CN111541536B - Continuous variable quantum key distribution system enhanced by phase sensitive amplification technology - Google Patents
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Abstract
The invention discloses a continuous variable quantum key distribution method enhanced by a phase sensitive amplification technology, which comprises the following steps: the optical transmitter modulates the radio frequency signal modulated by the quantum signal and generates a transmission optical signal, the transmission optical signal is input to the phase sensitive amplifier and amplified, and the optical receiver demodulates the amplified transmission optical signal to recover the regenerated quantum signal. The invention also discloses a continuous variable quantum key distribution system enhanced by the phase sensitive amplification technology, which consists of an optical transmitter, a phase sensitive amplifier and an optical receiver, wherein the optical transmitter and the quantum signal modulate a transmitting optical signal; the phase sensitive amplifier performs in-phase amplification and out-of-phase attenuation on the transmitted light signal; the optical receiver demodulates the amplified transmitted optical signal to recover the regenerated quantum signal. The invention provides a detailed system scheme which is low in hardware complexity and can be compatible with the current Gaussian, four-state and other CVQKD protocols.
Description
Technical Field
The invention relates to the technical field of quantum secret communication, in particular to a continuous variable quantum key distribution system with enhanced phase sensitive amplification technology.
Background
With the rise of Quantum physics and Quantum information theory, Quantum Key Distribution (QKD) technology with unconditional security is proposed by virtue of unique properties of Quantum signals. Quantum key distribution bears key information through specific quantum states, and a set of secure keys is generated between two legitimate communication parties. The uncertainty principle and the unclonable principle in quantum mechanics guarantee the security of the channel when an eavesdropper exists in the channel. At present, there are two main implementations of Quantum Key Distribution technology, namely Discrete-variable Quantum Key Distribution (DVQKD) and Continuous-variable Quantum Key Distribution (CVQKD).
However, the performance of the existing CVQKD technique is limited by the conversion efficiency and thermal noise level of the receiver. The specific reasons are as follows: for ease of discussion, reference is made to an agreement in cryptography, hereinafter the transmitter portion of key distribution will be referred to as Alice, the receiver portion as Bob, and the third party potential eavesdropper as Eve. The security of CVQKD is that the key information is encoded on a pair of non-orthogonal regular components of coherent states. Under the premise of reverse negotiation, Alice and the eavesdropper Eve simultaneously guess the key data in the hands of Bob according to the data in the hands. According to the quantum uncertainty principle, there is a lower bound on the product of the two estimated uncertainties for the two non-orthogonal components of Bob. That is, Alice and Bob can determine the upper limit of the information that an eavesdropper can obtain by estimating the covariance of the data between them, and then extract the final security key from the original data by technical means such as privacy enhancement. It is noted that the lower uncertainty limit between Alice and Eve is entirely determined by vacuum noise in the CVQKD system, and in addition to this, theoretically any additional noise, even including attenuation of the transmission channel, should be considered as eavesdropping behavior from an eavesdropper. CVQKD systems thus face in practice the limitation of noise from the different devices themselves. Particularly the photoelectric conversion efficiency and the electronic thermal noise of the balanced detector used by CVQKD. Due to technical limitations, today's balanced detectors have difficulty achieving high conversion efficiency and low thermal noise at high rates, resulting in severe limitations on the system speed and transmission distance of CVQKD.
The prior art PSA relies on optical cloning machines based on optical parametric processes, which are complex and introduce additional noise. The specific reasons are as follows: existing PSA technologies are not designed for QKD, ignoring many of the unique properties of QKD technologies. For example, in a classical communication scenario (such as a dense wavelength division multiplexing system), the format and bandwidth of a signal at a transmitting end are fixed, and there is little free bandwidth between signal channels, which results in that an existing PSA must clone a copy of an effective signal by means of an optical cloning machine based on a parametric process to achieve low-noise amplification of all phases of the effective signal by a second-stage parametric process. The sending end signal of the QKD system is not limited by the QKD system, and enough free bandwidth is provided for realizing the 'digital' cloning machine provided by the invention. On the other hand, the existing PSA scheme does not focus on the power leakage of the pump to the signal, the pump power itself can be very high, while in the QKD system, the quantum channel is extremely sensitive to any noise, and because the system bandwidth is limited, the pump signal is far from the quantum channel in frequency than in classical communication, so when applying PSA-enhanced QKD, the pump power of the PSA needs to be limited.
