Self-adaptive focusing method for laser quantum communication

Abstract

The invention discloses a self-adaptive focusing method for laser quantum communication, and relates to the technical field of laser quantum communication, and the method comprises the specific steps: a quantum signal is transmitted from a quantum signal transmitting end, and is transmitted to a quantum signal receiving end in the form of quantum signal light; according to the self-adaptive focusing method, the stability and the signal receiving rate of quantum communication are remarkably improved by monitoring and adjusting the focus position of quantum signal light in real time, in the quantum communication process, the wavefront of a light beam is monitored in real time through the wavefront curvature sensor, data are transmitted to the upper computer, the upper computer calculates the corresponding defocusing amount, and the quantum communication quality is improved. The position of the focusing lens is adjusted in real time through a PID control algorithm, and the self-adaptive focusing mechanism can quickly respond to the change of the light beam state and ensure that the light beam is always focused at the optimal position, so that the attenuation and distortion of signals are reduced, and the receiving rate of the signals is improved.

Description

Technical Field

[0001] The invention relates to the technical field of laser quantum communication, and in particular to an adaptive focusing method for laser quantum communication. Background Art

[0002] Laser quantum communication is a new communication method that uses the principles of quantum mechanics and laser technology for communication. In laser quantum communication, information is encoded in the quantum state of photons and transmitted, using quantum properties such as quantum entanglement and quantum teleportation to achieve secure communication. Compared with traditional communication methods, laser quantum communication has higher security and privacy, and can resist future attacks such as quantum computers.

[0003] However, in laser quantum communication, since the distance and size between the transmitter and the receiver change at any time, in order to ensure the stability and efficiency of quantum transmission, real-time focusing is required in a short time. However, due to the large proportion of defocus caused by atmospheric turbulence, the traditional focusing method uses deformable mirrors, which takes a lot of travel to correct the defocus. At the same time, focusing is time-consuming and the correction effect is not ideal. In addition, during the focusing process, the operator is required to manually complete the defocus adjustment by observing the defocus amount. The defocus compensation work efficiency is low, and it has high requirements on the operator's knowledge background, proficiency and real-time performance of the operating system. There are many limitations in actual application, which affect the practicality and stability of quantum communication.

[0004] In summary, an adaptive focusing method for laser quantum communication is proposed to improve the signal reception rate and enhance the transmission efficiency and stability of quantum communication. Summary of the invention

[0005] The purpose of the present invention is to make up for the shortcomings of the prior art and provide an adaptive focusing method for laser quantum communication. In quantum communication, the signal reception rate is significantly improved through the adaptive focusing method. The wavefront curvature sensor is used to monitor the wavefront aberration in real time, which is fed back to the signal processing unit. The defocus amount is calculated in combination with the focusing lens parameters. The position of the focusing lens is accurately adjusted through the PID (proportion integration differentiation) control algorithm, so that the focusing lens is always close to the optimal focusing state, effectively reducing signal loss and ensuring that the quantum signal can be received with higher quality.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: an adaptive focusing method for laser quantum communication, the specific steps of the method are:

[0007] S1, a quantum signal is sent from a quantum signal transmitting end and transmitted to a quantum signal receiving end in the form of quantum signal light, wherein the quantum signal receiving end includes a telescope system, a focusing lens and a wavefront curvature sensor, and the telescope system includes a telescope unit, a signal processing unit and a focusing execution unit, wherein:

[0008] The telescope unit images the target and receives quantum signal light;

[0009] The signal processing unit converts the calculated defocus amount into an electrical signal through digital-to-analog conversion, and controls the movement of the focusing mirror through a PID (proportion integration differentiation) control algorithm;

[0010] The focus execution unit is used to receive the electrical signal output by the signal processing unit to execute the focus action;

[0011] S2, the telescope unit in the telescope system receives the quantum signal light and images it, and the wavefront curvature sensor measures the light intensity signals I1 and I2 on the symmetrical defocus planes before and after the focus of the short focusing lens in real time to obtain the wavefront aberration;

