CN113541788B - Light polarization correction method for quantum key distribution - Google Patents
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Abstract
The invention discloses a light polarization correction method for quantum key distribution, which comprises the following steps: the Alice end sends a polarization correction command to the Bob end; the single photon detector at the Bob end starts to detect single photons; and carrying out HV base polarization correction at Alice terminal: continuously transmitting H photons at Alice end; the single photon detector at the Bob end receives and detects photons; the Alice terminal transmits a V photon to verify the quantum channel after the HV polarization base is corrected; the second control unit at the Bob end feeds back the counted values of the H photons and the V photons detected by the single photon detector to the Alice end, and Alice judges whether the absolute value of the V photons and the relative ratio of V to H are optimal or not, and newly adjusts HV base polarization offset correction; if the value is optimal, the HV base polarization correction is completed, and PN base polarization correction is started. The invention realizes high-precision and high-efficiency light polarization correction.
Description
Technical Field
The invention relates to the field of quantum information processing and quantum key synchronous correction, in particular to a light polarization correction method for quantum key distribution.
Background
In a QKD system, four polarization states of photons are taken according to the BB84 protocol, taking polarization four-state encoding as an example: vertical polarization (∈), horizontal polarization (→), +45° polarizationAnd-45 DEG polarization state->Abbreviated as H, V, P, N.
H and V are under HV groups, P and N are under PN groups, and both groups are conjugated. When the basis vector of the signal light is the same as the measuring basis, the signal light can be correctly measured, otherwise, the measurement can obtain a completely random result, so that the prior art needs to be improved to provide a multichannel synchronous output laser light source system with better precision and ensuring the safety of the system.
The agreed HV base code is 0 and the pn base code is 1. Under HV, the H polarization state is encoded as 0, and the V polarization state is encoded as 1; under the PN base, the P polarization state codes 0, and the N polarization state codes 1. The four polarization states are encoded as shown in table 1.
TABLE 1 polarization encoding modes
| Polarization state | Base coding | Polarization state encoding |
| H polarization state | 0 | 0 |
| V polarization state | 0 | 1 |
| P polarization state | 1 | 0 |
| N polarization state | 1 | 1 |
When polarized light is transmitted on the optical fiber link, a certain included angle θ may exist between the polarized light and the measurement base vector selected by the receiver when the polarized light reaches the receiver due to the birefringence effect of the optical fiber, so that further improvement on the prior art is needed to compensate the included angle, and the receiver can accurately measure four polarized lights.
Disclosure of Invention
In order to solve the technical problems, a light polarization correction method for realizing quantum key distribution of high-precision polarization state quickly through coarse adjustment without manual intervention is provided.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows: a light polarization modification method for quantum key distribution, the method being applied to a light polarization modification system, the method protecting the steps of:
step 1: the first control unit of the Alice end sends a polarization correction command to the second communication unit of the Bob end through a classical channel by the first communication unit;
step 2: after receiving the polarization correction command of the second communication unit, the second control unit at the Bob end controls the single photon detector to start detecting single photons;
step 3: and carrying out HV base polarization correction at Alice terminal:
the first control unit at Alice end controls the single photon polarization state generator to continuously send H photons;
step 4: the single photon detector at the Bob end receives and detects photons, and the second control unit at the Bob end feeds back the counted values of the H photons and the V photons detected by the single photon detector to the Alice end through the second communication unit and a classical channel;
step 5: the first control unit at the Alice end judges whether the absolute value of the H photon and the relative ratio of H to V are optimal or not, if so, the first control unit jumps to the step 7, and if not, the first control unit jumps to the step 6;
step 6: if the judgment result is not optimal, the first control unit adjusts the HV base polarization deviation by changing the X-axis, Y-axis and Z-axis control analog voltage values output to the polarization controller by the polarization driving control unit, then controls the single photon polarization state generator to continuously send H photons again, and then jumps to the step 5 until the polarization is optimal;
step 7: after the single photon polarization state generator reaches the optimal value, a first control unit at the Alice end controls the single photon polarization state generator to send a quantum channel after the V photons verify and correct the HV polarization base, and the next step is continued;
step 8: the second control unit at the Bob end sends the counted values of the H photons and the V photons detected by the single photon detector to the Alice end through the second communication unit, the first control unit of Alice judges that the absolute value of the V photons and the relative ratio of V to H are optimal, if the absolute value of the V photons and the relative ratio of V to H are optimal, the step 10 is skipped, and if the absolute value of the V photons and the relative ratio of V to H are not optimal, the step 9 is skipped:
step 9: if not, jumping to the step 8, and readjusting the HV base polarization offset to correct;
step 10: if the PN base polarization is optimal, finishing HV base polarization correction, starting PN base polarization correction, and continuing the next step;
step 11: PN base polarization correction procedure.
