Continuous Variable Quantum Key Distribution Pilot Delay Device and Method

Abstract

The present invention provides a pilot time delay device and method for continuous variable quantum key distribution. The unmodulated optical pulse signal is divided into a signal pulse and a pilot pulse by the beam splitter. The pilot pulse is reflected after being transmitted to the second Faraday mirror. The signal pulse passes through the optical fiber delay line so that the signal pulse is located in the middle of the pilot pulse. The phase modulator modulates the signal pulse and then is reflected after being transmitted to the first Faraday mirror. The two reflected pulses are superimposed at the beam splitter to output a time-division multiplexed signal. By adopting the Faraday-Michelson structure and utilizing the polarization-maintaining principle of the Faraday mirror, the present invention enables the two pulses of the long and short arms to maintain the same polarization direction when being superimposed after modulation, solving the stability problem of the AMZI structure.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum secure communication. Specifically, it relates to a pilot delay device and method for continuous variable quantum key distribution based on a Faraday-Michelson structure. Background Art

[0002] In today's highly developed information technology, information security issues have attracted much attention. Quantum key distribution in quantum technology provides a secure and effective key transmission method, which can provide information security protection for both communication parties. Continuous variable quantum key distribution technology is one of the quantum key distribution technologies. It uses easy-to-implement coherent detection technology and easy-to-integrate optical components, so it has advantages in terms of cost and integration with classical optical networks. It is one of the key technologies in the practical process of quantum key distribution.

[0003] In the actual implementation of continuous variable quantum key distribution, the detection end uses coherent detection technology to extract the information encoded on the canonical components of the optical field. This technology requires strong local oscillator light to be mixed with the signal light to achieve the amplification of the canonical components of the signal light. The local local oscillator scheme can make up for the security loopholes brought by transmitting the local oscillator light. In addition, it also has the advantages of easily reaching the shot noise limit detection and simplifying the optical path structure, making it a strong competitor for practical solutions. When the local local oscillator scheme is actually implemented, it is necessary to send pilot pulses carrying phase information. The commonly used pilot delay scheme in experiments has the basic idea of generating signal pulses and pilot pulses simultaneously to eliminate the errors caused by phase jitter. However, due to the problems of long and short arms in the traditional AMZI structure, the device needs to be very stable, and polarization-maintaining fibers need to be used to align the polarization of the two paths of pulses. A recently proposed pilot polarization multiplexing scheme can improve the stability, but still requires the use of relatively expensive polarization-maintaining fibers. Summary of the Invention

[0004] Aiming at the defects in the prior art, the purpose of the present invention is to provide a pilot delay device and method for continuous variable quantum key distribution.

[0005] A pilot delay device for continuous variable quantum key distribution according to the present invention includes: a beam splitter, an optical fiber delay line composed of single-mode optical fibers, a phase modulator, a first Faraday mirror, a second Faraday mirror, a random number generation module, and a radio frequency amplification module;

[0006] The first Faraday mirror is connected to the beam splitter through the phase modulator and the optical fiber delay line in sequence, the second Faraday mirror is connected to the beam splitter, and the random number generation module is connected to the radio frequency port of the phase modulator through the radio frequency amplification module;

[0007] The unmodulated optical pulse signal is split into a signal pulse and a pilot pulse by the beam splitter. The pilot pulse is transmitted to the second Faraday mirror and then reflected. The signal pulse passes through the optical fiber delay line so that the signal pulse is located in the middle of the pilot pulse. The phase modulator modulates the signal pulse and then transmits it to the first Faraday mirror and is reflected. The two reflected pulses are superimposed again at the beam splitter to output a time-division multiplexed signal.

[0008] Preferably, the beam splitter is a 99:1 beam splitter. The signal pulse output by splitting accounts for 1%, and the pilot pulse accounts for 99%.

[0009] Preferably, the first Faraday mirror and the second Faraday mirror keep the two reflected pulses in the same polarization direction during interference.

[0010] Preferably, when the signal pulse and the pilot pulse pass through the optical fiber and the Faraday mirror, the forward transmission matrix and the backward transmission matrix are respectively expressed as:

[0011]

[0012]

[0013] where θ is the angle of polarization change, exp() is the exponential function, i is the imaginary unit, is the phase change of the ordinary light during transmission; is the phase change of the extraordinary light during transmission.