Disclosure of Invention
In order to solve the problems, the invention provides a continuous variable quantum key distribution method and a system enhanced by a phase sensitive amplification technology, relieves the limitation of the efficiency and noise of the current optical detector on the performance of a CVQKD system, and provides a digital cloning machine, so that the PSA technology does not depend on the optical cloning machine based on an optical parameter process, excessive extra noise cannot be introduced due to the complex structure of the cloning machine, and the quality of a generated quantum signal copy is greatly improved. The invention uses the coherent heterodyne receiver to realize the signal demodulation after PSA amplification, compared with the mainstream coherent homodyne receiver, the structure is simpler, the demodulation of the quantum signal is mainly realized in a digital domain, and the accuracy is higher than that of the mainstream coherent homodyne receiver.
In order to achieve the technical effects, the invention is realized by the following technical scheme:
a continuous variable quantum key distribution method enhanced by a phase sensitive amplification technology is realized based on a distribution system consisting of an optical transmitter, a phase sensitive amplifier and an optical receiver, and the method comprises the following steps: the optical transmitter modulates the radio frequency signal modulated by the quantum signal and generates a transmission optical signal, the transmission optical signal is input to the phase sensitive amplifier and amplified, the optical receiver demodulates the transmission optical signal after receiving the amplified transmission optical signal to recover a regenerated quantum signal, and the quantum signal is a quantum key.
The method comprises the following steps:
s1: the optical transmitter generates a beam of laser, the laser is divided into two orthogonal polarizations by a polarization beam splitter, meanwhile, a quantum signal is modulated into a radio frequency signal, the radio frequency signal and one polarization are modulated into a radio frequency electrical carrier, and the radio frequency electrical carrier and the other polarization are modulated to generate a transmitting optical signal;
s2: transmitting optical signals enter a phase sensitive amplifier after being transmitted through a channel, a polarization controller corrects the transmitting optical signals and then divides the transmitting optical signals into two paths of optical signals through a polarization beam splitter, the first path of optical signals are input into a pump laser in an injection locking mode to carry out phase locking on the pump laser and generate pump light, the other path of optical signals serve as signal light and enter a nonlinear amplification unit together with the pump light for amplification, and the nonlinear amplification unit amplifies optical signals in the two paths of light, which are in the same phase with the pump light, and attenuates other light;
s3: the optical receiver receives the amplified transmit optical signal and then uses coherent heterodyne balancing to demodulate the quantum signal from the amplified transmit optical signal by adjusting the phase of the local oscillator light.
In step S1, the step of modulating the quantum signal into a radio frequency signal includes: and respectively modulating the quantum signal modulated by Gaussian modulation or quadrature phase shift keying and the conjugate thereof to positive and negative radio frequency carriers by an intensity modulator or an IQ modulator to obtain a radio frequency signal.
The continuous variable quantum key distribution system enhanced by the phase sensitive amplification technology comprises an optical transmitter, a phase sensitive amplifier and an optical receiver, wherein the optical transmitter and a quantum signal modulate an emitted optical signal;
the phase sensitive amplifier amplifies the transmitted optical signal in phase and attenuates the signal out of phase to obtain an amplified transmitted optical signal;
the optical receiver demodulates the amplified transmitted optical signal to recover the regenerated quantum signal.
The optical transmitter comprises a transmitting end laser, a polarization beam splitter, an electro-optical modulator and a polarization beam combiner which are fixed in sequence, wherein the transmitting end laser can emit a beam of laser, the polarization beam splitter decomposes the laser into two orthogonal polarizations, the electro-optical modulator modulates a radio frequency signal modulated by a quantum signal and one polarization to obtain a radio frequency electric carrier, and the polarization beam combiner modulates the other polarization and the radio frequency electric carrier to obtain a transmitting optical signal.
