Single photon reflection tomography method and device

Abstract

The present disclosure provides a single-photon reflection tomography method, comprising: operation S1: emitting a Gaussian beam into free space and applying it to a target object; operation S2: receiving a reflected beam obtained after the Gaussian beam acts on the target object to detect photon information; operation S3: obtaining a photon count-time histogram based on the photon information; operation S4: obtaining a time-domain waveform of the target object at a certain angle based on the photon count-time histogram; and operation S5: processing the time-domain waveforms at different angles to obtain a three-dimensional surface profile of the object. A single-photon reflection tomography device is also provided.

Description

Technical Field

[0001] The present disclosure relates to the field of laser active imaging technology, and in particular to a single-photon reflection tomography method and device. Background Art

[0002] For laser three-dimensional imaging systems, their lateral resolution capabilities are limited by the optical diffraction limit. For applications of long-distance, high-precision imaging, lidar is often required to have very high lateral resolution. To solve this problem, researchers have proposed super-resolution optical imaging solutions based on different principles and technical means, including optical synthetic aperture imaging, Fourier telescopes, large-aperture stitched telescopes, sub-pixel scanning, laser reflection tomography, etc. Among them, laser reflection tomography technology aims to restore the morphology of objects that were originally unable to be resolved laterally through high-precision distance information measurement. It obtains three-dimensional information of the target through relatively robust photon flight time measurement. However, current laser reflection tomography systems still require a large optical aperture and high laser power to achieve long-distance detection, making it difficult to achieve miniaturization and lightweighting. At the same time, it is difficult to balance the resolution and effective range of the system. Summary of the Invention

[0003] In one aspect of the present disclosure, a single photon reflection tomography method is provided, comprising:

[0004] Operation S1: emit a Gaussian beam into free space and act on the target object;

[0005] Operation S2: receiving a reflected light beam obtained after the Gaussian light beam acts on the target object to detect photon information;

[0006] Operation S3: obtaining a photon count-time histogram according to the photon information;

[0007] Operation S4: obtaining a time domain waveform of the target object at a certain angle based on the photon count-time histogram; and

[0008] Operation S5: Process the time domain waveforms at different angles to obtain a three-dimensional surface profile of the object.

[0009] According to an embodiment of the present disclosure, in operation S1 , the Gaussian beam is caused to act on the target object at different angles by changing the angle of the target object itself or the emission position of the Gaussian beam.

[0010] According to an embodiment of the present disclosure, in operation S2, photon information of the reflected light beam is detected by a single-photon avalanche diode, and the dead time during detection is set to be less than 1 μs.

[0011] According to an embodiment of the present disclosure, in operation S3, the photon flight time is obtained through a time-to-digital converter, and a photon count-time histogram is obtained based on the photon flight time.

[0012] According to an embodiment of the present disclosure, when a photon is detected by a single-photon avalanche diode, a pulse signal is output to a time-to-digital converter, which records the emission time of the pulse signal and the arrival time of the photon, thereby obtaining the flight time of the photon.

[0013] According to an embodiment of the present disclosure, operation S5 includes:

[0014] Operation S51: performing Fourier transform on the photon count histogram measured at each angle to obtain a frequency domain vector;

[0015] Operation S52: multiplying the frequency domain vector by the filter function to perform filtering;

[0016] Operation S53: performing Fourier transform on the filtered frequency domain vector to obtain filtered time domain data;

[0017] Operation S54: back-projecting each time domain data onto the object space voxel that contributes to the time domain data;

[0018] Operation S55: fitting the back-projected result based on the surface constraint to finally obtain the three-dimensional surface contour of the target object.

[0019] According to an embodiment of the present disclosure, the filter function in operation S52 is H(ω):

[0020] ;

[0021] Here ω represents the frequency, ω cut Represents the cutoff frequency, which is an adjustable parameter related to the signal-to-noise ratio.

[0022] Another aspect of the present disclosure provides a single photon reflection tomography apparatus, comprising:

[0023] A transmitting unit, used for emitting a Gaussian beam into free space and acting on a target object;

[0024] a receiving unit, receiving a reflected light beam obtained after the Gaussian light beam acts on a target object to detect photon information, and obtaining a photon count-time histogram based on the photon information; and

[0025] The processing unit obtains the time domain waveform of the target object at a certain angle based on the photon count-time histogram; and processes the time domain waveforms at different angles to obtain the three-dimensional surface profile of the object.