Preferably, the optimal criterion for the judgment in the step 5 is that the H photon count value is more than 6 orders of magnitude larger than the V photon count value.
Preferably, the optimal criterion for the determination in step 8 is that the V photon count value is much greater than the H photon count value by more than 6 orders of magnitude.
Preferably, in step 11, as in the PN-base polarization correction procedure HV-base correction procedure, only when the polarization correction is adjusted, a P photon is sent, and after the adjustment is completed, it is verified that the PN base sends an N photon.
Preferably, the step of adjusting the base polarization correction in the step 6 and the step 9 is as follows:
step A: the second control unit judges whether the absolute count value and the H/V or P/N count ratio (contrast) are larger than a rough adjustment threshold;
and (B) step (B): if the rough adjustment threshold is not met, the first control unit outputs the analog voltage values for controlling the X-axis, Y-axis and Z-axis three-axis control to the polarization controller through the polarization driving control unit to be initial values, and then the rough adjustment process is started;
step C: judging whether the H/V or the P/N reaches a threshold of a coarse adjustment absolute count value and a threshold of contrast, if not, continuing to enter a coarse adjustment flow;
step D: if the coarse adjustment threshold is reached, entering a fine adjustment flow:
judging whether the H/V or the P/N reaches a threshold of the fine-tuning absolute count value and a threshold of the contrast ratio, if not, continuing to enter a fine-tuning flow;
step E: and after the threshold of the fine-tuning count value and the threshold of the contrast ratio are reached, the adjustment is completed.
Preferably, wherein the coarse tuning step size is 1.5-3.5V; the absolute value of the coarse adjustment threshold range count is more than 2 ten thousand, and the contrast reaches 60-80.
Preferably, the threshold of the fine-tuning absolute count value is 30-50 ten thousand, and the contrast threshold is 1000-3000.
Preferably, the specific steps of coarse and fine tuning are as follows:
step B-1: determining initial values of X, Y and Z three-axis voltages;
the specific operation of determining the initial value is as follows: performing one-time traversing operation on three voltage values when the system performs polarization correction for the first time, performing one-time traversing scanning from 20V to 100V by taking 10V as a step length on each axis, recording voltage values when the minimum positions of each axis of X, Y and Z are counted, and using the obtained three initial values as initial values in the follow-up rough adjustment;
step B-2: coarse tuning is performed on initial values of X, Y and Z three-axis voltages: the polarization is adjusted by the step length of 2V, the voltage values of the three axes are adjusted to a count value, the contrast reaches a rough adjustment threshold, and preparation is made for subsequent accurate adjustment;
step B-3: fine-tuning the initial values of the X, Y and Z three axis voltages: the ratio step length is 0.1V, the change direction of the control voltage is fed back according to the combined result of the absolute count value and the contrast of the relative count value until the combined result is changed from small to large in the empirical value range, and the first peak value #1 is found out from large to small. The second peak #2 was found by scanning at 0.01V near the first peak #1, and the voltage values of the three axes X, Y and Z at the second peak #2 were stored and solidified into system polarization correction parameters to complete the adjustment of the light polarization.
