CN115913551B

CN115913551B - Measurement equipment independent quantum key distribution system for real-time calibration of reference system

Info

Publication number: CN115913551B
Application number: CN202310012991.4A
Authority: CN
Inventors: 赵义博; 王东
Original assignee: Beijing Zhongkeguoguang Quantum Technology Co ltd
Current assignee: Beijing Zhongkeguoguang Quantum Technology Co ltd
Priority date: 2023-01-05
Filing date: 2023-01-05
Publication date: 2023-05-09
Anticipated expiration: 2043-01-05
Also published as: CN115913551A

Abstract

The invention belongs to the technical field of quantum safety communication and discloses a measuring equipment independent quantum key distribution system for real-time calibration of a reference system, which comprises two transmitting ends and a measuring end, wherein the measuring end comprises a first electric control polarization controller, a second electric control polarization controller, a polarization beam splitting and transmitting module, a second single photon detector, a fifth beam splitter, a third single photon detector and a fourth single photon detector. In addition, only one single photon detector is additionally arranged at the measuring end for real-time polarization feedback control of one path of optical signals, and the single photon detector for performing Bell state measurement can be used for real-time polarization feedback control of the other path of optical signals in a time division multiplexing mode. Thereby improving the stability and practicality of the system.

Description

Measurement equipment independent quantum key distribution system for real-time calibration of reference system

Technical Field

The invention relates to the technical field of quantum security communication, in particular to a measuring equipment independent quantum key distribution system for real-time calibration of a reference system.

Background

Quantum key distribution can provide information theory security for both communication parties, but due to the non-perfection of actual devices, security vulnerabilities exist in the system, wherein the most common vulnerabilities are found in the aspect of measuring equipment. The proposal of a measurement device independent quantum key distribution protocol (MDI-QKD) removes the trusted requirement on a measurement end, can immunize all attacks aiming at the measurement end, and greatly improves the actual security of the system.

The time phase coding MDI-QKD protocol is characterized in that two sending ends Alice and Bob respectively prepare time phase quantum states and send the time phase quantum states to an untrusted third party measuring end Charlie to carry out Bell state measurement. For the scheme that two time modes are prepared by using independent unequal arm interferometers at two sending ends, the phase difference between the two time modes is related to the arm length difference of the long and short arms of the unequal arm interferometers and the environment where the unequal arm interferometers are positioned, so that relative drift of a phase reference system exists between time phase coding quantum states prepared by the two sending ends, a measurement result can be influenced, and a system can not generate a security key in severe cases. In addition, as the quantum states sent by the two sending ends are transmitted to the measuring end through different optical fiber channels, the polarization state of photons changes randomly along with the environment in the propagation process due to the double refraction effect of the optical fibers, so that the polarization states of photons are inconsistent when the photons reach the Charlie end for Bell state measurement, and the measurement result is also influenced.

To address the problem of Phase reference frame drift, one approach is to employ a passive approach, such as that described in literature Tang, g.z., et al, "Time-Bin Phase-Encoding Measurement-Device-Independent Quantum Key Distribution with Four Single-Photon detectors," Chinese Phys. Lett. 33,120301 (2016). The problem of drift is mitigated by placing the unequal arm interferometers in a thermally insulated, shock-proof box, but periodic variations in the measurement result still occur, resulting in unstable system performance. The document Tang, g.z. "Polarization discriminated time-bin phase-encoding measurement-device-independent quantum key distribution" Quantum Engineering (2021) adopts an active phase compensation scheme based on the previous one, and adjusts the phase difference between two time modes by adding a phase compensation unit to two transmitting ends respectively, but the scheme requires interrupting the quantum state transmission process to perform the phase compensation process, increasing the complexity of the system and reducing the effective key distribution ratio in unit time. The literature Tang, y.l., et al, "Measurement-device-independent quantum key distribution over, 200, km," Phys.rev. Lett 113, 190501 (2014), and literature Liu, h., et al, "Experimental demonstration of high-rate Measurement-device-independent quantum key distribution over asymmetric channels," phys.rev. Lett 122,160501 (2018) uses a real-time phase reference system calibration scheme to connect the interferometers at the two transmit ends through additional fiber optic channels, and uses an additional laser of the same wavelength as the quantum light pulses to inject light pulses into one of the unequal arm interferometers, with the intensity of the light emitted by the other end interferometer as a reference, to adjust the phase shifter on one arm of the interferometer to achieve correction of the phase reference system. However, this approach requires additional lasers and separate fibre channel resources, increasing the complexity of the system and the cost of field deployment. For the problem of polarization drift, the conventional solution is to calibrate the polarization reference system in real time by adopting an active polarization compensation module, and generally, after each path of optical signal is polarized and split by using one polarization beam splitter at the measurement end, one of the split components is detected as a feedback control signal of a polarization controller to calibrate the polarization reference system in real time, so that two additional single photon detectors are required, and the cost and complexity of the system are increased.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a measuring equipment independent quantum key distribution system with a reference system calibrated in real time.

The technical scheme of the invention is realized as follows:

a measuring equipment independent quantum key distribution system for real-time calibration of a reference system comprises a first transmitting end, a second transmitting end and a measuring end; the first transmitting end comprises a first laser, a first beam splitter, a second beam splitter, a first time phase encoding module, a first polarization beam splitter and a first adjustable attenuator;

the first laser is connected with an input port of the first beam splitter; the two output ports of the first beam splitter are respectively connected with the two input ports of the second beam splitter to form a first unequal arm interferometer; the input port and the output port of the first time phase encoding module are respectively connected with one output port of the second beam splitter and one input port of the first polarization beam splitter; the other output port of the second beam splitter is connected with the other input port of the first polarization beam splitter; the output port of the first polarization beam splitter is connected with the input port of the first adjustable attenuator;

The second transmitting end comprises a second laser, a first optical fiber isolator, a first single photon detector, a third beam splitter, a fourth beam splitter, a phase shifter, a second time phase encoding module, a second adjustable attenuator, a second optical fiber isolator, a third optical fiber isolator and a second polarization beam splitter;

the second laser is connected with one input port of the third beam splitter through the first optical fiber isolator; the first single photon detector is connected with the other input port of the third beam splitter; the two output ports of the third beam splitter are respectively connected with the two input ports of the fourth beam splitter to form a second unequal arm interferometer; the phase shifter is positioned on a long arm of the second unequal arm interferometer; an output port of the fourth beam splitter is sequentially connected with the second time phase encoding module, the second adjustable attenuator and the second optical fiber isolator and then connected with an input port of the second polarization beam splitter; the other output port of the fourth beam splitter is connected with the other input port of the second polarization beam splitter through a third optical fiber isolator;

the measuring end comprises a first electric control polarization controller, a second electric control polarization controller, a polarization beam splitting and transmitting module, a second single photon detector, a fifth beam splitter, a third single photon detector and a fourth single photon detector;

The input port of the first electric control polarization controller and the input port of the second electric control polarization controller are correspondingly connected with the output port of the first adjustable attenuator and the output port of the second polarization beam splitter through optical fiber channels respectively; the output port of the first electric control polarization controller and the output port of the second electric control polarization controller are respectively and correspondingly connected with the first port and the third port of the polarization beam splitting and transmission module; the second port of the polarization beam splitting and transmission module is connected with a second single photon detector; the fourth port and the fifth port of the polarization beam splitting and transmission module are respectively connected with two input ports of a fifth beam splitter; and two output ports of the fifth beam splitter are respectively connected with a third single photon detector and a fourth single photon detector.

