A high-precision photon fast ranging system based on laser radar assistance

Abstract

The present invention proposes a laser radar-assisted photon fast ranging system, which includes a mechanically rotating three-dimensional multi-line laser radar and an entangled photon ranging platform. First, the laser radar device is fixedly installed on the quantum ranging platform, the laser radar is started to obtain the target point cloud data, the point set with a large reflection intensity value is screened out, and the abnormal value is filtered out; secondly, through the angle relationship between the laser radar and the quantum ranging platform, the vertical angle of the data point under the laser radar is calculated to obtain the corresponding vertical angle under the quantum ranging platform, the reflector is adjusted to align the target point with the quantum ranging platform, and the distance value of the target ranging point is calculated by the coincidence count and the second-order correlation function; finally, the quantum ranging results obtained under the same target are averaged to obtain the quantum ranging result of the target.

Description

Technical Field

[0001] The present invention relates to the field of quantum precision measurement, specifically to determining the orientation of a target using the angular resolution of a laser radar, and then measuring the distance of the target using coincidence counting based on the correlation characteristics of entangled light quanta, thereby greatly reducing the time required for target alignment in the quantum ranging process and improving the ranging accuracy. Background Art

[0002] In recent years, LiDAR technology has developed rapidly around the world and is mainly used for environmental detection and map construction. Mechanical rotary LiDAR represented by time of flight (TOF) is mainly based on the theory of light speed ranging. A laser pulse is emitted by a laser, and the emission time is recorded by a timer. The return light is received by a receiver, and the return time is recorded by a timer. The "flight time" of light is obtained by subtracting the two times, and the distance information is obtained by calculating the speed of light.

[0003] The echo signal of the laser radar is a key factor affecting the ranging accuracy, and the threshold detection module is a key part of the echo signal detection. The threshold detection circuit in the receiver is a pulse peak comparator. When the echo pulse amplitude exceeds the threshold, the echo is considered to have arrived. The advantage of this method is simplicity, but there are two main disadvantages. First, whether it is a co-wave pulse or a clutter interference pulse, as long as one pulse amplitude exceeds the threshold, the detection circuit will determine it as an echo, resulting in a false alarm; secondly, the change in the echo pulse amplitude will cause an error in the arrival time, resulting in a ranging error. Therefore, when the laser radar system measures targets at different distances, the threshold detection circuit judgment deviation caused by changes in pulse amplitude and pulse shape will have a greater impact on the laser radar ranging accuracy.

[0004] The photon ranging system utilizes the unique frequency entanglement characteristics of photons, and uses single-photon detectors to receive two entangled optical signals (reference optical path and signal optical path) respectively. Finally, the two collected signals are counted by coincidence to obtain the delay, and then the measurement result is obtained. Only when the frequency entangled photon pairs are counted by coincidence, the fitted curve satisfies the second-order correlation characteristics, and the single-photon detector involved in this method is an ultra-high sensitivity and ultra-low noise device that can detect the minimum energy quantum of light - photons, and is expected to achieve high-precision ranging at long distances. The photon ranging system avoids the direct identification of the amplitude and shape of the rising / falling edge of the optical pulse during the laser radar ranging process, and utilizes the second-order correlation characteristics of entangled photons and counts the entangled photon pairs by coincidence, thereby improving the measurement accuracy of the pulse delay. This ranging system based on quantum mechanics can break through the ranging accuracy limitations caused by signal bandwidth and power, and can achieve picosecond-level time synchronization error accuracy, which will greatly improve the ranging accuracy of traditional ranging technology.

[0005] However, when using the photon ranging system to measure the target with current technical means, the optical path must be adjusted to align with the target. However, the optical signal emitted by the photon ranging system covers a very small area, which makes it difficult to quickly and accurately locate the approximate position of the target, thereby prolonging the time required for ranging. Therefore, considering the impact of the selection of ranging points on the photon ranging system, the spatial resolution capability of the lidar can effectively reduce the time required for target alignment during quantum ranging. Summary of the invention

[0006] The purpose of the present invention is to provide a laser radar-assisted photon rapid ranging system. Compared with pure laser radar ranging, the present invention utilizes the entanglement characteristics of photons and the second-order correlation characteristics of entangled photons to count the coincidences of two entangled photons collected within a certain period of time to improve the positioning accuracy. The system can achieve picosecond-level time synchronization error accuracy. At the same time, considering the condition that photon ranging requires the optical path to be strictly aligned with the target, laser radar is used to assist quantum ranging to reduce the time required for target alignment during photon ranging.

