Entangled light quantum three-dimensional color imaging method based on photon flight time

Abstract

The invention provides an entangled light quantum three-dimensional color imaging method based on photon flight time. The method comprises the following steps: firstly, irradiating pump light to a periodically poled potassium titanyl phosphate crystal, and generating a spontaneous parametric down-conversion process to obtain entangled photon pairs; then, photon arrival time pulse sequences of the signal light path and the reference light path are collected through a single photon detector; secondly, calculating the flight time difference of the signal light and the reference light at each pixel point through coincidence measurement to obtain the distance between the corresponding position and the light source; thirdly, estimating the target reflectivity according to the probability density function of coincidence counting of the two paths of photons; and finally, realizing quantum three-dimensional color imaging according to the distance information of the corresponding position of each pixel point and the target reflectivity.

Description

Technical Field

[0001] The present invention belongs to the field of quantum precision measurement, and specifically refers to performing coincidence measurement on the photon arrival time pulse sequence of the signal light path and the reference light path during entangled light quantum imaging, calculating the flight time difference between the signal light and the reference light of each pixel point, obtaining the distance between the corresponding position and the light source, and realizing quantum three-dimensional color imaging in combination with the target reflectivity. Background Art

[0002] Entangled photon imaging technology utilizes the spatial correlation characteristics of entangled photons to achieve high-resolution and high-sensitivity imaging under extremely low light conditions, overcoming the limitation of traditional imaging technology in resolution due to the optical diffraction limit. In addition, by separating the detection process from the imaging process, entangled photon imaging technology can effectively suppress the impact of environmental factors such as atmospheric turbulence and smoke on the imaging quality, thereby achieving high-quality imaging under complex environmental conditions. In recent years, quantum three-dimensional imaging technology has gradually emerged, mainly achieved through photon time-of-flight technology and photometric stereo vision technology, and compared with traditional two-dimensional quantum imaging, three-dimensional quantum imaging can better identify the details and morphology of the target.

[0003] At present, the main challenge facing quantum 3D imaging is the contradiction between imaging speed and signal-to-noise ratio. Research is mainly focused on single-photon 3D imaging, single-pixel 3D imaging, and photon counting 3D imaging. Single-photon 3D imaging uses single-photon detection technology to achieve high-precision depth measurement, which can be used for remote sensing applications such as terrain mapping and target identification, especially in military reconnaissance. It can provide high-precision detection capabilities; single-pixel 3D imaging combines quantum imaging technology and modulated optical elements to reconstruct high-resolution images under low-light conditions, which is suitable for medical imaging and environmental monitoring; photon counting 3D imaging focuses on sparse reconstruction under low signal-to-noise ratio conditions, which is suitable for astronomical observation and depth detection.

[0004] The present invention uses the entangled characteristics of entangled photon pairs to achieve accurate measurement of photon flight time, which can not only provide high-quality images under extremely low light conditions, but also achieve three-dimensional color reconstruction. This technology has important application value in many fields such as medical imaging, remote sensing detection, and military exploration. Summary of the invention

[0005] The purpose of the present invention is to provide a method for three-dimensional color imaging of entangled light quanta based on photon flight time. The specific steps are as follows:

[0006] Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light. The pump light passes through an isolator to isolate the reflected light in the optical fiber channel and improve the beam quality.

[0007] Step 2: The pump light passes through a collimator to convert the light beam into parallel light, and a half-wave plate (HWP) and a quarter-wave plate (QWP) are used to modulate the parallel light into linearly polarized light. At the same time, lenses 1 and 2 are combined into a beam reduction optical system to concentrate the energy of the beam.

[0008] Step 3: Irradiate linearly polarized light to a periodically polarized potassium titanyl phosphate (PPKTP) crystal. At this time, the photons in the light beam undergo spontaneous parametric down-conversion (SPDC) with a certain probability, generating entangled photon pairs.

[0009] Step 4: Use lenses 3 and 4 to form a beam expansion optical system, and use a polarization beam splitter (PBS) to split the entangled photon pair into a signal photon and a reference photon;

[0010] Step 5: The reference photon is irradiated to the reflector and reaches the digital micromirror device (DMD), and the beam is reduced by using lenses 5 and 6. Then, the stray light is filtered out by a narrow-band filter 1, and the reference photon is detected by a single-photon detector 1 through a collimator to obtain the arrival time pulse sequence R of the reference photon. t ;

[0011] Step 6: The signal photons are irradiated to the three-dimensional target to be imaged through free space, and the beam is reduced by using lenses 8 and 9. Then, after passing through the narrow-band filter 2, the signal photons are detected by the single-photon detector 2 to obtain the arrival time pulse sequence S t ;

[0012] Step 7: By R t and S t Perform coincidence measurement to obtain the coincidence count value C at each pixel point x,y And the corresponding flight time difference τ between the signal light and the reference light x,y , and then calculate the distance between the corresponding position and the light source;

