CN110880971B - Chirp-based continuous variable quantum key distribution method and system - Google Patents
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Abstract
本发明公开了一种基于啁啾的连续变量量子密钥分发方法，包括量子密钥发送端调制量子信号；量子密钥发送端将调制好的量子信号通过量子信道发送至量子密钥接收端；量子密钥接收端将接收到的量子信号进行相干检测并得到检测结果；将检测结果进行后处理得到最终的量子密钥。本发明还公开了一种实现所述基于啁啾的连续变量量子密钥分发方法的分发系统。本发明消除了中距离传输中由于频率啁啾效应对信号产生的不利影响，增大了传输的可靠性；同时，此方法不需要在发送端使用外差调制器，仅需要在传输的开始进行啁啾系数的估计，有效的节约了成本，而且可靠性高、性能较好且成本低廉、实施方便。
The invention discloses a continuous variable quantum key distribution method based on chirp, which comprises a quantum key transmitting end modulating a quantum signal; the quantum key transmitting end sending the modulated quantum signal to a quantum key receiving end through a quantum channel; The quantum key receiving end performs coherent detection on the received quantum signal and obtains the detection result; the detection result is post-processed to obtain the final quantum key. The invention also discloses a distribution system for realizing the chirp-based continuous variable quantum key distribution method. The present invention eliminates the adverse influence on the signal due to the frequency chirp effect in the medium-distance transmission, and increases the reliability of the transmission; at the same time, the method does not require the use of a heterodyne modulator at the transmitting end, and only needs to be performed at the beginning of the transmission. The estimation of the chirp coefficient effectively saves the cost, and has high reliability, good performance, low cost and convenient implementation.
Description
Technical Field
The invention belongs to the field of quantum communication, and particularly relates to a chirp-based continuous variable quantum key distribution method and system.
Background
With the development of economic technology and the improvement of living standard of people, communication has been extensively deepened into the production and life of people, and brings endless convenience to the production and life of people. With the advent of the intelligent era and the data era, the security of communication data is more and more emphasized by people.
The quantum key distribution can ensure that both legal communication parties can safely share the key in an untrusted quantum channel, and the safety of the legal communication parties is ensured by the inaccuracy measurement principle of quantum mechanics and the quantum unclonable theorem. Currently, quantum key distribution is divided into two directions of discrete variable and continuous variable by the difference of information carriers. Compared with a discrete variable quantum key distribution protocol, the quantum state of the continuous variable quantum key distribution protocol is easier to prepare and can be integrated into the existing optical fiber system, so that the continuous variable quantum key distribution scheme is easier to enter the commercialization field.
In a continuous variable quantum key distribution scheme over short distances (below 20 km), the use of direct modulators and direct detection can be cost effective to facilitate faster commercialization. However, in transmissions over 20km, the use of a direct modulation and direct detection distribution scheme will result in a significant performance loss due to the presence of significant dispersion in the channel. Therefore, the industry has adopted solutions based on external modulation and coherent detection, which exhibit good performance and cost performance over transmission distances of over 1000 km. However, the use of external modulation and coherent detection at medium-range transmissions of 20-1000 km has the following disadvantages: (1) the scheme has huge cost and low neutral price ratio when used in a medium-distance transmission scheme; (2) the external modulator is too bulky to be integrated into a compact transmitter optical assembly.
In order to solve the above problems, I/O transmitters based on direct modulators have been proposed, but this scheme relies on complex optical injection locking, requires a high performance laser in addition to the direct modulator, and is costly. In addition, a VCSEL-based DP PAM-4 transmitter has also been proposed. However, this scheme only performs sign determination based on the light intensity at the receiving end, discarding the phase information, resulting in a large performance gap from the conventional scheme. Therefore, in the middle-distance transmission, a better technical scheme which has both cost and performance at the same time does not exist at present.
Disclosure of Invention
One of the objectives of the present invention is to provide a chirp-based continuously variable quantum key distribution method with high reliability, good performance, low cost and convenient implementation.
