CN109586799B - Polarization feedback method and device for polarization coding measurement equipment independent system - Google Patents
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Abstract
The invention discloses a polarization feedback method and a device for a polarization coding measurement device independent system. The polarization feedback method is used for automatically calibrating an Alice end, a Bob end and a Charlie end of the system to ensure that the three ends simultaneously meet the base mismatch consistency, and comprises the following steps of: adjusting step one, namely adjusting the mismatch of an Alice terminal and a Charlie terminal: two paths behind the Charlie end optical beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors; and step two, adjusting the base loss of the Bob end by using the calibrated H/V base and P/N base loss measurement end of the Charlie end, so that the H/V base and P/N base loss of the Bob end are consistent with the corresponding base loss of the Charlie end. The three ends of the system are automatically calibrated, meanwhile, the base mismatch consistency is met, and the problem that high error rate is easily caused by unmatched three-end base vectors of MDIQKD is solved.
Description
Technical Field
The invention relates to a polarization feedback method of a quantum encryption communication technology system, in particular to a polarization feedback method of a polarization coding Measurement equipment independent (Measurement-device-independentquantumkeydistribution, MDIQKD) system.
Background
In the polarization coding MDIQKD system, both the Alice end and the Bob end are used as transmitting ends, and the Charlie end is used as a receiving end. The Alice end and the Bob end respectively and independently prepare 4 polarization states, such as H, V, P, N states, according to a polarization coding scheme. The Charlie terminal performs bell state measurement on the polarization states sent by the Alice terminal and the Bob terminal to obtain bell states, such asAnd/>In order to accurately measure the Bell state to reduce the bit error rate, it is required that Alice end and Bob end must share the same polarization reference system. The purpose of polarization feedback is then to have Alice, bob and Charlie ends share the same polarization reference system.
Polarization feedback for current polarization encoding MDIQKD systems, one way is to manually adjust the polarization state: performing QKD manual adjustment calibrates H, V, P, N contributions at both Alice and Bob ends to be consistent. Another approach to semi-automatic adjustment is shown schematically in reference 1"ExperimentalDemonstrationofPolarizationEncodingMeasurement-Device-IndependentQuantumKeyDistribution",, particularly in the device of fig. 1-MDIQKD.
In fig. 1, the region (a) is a schematic diagram of Alice and Bob outputting polarization encoded weak coherent pulses (with decoy states) to Charlie. After being received by the Charlie end, the Bell state measurement is carried out by utilizing a light Beam Splitter (BS), a polarized light beam splitter (PBS) and a single photon detector. Region (b) is a schematic diagram of a polarization controller (i.e., triaxial fiber optic extruder fibersqueezers of region (a) in fig. 1). Region (c) is a schematic diagram geometrically representing Alice-end and Bob-end reference frame calibrations on a bond ball. . This is accomplished by manual Polarization Controller (PC) co-tuning with an Electric Polarization Controller (EPC). Region (b) in fig. 1 is a schematic diagram of an Electric Polarization Controller (EPC) comprising three fiber squeezers (controlled by piezoelectric actuators) each adjusted by 0 °,45 °,0 °.
First, alice and Bob ends align their right-angle basis vector (H/V basis vector) polarization states (H and V states) with the polarization axis of the Charlie end Polarizing Beam Splitter (PBS) at the Charlie end. This can be achieved by letting Alice and Bob send H-polarization pulses and adjusting the manual PC to minimize the detection contrast (measured by a single photon detector) at the two respective outputs of the PBS. At this point they have the same rectangular basis vector as shown in region (c) of fig. 1, on a bungjia sphere, where Alice sends H and V states that are the same polarization state as Bob sends H and V states when they reach the Charlie end, and are aligned with the polarization axis of the Polarization Beam Splitter (PBS) at the Charlie end. This allows the H/V basis vector adjustment at Alice and Bob ends to be consistent. The polarization axis of the Polarization Beam Splitter (PBS) at the Charlie end is also the polarization axis of the H/V basis vector.
