Single-pixel diffraction imaging method

Abstract

The application provides a single-pixel diffraction imaging method and device, and belongs to the field of coherent diffraction imaging and computational photography, wherein the method comprises the following steps: (1) in the single-pixel imaging light path, different modulation sequences are used to modulate the illumination light beam of the target scene, and a single-pixel detector is used to record the intensity value of a one-dimensional sequence; (2) the intensity value corresponding to the different modulation sequences is used to replace the amplitude value of the reconstructed diffraction light field on the detector plane, and then alternating iteration calculation is performed until the target scene is reconstructed. The application has the advantages of simple structure, strong operability, wide application range and strong expandability. Through the application, the cost of single-pixel diffraction imaging can be reduced, fast and accurate measurement of the target scene is realized, and convenience is brought to high-quality single-pixel imaging.

Description

Technical Field

[0001] This invention relates to a single-pixel diffraction imaging method, belonging to the fields of coherent diffraction imaging and computational photography. Background Technology

[0002] Single-pixel imaging (SPI), as a computational imaging method that uses only a single-unit photodetector for imaging and detection, has solved many problems that traditional imaging techniques cannot solve, making it widely used in many fields today. SPI mainly consists of a single-pixel detector and a related beam modulator. Its typical operation is as follows: first, the object is illuminated using a sequence of modulated light fields; then, the single-pixel detector records the corresponding one-dimensional intensity values; finally, the mask information and the corresponding recorded intensity are combined to reconstruct the two-dimensional information of the object. Therefore, compared with traditional imaging techniques using array detectors, single-pixel imaging has the following advantages: (1) The single-point detector in single-pixel imaging has better detector characteristics, higher detection efficiency, and higher sensitivity than array detectors, and can perform imaging and detection even under extremely weak light, atmospheric turbulence, and scattering media conditions; (2) The development of single-pixel detectors always precedes that of array detectors, and single-pixel detectors have a wider detection band than array detectors; (3) Compressed sensing and deep learning algorithms can make single-pixel imaging more efficient.

[0003] In single-pixel imaging technologies, the main approach involves using modulation masks and recorded one-dimensional intensity sequences, followed by algorithms to reconstruct the corresponding two-dimensional scene. Traditional reconstruction algorithms include non-iterative reconstruction methods, deep learning reconstruction methods, and iterative reconstruction methods. Non-iterative reconstruction methods primarily include fluctuation correlation imaging, fast Walsh-Hadamard transform, and Fourier domain regularized inverse transform. Fluctuation correlation imaging utilizes the characteristics of light field fluctuations, eliminating background terms and significantly improving image quality compared to direct correlation imaging. The fast Walsh-Hadamard transform algorithm leverages the binary orthogonalization of the Hadamard matrix, accelerating the calculation of the reconstructed object and reducing the algorithm's spatial complexity and operational difficulty. The Fourier domain regularized inverse transform reconstruction method overcomes the challenge of most non-iterative methods failing to reconstruct single-pixel images under undersampling conditions, thus enabling real-time imaging of object scenes. Deep learning-based reconstruction methods have been gradually applied in single-pixel imaging technologies, and have proven to offer significant advantages in imaging speed and quality for linear reconstruction algorithms and compressed sensing algorithms under low sampling rates. Among iterative reconstruction algorithms, gradient descent models the single-pixel imaging reconstruction problem as a quadratic optimization problem, requiring a high sampling rate and exhibiting slow convergence. Alternating projection uses each mask matrix and detector intensity value as constraints in the spatial and frequency domains, respectively, applying constraints through alternating projections in both spaces to reconstruct the scene of the object under test. While this method can eliminate background noise, its reconstruction quality is highly dependent on the sampling rate and exhibits poor robustness.