Preferably, the polarization beam splitting and transmitting module comprises a third polarization beam splitter, a first circulator and a fourth polarization beam splitter, wherein an input port of the third polarization beam splitter and an input port of the fourth polarization beam splitter are respectively used as a first port and a third port of the polarization beam splitting and transmitting module; one output port of the third polarization beam splitter and one output port of the fourth polarization beam splitter are respectively and correspondingly connected with a first port and a second port of the first circulator; the third port of the first circulator, the other output port of the third polarization beam splitter and the other output port of the fourth polarization beam splitter are respectively used as a second port, a fifth port and a fourth port of the polarization beam splitting and transmitting module.

Preferably, the polarization beam splitting and transmitting module comprises a third polarization beam splitter, a first circulator and a fourth polarization beam splitter, wherein the first port, the third port and the input port of the fourth polarization beam splitter are respectively used as the first port, the second port and the third port of the polarization beam splitting and transmitting module; the second port of the first circulator is connected with the input port of the third polarization beam splitter; an output port of the third polarization beam splitter is connected with an output port of the fourth polarization beam splitter; the other output port of the third polarization beam splitter and the other output port of the fourth polarization beam splitter are respectively used as a fifth port and a fourth port of the polarization beam splitting and transmitting module.

Preferably, the polarization beam splitting and transmitting module comprises a first circulator and a fifth polarization beam splitter, wherein a first port, a third port and a second port of the fifth polarization beam splitter are respectively used as a first port, a second port and a third port of the polarization beam splitting and transmitting module; the second port of the first circulator is connected with the first port of the fifth polarization beam splitter; the third port and the fourth port of the fifth polarization beam splitter are respectively used as a fourth port and a fifth port of the polarization beam splitting and transmitting module; and the polarization maintaining optical fibers of the second port and the third port of the fifth polarization beam splitter are respectively welded at 90 degrees.

Preferably, the first time phase encoding module comprises a first intensity modulator and a first phase modulator, wherein two ends of the first intensity modulator are respectively connected with one output port of the second beam splitter and one end of the first phase modulator; the other end of the first phase modulator is connected with one input port of the first polarization beam splitter;

the second time phase encoding module comprises a second intensity modulator and a second phase modulator, and two ends of the second intensity modulator are respectively connected with one output port of the fourth beam splitter and one end of the second phase modulator; the other end of the second phase modulator is connected with a second adjustable attenuator.

Preferably, the first time phase encoding module comprises a second circulator, a third phase modulator and a first faraday mirror, wherein a first port and a third port of the second circulator are respectively connected with one output port of the second beam splitter and one input port of the first polarization beam splitter; the second port of the second circulator is connected with one end of the third phase modulator through 45-degree fusion welding of the polarization maintaining fiber; the other end of the third phase modulator is connected with a first Faraday mirror;

the second time phase encoding module comprises a third circulator, a fourth phase modulator and a second Faraday mirror, wherein a first port and a third port of the third circulator are respectively connected with one output port of a fourth beam splitter and a second adjustable attenuator; the second port of the third circulator is connected with one end of the fourth phase modulator through 45-degree fusion welding of the polarization maintaining fiber; the other end of the fourth phase modulator is connected with a second Faraday mirror.

Preferably, the first time phase encoding module comprises a second circulator, a sixth polarization beam splitter and a fifth phase modulator, wherein a first port and a third port of the second circulator are respectively connected with one output port of the second beam splitter and one input port of the first polarization beam splitter; the second port of the second circulator is connected with the input port of the sixth polarization beam splitter through 45-degree fusion welding of the polarization maintaining fiber; two output ports of the sixth polarization beam splitter are respectively connected with two ends of the fifth phase modulator;

the second time phase encoding module comprises a third circulator, a seventh polarization beam splitter and a sixth phase modulator, wherein a first port and a third port of the third circulator are respectively connected with one output port of a fourth beam splitter and a second adjustable attenuator; the second port of the third circulator is connected with the input port of the seventh polarization beam splitter through 45-degree fusion welding of the polarization maintaining fiber; and two output ports of the seventh polarization beam splitter are respectively connected with two ends of the sixth phase modulator.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a measuring equipment independent quantum key distribution system with real-time compensation of a reference system, which is characterized in that two paths of optical signals generated by an unequal arm interferometer of one transmitting end are subjected to time and polarization multiplexing, one path of the optical signals is subjected to time phase coding modulation, the other path of the optical signals is used as a prepared quantum state, phase reference system information is carried by the other path of the optical signals to reach the unequal arm interferometer of the other transmitting end through the measuring end to interfere, the phase reference system is calibrated according to the light intensity output by measuring interference, a laser and an independent optical fiber channel are not required to be additionally added, and the quantum key transmission process is not required to be interrupted, so that the real-time calibration can be performed. In addition, only one single photon detector is additionally arranged at the measuring end for real-time polarization feedback control of one path of optical signals, and the single photon detector for performing Bell state measurement can be used for real-time polarization feedback control of the other path of optical signals in a time division multiplexing mode. Therefore, the complexity of the system can be reduced, and the stability and the practicability of the system are improved.

Drawings

FIG. 1 is a schematic diagram of a measuring device independent quantum key distribution system with reference frame real-time compensation according to the present invention;

FIG. 2 is a schematic diagram of a first embodiment of a measurement device independent quantum key distribution system for real-time reference frame compensation in accordance with the present invention;

FIG. 3 is a schematic diagram of a second embodiment of a measurement device independent quantum key distribution system for real-time reference frame compensation in accordance with the present invention;

fig. 4 is a schematic diagram of a third embodiment of a measurement device independent quantum key distribution system for real-time reference frame compensation in accordance with the present invention.

Detailed Description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown.