The phase-sensitive amplifier comprises a polarization controller, a polarization beam splitter, a pump laser, a nonlinear amplification unit and a polarization beam combiner, wherein the polarization controller can correct an emitted light signal, the polarization beam splitter can divide the emitted light signal into two paths of light signals, the pump laser can be injected by one path of light signal and locked to form pump light, the nonlinear amplification unit can perform in-phase amplification and out-of-phase attenuation on the pump light and the other path of light signal which enter together, and the polarization beam combiner combines the two paths of light signals.
The optical receiver comprises an optical coupler, a balance detector, an electric signal amplifier, an analog-to-digital converter and a digital signal processor, wherein the optical coupler combines the amplified emitted optical signals, the balance detector reduces the noise of the emitted optical signals, the electric signal amplifier carries out photoelectric conversion on the emitted optical signals after the noise reduction to form analog electric signals, the analog-to-digital converter converts the analog electric signals into digital signals, and the digital signal processor carries out secondary demodulation and a channel damage compensation algorithm on the digital signals to recover the regenerated quantum signals.
The nonlinear amplification unit adopts a nonlinear fiber loop mirror.
The invention has the beneficial effects that:
1. the current PSA enhanced CVQKD only has a theoretical model and analysis, and has no practical system scheme, but the invention provides a detailed system scheme which can be realized, the hardware complexity of the system is low, and the system can be compatible with the current Gaussian, four-state and other CVQKD protocols;
2. the invention utilizes the 'digital' cloning machine to generate the copy of the quantum signal, compared with the prior cloning machine, the structure of the invention is greatly simplified, and the cloning quality is greatly improved;
3. the invention mainly improves the structure of the cloning machine, namely, the existing optical cloning machine based on a parametric process is converted into a digital cloning machine based on signal processing and electro-optical modulation;
4. the invention provides a complete technical scheme for integrating a CVQKD protocol, a 'digital' cloning machine and a PSA enhanced receiver into a system.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a block diagram of the structure of the optical transmitter;
FIG. 2 is a schematic diagram of the emitted optical signal generation;
FIG. 3 is a block diagram of the structure of the phase sensitive amplifier;
FIG. 4 is a block diagram of a non-linear amplifying unit of the phase sensitive amplifier;
fig. 5 is a block diagram of the optical receiver structure.
In the drawings, the names of the components identified by the respective reference numerals are as follows:
the system comprises a 1-optical transmitter, a 2-phase sensitive amplifier, a 3-circulator a, a 4-optical coupler, a 5-optical receiver, a 11-transmitting end laser, a 12-polarization beam splitter, a 13-electro-optical modulator, a 14-polarization beam combiner, a 21-polarization controller, a 22-pump laser, a 23-nonlinear amplification unit, a 51-balance detector, a 52-electric signal amplifier, a 53-analog-to-digital converter and a 54-digital signal processor.
Detailed Description
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "including" and "having," and any variations thereof, in the description and claims of this application and the description of the above figures are intended to cover non-exclusive inclusions. The terms "first," "second," and the like in the description and claims of this application or in the above-described drawings are used for distinguishing between different objects and not for describing a particular order.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by one skilled in the art that the embodiments described herein can be combined with other embodiments.
The continuous variable quantum key distribution method enhanced by the phase sensitive amplification technology comprises the following steps:
s1: the optical transmitter 1 generates a beam of laser, the laser is divided into two orthogonal polarizations by a polarization beam splitter 12, meanwhile, a quantum signal is modulated into a radio frequency signal, the radio frequency signal and one polarization are modulated into a radio frequency electrical carrier, and the radio frequency electrical carrier and the other polarization are modulated to generate an emission optical signal;
s2: the method comprises the steps that an emitted light signal enters a phase-sensitive amplifier 2 after being transmitted through a channel, a polarization controller 21 corrects the emitted light signal and then is divided into two paths of light signals through a polarization beam splitter 12, the first path of light signal is input into a pump laser 22 in an injection locking mode to carry out phase locking on pump laser and generate pump light, the other path of light signal serving as signal light and the pump light enter a nonlinear amplification unit 23 to be amplified, and the nonlinear amplification unit 23 amplifies light signals in the two paths of light, wherein the light signals are in the same phase as the pump light, and attenuates other light;
s3: the optical receiver 5 receives the amplified transmit optical signal and then uses coherent heterodyne balancing to demodulate the quantum signal from the amplified transmit optical signal by adjusting the phase of the local oscillator light.
