Self-adaptive coincidence gate width optimization quantum imaging method based on scattering free path

Abstract

The invention provides an adaptive coincidence gate width optimization quantum imaging method based on a scattering free path. Firstly, pump light pumps a PPKTP crystal, and an entangled photon pair is generated through the SPDC process; then, separating the photons by using a PBS (Phosphate Buffer Solution), transmitting the photons along a reference light path and a signal light path containing a scattering environment respectively, and acquiring a photon arrival time sequence by a corresponding detector; thirdly, simulating a transmission process of signal photons in a scattering environment based on a Monte Carlo method, calculating a total scattering free path, counting the number of photons of each pixel point under different scattering times, and further screening out the optimal scattering times with the maximum number of photons; then, calculating a delay inequality according to a minimum total scattering free path corresponding to the optimal number of scattering times, and determining a self-adaptive coincidence gate width in combination with a fluctuation range of the total scattering free path; and finally, correcting a signal photon arrival time sequence by using the delay inequality, completing pixel-by-pixel coincidence counting based on the corrected time sequence and the coincidence gate width, and obtaining a quantum grayscale image through linear mapping.

Description

Technical Field

[0001] This invention belongs to the field of quantum imaging technology, and specifically relates to the optimization of quantum imaging quality under dynamic scattering environment. More specifically, it relates to an adaptive coincidence gate width adjustment method based on real-time estimation of scattering free path, which aims to improve the resolution of quantum imaging in complex scattering scenarios. Background Technology

[0002] Traditional optical imaging techniques face numerous bottlenecks in complex scattering environments, such as atmospheric scattering, biological tissue scattering, and turbid water scattering. When photons propagate through a scattering medium, they undergo multiple scatterings with medium particles, leading to deviations in the propagation direction and phase disturbances of the imaging beam. This results in reduced imaging resolution, blurred target details, and increased background noise, making it difficult to achieve effective target detection and imaging.

[0003] Quantum imaging technology, with its unique quantum entanglement properties, has shown great application potential in fields such as super-resolution imaging and imaging through scattering media. Unlike traditional optical imaging, which relies on the intensity distribution of a single beam, quantum imaging systems detect entangled photon pairs or correlated photon pairs in a thermal field, utilizing the quantum correlation between signal photons and reference photons to achieve imaging. This correlation characteristic allows the system to effectively distinguish between effective signal photons reflected from the target and noise photons generated by scattering, significantly improving the imaging's resistance to scattering interference. Simultaneously, quantum imaging technology has significant advantages in low-light detection scenarios; even when photon energy is significantly attenuated due to scattering media, weak effective signals can still be captured through correlation measurements, ensuring the effectiveness of the imaging. Furthermore, the non-local nature of quantum imaging can overcome the obstruction limitations of scattering media, enabling indirect imaging of concealed targets and expanding the application boundaries of imaging technology in scattering environments. This has important application value in key areas such as remote sensing monitoring, biomedical deep imaging, and target identification in severe weather.

[0004] Coincidence measurement is the core step in quantum imaging for extracting correlated signals. The coincidence gate width, as a key parameter in coincidence measurement, directly determines the matching accuracy between signal photons and reference photons, thus affecting image quality and overall system performance. Currently, quantum imaging technology often uses a fixed coincidence gate width in scattering environments. This approach is simple to operate and has low system implementation costs, but it is difficult to adapt to the dynamic characteristics of scattering environments. In different scattering scenarios, the scattering intensity of the medium varies, and the number of scattering events and scattering angles during photon transmission differ, resulting in significant differences in the range of propagation time difference fluctuations between signal photons and idle photons. When the scattering intensity is high, a fixed coincidence gate width often cannot completely cover the range of propagation time difference fluctuations. Some effective signal photons will be misjudged as noise and discarded because they exceed the gate width range, leading to decreased imaging contrast and reduced effective signal utilization. When the scattering intensity is low, a fixed wide gate width will introduce a large number of background noise photons, reducing the specificity of the coincidence measurement and worsening the system's signal-to-noise ratio.

[0005] To address the aforementioned issues and achieve high-resolution quantum imaging under dynamic scattering environments, this invention proposes an adaptive coincidence gate width optimization quantum imaging method based on the scattering free path, aiming to improve the imaging quality of quantum imaging under scattering environments. Summary of the Invention

[0006] The purpose of this invention is to provide a quantum imaging method based on adaptive coincidence gate optimization using the scattering free path. This method dynamically adjusts the coincidence measurement gate width parameter by estimating the scattering free path of the imaging environment in real time, thereby solving the problem of poor imaging quality in dynamic scattering environments with a fixed coincidence gate width and improving the resolution of quantum imaging.