As shown in fig. 1, a measuring device independent quantum key distribution system with reference system real-time compensation comprises a first transmitting end 1, a second transmitting end 2 and a measuring end 3; the first transmitting end 1 comprises a first laser 1-1, a first beam splitter 1-2, a second beam splitter 1-3, a first time phase encoding module 1-4, a first polarization beam splitter 1-5 and a first adjustable attenuator 1-6;

the first laser 1-1 is connected with an input port of the first beam splitter 1-2; the two output ports of the first beam splitter 1-2 are respectively connected with the two input ports of the second beam splitter 1-3 to form a first unequal arm interferometer; the input port and the output port of the first time phase encoding module 1-4 are respectively connected with one output port of the second beam splitter 1-3 and one input port of the first polarization beam splitter 1-5; the other output port of the second beam splitter 1-3 is connected with the other input port of the first polarization beam splitter 1-5; the output port of the first polarization beam splitter 1-5 is connected with the input port of the first adjustable attenuator 1-6;

The second transmitting end 2 comprises a second laser 2-1, a first optical fiber isolator 2-2, a first single photon detector 2-3, a third beam splitter 2-4, a fourth beam splitter 2-5, a phase shifter 2-6, a second time phase encoding module 2-7, a second adjustable attenuator 2-8, a second optical fiber isolator 2-9, a third optical fiber isolator 2-10 and a second polarization beam splitter 2-11;

the second laser 2-1 is connected with one input port of the third beam splitter 2-4 through the first optical fiber isolator 2-2; the first single photon detector 2-3 is connected with the other input port of the third beam splitter 2-4; the two output ports of the third beam splitter 2-4 are respectively connected with the two input ports of the fourth beam splitter 2-5 to form a second unequal arm interferometer; the phase shifters 2-6 are located on the long arms of the second unequal arm interferometer; an output port of the fourth beam splitter 2-5 is sequentially connected with a second time phase encoding module 2-7, a second adjustable attenuator 2-8 and a second optical fiber isolator 2-9 and then connected with an input port of a second polarization beam splitter 2-11; the other output port of the fourth beam splitter 2-5 is connected with the other input port of the second polarization beam splitter 2-11 through a third optical fiber isolator 2-10;

The measuring end 3 comprises a first electric control polarization controller 3-1, a second electric control polarization controller 3-2, a polarization beam splitting and transmitting module 3-3, a second single photon detector 3-4, a fifth beam splitter 3-5, a third single photon detector 3-6 and a fourth single photon detector 3-7;

the input port of the first electric control polarization controller 3-1 and the input port of the second electric control polarization controller 3-2 are correspondingly connected with the output port of the first adjustable attenuator 1-6 and the output port of the second polarization beam splitter 2-11 through optical fiber channels respectively; the output port of the first electric control polarization controller 3-1 and the output port of the second electric control polarization controller 3-2 are respectively and correspondingly connected with a first port and a third port of the polarization beam splitting and transmitting module 3-3; the second port of the polarization beam splitting and transmission module 3-3 is connected with a second single photon detector 3-4; the fourth port and the fifth port of the polarization beam splitting and transmission module 3-3 are respectively connected with two input ports of the fifth beam splitter 3-5; the two output ports of the fifth beam splitter 3-5 are respectively connected with the third single photon detector 3-6 and the fourth single photon detector 3-7.

The specific working process is as follows:

at the first transmitting end 1, the first laser 1-1 generates a horizontally polarized light pulse, and after passing through a first unequal-arm interferometer formed by the first beam splitter 1-2 and the second beam splitter 1-3, two paths of first light signals and second light signals respectively emitted from two output ports of the second beam splitter 1-3 are generated. Wherein the first optical signal comprises a first sub-pulse and a second sub-pulse with a phase difference of

The time difference is the time difference corresponding to the arm length difference of the first unequal arm interferometer. The second optical signal comprises a third sub-pulse and a fourth sub-pulse with a phase difference of

The time difference is also the time difference corresponding to the arm length difference of the first unequal arm interferometer.

The first optical signal is subjected to time phase encoding by the first time phase encoding module 1-4, and 2 time states under the Z base and 2 phase states under the X base are randomly generated. Then, the second optical signal and the first optical signal enter two input ports of the first polarization beam splitter 1-5 respectively and exit from the output ports thereof in sequence, and the two optical signals are subjected to time and polarization multiplexing. The first optical signal is horizontally polarized, the second optical signal is vertically polarized, the first optical signal and the second optical signal are attenuated to a single photon level through the first adjustable attenuator 1-6, become a first quantum optical signal and a phase reference optical signal respectively, and finally are transmitted to a measuring end through an optical fiber channel.

At the second transmitting end 2, the second laser 2-1 generates a light pulse with horizontal polarization, and the light pulse enters a second unequal arm interferometer formed by a third beam splitter 2-4 and a fourth beam splitter 2-5 after passing through the first optical fiber isolator 2-2, so as to generate two paths of third light signals and fourth light signals which are respectively emitted from two output ports of the fourth beam splitter 2-5. Wherein the third optical signal comprises a fifth sub-pulse and a sixth sub-pulse with a phase difference of

The time difference is the time difference corresponding to the arm length difference of the second unequal arm interferometer, and the time difference corresponding to the arm length difference of the first unequal arm interferometer is equal. The fourth optical signal enters the third optical fiber isolator 2-10 to be isolated, and cannot enter the second polarization beam splitter 2-11, and is not considered later.

The third optical signal is subjected to time phase encoding by the second time phase encoding module 2-7, and 2 time states under the Z base and 2 phase states under the X base are randomly generated. Then, the third optical signal is attenuated to a single photon level by the second adjustable attenuator 2-8, becomes a second quantum optical signal, enters one input port of the second polarization beam splitter 2-11 after passing through the second optical fiber isolator 2-9, is horizontally polarized when exiting from an output port thereof, and finally is sent to a measuring end through an optical fiber channel.

At the measuring end 3, the phase reference optical signal and the first quantum optical signal sent by the first sending end 1 reach the first electric control polarization controller 3-1 in sequence to perform polarization compensation, and then enter the first port of the polarization beam splitting and transmitting module 3-3. The polarization beam splitting and transmitting module 3-3 performs polarization beam splitting on the phase reference optical signal and the first quantum optical signal, so that horizontal polarization components of the phase reference optical signal and the first quantum optical signal are emitted from a fifth port of the phase reference optical signal and the first quantum optical signal to enter an input port of the fifth beam splitter 3-5, and vertical polarization components are emitted from a third port of the phase reference optical signal and the first quantum optical signal to reversely enter the second electric control polarization controller 3-2. The horizontal polarization component of the phase reference optical signal passes through the fifth beam splitter 3-5 and then reaches the third single photon detector 3-6 and the fourth single photon detector 3-7 to be detected, the generated count is used as a feedback control signal of the first electric control polarization controller 3-1, the voltage of the first electric control polarization controller 3-1 is regulated through a feedback algorithm so that the sum of the counts of the third single photon detector 3-6 and the fourth single photon detector 3-7 is kept to be the lowest, the polarization state of the phase reference optical signal can be recovered, and the first quantum optical signal with the polarization state perpendicular to the polarization state can be recovered at the same time. The second quantum optical signal sent by the second sending end 2 is subjected to polarization compensation through the second electric control polarization controller 3-2, then enters a third port of the polarization beam splitting and transmitting module 3-3 and is polarized and split by the third port, and a horizontal polarization component of the second quantum optical signal exits from a fourth port of the polarization beam splitting and transmitting module 3-3 and reaches the other input port of the fifth beam splitter 3-5; the vertical polarization component of the second quantum optical signal exits from the second port of the polarization beam splitting and transmitting module 3-3, enters the second single photon detector 3-4 for detection, the generated count is used as a feedback control signal of the second electric control polarization controller 3-2, and the voltage of the second electric control polarization controller 3-2 is regulated through a feedback algorithm so that the count of the second single photon detector 3-4 is kept to be the lowest, and the polarization state of the second quantum optical signal can be recovered. Thus, the method is applicable to a variety of applications. The polarization is the same when the first quantum optical signal and the second quantum optical signal arrive at the fifth beam splitter 3-5 at the same time to interfere, and the condition that the polarization states are consistent is satisfied when the Bell state measurement is required.

