback to adjust the polarization controller in the free space continuous variable quantum key distribution. Therefore, the purpose of the present invention is to provide a free space local local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing, which can avoid using the polarization controller to recover the polarization from the data end. Secondly, in the local local oscillator scheme, the quantum signal and the local oscillator are not homologous light, resulting in a large phase deviation. Therefore, the purpose of the present invention is to provide a free space local local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing, which can accurately perform phase compensation.

[0085] According to one aspect of the present invention, a free-space local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing is provided, such as Figure 1 As shown, the free space local oscillator continuous variable quantum key distribution scheme based on pilot polarization multiplexing:

[0086] Step 1, generating pulsed light; after generating continuous light through a laser, the continuous light is cut into pulsed light through an intensity modulator;

[0087] Step 2: Use a beam splitter to divide the pulse signal into a pilot signal and a quantum signal and modulate the quantum signal; use a 99:1 beam splitter to divide the pulse light into a larger-power pilot signal and a smaller-power quantum signal; the signal light is QPSK modulated by a phase modulator;

[0088] Step 3: polarization multiplexing of the pilot signal and the quantum signal; the signal light and the pilot signal are polarization multiplexed through a polarization beam combiner;

[0089] Step 4: monitor the signal and separate the pilot signal from the quantum signal. First, a small portion of the light is separated through a 99:1 beam splitter as signal power monitoring, and the remaining light is separated from the pilot signal and the quantum signal through a polarization beam splitter.

[0090] Step 5: Dual-path interference detection: A laser with the same frequency is used at the receiving end to generate local oscillator light, and coherent detection is performed with the pilot signal and the quantum signal respectively;

[0091] Step six, polarization compensation and phase compensation: Use the radius-oriented Kalman filtering method to correct the polarization of the pilot and quantum signals, and use the pilot signal phase to compensate the quantum signal phase.

[0092] The quantum signal modulation is QPSK.

[0093] A small portion of light is separated at the receiving end as signal and pilot power monitoring.

[0094] The pilot signal is generated simultaneously with the quantum signal, so its phase change will be consistent with the quantum signal, playing the role of compensating the phase of the quantum signal.

[0095] Based on the above system and method, specific application examples are provided below:

[0096] First, a frequency-locked laser is used as a coherent light source at the transmitting end. Its output light is passed through a pulse modulator with an extinction ratio of 60dB to generate a 100MHz pulse sequence with a pulse width of 1ns.

[0097] Then it is divided into two beams through a 99:1 beam splitter, one beam with low power is used as the quantum signal, and the other beam with high power is used as the pilot signal, and the quantum signal is modulated by QPSK.

[0098] The quantum signal and the pilot signal are polarization multiplexed by a polarization beam combiner and transmitted through a free space channel.

[0099] At the receiving end, a local oscillator light is generated by another frequency-locked laser, and interferes with the above-mentioned separated pilot reference signal and quantum signal respectively;

[0100] The two interference signals are sampled and data processed. First, polarization recovery is performed. Since the polarization state changes during the transmission process, that is, the signal at the receiving end is multiplied by a Jones matrix compared to the signal at the transmitting end, the signal needs to be multiplied by the inverse of a Jones matrix when performing data compensation at the data end, and its form is such as [a+jb c+jd -c+jd a-jb]. Therefore, the values ​​of real numbers a, b, c, d can be calculated by the radius-oriented Kalman filtering method, where the constraint radius can be obtained from the monitored power. Secondly, phase compensation is performed. First, the phase information of the pilot signal is calculated, and then the phase of the quantum signal is subtracted from the phase of the pilot signal to eliminate the phase offset. The principle is that the pilot signal and the quantum signal are co-source light, and the two signals are transmitted together, so the phase information modulated on the quantum signal is removed, and the remaining phases are consistent.

[0101] Those skilled in the art know that, in addition to implementing the system, device and its various modules provided by the present invention in a purely computer-readable program code, it is entirely possible to implement the same program in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers and embedded microcontrollers by logically programming the method steps. Therefore, the system, device and its various modules provided by the present invention can be considered as a hardware component, and the modules included therein for implementing various programs can also be considered as structures within the hardware component; the modules for implementing various functions can also be considered as both software programs for implementing the method and structures within the hardware component.