[0026] According to an embodiment of the present disclosure, the transmitting unit includes a laser, a single-mode optical fiber, a collimator, and a beam expander; the receiving unit includes a beam expander, a bandpass filter, a long-pass filter, an optical fiber filter, a single-photon detector, and a time-to-digital converter; the imaging device also includes a signal generator for providing a timing signal.

[0027] It can be seen from the above technical solutions that the single photon reflection tomography method and device disclosed herein have at least one or part of the following beneficial effects:

[0028] (1) Long detection distance: The device uses a single-photon avalanche diode for detection, which can achieve the ultimate sensitivity of the single-photon level. At the same time, the device operates in the near-infrared band and has good atmospheric transmittance. The system uses multi-stage spectral filtering, time domain and spatial domain filtering to greatly reduce noise. The good sensitivity and signal-to-noise ratio enable the device to achieve long-distance detection.

[0029] (2) Miniaturization and lightweight: Based on single-photon detection, it has high sensitivity and therefore does not require high-power lasers and large-aperture telescopes. At the same time, the device can use miniaturized components, which can achieve integration and lightweight.

[0030] (3) High measurement accuracy: Based on single-photon detection, the time-to-digital converter is used to measure the time of flight of photons. The time accuracy can reach tens of ps, and the corresponding distance resolution can be less than 1 cm, which can achieve high imaging accuracy.

[0031] (4) Three-dimensional imaging can be achieved: the three-dimensional surface morphology of an object can be restored based on measurement data at different angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the reflection tomography principle.

[0033] Figure 2A Schematic diagram of the process of the single photon reflection tomography method according to an embodiment of the present disclosure.

[0034] Figure 2B Schematic diagram of the composition of the single-photon reflection tomography imaging device according to an embodiment of the present disclosure.

[0035] Figure 3A Schematic diagram of the imaging target according to an embodiment of the present disclosure.

[0036] Figure 3B For collection Figure 3A The time domain waveform data of the imaging target is shown.

[0037] Figure 4 for Figure 3A Results of 3D imaging experiments of the imaging targets shown. DETAILED DESCRIPTION

[0038] The present disclosure provides a single-photon reflection tomography method and device, which breaks through the performance bottleneck of traditional lidar systems by applying high-sensitivity and high-time-resolution single-photon detection technology to reflection tomography; and has the advantages of miniaturization, low power consumption, long distance, and high precision, and can achieve three-dimensional imaging.

[0039] like Figure 1 As shown, laser reflection tomography technology collects one-dimensional depth projection waveforms of the target at different angles, and uses an inverse algorithm to reconstruct a high-resolution image of a distant, indistinguishable target. Its imaging resolution is not affected by the system aperture and imaging distance, but only depends on the depth resolution of the system. Laser reflection tomography technology has received widespread attention at home and abroad. For example, a foreign laboratory has verified the reflection tomography imaging of two reflectors on a satellite 514 km away. In China, a research institute has achieved imaging of small targets 10.4 km away. However, current laser reflection tomography imaging devices still require a larger optical aperture and higher laser power to achieve long-distance detection, making it difficult to achieve miniaturization and lightweighting. At the same time, it is difficult to balance the resolution and effective range of the system. Therefore, the present disclosure provides a single-photon reflection tomography method and device to alleviate the above-mentioned technical problems.

[0040] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0041] In an embodiment of the present disclosure, a single-photon reflection tomography method is provided, which is used for long-distance, high-precision reflection tomography of single-photon detection, such as Figure 2A and combined Figure 2B As shown, the single photon reflection tomography method includes:

[0042] Operation S1: emit a Gaussian beam into free space and act on the target object;

[0043] Operation S2: receiving a reflected light beam obtained after the Gaussian light beam acts on the target object to detect photon information;

[0044] Operation S3: obtaining a photon count-time histogram according to the photon information;

[0045] Operation S4: obtaining a time domain waveform of the target object at a certain angle based on the photon count-time histogram; and

[0046] Operation S5: Process the time domain waveforms at different angles to obtain a three-dimensional surface profile of the object.

[0047] In operation S1 , the Gaussian beam is made to act on the target object at different angles by changing the angle of the target object itself or the emission position of the Gaussian beam.

[0048] In operation S2, the photon information of the reflected light beam is detected by a single-photon avalanche diode, and the dead time during detection is set to be less than 1 μs.

[0049] In operation S3, the photon flight time is obtained by a time-to-digital converter (TDC), and a photon count-time histogram is generated based on the photon flight time. When a photon is detected by the single-photon avalanche diode (SPAD), a pulse signal is output to the TDC. The TDC records the emission time of the pulse signal and the arrival time of the photon, thereby obtaining the photon flight time.

