A non-scanning single-photon polarization three-dimensional imaging method

Abstract

The present application relates to a kind of non-scanning single-photon polarization three-dimensional imaging method, comprising: constructing pulse laser echo photon number calculation model: pulse laser emits laser pulse, after each light pulse is irradiated to target, the photon number of return to single-photon avalanche photodetector each pixel is related to detection distance;Construct single-photon detector signal and noise model: signal photon and background photon are incident on the photosensitive surface of detector to complete photon injection, based on the quantum efficiency of detector, photoelectric conversion is generated echo electron and canister noise electron, noise electron is generated by thermal current, tunneling current, then carries out electric injection, then based on avalanche probability, avalanche multiplication is completed, and finally, the signal is read out through avalanche signal detection;Construct polarization modulation laser radar ranging model, improve target polarization three-dimensional imaging distance.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of non-scanning single-photon polarization three-dimensional imaging method, belong to advanced optical imaging technical field. BACKGROUND

[0002] Single-photon imaging technology, according to the high sensitivity detection characteristics of single-photon detector, based on photon counting Poisson statistical filtering system, measure photon time of flight, obtain target distance information, inversion target three-dimensional characteristics, linear polarization characteristics of pulse laser signal are used in the process, after polarization modulation, emit vertical polarization light, after backscattering of vertical polarization light by optical system, polarization direction does not change, after target diffuse reflection, become random polarized light, when receiving, again after polarization beam splitter filtering, receive horizontal polarization light, so as to eliminate the influence of optical system backscattering photon, the detection distance exceeds 200km.

[0003] Polarization three-dimensional imaging technology, according to the uniqueness of the three-dimensional information of target surface microelement and normal vector, based on polarization modulation laser radar imaging system, measure microelement exit light polarization degree and reflectivity, estimate incident angle and azimuth, obtain target microelement normal vector, inversion target three-dimensional characteristics, in the process, the difference between the perpendicular direction vibration component and the parallel direction vibration component of specular reflection and diffuse reflection light is used to realize target anti-stealth. However, in some special application fields, such as 500km detection distance stealth target observation, etc., the effective information of stealth target under natural scene background condition cannot be obtained. SUMMARY

[0004] The technical problem solved by the present application is to overcome the shortcomings of the prior art, and to provide a non-scanning single-photon polarization three-dimensional imaging method, which solves the problems in the prior art that only gray-scale imaging or three-dimensional imaging or polarization imaging of the target can be performed, the target gray-scale information, three-dimensional information and polarization information cannot be considered, the above information cannot be obtained by single camera non-scanning imaging, and the small stealth target cannot be imaged under the condition of long distance and strong background noise.

[0005] The technical solution of the present application is:

[0006] A non-scanning single-photon polarization three-dimensional imaging method, comprising:

[0007] Constructing a pulse laser echo photon number calculation model: the pulse laser emits laser pulses, and the number of photons returned to each pixel of the single-photon avalanche photodetector after each light pulse irradiates the target is related to the detection distance,

[0008] In the formula: N photon (H) is the number of photons received by each pixel; P is the output power of the pulse laser; p is the target reflectivity; τ atm is the atmospheric transmittance of a specific laser wavelength; τi denoted as , where is the transmittance of the optical system through the corresponding micro-polarization array along its polarization direction; f is the focal length of the optical system; F is the F-number of the optical system; p is the pixel size; l is the array size; FF is the detector pixel fill factor; R is the detection distance; T is the pulse width; λ is the laser wavelength; h is Planck's constant; and c is the speed of light.

[0009] Construct a signal and noise model for a single-photon detector: Signal photons and background photons are incident on the photosensitive surface of the detector to complete photon injection. Based on the detector's quantum efficiency, photoelectric conversion is performed to generate echo electrons and shot noise electrons. Noise electrons are generated by thermal current and tunneling current, and then electrical injection is performed. Next, avalanche multiplication is performed based on avalanche probability. Finally, the signal is read out through avalanche signal detection.

[0010] Constructing a Poisson statistical filter photon counting model: Under the condition of long detection distance, the average number of photons in the echo is much smaller than the speckle degrees of freedom of the optical system. The laser echo signal follows a negative binomial distribution, approximately a Poisson distribution. Within the gate opening time interval t, the probability of the echo signal generating k photoelectrons is...