[0007] The technical solution adopted in this invention is: an adaptive coincidence gate width optimization quantum imaging method based on scattering free path, comprising the following specific steps:

[0008] Step 1: Select a 405nm wavelength laser as the pump light, output from the pump source, and pass sequentially through a collimator, lens, half-wave plate (HWP), quarter-wave plate (QWP), and polarizing beam splitter (PBS); through the synergistic effect of HWP and QWP, the pump light is adjusted to a linear polarization state;

[0009] Step 2: The pump light is then focused by a lens and incident on a periodically polarized potassium titanium phosphate (PKTP) crystal. Under quasi-phase-matching conditions, a pair of signal photons and reference photons with a wavelength of 810 nm and polarization entanglement characteristics are generated with a certain probability.

[0010] Step 3: The entangled photon pairs are then incident on the PBS, where the PBS separates them into the signal path and the reference path according to the photon polarization direction;

[0011] Step 4: After the signal light passes through the smoke environment, it reaches the barrel detector, while the reference light is incident on the DMD for two-dimensional planar scanning and is finally received by the surface detector.

[0012] Step 5: Record the arrival time series received by the bucket detector and the area detector at a certain pixel (i, j), and record them as follows: and ;

[0013] Step Six: Simulate the transmission process of signal light in a smoky environment using the Monte Carlo method, so as to analyze the arrival time series of signal photons collected in Step Five based on the photon transmission path in subsequent steps. Perform analysis;

[0014] Step 7: Perform photon tracking on each pixel, including the complete process of photons originating from the PBS, traveling through the smoke environment to the detector, and counting the cumulative number of photon scatterings k.

[0015] Step 8: Based on Step 6, when a photon experiences a total of k collisions during transmission, its total scattering free path can be expressed as:

[0016]

[0017] Step 9: Based on the correspondence between the number of scattering events and the total scattering free path established in the previous steps, count and select the optimal number of scattering events that maximizes the number of photons at pixel (i, j). ; based on the number of scatterings The flight time of the next photon is used as the delay difference between the signal optical path and the reference optical path. This is used for subsequent time-series correction; simultaneously, it determines the fluctuation range of the photon free path for this number of scattering events, and then calculates the adaptive coincidence gate width for subsequent coincidence counting. ;

[0018] Step 10: The reference photon does not need to pass through the smoke environment; its arrival time series Keep it unchanged; use the time delay difference calculated in step nine. For the arrival time series of signal photons Correction is performed to obtain the corrected signal photon arrival time series. The expression is:

[0019]

[0020] Step 11: For this pixel, based on the corrected signal optical path arrival time sequence and the conforming door width obtained in step nine Perform coincidence counting operate;

[0021] Step 12: Repeat the above operation in pixels to traverse all pixels in the imaging area and complete the coincidence count to obtain the coincidence count matrix of the entire area;

[0022] Step 13: Arrange the coincidence count matrix according to the two-dimensional coordinates of the pixels, and then apply the linear mapping method to... The image is mapped to grayscale values, and the quantum grayscale image of the target is finally obtained, thus completing the global imaging operation.

[0023] Step six includes the following steps:

[0024] Step Six (I) Based on smoke concentration Smoke density Given the smoke particle radius r, the smoke particle density is calculated as follows:

[0025]

[0026] Step 6 (II): Let the scattering cross section of a single smoke particle be... Based on the anisotropy factor g, the total scattering probability of photons per unit volume can be calculated as follows:

[0027]

[0028] in , The scattering phase function, The scattering angle;

[0029] Step 6 (3): Based on the Lambert-Beer law, the expression for the scattering free path of a photon during propagation is derived as follows:

[0030]

[0031] In the formula, To take values ​​in Random numbers between It is the probability density function of photon scattering;

[0032] Step Six (IV): Based on the core idea of ​​Monte Carlo simulation, the scattering process of photons is simulated using random numbers, specifically defined as: introducing random numbers... and This is used to simulate the scattering free path of photons in actual scattering environments and ideal no-scattering conditions, respectively. ;

[0033] Step Six (V): The scattering free path of photons after the nth collision with smoke particles in a smoky environment. It can be represented as:

[0034]

[0035] in, After the nth collision, the photon passes through The number of photons remaining after reaching the (n+1)th collision point. It is the number of photons remaining at the nth collision point. If the photons do not collide with smoke particles during transmission, then under this ideal no-scattering condition, there are... .