The invention also aims to provide a distribution system for realizing the chirp-based continuous variable quantum key distribution method.
The chirp-based continuous variable quantum key distribution method provided by the invention comprises the following steps:
s1, a quantum key sending end modulates a quantum signal;
s2, the quantum key sending end sends the modulated quantum signals to a quantum key receiving end through a quantum channel;
s3, carrying out coherent detection on the received quantum signals by the quantum key receiving end so as to obtain a detection result;
and S4, carrying out post-processing on the detection result obtained in the step S3 to obtain a final quantum key.
The quantum key transmitting terminal described in step S1 modulates a quantum signal, specifically, the quantum key transmitting terminal generates coherent optical pulses, and then performs polarization and then separates the coherent optical pulses into signal light and local oscillator light; the signal light is coupled with the local oscillator light after being subjected to amplitude modulation and phase modulation, so that a modulated quantum signal is obtained.
The quantum key receiving end in step S3 performs coherent detection on the received quantum signal, so as to obtain a detection result, specifically, the quantum key receiving end adjusts the polarization state of the received quantum signal, and then divides the received signal into signal light and local oscillator light; and after the local oscillation light is subjected to random phase modulation, the local oscillation light is interfered with the signal light, and the interfered signal is detected by a homodyne detector, so that a detection result is obtained.
Performing post-processing on the detection result obtained in the step S3 in the step S4 to obtain a final quantum key, specifically, sampling the detection result and obtaining an amplitude signal and a phase signal; for the amplitude signal, obtaining signal strength information after passing through a filter; for a phase signal, firstly carrying out frequency offset compensation, then carrying out chirp coefficient estimation, and finally carrying out differential phase reconstruction through chirp information obtained by estimation to obtain differential phase information; and finally, performing symbol judgment on the obtained signal intensity information and the obtained differential phase information to obtain a final quantum key.
And the signal intensity information is obtained after passing through the filter, specifically, the signal intensity information is obtained after passing through the Bessel filter.
The symbol decision is performed on the obtained signal strength information and the obtained differential phase information, specifically, the symbol decision is performed on the obtained signal strength information and the obtained differential phase information by using maximum likelihood sequence estimation based on a viterbi algorithm.
The chirp coefficient estimation is specifically to perform chirp coefficient estimation by adopting the following steps:
A. the frequency chirp and signal strength of the laser are calculated using the following equations:
wherein P (t) is the signal strength; alpha is a linewidth enhancement factor; kappa is the adiabatic chirp coefficient;
B. performing time integration on the formula obtained in the step A to obtain the phase
In the formula
Is the initial phase;
is laser phase noise;
C. calculating t by the following equation1Time t and2phase difference between two consecutive symbols of a time instant
D. For the phase difference obtained in the step C
The calculation formula of (a) is simplified to obtain:
wherein T is T2-t1Is one symbol period;
E. the quantum key sending end sends a first test waveform to the quantum keyA key receiving end, wherein after receiving the first test waveform, the quantum key receiving end calculates a first chirp coefficient c by adopting the following formula1：
In the formula
Is a differential phase between adjacent low and high levels in the first test waveform;
is a differential phase between adjacent high and low levels in the first test waveform; the first test waveform is a test waveform of LHLH … … cycle, wherein L is low level, and H is high level;
F. the quantum key sending end sends a second test waveform to the quantum key receiving end, and after the quantum key receiving end receives the second test waveform, a second chirp coefficient c is calculated by adopting the following formula2：
In the formula
Is the differential phase between adjacent low levels and low levels in the second test waveform;
is a differential phase between adjacent high and high levels in a second test waveform, which is a test waveform of LLHHLLHH … … cycles, where L is low and H is high.
Step F, calculating the second chirp coefficient, specifically, calculating the second chirp coefficient by using the following formula, thereby improving the calculation accuracy
The chirp coefficient estimation specifically includes performing chirp coefficient estimation once before performing quantum key transmission for the first time at a quantum key sending end and a quantum key receiving end, so as to obtain a chirp coefficient.