In step S1, the step of modulating the quantum signal into a radio frequency signal includes: and respectively modulating the quantum signal modulated by Gaussian modulation or quadrature phase shift keying and the conjugate thereof to positive and negative radio frequency carriers by an intensity modulator or an IQ modulator to obtain a radio frequency signal.
The continuous variable quantum key distribution system enhanced by the phase sensitive amplification technology comprises an optical transmitter 1, a phase sensitive amplifier 2 and an optical receiver 5, wherein the optical transmitter 1 and a quantum signal modulate a transmission optical signal;
the phase sensitive amplifier 2 amplifies the transmission optical signal in phase and attenuates the transmission optical signal out of phase to obtain an amplified transmission optical signal;
the optical receiver 5 demodulates the amplified transmitted optical signal to recover the regenerated quantum signal.
As shown in fig. 1, the optical transmitter 1 includes a transmitting end laser 11, a polarization beam splitter 12, an electro-optical modulator 13, and a polarization beam combiner 14, which are fixed in sequence, where the transmitting end laser 11 can emit a beam of laser, the polarization beam splitter 12 splits the laser into two orthogonal polarizations, the electro-optical modulator 13 modulates a radio frequency signal modulated by a quantum signal with one polarization to obtain a radio frequency electrical carrier, and the polarization beam combiner 14 modulates the other polarization with the radio frequency electrical carrier to obtain an emitted optical signal.
As shown in fig. 3, the phase sensitive amplifier 2 includes a polarization controller 21, a polarization beam splitter 12, a pump laser 22, a nonlinear amplification unit 23, and a polarization beam combiner 14, where the polarization controller 21 can correct an emitted optical signal, the polarization beam splitter 12 can divide the emitted optical signal into two optical signals, the pump laser 22 can be injected by one of the optical signals and locked to form a pump light, the nonlinear amplification unit 23 can perform in-phase amplification and out-of-phase attenuation on the pump light and the other optical signal entering together, and the polarization beam combiner 14 combines the two optical signals.
As shown in fig. 5, the optical receiver 5 includes an optical coupler 4, a balanced detector 51, an electrical signal amplifier 52, an analog-to-digital converter 53 and a digital signal processor 54, the optical coupler 4 combines the amplified transmission optical signals, the balanced detector 51 reduces the noise of the transmission optical signals, the electrical signal amplifier 52 performs optical-to-electrical conversion on the reduced transmission optical signals to obtain analog electrical signals, the analog-to-digital converter 53 converts the analog electrical signals to digital signals, and the digital signal processor 54 performs secondary demodulation and a channel impairment compensation algorithm on the digital signals to recover the regenerated quantum signals.
One specific application of the system is as follows:
1. the process by which the optical transmitter generates the transmitted optical signal is as follows:
as shown in fig. 1, an optical transmitter 1 uses a transmitting end laser 11 to generate a laser beam, which is divided into two orthogonal polarizations by a polarization beam splitter 12, one of which is used as a carrier without any modulation, and the other uses subcarrier modulation to generate an optical signal as shown in fig. 2, and the principle and mathematical model thereof are as follows: quantum signal X (t) modulated by Gaussian modulation or Quadrature Phase Shift Keying (QPSK) and conjugate X (t)*Respectively modulating the signals to positive and negative radio frequency carriers by an intensity modulator or an IQ modulator to obtain radio frequency signals:
s(t)＝X(t)exp(j(2πfct))+X(t)*exp(-j2πfet) (1)
wherein f iseIs the frequency of a radio frequency electrical carrier wave. Further, the RF signal S (t) is modulated onto the emitted light carrier to obtain the emitted light signal Et(t)：
Wherein the content of the first and second substances,
P、fc、
respectively, the power, center frequency, phase of the emitted optical carrier.