[0036] Step nine includes the following steps:

[0037] Step 9 (a): Extract the arrival time series of signal photons collected by the bucket detector at pixel (i,j). Based on the correspondence between photon arrival time and total scattering free path, count the number of photons corresponding to different scattering times k at this pixel. ;

[0038] Step Nine (II): Determine the number of photons The number of scatterings corresponding to the peak value is the optimal number of scatterings. It satisfies:

[0039]

[0040] in, Indicates to make The photon corresponding to the number of scattering events that achieves the maximum value of k is the main component of the signal photon;

[0041] Step Nine (III): Based on the optimal number of scattering operations From all those with Extract the corresponding minimum total scattering free path from the secondary scattered photons. And calculate the time delay difference between the signal optical path and the reference optical path. :

[0042]

[0043] in, Indicates the number of scatterings The minimum total scattering free path of a photon; c is the speed of light, its value is... This time delay difference is the reference time difference between the signal photon and the reference photon arriving at the detector at pixel (i,j);

[0044] Step Nine (IV) At the optimal number of scattering operations Below, the maximum value of the total scattering free path of photons is extracted. and minimum value ,calculate Range of free path of total photon scattering under secondary scattering :

[0045]

[0046] Step 9 (5): Convert the free path fluctuation range into a time fluctuation range, and calculate the adaptive coincidence gate width of the current pixel. :

[0047]

[0048] The door width can accurately cover The arrival time range of effective signal photons under secondary scattering. Attached Figure Description

[0049] Figure 1 This is the optical path diagram for quantum imaging in a smoky environment according to the present invention;

[0050] Figure 2 The number of scattering events in this invention The photon propagation path below;

[0051] Figure 3 This is a schematic diagram of the adaptive conformal gate width optimization method of the present invention;

[0052] Figure 4 This is a schematic diagram illustrating the counting principle of the present invention. Detailed Implementation Plan

[0053] The present invention will now be described in further detail with reference to the accompanying drawings:

[0054] Step 1: Select a 405nm wavelength laser as the pump light, output from the pump source, and pass sequentially through collimator 1, lens 1, half-wave plate (HWP), quarter-wave plate (QWP), and polarizing beam splitter 1 (PBS); through the synergistic effect of HWP and QWP, the pump light is adjusted to a linear polarization state;

[0055] Step 2: The pump light is then focused by lens 2 and incident on a periodically polarized potassium titanium phosphate (PKTP) crystal. Under quasi-phase matching conditions, a pair of signal photons and reference photons with a wavelength of 810 nm and polarization entanglement characteristics are generated with a certain probability.

[0056] Step 3: The entangled photon pairs are then incident on PBS2, where PBS2 separates them into the signal path and the reference path according to the photon polarization direction;

[0057] Step 4: After passing through the smoke environment, the signal light reaches the barrel detector, while the reference light is incident on the Digital Micromirror Device (DMD) for two-dimensional planar scanning and is finally received by the surface detector.

[0058] Step 5: When the DMD scans pixel by pixel within the imaging area, record the single-pixel scan time. The arrival time pulse sequence of signal photons at pixel (i, j) detected by the inner barrel detector and the surface detector, respectively. and reference photon arrival time pulse sequence ,in , It is the duty cycle time of a single-photon detector;

[0059] Step Six: Simulate the transmission process of signal light in a smoky environment using the Monte Carlo method, so as to analyze the arrival time series of signal photons collected in Step Five based on the photon transmission path in subsequent steps. Perform analysis;

[0060] Step 7: Perform photon tracking on each pixel, including the complete process of photons originating from the PBS, traveling through the smoke environment to the detector, and counting the cumulative number of photon scatterings k.

[0061] Step 8: As shown in Step 6, when a photon undergoes k scattering events during transmission, its total scattering free path can be expressed as:

[0062]

[0063] Step 9: Based on the correspondence between the number of scattering events and the total scattering free path established in the previous steps, count and determine the optimal number of scattering events that maximizes the number of photons at pixel (i, j). ; based on the number of scatterings The flight time of the next photon is used as the delay difference between the signal optical path and the reference optical path. This is used for subsequent time series correction; simultaneously, the fluctuation range of the photon free path under this scattering number is determined, and then the adaptive coincidence gate width for subsequent coincidence counting is calculated. ;

[0064] Step 10: The reference photon does not need to pass through the smoke environment; its arrival time series Keep it unchanged; use the time delay difference obtained in step nine. Time series of signal photons Perform correction to obtain the corrected sequence. The expression is:

[0065]

[0066] Step 11: For this pixel, based on the corrected signal optical path arrival time sequence and the conforming gate width calculated in step nine Perform conformity counting operate;

[0067] Step 12: Repeat the above operation in pixels to traverse all pixels in the imaging area and complete the coincidence count to obtain the coincidence count matrix of the entire area;

[0068] Step 13: Arrange the coincidence count matrix according to the two-dimensional coordinates of the pixels, and then apply the linear mapping method to... The image is mapped to grayscale values, and the quantum grayscale image of the target is finally obtained, thus completing the global imaging operation.