[0011]

[0012]

[0013] Where: N electron (t) represents the number of echo photoelectrons; n signal (t) represents the signal photon velocity; n background (t) represents the background photon velocity; t1 represents the gating start time; t2 represents the gating end time;

[0014] Constructing a polarization-modulated lidar ranging model:

[0015] Polarization modulation is achieved by a Polknell cell placed between two orthogonal polarizers. When a voltage is applied to the Polknell cell, the phase delay of the polarized light is proportional to the applied voltage, expressed as:

[0016]

[0017] In the formula: Γ is the phase delay; λ is the laser wavelength; n0 is the constant refractive index at the center of the Pockels cell; r 63 is the electro-optic coefficient; V(t) is the Pockels cell voltage.

[0018] Furthermore, the performance parameters of a single-photon avalanche photodetector include: detection efficiency, dark count rate, afterpulse probability, dead time, and time jitter. Detection efficiency represents the probability that a single photon incident on the SPAD will generate a detectable avalanche signal, PDE = QE·P. ava ·P det

[0019] In the formula: PDE is the detection efficiency; QE is the quantum efficiency; P ava P represents the avalanche probability. det This represents the detection probability.

[0020] Furthermore, the probability that no photoelectron event occurs during the door opening time is...

[0021]

[0022] Furthermore, the probability of at least one photoelectron event generating an avalanche signal and being detected is...

[0023]

[0024] This refers to the photon count caused by signal photons and background photons.

[0025] Furthermore, during the opening time interval, the probability of k photoelectrons being induced by shot noise and dark noise is...

[0026]

[0027] N noise (t)=N SHOT (t)+N DCR (t)

[0028]

[0029] N DCR (t)=DCR·t

[0030] Where: N noise (t) represents the number of electrons in shotgun noise and other dark noise; N SHOT (t) represents the number of shotgun noise electrons; N DCR (t) represents the number of dark noise electrons; DCR represents the dark count rate.

[0031] Furthermore, the probability that no photoelectron event occurs during the door opening time is...

[0032]

[0033] Furthermore, the probability of at least one photoelectron event generating an avalanche signal and being detected is...

[0034]

[0035] This refers to the photon count caused by shot noise and dark noise.

[0036] Furthermore, the applied voltage is linear, expressed as

[0037]

[0038] In the formula: t0 is the delay time; T r V is the voltage rise time. π It is a half-wave voltage.

[0039] Furthermore, the half-wave voltage is expressed as

[0040]

[0041] Furthermore, the phase delay of polarized light can be simplified to a function of time, expressed as:

[0042]

[0043] The micro-polarization array consists of multiple groups of polarizers, including four linear polarizers at 0°, 45°, 90°, and 135°. The light intensity after passing through each group of four polarizers can be expressed as...

[0044]

[0045]

[0046]

[0047]

[0048] The phase delay can be obtained by measuring the four light intensities mentioned above. The phase delay calculation is expressed as follows:

[0049]

[0050] The target distance obtained by this method is expressed as:

[0051]

[0052] The distance to the target is determined by measuring the light intensity, thus eliminating the influence of time errors.

[0053] The advantages of this invention compared to the prior art are:

[0054] (1) The device of the present invention can acquire target grayscale information, three-dimensional information and polarization information based on non-scanning imaging of a single camera;

[0055] (2) This invention uses a single-photon counting method to statistically analyze the intensity information of the target echo in four polarization directions: 0°, 45°, 90°, and 135°, thereby improving the target polarization three-dimensional imaging distance. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of a non-scanning single-photon polarization three-dimensional imaging device according to an embodiment of the present invention.

[0057] Figure 2 This is a schematic diagram of a micro-polarization array according to an embodiment of the present invention.

[0058] Figure 3 This is a schematic diagram of a large-scale free-running mode single-photon detector array according to an embodiment of the present invention.

[0059] Figure 4 This is a schematic diagram of the single-photon detector unit structure according to an embodiment of the present invention.

[0060] Figure 5 This is a schematic diagram of the single-photon detector signal and noise model according to an embodiment of the present invention.

[0061] Figure 6 This is a schematic diagram of the Poisson statistical photon counting process according to an embodiment of the present invention. Detailed Implementation

[0062] The present invention will be further described below with reference to the embodiments.

[0063] For details of the non-scanning single-photon polarization three-dimensional imaging device of the present invention, please refer to [link / reference]. Figure 1 .

[0064] For details of the micro-polarization array of the present invention, please refer to [link / reference]. Figure 2 .

[0065] For details of the large-scale free-running mode single-photon detector array of the present invention, please refer to [link / reference]. Figure 3 .

[0066] For details of the single-photon detector unit structure of the present invention, please refer to [link / reference]. Figure 4 .

[0067] This invention proposes a non-scanning single-photon polarization three-dimensional imaging device and method, which solves the problems of existing technologies that can only perform grayscale imaging, three-dimensional imaging, or polarization imaging of targets, cannot take into account the grayscale information, three-dimensional information, and polarization information of targets, cannot obtain the above information through non-scanning imaging with a single camera, and cannot image weak and stealthy targets at long distances under strong background noise conditions.