The invention also discloses a distribution system for realizing the chirp-based continuous variable quantum key distribution method, which comprises a quantum key sending end and a quantum key receiving end; the quantum key sending terminal comprises a sending terminal pulse laser, a sending terminal polarizer, a sending terminal beam splitter, a sending terminal electro-optic intensity modulator, a sending terminal electro-optic phase modulator, a sending terminal random number generator, a sending terminal adjustable attenuator and a sending terminal polarization coupler; the transmitting end pulse laser, the transmitting end polarizer, the transmitting end beam splitter, the transmitting end electro-optical intensity modulator, the transmitting end electro-optical phase modulator, the transmitting end adjustable attenuator and the transmitting end polarization coupler are sequentially connected in series; the sending end random number generator is connected with the sending end electro-optical phase modulator; the sending end pulse laser is used for generating coherent light pulses and sending the coherent light pulses to the sending end polarizer; the transmitting end polarizer is used for controlling the polarization state of the signal light generated by the pulse laser and transmitting the signal light to the transmitting end beam splitter; the transmitting end beam splitter is used for splitting the pulse light into signal light and local oscillation light; the transmitting end electro-optical intensity modulator is used for carrying out amplitude modulation on the signal light and transmitting the signal light to the transmitting end electro-optical phase modulator; the sending end electro-optical phase modulator is used for carrying out phase modulation on the signal light after amplitude modulation according to the control signal generated by the sending end random number generator and sending the signal light to the sending end adjustable attenuator; the sending end random number generator is used for randomly generating a control signal of phase modulation required by the sending end electro-optic phase modulator and sending the control signal to the sending end electro-optic phase modulator; the transmitting end adjustable attenuator is used for attenuating the received signal to the quantum level and transmitting the signal to the transmitting end polarization coupler; the transmitting terminal polarization coupler is used for coupling the local oscillator light and the received signal light into a quantum signal and transmitting the quantum signal to the quantum key receiving terminal through a quantum channel; the quantum key receiving end comprises a receiving end polarization controller, a receiving end polarization beam splitter, a receiving end electro-optic phase modulator, a receiving end random number generator, a receiving end beam splitter, a receiving end homodyne detector and a receiving end post processor; the receiving end polarization controller, the receiving end polarization beam splitter, the receiving end electro-optic phase modulator, the receiving end beam splitter, the receiving end homodyne detector and the receiving end post processor are sequentially connected in series; the receiving end random number generator is connected with the receiving end electro-optic phase modulator; the receiving end polarization controller is used for calibrating the polarization state of the quantum signal sent by the quantum channel and sending the polarization state to the polarization beam splitter; the receiving end polarization beam splitter is used for splitting the received quantum signals into 50% of signal light and 50% of local oscillation light; the receiving end electro-optical phase modulator is used for carrying out phase modulation on the received signal light according to a phase modulation control command generated by the receiving end random number generator and then sending the signal light to the receiving end beam splitter; the receiving end random number generator is used for randomly generating a phase modulation control command required by the receiving end electro-optic phase modulator and sending the phase modulation control command to the receiving end electro-optic phase modulator; the receiving end beam splitter is used for interfering the local oscillation light sent by the receiving end polarization beam splitter with the signal light sent by the receiving end electro-optic phase modulator and sending the signal light to the receiving end homodyne detector; the receiving end homodyne detector is used for carrying out homodyne detection on the received local oscillator light and signal light and sending a detection result to the receiving end post processor; and the receiving end post processor is used for post-processing the received detection result so as to obtain a final quantum key.