[0012] S3, using the wavefront aberration data as feedback information, and transmitting it to the signal processing unit in the telescope system in real time. The signal processing unit receives the wavefront aberration data from the wavefront curvature sensor and combines it with the focusing lens, and calculates the relative defocus amount ΔpV using the relationship between the inherent defocus aberration pV1 and the actual defocus aberration pV2. The relationship between pV1 and pV2 is: the radius from the optical center to the edge of the focusing lens is R, and the focal length of the focusing lens is f, then Then the relative defocus amount ΔpV=|pV2-pV1|=ΔL, where pV1 represents the inherent defocus aberration, pV2 represents the actual defocus aberration, ΔL represents the deviation between the actual position of the focusing lens and the ideal position, and R and f are the inherent optical parameters of the focusing lens, namely the focal length and the inner diameter, which are used to calculate the defocus aberration;

[0013] The signal processing unit inputs the calculated relative defocus amount ΔpV as an error error into a PID control algorithm, wherein the PID (proportion integration differentiation) control algorithm is composed of a proportional control algorithm, an integral control algorithm and a differential control algorithm, and calculates a displacement information instruction of a distance and direction in which the focusing mirror moves;

[0014] S4, the focus execution unit receives the control instruction containing the adjustment displacement information output by the signal processing unit;

[0015] According to the control instructions, the focusing lens is accurately driven to move the corresponding distance, changing the propagation path of the quantum signal light to achieve focus adjustment;

[0016] S5, after the focusing lens moves, the wavefront curvature sensor again measures the wavefront aberration of the adjusted quantum signal light;

[0017] Feeding back the new wavefront aberration measurement data to the signal processing unit, the quantum signal receiving end cyclically executes S3 and S4;

[0018] The cycle continues, constantly adjusting the position of the focusing lens until the calculated relative defocus reaches a minimum, that is, ΔpV≈0, achieving the optimal focusing state, allowing quantum communication to transmit signals under stable focusing conditions.

[0019] Furthermore, the proportional control algorithm part of the PID control algorithm in S3 calculates the adjustment displacement u P =a*eRror, where a is the proportional coefficient, which determines the adjustment displacement u P The proportional relationship between the error and the error affects the adjustment speed of the focus lens. Error is the relative defocus amount ΔpV, that is, the degree of deviation between the current focus lens position and the ideal focus position.

[0020] Furthermore, the integral control algorithm part of the PID (proportion integration differentiation) control algorithm in S3 calculates u I =b*∫error, where b is the integral coefficient, ∫error is the integral of the error error, and the integral coefficient b affects the ability to eliminate steady-state errors. The focus lens position is adjusted by accumulating errors so that the focus lens reaches the ideal focus position, that is, the relative defocus amount ΔpV=0.

[0021] Furthermore, the differential control algorithm part of the PID control algorithm in S3 calculates u D =c*(error(n1)-error(n2)), where c is the differential coefficient, error(n1) and error(n2) are the error values ​​at two adjacent moments respectively, and the differential coefficient c adjusts the movement of the focus lens according to the rate of change of the error, and prevents the focus lens from crossing the ideal focus position in the target due to excessive execution of the focus execution unit, thereby ensuring the accuracy and smoothness of the focusing process.

[0022] Furthermore, the final control instruction of S4 is u=u P +u I +u D , the results of the proportional, integral and differential control algorithms are integrated to accurately control the movement of the focusing lens, so that the laser signal in quantum communication can be adaptively focused.

[0023] Furthermore, the focusing lens in S1 is a convex lens with a focal length of f and an inner diameter of R. When the distance between the focusing lens and the focal plane is equal to twice the focal length f, the clearest image is obtained on the focal plane, which is an ideal state. The image is an inverted real image of the actual object being measured.

[0024] Furthermore, the focusing lens in S1 differs from the focusing lens in the ideal state by ΔL, but the focal length f remains unchanged. When the distance between the focal plane and the center of the focusing lens is greater than the focal length f but not equal to 2f, the image on the focal plane is scattered and blurred. When the distance between the focal plane and the center of the focusing lens is less than f, the image cannot be received on the focal plane, which is a non-ideal state. When ΔL is equal to zero, the focal plane obtains a clear and equal-sized image.

[0025] Furthermore, in S3, the defocus amount is automatically calculated by the host computer, and the data received by the wavefront curvature sensor is transmitted to the host computer to automatically calculate the defocus amount.