[0068] A non-scanning single-photon polarization 3D imaging device includes a non-scanning single-photon polarization 3D imaging transmitting optical path and a receiving optical path. The device illuminates the target with a high-repetition-rate, narrow-pulse-width polarization-modulated pulsed laser and records the emission time. A large-aperture optical lens collects the echo photons, which are then modulated by an electro-optic modulation crystal to change the echo polarization state. The echo photons pass through a micro-polarization array and enter a free-running single-photon detector array to complete photoelectric conversion, generating an avalanche signal. The photon arrival time is recorded, and a photon counter records the number of signals in the target echo at four polarization directions: 0°, 45°, 90°, and 135°. Based on Poisson statistics, by increasing the repetition count, target light intensity information, distance information, and polarization information are accumulated, thereby achieving grayscale imaging, 3D imaging, and polarization imaging of the target.

[0069] The non-scanning single-photon polarization three-dimensional imaging device includes a passively Q-switched laser source 1, lens 2, lens 3, half-wave plate 4, polarization beam splitter 5, half-wave plate 6, polarization beam splitter 7, quarter-wave plate 8, primary mirror 9, secondary mirror 10, photodiode 11, polarizer 12, Pockels cell 13, quarter-wave plate 14, lens 15, micro-polarization array 16, and single-photon detector array 17. The single-photon detector array 17 is an InGaAs / InP single-photon detector array, with each unit employing a separated absorption graded charge multiplication structure (SAGCM), including: a P-type heavily doped InGaAs contact layer 1, a P-type heavily doped InP layer 2, an InP multiplication layer 3, a base n-type InP charge layer 4, an InGaAsP buffer layer 5, an InGaAs absorption layer 6, and an N-type heavily doped InP contact layer 7.

[0070] The non-scanning single-photon polarization three-dimensional imaging device emits a laser beam from a dynamically Q-switched laser source 1. This beam is collimated and expanded by lenses 2 and 3, and its polarization direction is deflected by a half-wave plate 4. The beam is then split into two mutually perpendicular beams by a polarization beam splitter 5. Rotating the half-wave plate 4 allows for arbitrary intensity ratios. The beam reflected by the polarization beam splitter 5 is received by a photodiode, generating a start signal. This start signal serves as the trigger signal for a delay pulse generator. The beam transmitted through the polarization beam splitter 5 undergoes intensity adjustment via a combination of a half-wave plate 6 and a polarization beam splitter 7. It is then switched on by a quarter-wave plate 8, passes through the central hole of the primary reflector 9, is reflected again by a secondary reflector 10, and finally emitted to the target.

[0071] The non-scanning single-photon polarization three-dimensional imaging device receives a target-scattered beam, which is reflected by the primary reflector 9 to the secondary reflector 10. The reflected beam passes through the central hole of the primary reflector 9, is received by the quarter-wave plate 8, is reflected by the polarization beam splitter 7, passes through the polarizer 12, is electro-optically modulated by the Pockels cell 13, is received by the quarter-wave plate 14, is converged by the lens 15 to the micro-polarization array 16, and is incident on the single-photon detector array 17.

[0072] The device of the present invention can acquire target grayscale information, three-dimensional information, and polarization information based on non-scanning imaging with a single camera.

[0073] This invention improves the target polarization three-dimensional imaging distance by using a single-photon counting method to statistically analyze the intensity information of the target echo in four polarization directions: 0°, 45°, 90°, and 135°.

[0074] A non-scanning single-photon polarization three-dimensional imaging method, comprising:

[0075] 1) Pulsed laser echo photon number calculation model

[0076] A pulsed laser emits laser pulses. After each pulse illuminates the target, it returns to the single-photon avalanche photodetector. The number of photons per pixel is related to the detection distance, and the calculation method is shown in the following formula.

[0077]

[0078] Where: N photon (H) is the number of photons received per pixel; P is the output power of the pulsed laser; ρ is the target reflectivity; τ atm Atmospheric transmittance for a specific laser wavelength; τ i denoted as , where is the transmittance of the optical system through the polarization direction of the corresponding micro-polarization array; f is the focal length of the optical system; F is the F-number of the optical system; p is the pixel size; l is the array size; FF is the detector pixel fill factor; R is the detection distance; T is the pulse width; λ is the laser wavelength; h is Planck's constant; and c is the speed of light.