Then, alice and Bob ends align their polarization states (P and N states) of the diagonal basis vectors (P/N basis vectors) at the Charlie end. It should be noted that the above alignment of the right angle basis vectors (H/V basis vectors) also requires aligning the H polarization state at Alice end with the fast or slow axis of the first (from left) fiber squeezer placed in the Electric Polarization Controller (EPC) in region (b) of fig. 1 at Alice end. On this basis, a voltage is applied to the first extruder such that there is a relative phase change between the slow and fast axes. As shown in region (c) of FIG. 1, this is equivalent to the Alice end performing an orthogonal transformation U on the Ponga sphere to become the P/N basis vectorThe voltage is adjusted until the diagonal basis vectors at Alice and Bob are aligned (english text "theveltageis usabedsuchthatherculegarbarasesaleigned"). After calibration, the voltage of the first extruder is set back to the state of Alice's calibration rectangular vector, so this operation does not affect the rectangular vector calibrated before Alice's end.
In addition, in the standard BB84 system different from MDIQKD system, alice end is used as the transmitting end, and Bob end is used as the receiving end. The purpose of polarization feedback is to make Alice end and Bob end share the same polarization reference system. A typical polarization feedback system is shown in fig. 2 below, and mainly comprises a beam splitter BS, two-way polarization controllers, two polarization beam splitters, and 4 single photon detectors. The receiving end adopts passive basis vector selection, and the detectors of the H/V basis vector and the P/N basis vector are positioned in separate light paths behind the beam splitter, so that the independent polarization feedback schemes of the H/V basis vector and the P/N basis vector can be adopted simply. For example, the polarization feedback of the H/V basis vector is performed first, and then the polarization feedback of the P/N basis vector is performed. For H/V polarization feedback, the Alice end sends H polarized light, and the receiving end determines the feedback compensation amount according to the contrast level of the H path count and the V path count and controls the EPC of the H/V path. And when the contrast ratio of the final polarization feedback meets the requirement, locking the voltage point to finish the polarization feedback.
Problems with the prior art described above:
1) The polarization encoding MDIQKD system does not realize automatic polarization feedback, and if the error rate exceeds a threshold value in the operation of the system, manual adjustment and calibration are needed, which is not beneficial to the automatic processing of the system and the industrialization. In addition, the manual adjustment has low accuracy, and the relatively accurate three-terminal polarization calibration can not be carried out on the Alice terminal, the Bob terminal and the Charlie terminal. If the calibration cannot be accurately performed, the bit rate is affected to a certain extent.
2) The electronically controlled polarization controller used in reference 1 (fibersqueezers in region (a) in fig. 1, or region (b) in fig. 1) requires that Alice and Charlie be aligned with the right-angle basis vector (H/V basis vector) while simultaneously aligning the polarization state H-state with the fast or slow axis of the first (from left) fiber optic extruder in the electronic polarization controller in fig. 1 (b). The subsequent operation can be completed depending on the condition, so that the calibration puts higher requirements on the electric control polarization controller and the operation mode of the device is troublesome.
3) Reference 1 does not explain further "theoltageis adjust schalt the ir circle barese aligned" in aligning the diagonal basis vectors (P/N basis vectors) of Alice terminal and Bob terminal until the diagonal basis vectors of Alice terminal are aligned with the diagonal basis vectors of Bob terminal ". The means for detecting whether the diagonal basis vectors are aligned and what the detected signal is are not cross-bred. In conventional methods, detection of the polarization state typically requires a PBS that utilizes a corresponding basis vector, such as a diagonally opposite basis vector polarization state that requires detection of the contrast of the exit light intensity with a diagonally opposite basis vector PBS, while other basis vectors do not. The PBS of the reference 1 is aligned with the polarization axis of the Charlie Polarizing Beam Splitter (PBS) when the Alice end and Bob end align right angle basis vectors, and a PBS without diagonal basis vectors is available.
4) In contrast, polarization feedback of the polarization-encoded BB84 system, while there are schemes employing automatic electronically controlled polarization feedback, is not suitable for direct application to MDIQKD systems. Because the standard BB84 system only needs to calibrate the polarization of one transmitting end and one receiving end, the polarization reference systems are consistent; and MDIQKD, because of involving 2 sending ends and one receiving end, three parties are required to meet the requirement of consistent reference system, otherwise, the error rate is increased.