The beneficial technical effects of the invention are as follows: in the invention, alice end adjusts light polarization, combines quantum channel and classical channel, forms closed loop feedback with Bob end, and realizes high-precision and fast speed regulation of polarization state and high-precision and high-efficiency light polarization correction by utilizing the cooperation of a control unit and a polarization controller driving unit.
Drawings
FIG. 1 is a diagram showing the measurement of the basis vector of signal light and the measurement basis in the prior art;
FIG. 2 is a schematic diagram of the prior art where the basis vector of the signal light is the same as the measurement basis;
FIG. 3 is a schematic representation of polarization state change during fiber transmission in the prior art;
FIG. 4 is a schematic block diagram of a light polarization modifying system according to the present invention;
FIG. 5 is a flowchart of an algorithm for polarized light modification according to the present invention;
FIG. 6 is a schematic block diagram of the drive hardware of the light polarization controller of the present invention;
FIG. 7 is a schematic block diagram of the interior of the DRV7200 according to the present invention;
FIG. 8 is a schematic diagram of input/output waveforms of the analog signal generating circuit and the shaft driving circuit according to the present invention;
FIG. 9 is a graph of linearity of the high voltage amplification input/output of the present invention;
fig. 10 is a graph of REXT setting versus output current for the present invention.
Detailed Description
The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.
As shown in fig. 1-10, a light polarization modification method for quantum key distribution is applied to a light polarization modification system, and the light polarization modification system is described first.
The optical bias correction system applied by the method comprises an Alice end and a Bob end, wherein:
the Alice terminal comprises a first control unit, a first communication unit, a single photon polarization state H, V, P, N generator, a polarization controller driving unit and a polarization controller;
the Bob end comprises a single photon detector, a second control unit and a second communication unit.
The communication connection channel between Alice and Bob comprises a quantum channel and a classical channel;
specifically, the connection relationship between the units of Alice and Bob is as follows:
the first communication unit is connected with the second communication unit through a classical channel;
the first control unit is respectively connected with a single photon polarization state H, V, P, N generator and a polarization controller driving unit, an output port of the polarization state H, V, P, N generator is connected with the polarization controller, and the polarization controller is connected with a single photon detector at the Bob end through a quantum channel;
the output port of the polarization controller driving unit is connected with the polarization controller;
the single photon detector is connected with a second control unit which in turn controls the second communication unit
At Alice's end, a single photon polarization H, V, P, N generator randomly generates four polarization states and sends the four polarization states to a polarization controller, the polarization controller can adjust the polarization offset of the HV base and PN base, and the single photon signal adjusted by the polarization controller is sent to Bob through a quantum channel;
the polarization controller driving unit adjusts the single photon polarization by changing parameters of the polarization controller. The first control unit is responsible for controlling the single photon polarization state H, V, P, N generator and the polarization controller driving unit;
the first communication unit interacts with Bob through a classical channel and transmits effective feedback information to the first control unit at Alice's end. The first control unit adjusts the polarization of the HV or PN base according to the feedback information.
And the Bob end single photon detector sends the detected H, V, P, N photon counting result to the second control unit, and the second control unit sends the detecting result of the single photon detector to Alice through the second communication unit.
Specifically, the first control unit adopts an FPGA processing unit, the polarization control driving unit comprises a first path of analog quantity generating circuit, a third path of analog quantity generating circuit, an X-axis driving circuit, a Y-axis driving circuit and a Z-axis driving circuit, and the first path of analog quantity generating circuit, the second path of analog quantity generating circuit, the third path of analog quantity generating circuit and the Z-axis driving circuit are respectively connected with the X-axis driving circuit, the Y-axis driving circuit and the Z-axis driving circuit one by one.
The analog quantity generating circuit generates an analog quantity for control according to a control signal of the FPGA control unit, and the analog quantity is amplified into a high-voltage analog signal by the shaft driving circuit to control the polarization controller.