[0004] Patent document CN110864817 discloses a non-interferometric quantitative phase imaging method based on a single-pixel detector. This method measures the DC component of an object in the far field by performing independent phase and amplitude modulation under monochromatic illumination. By modulating both phase and amplitude separately, its correlation is detected to obtain the object's phase information. Furthermore, the constant phase shift is determined by the object itself, eliminating interference measurements in quantitative phase imaging. However, this patented technology requires not only separate amplitude and phase modulation of the illumination field to record different intensities for separate amplitude and phase resolution, but also the use of a 4f system to filter the diffraction frequency stages of the illumination light. The single-pixel diffraction imaging method proposed in this paper, apart from the mentioned modulators (DMD and SLM), requires no other spatial or frequency domain correlation modulation and can simultaneously reconstruct the amplitude and phase of the detected target scene. Summary of the Invention

[0005] To overcome the shortcomings of existing single-pixel imaging techniques using iterative algorithms, such as the gradient descent method requiring a high sampling rate and the alternating projection method having poor robustness, this invention proposes a single-pixel diffraction imaging method that enables accurate reconstruction of the complex amplitude of the sample under test under low sampling rate conditions.

[0006] The technical solution of the present invention is as follows:

[0007] A single-pixel diffraction imaging method is characterized by including two processes: optical field modulation detection and computational demodulation reconstruction.

[0008] (1) Optical Field Modulation Detection Process: In single-pixel diffraction imaging, monochromatic plane light is used as the illumination source for detection. Digital micromirror devices (DMDs) and spatial light modulators (SLMs) are used to modulate the amplitude and phase of the incident light field, respectively. Modulation matrices are loaded onto the DMD and SLM, respectively. The incident light field, after amplitude and phase modulation, is emitted onto the target scene, then transmitted through the target scene to a converging lens behind it. Finally, the converging lens focuses the light onto a single-pixel detector placed at the focal point behind the lens, thus obtaining the light field intensity sequence I of the target scene. i ;

[0009] (2) Calculation demodulation and reconstruction process: Input the light field intensity sequence and the corresponding modulation matrix into the reconstruction algorithm respectively. Set the initial guess of the target scene reconstruction as random distribution. Transmit back and forth between the target scene plane and the recording plane, as well as between the spatial domain and the frequency domain. Iterate and calculate alternately to reconstruct the target scene. Stop the calculation when the result of the iterative calculation meets the expectations.

[0010] Furthermore, the reconstruction algorithm comprises the following specific steps:

[0011] ① Set the initial guess g for the target scene o (u,v), input the corresponding amplitude modulation matrix and phase modulation matrix

[0012] ②The lighting distribution of the target scene is represented as follows: The initial guess is that the emitted beam from the target scene is φ i (u,v)=p i (u,v)×g o (u,v);

[0013] ③ The light field intensity of the recording surface of a single-pixel detector is expressed as:

[0014]

[0015] in, For diffraction propagation symbols;

[0016] ④ Use the intensity value of the recorded light field to constrain the guessed recording surface light field, that is, use the square root of the recorded intensity value as the amplitude of the constrained region in the light field to obtain a new light field:

[0017]

[0018] Where δ is the aperture function associated with the surface element of a single-pixel detector.

[0019] ⑤ The replaced light field is transmitted back to the target scene plane, resulting in:

[0020]

[0021] Right now:

[0022] in, This is the symbol for reverse diffraction propagation;

[0023] ⑥ Then update the light field on the target scene plane:

[0024]

[0025] Where * represents the conjugate symbol, and α is a constant of 0.01;

[0026] ⑦ Repeat steps ②-⑥ until the reconstruction result matches the expectation.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) Compared with other methods, the present invention has a simple structure and is easy to operate: (i) In the process of modulation recording, the transformation of the illumination field on the target scene can be achieved by simply changing the modulation input of DMD and SLM through a computer; (ii) In actual operation, the required modulation input pattern can be automatically generated by the corresponding control software; (iii) In the reconstruction process, the reconstruction of the complex amplitude scene can be achieved by simply inputting the recorded intensity value and the corresponding modulation image into the reconstruction algorithm mentioned above.

[0029] (2) Compared with other methods, the detection process of this invention is simple and does not require complex operation of the incident light field: (i) In the proposed single-pixel diffraction imaging method, since the amplitude and phase of the illumination light field are modulated simultaneously, after recording the corresponding diffraction intensity, the complex amplitude reconstruction of the target scene can be achieved simultaneously by the reconstruction method mentioned above, without having to separate the amplitude and phase of the target scene for reconstruction; (ii) In the illumination light field used, only a relatively simple initial filtering modulation of the laser is required to obtain the parallel illumination light required for illumination; (iii) In this method, apart from the proposed modulators (DMD and SLM), there is no need to perform any spatial or frequency domain modulation on the subsequent illumination beam.