[0026] Compared with the prior art, this adaptive focusing method for laser quantum communication has the following beneficial effects:

[0027] 1. The adaptive focusing method of the present invention significantly improves the stability and signal reception rate of quantum communication by real-time monitoring and adjusting the focal position of quantum signal light. During the quantum communication process, the wavefront aberration of the light beam is monitored in real time by a wavefront curvature sensor, and the data is transmitted to a host computer. The host computer accurately calculates the defocus amount and adjusts the position of the focusing lens in real time through a PID control algorithm. This adaptive focusing mechanism can quickly respond to changes in the state of the light beam, ensuring that the light beam is always focused at the optimal position, thereby reducing signal attenuation and distortion and improving the signal reception rate.

[0028] 2. The present invention effectively solves the problem that the defocus aberration occupies a large part of the deformable mirror's travel by introducing a focusing mirror and a PID control algorithm, thereby significantly improving the integration and work efficiency. By adding a focusing mirror to correct a wide range of defocus aberrations, the workload of the deformable mirror is reduced. The introduction of the focusing mirror enables the deformable mirror to better focus on the correction of high-order aberrations, thereby improving the overall correction accuracy and imaging quality. At the same time, the PID control algorithm continuously controls the defocus amount calculated by the host computer, thereby realizing precise adjustment of the focusing mirror and further improving the level of automation.

[0029] Other advantages, objectives and features of the present invention will be set forth in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative work.

[0031] Figure 1 A flowchart of an adaptive focusing method for laser quantum communication;

[0032] Figure 2 A schematic plan view of an adaptive focusing method for laser quantum communication;

[0033] Figure 3 A working principle diagram of a focusing lens in an adaptive focusing method for laser quantum communication;

[0034] Figure 4 This is a schematic diagram of the principle of quantum signal light measurement by the wavefront curvature sensor in Example 1. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Embodiment 1

[0037] This embodiment describes in detail the application process of an adaptive focusing method for laser quantum communication in a quantum secure communication network system, and describes how to achieve efficient and stable quantum communication through the collaborative work of various components when dealing with interference in the metropolitan environment and switching of communication needs, thereby ensuring the secure transmission of information and improving the significant advantages of quantum communication performance in a complex metropolitan environment.

[0038] In the specific implementation, first, the quantum signal transmitting node is located at the transmitting end in the metropolitan area network. Its core function is to encode and modulate the quantum information that needs to be transmitted confidentially, generate quantum signal light, and send it to the target receiving node. The quantum signal receiving node is composed of a telescope unit, a wavefront curvature sensor, a focusing lens, a signal processing unit, and a focusing execution unit. The telescope unit focuses the quantum signal light in the receiving node, images it on the detector, and converts the optical signal into an electrical signal. The wavefront measurement monitors the wavefront state of the light beam received by the telescope unit in real time. It can quickly and accurately measure the near-field wavefront phase distribution of the light and its relationship with time, and obtain wavefront aberration information. In the metropolitan environment, the optical path is unstable due to factors such as building obstruction and temperature changes. The real-time wavefront aberration data provided by the wavefront curvature sensor becomes the key basis for the adaptive adjustment of the system, enabling the system to respond to the impact of environmental changes on the signal in a timely manner; the focusing lens changes the propagation path of the quantum signal light by precisely adjusting its own position according to the instructions of the signal processing unit to achieve the focusing function. In the metropolitan area node communication, it can effectively compensate for the defocus phenomenon caused by environmental interference and ensure that the signal can be clearly imaged on the focal plane under different conditions, thereby improving the signal acceptance rate and communication quality; the signal processing unit is the intelligent control center of the receiving node, which receives the electrical signal from the telescope unit and the wavefront aberration data of the wavefront curvature sensor, uses the algorithm to process the data, calculates the relative defocus amount by combining the focusing lens parameters, and inputs it into the PID (proportion The signal processing unit is also responsible for system status monitoring, communication protocol processing, and data interaction with other nodes to ensure the orderly progress of the entire communication process; the focusing execution unit is responsible for converting the instructions of the signal processing unit into the actual action of the focusing lens. It is composed of a motor and a transmission mechanism. The motor generates corresponding torque according to the control signal, and the transmission mechanism accurately converts the rotational motion of the motor into the linear displacement of the focusing lens, ensuring that the focusing lens can be adjusted to the optimal position in time to adapt to environmental changes and communication demand switching. The quantum signal transmitting node in the metropolitan area network encodes and modulates the quantum information to be transmitted according to the quantum secure communication protocol, generates quantum signal light of specific wavelength and coding format, and sends it to the target receiving node. The telescope unit of the receiving node receives the quantum signal light, and its optical system focuses the signal light on the detector, which converts the optical signal into an electrical signal.