Disclosure of Invention
In order to solve the problem that the three-terminal vector of MDIQKD is not matched and is easy to cause high error rate and overcome the defects that the automatic feedback is not performed and the manual adjustment is difficult to control accurately, the invention provides a polarization feedback method of a polarization coding MDIQKD system, which can utilize the existing MDIQKD system without an additional detection device to perform accurate automatic calibration on the Alice, bob, charlie three terminals.
The technical problems to be solved by the invention can be realized by the following technical scheme: a polarization feedback method of a polarization coding measurement equipment independent system is used for automatically calibrating an Alice end, a Bob end and a Charlie end of the system to enable the three ends to simultaneously meet the consistency of basic vectors; the polarization feedback method comprises the following steps:
Adjusting step one, adjusting Alice end to be consistent with Charlie end group vector: two paths behind the Charlie end optical beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors;
and step two, adjusting the base vector of the Bob end by using the calibrated H/V base vector and P/N base vector measuring end of the Charlie end, so that the H/V base vector and P/N base vector of the Bob end are consistent with the corresponding base vector of the Charlie end.
As a further improvement of the above scheme, the polarization feedback method further includes a step of adjusting step three to restore the P/N basis vector of the Charlie end to an H/V basis vector.
As a further improvement of the above-described aspect, the adjusting method of the adjusting step one includes the steps of:
enabling an Alice end to firstly send H polarization state laser, enabling the H polarization state laser to enter a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through a light beam splitter BS1:1 at the Charlie end, focusing on the counting rate of the detector D1 and the detector D2 at the moment, and adjusting polarization controllers EPC-1 of one of two rear arms of the light beam splitter BS to enable the contrast ratio of polarization feedback of D1:D2 to meet the set requirement;
Locking the voltage point of the polarization controller EPC-1, wherein the polarization controller EPC-1, the detector D1 and the detector D2 are arranged as one path of the measuring H/V basic vector in two paths behind the optical beam splitter BS;
Then enabling an Alice end to send P polarized laser, enabling the P polarized laser to enter a detector D1, a detector D2, a detector D3 and a detector D4 through a light beam splitter BS1:1 at the Charlie end, focusing on the counting rate of the detector D3 and the detector D4, and adjusting polarization controllers EPC-2 of one of two arms behind the light beam splitter BS to enable the contrast ratio of polarization feedback of D3:D4 to meet the set requirement;
The voltage point of the polarization controller EPC-2 is locked here, and the polarization controller EPC-2, the detector D3 and the detector D4 are set to one of the measurement P/N basis vectors in two paths after the beam splitter BS.
As a further improvement of the above scheme, the adjusting method of the adjusting step two is as follows:
Controlling Bob end to emit H laser;
inquiring the contrast ratio of Charlie D1:D2;
Controlling Bob end-emitting P laser;
inquiring the contrast ratio of Charlie D3:D4;
And integrating the contrast ratio of D1:D 2 and D3:D 4, and judging whether the contrast ratio meets the target contrast ratio requirement or not. If yes, ending, otherwise, calculating voltage compensation quantity of the polarization controller EPC-B and issuing, and returning to the steps: the iteration is continued by controlling Bob to end-fire H laser.
Further, the adjusting method of the adjusting step three comprises the following steps: and (3) enabling the Bob end or the Alice end to send H laser, enabling the Charlie end to calibrate a polarization controller EPC-2 of a path of the P/N base vector after the optical beam splitter BS, and enabling the P/N base vector state to be converted into an H/V base vector state.
The invention also provides a polarization feedback device of the polarization coding measurement equipment independent system, which is used for automatically calibrating the Alice end, the Bob end and the Charlie end of the system to ensure that the three ends simultaneously meet the consistency of basic vectors; the polarization feedback device includes:
the first adjusting module is used for adjusting Alice end to be consistent with Charlie end group vector: two paths behind the Charlie end optical beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors;
And the second adjusting module is used for adjusting the base vector of the Bob end by using the calibrated H/V base vector and P/N base vector measuring end of the Charlie end, so that the H/V base vector and P/N base vector of the Bob end are consistent with the base vectors of the Alice end and the Charlie end.