[0014] Preferably, the first Faraday mirror and the second Faraday mirror include a 45° Faraday rotator and a plane mirror, and the Jones matrix is expressed as:

[0015]

[0016] The Jones matrix of the continuous variable quantum key distribution pilot time delay device is:

[0017]

[0018] where,

[0019] According to a continuous variable quantum key distribution pilot time delay method provided by the present invention, using the continuous variable quantum key distribution pilot time delay device, the method includes:

[0020] Step S1, the random number generation module generates a random number voltage signal, and amplifies the generated random number voltage signal through the radio frequency amplification module as the modulation signal of the phase modulator;

[0021] Step S2: Input the unmodulated optical pulse signal into a beam splitter to divide it into a signal pulse and a pilot pulse. The pilot pulse is transmitted to the second Faraday mirror and then reflected. The signal pulse passes through the optical fiber delay line so that the signal pulse is located in the middle of the pilot pulse. The phase modulator modulates the signal pulse and then transmits it to the first Faraday mirror and is reflected. The two reflected pulses are superimposed again at the beam splitter to output a time-division multiplexed signal.

[0022] Preferably, the beam splitter is a 99:1 beam splitter. The signal pulse output by beam splitting accounts for 1%, and the pilot pulse accounts for 99%.

[0023] Preferably, the first Faraday mirror and the second Faraday mirror keep the two reflected pulses in the same polarization direction during interference.

[0024] Preferably, when the signal pulse and the pilot pulse pass through the optical fiber and the Faraday mirror, the forward transmission matrix and the backward transmission matrix are respectively expressed as:

[0025]

[0026]

[0027] where θ is the angle of polarization change, exp() is the exponential function, i is the imaginary unit, is the phase change of the ordinary light during the transmission process; is the phase change of the extraordinary light during the transmission process.

[0028] Preferably, the first Faraday mirror and the second Faraday mirror include a 45° Faraday rotator and a plane mirror, and the Jones matrix is expressed as:

[0029]

[0030] The Jones matrix of the continuous variable quantum key distribution pilot time delay device is:

[0031]

[0032] where,

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] By adopting the Faraday-Michelson structure and using the polarization-preserving principle of the Faraday mirror, the present invention enables the two pulses of the long and short arms to maintain the same polarization direction when they are superimposed after modulation, and solves the stability problem of the AMZI structure. Description of the Drawings

[0035] Other features, objectives, and advantages of the present invention will become more apparent by reading the following detailed description of non - restrictive embodiments with reference to the accompanying drawings:

[0036] Figure 1 It is a schematic structural diagram of a pilot time - delay device for continuous - variable quantum key distribution of the present invention;

[0037] Figure 2 It is a timing diagram of signal pulses and pilot pulses in the embodiment. Specific Embodiments

[0038] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all fall within the protection scope of the present invention.

[0039] As Figure 1 shown, a pilot time - delay device for continuous - variable quantum key distribution includes: a beam splitter, an optical fiber delay line, a phase modulator, a first Faraday mirror, a second Faraday mirror, a random number generation module, and a radio - frequency amplification module. The first Faraday mirror is connected to the beam splitter through the phase modulator and the optical fiber delay line in sequence. The second Faraday mirror is connected to the beam splitter. The random number generation module is connected to the radio - frequency port of the phase modulator through the radio - frequency amplification module. In this embodiment, the beam splitter is a 99:1 beam splitter, and the signal pulses output by beam splitting account for 1%, while the pilot pulses account for 99%.

[0040] The un - modulated optical pulse signal is split into signal pulses and pilot pulses by the beam splitter. The pilot pulses are reflected after being transmitted to the second Faraday mirror. The signal pulses pass through the optical fiber delay line, so that the signal pulses are located in the middle of the pilot pulses. The phase modulator modulates the signal pulses and then transmits them to the first Faraday mirror for reflection. The two reflected pulses are superposed again at the beam splitter to output a time - division multiplexed signal. The first Faraday mirror and the second Faraday mirror keep the two reflected pulses in the same polarization direction during interference.

[0041] Using single - mode optical fiber instead of polarization - maintaining optical fiber reduces the cost of the system. When the signal pulses and pilot pulses pass through the single - mode optical fiber and the Faraday mirror, the forward - transmission matrix and the backward - transmission matrix are respectively expressed as:

[0042]

[0043]

[0044] where θ is the angle of polarization change, exp() is the exponential function, and i is the imaginary unit, is the phase change of the ordinary light during transmission; is the phase change of the extraordinary light during transmission.

[0045] The first Faraday mirror and the second Faraday mirror include a 45° Faraday rotator and a plane mirror, and the Jones matrix is expressed as:

[0046]

[0047] The Jones matrix of the continuous variable quantum key distribution pilot time delay device is:

[0048]

[0049] wherein, Therefore, regardless of the birefringence effect of the medium and the input polarization state, the polarization of the output state is always orthogonal to the polarization of the input state. So the pilot pulse and the signal pulse can finally maintain the same polarization state.