The compensation effect of the second electric control polarization controller 3-2 restores the second quantum light signal with horizontal polarization to be in a random polarization state after passing through the optical fiber channel, so that the second quantum light signal still has horizontal polarization when exiting from the second electric control polarization controller 3-2, and the combined action of the optical fiber channel and the second electric control polarization controller 3-2 is used as a unit matrix. According to the reversibility of the optical path, the vertically polarized phase reference optical signal is emitted from the third port of the polarization beam splitting and transmitting module 3-3, and then reversely passes through the second electric control polarization controller 3-2 and the optical fiber channel, which is equivalent to passing through a unit matrix, and is still vertically polarized when reaching the second transmitting end 2. The phase reference light signal reaches the third optical fiber isolator 2-10 through the second polarizing beam splitter 2-11, is directly transmitted and reversely enters the second unequal arm interferometer, and after interference, the first single photon detector 2-3 is used for detecting part of interference results. The first fiber isolator 2-2 can isolate another part of the interference result from affecting the second laser 2-1. The phase reference optical signals carry the phase reference system information of the first unequal arm interferometers, and the voltage of the phase shifters 2-6 is regulated in real time according to the count of the first single photon detector 2-3, so that the phase reference systems of the two unequal arm interferometers can be kept consistent, the real-time calibration of the phase reference systems of the first quantum optical signals sent by the first sending end 1 and the second quantum optical signals sent by the second sending end 2 is realized, and the condition that the phase reference systems are consistent is required by Bell state measurement is met.

As shown in fig. 2, in a first embodiment of the present invention:

the structure of the measuring equipment independent quantum key distribution system with the reference system real-time compensation is as follows: the polarization beam splitting and transmitting module 3-3 comprises a third polarization beam splitter 3-3-1, a first circulator 3-3-2 and a fourth polarization beam splitter 3-3, wherein an input port of the third polarization beam splitter 3-3-1 and an input port of the fourth polarization beam splitter 3-3-3 are respectively used as a first port and a third port of the polarization beam splitting and transmitting module 3-3; one output port of the third polarization beam splitter 3-3-1 and one output port of the fourth polarization beam splitter 3-3-2 are respectively and correspondingly connected with a first port and a second port of the first circulator 3-3-2; the third port of the first circulator 3-3-2, the other output port of the third polarization beam splitter 3-3-1, and the other output port of the fourth polarization beam splitter 3-3 are respectively used as a second port, a fifth port, and a fourth port of the polarization beam splitting and transmitting module 3-3.

The first time phase encoding module 1-4 comprises a second circulator 1-4-3, a third phase modulator 1-4-4 and a first Faraday mirror 1-4-5, wherein a first port and a third port of the second circulator 1-4-3 are respectively connected with one output port of the second beam splitter 1-3 and one input port of the first polarization beam splitter 1-5; the second port of the second circulator 1-4-3 is connected with one end of the third phase modulator 1-4-4 through 45-degree fusion welding of a polarization maintaining fiber; the other end of the third phase modulator 1-4-4 is connected with a first Faraday mirror 1-4-5;

The second time phase encoding module 2-7 comprises a third circulator 2-7-3, a fourth phase modulator 2-7-4 and a second Faraday mirror 2-7-5, wherein a first port and a third port of the third circulator 2-7-3 are respectively connected with one output port of the fourth beam splitter 2-5 and a second adjustable attenuator 2-8; the second port of the third circulator 2-7-3 is connected with one end of the fourth phase modulator 2-7-4 through 45-degree fusion welding of a polarization maintaining fiber; the other end of the fourth phase modulator 2-7-4 is connected with a second Faraday mirror 2-7-5.

A specific working procedure of the embodiment is as follows:

The first optical signal modulates the intensities of the first sub-pulse and the second sub-pulse through the first intensity modulator 1-4-1, and then modulates the phase difference of the first sub-pulse and the second sub-pulse through the first phase modulator 1-4-2, so that 2 time states under Z base and 2 phase states under X base are randomly generated. Then, the second optical signal and the first optical signal enter two input ports of the first polarization beam splitter 1-5 respectively and exit from the output ports thereof in sequence, and the two optical signals are subjected to time and polarization multiplexing. The first optical signal is horizontally polarized, the second optical signal is vertically polarized, the first optical signal and the second optical signal are attenuated to a single photon level through the first adjustable attenuator 1-6, become a first quantum optical signal and a phase reference optical signal respectively, and finally are transmitted to a measuring end through an optical fiber channel.

The third optical signal modulates the intensities of the fifth sub-pulse and the sixth sub-pulse through the second intensity modulator 2-7-1, respectively, and then modulates the phase difference of the fifth sub-pulse and the sixth sub-pulse through the second phase modulator 2-7-2, randomly generating 2 time states under the Z base and 2 phase states under the X base. Then, the third optical signal is attenuated to a single photon level by the second adjustable attenuator 2-8, becomes a second quantum optical signal, enters one input port of the second polarization beam splitter 2-11 after passing through the second optical fiber isolator 2-9, is horizontally polarized when exiting from an output port thereof, and finally is sent to a measuring end through an optical fiber channel.

At the measuring end 3, the phase reference optical signal and the first quantum optical signal sent by the first sending end 1 sequentially reach the first electric control polarization controller 3-1 to perform polarization compensation, and then enter the input port of the third polarization beam splitter 3-3-1. The third polarization beam splitter 3-3-1 performs polarization beam splitting on the phase reference optical signal and the first quantum optical signal, so that horizontal polarization components of the phase reference optical signal and the first quantum optical signal are emitted from one output port of the third polarization beam splitter and enter one input port of the fifth beam splitter 3-5; the vertically polarized component exits from the other output port, enters the first port of the first circulator 3-2-1, exits from the second port, reaches the fourth polarization beam splitter 3-3, and finally exits from the input port of the fourth polarization beam splitter 3-3-3, and is still vertically polarized. The horizontal polarization component of the phase reference optical signal passes through the fifth beam splitter 3-5 and then reaches the third single photon detector 3-6 and the fourth single photon detector 3-7 to be detected, the generated count is used as a feedback control signal of the first electric control polarization controller 3-1, the voltage of the first electric control polarization controller 3-1 is regulated through a feedback algorithm so that the sum of the counts of the third single photon detector 3-6 and the fourth single photon detector 3-7 is kept to be the lowest, the polarization state of the phase reference optical signal can be recovered, and the first quantum optical signal with the polarization state perpendicular to the polarization state can be recovered at the same time. The second quantum optical signal sent by the second sending end 2 is subjected to polarization compensation through the second electric control polarization controller 3-2, then enters the input port of the fourth polarization beam splitter 3-3-2 and is polarized and split by the second electric control polarization controller, and the horizontal polarization component and the vertical polarization component of the second quantum optical signal are respectively emitted from the two output ports of the fourth polarization beam splitter 3-3-2. Wherein the vertically polarized component of the second quantum optical signal enters the other input port of the fifth beam splitter 3-5; the vertical polarization component enters the second port of the first circulator 3-3-2, and exits from the third port to enter the second single photon detector 3-4 for detection, the generated count is used as a feedback control signal of the second electric control polarization controller 3-2, and the voltage of the second electric control polarization controller 3-2 is regulated through a feedback algorithm so that the count of the second single photon detector 3-4 is kept to be the lowest, and the polarization state of the second quantum optical signal can be recovered. Thus, the method is applicable to a variety of applications. The polarization is the same when the first quantum optical signal and the second quantum optical signal arrive at the fifth beam splitter 3-5 at the same time to interfere, and the condition that the polarization states are consistent is satisfied when the Bell state measurement is required.