[0050] Operation S5 includes:

[0051] Operation S51: performing Fourier transform on the photon count histogram measured at each angle to obtain a frequency domain vector;

[0052] Operation S52: multiplying the frequency domain vector by the filter function to perform filtering;

[0053] Operation S53: performing Fourier transform on the filtered frequency domain vector to obtain filtered time domain data;

[0054] Operation S54: back-projecting each time domain data onto the object space voxel that contributes to the time domain data;

[0055] Operation S55: fitting the back-projected result based on the surface constraint to finally obtain the three-dimensional surface contour of the target object.

[0056] The filter function in operation S52 is H(ω):

[0057] ;

[0058] Here ω represents the frequency, ω cut Represents the cutoff frequency, which is an adjustable parameter related to the signal-to-noise ratio.

[0059] In the embodiment of the present disclosure, a filtered back projection method based on a Hanning window is used to process data. The measured data is the time domain waveform (photon count-time histogram) of the object at different angles.

[0060] The above time domain waveform processing is written based on CUDA language and adopts GPU parallel computing.

[0061] like Figure 2B Combined with Figure 2A As shown, the present disclosure also provides a single photon reflection tomography device, comprising:

[0062] A transmitting unit, used for emitting a Gaussian beam into free space and acting on a target object;

[0063] a receiving unit, receiving a reflected light beam obtained after the Gaussian light beam acts on a target object to detect photon information, and obtaining a photon count-time histogram based on the photon information; and

[0064] The processing unit obtains the time domain waveform of the target object at a certain angle based on the photon count-time histogram; and processes the time domain waveforms at different angles to obtain the three-dimensional surface profile of the object.

[0065] The transmitting unit includes a laser, a single-mode optical fiber, a collimator, and a beam expander; the receiving unit includes a beam expander, a bandpass filter, a long-pass filter, an optical fiber filter, a single-photon detector, and a time-to-digital converter; the imaging device also includes a signal generator for providing a timing signal.

[0066] According to the embodiment of the present disclosure, Figure 2B As shown, a near-infrared picosecond pulsed fiber laser is used as the light source. The near-infrared band has high atmospheric transmittance and low sunlight noise. The laser uses a high pulse repetition rate (hundreds of kHz) to enable rapid signal waveform measurement. The laser is emitted from a single-mode fiber, collimated by a collimator, and finally transformed into a Gaussian beam by a beam expander, propagating into free space to illuminate the target.

[0067] The receiving optical path uses the same optical setup as the transmitting optical path, with a certain distance between the transmitting and receiving beam expanders to prevent excessive atmospheric backscatter noise from being received by the detector. The signal collected by the receiving beam expander passes through a bandpass filter and a longpass filter before being coupled into a fiber filter. The other end of the filter is connected to a single-photon detector.

[0068] The imaging device uses a miniaturized free-running InGaAs / InP single-photon avalanche diode (SPAD) for signal detection. The detector's dead time is set to less than 1μs to achieve a sufficient maximum count rate. When a photon is detected, the detector outputs a pulse signal to a time-to-digital converter (TDC). The TDC records the emission moment of the pulse and the arrival moment of the photon to obtain the photon's time of flight. The TDC also calculates the measured photon flight time into a photon count-time histogram and transmits it to a computer. The photon count-time histogram reflects the one-dimensional depth projection waveform of the target at a certain angle, which is used for subsequent time domain waveform processing to restore the target's three-dimensional image.

[0069] In the embodiment of the present disclosure, a single photon reflection tomography device is used, and a three-dimensional imaging experiment is performed, such as Figure 3AAs shown in Figure 1, a rabbit model is used as the imaging target. The target model is fixed on a two-axis rotating platform, and the time domain waveform data of the target at different angles is collected, as shown in Figure 1. Figure 3B The results of the three-dimensional imaging experiment are shown in Figure 4 As shown in the figure, the photon time-count histogram of the rabbit model at 257 different angles was collected, and the reconstructed three-dimensional image has 81×81×81 pixels, representing 40×40×40 cm 3 From the figure, we can see that reflection tomography can well restore the surface morphology of the rabbit, with a depth error of less than 1 cm.

[0070] The embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that any implementations not depicted or described in the drawings or the main text of the specification are known to those skilled in the art and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the various specific structures, shapes, or methods described in the embodiments, and can be easily modified or replaced by those skilled in the art.

[0071] Based on the above description, those skilled in the art should have a clear understanding of the single photon reflection tomography method and device disclosed herein.