[0007] The technical solution adopted by the present invention is: a high-precision photon fast ranging system based on laser radar assistance, which includes a mechanical rotating three-dimensional multi-line laser radar and an entangled photon ranging platform, and specifically includes the following steps:

[0008] Step 1: Fix the laser radar device on the quantum ranging platform, and adjust the laser radar output port so that it is located in the same vertical plane as the signal light path output port of the quantum ranging platform, and the vertical spacing between the two output ports is fixed to d, corresponding to the number of vertical beams of the laser radar is γ;

[0009] Step 2: First, attach reflective material to the surface of the target to be measured so that the approximate position of the ranging target can be quickly found in the data obtained by the laser radar;

[0010] Step 3: Start the laser radar, obtain point cloud data through the connected computer, and select the point set M={m1,…,m i ,…,m n};

[0011] Step 4: Determine the ranging target point set L collected by the laser radar based on the point set M and the corresponding vertical azimuth angle value α = {l1,…,l i ,…,l N};

[0012] Step 5: For the target point set L, the angular relationship between the laser radar and the quantum ranging platform is used to calculate the vertical angle β corresponding to the point under the quantum ranging platform from the vertical angle α of the data point, and the vertical angle β, horizontal angle h and distance value d are calculated. l The vertical angle α and the vertical angle β have the following relationship:

[0013]

[0014] This equation is derived using the angle relationship between the lidar and the quantum ranging platform;

[0015] Step 6: Repeat step 5 N times. According to the received vertical angle β and horizontal angle h of the measured point, the angle values ​​β and h of the measuring point are averaged in pairs. Operations, a total of The target points to be measured are obtained by obtaining the quantum distance target point set Q = {q1,…,q i ,…,q N(N-1) / 2};

[0016] Step 7: Start the quantum distance measurement platform. According to the horizontal and vertical angle values ​​corresponding to each point in the target point set Q, adjust the reflector to align the quantum distance measurement platform with the target point to be measured. According to the coincidence count value n(τ) and the second-order correlation function G (2) (τ) can be used to obtain the time delay τ, and then the quantum distance measurement result d of the measured point can be obtained. q , the process is expressed as:

[0017]

[0018] Among them, T is the sampling time of the single-photon detector; R1 and R2 are the photon counting rates of the two single-photon detectors in the signal light path and the reference light path respectively, and γ1 and γ2 are their dark counting rates respectively. From the above formula, we can get:

[0019]

[0020] When R i ≥γ i When (i=1,2), we can get:

[0021]

[0022] Among them, g (2) (τ) is the normalized second-order correlation function, and the discrete points (τ, g (2) (τ)) is used for curve fitting. The abscissa corresponding to the peak of the curve is the time domain measurement result, that is, the flight time difference between the signal light and the reference light. The quantum distance measurement result of the target point is obtained as follows:

[0023]

[0024] Step 8: Repeat step 6 times, get information about the target The quantum distance measurement results are d q1 ,d q2 ,…,d qN(N-1) / 2 ;

[0025] Step 9: Get The average of the quantum distance measurement results is obtained to obtain the quantum distance measurement result for the target. The expression is:

[0026]

[0027] in, BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the optical path diagram of the entangled photon ranging platform of the present invention;

[0029] Figure 2 This is a diagram showing the placement of the laser radar and quantum ranging platform of the present invention;

[0030] Figure 3 This is a diagram showing the angle relationship between the laser radar and the quantum ranging platform of the present invention;

[0031] Figure 4 This is the target point diagram to be measured by the quantum distance measurement platform of the present invention. Specific implementation plan

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0033] Step 1: Fix the laser radar device on the quantum ranging platform, and adjust the laser radar output port so that it is located in the same vertical plane as the signal light path output port of the quantum ranging platform, and the vertical spacing between the two output ports is fixed to d, corresponding to the number of vertical beams of the laser radar is γ;

[0034] Step 2: First, attach reflective material to the surface of the target to be measured so that the approximate position of the ranging target can be quickly found in the data obtained by the laser radar;

[0035] Step 3: Start the laser radar, obtain point cloud data through the connected computer, and select the point set M={m1,…,m i ,…,m n}, the reflection intensity value here refers to the relative intensity value in the laser radar (expressed in 0 to 255). Usually, the reflection intensity value of the object is within 100, while the reflection intensity value of the point set M is required to be greater than or equal to 150;