The compensation effect of the second electric control polarization controller 3-2 restores the second quantum light signal with horizontal polarization to be in a random polarization state after passing through the optical fiber channel, so that the second quantum light signal still has horizontal polarization when exiting from the second electric control polarization controller 3-2, and the combined action of the optical fiber channel and the second electric control polarization controller 3-2 is used as a unit matrix. According to the reversibility of the optical path, the vertically polarized phase reference optical signal is emitted from the input port of the fourth polarization beam splitter 3-3-3, and then reversely passes through the second electric control polarization controller 3-2 and the optical fiber channel, which is equivalent to passing through a unit matrix, and is still vertically polarized when reaching the second transmitting end 2. The phase reference light signal reaches the third optical fiber isolator 2-10 through the second polarizing beam splitter 2-11, is directly transmitted and reversely enters the second unequal arm interferometer, and after interference, the first single photon detector 2-3 is used for detecting part of interference results. The first fiber isolator 2-2 can isolate another part of the interference result from affecting the second laser 2-1. The phase reference optical signals carry the phase reference system information of the first unequal arm interferometers, and the voltage of the phase shifters 2-6 is regulated in real time according to the count of the first single photon detector 2-3, so that the phase reference systems of the two unequal arm interferometers can be kept consistent, the real-time calibration of the phase reference systems of the first quantum optical signals sent by the first sending end 1 and the second quantum optical signals sent by the second sending end 2 is realized, and the condition that the phase reference systems are consistent is required by Bell state measurement is met.

As shown in fig. 3, in a second embodiment of the present invention:

the structure of the measuring equipment independent quantum key distribution system with the reference system real-time compensation is as follows: the polarization beam splitting and transmitting module 3-3 comprises a third polarization beam splitter 3-3-1, a first circulator 3-3-2 and a fourth polarization beam splitter 3-3, wherein a first port, a third port and an input port of the first circulator 3-3-2 are respectively used as a first port, a second port and a third port of the polarization beam splitting and transmitting module 3-3; the second port of the first circulator 3-3-2 is connected with the input port of the third polarization beam splitter 3-3-1; an output port of the third polarization beam splitter 3-3-1 is connected with an output port of the fourth polarization beam splitter 3-3-3; the other output port of the third polarization beam splitter 3-3-1 and the other output port of the fourth polarization beam splitter 3-3-3 are respectively used as a fifth port and a fourth port of the polarization beam splitting and transmitting module 3-3.

The specific working procedure of the second embodiment is as follows:

The first optical signal is rotated by 45 degrees to be changed into 45 degrees of linear polarization after passing through the second circulator 1-4-3, then the first optical signal is modulated by the third phase modulator 1-4-4 in phase, reflected by the first Faraday mirror 1-4-5, and then modulated by the third phase modulator 1-4-4 again, and finally the first sub-pulse and the second sub-pulse can be respectively modulated into different polarization states after being rotated by 45 degrees of polarization. When the polarization states of the modulated first sub-pulse and the modulated second sub-pulse are respectively horizontal polarization H and vertical polarization V, the two polarization states are changed into a time state 0 after passing through the first polarization beam splitters 1-5; when the polarization states of the modulated first sub-pulse and the modulated second sub-pulse are V and H respectively, the first sub-pulse and the modulated second sub-pulse are changed into a time state 1 after passing through the first polarization beam splitters 1-5; when the polarization states of the first sub pulse and the second sub pulse are circularly polarized light and the phase difference is 0 or pi, the two polarization states are changed into phase states after passing through the first polarization beam splitters 1-5, namely, 2 time states under Z groups and 2 phase states under X groups can be randomly generated. The second optical signal and the first optical signal respectively enter two input ports of the first polarization beam splitter 1-5 and are emitted from the output ports thereof in sequence, and the two optical signals are subjected to time and polarization multiplexing. The first optical signal is horizontally polarized, the second optical signal is vertically polarized, the first optical signal and the second optical signal are attenuated to a single photon level through the first adjustable attenuator 1-6, become a first quantum optical signal and a phase reference optical signal respectively, and finally are transmitted to a measuring end through an optical fiber channel.

The third optical signal is rotated by 45 degrees to be changed into 45 degrees of linear polarization after passing through the third circulator 2-7-3, then the third optical signal is modulated by the fourth phase modulator 2-7-4 in phase, reflected by the second Faraday mirror 2-7-5, and then modulated by the fourth phase modulator 2-7-4 again, and finally the fifth sub-pulse and the sixth sub-pulse can be respectively modulated into different polarization states after being rotated by 45 degrees of polarization. Through a similar time phase encoding process as the first transmitting end 1, 2 time states under the Z-base and 2 phase states under the X-base can be randomly generated. Then, the third optical signal is attenuated to a single photon level by the second adjustable attenuator 2-8, becomes a second quantum optical signal, enters one input port of the second polarization beam splitter 2-11 after passing through the second optical fiber isolator 2-9, is horizontally polarized when exiting from an output port thereof, and finally is sent to a measuring end through an optical fiber channel.