As a further improvement of the above solution, the polarization feedback device further comprises a third adjusting module for adjusting the polarization of the light beam
The P/N basis vector locked by the detector D3 and the detector D4 at the Charlie end is restored to be the H/V basis vector.
As a further improvement of the above solution, the first adjusting module includes:
Polarization controller EPC-1 and control driving unit thereof;
Polarization controller EPC-2 and control driving unit thereof;
The H/V base vector unit is used for enabling the Alice end to firstly send laser in an H polarization state, and enabling the laser to enter a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through a light beam splitter BS1:1, wherein at the moment, only the counting rate of the detector D1 and the detector D2 is concerned, and a polarization controller EPC-1 of one of two rear arms of the light beam splitter BS is adjusted to enable the contrast ratio of polarization feedback of the D1:D2 to meet the set requirement;
A locking unit I for locking the voltage point of the polarization controller EPC-1, wherein the polarization controller EPC-1, the detector D1 and the detector D2 are arranged as one path for measuring the H/V basis vector in two paths behind the optical beam splitter BS; the P/N base vector unit is used for enabling the Alice end to send P polarized laser, the P polarized laser enters the detector D1, the detector D2, the detector D3 and the detector D4 through the optical beam splitter BS1:1 at the Charlie end, only the counting rate of the detector D3 and the counting rate of the detector D4 are concerned at the moment, and the polarization controller EPC-2 of one of the two arms behind the optical beam splitter BS are adjusted to enable the contrast ratio of polarization feedback of the D3:D4 to meet the set requirement;
And a second locking unit for locking the voltage point of the polarization controller EPC-2, wherein the polarization controller EPC-2, the detector D3 and the detector D4 are arranged as one path for measuring the P/N basis vector in two paths behind the optical beam splitter BS.
As a further improvement of the above solution, the second adjusting module includes:
polarization controller EPC-B and control driving unit thereof;
The H laser control unit is used for controlling the Bob end to emit H laser;
the first query unit is used for querying the contrast ratio D1:D 2 of Charlie; the P laser control unit is used for controlling the Bob end to emit P laser;
A second query unit, configured to query a Charlie D3:d4 contrast;
The judging unit is used for integrating the contrast ratio of D1:D2 and D3:D4 and judging whether the contrast ratio meets the target contrast ratio requirement or not;
The calculating unit is used for calculating the voltage compensation quantity of the polarization controller EPC-B and issuing the voltage compensation quantity when the contrast does not meet the target contrast requirement, and then starting the H laser control unit to continue iteration; and ending the iteration when the contrast meets the target contrast requirement.
The invention also provides a polarization coding measurement equipment irrelevant system, which applies any polarization feedback method; light sent by the light source sending end of the Alice end and the Bob end of the system is respectively sent to two input ports of the light beam splitter BS of the Charlie end of the system, wherein a polarization controller EPC-B is inserted between the light source sending end of the Bob end (or Alice end) and the corresponding input port of the light beam splitter BS of the Charlie end; in the rear optical path of the two output ports of the beam splitter BS, the first output port of the beam splitter BS is connected to the polarization beam splitter PBS1 through the polarization controller EPC-1, then the two output ports of the polarization beam splitter PBS1 are respectively connected to the detectors D1 and D2 of the system, the second output port of the beam splitter BS is connected to the polarization beam splitter PBS2 through the polarization controller EPC-2, and then the two output ports of the polarization beam splitter PBS2 are respectively connected to the detectors D3 and D4 of the system.
The polarization coding MDIQKD system in the prior art adopts manual adjustment, and the method is not automatic and has lower accuracy than automatic adjustment, so that the system code rate can be influenced. The method realizes high-precision polarization feedback adjustment by a full-automatic feedback method. Compared with the requirement of reference 1 on an electric control polarization controller (fibersqueezers in the area (a) in fig. 1 or the area (b) in fig. 1) in the process of calibrating a right angle basis vector (H/V basis vector), namely that the polarization state H state sent by Alice is aligned with the fast axis or the slow axis of the first optical fiber extruder in the electric polarization controller, the method has no requirement on the electric control polarization controller in the process of calibrating the right angle basis vector (H/V basis vector), and has simpler operation and quicker feedback; compared with the unclear explanation of 'theevoltageisadjustedsuchthatherculegarbase saw alignment' in the process of calibrating diagonal basis vectors (P/N basis vectors) in reference 1, and other devices possibly utilized based on the deduction, the polarization feedback method proposed by the method can utilize the existing MDIQKD system without an additional detection device, so that the system flow is clearer and simpler, and the cost and industrialization are easier to reduce.