Specifically, digital signals generated by the FPGA processing unit are converted into analog output through three analog quantity generating circuits. The three analog quantities pass through X, Y and a Z-axis driving circuit to generate a high-voltage driving signal of the polarization controller. The analog quantity generating circuit of any path comprises a digital-to-analog converter, the digital-to-analog converter is connected with the FPGA processing unit through an SPI digital access interface, and the output analog quantity value of the digital-to-analog converter is updated through a register configured by the FPGA processing unit.
Specifically, the analog quantity generating circuit selects a bipolar output AD57X1 series digital-to-analog converter, the AD57X1 series chip is a 16-bit DAC, and 8 software programmable output ranges are: 0V to 5V, 0V to 10V, 0V to 16V, 0V to 20V, + -3V, + -5V, + -10V and-2.5V to +7.5V, built-in low drift 2.5V voltage references, build-up time 7.5us, provide SPI digital access interface with processor or FPGA, through which processor or FPGA can configure the register of this DAC, can update the output analog value of DAC.
The output range of the AD57X1 series is +/-3V, analog power supply is +/-10V, and digital interface power supply is +3.3V.
The polarization control driving unit is controlled by the FPGA processing unit, outputs X, Y, Z three-axis high voltage, and the combination of the three voltages HV_ X, HV _ Y, HV _Z determines the polarization state of the optical signal passing through the polarization controller.
X, Y and Z-axis drive circuits can output 0V-140V per channel, the maximum drive current per channel is 60mA, and the voltage amplification factors of X-axis, Y-axis and Z-axis are configurable.
Since the polarization controller requires high voltage control, a circuit for amplifying a small signal to a high voltage signal needs to be designed, and in order to precisely adjust polarization, the amplifying function must have good linearity in an amplifying section. Since the output is a voltage up to 140V, conventional op-amps cannot be implemented. Therefore, the booster circuit and the high-voltage amplifying circuit are arranged in the X, Y and Z-axis driving circuit of the embodiment, the high-voltage generated by the booster circuit is output to the high-voltage amplifying circuit, and the high-voltage amplifying circuit outputs a high-voltage excitation signal capable of controlling the polarization state of the polarization controller after amplifying and driving the high voltage through the internal gain.
X, Y and Z-axis drive circuit integrate BOOST and high voltage amplifying chip, and the high voltage amplifying chip adopts DRV270X series chip.
The voltage amplifying chip comprises a booster circuit and a high-voltage amplifying circuit. The two parts can be used separately and independently, or can be combined for application. In this embodiment, the two parts are combined, and the high voltage generated by the boost circuit BST is output to supply power to the PVDD pin of the high voltage amplifying circuit.
When pvdd=80V, a voltage of 150 volts Vpp can be output between out+, OUT-. The input signals IN+ and IN-of the high-voltage amplifier are amplified and driven by the gain adjustment IN the DRV270X series chip, and then output high-voltage excitation signals OUT+ and OUT-capable of controlling the polarization state of the polarization controller.
X, Y and Z-axis driving circuits are realized by DRV series chips, and voltage output of a boost circuit in X, Y and Z-axis driving circuits is VBST=1.3 (1+750/12.4) =80V
The circuit design shorts PVDD with BST1 and BST2, a high-voltage amplifier in the DRV2700 supplies 80V, and pins OUT+ and OUT-can output a high-voltage signal of 150 Vpp.
X, Y and Z-axis drive circuitry support high voltage adjustment accuracy calculations:
analog signal amount vpp=6v, amplification of 28.8db estimated as 30-fold voltage amplification, 16-bit DAC:
(6Vpp*30)/65536＝0.0027V＝2.7mV。
therefore, the high-voltage output of the drive circuit of the polarization controller can reach 3mV in the precision of the regulated voltage, the precision is high, the amplification linearity of the input and the output is good, the algorithm is favorably and rapidly regulated, and the polarization correction is rapid.