At the measuring end 3, the phase reference optical signal and the first quantum optical signal sent by the first sending end 1 sequentially reach the first electric control polarization controller 3-1 to perform polarization compensation, then enter the first port of the first circulator 3-3-2, and reach the input port of the third polarization beam splitter 3-3-1 after exiting from the second port. The third polarization beam splitter 3-3-1 performs polarization beam splitting on the phase reference optical signal and the first quantum optical signal, so that horizontal polarization components of the phase reference optical signal and the first quantum optical signal are emitted from one output port of the third polarization beam splitter and enter one input port of the fifth beam splitter 3-5; the vertically polarized component exits from the other output port to the fourth polarization beam splitter 3-3-3 and finally exits from the input port of the fourth polarization beam splitter 3-3-3, still vertically polarized. The horizontal polarization component of the phase reference optical signal passes through the fifth beam splitter 3-5 and then reaches the third single photon detector 3-6 and the fourth single photon detector 3-7 to be detected, the generated count is used as a feedback control signal of the first electric control polarization controller 3-1, the voltage of the first electric control polarization controller 3-1 is regulated through a feedback algorithm so that the sum of the counts of the third single photon detector 3-6 and the fourth single photon detector 3-7 is kept to be the lowest, the polarization state of the phase reference optical signal can be recovered, and the first quantum optical signal with the polarization state perpendicular to the polarization state can be recovered at the same time. The second quantum optical signal sent by the second sending end 2 is subjected to polarization compensation through the second electric control polarization controller 3-2, then enters the input port of the fourth polarization beam splitter 3-3-2 and is polarized and split by the second electric control polarization controller, and the horizontal polarization component and the vertical polarization component of the second quantum optical signal are respectively emitted from the two output ports of the fourth polarization beam splitter 3-3-2. Wherein the horizontally polarized component of the second quantum optical signal enters the other input port of the fifth beam splitter 3-5; the vertical polarization component enters the second port of the first circulator 3-3-2 through the third polarization beam splitter 3-3-1, enters the second single photon detector 3-4 for detection after exiting from the third port, and the generated count is used as a feedback control signal of the second electric control polarization controller 3-2, and the voltage of the second electric control polarization controller 3-2 is regulated through a feedback algorithm so that the count of the second single photon detector 3-4 is kept to be the lowest, so that the polarization state of the second quantum optical signal can be recovered. Thus, the method is applicable to a variety of applications. The polarization is the same when the first quantum optical signal and the second quantum optical signal arrive at the fifth beam splitter 3-5 at the same time to interfere, and the condition that the polarization states are consistent is satisfied when the Bell state measurement is required.

After exiting from the input port of the fourth polarization beam splitter 3-3-3, the vertically polarized phase reference optical signal reversely passes through the second electric control polarization controller 3-2 and the optical fiber channel, which is equivalent to passing through a unit matrix, and is still vertically polarized when reaching the second transmitting end 2. The phase reference light signal reaches the third optical fiber isolator 2-10 through the second polarizing beam splitter 2-11, is directly transmitted and reversely enters the second unequal arm interferometer, and the interference result is detected by the first single photon detector 2-3 after interference. The phase reference optical signals carry the phase reference system information of the first unequal arm interferometers, and the voltage of the phase shifters 2-6 is regulated in real time according to the count of the first single photon detector 2-3, so that the phase reference systems of the two unequal arm interferometers can be kept consistent, the real-time calibration of the phase reference systems of the first quantum optical signals sent by the first sending end 1 and the second quantum optical signals sent by the second sending end 2 is realized, and the condition that the phase reference systems are consistent is required by Bell state measurement is met.

As shown in fig. 4, a third embodiment of the present invention:

The first time phase encoding module 1-4 comprises a second circulator 1-4-3, a sixth polarization beam splitter 1-4-6 and a fifth phase modulator 1-4-7, wherein a first port and a third port of the second circulator 1-4-3 are respectively connected with one output port of the second beam splitter 1-3 and one input port of the first polarization beam splitter 1-5; the second port of the second circulator 1-4-3 is connected with the input port of the sixth polarization beam splitter 1-4-6 through 45-degree fusion welding of the polarization maintaining fiber; two output ports of the sixth polarization beam splitter 1-4-6 are respectively connected with two ends of the fifth phase modulator 1-4-7;

the second time phase encoding module 2-7 comprises a third circulator 2-7-3, a seventh polarization beam splitter 2-7-6 and a sixth phase modulator 2-7-7, wherein a first port and a third port of the third circulator 2-7-3 are respectively connected with one output port of the fourth beam splitter 2-5 and a second adjustable attenuator 2-8; the second port of the third circulator 2-7-3 is connected with the input port of the seventh polarization beam splitter 2-7-6 through 45-degree fusion welding of the polarization maintaining optical fiber; the two output ports of the seventh polarization beam splitter 2-7-6 are respectively connected with the two ends of the sixth phase modulator 2-7-7.

The working procedure of the third embodiment is as follows:

At the first transmitting end 1, the first laser 1-1 generates light pulse with horizontal polarization, and after passing through the first unequal-arm interferometer formed by the first beam splitter 1-2 and the second beam splitter 1-3, two paths are generated to respectively emit from two output ports of the second beam splitter 1-3Is provided, and a second optical signal. Wherein the first optical signal comprises a first sub-pulse and a second sub-pulse with a phase difference of

The first optical signal is rotated by 45 degrees to be changed into 45 degrees of linear polarization after passing through the second circulator 1-4-3, then enters the sixth polarization beam splitter 1-4-6 to carry out polarization beam splitting, generates horizontal polarization components and vertical polarization components which respectively pass through the fifth phase modulator 1-4-7 in the forward direction and the reverse direction to modulate different phases, returns to the sixth polarization beam splitter 1-4-6 to carry out polarization beam combination and then is emitted, and finally the first sub-pulse and the second sub-pulse can respectively modulate different polarization states after being rotated by 45 degrees of polarization. When the polarization states of the modulated first sub-pulse and the modulated second sub-pulse are respectively horizontal polarization H and vertical polarization V, the two polarization states are changed into a time state 0 after passing through the first polarization beam splitters 1-5; when the polarization states of the modulated first sub-pulse and the modulated second sub-pulse are V and H respectively, the first sub-pulse and the modulated second sub-pulse are changed into a time state 1 after passing through the first polarization beam splitters 1-5; when the polarization states of the first sub pulse and the second sub pulse are circularly polarized light and the phase difference is 0 or pi, the two polarization states are changed into phase states after passing through the first polarization beam splitters 1-5, namely, 2 time states under Z groups and 2 phase states under X groups can be randomly generated. The second optical signal and the first optical signal respectively enter two input ports of the first polarization beam splitter 1-5 and are emitted from the output ports thereof in sequence, and the two optical signals are subjected to time and polarization multiplexing. The first optical signal is horizontally polarized, the second optical signal is vertically polarized, the first optical signal and the second optical signal are attenuated to a single photon level through the first adjustable attenuator 1-6, become a first quantum optical signal and a phase reference optical signal respectively, and finally are transmitted to a measuring end through an optical fiber channel.

At the second transmissionThe end 2, the second laser 2-1 produces the horizontal polarized light pulse, enter the second unequal arm interferometer formed by the third beam splitter 2-4 and the fourth beam splitter 2-5 after passing through the first optical fiber isolator 2-2, produce the third optical signal and the fourth optical signal that two ways are outgoing from two output ports of the fourth beam splitter 2-5 respectively. Wherein the third optical signal comprises a fifth sub-pulse and a sixth sub-pulse with a phase difference of

The third optical signal is rotated by 45 degrees to be changed into 45 degrees of linear polarization after passing through the third circulator 2-7-3, then enters the seventh polarization beam splitter 2-7-6 to carry out polarization beam splitting, generates horizontal polarization components and vertical polarization components which respectively pass through the sixth phase modulator 2-7-7 in the forward direction and the reverse direction to modulate different phases, returns to the seventh polarization beam splitter 2-7-6 to carry out polarization beam combination and then is emitted, and finally the fifth sub-pulse and the sixth sub-pulse can respectively modulate different polarization states after being rotated by 45 degrees of polarization. Through a similar time phase encoding process as the first transmitting end 1, 2 time states under the Z-base and 2 phase states under the X-base can be randomly generated. Then, the third optical signal is attenuated to a single photon level by the second adjustable attenuator 2-8, becomes a second quantum optical signal, enters one input port of the second polarization beam splitter 2-11 after passing through the second optical fiber isolator 2-9, is horizontally polarized when exiting from an output port thereof, and finally is sent to a measuring end through an optical fiber channel.