Drawings
FIG. 1 is a polarization feedback light path diagram of a prior art measurement device independent system.
Fig. 2 is a polarization feedback optical path diagram of a conventional polarization encoding BB84 system.
FIG. 3 is a polarization encoding measurement device independent system of the present invention.
FIG. 4 is a flow chart of a polarization feedback method of a polarization encoding measurement device independent system of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
The system automatically initiates the polarization feedback mechanism when a higher bit error rate condition is detected during the polarization encoding measurement device independent system initialization phase and QKD operation phase shown in fig. 3. As shown in fig. 4, the polarization feedback method of the polarization encoding measurement device independent system is used for automatically calibrating Alice end, bob end and Charlie end of the system to enable the three ends to simultaneously meet the basis vector consistency, and the specific scheme steps of the polarization feedback method are described as follows.
1) Adjusting Alice to be consistent with the Charlie base vector mainly means that: two paths behind the Charlie end beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors.
The adjustment method for the consistency of Alice terminal and Charlie terminal group vector is as follows:
At the Charlie end, the H-polarized laser enters a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through a beam splitter BS 1:1.
At this time, only the counting rates of the two detectors D1 and D2 are concerned, and the polarization controller EPC-1 of one of the two arms behind the beam splitter BS is adjusted to make the contrast ratio of the polarization feedback of D1:d2 meet the set requirement, for example, D1:d2 >100. The voltage point of the polarization controller EPC-1 is locked here. At this time, the polarization controller EPC-1, the detector D1 and the detector D2 are set to one of two paths after the beam splitter BS to measure the H/V basis vector.
And then enabling the Alice end to send P polarized laser, and enabling the P polarized laser to enter the detectors D1, D2, D3 and D4 through the beam splitter BS1:1 at the Charlie end.
At this time, only the counting rates of the two detectors D3 and D4 are concerned, and the polarization controller EPC-2 of one of the two arms behind the beam splitter BS is adjusted to make the contrast ratio of the polarization feedback of D3:d4 meet the set requirement, for example, D3:d4 >100. The polarization controller EPC-2 voltage point is locked here. At this time, the EPC-2, detector D3 and detector D4 are set to measure one of the P/N basis vectors in two paths after the beam splitter BS.
At this time, two paths after the Charlie terminal BS are respectively an HV base vector and a PN base vector measuring terminal which are consistent with the Alice end vector.
2) And regulating the Bob end base vector by using the calibrated HV base vector and PN base vector measuring end of the Charlie end, so that the HV base vector and PN base vector of the Bob end are consistent with the Alice end and the Charlie end base vector.
As shown in fig. 4, the specific manner is preferably:
Controlling Bob end to emit H laser;
inquiring the contrast ratio of Charlie D1:D2;
Controlling Bob end-emitting P laser;
inquiring the contrast ratio of Charlie D3:D4;
Comprehensively combining the contrast of D1:D2 and D3:D4, and judging whether the contrast meets the target contrast requirement? If yes, ending, otherwise, calculating voltage compensation quantity of the polarization controller EPC-B and issuing, and returning to the steps: "control Bob end-lased H".
3) Since the Bell state measurement end of the Charlie receiving end of the MDIQKD system can adjust both PBS to be the same base vector, for example, both PBS are H/V base vectors, the base vector P/N locked by the D3 detector and the D4 detector of the Charlie end can be recovered to be the base vector H/V. The specific process comprises the following steps: and (3) enabling the Bob end (or the Alice end) to send H-state light, and enabling the Charlie end to calibrate EPC-2 of a path of the P/N base vector after the BS so as to enable the P/N base vector state to be converted into the H/V base vector state.