[0036] Step 4: Determine the ranging target point set L collected by the laser radar based on the point set M and the corresponding vertical azimuth angle value α = {l1,…,l i ,…,l N}, and satisfy:

[0037]

[0038] Where 1≤i,j≤N and i≠j, d l is the distance measurement value of the laser radar to the target point, γ is the number of vertical beams of the laser radar corresponding to the vertical spacing d of the system output port, and the angle interval corresponding to each vertical beam is 2°. The abnormal values ​​outside the target range are filtered out by the proportional relationship between the distance measurement value and d;

[0039] Step 5: For the target point set L, the angular relationship between the laser radar and the quantum ranging platform is used to calculate the vertical angle β corresponding to the point under the quantum ranging platform from the vertical angle α of the data point, and the vertical angle β, horizontal angle h and distance value d are calculated. l The vertical angle α and the vertical angle β have the following relationship:

[0040]

[0041] This equation is derived using the angle relationship between the lidar and the quantum ranging platform;

[0042] Step 6: Repeat step 5 N times. According to the received vertical angle β and horizontal angle h of the measured point, the angle values ​​β and h of the measuring point are averaged in pairs. Operations, a total of The target points to be measured are obtained by obtaining the quantum distance target point set Q = {q1,…,q i ,…,q N(N-1) / 2};

[0043] Step 7: Start the quantum distance measurement platform. According to the horizontal and vertical angle values ​​corresponding to each point in the target point set Q, adjust the reflector to align the quantum distance measurement platform with the target point to be measured. According to the coincidence count value n(τ) and the second-order correlation function G (2) (τ) can be used to obtain the time delay τ, and then the quantum distance measurement result d of the measured point can be obtained. q , the process is expressed as:

[0044]

[0045] Among them, T is the sampling time of the single-photon detector; R1 and R2 are the photon counting rates of the two single-photon detectors in the signal light path and the reference light path respectively, and γ1 and γ2 are their dark counting rates respectively. From the above formula, we can get:

[0046]

[0047] When R i ≥γ i When (i=1,2), we can get:

[0048]

[0049] Among them, g (2) (τ) is the normalized second-order correlation function, and the discrete points (τ, g (2) (τ)) is used for curve fitting. The abscissa corresponding to the peak of the curve is the time domain measurement result, that is, the flight time difference between the signal light and the reference light. The quantum distance measurement result of the target point is obtained as follows:

[0050]

[0051] Step 8: Repeat step 6 times, get information about the target The quantum distance measurement results are d q1 ,d q2 ,…,d qN(N-1) / 2 ;

[0052] Step 9: Get The average of the quantum distance measurement results is obtained to obtain the quantum distance measurement result for the target. The expression is:

[0053]

[0054] in,

[0055] The step five comprises the following steps:

[0056] Step 5 (a): Use the vertical angle α measured by the laser radar to obtain the vertical distance d of the ranging point l sinα, and the vertical spacing of the exit is d. Using the principle of similar triangles, the length of the line segment k intercepted by the line connecting the quantum ranging platform and the ranging point in the horizontal direction of the laser radar and the ranging point can be obtained, satisfying the relationship:

[0057]

[0058] So, k = d l 2 sinαcosα / (d l sinα+d);

[0059] Step 5 (ii): According to the parallel relationship and the angle relationship of the truncated triangle, the corresponding vertical angle β under the quantum ranging platform can be obtained, satisfying:

[0060]

[0061] Substituting k, we can get β = arctan[(d+d l sinα) / d l cosα];

[0062] Step 5 (iii): The vertical angle β, horizontal angle h and distance value d corresponding to the distance measurement point l Transfer to the quantum distance measurement platform; the step six comprises the following steps:

[0063] Step 6 (a), according to step 5, obtain the vertical angle β and horizontal angle h corresponding to the target point set L, and the angle values ​​of β and h of N points in total;

[0064] Step 6 (ii): calculate the average value of β and h of N points in pairs to expand the number of target distance measurement points. Operations, a total of The target points to be measured are finally obtained as the quantum distance target point set Q = {q1,…,q i ,…,q N(N-1) / 2}.