The system to be adopted by the method, the method for correcting the light deviation by utilizing the light deviation correcting system comprises the following steps:
step 1: the first control unit of the Alice end sends a polarization correction command to the second communication unit of the Bob end through a classical channel by the first communication unit;
step 2: after receiving the polarization correction command of the second communication unit, the second control unit at the Bob end controls the single photon detector to start detecting single photons;
step 3: the Alice terminal carries out HV base polarization correction firstly:
the first control unit 1 of Alice controls the single photon polarization state generator to continuously send H photons;
step 4: the single photon detector at the Bob end receives and detects photons and calculates the number of the received photons to obtain a count value, and the second control unit at the Bob end feeds back the count values of the number of the H photons and the number of the V photons detected by the single photon detector to Alice through the second communication unit and a classical channel;
step 5: the first Alice control unit judges whether the absolute value of the number of H photons and the ratio H/V of the number of H photons to the number of V photons are optimal or not, and the optimal judgment criterion is that the number of H photons is more than 6 orders of magnitude larger than the number of V photons, namely the number of H photons is far larger than the number of V photons, for example, the number of H photons is hundreds of thousands, the number of V photons is only hundreds, and even the number of V photons is close to zero.
If the judgment result is not optimal, the first control unit adjusts the HV base polarization deviation by changing the X-axis, Y-axis and Z-axis control analog voltage values output by the polarization driving control unit to the polarization controller, then the single-photon polarization state generator is controlled again to continuously send H photons, the second control unit #2 of Bob feeds back the counted values of the number of the H photons and the number of the V photons detected by the single-photon detector to the Alice terminal through the second communication unit, and the first control unit of the Alice terminal judges whether the absolute value of the counted value of the number of the H photons and the ratio H/V (the number of the H photons divided by the number of the V photons) of the number of the H photons are optimal or not again, and the polarization deviation of the HV base is adjusted again through the polarization controller driving unit, and the steps are repeated until the value is optimal;
step 6: after the optimization is achieved, the Alice end first control unit controls the single photon polarization state generator to send a quantum channel after the V photons verify and correct the HV polarization base;
step 7: the second control unit at Bob end sends the count values of the number of the H photons and the number of the V photons detected by the single photon detector to Alice through the second communication unit, the first control unit of Alice judges whether the ratio V/H of the absolute value of the calculated value of the V photons and the number of the V and H photons is optimal or not, and similarly, the optimal judgment criterion is that the number of the V photons is far greater than the number of the H photons by more than 6 orders of magnitude, i.e., the number of the V photons is far greater than the number of the H photons, for example, the absolute number of the V photons is hundreds of thousands, the number of the H photons is just hundreds of, even is close to zero (theoretically, the absolute value of the H photons and the relative ratio of H and V are close to each other when the H photons are singly sent):
if the HV base polarization deviation is not optimal, the HV base polarization deviation is readjusted, and correction is carried out;
if the PN base polarization correction is optimal, the HV base polarization correction is completed, and PN base polarization correction is started;
step 8: the PN base polarization correction flow is similar to the HV base, except that P photons are transmitted during polarization correction adjustment, and after adjustment is completed, the PN base is verified to transmit N photons.
Specifically, the step of adjusting the base polarization correction is as follows:
step A: entering a light polarization correction processing flow, and judging whether the ratio of the absolute value of the count value of the received H photon, V photon or P photon to the number of H/V, V/H or P/N photons is larger than the threshold value of the count absolute value and the photon number ratio in a set coarse adjustment range by a second control unit;
the coarse adjustment step length is larger, wherein the coarse adjustment step length is 1.5-3.5V; in this embodiment, the coarse tuning step is 2V, and the purpose of the coarse tuning is to find the approximate range of the tuning target first, and then fine tune (fine tune scans with a smaller step, such as a 0.1V step), thereby reducing the total tuning time. The photon count absolute value in the coarse tuning threshold range is larger than 20000, the ratio of the coarse tuning photon number is 60-80, and if the coarse tuning threshold is met, the fine tuning flow is entered;
and (B) step (B): if the coarse adjustment threshold is not met, then through the first control
The control unit outputs the control analog voltage values of the X axis, the Y axis and the Z axis to the polarization controller through the polarization driving control unit to be initial values, and then enters a rough adjustment process;
step C: judging whether the H/V or P/N photon number ratio reaches a coarse adjustment absolute count value threshold and a contrast threshold, if not, continuing to enter a coarse adjustment flow;
step D: if the H/V or P/N reaches the threshold of the fine adjustment absolute count value and the contrast threshold, the threshold of the fine adjustment absolute count value is 30 ten thousand to 50 ten thousand, the ratio of the fine adjustment photon number is 1000 to 3000, if the H/V or P/N does not reach the threshold of the fine adjustment absolute count value, the fine adjustment process is continued;
step E: and after the threshold of the fine-tuning count value and the threshold of the photon number ratio are reached, the adjustment is completed.
