Single-photon imaging methods based on time information stamping

Abstract

A time-stamped single-photon imaging method includes: acquiring a single-frame binary image containing timestamps by collecting sparse photons transmitted through a sample; obtaining an estimate of the spatial coordinates of the incident photons through PSF fitting and centroid averaging; obtaining an initial reconstructed image containing an estimate of the average photon number through timestamp reconstruction; and obtaining a final reconstructed image through denoising and optimization processing. This invention records the arrival time of photon events, reconstructs a probability distribution image of photons using a timestamp algorithm, and optimizes the image through post-processing algorithms such as position calibration and filtering / denoising to obtain a clear low-light imaging result.

Description

Technical Field

[0001] This invention relates to a technology in the field of quantum imaging, specifically a single-photon imaging method based on time information marking. Background Technology

[0002] Traditional imaging schemes suffer from severely limited dynamic range and performance under ultra-low light conditions, often making it difficult to obtain clear images. This poses a significant limitation to applications such as long-distance remote sensing and biological microscopy. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies, such as difficulty in achieving clear imaging under ultra-low light conditions, small detection dynamic range, and low detection sensitivity. It proposes a single-photon imaging method based on time information stamping. By recording the arrival time of photon events, a probability distribution image of photons is reconstructed using a timestamp algorithm. The image is then optimized through post-processing algorithms such as position calibration and filtering to obtain clear low-light imaging results.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a single-photon imaging method based on time information marking, comprising: obtaining a single-frame binary image containing timestamps by acquiring sparse photons transmitted through a sample; obtaining an estimate of the spatial coordinates of the incident photons by PSF fitting and centroid averaging; obtaining an initial reconstructed image containing an estimate of the average photon number by reconstructing the timestamps; and obtaining a final reconstructed image by denoising optimization processing.

[0006] The sparse photon refers to a photon that, after attenuation and loss during propagation, reaches the detector only once in a single smallest unit of time, excluding multi-photon arrival events.

[0007] The timestamp, which is the time when a photon arrives at the camera, is derived from the camera time value or from the number of frames per second and the position of the photon at the corresponding frame.

[0008] The camera is preferably a device capable of detecting a single photon, including a single-photon detector, a single-photon camera with a large-area array, or an enhanced single-photon camera.

[0009] The sample is a transparent sample, and light emitted from the sample is received by the camera.

[0010] The timestamp reconstruction refers to reconstructing the probability distribution information of photons based on their time information.

[0011] The probability distribution information mentioned refers to the spatial distribution information of photons.

[0012] The PSF fitting mentioned above refers to restoring the distorted original data based on the point spread function theory.

[0013] The aforementioned centroid averaging refers to calculating the centroid position of a photon based on statistical averaging.

[0014] This invention relates to a system for implementing the above method, comprising: a single-photon source generation unit, a single-photon camera, and a data processing unit, wherein: the single-photon source generation unit generates sparse single-photon events; the single-photon camera acquires transmitted light passing through the sample to be tested and extracts the arrival time information of the photons; the data processing unit performs PSF fitting and centroid averaging based on the arrival time information to obtain an estimate of the spatial coordinates of the incident photons; and the final reconstructed image is obtained through timestamp reconstruction and denoising optimization processing.

[0015] Technical effect

[0016] This invention, through a tagging and data processing algorithm based on timestamp information from a single-photon array camera, enables a wider dynamic range and higher detection sensitivity under low-light detection conditions. Attached Figure Description

[0017] Figure 1 This is a flowchart of the present invention;

[0018] Figure 2 This is a schematic diagram of a single-photon source generation unit;

[0019] In the figure: 1. Object under test, 2. Single-photon array camera, 3. Single-photon detector, 4. PPKTP crystal, 5. Laser, 6. Delay line, 7. Waveplate, 8. Filter;

[0020] Figure 3 This is a schematic diagram for fitting the spatial location of a photon event.

[0021] Figure 4 This is a schematic diagram illustrating the effect of an example. Detailed Implementation

[0022] like Figure 1 As shown, this embodiment relates to a single-photon imaging method based on time information marking, including:

[0023] Step 1, Preparation of a single-photon source: such as Figure 1 As shown, a spontaneous parametric downconversion process is induced in a 25 mm long periodically polarized KTP crystal (PPKTP) by pumping a semiconductor laser with a wavelength of 405 nm to generate correlated photon pairs at 810 nm.