Further derivation of equations (1) and (2) can be found:
wherein, Re (x (t), Im (x (t)) are the real part and imaginary part of the quantum signal x (t), respectively. It can be seen that the optical carrier fcCarries a real signal s (t).
2. The phase sensitive amplifier 2 amplifies the transmitted optical signal as follows:
the phase sensitive amplifier 2 is sensitive to the phase of the optical signal to be amplified, and amplifies only the optical signal in phase with the pump light, while it attenuates the other light without amplification, wherein the attenuation of the optical signal orthogonal to the pump light is the strongest. The structure of the phase sensitive amplifier is shown in fig. 3, and the principle and mathematical model thereof are as follows:
optical signal E generated by an optical transmittert(t) polarization correction is effected first by means of a polarization controller 21 after transmission through the channel, and is then divided into two optical signals E by means of a polarization beam splitter 121，2(t) of (d). One path of optical signal E1(t) is input to the pump laser 22 by injection locking to achieve phase locking of the pump light. And the other path of the signal light and the pump light after injection locking enter the phase sensitive amplifier together.
The phase-sensitive amplification of the signal light can be realized in particular by a nonlinear unit. One of the non-linear amplification units 23 of PSA based on Four-Wave Mixing (FWM) effect is shown in fig. 4, and a high non-linear fiber is used to split a light beam with a ratio of 50: the two output ports of the 50 fiber optic couplers are connected to form a ring. Optical signal E2(t) is inputted from port a1 of circulator a, and the pump light is inputted from port b1 of circulator b. Optical signal E2(t) andthe pumping light is applied to the nonlinear amplification unit 23 and then outputted from ports a3 and b3 of the circulators a and b, respectively.
By adjusting the phase of the pump light or the phase of the signal light (for example by adjusting the length of the fiber or by using a phase modulator), it is possible to achieve amplification of only the emitted optical signal ErThe real part of (t), i.e. the optical signal E after amplification by a phase-sensitive amplifierr(t) can be expressed as:
wherein g is the power gain of the phase sensitive amplifier; RE (E)t(t))、Im(Et(t)) are the emission light signals E, respectivelytReal and imaginary parts of (t).
Further derivation of equations (3) and (4) can be found:
3. the process of receiving the amplified optical signal and demodulating and recovering the quantum signal by the optical receiver 5 is as follows:
as shown in fig. 5, the optical receiver 5 uses coherent heterodyne balanced detection to implement the amplified optical signal E by adjusting the phase of the local oscillator lightr(t) demodulation, the principle and mathematical model of which are as follows:
the local oscillator light generated by the local oscillator laser may be expressed as:
Elo(t)＝Aloexp(j(2πflot+θlo)) (6)
wherein the content of the first and second substances,
Plo、flo、θlothe power, the center frequency and the phase of the local oscillator light are respectively.
When the phase theta of the local oscillator lightl0Equal to the phase of the transmitted optical carrier
The output photocurrent i (t) of the balance detecting probe 51 is:
I(t)＝4R×Re(Er(t))×conj(Elo(t)) (7)
wherein Re is the response coefficient of the balance detection detector; re (E)r(t))×conj(Elo(t)) is Er(t)×conj(Elo(t)) the real part of the image.
Further derivation of equations (5), (6) and (7) can be found:
wherein f isif＝fc-floIs the frequency difference between the transmitted optical carrier and the local oscillator light.
The output photocurrent i (t) of the balance detecting detector 51 is sampled by an analog-to-digital converter 53, the sampled signal is converted into an analog electrical signal by an electrical signal amplifier 52, the analog electrical signal is converted into a digital signal by the analog-to-digital converter 53 and transmitted to a digital signal processor 54, and the digital signal processor 54 can recover the regenerated quantum signal x (t) by digital signal processing algorithms such as secondary demodulation and channel damage compensation.