The first control unit outputs the control analog voltage values of the three axes of X axis, Y axis and Z axis to the polarization controller through the polarization driving control unit as initial values:
(1) Determining initial values of X, Y and Z three-axis voltages;
the specific operation in which the initial value is determined is: the system carries out one-time traversing operation on three voltage values when carrying out polarization correction for the first time, each axis carries out one-time traversing scanning from 20V to 100V by taking 10V as a step length, the voltage value when counting the minimum position of each axis of the three axes is recorded, and the obtained three initial values are used as initial values in the follow-up rough adjustment.
(2) Coarse tuning is performed on initial values of X, Y and Z three-axis voltages: the polarization is adjusted by the step length of 2V, and the voltage values of the three axes are adjusted until the contrast of one counting value reaches a rough adjustment threshold, so that preparation is made for the follow-up accurate adjustment.
(3) Fine-tuning the initial values of the X, Y and Z three axis voltages: the step length is 0.1V, and the change direction of the control voltage is fed back according to the comprehensive result of the count absolute value and the photon number ratio. And finding out the first peak value #1 from the large to the small until the comprehensive result is changed from the small to the large in the empirical value range. The second peak #2 was found by scanning at 0.01V near the first peak #1, and the control voltage values of the three axes at the time of the second peak #2 were saved, and solidified into a system polarization correction parameter, thereby completing the adjustment of the light polarization.
According to the invention, an HV measuring base and a PN measuring base of a Bob receiving end are fixed, and when polarization correction is performed on a system, the polarization correction is performed by adjusting the polarization angle of a single photon H, V base vector and the polarization angle of a single photon P, N base vector of an Alice transmitting end, so that the polarization state deviation reaching the Bob end caused by polarization mode dispersion of an optical fiber transmission path is compensated. The light polarization correction is generally performed during initial system installation, parameters are cured after calibration, QKD is restarted, and cured parameters are called during initialization. In addition, when the system detection rate is not high and the code rate is low, whether the light polarization correction is carried out again is considered.
According to the invention, the quantum channel is combined to transmit a single photon signal, and classical channel Alice interacts with Bob protocol, so that the closed-loop control of the optical polarization correction system is realized. The system can be triggered by software and automatically performed without manual intervention. Under the same condition, the coding performance of the QKD system subjected to light polarization correction is better than that of the QKD system without correction by more than 50%.
Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.