[0024] In this embodiment, one of the light paths is selected as the signal light, which passes through the object and is then received by the single-photon area array camera. The other light path is used as the reference light, collected by the single-photon detector, and then used as the electrical signal to trigger the shutter of the area array camera.

[0025] Step 2, Target Selection: The target is a transparent object. Photons transmitted through the object are collected and analyzed in the experiment. A black and white letter image is selected as the sample, as light can pass through the white portion and be received by the camera.

[0026] Step 3, Signal detection and collection: The optical path of the two light sources is the same through the delay line. The arrival of the reference light is used as an electrical signal to control the trigger switch of the camera intensifier to realize data acquisition. By adjusting the camera's exposure time (50μs), the image intensifier's on time (10ns), and the intensity of the light source, the captured image is controlled so that each pixel contains at most one photon, thus obtaining a single frame of 0 and 1 binary images with and without photons.

[0027] The image intensifier is a device placed at the front of the camera, which can amplify the signal, thereby enabling the camera to accurately capture single-photon events.

[0028] Step 4, data post-processing, specifically includes:

[0029] 4.1 Spatial position calibration: such as Figure 3 As shown, after statistically analyzing multiple frames of images of a certain light spot and calculating its average centroid position, i.e. the position where photons are most concentrated, the light spot is corrected by fitting the PSF to the centroid.

[0030] 4.2 The average photon number is estimated for each pixel in the calibrated image, and normalized to obtain the initial single-photon image. Specifically, when the acquisition rate is 100 frames per second, for example, the 10th frame corresponds to the signal acquisition at 0.1s. The arrival times t1, t2, t3… of each photon are extracted, and the time intervals are obtained by subtracting them: t1, t2 - t1, t3 - t2… The time intervals satisfy the following relationship: Where: τ i Let be the time interval, which satisfies: ∑ i p i =1, p i Given the Poisson distribution probability of the i-th photon, the average photon time interval τ is obtained statistically. i It satisfies τ i = 1 / n, where: n is the average number of photons for τ i Taking the reciprocal gives an estimate of the average photon number at that location.

[0031] 4.3 The initial single-photon image is filtered and convex optimization processed to obtain the final reconstructed image.

[0032] The convex optimization process described herein employs, but is not limited to, the techniques described by Harmany ZT, Marcia RF, and Willett R M in "Sparse Poisson intensity reconstruction algorithms" (2009 IEEE / SP 15th Workshop on Statistical Signal Processing. 2009: 634-637.).

[0033] Through specific practical experiments, in a dark laboratory environment, with a camera exposure time of 50 μs, an image intensifier on-time of 10 ns, and a camera cooling temperature of -30°C, and by adjusting the optical path attenuation to achieve an average of 500 photons per second per frame, a total of 50,000 frames of images were obtained using this method. The experimental results are shown below. Figure 4 .

[0034] like Figure 4 The images shown are: the original image (a), the result of simply accumulating 5000 frames without timestamps (b), the result of timestamping the data but without optimization, and the result of timestamping (c) and optimization (d). It can be seen that adding timestamp processing can significantly remove most of the background noise and improve the image's signal-to-noise ratio; adding optimization algorithms can improve image edge reconstruction, smoothness, and contrast. Compared to the direct accumulation method, the image contrast of the timestamp-based optimized reconstruction result of this invention is improved by 2.25 times.

[0035] In summary, this invention can significantly improve the dynamic range and imaging quality of single-photon imaging under extremely low light conditions. Traditional cumulative imaging under low light conditions is often limited by the large differences in photon counts, leading to significant image deviations in the reconstructed image. The timestamp scheme is based on the exploitation of temporal degrees of freedom; lower photon intensities correspond to longer time intervals. When the system has high temporal resolution, the timestamp scheme can obtain more accurate photon count estimation results, thereby obtaining a clearer reconstructed image. This invention has enormous application potential in fields such as biological microscopy and long-distance remote sensing.