It should be noted that, for simplicity of description, the above-mentioned method embodiments are described as a series of action combinations, but those skilled in the art should understand that the present invention is not limited by the described action sequence, because some steps may be performed in other sequences or simultaneously according to the present invention. Further, those skilled in the art should also appreciate that the embodiments described in the specification are preferred embodiments and that acts and modules referred to are not necessarily required by the invention.
In the embodiments provided in the present application, it should be understood that the disclosed apparatus may be implemented in other manners. For example, the above-described embodiments of the apparatus are merely illustrative, and for example, the above-described division of the units is only one type of division of logical functions, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or communication connection may be an indirect coupling or communication connection between devices or units through some interfaces, and may be in a telecommunication or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
The above embodiments are only used to illustrate the technical solution of the present invention, and do not limit the protection scope of the present invention. It is to be understood that the embodiments described are only some embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from these embodiments without any inventive step, are within the scope of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still make no creative work on the condition of conflict, and make mutual combination, addition and deletion, or other adjustments according to the features in the embodiments of the present invention, thereby obtaining other technical solutions which are different and do not depart from the concept of the present invention, and these technical solutions also belong to the scope to be protected by the present invention.
Claims (2)
1. The continuous variable quantum key distribution system enhanced by the phase sensitive amplification technology is characterized by comprising an optical transmitter, a phase sensitive amplifier and an optical receiver, wherein the optical transmitter and a quantum signal modulate an emitted optical signal;
the phase sensitive amplifier amplifies the transmitted optical signal in phase and attenuates the signal out of phase to obtain an amplified transmitted optical signal;
the optical receiver demodulates the amplified transmission optical signal to recover a regenerated quantum signal, namely a quantum key;
wherein the content of the first and second substances,
the optical transmitter comprises a transmitting end laser, a polarization beam splitter, an electro-optical modulator and a polarization beam combiner which are fixed in sequence, wherein the transmitting end laser can emit a beam of laser, the polarization beam splitter divides the laser into two orthogonal polarizations, the electro-optical modulator modulates a radio frequency signal modulated by a quantum signal and one polarization to obtain a radio frequency electric carrier, and the polarization beam combiner modulates the unmodulated polarization and the radio frequency electric carrier to obtain a transmitting optical signal;
the phase sensitive amplifier comprises a polarization controller, a polarization beam splitter, a pump laser, a nonlinear amplification unit and a polarization beam combiner, wherein the polarization controller can correct an emitted light signal, the polarization beam splitter can divide the emitted light signal into two paths of light signals, the pump laser can be injected by one path of light signals and locked to form pump light, and the nonlinear amplification unit can perform in-phase amplification and out-of-phase attenuation on the pump light and the other path of light signals which enter together;
the optical receiver comprises an optical coupler, a balance detector, an electric signal amplifier, an analog-to-digital converter and a digital signal processor, wherein the optical coupler combines the amplified emitted optical signals, the balance detector reduces the noise of the emitted optical signals, the electric signal amplifier carries out photoelectric conversion on the emitted optical signals after the noise reduction to form analog electric signals, the analog-to-digital converter converts the analog electric signals into digital signals, and the digital signal processor carries out secondary demodulation and a channel damage compensation algorithm on the digital signals to recover the regenerated quantum signals.
2. The system for distributed continuous variable quantum key distribution with enhanced phase sensitive amplification of claim 1, wherein the nonlinear amplification unit employs a nonlinear fiber loop mirror.
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| 《Performance improvement of eight-state continuous-variable quantum key distribution with an optical amplifier》;Ying Guo等;《Physics Letters A》;20171211;全文 * |
| 《基于光纤通信的连续变量量子密钥分发改进研究》;龚峰;《中国优秀硕士学位论文全文数据库 基础科学辑》;20190915(第9期);全文 * |
| 《连续变量量子密钥分发网络的理论研究》;胡林曦;《中国优秀硕士学位论文全文数据库 基础科学辑》;20200115(第1期);全文 * |
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