At the measuring end 3, the phase reference optical signal and the first quantum optical signal sent by the first sending end 1 sequentially reach the first electric control polarization controller 3-1 to perform polarization compensation, then enter the first port of the first circulator 3-3-2, and reach the first port of the fifth polarization beam splitter 3-3-4 after exiting from the second port. The fifth polarization beam splitter 3-3-4 performs polarization beam splitting on the phase reference optical signal and the first quantum optical signal, so that horizontal polarization components of the phase reference optical signal and the first quantum optical signal are emitted from a fourth port of the fifth polarization beam splitter and enter an input port of the fifth polarization beam splitter 3-5; the vertically polarized component exits from its second port and is still vertically polarized after 90 polarization rotation. The horizontal polarization component of the phase reference optical signal passes through the fifth beam splitter 3-5 and then reaches the third single photon detector 3-6 and the fourth single photon detector 3-7 to be detected, the generated count is used as a feedback control signal of the first electric control polarization controller 3-1, the voltage of the first electric control polarization controller 3-1 is regulated through a feedback algorithm so that the sum of the counts of the third single photon detector 3-6 and the fourth single photon detector 3-7 is kept to be the lowest, the polarization state of the phase reference optical signal can be recovered, and the first quantum optical signal with the polarization state perpendicular to the polarization state can be recovered at the same time. The second quantum optical signal sent by the second sending end 2 is subjected to polarization compensation through a second electric control polarization controller 3-2, polarization is rotated by 90 degrees, enters a second port of a fifth polarization beam splitter 3-3-4 and is split by polarization, and vertical components are emitted from a third port of the fifth polarization beam splitter 3-3-4, are converted into horizontal polarization through 90-degree polarization rotation and enter the other input port of the fifth polarization beam splitter 3-5; the horizontal polarization component exits from the first port of the fifth polarization beam splitter 3-3-4, enters the second port of the first circulator 3-3-2, enters the second single photon detector 3-4 for detection after exiting from the third port, and the generated count is used as a feedback control signal of the second electric control polarization controller 3-2, and the voltage of the second electric control polarization controller 3-2 is regulated through a feedback algorithm so that the count of the second single photon detector 3-4 is kept to be the lowest, so that the polarization state of the second quantum optical signal can be recovered. Thus, the method is applicable to a variety of applications. The polarization is the same when the first quantum optical signal and the second quantum optical signal arrive at the fifth beam splitter 3-5 at the same time to interfere, and the condition that the polarization states are consistent is satisfied when the Bell state measurement is required.

The vertically polarized phase reference optical signal passes reversely through the second electrically controlled polarization controller 3-2 and the optical fiber channel, which is equivalent to passing through an identity matrix, and is still vertically polarized when reaching the second transmitting end 2. The phase reference light signal reaches the third optical fiber isolator 2-10 through the second polarizing beam splitter 2-11, is directly transmitted and reversely enters the second unequal arm interferometer, and the interference result is detected by the first single photon detector 2-3 after interference. The phase reference optical signals carry the phase reference system information of the first unequal arm interferometers, and the voltage of the phase shifters 2-6 is regulated in real time according to the count of the first single photon detector 2-3, so that the phase reference systems of the two unequal arm interferometers can be kept consistent, the real-time calibration of the phase reference systems of the first quantum optical signals sent by the first sending end 1 and the second quantum optical signals sent by the second sending end 2 is realized, and the condition that the phase reference systems are consistent is required by Bell state measurement is met.

As can be seen from the comprehensive embodiments of the present invention, the present invention provides a reference frame real-time compensation measurement device independent quantum key distribution system, which multiplexes two paths of optical signals generated by different-arm interferometers at one transmitting end with time and polarization, one path of the optical signals is modulated by time phase coding, and the other path of the optical signals is used as a prepared quantum state, and carries phase reference frame information to reach the different-arm interferometers at the other transmitting end through the measuring end to interfere, and performs phase reference frame calibration according to the light intensity output by measuring interference, without adding additional lasers and separate optical fiber channels, and without interrupting the quantum key transmission process, so that real-time calibration can be performed. In addition, only one single photon detector is additionally arranged at the measuring end for real-time polarization feedback control of one path of optical signals, and the single photon detector for performing Bell state measurement can be used for real-time polarization feedback control of the other path of optical signals in a time division multiplexing mode. Therefore, the complexity of the system can be reduced, and the stability and the practicability of the system are improved.

Claims

1. The measuring equipment independent quantum key distribution system for real-time calibration of the reference system is characterized by comprising a first transmitting end (1), a second transmitting end (2) and a measuring end (3); the first transmitting end (1) comprises a first laser (1-1), a first beam splitter (1-2), a second beam splitter (1-3), a first time phase encoding module (1-4), a first polarization beam splitter (1-5) and a first adjustable attenuator (1-6);

the first laser (1-1) is connected with an input port of the first beam splitter (1-2); the two output ports of the first beam splitter (1-2) are respectively connected with the two input ports of the second beam splitter (1-3) to form a first unequal arm interferometer; the input port and the output port of the first time phase encoding module (1-4) are respectively connected with one output port of the second beam splitter (1-3) and one input port of the first polarization beam splitter (1-5); the other output port of the second beam splitter (1-3) is connected with the other input port of the first polarization beam splitter (1-5); the output port of the first polarization beam splitter (1-5) is connected with the input port of the first adjustable attenuator (1-6);

The second transmitting end (2) comprises a second laser (2-1), a first optical fiber isolator (2-2), a first single photon detector (2-3), a third beam splitter (2-4), a fourth beam splitter (2-5), a phase shifter (2-6), a second time phase encoding module (2-7), a second adjustable attenuator (2-8), a second optical fiber isolator (2-9), a third optical fiber isolator (2-10) and a second polarization beam splitter (2-11);

the second laser (2-1) is connected with one input port of the third beam splitter (2-4) through the first optical fiber isolator (2-2); the first single photon detector (2-3) is connected with one output port of the third beam splitter (2-4); the other two output ports of the third beam splitter (2-4) are respectively connected with the two input ports of the fourth beam splitter (2-5) to form a second unequal arm interferometer; the phase shifters (2-6) are positioned on the long arms of the second unequal arm interferometer; an output port of the fourth beam splitter (2-5) is sequentially connected with a second time phase encoding module (2-7), a second adjustable attenuator (2-8) and a second optical fiber isolator (2-9) and then connected with an input port of a second polarization beam splitter (2-11); the other input port of the fourth beam splitter (2-5) is connected with one output port of the second polarization beam splitter (2-11) through a third optical fiber isolator (2-10);

The measuring end (3) comprises a first electric control polarization controller (3-1), a second electric control polarization controller (3-2), a polarization beam splitting and transmitting module (3-3), a second single photon detector (3-4), a fifth beam splitter (3-5), a third single photon detector (3-6) and a fourth single photon detector (3-7);

the input port of the first electric control polarization controller (3-1) and the input port of the second electric control polarization controller (3-2) are correspondingly connected with the output port of the first adjustable attenuator (1-6) and the output port of the second polarization beam splitter (2-11) through optical fiber channels respectively; the output port of the first electric control polarization controller (3-1) and the output port of the second electric control polarization controller (3-2) are respectively and correspondingly connected with a first port and a third port of the polarization beam splitting and transmission module (3-3); the second port of the polarization beam splitting and transmission module (3-3) is connected with a second single photon detector (3-4); the fourth port and the fifth port of the polarization beam splitting and transmission module (3-3) are respectively connected with two input ports of the fifth beam splitter (3-5); two output ports of the fifth beam splitter (3-5) are respectively connected with the third single photon detector (3-6) and the fourth single photon detector (3-7).