[0079] 2) Single-photon detector signal and noise model

[0080] See Figure 5 The single-photon avalanche photodetector system mainly includes: a single-photon avalanche photodetector, a driving circuit, a signal detection circuit, and a photon counter. The signal and noise model is as follows: Figure 4 As shown, signal photons and background photons are incident on the photosensitive surface of the detector to complete photon injection. Based on the detector's quantum efficiency, photoelectric conversion is performed to generate echo electrons and shot noise electrons. Noise electrons are generated by other means such as thermal current and tunneling current, and then electrical injection is performed. Next, avalanche multiplication is performed based on the avalanche probability, and finally the signal is read out through avalanche signal detection.

[0081] The main performance parameters of a single-photon avalanche photodetector (SPAD) include: detection efficiency, dark count rate, afterpulse probability, dead time, and time jitter. Detection efficiency represents the probability that a single photon incident on the SPAD will generate a detectable avalanche signal, and its calculation method is shown in the following formula.

[0082] PDE = QE·P ava·P det

[0083] In the formula: PDE is the detection efficiency; QE is the quantum efficiency; P ava P represents the avalanche probability. det This represents the detection probability.

[0084] 3) Poisson statistical filter photon counting model

[0085] See Figure 6 Under conditions of long detection distance, the average number of photons in the echo is much smaller than the speckle degrees of freedom of the optical system. The laser echo signal follows a negative binomial distribution, which can be approximated as a Poisson distribution. Therefore, within the opening time interval t, the probability of the echo signal generating k photoelectrons is...

[0086]

[0087]

[0088] Where: N electron (t) represents the number of echo photoelectrons; n signal (t) represents the signal photon velocity; n background (t) represents the background photon velocity; t1 is the gating start time; t2 is the gating end time. Therefore, the probability that no photoelectron event occurs within the gating time is...

[0089]

[0090] Therefore, the probability of at least one photoelectron event generating an avalanche signal and being detected is...

[0091]

[0092] The above formula represents the photon count caused by signal photons and background photons.

[0093] Due to the discrete nature of photoelectron generation, shot noise is also generated when signal photons are input. Shot noise is proportional to the root mean square of the number of signal electrons. In addition, dark noise from carriers generated by other pathways such as thermal current and tunneling current can also cause avalanche signals, which can then be detected. Therefore, within the gate opening time interval, the probability of shot noise and dark noise generating k photoelectrons is...

[0094]

[0095] N noise (t)=N SHOT (t)+N DCR (t)

[0096]

[0097] NDCR (t)=DCR·t

[0098] Where: N noise (t) represents the number of electrons in shotgun noise and other dark noise; N SHOT (t) represents the number of shotgun noise electrons; N DCR (t) represents the number of dark noise electrons; DCR represents the dark count rate. Therefore, the probability that no photoelectron event occurs during the gate opening time is...

[0099]

[0100] Therefore, the probability of at least one photoelectron event generating an avalanche signal and being detected is...

[0101]

[0102] The above formula represents the photon count caused by shot noise and dark noise.

[0103] 4) Polarization-modulated lidar ranging model

[0104] Polarization modulation is achieved by a Pockels cell placed between two orthogonal polarizers. When a voltage is applied to the Pockels cell, the phase delay of the polarized light is proportional to the applied voltage, which can be expressed as:

[0105]

[0106] In the formula: Γ is the phase delay; λ is the laser wavelength; n0 is the constant refractive index at the center of the Pockels cell; r 63 Let V(t) be the electro-optic coefficient; V(t) be the Pockels cell voltage. The applied voltage is linear and can be expressed as...

[0107]

[0108] In the formula: t0 is the delay time; T r V is the voltage rise time. π This is the half-wave voltage. The half-wave voltage can be expressed as...

[0109]

[0110] Therefore, the phase delay of polarized light can be simplified to a function of time, and can be expressed as:

[0111]

[0112] The micro-polarization array consists of multiple groups of polarizers (including four linear polarizers at 0°, 45°, 90°, and 135°). The light intensity after passing through each group of four polarizers can be expressed as...

[0113]

[0114]

[0115]

[0116]

[0117] By measuring the four light intensities mentioned above, the phase delay can be obtained. The phase delay calculation method can be expressed as follows:

[0118]

[0119] The target distance obtained by this method can be expressed as:

[0120]

[0121] Therefore, the distance to the target can be determined by measuring the light intensity, thus eliminating the influence of time errors.