The receiving end post processor comprises a receiving end digital sampling oscilloscope, a receiving end digital signal processor and a receiving end data acquisition card; the receiving end digital sampling oscilloscope is used for sampling, collecting and offline processing a received signal sent by the receiving end homodyne detector, separating amplitude and phase information of the received signal and sending the amplitude and phase information to the digital signal processing module; the receiving end digital signal processor is used for respectively processing the amplitude and phase information sent by the digital sampling oscilloscope, the amplitude information obtains the strength of a sent signal through a Bessel filter, the phase information carries out chirp coefficient estimation through an algorithm, a differential phase is reconstructed by using the obtained chirp coefficient, the original signal is recovered by using the signal strength and the differential reconstruction phase together through maximum likelihood sequence estimation based on a Viterbi algorithm, and the signal is sent to a receiving end data acquisition card; and the receiving end data acquisition card is used for acquiring the recovery signal after the digital signal processing.
According to the chirp-based continuous variable quantum key distribution method and system, the chirp coefficient of a received signal is estimated, the obtained chirp coefficient is used for reconstructing a differential phase, and symbol judgment is carried out through maximum likelihood sequence estimation based on a Viterbi algorithm, so that adverse effects on the signal due to the frequency chirp effect in medium-distance transmission are eliminated, and the transmission reliability is improved; meanwhile, the method does not need to use a heterodyne modulator at the transmitting end, only needs to estimate the chirp coefficient at the beginning of transmission, effectively saves the cost, and has high reliability, better performance, low cost and convenient implementation.
Drawings
FIG. 1 is a schematic process flow diagram of the process of the present invention.
FIG. 2 is a functional block diagram of the system of the present invention.
Detailed Description
FIG. 1 is a schematic flow chart of the method of the present invention: the chirp-based continuous variable quantum key distribution method provided by the invention comprises the following steps:
s1, a quantum key sending end modulates a quantum signal; specifically, a quantum key sending end generates coherent light pulses, and then the coherent light pulses are polarized and separated into signal light and local oscillator light; after amplitude modulation and phase modulation, the signal light is coupled with local oscillator light, so that a modulated quantum signal is obtained;
s2, the quantum key sending end sends the modulated quantum signals to a quantum key receiving end through a quantum channel;
s3, carrying out coherent detection on the received quantum signals by the quantum key receiving end so as to obtain a detection result; specifically, a quantum key receiving end adjusts the polarization state of a received quantum signal, and then divides the received signal into signal light and local oscillator light; after the local oscillation light is subjected to random phase modulation, the local oscillation light is interfered with the signal light, and the interfered signal is detected by a homodyne detector, so that a detection result is obtained;
s4, carrying out post-processing on the detection result obtained in the step S3 to obtain a final quantum key; specifically, sampling a detection result to obtain an amplitude signal and a phase signal; for the amplitude signal, obtaining signal strength information after passing through a filter (such as a Bessel filter); for a phase signal, firstly carrying out frequency offset compensation, then carrying out chirp coefficient estimation, and finally carrying out differential phase reconstruction through chirp information obtained by estimation to obtain differential phase information; and finally, performing symbol decision on the obtained signal strength information and the obtained differential phase information (for example, performing symbol decision on the obtained signal strength information and the obtained differential phase information by using maximum likelihood sequence estimation based on a viterbi algorithm), thereby obtaining a final quantum key.