2. The measurement device independent quantum key distribution system of real-time calibration of a reference frame according to claim 1, wherein the polarization beam splitting and transmission module (3-3) comprises a third polarization beam splitter (3-3-1), a first circulator (3-3-2) and a fourth polarization beam splitter (3-3), an input port of the third polarization beam splitter (3-3-1) and an input port of the fourth polarization beam splitter (3-3-3) are respectively used as a first port and a third port of the polarization beam splitting and transmission module (3-3); one output port of the third polarization beam splitter (3-3-1) and one output port of the fourth polarization beam splitter (3-3-3) are respectively and correspondingly connected with a first port and a second port of the first circulator (3-3-2); the third port of the first circulator (3-3-2), the other output port of the third polarization beam splitter (3-3-1) and the other output port of the fourth polarization beam splitter (3-3) are respectively used as a second port, a fifth port and a fourth port of the polarization beam splitting and transmitting module (3-3).

3. The measurement device independent quantum key distribution system of real-time calibration of a reference frame according to claim 1, wherein the polarization beam splitting and transmission module (3-3) comprises a third polarization beam splitter (3-3-1), a first circulator (3-3-2) and a fourth polarization beam splitter (3-3-3), the first port, the third port of the first circulator (3-3-2) and the input port of the fourth polarization beam splitter (3-3-3) being the first port, the second port and the third port of the polarization beam splitting and transmission module (3-3), respectively; the second port of the first circulator (3-3-2) is connected with the input port of the third polarization beam splitter (3-3-1); an output port of the third polarization beam splitter (3-3-1) is connected with an output port of the fourth polarization beam splitter (3-3-3); the other output port of the third polarization beam splitter (3-3-1) and the other output port of the fourth polarization beam splitter (3-3-3) are respectively used as a fifth port and a fourth port of the polarization beam splitting and transmitting module (3-3).

4. The measurement device independent quantum key distribution system calibrated in real time of reference frame according to claim 1, wherein the polarization beam splitting and transmitting module (3-3) comprises a first circulator (3-3-2) and a fifth polarization beam splitter (3-3-4), the first port, the third port of the first circulator (3-3-2) and the second port of the fifth polarization beam splitter (3-3-4) being respectively the first port, the second port and the third port of the polarization beam splitting and transmitting module (3-3); the second port of the first circulator (3-3-2) is connected with the first port of the fifth polarization beam splitter (3-3-4); the third port and the fourth port of the fifth polarization beam splitter (3-3-4) are respectively used as a fourth port and a fifth port of the polarization beam splitting and transmitting module (3-3); and the polarization maintaining optical fibers of the second port and the third port of the fifth polarization beam splitter (3-3-4) are respectively welded at 90 degrees.

5. Measuring device independent quantum key distribution system calibrated in real time with reference system according to claim 1 or 2 or 3 or 4, characterized in that the first time phase encoding module (1-4) comprises a first intensity modulator (1-4-1) and a first phase modulator (1-4-2), the two ends of the first intensity modulator (1-4-1) being connected to one output port of the second beam splitter (1-3), one end of the first phase modulator (1-4-2), respectively; the other end of the first phase modulator (1-4-2) is connected with one input port of the first polarization beam splitter (1-5);

The second time phase encoding module (2-7) comprises a second intensity modulator (2-7-1) and a second phase modulator (2-7-2), and two ends of the second intensity modulator (2-7-1) are respectively connected with one output port of the fourth beam splitter (2-5) and one end of the second phase modulator (2-7-2); the other end of the second phase modulator (2-7-2) is connected with a second adjustable attenuator (2-8).

6. The measurement device independent quantum key distribution system of real time calibration of a reference frame according to claim 1 or 2 or 3 or 4, wherein the first time phase encoding module (1-4) comprises a second circulator (1-4-3), a third phase modulator (1-4-4) and a first faraday mirror (1-4-5), the first port, the third port of the second circulator (1-4-3) being connected to one output port of the second beam splitter (1-3), one input port of the first polarizing beam splitter (1-5), respectively; the second port of the second circulator (1-4-3) is connected with one end of the third phase modulator (1-4-4) through 45-degree welding of the polarization maintaining fiber; the other end of the third phase modulator (1-4-4) is connected with a first Faraday mirror (1-4-5);

the second time phase encoding module (2-7) comprises a third circulator (2-7-3), a fourth phase modulator (2-7-4) and a second Faraday mirror (2-7-5), wherein a first port and a third port of the third circulator (2-7-3) are respectively connected with one output port of the fourth beam splitter (2-5) and a second adjustable attenuator (2-8); the second port of the third circulator (2-7-3) is connected with one end of the fourth phase modulator (2-7-4) through 45-degree welding of a polarization maintaining fiber; the other end of the fourth phase modulator (2-7-4) is connected with a second Faraday mirror (2-7-5).

7. The measurement device independent quantum key distribution system of real time calibration of a reference frame according to claim 1 or 2 or 3 or 4, wherein the first time phase encoding module (1-4) comprises a second circulator (1-4-3), a sixth polarizing beam splitter (1-4-6) and a fifth phase modulator (1-4-7), the first port and the third port of the second circulator (1-4-3) being connected to one output port of the second beam splitter (1-3) and one input port of the first polarizing beam splitter (1-5), respectively; the second port of the second circulator (1-4-3) is connected with the input port of the sixth polarization beam splitter (1-4-6) through 45-degree welding of the polarization maintaining fiber; two output ports of the sixth polarization beam splitter (1-4-6) are respectively connected with two ends of the fifth phase modulator (1-4-7);

the second time phase encoding module (2-7) comprises a third circulator (2-7-3), a seventh polarization beam splitter (2-7-6) and a sixth phase modulator (2-7-7), wherein a first port and a third port of the third circulator (2-7-3) are respectively connected with one output port of a fourth beam splitter (2-5) and a second adjustable attenuator (2-8); the second port of the third circulator (2-7-3) is connected with the input port of the seventh polarization beam splitter (2-7-6) through 45-degree welding of the polarization maintaining fiber; two output ports of the seventh polarization beam splitter (2-7-6) are respectively connected with two ends of the sixth phase modulator (2-7-7).