[0069] Step six includes the following steps:

[0070] Step Six (I) Based on smoke concentration Smoke density Given the smoke particle radius r, the smoke particle density is calculated as follows:

[0071]

[0072] Step 6 (II): Let the scattering cross section of a single smoke particle be... Based on the anisotropy factor g, the total scattering probability of photons per unit volume can be calculated as follows:

[0073]

[0074] in, , The scattering phase function, The scattering angle;

[0075] Step 6 (3): Based on the Lambert-Beer law, the expression for the scattering free path of a photon during propagation is derived as follows:

[0076]

[0077] In the formula, To take values ​​in Random numbers between It is the probability density function of photon scattering;

[0078] Step Six (IV): Based on the core idea of ​​the Monte Carlo method, random numbers are used to simulate the photon scattering process. Specifically, this is defined as: introducing random numbers... and This is used to simulate the scattering free path of photons in actual scattering environments and ideal no-scattering conditions, respectively. ;

[0079] Step Six (V): In a smoky environment, after the photon collides with the smoke particles for the nth time, its scattering free path... It can be represented as:

[0080]

[0081] in, After the nth collision of the photon, The number of photons remaining after reaching the (n+1)th collision point. It is the number of photons remaining at the nth collision point; if the photons do not collide with smoke particles during transmission, then under ideal no-scattering conditions, there are .

[0082] Step nine includes the following steps:

[0083] Step 9 (i): Extract the arrival time series of signal photons collected by the bucket detector at pixel (i, j). Based on the correspondence between photon arrival time and total scattering free path, count the number of photons corresponding to this pixel at different scattering times k. ;

[0084] Step Nine (II): Determine the number of photons The number of scatterings corresponding to the peak value is the optimal number of scatterings. It satisfies:

[0085]

[0086] in, Indicates to make The k value that achieves the maximum value corresponds to the photons that constitute the main component of the signal photons.

[0087] Step Nine (III): Based on the optimal number of scattering operations From all experiences Extract the corresponding minimum total scattering free path from the secondary scattered photons. And calculate the time delay difference between the signal optical path and the reference optical path. :

[0088]

[0089] in, Indicates the number of scatterings The minimum total scattering free path of a photon; c is the speed of light, its value is... This time delay difference is the reference time difference between the signal photon and the reference photon arriving at the detector at pixel (i, j);

[0090] Step Nine (IV) At the optimal number of scattering operations Below, the maximum value of the total scattering free path of photons is extracted. and minimum value ,calculate Range of free path of total photon scattering under secondary scattering :

[0091]

[0092] Step 9 (5): Convert the free path fluctuation range into a time fluctuation range to obtain the adaptive conformance gate width of the current pixel. :

[0093]

[0094] The door width can accurately cover The arrival time range of effective signal photons under secondary scattering.