[0036] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A single-photon imaging method based on time-stamped information, characterized in that, include: A single-frame binary image containing timestamps is obtained by acquiring sparse photons transmitted through the sample. The spatial coordinates of the incident photons are estimated by PSF fitting and centroid averaging. An initial reconstructed image containing the average photon number estimate is obtained by reconstructing the timestamps. The final reconstructed image is obtained by denoising and optimization. The sparse photons refer to those that, after attenuation and loss during propagation, arrive at the detector in a single minimum time unit, excluding multi-photon arrival events; The timestamp, which is the time when a photon arrives at the camera, is derived from the camera time value or from the number of frames per second and the position of the photon at the corresponding frame. The reconstructed image is obtained in the following way: i. Spatial position calibration: After statistically analyzing multiple frames of images of a certain spot, calculating its average centroid position, i.e. the position where photon distribution is most concentrated, the spot is corrected by fitting the PSF to the centroid. ii. For each pixel in the calibrated image, the average photon number is estimated and normalized to obtain the initial single-photon image. Specifically, the arrival times t1, t2, t3... of each photon are extracted and subtracted to obtain the time intervals t1, t2 −t1, t3 −t2..., which satisfy the following relationship: ,in: Let be the time interval, which satisfies: , Given the Poisson distribution probability of the i-th photon, the average photon time interval is obtained statistically. Its satisfaction =1 / n, where: n is the average number of photons, for Taking the reciprocal yields an estimate of the average photon number at that location. iii. The initial single-photon image is filtered and convex optimized to obtain the final reconstructed image.

2. The single-photon imaging method based on time information markers according to claim 1, characterized in that, The camera is a single-photon detector, a large-area array single-photon camera, or an enhanced single-photon camera.

3. The single-photon imaging method based on time information markers according to claim 1, characterized in that, The timestamp reconstruction refers to reconstructing the probability distribution information of photons based on their time information, that is, the spatial distribution information of photons.

4. The single-photon imaging method based on time information markers according to claim 1, characterized in that, The PSF fitting mentioned above refers to restoring the distorted original data based on the point spread function theory.

5. The single-photon imaging method based on time information markers according to claim 1, characterized in that, The aforementioned centroid averaging refers to calculating the centroid position of a photon based on statistical averaging.

6. The single-photon imaging method based on time information markers according to any one of claims 1-5, characterized in that, specifically include: Step 1: Preparation of single-photon source: A 25mm long periodically polarized KTP crystal is pumped by a semiconductor laser with a wavelength of 405nm to induce a spontaneous parametric downconversion process to generate 810nm correlated photon pairs. One of them is selected as the signal light and passes through the object, and is then received by a single-photon area array camera. The other is used as the reference light and is collected by a single-photon detector to serve as the electrical signal that triggers the shutter of the area array camera. Step 2, Target selection: The target is a transparent object. Photons transmitted through the object are collected and analyzed in the experiment. Step 3, Signal detection and collection: The delay line ensures that the optical path of the two light sources is the same. The arrival of the reference light is used as an electrical signal to control the trigger switch of the camera intensifier to achieve data acquisition. By adjusting the camera's exposure time, the on-time of the image intensifier, and the intensity of the light source, the captured image is controlled so that each pixel contains at most one photon, thus obtaining a single frame of binary image with and without photons. Step 4, data post-processing, specifically includes: 4.1 Spatial Position Calibration: After statistically analyzing multiple frames of images of a certain light spot, calculating its average centroid position, i.e. the position where photon distribution is most concentrated, the light spot is corrected by fitting the PSF to the centroid. 4.2 For each pixel in the calibrated image, the average photon number is estimated and normalized to obtain the initial single-photon image. Specifically, the arrival times t1, t2, t3... of each photon are extracted and subtracted to obtain the time intervals t1, t2 −t1, t3 −t2..., which satisfy the following relationship: ,in: Let be the time interval, which satisfies: , Given the Poisson distribution probability of the i-th photon, the average photon time interval is obtained statistically. Its satisfaction =1 / n, where: n is the average number of photons, for Taking the reciprocal yields an estimate of the average photon number at that location. 4.3 The initial single-photon image is filtered and convex optimization processed to obtain the final reconstructed image.

7. A time-stamped single-photon imaging system implementing the method of any one of claims 1-6, characterized in that, include: The system comprises a single-photon source generation unit, a single-photon camera, and a data processing unit. The single-photon source generation unit generates sparse single-photon events. The single-photon camera collects transmitted light passing through the sample under test and extracts the arrival time information of the photons. The data processing unit performs PSF fitting and centroid averaging based on the arrival time information to obtain the estimated spatial coordinates of the incident photons. The final reconstructed image is obtained after timestamp reconstruction and denoising optimization.

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