[0039] Then, the wavefront curvature sensor measures the quantum signal light received by the telescope unit in real time. According to the diffraction and spectral characteristics of the Fresnel zone plate (Fresnel zone plate, FZP), the incident quantum light will diffract into a divergent beam and a converging beam after passing through the FZP, so the incident beam After passing through the off-axis FZP and the short focusing lens in sequence, the photodetector on the focal plane of the lens can synchronously record the light intensity signals I1 and I2 on the symmetrical defocus planes before and after the focus, as shown in Figure 2. Figure 4 As shown, the relationship between the normalized intensity difference and the wavefront curvature and the normal differential of the wavefront to the pupil boundary is the Poisson equation under the Neumann boundary condition, that is:

[0040]

[0041] Where I1 and I2 are the light intensity data matrices on two symmetrical defocus planes, S(r) is the normalized signal of the light intensity difference, r represents the vector variable on the incident pupil area, and C is a constant determined by parameters such as the zone plate and lens focal length. is the Laplace operator, represents the incident light phase on the pupil plane, n is the normal slope unit vector at the pupil edge, σ c is the boundary of the pupil area. The wavefront aberration can be solved by calculating the above Poisson equation through the pattern algorithm based on the Laplace operator eigenfunction The Laplace operator eigenfunction is expressed on the unit circle domain as:

[0042]

[0043] where μ = |m|, J μ (γ μm r) is an integer-order Bessel function, μ=0,1,2,…,γ μn for The nth positive root of , n = 1, 2, .... The wavefront aberration It accurately reflects the deviation between the wavefront state of the light beam after being disturbed in the complex environment of the urban area and the ideal wavefront. The wavefront curvature sensor transmits the measured wavefront aberration data to the signal processing unit in real time through the high-speed data bus. After receiving the wavefront aberration data from the wavefront curvature sensor, the signal processing unit calculates the relative defocus amount ΔpV based on the inherent parameters of the focusing lens (focal length f and inner diameter R). According to the relationship between the inherent defocus aberration pV1 and the actual defocus aberration pV2 Calculate the relative defocus amount ΔpV=|pV2-pV1|=ΔL, wherein pV1 represents the inherent defocus aberration, pV2 represents the actual defocus aberration, ΔL represents the deviation between the actual position of the focusing lens and the ideal position, R and f are the inherent optical parameters of the focusing lens, and the signal processing unit inputs the calculated relative defocus amount ΔpV as an error error into a PID (proportion integration differentiation) control algorithm, which includes a proportional control algorithm, a differential control algorithm and an integral control algorithm, and is used to calculate the displacement information instruction of the distance and direction of the focusing lens movement, and the proportional control algorithm part: calculates the adjustment displacement u P =a*error, where a is the proportional coefficient, which determines the adjustment displacement u P The proportional relationship between the error and the error, thus affecting the adjustment speed of the focusing lens. Error is the relative defocus amount ΔpV, that is, the degree of deviation between the current focusing lens position and the ideal focusing position. In the urban environment, the setting of the proportional coefficient a takes into account the frequency and amplitude of environmental changes. When the signal is suddenly weakened and the wavefront aberration changes sharply due to building occlusion, the value of a is increased so that the focusing lens can respond quickly and initially adjust to a position close to the ideal focusing position to reduce signal loss. Integral control algorithm part: Calculate the adjustment displacement u I = b * ∫ error, where b is the integral coefficient. In metropolitan area node communications, the ambient temperature change may cause long-term small defocus errors. The integral control algorithm gradually eliminates these steady-state errors by accumulating errors to ensure that the focusing lens maintains accurate focus during long-term operation, that is, the relative defocus amount ΔpV = 0. The differential control algorithm part: Calculate the adjustment displacement u D =c*(error(n1)-error(n2)), where c is the differential coefficient, error(n1) and error(n2) are the error values ​​at two adjacent moments, respectively. The differential coefficient c is mainly used to suppress the overshoot phenomenon of the focusing lens during the adjustment process. When the communication task between nodes is switched, the communication distance and direction suddenly change, and the wavefront aberration changes rapidly, the differential control algorithm adjusts the moving speed of the focusing lens in time according to the error change rate to prevent the focusing lens from crossing the ideal focus position in the target due to excessive adjustment, thereby ensuring the stability of the focusing process. The final control instruction u=u P +u I +u D , the signal processing unit sends this instruction to the focusing execution unit.