Claims

1. A quantum imaging method based on adaptive coincidence gate width optimization using scattering free path, characterized in that... Includes the following steps: Step 1: Select a 405nm wavelength laser as the pump light, output from the pump source, and pass sequentially through collimator 1, lens 1, half-wave plate (HWP), quarter-wave plate (QWP), and polarizing beam splitter 1 (PBS); through the synergistic effect of HWP and QWP, the pump light is adjusted to a linear polarization state; Step 2: The pump light is then focused by lens 2 and incident on a periodically polarized potassium titanium phosphate (PPKTP) crystal. Under quasi-phase matching conditions, a pair of signal photons and reference photons with a wavelength of 810 nm and polarization entanglement characteristics are generated with a certain probability. Step 3: The entangled photon pairs are then incident on PBS2, where PBS2 separates them into the signal path and the reference path according to the photon polarization direction; Step 4: After passing through the smoke environment, the signal light reaches the barrel detector, while the reference light is incident on the Digital Micromirror Device (DMD) for two-dimensional planar scanning and is finally received by the surface detector. Step 5: When the DMD scans pixel by pixel within the imaging area, record the single-pixel scan time. The arrival time pulse sequence of signal photons at pixel (i, j) detected by the inner barrel detector and the surface detector, respectively. and reference photon arrival time pulse sequence ,in , It is the duty cycle time of a single-photon detector; Step Six: Simulate the transmission process of signal light in a smoky environment using the Monte Carlo method, so as to analyze the arrival time series of signal photons collected in Step Five based on the photon transmission path in subsequent steps. Perform analysis; Step 7: Perform photon tracking on each pixel, including the complete process of photons originating from the PBS, traveling through the smoke environment to the detector, and counting the cumulative number of photon scatterings k. Step 8: As shown in Step 6, when a photon undergoes k scattering events during transmission, its total scattering free path can be expressed as: Step 9: Based on the correspondence between the number of scattering events and the total scattering free path established in the previous steps, count and determine the optimal number of scattering events that maximizes the number of photons at pixel (i, j). ; based on the number of scatterings The flight time of the next photon is used as the delay difference between the signal optical path and the reference optical path. This is used for subsequent time series correction; simultaneously, the fluctuation range of the photon free path under this scattering number is determined, and then the adaptive coincidence gate width for subsequent coincidence counting is calculated. ; Step 10: The reference photon does not need to pass through the smoke environment; its arrival time series Keep it unchanged; use the time delay difference obtained in step nine. Time series of signal photons The corrected sequence is obtained by performing correction. The expression is: Step 11: For this pixel, based on the corrected signal optical path arrival time sequence and the conforming gate width calculated in step nine Perform conformity counting operate; Step 12: Repeat the above operation in pixels to traverse all pixels in the imaging area and complete the coincidence count to obtain the coincidence count matrix of the entire area; Step 13: Arrange the coincidence count matrix according to the two-dimensional coordinates of the pixels, and then apply the linear mapping method to... The image is mapped to grayscale values, and the quantum grayscale image of the target is finally obtained, thus completing the global imaging operation.

2. The photon transmission path simulation method in the adaptive coincidence gate width optimization quantum imaging method based on scattering free path as described in claim 2, characterized in that: Step six includes the following steps: Step Six (I) Based on smoke concentration Smoke density Given the smoke particle radius r, the smoke particle density is calculated as follows: Step 6 (II): Let the scattering cross section of a single smoke particle be... Based on the anisotropy factor g, the total scattering probability of photons per unit volume can be calculated as follows: in, , The scattering phase function, The scattering angle; Step 6 (3): Based on the Lambert-Beer law, the expression for the scattering free path of a photon during propagation is derived as follows: In the formula, To take values ​​in Random numbers between It is the probability density function of photon scattering; Step Six (IV): Based on the core idea of ​​the Monte Carlo method, random numbers are used to simulate the photon scattering process. Specifically, this is defined as: introducing random numbers... and This is used to simulate the scattering free path of photons in actual scattering environments and ideal no-scattering conditions, respectively. ; Step Six (V): In a smoky environment, after the photon collides with the smoke particles for the nth time, its scattering free path... It can be represented as: in, After the nth collision of the photon, The number of photons remaining after reaching the (n+1)th collision point. It is the number of photons remaining at the nth collision point; if the photons do not collide with smoke particles during transmission, then under ideal no-scattering conditions, there are .

3. The coincidence gate calculation method in the adaptive coincidence gate width optimization quantum imaging method based on scattering free path according to claim 1, characterized in that: Step nine includes the following steps: Step 9 (i): Extract the arrival time series of signal photons collected by the bucket detector at pixel (i, j). Based on the correspondence between photon arrival time and total scattering free path, count the number of photons corresponding to this pixel at different scattering times k. ; Step Nine (II): Determine the number of photons The number of scatterings corresponding to the peak value is the optimal number of scatterings. It satisfies: in, Indicates to make The k value that achieves the maximum value corresponds to the photons that constitute the main component of the signal photons. Step Nine (III): Based on the optimal number of scattering operations From all experiences Extract the corresponding minimum total scattering free path from the secondary scattered photons. And calculate the time delay difference between the signal optical path and the reference optical path. : in, Indicates the number of scatterings The minimum total scattering free path of a photon; c is the speed of light, its value is... This time delay difference is the reference time difference between the signal photon and the reference photon arriving at the detector at pixel (i, j); Step Nine (IV) At the optimal number of scattering operations Below, the maximum value of the total scattering free path of photons is extracted. and minimum value ,calculate Range of free path of total photon scattering under secondary scattering : Step 9 (5): Convert the free path fluctuation range into a time fluctuation range to obtain the adaptive conformance gate width of the current pixel. : The door width can accurately cover The arrival time range of effective signal photons under secondary scattering.

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