[0013] Step 8: Calculate the number of photons in the signal light path and the reference light path at each pixel point, and estimate the reflectivity of the three-dimensional target at the corresponding position based on the probability density function of the photons in the two paths meeting the count value;

[0014] Step 9: Generate point cloud coordinates (x, y, d) based on the distance information of the corresponding positions of each pixel point x,y), and fit the point cloud coordinates into a continuous three-dimensional target surface. At the same time, the estimated three-dimensional target reflectivity is used to perform color mapping on the target surface to achieve three-dimensional color imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the optical path of the method of the present invention;

[0016] Figure 2 It is an algorithm block diagram of the method of the present invention. Specific implementation plan

[0017] The method of the present invention is further described below in conjunction with the accompanying drawings, and the specific contents are as follows:

[0018] Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light. The pump light passes through an isolator to isolate the reflected light in the optical fiber channel and improve the beam quality.

[0019] Step 2: The pump light passes through a collimator to convert the light beam into parallel light, and a half-wave plate (HWP) and a quarter-wave plate (QWP) are used to modulate the parallel light into linearly polarized light. At the same time, lenses 1 and 2 are combined into a beam reduction optical system to concentrate the energy of the beam.

[0020] Step 3: Irradiate linearly polarized light to a periodically polarized potassium titanyl phosphate (PPKTP) crystal. At this time, the photons in the light beam undergo spontaneous parametric down-conversion (SPDC) with a certain probability, generating entangled photon pairs.

[0021] Step 4: Use lenses 3 and 4 to form a beam expansion optical system, and use a polarization beam splitter (PBS) to split the entangled photon pair into a signal photon and a reference photon;

[0022] Step 5: The reference photon is irradiated to the reflector and reaches the digital micromirror device (DMD), and the beam is reduced by using lenses 5 and 6. Then, the stray light is filtered out by a narrow-band filter 1, and the reference photon is detected by a single-photon detector 1 through a collimator to obtain the arrival time pulse sequence R of the reference photon. t ;

[0023] Step 6: The signal photons are irradiated to the three-dimensional target to be imaged through free space, and the beam is reduced by using lenses 8 and 9. Then, after passing through the narrow-band filter 2, the signal photons are detected by the single-photon detector 2 to obtain the arrival time pulse sequence St ;

[0024] Step 7: By R t and S t Perform coincidence measurement to obtain the coincidence count value C at each pixel point x,y And the corresponding flight time difference τ between the signal light and the reference light x,y , and then calculate the distance between the corresponding position and the light source;

[0025] Step 8: Calculate the number of photons in the signal light path and the reference light path at each pixel point, and estimate the reflectivity of the three-dimensional target at the corresponding position based on the probability density function of the photons in the two paths meeting the count value;

[0026] Step 9: Generate point cloud coordinates (x, y, d) based on the distance information of the corresponding positions of each pixel point x,y ), and fit the point cloud coordinates into a continuous three-dimensional target surface. At the same time, the estimated three-dimensional target reflectivity is used to perform color mapping on the target surface to achieve three-dimensional color imaging.

[0027] The step seven comprises the following steps:

[0028] Step 7 (a): R t and S t Each group is divided into P groups, namely and Where P is the number of pixels, Represents R t (i.e. j = 1) or S t The photon arrival time pulse sequence (length n) at the i-th (i=1,…,P) pixel in (i.e. j=2) i );

[0029] Step 7 (ii): Pulse sequence of photon arrival times at different pixels and The coincidence measurement is performed to obtain the second-order correlation curve. The ordinate and abscissa corresponding to the peak of the curve are the coincidence count values ​​c x,y and the corresponding time difference of flight between the signal light and the reference light τ x,y , and then calculate the distance between the corresponding position and the light source Where c is the speed of light;

[0030] The step eight comprises the following steps:

[0031] Step 8 (a): In the single-shot response time slot (t k-1 ,t k ), the light flux of the signal photon passing through the free space to the target to be imaged is Φ(x,y)=η a N, where ηa is the free space transmittance, N is (t i-1 ,t i ) The number of entangled photon pairs generated in

[0032] Step 8 (ii): After the signal photon is reflected by the target, the number of photons detected by the single photon detector 2 is Among them, η q is the comprehensive quantum efficiency of the single-photon detector, α x,y is the target reflectivity corresponding to the pixel point (x, y), θ t is the divergence angle of the signal light emission, A r is the receiving area of ​​the receiving optical system, N b is the background noise photon generation rate, N d is the dark count rate of the single-photon detector, and the probability that the single-photon detector 2 detects a photon is P S =1-exp[-m S (t k-1 ,t k )]. Similarly, the number of photons detected by single-photon detector 1 is m I (t k-1 ,t k )=Nη q +N d ·(t k-1 ,t k ), and the corresponding photon detection probability is P I =1-exp[-m I (t k-1 ,t k )];