The polarization coding MDIQKD system in the prior art adopts manual adjustment, the method is not automatic, the accuracy is not as high as that of automatic adjustment, and the system code rate can be influenced. The method realizes high-precision polarization feedback adjustment by a full-automatic feedback method. Compared with the requirement of reference 1 on an electric control polarization controller (fibersqueezers in the area (a) in fig. 1 or the area (b) in fig. 1) in the process of calibrating a right angle basis vector (H/V basis vector), namely that the polarization state H state sent by Alice is aligned with the fast axis or the slow axis of the first optical fiber extruder in the electric polarization controller, the method has no requirement on the electric control polarization controller in the process of calibrating the right angle basis vector (H/V basis vector), and has simpler operation and quicker feedback; compared with the unclear explanation of 'theevoltageisadjustedsuchthatherculegarbase saw alignment' in the process of calibrating diagonal basis vectors (P/N basis vectors) in reference 1, and other devices possibly utilized based on the deduction, the polarization feedback method proposed by the method can utilize the existing MDIQKD system without an additional detection device, so that the system flow is clearer and simpler, and the cost and industrialization are easier to reduce.
Example 2
The polarization feedback method of the polarization coding measurement device independent system can be set into a modular structure, such as a polarization feedback device designed into a corresponding polarization coding measurement device independent system, wherein the polarization feedback device is used for automatically calibrating an Alice end, a Bob end and a Charlie end of the system to enable the three ends to simultaneously meet the basis vector consistency, and comprises a first adjusting module, a second adjusting module and a third adjusting module.
The adjusting module is used for adjusting Alice end to be consistent with Charlie end group vector: two paths behind the Charlie end beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors. The first adjusting module comprises an H polarization state unit, a first locking unit, a P polarization state unit and a second locking unit.
The H polarization state unit is used for enabling the Alice end to firstly send H polarization state laser, the H polarization state laser enters the detectors D1, D2, D3 and D4 of the Charlie end through the optical beam splitter BS1:1, at the moment, only the counting rate of the detectors D1 and D2 is concerned, and the polarization controller EPC-1 of one of the two arms behind the optical beam splitter BS is regulated to enable the contrast ratio of the polarization feedback of the D1:D2 to meet the set requirement. As soon as the locking unit is used to lock the voltage point of the polarization controller EPC-1 here, the polarization controller EPC-1, the detector D1 and the detector D2 are now arranged as one of the measuring H/V basis vectors in the two paths after the beam splitter BS. The P polarization state unit is used for enabling the Alice end to send P polarization state laser, the P polarization state laser enters the detector D1, the detector D2, the detector D3 and the detector D4 through the optical beam splitter BS1:1 at the Charlie end, only the counting rate of the detector D3 and the counting rate of the detector D4 are concerned at the moment, and the polarization controller EPC-2 of one of the two arms behind the optical beam splitter BS are adjusted to enable the contrast ratio of polarization feedback of the D3:D4 to meet the set requirement. The second locking unit is used for locking the voltage point of the polarization controller EPC-2, and the polarization controller EPC-2, the detector D3 and the detector D4 are set to be one path for measuring the P/N basis vector in two paths behind the optical beam splitter BS.
The second adjusting module is used for adjusting the base vector of the Bob end by using the calibrated H/V base vector and the P/N base vector measuring end of the Charlie end, so that the H/V base vector and the P/N base vector of the Bob end are consistent with the base vectors of the Alice end and the Charlie end.
The second adjusting module comprises: the H laser control unit is used for controlling the Bob end to emit H laser; the first query unit is used for querying the contrast ratio D1:D 2 of Charlie; the P laser control unit is used for controlling the Bob end to emit P laser; a second query unit, configured to query a Charlie D3:d4 contrast; a determination unit configured to integrate the contrast of D1:d2 and D3:d4, and determine whether the contrast satisfies a target contrast requirement? And the calculating unit is used for calculating the voltage compensation quantity of the polarization controller EPC-B and issuing the voltage compensation quantity when the contrast does not meet the target contrast requirement, and then starting the H laser control unit.