[0050] The present invention also provides a continuous variable quantum key distribution pilot time delay method, which adopts the above-mentioned continuous variable quantum key distribution pilot time delay device, and the method includes:

[0051] Step S1, a random number generation module generates a random number voltage signal, and the generated random number voltage signal is amplified by a radio frequency amplification module as the modulation signal of the phase modulator;

[0052] Step S2, an unmodulated optical pulse signal is input into a beam splitter to be divided into a signal pulse and a pilot pulse. The pilot pulse is reflected after being transmitted to the second Faraday mirror. The signal pulse passes through the optical fiber delay line, so that the signal pulse is located in the middle of the pilot pulse. The phase modulator modulates the signal pulse, and then it is reflected after being transmitted to the first Faraday mirror. The two reflected pulses are superimposed again at the beam splitter to output a time-division multiplexed signal.

[0053] The specific embodiments of the present invention have been described above. 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. Without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A pilot time delay device for continuous variable quantum key distribution, characterized in that Including: A beam splitter, an optical fiber delay line, a phase modulator, a first Faraday mirror, a second Faraday mirror, a random number generation module, and a radio frequency amplification module; The first Faraday mirror is sequentially connected to the beam splitter through the phase modulator and the optical fiber delay line, the second Faraday mirror is connected to the beam splitter, and the random number generation module is connected to the radio frequency port of the phase modulator through the radio frequency amplification module; The first Faraday mirror and the second Faraday mirror include a 45° Faraday rotator and a plane mirror; The unmodulated optical pulse signal is divided into a signal pulse and a pilot pulse by the beam splitter. The pilot pulse is reflected after being transmitted to the second Faraday mirror. The signal pulse passes through the optical fiber delay line so that the signal pulse is in the middle of the pilot pulse. The phase modulator modulates the signal pulse and then reflects it after being transmitted to the first Faraday mirror. The two reflected pulses are superimposed again at the beam splitter to output a time-division multiplexed signal.

2. The pilot time delay device for continuous variable quantum key distribution according to claim 1, wherein The beam splitter is a 99:1 beam splitter, and the signal pulse output by beam splitting accounts for 1%, and the pilot pulse accounts for 99%.

3. The pilot time delay device for continuous variable quantum key distribution according to claim 1, characterized in that The first Faraday mirror and the second Faraday mirror keep the two reflected pulses in the same polarization direction during interference.

4. The pilot time delay device for continuous variable quantum key distribution according to claim 1, characterized in that When the signal pulse and the pilot pulse pass through the optical fiber and the Faraday mirror, the forward transmission matrix and the backward transmission matrix are respectively expressed as: where θ is the angle of polarization change, exp() is the exponential function, and i is the imaginary unit, is the phase change of the ordinary ray during transmission; is the phase change of the extraordinary ray during transmission.

5. The pilot time delay device for continuous variable quantum key distribution according to claim 4, wherein The Jones matrix is expressed as: The Jones matrix of the continuous variable quantum key distribution pilot time delay device is: Among them, 6. A method for pilot delay in continuous variable quantum key distribution, characterized in that, Using the continuous variable quantum key distribution pilot time delay device described in claim 1, the method includes: Step S1, the random number generation module generates a random number voltage signal, and the generated random number voltage signal is amplified by the radio frequency amplification module as the modulation signal of the phase modulator; Step S2, input the unmodulated optical pulse signal into the beam splitter to be divided into a signal pulse and a pilot pulse. The pilot pulse is reflected after being transmitted to the second Faraday mirror. The signal pulse passes through the optical fiber delay line so that the signal pulse is in the middle of the pilot pulse. The phase modulator modulates the signal pulse and then reflects it after being transmitted to the first Faraday mirror. The two reflected pulses are superimposed again at the beam splitter to output a time-division multiplexed signal.

7. The method for pilot time delay of continuous variable quantum key distribution according to claim 6, characterized in that The beam splitter is a 99:1 beam splitter, and the signal pulse output by beam splitting accounts for 1%, and the pilot pulse accounts for 99%.

8. The method for pilot delay in continuous variable quantum key distribution according to claim 6, wherein The first Faraday mirror and the second Faraday mirror keep the two reflected pulses in the same polarization direction during interference.

9. The method for pilot time delay of continuous variable quantum key distribution according to claim 6, characterized in that When the signal pulse and the pilot pulse pass through the optical fiber and the Faraday mirror, the forward transmission matrix and the backward transmission matrix are respectively expressed as: where θ is the angle of polarization change, exp() is the exponential function, and i is the imaginary unit, is the phase change of the ordinary ray during transmission; is the phase change of the extraordinary ray during transmission.

10. The method for pilot time delay of continuous variable quantum key distribution according to claim 9, wherein The first Faraday mirror and the second Faraday mirror include a 45° Faraday rotator and a plane mirror, and the Jones matrix is expressed as: The Jones matrix of the continuous variable quantum key distribution pilot time delay device is: Among them,

Images