[0044] Subsequently, the focusing execution unit receives the control instruction containing the adjustment displacement information output by the signal processing unit. According to the control instruction, the driving motor accurately drives the focusing lens to move the corresponding distance, thereby changing the propagation path of the quantum signal light and refocusing the light beam.

[0045] Finally, after the focusing lens moves, the wavefront curvature sensor again measures the wavefront aberration of the adjusted quantum signal light, and repeats the relative defocus calculation, that is, the new wavefront aberration measurement data is fed back to the signal processing unit, the signal processing unit calculates the new displacement instruction again, and the focusing execution unit adjusts the position of the focusing lens, and continuously adjusts the position of the focusing lens. During the whole process, it is continuously judged whether the calculated relative defocus amount ΔpV reaches the minimum (close to zero). According to the set error threshold ε, when |ΔpV|≤ε, it is considered that the system has achieved acceptable focusing accuracy and stops adjusting the focusing lens; when |ΔpV|>ε, the adjustment is continued in a loop. At the same time, in metropolitan area node communication, when the communication demand between nodes switches, such as switching from short-distance communication to long-distance communication, the system can respond quickly and readjust the focus state to ensure the continuity and stability of communication.

[0046] To sum up, in the metropolitan node communication of the quantum secure communication network system, the adaptive focusing method of this embodiment, through the close collaboration of the components of the transmitting node and the receiving node, from signal transmission to precise reception, the various links in the whole process cooperate with each other, accurate wavefront aberration measurement, efficient signal processing, precise focusing execution and continuous feedback optimization, ensure the high-quality transmission of quantum signals in complex metropolitan environments, improve the signal acceptance rate, and ensure the stability of quantum communication.

[0047] Embodiment 2

[0048] This embodiment introduces in detail the working principle of a focusing lens in an adaptive focusing method for laser quantum communication and the calculation process of the relative defocus amount. The defocus amount is calculated in combination with the focusing lens parameters, and the position of the focusing lens is accurately adjusted through a PID control algorithm, so that the focusing lens is always close to the optimal focusing state, thereby significantly improving the stability of quantum communication and the signal reception rate.

[0049] In the adaptive focusing method, the focusing lens processes the light beam between the telescope system and the wavefront curvature sensor. The working principle of the focusing lens is as follows: Figure 3 As shown, it is a convex lens with a focal length of f and an inner diameter of R. Under ideal conditions, when the distance between the focusing lens and the focal plane is equal to twice the focal length f, the clearest image can be obtained on the focal plane, which is an equal-sized inverted real image of the actual object being measured. The focusing lens distance under non-ideal conditions differs from that under ideal conditions by ΔL, but the focal length f remains unchanged. If the distance between the focal plane and the center of the focusing lens is greater than the focal length f but not equal to 2f, the image on the focal plane is scattered and blurred; if the distance between the focal plane and the center of the focusing lens is less than f, the image cannot be received on the focal plane. The adaptive focusing method is to move the focusing lens to make ΔL equal to zero, so that the focal plane can obtain the clearest and equal-sized image.