The chirp coefficient estimation is specifically to perform chirp coefficient estimation by adopting the following steps:
A. the frequency chirp and signal strength of the laser are calculated using the following equations:
wherein P (t) is the signal strength; alpha is a linewidth enhancement factor; kappa is the adiabatic chirp coefficient;
B. performing time integration on the formula obtained in the step A to obtain the phase
In the formula
Is the initial phase;
is laser phase noise;
C. calculating t by the following equation1Time t and2phase difference between two consecutive symbols of a time instant
D. For the phase difference obtained in the step C
The calculation formula of (a) is simplified to obtain:
wherein T is T2-t1Is one symbol period;
E. the quantum key sending end sends a first test waveform to the quantum key receiving end, and after the quantum key receiving end receives the first test waveform, the quantum key receiving end calculates a first chirp coefficient c by adopting the following formula1：
In the formula
Is a differential phase between adjacent low and high levels in the first test waveform;
is a differential phase between adjacent high and low levels in the first test waveform;
in particular implementations, the first test waveform is a test waveform of LHLHLH … … cycles, where L is low and H is high;
F. the quantum key sending end sends a second test waveform to the quantum key receiving end, and after the quantum key receiving end receives the second test waveform, a second chirp coefficient c is calculated by adopting the following formula2：
In the formula
Is the differential phase between adjacent low levels and low levels in the second test waveform;
is a differential phase between adjacent high levels and high levels in the second test waveform;
in particular implementations, the second test waveform is a LLHHLLHH … … cycle of test waveforms, where L is low and H is high;
in step F, the second chirp coefficient may also be calculated by the following equation, thereby improving the calculation accuracy
Meanwhile, in the chirp coefficient estimation, only one chirp coefficient estimation is performed before the quantum key sending end and the quantum key receiving end perform the first quantum key transmission, and after the chirp coefficient is obtained, the subsequent signal transmission does not need to perform the chirp coefficient estimation any more.
FIG. 2 shows a functional block diagram of the system of the present invention: the distribution system for realizing the chirp-based continuous variable quantum key distribution method comprises a quantum key sending end and a quantum key receiving end; the quantum key sending terminal comprises a sending terminal pulse laser, a sending terminal polarizer, a sending terminal beam splitter, a sending terminal electro-optic intensity modulator, a sending terminal electro-optic phase modulator, a sending terminal random number generator, a sending terminal adjustable attenuator and a sending terminal polarization coupler; the transmitting end pulse laser, the transmitting end polarizer, the transmitting end beam splitter, the transmitting end electro-optical intensity modulator, the transmitting end electro-optical phase modulator, the transmitting end adjustable attenuator and the transmitting end polarization coupler are sequentially connected in series; the sending end random number generator is connected with the sending end electro-optical phase modulator; the sending end pulse laser is used for generating coherent light pulses and sending the coherent light pulses to the sending end polarizer; the transmitting end polarizer is used for controlling the polarization state of the signal light generated by the pulse laser and transmitting the signal light to the transmitting end beam splitter; the transmitting end beam splitter is used for splitting the pulse light into signal light and local oscillation light; the transmitting end electro-optical intensity modulator is used for carrying out amplitude modulation on the signal light and transmitting the signal light to the transmitting end electro-optical phase modulator; the sending end electro-optical phase modulator is used for carrying out phase modulation on the signal light after amplitude modulation according to the control signal generated by the sending end random number generator and sending the signal light to the sending end adjustable attenuator; the sending end random number generator is used for randomly generating a control signal of phase modulation required by the sending end electro-optic phase modulator and sending the control signal to the sending end electro-optic phase modulator; the transmitting end adjustable attenuator is used for attenuating the received signal to the quantum level and transmitting the signal to the transmitting end polarization coupler; the transmitting terminal polarization coupler is used for coupling the local oscillator light and the received signal light into a quantum signal and transmitting the quantum signal to the quantum key receiving terminal through a quantum channel; the quantum key receiving end comprises a receiving end polarization controller, a receiving end polarization beam splitter, a receiving end electro-optic phase modulator, a receiving end random number generator, a receiving end beam splitter, a receiving end homodyne detector and a receiving end post processor; the receiving end polarization controller, the receiving end polarization beam splitter, the receiving end electro-optic phase modulator, the receiving end beam splitter, the receiving end homodyne detector and the receiving end post processor are sequentially connected in series; the receiving end random number generator is connected with the receiving end electro-optic phase modulator; the receiving end polarization controller is used for calibrating the polarization state of the quantum signal sent by the quantum channel and sending the polarization state to the polarization beam splitter; the receiving end polarization beam splitter is used for splitting the received quantum signals into 50% of signal light and 50% of local oscillation light; the receiving end electro-optical phase modulator is used for carrying out phase modulation on the received signal light according to a phase modulation control command generated by the receiving end random number generator and then sending the signal light to the receiving end beam splitter; the receiving end random number generator is used for randomly generating a phase modulation control command required by the receiving end electro-optic phase modulator and sending the phase modulation control command to the receiving end electro-optic phase modulator; the receiving end beam splitter is used for interfering the local oscillation light sent by the receiving end polarization beam splitter with the signal light sent by the receiving end electro-optic phase modulator and sending the signal light to the receiving end homodyne detector; the receiving end homodyne detector is used for carrying out homodyne detection on the received local oscillator light and signal light and sending a detection result to the receiving end post processor; and the receiving end post processor is used for post-processing the received detection result so as to obtain a final quantum key.