[0072] In summary, this disclosure provides a single-photon reflection tomography method and device. By applying high-sensitivity, high-temporal-resolution single-photon detection technology to reflection tomography, this method and device overcome the performance bottleneck of traditional lidar devices. This imaging method and device offer the advantages of miniaturization, low power consumption, long range, and high precision, enabling three-dimensional imaging and possessing potential value in remote sensing.

[0073] It should also be noted that the above are different embodiments provided by the present disclosure. These embodiments are used to illustrate the technical content of the present disclosure and are not intended to limit the scope of protection of the present disclosure. A feature of one embodiment can be applied to other embodiments through appropriate modification, replacement, combination, or separation.

[0074] It should be noted that, herein, unless otherwise specified, “a” element is not limited to a single element, but may include one or more elements.

[0075] In this document, unless otherwise specified, the so-called feature A "or" or "and / or" feature B means that A exists alone, B exists alone, or A and B exist at the same time; the so-called feature A "and" or "and" or "and" feature B means that A and B exist at the same time; the so-called "include", "comprise", "have" and "contain" mean including but not limited to these.

[0076] Furthermore, in this document, terms such as "upper," "lower," "left," "right," "front," "back," or "between" are used solely to describe the relative positions of multiple elements and can be interpreted to include translation, rotation, or mirroring. Furthermore, in this document, unless otherwise specified, "an element is on another element" or similar descriptions do not necessarily mean that the element contacts the other element.

[0077] Furthermore, unless specifically described or required to occur sequentially, the order of the steps is not limited to the order listed above and may be varied or rearranged based on desired design requirements. Furthermore, the above embodiments may be mixed and matched with each other or with other embodiments based on design and reliability considerations. That is, the technical features of different embodiments may be freely combined to form more embodiments.

[0078] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A single photon reflection tomography method, comprising: Operation S1: emit a Gaussian beam into free space and act on the target object; Operation S2: receiving a reflected light beam obtained after the Gaussian light beam acts on the target object to detect photon information; Operation S3: obtaining a photon count-time histogram according to the photon information; Operation S4: obtaining a time domain waveform of the target object at a certain angle based on the photon count-time histogram; as well as Operation S5: Processing the time domain waveforms at different angles to obtain a three-dimensional surface profile of the object; The operation S5 includes: Operation S51: performing Fourier transform on the photon count histogram measured at each angle to obtain a frequency domain vector; Operation S52: multiplying the frequency domain vector by the filter function to perform filtering; Operation S53: performing Fourier transform on the filtered frequency domain vector to obtain filtered time domain data; Operation S54: back-projecting each time domain data onto the object space voxel that contributes to the time domain data; Operation S55: fitting the back-projected result based on the surface constraint to finally obtain the three-dimensional surface contour of the target object.

2. The single photon reflection tomography method according to claim 1, wherein in operation S1, the Gaussian beam is caused to act on the target object at different angles by changing the angle of the target object itself or the emission position of the Gaussian beam. 3 . The single photon reflection tomography method according to claim 1 , wherein in operation S2 , photon information of the reflected light beam is detected by a single photon avalanche diode. 4 . The single photon reflection tomography method according to claim 3 , wherein the dead time during detection is set to be less than 1 μs. 5 . The single photon reflection tomography method according to claim 1 , wherein in operation S3 , a photon flight time is obtained by a time-to-digital converter, and a photon count-time histogram is obtained based on the photon flight time.

6. The single-photon reflection tomography method according to claim 5, wherein when a photon is detected by a single-photon avalanche diode, a pulse signal is output to a time-to-digital converter, which records the emission time of the pulse signal and the arrival time of the photon, thereby obtaining the flight time of the photon.

7. The single photon reflection tomography method according to claim 1, wherein the filter function in operation S52 is: ； Here ω represents the frequency, ω cut Represents the cutoff frequency, which is an adjustable parameter related to the signal-to-noise ratio.

8. A single photon reflection tomography device, comprising: A transmitting unit, used for emitting a Gaussian beam into free space and acting on a target object; a receiving unit, receiving a reflected light beam obtained after the Gaussian light beam acts on the target object to detect photon information, and obtaining a photon count-time histogram based on the photon information; as well as A processing unit obtains a time domain waveform of the target object at a certain angle based on the photon count-time histogram, and processes the time domain waveforms at different angles to obtain a three-dimensional surface profile of the object.

9. The single photon reflection tomography imaging device according to claim 8, wherein: The transmitting unit includes a laser, a single-mode optical fiber, a collimator, and a beam expander; The receiving unit includes a beam expander, a bandpass filter, a longpass filter, an optical fiber filter, a single photon detector, and a time-to-digital converter; The imaging device further includes a signal generator for providing a timing signal.

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