CN-121995680-A - Self-adaptive coincidence gate width optimization quantum imaging method based on scattering free range

Abstract

The invention provides a self-adaptive coincidence gate width optimization quantum imaging method based on a scattering free range. The method comprises the steps of generating a pair of entangled photon pairs by pumping PPKTP crystals through an SPDC process, separating the entangled photon pairs by utilizing PBS, respectively transmitting the entangled photon pairs along a reference light path and a signal light path containing a scattering environment, collecting photon arrival time sequences by corresponding detectors, simulating the transmission process of signal photons in the scattering environment based on a Monte Carlo method, calculating total scattering free ranges, counting the number of photons of each pixel under different scattering times, further screening out the optimal scattering times with the maximum number of photons, calculating time delay difference according to the minimum total scattering free ranges corresponding to the optimal scattering times, determining self-adaptive coincidence gate width by combining the fluctuation range of the total scattering free ranges, correcting the signal photon arrival time sequences by utilizing the time delay difference, finishing pixel-by-pixel coincidence counting based on the corrected time sequences and the coincidence gate width, and linearly mapping to obtain a quantum gray image.

Inventors

• ZHANG MUYU
• ZHOU MU
• CAO JINGYANG
• PU QIAOLIN
• FANG JIE

Assignees

• 重庆邮电大学

Dates

Publication Date

20260508

Application Date

20260123

Claims (3)

1. 1. The self-adaptive coincidence gate width optimized quantum imaging method based on scattering free range is characterized by comprising the following steps: the method comprises the steps of selecting laser with the wavelength of 405nm as pump light, outputting the pump light by a pump light source, sequentially passing through a collimator 1, a lens 1, a half wave plate (HALF WAVE PLATE, HWP), a Quarter wave plate (quartz WAVE PLATE, QWP) and a polarization beam splitter 1 (Polarizing Beam Splitter, PBS), and adjusting the pump light into a linear polarization state through the synergistic effect of HWP and QWP; Step two, the pump light is condensed by a lens 2 and is incident to a periodically polarized potassium titanyl phosphate (Periodically Poled KTiOPO, PPKTP) crystal, and a pair of signal photons with 810nm wavelength and polarization entanglement characteristic and reference photons are generated with a certain probability under the quasi-phase matching condition; Step three, the entangled photon pair is then incident to PBS2, and the entangled photon pair is separated into a signal light path and a reference light path by the PBS2 according to the polarization direction of the photon; the signal light passes through the smoke environment and then reaches the barrel detector, and the reference light is incident to a digital micromirror device (Digital Micromirror Devices, DMD) to perform two-dimensional plane scanning and finally received by the face detector; Fifth, when the DMD scans point by point in the imaging area in pixel units, recording single pixel scanning time Signal photon arrival time pulse sequence at pixel point (i, j) detected by inner barrel detector and surface detector respectively And a reference photon arrival time pulse sequence Wherein , Is the duty cycle time of a single photon detector; Simulating the transmission process of the signal light in the smoke environment by adopting a Monte Carlo method so as to enable the signal photons acquired in the fifth step to arrive at a time sequence based on a photon transmission path in the subsequent step Analyzing; step seven, respectively carrying out photon tracking on each pixel point, including the complete process that photons start from PBS and are transmitted to a detector through a smoke environment, and counting the accumulated scattering times k of the photons; step eight, according to the step six, when the photons are scattered for k times in the transmission process, the total scattering free path can be expressed as: Step nine, counting and determining the optimal scattering times with the highest photon number at the pixel point (i, j) according to the corresponding relation between the scattering times and the total scattering free range established in the previous step And the scattering times are used The time of flight of the lower photon is used as the delay difference between the signal light path and the reference light path And simultaneously, determining the fluctuation range of the photon free path under the scattering times, and further calculating the self-adaptive coincidence gate width for subsequent coincidence counting ; Tenth step, the reference photon does not need to pass through the smoke environment, its arrival time sequence Keeping unchanged by using the time delay difference obtained in the step nine For time series of arrival of signal photons Correcting to obtain corrected sequence The expression is: Step eleven, aiming at the pixel point, according to the corrected signal light path arrival time sequence And step nine, calculating to obtain the coincidence door width Performing coincidence counting Operating; The twelve steps are that the pixel is used as a unit, the operation is repeated, all pixel points in the imaging area are traversed, coincidence counting is completed, and a coincidence count value matrix of the whole area is obtained; Thirteenth, arranging the matrix conforming to the count value according to the two-dimensional coordinates of the pixel points, and using the linear mapping method Mapping the image into gray values to finally obtain a quantum gray image of the target, so as to finish global imaging operation.
2. 2. The method for simulating a photon transmission path in an adaptive coincidence gate width optimized quantum imaging method based on free scattering path of claim, wherein said step six comprises the steps of: step six (one) based on smoke concentration Density of smoke And the radius r of the smoke particles, and the density of the smoke particles is calculated as follows: Step six (two), setting the scattering cross section of single smoke particles as Based on the anisotropy factor g, the total scattering probability of photons per unit volume can be calculated as: Wherein, the , As a function of the scattering phase, Is a scattering angle; step six (three), deriving a scattering free range expression of photons in the transmission process according to the lambert-beer law, wherein the expression is as follows: in the formula, To take the value at A random number between the two random numbers, Is a function of the scattering probability density of photons; Step six (four), based on the core idea of Monte Carlo method, adopting random numbers to simulate the scattering process of photons, specifically defined as respectively introducing random numbers And For simulating the free scattering path of photons in an actual scattering environment and in ideal non-scattering conditions, respectively, wherein ; Step six (fifth), in the smoke environment, after the photon and the smoke particle collide for the nth time, the photon and the smoke particle scatter the free path Can be expressed as: Wherein, the After the nth collision of the photons, the optical fiber is processed by The number of residual photons reaching the n+1st collision point, The number of remaining photons at the nth collision point is the number of remaining photons at the nth collision point if the photons do not collide with smoke particles during transmission, the photons are under ideal scattering-free conditions 。
3. 3. The method for computing the coincidence gate width in the adaptive coincidence gate width optimized quantum imaging method based on free scattering path of claim, wherein step nine comprises the following steps: Step nine, extracting a signal photon arrival time sequence acquired by a barrel detector at a pixel point (i, j), and counting the photon quantity corresponding to the pixel point under different scattering times k according to the corresponding relation between photon arrival time and total scattering free range ; Step nine (two), determining photon number The scattering times corresponding to the peak value of (a) is the optimal scattering times It satisfies the following conditions: Wherein, the Representation and rendering of Obtaining the k value of the maximum value, wherein photons corresponding to the scattering times form the main component of the signal photons; step nine (three) based on optimal scattering times From all experiences Extracting the corresponding minimum total scattering free range from the sub-scattered photons And calculates the time delay difference between the signal light path and the reference light path : Wherein, the Expressed in scattering times The minimum total scattering free path of the lower photon, c is the speed of light, which is . The time delay difference is the reference time difference between the signal photon and the reference photon at the pixel point (i, j) and reaching the detector; step nine (four), at the optimal scattering times Extracting the maximum value of the total scattering free path of photons And minimum value of Calculation of Fluctuation range of total scattering free range of photons under secondary scattering : Step nine (fifth), converting the free range fluctuation range into a time floating range to obtain the self-adaptive coincidence gate width of the current pixel point : The door width can be accurately covered Time range of arrival of the useful signal photons at the secondary scattering.