Claims

1. A high-precision photon rapid ranging system based on laser radar assistance, comprising a mechanically rotating three-dimensional multi-line laser radar and an entangled photon ranging platform, characterized in that The following steps are involved: Step 1: Fix the laser radar device on the quantum ranging platform, and adjust the laser radar output port so that it is located in the same vertical plane as the signal light path output port of the quantum ranging platform, and the vertical spacing between the two output ports is fixed to d, corresponding to the number of vertical beams of the laser radar is γ; Step 2: First, attach reflective material to the surface of the target to be measured so that the approximate position of the ranging target can be quickly found in the data obtained by the laser radar; Step 3: Start the laser radar, obtain point cloud data through the connected computer, and select the point set with larger reflection intensity value M={m1,···,m i ,···,m n }; Step 4: Combine the point set M with the corresponding vertical azimuth angle value α to determine the ranging target point set L collected by the laser radar = {l1,···,l i ,···,l N }, and satisfy: Where 1≤i,j≤N and i≠j, d l is the distance measurement value of the laser radar to the target point, γ is the number of vertical beams of the laser radar corresponding to the vertical spacing d of the system output port, and the angle interval corresponding to each vertical beam is 2°. The abnormal values ​​outside the target range are filtered out by the proportional relationship between the distance measurement value and d; Step 5: For the target point set L, the angular relationship between the laser radar and the quantum ranging platform is used to calculate the vertical angle β corresponding to the point under the quantum ranging platform from the vertical angle α of the data point, and the vertical angle β, horizontal angle h and distance value d are calculated. l Transmitted to the quantum ranging platform; the vertical angle α and the vertical angle β have the following relationship: This equation is derived using the angle relationship between the lidar and the quantum ranging platform; Step 6: Repeat step 5 N times. According to the received vertical angle β and horizontal angle h of the measured point, the angle values ​​β and h of the measuring point are averaged in pairs. Operations, a total of The target points to be measured are obtained by obtaining the quantum distance target point set Q = {q1, ···, q i ,···,q N(N-1) / 2 }; Step 7: Start the quantum distance measurement platform. According to the horizontal and vertical angle values ​​corresponding to each point in the target point set Q, adjust the reflector to align the quantum distance measurement platform with the target point to be measured. According to the coincidence count value n(τ) and the second-order correlation function G (2) (τ) to obtain the time delay τ, and then obtain the quantum distance measurement result d of the point to be measured q , the process is expressed as: Among them, T is the sampling time of the single-photon detector; R1 and R2 are the photon counting rates of the two single-photon detectors in the signal light path and the reference light path respectively, and γ1 and γ2 are their dark counting rates respectively. From the above formula, we can get: When R i ≥γ i ,i=1,2, we get: Among them, g (2) (τ) is the normalized second-order correlation function, and the discrete points (τ, g (2) (τ)) is used for curve fitting. The abscissa corresponding to the peak of the curve is the time domain measurement result, that is, the flight time difference between the signal light and the reference light. The quantum distance measurement result of the target point is obtained as follows: Step 8: Repeat step 6 times, get information about the target The quantum distance measurement results are d q1 ,d q2 ,···,d qN(N-1) / 2 ; Step 9: Get The average of the quantum distance measurement results is obtained to obtain the quantum distance measurement result for the target. The expression is: in, The step five comprises the following steps: Step 5 (a): Use the vertical angle α measured by the laser radar to obtain the vertical distance d of the ranging point l sinα, and the vertical spacing of the exit is d. The length of the line segment k intercepted by the line connecting the quantum ranging platform and the ranging point in the horizontal direction of the laser radar and the ranging point is obtained by using the principle of similar triangles, satisfying the relationship: It is obtained that k = d l 2 sinαcosα / (d l sinα + d); Step 5 (ii): According to the parallel relationship and the angle relationship of the truncated triangle, the corresponding vertical angle β under the quantum ranging platform is obtained, satisfying: Substituting k, we get β = arctan[(d+d l sinα) / d l cosα]; Step 5 (iii): The vertical angle β, horizontal angle h and distance value d corresponding to the distance measurement point l Transfer to the quantum distance measurement platform; the step six comprises the following steps: Step 6 (a), according to step 5, obtain the vertical angle β and horizontal angle h corresponding to the target point set L, and the angle values ​​of β and h of N points in total; Step 6 (ii): calculate the average value of β and h of N points in pairs to expand the number of target distance measurement points. Operations, a total of The target points to be measured are finally obtained as the quantum distance target point set Q = {q1, ···, q i ,···,q N(N-1) / 2 }.

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