And the third adjusting module is used for restoring the P/N base vector locked by the detector D3 and the detector D4 at the Charlie end into an H/V base vector. And the adjusting module enables the Bob end or the Alice end to send H laser, and after the Charlie end calibrates the optical beam splitter BS, the P/N base vector state is converted into an H/V base vector state by the polarization controller EPC-2 on one path of the P/N base vector.
Because the polarization feedback method of the polarization encoding measurement equipment independent system and the polarization feedback device of the polarization encoding measurement equipment independent system are in one-to-one correspondence, the polarization feedback device is not repeatedly discussed.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (6)
1. A polarization feedback method of a polarization coding measurement equipment independent system is used for automatically calibrating an Alice end, a Bob end and a Charlie end of the system to enable the three ends to simultaneously meet the consistency of basic vectors; the method is characterized in that: the polarization feedback method comprises the following steps:
Adjusting step one, adjusting Alice end to be consistent with Charlie end group vector: two paths behind the Charlie end optical beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors;
Adjusting step two, namely adjusting the base vector of the Bob end by using the calibrated H/V base vector and P/N base vector measuring end of the Charlie end, so that the H/V base vector and P/N base vector of the Bob end are consistent with the corresponding base vector of the Charlie end;
the adjusting method of the adjusting step one comprises the following steps:
enabling an Alice end to firstly send H polarization state laser, enabling the H polarization state laser to enter a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through a light beam splitter BS1:1 at the Charlie end, focusing on the counting rate of the detector D1 and the detector D2 at the moment, and adjusting polarization controllers EPC-1 of one of two rear arms of the light beam splitter BS to enable the contrast ratio of polarization feedback of D1:D2 to meet the set requirement;
Locking the voltage point of the polarization controller EPC-1, wherein the polarization controller EPC-1, the detector D1 and the detector D2 are arranged as one path of the measuring H/V basic vector in two paths behind the optical beam splitter BS;
then enabling an Alice end to send P polarized laser, enabling the P polarized laser to enter a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through a light beam splitter BS1:1 at the Charlie end, focusing on the counting rate of the detector D3 and the detector D4, and adjusting the polarization controller EPC-2 of one of the two rear arms of the light beam splitter BS to enable the contrast ratio of polarization feedback of D3:D4 to meet the set requirement;
Locking the voltage point of the polarization controller EPC-2, wherein the polarization controller EPC-2, the detector D3 and the detector D4 are arranged as one path of measuring P/N basis vectors in two paths behind the optical beam splitter BS;
The adjusting method of the second adjusting step is as follows:
Controlling Bob end to emit H laser;
inquiring the contrast ratio of Charlie D1:D2;
Controlling Bob end-emitting P laser;
inquiring the contrast ratio of Charlie D3:D4;
synthesizing the contrast ratio of D1:D 2 and D3:D 4, and judging whether the contrast ratio meets the target contrast ratio requirement or not; if yes, ending, otherwise, calculating voltage compensation quantity of the polarization controller EPC-B and issuing, and returning to the steps: the iteration is continued by controlling Bob to end-fire H laser.
2. The polarization feedback method of a polarization-encoded measurement device-independent system of claim 1, further comprising a step of adjusting step three to restore the P/N basis vector of the Charlie end to an H/V basis vector.
3. The polarization feedback method of a polarization-encoded measurement device-independent system of claim 2, wherein: the adjusting method of the adjusting step three comprises the following steps: and (3) enabling the Bob end or the Alice end to send H laser, enabling the Charlie end to calibrate a polarization controller EPC-2 of a path of the P/N base vector after the optical beam splitter BS, and enabling the P/N base vector state to be converted into an H/V base vector state.