Claims (4)
1. A light polarization modification method for quantum key distribution, the method being applied to a light polarization modification system, characterized in that the method protects the steps of:
step 1: the first control unit of the Alice end sends a polarization correction command to the second communication unit of the Bob end through a classical channel by the first communication unit;
step 2: after receiving the polarization correction command of the second communication unit, the second control unit at the Bob end controls the single photon detector to start detecting single photons;
step 3: and carrying out HV base polarization correction at Alice terminal:
the first control unit at Alice end controls the single photon polarization state generator to continuously send H photons;
step 4: the single photon detector at the Bob end receives and detects photons, and the second control unit at the Bob end feeds back the count values of the number of H photons and the number of V photons detected by the single photon detector to the Alice end through the second communication unit and a classical channel;
step 5: the first control unit at the Alice end judges whether the absolute value of the received H photon number count value and the ratio H/V of the H photon number to the V photon number are optimal or not, if so, the step 7 is skipped, and if not, the step 6 is skipped;
step 6: if the judgment result is not optimal, the first control unit adjusts the HV base polarization deviation by changing the X-axis, Y-axis and Z-axis control analog voltage values output to the polarization controller by the polarization driving control unit, then controls the single photon polarization state generator to continuously send H photons again, and then jumps to the step 5 until the polarization is optimal;
step 7: after the best is achieved, the Alice terminal carries out VP-based polarization correction flow;
step 8: after VP base polarization correction is completed, the Alice terminal carries out PN base polarization correction flow;
in the step 5, the optimal criterion is that the H photon count value is more than 6 orders of magnitude larger than the V photon count value;
the step of adjusting the base polarization correction in the step 6-8 is as follows:
step A: the second control unit judges whether the ratio of the absolute value of the photon number count value to the H/V, V/P or P/N photon count value is larger than the absolute value of the coarse adjustment range and the ratio threshold;
and (B) step (B): if the rough adjustment threshold is not met, the first control unit outputs the analog voltage values for controlling the X-axis, Y-axis and Z-axis three-axis control to the polarization controller through the polarization driving control unit to be initial values, and then the rough adjustment process is started;
step C: judging whether the ratio of the photon count values of H/V, V/P or P/N reaches the threshold value of the ratio of the absolute value of the photon count value and the photon count value of coarse adjustment, if not, continuing to enter the coarse adjustment flow;
step D: if the coarse adjustment threshold is reached, entering a fine adjustment flow:
judging whether the ratio of the absolute value of the photon number count value to the H/V, V/P or P/N photon count value reaches the absolute value threshold of the fine-tuning photon number count value and the photon count value ratio threshold, if not, continuing to enter the fine-tuning flow;
step E: after reaching the absolute value threshold of the photon number count value and the ratio threshold of the photon count value, finishing adjustment;
the specific steps of coarse and fine adjustment are as follows:
step B-1: determining initial values of X, Y and Z three-axis voltages;
the specific operation of determining the initial value is as follows: performing one-time traversing operation on three voltage values when the system performs polarization correction for the first time, performing one-time traversing scanning from 20V to 100V by taking 10V as a step length on each axis, recording voltage values when the minimum positions of each axis of X, Y and Z are counted, and using the obtained three initial values as initial values in the follow-up rough adjustment;
step B-2: coarse tuning is performed on initial values of X, Y and Z three-axis voltages: the polarization is adjusted by the step length of 2V, the voltage values of the three axes are adjusted to a count value ratio to reach a rough adjustment threshold, and preparation is made for subsequent accurate adjustment;
step B-3: fine-tuning the initial values of the X, Y and Z three axis voltages: the step length is 0.1V, the change direction of the control voltage is fed back according to the comprehensive result of the absolute count value and the relative count value ratio, the first peak value #1 is found out from the comprehensive result to be changed from small to large in the empirical value range, the second peak value #2 is found out by scanning the first peak value #1 according to 0.01V, the voltage values of the three axes X, Y and Z of the second peak value #2 are stored, the voltage values are solidified into system polarization correction parameters, and the adjustment of light polarization is completed.
2. A light polarization modification method for quantum key distribution as recited in claim 1, wherein: the VP base polarization correction transmits a V photon, and after adjustment is completed, the VP base is verified to transmit the V photon;
and P photons are transmitted by the PN base polarization correction, and after adjustment is finished, the N photons transmitted by the PN base are verified.
3. A light polarization modification method for quantum key distribution as recited in claim 1, wherein: the absolute value of the counting of the coarse tuning threshold range is larger than 20000, and the ratio of photon counting values is 60-80.
4. A light polarization modification method for quantum key distribution as recited in claim 1, wherein: the threshold of the fine-tuning absolute count value is 30-50 ten thousand, and the ratio of the fine-tuning photon count value is 1000-3000.
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