[0122] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A non-scanning single-photon polarization three-dimensional imaging method, characterized in that, include: A model for calculating the photon count of pulsed laser echoes is constructed: A pulsed laser emits laser pulses, and after each pulse illuminates the target, it returns to the single-photon avalanche photodetector. The number of photons per pixel is related to the detection distance. Where: N photon (H) is the number of photons received per pixel; P is the output power of the pulsed laser; ρ is the target reflectivity; τ atm Atmospheric transmittance for a specific laser wavelength; τ i denoted as , where is the transmittance of the optical system through the corresponding micro-polarization array along its polarization direction; f is the focal length of the optical system; F is the F-number of the optical system; p is the pixel size; l is the array size; FF is the detector pixel fill factor; R is the detection distance; T is the pulse width; λ is the laser wavelength; h is Planck's constant; and c is the speed of light. Construct a signal and noise model for a single-photon detector: Signal photons and background photons are incident on the photosensitive surface of the detector to complete photon injection. Based on the detector's quantum efficiency, photoelectric conversion is performed to generate echo electrons and shot noise electrons. Noise electrons are generated by thermal current and tunneling current, and then electrical injection is performed. Next, avalanche multiplication is performed based on avalanche probability. Finally, the signal is read out through avalanche signal detection. Constructing a Poisson statistical filter photon counting model: Under the condition of long detection distance, the average number of photons in the echo is much smaller than the speckle degrees of freedom of the optical system. The laser echo signal follows a negative binomial distribution, approximately a Poisson distribution. Within the gate opening time interval t, the probability of the echo signal generating k photoelectrons is... Where: N electron (t) represents the number of echo photoelectrons; n signal (t) represents the signal photon velocity; n background (t) represents the background photon velocity; t1 represents the gating start time; t2 represents the gating end time; Constructing a polarization-modulated lidar ranging model: Polarization modulation is achieved by a Polknell cell placed between two orthogonal polarizers. When a voltage is applied to the Polknell cell, the phase delay of the polarized light is proportional to the applied voltage, expressed as: In the formula: Γ is the phase delay; λ is the laser wavelength; n0 is the constant refractive index at the center of the Pockels cell; r 63 is the electro-optic coefficient; V(t) is the Pockels cell voltage.

2. The non-scanning single-photon polarization three-dimensional imaging method according to claim 1, characterized in that, The performance parameters of a single-photon avalanche photodetector (SPAD) include: detection efficiency, dark count rate, afterpulse probability, dead time, and time jitter. Detection efficiency represents the probability that a single photon incident on the SPAD will generate a detectable avalanche signal, PDE = QE·P. ava ·P det In the formula: PDE is the detection efficiency; QE is the quantum efficiency; P ava P represents the avalanche probability. det This represents the detection probability.

3. The non-scanning single-photon polarization three-dimensional imaging method according to claim 1, characterized in that, The probability that no photoelectron event occurs during the door opening time is 4. The non-scanning single-photon polarization three-dimensional imaging method according to claim 3, characterized in that, The probability of at least one photoelectron event generating an avalanche signal and being detected is: This refers to the photon count caused by signal photons and background photons.

5. The non-scanning single-photon polarization three-dimensional imaging method according to claim 1, characterized in that, During the opening time interval, the probability of k photoelectrons caused by shot noise and dark noise is: N noise (t)=N SHOT (t)+N DCR (t) N DCR (t)=DCR·t Where: N noise (t) represents the number of electrons in shotgun noise and other dark noise; N SHOT (t) represents the number of shotgun noise electrons; N DCR (t) represents the number of dark noise electrons; DCR represents the dark count rate.

6. The non-scanning single-photon polarization three-dimensional imaging method according to claim 5, characterized in that, The probability that no photoelectron event occurs during the door opening time is 7. The non-scanning single-photon polarization three-dimensional imaging method according to claim 6, characterized in that, The probability of at least one photoelectron event generating an avalanche signal and being detected is: This refers to the photon count caused by shot noise and dark noise.

8. The non-scanning single-photon polarization three-dimensional imaging method according to claim 1, characterized in that, The applied voltage is linear, represented as In the formula: t0 is the delay time; T r V is the voltage rise time. π It is a half-wave voltage.

9. A non-scanning single-photon polarization three-dimensional imaging method according to claim 8, characterized in that, Half-wave voltage is expressed as 10. A non-scanning single-photon polarization three-dimensional imaging method according to claim 9, characterized in that, The phase delay of polarized light can be simplified to a function of time, expressed as: The micro-polarization array consists of multiple groups of polarizers, including four linear polarizers at 0°, 45°, 90°, and 135°. The light intensity after passing through each group of four polarizers can be expressed as... The phase delay can be obtained by measuring the four light intensities mentioned above. The phase delay calculation is expressed as follows: The target distance obtained by this method is expressed as: The distance to the target is determined by measuring the light intensity, thus eliminating the influence of time errors.

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