[0050] In an ideal state, there is also an inherent defocus aberration pV1, and the actual defocus aberration pV2 differs from the inherent defocus aberration by ΔL. The relationship between the actual defocus aberration pV2 and the inherent defocus aberration pV1 is: Where R is the radius from the optical center to the edge of the focusing lens, and f is the focal length of the focusing lens. The relative defocus is: ΔpV = |pV2-pV1| = ΔL. When the relative defocus is ΔpV = 0, the clearest imaging can be obtained on the focal plane. In the actual optical path, after the non-ideal light beam enters the wavefront curvature sensor, the obtained wavefront aberration enters the host computer as feedback. The focusing lens is continuously moved until the defocus aberration obtained by the wavefront curvature sensor is minimized. The PID control algorithm is used. The PID control algorithm adjusts and controls the feedback, that is, the imaging of the wavefront curvature sensor. The PID control algorithm consists of a proportional control algorithm, an integral control algorithm, and a differential control algorithm. The working principle of the proportional control algorithm is: at the initial moment, ΔpV = 10㎜, then there is an error between the current position of the focusing lens and the target position, and the error is 10. The position of the focusing lens is changed by moving the control console to adjust the displacement u and the error e. rror is proportional, that is, u=a*error, set a=0.2, when the force n=1 is applied to the turntable (indicates the first time to apply force to the console, that is, the first time to control the system), then u=0.2*10=2, so the force applied to the console will reduce the focus lens by 2mm on the basis of the error of 10mm, and obtain a new ΔpV=8mm; then, n=2 (the second time to apply control), the current ΔpV=8mm, so the error is 8, then u=0.2* 8=1.6, which will cause the focusing lens to move another 1.6㎜. At this moment, ΔpV=6.4㎜... and so on. The cycle continues until the focusing lens reaches the target position under ideal conditions. At the same time, in order to eliminate the steady-state error, various factors are considered (component insensitivity, zero drift, aging, and clearance and friction of various transmission mechanisms). The steady-state error causes the original target to be ΔpV=0, but when the system finally reaches a non-zero value, it no longer changes, and the system has reached stability, resulting in the error. Introducing the integral control algorithm, that is, introducing another component in the control, the component is proportional to the integral of the error, the proportional + integral control algorithm is: u = a*error + b*error, so far, the integral of the error (the integral is accumulated in the discrete case), in the case of only proportional terms, due to the existence of the integral term, the input will increase, so that the displacement of the focusing lens can be greater than the increase, getting rid of the steady-state error. In the discrete case, it is the difference in error, that is, the difference in error when n = 1 and when n = 2: u = c*(error(n1)-error(n2)), where c is a coefficient term. In the process of moving the focusing lens, the error becomes smaller and smaller, so the differential control term is a negative number. A negative term is added to the control to prevent the focusing lens from exceeding the ideal position in the target due to excessive force on the console.

[0051] In summary, the control unit makes adjustments by analyzing the feedback amount on the host computer. This method has few adjustment parameters, and both the open-loop model and the closed-loop model can realize automatic control of the displacement of the focusing mirror.