[0102] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A free-space local oscillator continuous variable quantum key distribution method, characterized in that: include: Step S1: Generate pulse light, use a beam splitter to split the pulse signal into a pilot signal and a quantum signal, and modulate the quantum signal; Step S2: polarization multiplexing of the pilot signal and the quantum signal; Step S3: monitor the signal and separate the pilot signal and the quantum signal; Step S4: using a laser of the same frequency to generate local oscillator light at the receiving end, and performing coherent detection with the pilot signal and the quantum signal respectively; Step S5: Correcting the polarization of the pilot and quantum signal, and compensating the phase of the quantum signal; Polarization correction is performed. Since the polarization state changes during the transmission process, the signal at the receiving end is multiplied by a Jones matrix compared to the signal at the transmitting end. When data compensation is performed at the data end, the signal is multiplied by the inverse of the Jones matrix, which is in the form of: a+jb c+jd -c+jd a-jb; The values ​​of real numbers a, b, c, d are calculated using a radius-directed Kalman filter method, where the constraint radius is obtained from the monitored power; Phase compensation is performed, the phase information of the pilot signal is calculated, and the phase of the quantum signal is subtracted from the phase of the pilot signal to eliminate the phase offset; the pilot signal and the quantum signal are co-source light, and the two signals are transmitted together, so the phase information modulated on the quantum signal is removed, and the remaining phases are consistent.

2. The free-space local oscillator continuous variable quantum key distribution method according to claim 1, characterized in that: In step S1: After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator; The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator; The pilot signal is generated simultaneously with the quantum signal.

3. The free-space local oscillator continuous variable quantum key distribution method according to claim 1, characterized in that: In step S2: The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

4. The free-space local oscillator continuous variable quantum key distribution method according to claim 1, characterized in that: In step S3: The beam splitter is used to separate the light in a preset range for signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

5. The free-space local oscillator continuous variable quantum key distribution method according to claim 1, characterized in that: In step S5: The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

6. A free-space local oscillator continuous variable quantum key distribution system, characterized in that: include: Module M1: Generates pulsed light, uses a beam splitter to separate the pulse signal into a pilot signal and a quantum signal, and modulates the quantum signal; Module M2: pilot signal and quantum signal polarization multiplexing; Module M3: monitors the signal and separates the pilot signal from the quantum signal; Module M4: A laser with the same frequency is used at the receiving end to generate local oscillator light, and coherent detection is performed with the pilot signal and quantum signal respectively; Module M5: corrects the polarization of the pilot and quantum signal, and compensates the phase of the quantum signal; Polarization correction is performed. Since the polarization state changes during the transmission process, the signal at the receiving end is multiplied by a Jones matrix compared to the signal at the transmitting end. When data compensation is performed at the data end, the signal is multiplied by the inverse of the Jones matrix, which is in the form of: a+jb c+jd-c+jd a-jb; The values ​​of real numbers a, b, c, d are calculated using a radius-directed Kalman filter method, where the constraint radius is obtained from the monitored power; Phase compensation is performed, the phase information of the pilot signal is calculated, and the phase of the quantum signal is subtracted from the phase of the pilot signal to eliminate the phase offset; the pilot signal and the quantum signal are co-source light, and the two signals are transmitted together, so the phase information modulated on the quantum signal is removed, and the remaining phases are consistent.

7. The free-space local oscillator continuous variable quantum key distribution system according to claim 6, characterized in that: In the module M1: After the continuous light is generated by the laser, it is cut into pulsed light by an intensity modulator; The pulse light is divided into a larger-power pilot signal and a smaller-power quantum signal by a beam splitter; the signal light is QPSK modulated by a phase modulator; The pilot signal is generated simultaneously with the quantum signal.

8. The free-space local oscillator continuous variable quantum key distribution system according to claim 6, characterized in that: In the module M2: The signal light and the pilot signal are polarization multiplexed through a polarization beam combiner.

9. The free-space local oscillator continuous variable quantum key distribution system according to claim 6, characterized in that: In the module M3: The beam splitter is used to separate the light in a preset range for signal power monitoring, and the remaining light is then separated into the pilot signal and the quantum signal through a polarization beam splitter.

10. The free-space local oscillator continuous variable quantum key distribution system according to claim 6, characterized in that: In the module M5: The polarization of the pilot and quantum signals is corrected using a radius-oriented Kalman filtering method, and the phase of the quantum signal is compensated with the phase of the pilot signal.

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