[0033] Step 8 (iii): Let the total imaging time (t start ,t end ) is N. sum , then the probability density function of the coincident count value at each pixel is:

[0034]

[0035] Then, the three-dimensional target reflectivity at the corresponding position can be calculated by the maximum likelihood estimation method:

[0036]

Claims

1. The present invention proposes a method for three-dimensional color imaging of entangled light quanta based on photon flight time, characterized in that The following steps are involved: Step 1: Use a semiconductor laser with a wavelength of 405nm to generate pump light. The pump light passes through an isolator to isolate the reflected light in the optical fiber channel and improve the beam quality. Step 2: The pump light passes through a collimator to convert the light beam into parallel light, and a half-wave plate (HWP) and a quarter-wave plate (QWP) are used to modulate the parallel light into linearly polarized light. At the same time, lenses 1 and 2 are combined into a beam reduction optical system to concentrate the energy of the beam. Step 3: Irradiate linearly polarized light to a periodically polarized potassium titanyl phosphate (PPKTP) crystal. At this time, the photons in the light beam undergo spontaneous parametric down-conversion (SPDC) with a certain probability, generating entangled photon pairs. Step 4: Use lenses 3 and 4 to form a beam expansion optical system, and use a polarization beam splitter (PBS) to split the entangled photon pair into a signal photon and a reference photon; Step 5: The reference photon irradiates the reflector and reaches the digital micromirror device (DMD), and the beam is reduced by using lenses 5 and 6. Then, the stray light is filtered out by a narrow-band filter 1, and the reference photon is detected by a single-photon detector 1 through a collimator to obtain the arrival time pulse sequence R of the reference photon. t ; Step 6: The signal photons are irradiated to the three-dimensional target to be imaged through free space, and the beam is reduced by using lenses 8 and 9. Then, after passing through the narrow-band filter 2, the signal photons are detected by the single-photon detector 2 to obtain the arrival time pulse sequence S t ; Step 7: By R t and S t Perform coincidence measurement to obtain the coincidence count value C at each pixel point x,y And the corresponding time difference τ between the signal light and the reference light x,y , and then calculate the distance between the corresponding position and the light source; Step 8: Calculate the number of photons in the signal light path and the reference light path at each pixel point, and estimate the reflectivity of the three-dimensional target at the corresponding position based on the probability density function of the photon count values ​​of the two paths; Step 9: Generate point cloud coordinates (x, y, d) based on the distance information of the corresponding positions of each pixel point x,y ), and fit the point cloud coordinates into a continuous three-dimensional target surface. At the same time, the estimated three-dimensional target reflectivity is used to perform color mapping on the target surface to achieve three-dimensional color imaging. The step seven comprises the following steps: Step 7 (a): R t and S t Each group is divided into P groups, namely and Where P is the number of pixels, Represents R t (i.e. j = 1) or S t The photon arrival time pulse sequence (length n) at the i-th (i=1,…,P) pixel in (i.e. j=2) i ); Step 7 (ii): Time pulse sequence T of photon arrival at different pixel points i 1 With T i 2 The coincidence measurement is performed to obtain the second-order correlation curve. The ordinate and abscissa corresponding to the peak of the curve are the coincidence count values ​​c x,y and the corresponding time difference of flight between the signal light and the reference light τ x,y , and then calculate the distance between the corresponding position and the light source Where c is the speed of light; The step eight comprises the following steps: Step 8 (a): In the single-shot response time slot (t k-1 ,t k ), the light flux of the signal photon passing through the free space to the target to be imaged is Φ(x,y)=η a N, where η a is the free space transmittance, N is (t i-1 ,t i ) The number of entangled photon pairs generated in Step 8 (ii): After the signal photon is reflected by the target, the number of photons detected by the single photon detector 2 is Among them, η q is the comprehensive quantum efficiency of the single-photon detector, α x,y is the target reflectivity corresponding to the pixel point (x, y), θ t is the divergence angle of the signal light emission, A r is the receiving area of ​​the receiving optical system, N b is the background noise photon generation rate, N d is the dark count rate of the single-photon detector, and the probability that the single-photon detector 2 detects a photon is P S =1-exp[-m S (t k-1 ,t k )]. Similarly, the number of photons detected by single-photon detector 1 is m I (t k-1 ,t k )=Nη q +N d ·(t k-1 ,t k ), and the corresponding photon detection probability is P I =1-exp[-m I (t k-1 ,t k )]; Step 8 (iii): Let the total imaging time (t start ,t end ) is N. sum , then the probability density function of the coincident count value at each pixel is: Then, the three-dimensional target reflectivity at the corresponding position can be calculated by the maximum likelihood estimation method:

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