Description

Self-adaptive coincidence gate width optimization quantum imaging method based on scattering free range Technical Field The invention belongs to the technical field of quantum imaging, in particular relates to quantum imaging quality optimization in a dynamic scattering environment, and particularly relates to a self-adaptive coincidence gate width adjustment method based on scattering free range real-time estimation, aiming at improving the resolution of quantum imaging in a complex scattering scene. Background In complex scattering environments such as atmospheric scattering, biological tissue scattering, turbid water scattering and the like, the traditional optical imaging technology faces a plurality of bottlenecks. When photons are transmitted in a scattering medium, the photons can be scattered with medium particles for multiple times, so that the propagation direction of an imaging beam is deviated and the phase is disordered, and finally the problems of reduced imaging resolution, fuzzy target details, enhanced background noise and the like are presented, and effective detection and imaging of a target are difficult to realize. The quantum imaging technology has great application potential in the fields of super-resolution imaging, penetrating scattering medium imaging and the like by virtue of the unique quantum entanglement characteristic. Unlike traditional optical imaging which relies on the intensity distribution of a single beam, quantum imaging systems utilize quantum correlation between signal photons and reference photons by detecting entangled photon pairs or correlated photon pairs in a thermal optical field. The correlation characteristic enables the system to effectively distinguish effective signal photons reflected by the target from noise photons generated by scattering, remarkably improves the anti-scattering interference capability of imaging, simultaneously, the quantum imaging technology has great advantages in a weak light detection scene, even under the condition that photon energy is greatly attenuated by a scattering medium, weak effective signals can be captured through correlation measurement, the imaging effectiveness is ensured, in addition, the non-local characteristic of the quantum imaging can break through the shielding limit of the scattering medium, the indirect imaging of a hidden target is realized, the application boundary of the imaging technology in a scattering environment is expanded, and the quantum imaging technology has important application value in key fields such as remote sensing monitoring, biomedical deep imaging, bad weather target identification and the like. The coincidence measurement is a core link for realizing the extraction of the associated signals by quantum imaging, the coincidence gate width is taken as a key parameter of the coincidence measurement, and the rationality of the coincidence measurement is set to directly determine the matching precision of the signal photons and the reference photons, thereby influencing the imaging quality and the overall performance of the system. Currently, the quantum imaging technology mostly adopts a fixed value scheme in accordance with the gate width in a scattering environment. The scheme is simple and convenient to operate, and the system implementation cost is low, but the dynamic change characteristic of the scattering environment is difficult to adapt. Under different scattering scenes, the scattering intensity of the medium is different, and the scattering times and the scattering angles in the photon transmission process are different, so that the fluctuation range of the propagation time difference between the signal photons and the idle photons is obviously different. When the scattering intensity is higher, the fixed coincidence gate width often cannot fully cover the fluctuation interval of the propagation time difference, part of effective signal photons can be discarded due to misjudgment as noise beyond the gate width range, so that the imaging contrast is reduced and the effective signal utilization rate is reduced, and when the scattering intensity is lower, a large amount of background noise photons can be introduced into the fixed coincidence gate width, the coincidence measurement specificity is reduced, and the signal to noise ratio of the system is deteriorated. In order to solve the problems, high-resolution quantum imaging in a dynamic scattering environment is realized, and the invention provides a self-adaptive coincidence gate width optimization quantum imaging method based on a scattering free range, aiming at improving the imaging quality of quantum imaging in the scattering environment. Disclosure of Invention The invention aims to provide a quantum imaging method based on self-adaptive coincidence gate width optimization of a scattering free range. According to the method, the scattering free range of the imaging environment is estimated in real time, the door width par