4. The polarization feedback device of the polarization coding measurement equipment independent system is used for automatically calibrating an Alice end, a Bob end and a Charlie end of the system to ensure that the three ends simultaneously meet the consistency of basic vectors; the method is characterized in that: the polarization feedback device includes:
the first adjusting module is used for adjusting Alice end to be consistent with Charlie end group vector: two paths behind the Charlie end optical beam splitter BS are respectively an H/V base vector and a P/N base vector measuring end which are consistent with Alice end base vectors;
the second adjusting module is used for adjusting the basic vector of the Bob end by using the calibrated H/V basic vector and P/N basic vector measuring end of the Charlie end, so that the H/V basic vector and P/N basic vector of the Bob end are consistent with the basic vectors of the Alice end and the Charlie end;
the first adjusting module comprises:
Polarization controller EPC-1 and control driving unit thereof;
Polarization controller EPC-2 and control driving unit thereof;
The H/V base vector unit is used for enabling an Alice end to firstly send H polarization state laser, the H polarization state laser enters a detector D1, a detector D2, a detector D3 and a detector D4 of the Charlie end through an optical beam splitter BS1:1 at the Charlie end, at the moment, only the counting rate of the detector D1 and the detector D2 is concerned, and a polarization controller EPC-1 of one of two arms behind the optical beam splitter BS is regulated to enable the contrast ratio of polarization feedback of D1:D2 to meet the set requirement;
a locking unit I for locking the voltage point of the polarization controller EPC-1, wherein the polarization controller EPC-1, the detector D1 and the detector D2 are arranged as one path for measuring the H/V basis vector in two paths behind the optical beam splitter BS;
The P/N base vector unit is used for enabling the Alice end to send P polarized laser, the P polarized laser enters the detectors D1, D2, D3 and D4 of the Charlie end through the optical beam splitter BS1:1, only the counting rate of the detectors D3 and D4 is concerned at the moment, and the polarization controller EPC-2 of one of two arms behind the optical beam splitter BS is adjusted to enable the contrast ratio of polarization feedback of D3:D4 to meet the set requirement;
A second locking unit for locking the voltage point of the polarization controller EPC-2, wherein the polarization controller EPC-2, the detector D3 and the detector D4 are set as one path for measuring the P/N basis vector in two paths behind the optical beam splitter BS;
the second adjusting module comprises:
polarization controller EPC-B and control driving unit thereof;
The H laser control unit is used for controlling the Bob end to emit H laser;
the first query unit is used for querying the contrast ratio D1:D 2 of Charlie; the P laser control unit is used for controlling the Bob end to emit P laser;
A second query unit, configured to query a Charlie D3:d4 contrast;
The judging unit is used for integrating the contrast ratio of D1:D2 and D3:D4 and judging whether the contrast ratio meets the target contrast ratio requirement or not;
The calculating unit is used for calculating the voltage compensation quantity of the polarization controller EPC-B and issuing the voltage compensation quantity when the contrast does not meet the target contrast requirement, and then starting the H laser control unit to continue iteration; and ending the iteration when the contrast meets the target contrast requirement.
5. The polarization feedback device of a polarization-encoded measurement device-independent system of claim 4, wherein: the polarization feedback device further comprises an adjusting module III, wherein the adjusting module III is used for restoring the P/N base vector locked by the detector D3 and the detector D4 at the Charlie end into the H/V base vector.
6. A polarization encoding measurement device independent system applying the polarization feedback method according to any one of claims 1 to 3; the method is characterized in that: light sent by the light source sending end of the Alice end and the Bob end of the system is respectively sent to two input ports of the light beam splitter BS of the Charlie end of the system, wherein a polarization controller EPC-B is inserted between the light source sending end of the Bob end (or Alice end) and the corresponding input port of the light beam splitter BS of the Charlie end; in the rear optical path of the two output ports of the beam splitter BS, the first output port of the beam splitter BS is connected to the polarization beam splitter PBS1 through the polarization controller EPC-1, then the two output ports of the polarization beam splitter PBS1 are respectively connected to the detectors D1 and D2 of the system, the second output port of the beam splitter BS is connected to the polarization beam splitter PBS2 through the polarization controller EPC-2, and then the two output ports of the polarization beam splitter PBS2 are respectively connected to the detectors D3 and D4 of the system.
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| CN111371554B (en) * | 2020-03-16 | 2022-09-27 | 华南师范大学 | Intrinsic stable coding device and method for automatically calibrating input polarization state |
| CN111555868B (en) * | 2020-04-10 | 2023-05-05 | 中国人民解放军国防科技大学 | Measurement equipment irrelevant quantum key distribution method based on modulation retro-reflection |
| CN112039668A (en) * | 2020-09-07 | 2020-12-04 | 南京大学 | Quantum conference key negotiation method and system based on coherent detection |
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