[0052] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. An adaptive focusing method for laser quantum communication, characterized in that: The specific steps of this method are: S1, a quantum signal is sent from a quantum signal transmitting end and transmitted to a quantum signal receiving end in the form of quantum signal light, wherein the quantum signal receiving end includes a telescope system, a focusing lens and a wavefront curvature sensor, and the telescope system includes a telescope unit, a signal processing unit and a focusing execution unit, wherein: The telescope unit images the target and receives quantum signal light; The signal processing unit converts the calculated defocus amount into an electrical signal through digital-to-analog conversion, and controls the movement of the focusing mirror through a PID (proportion integration differentiation) control algorithm; The focus execution unit is used to receive the electrical signal output by the signal processing unit to execute the focus action; S2, the telescope unit in the telescope system receives the quantum signal light and images it. The wavefront curvature sensor measures the light intensity signals I1 and I2 on the symmetrical defocus planes before and after the focus of the short focusing lens in real time. From a qualitative analysis from the perspective of geometric optics, when the incident wavefront is an ideal plane wave, I1 and I2 are exactly the same. When the incident wavefront is distorted, the wavefront phase will change and thus change the light intensity distribution on the defocus plane. When the light intensity at one point on one plane increases, the light intensity at the corresponding point on the other plane decreases. Therefore, the light intensity difference on the defocus plane reflects the curvature information of the wavefront. Therefore, it can be deduced that the relationship between the normalized light intensity difference and the wavefront curvature and the normal differential of the wavefront at the pupil boundary is the Poisson equation under the Neumann boundary condition: By solving the Poisson equation, the wavefront to be measured can be restored S3, using the wavefront data as feedback information, and transmitting it to the signal processing unit in the telescope system in real time. The signal processing unit receives the wavefront data from the wavefront curvature sensor and combines it with the focusing lens to calculate the relative defocus amount ΔpV using the relationship between the inherent defocus aberration pV1 and the actual defocus aberration pV2. The relationship between pV1 and pV2 is: the radius from the optical center to the edge of the focusing lens is R, and the focal length of the focusing lens is f, then Then the relative defocus amount ΔpV=|pV2-pV1|=ΔL, where pV1 represents the inherent defocus aberration, pV2 represents the actual defocus aberration, ΔL represents the deviation between the actual position of the focusing lens and the ideal position, and R and f are the inherent optical parameters of the focusing lens, namely the focal length and the inner diameter, which are used to calculate the defocus aberration; The signal processing unit inputs the calculated relative defocus amount ΔpV as an error error into a PID control algorithm, wherein the PID control algorithm is composed of a proportional control algorithm, an integral control algorithm, and a differential control algorithm, and calculates a displacement information instruction of a moving distance and direction of the focusing mirror; S4, the focus execution unit receives the control instruction containing the adjustment displacement information output by the signal processing unit; According to the control instructions, the focusing lens is accurately driven to move the corresponding distance, changing the propagation path of the quantum signal light to achieve focus adjustment; S5, after the focusing lens moves, the wavefront curvature sensor again measures the wavefront aberration of the adjusted quantum signal light; Feeding back the new wavefront aberration measurement data to the signal processing unit, the quantum signal receiving end cyclically executes S3 and S4; The cycle continues, constantly adjusting the position of the focusing lens until the calculated relative defocus reaches a minimum, that is, ΔpV≈0, achieving the optimal focusing state, allowing quantum communication to transmit signals under stable focusing conditions.

2. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The proportional control algorithm part of the PID (proportion integration differentiation) control algorithm in S3 calculates the adjustment displacement u P =a*error, where a is the proportional coefficient, which determines the adjustment displacement u P The proportional relationship between the error and the error affects the adjustment speed of the focus lens. Error is the relative defocus amount ΔpV, that is, the degree of deviation between the current focus lens position and the ideal focus position.

3. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The integral control algorithm of the PID control algorithm in S3 calculates the adjustment displacement u I =b*∫error, where b is the integral coefficient, ∫error is the integral of the error error, and the integral coefficient b affects the ability to eliminate steady-state errors. The focus lens position is adjusted by accumulating errors so that the focus lens reaches the ideal focus position, that is, the relative defocus amount ΔpV=0.

4. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The differential control algorithm part of the PID (proportion integration differentiation) control algorithm in S3 calculates the adjustment displacement u D =c*(error(n1)-error(n2)), where c is the differential coefficient, error(n1) and error(n2) are the error values ​​at two adjacent moments respectively, and the differential coefficient c adjusts the movement of the focus lens according to the rate of change of the error, and prevents the focus lens from crossing the ideal focus position in the target due to excessive execution of the focus execution unit, thereby ensuring the accuracy and smoothness of the focusing process.

5. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The final control instruction of S4 is u=u P +u I +u D , the results of the proportional, integral and differential control algorithms are integrated to accurately control the movement of the focusing lens, allowing the laser signal in quantum communication to be adaptively focused.

6. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The focusing lens in S1 is a convex lens with a focal length of f and an inner diameter of R. When the distance between the focusing lens and the focal plane is equal to twice the focal length f, the clearest image is obtained on the focal plane, which is an ideal state. The image is an inverted real image of the actual object being measured.

7. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: The focusing lens in S1 differs from the focusing lens in the ideal state by ΔL, but the focal length f remains unchanged. When the distance between the focal plane and the center of the focusing lens is greater than the focal length f but not equal to 2f, the image on the focal plane is scattered and blurred. When the distance between the focal plane and the center of the focusing lens is less than f, the image cannot be received on the focal plane, which is a non-ideal state. When ΔL is equal to zero, the focal plane obtains a clear and equal-sized image.

8. The adaptive focusing method for laser quantum communication according to claim 1, characterized in that: In the S3, the host computer automatically calculates the defocus amount, and transmits the data received by the wavefront curvature sensor to the host computer to automatically calculate the defocus amount.

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