The receiving end post processor comprises a receiving end digital sampling oscilloscope, a receiving end digital signal processor and a receiving end data acquisition card; the receiving end digital sampling oscilloscope is used for sampling, collecting and offline processing a received signal sent by the receiving end homodyne detector, separating amplitude and phase information of the received signal and sending the amplitude and phase information to the digital signal processing module; the receiving end digital signal processor is used for respectively processing the amplitude and phase information sent by the digital sampling oscilloscope, the amplitude information obtains the strength of a sent signal through a Bessel filter, the phase information carries out chirp coefficient estimation through an algorithm, a differential phase is reconstructed by using the obtained chirp coefficient, the original signal is recovered by using the signal strength and the differential reconstruction phase together through maximum likelihood sequence estimation based on a Viterbi algorithm, and the signal is sent to a receiving end data acquisition card; and the receiving end data acquisition card is used for acquiring the recovery signal after the digital signal processing.
In specific implementation, a Thorlabs OPG1015 picosecond optical pulse generator is adopted as the transmitting end pulse laser, and laser pulses with the frequency of 10GHz and less than or equal to 3ps can be generated; the sending end electro-optical intensity modulator adopts Photoline MX-LN-10, and has the characteristics of high extinction ratio (>20dB), low loss (2.5dB) and high bandwidth (10 GHz); the electro-optic phase modulator at the transmitting end and the electro-optic phase modulator at the receiving end both adopt the electro-optic phase modulators of model MPZ-LN-10, have the characteristics of high extinction ratio (>20dB), low loss (2.5dB) and high bandwidth (10GHz), can meet the quantum key communication system with higher speed, and reduce the extra loss brought by optical devices as much as possible; the transmitting end polarization coupler adopts a Thorlabs PBC980PM-FC polarization beam coupler to couple two beams of orthogonal polarized light into one optical fiber; high extinction ratio (>18dB), low loss (<2 dB); the homodyne detector at the receiving end adopts a Thorlabs PDA435A balanced amplification photoelectric detector, the common mode rejection ratio is greater than 20Db, and the bandwidth can reach 350 MHz; the receiving end digital sampling oscilloscope adopts a TektronixDSA71604C digital oscilloscope, the rise time is 9ps, the bandwidth can reach 23GHz, and the real-time sampling rate can reach 50 Gs/s; the quantum channel for communication between the quantum key sending end and the quantum key receiving end is a transmission medium formed by single-mode optical fibers or free space, the single-mode optical fibers have stable attenuation coefficient which is about 0.2dB/km, and are high in anti-interference capability and low in cost.
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| CN107070561A (en) * | 2016-12-19 | 2017-08-18 | 北京大学 | Channel multiplexing device based on two-way plug and play QKD system |
| CN106788849A (en) * | 2016-12-30 | 2017-05-31 | 北京信息科学技术研究院 | A kind of delay compensation method for adaptive optic fiber length in quantum key dispatching system |
| CN109905240A (en) * | 2019-03-26 | 2019-06-18 | 全球能源互联网研究院有限公司 | Optical fiber quantum key distribution system and method and device for improving quantum key generation rate |
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