[0030] (3) By improving the device of the present invention, higher measurement accuracy and sensitivity can be obtained, which increases the practicality of the device: (i) Since the entire operating system changes the light field by changing the modulation input only through the online computer, the present invention reduces or avoids the recording error caused by mechanical changes as much as possible; (ii) By replacing the illumination source with a shorter wavelength and a better modulation device, higher measurement accuracy and sensitivity can be obtained. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the optical path of the single-pixel diffraction imaging device of the present invention. In the figure: 1-Helium-neon laser, 2-Attenuator, 3-Beam collimation and beam expansion system, 4-DMD, 5-SLM, 6-Converging lens, 7-Single-pixel detector;

[0032] Figure 2 This is a schematic flowchart of the single-pixel diffraction imaging method of the present invention;

[0033] Figure 3 This is a schematic diagram of the reconstruction method in this invention;

[0034] Figure 4 These are the effect diagrams of the single-pixel diffraction imaging method of the present invention, wherein (a) is the target scene image, (b) is the intensity sequence recorded by the single-pixel detector, and (c) is the reconstructed target scene image. Detailed Implementation

[0035] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the specific implementation elements are the same as those described above. It should be noted that the examples described with reference to the accompanying drawings are illustrative of the invention and are intended to explain the content and principles of the present invention.

[0036] It should be noted that the resolution of the target scene image used in this embodiment is 128×128, and u, v and x, y are used to represent the spatial coordinates of the object plane and the detector plane, respectively, in the calculation.

[0037] A single-pixel diffraction imaging method includes the following steps:

[0038] S1. Construct a single-pixel diffraction imaging system: such as Figure 1 As shown, a helium-neon laser 1 is placed, and along the output beam transmission direction of the helium-neon laser 1, an attenuator 2, a beam collimation and expansion system 3, a DMD 4, an SLM 5, a converging lens 6, and a single-pixel detector 7 are placed sequentially. The single-pixel detector 7 is located at the focal point of the converging lens 6. The beam collimation and expansion system 3 is adjusted so that the coherent beam emitted from the system is a parallel beam. After the DMD 4 modulates the input pattern to achieve amplitude modulation of the light field, the emitted light illuminates the SLM 5. The phase modulation of the light field achieved by the SLM 5 modulates the input pattern, and the intensity of the light field after being converged by the converging lens 6 can be received by the single-pixel detector 7.

[0039] S2. The target scene image is placed in the incident light path of the converging lens 6. The outgoing light illuminating the target scene image is converged by the converging lens 6 and received by the single-pixel detector 7, thus changing the loading matrix of the DMD and SLM. and And the corresponding intensity value data I is recorded by the single-pixel detector 7. i [like Figure 4 [As shown in (b)], where i = 1, 2, 3, ..., 1.6 × 10 4 It should be noted that the subscript i represents the sequence value of the recorded intensity sequence. Since the resolution of the object image used in the demonstration is 128×128, it is necessary to record 16384 times in order to achieve sufficient sampling of the object.

[0040] S3. Record the one-dimensional intensity sequence data I i The corresponding modulation matrix Combined with the corresponding calculation algorithm, the flowchart is as follows: Figure 3 As shown, the specific process is as follows:

[0041] (a) Set the initial guess g of the object o (u,v) is a 128×128 random distribution matrix; input the corresponding amplitude modulation matrix. and phase modulation matrix

[0042] (b) The illumination distribution of an object can be represented as Therefore, the initial guess

[0043] The emitted beam after measuring the object is φ i (u,v)=p i (u,v)×g o(u,v);

[0044] (c) The light field on the recording surface of a single-pixel detector can be expressed as:

[0045]

[0046] in, For diffraction propagation symbols;

[0047] (d) Use the recorded intensity to constrain the conjectured light field of the recording surface, i.e., use the average of the recorded intensity values.

[0048] The square root is used as the amplitude value of the light field to obtain a new light field:

[0049]

[0050] Where δ is the aperture function associated with the detector element.

[0051] (e) The replaced light field is propagated back to the object plane, thus obtaining:

[0052]

[0053] Right now:

[0054] in, This is the symbol for reverse diffraction propagation;

[0055] (f) Then update the light field on the object plane:

[0056]

[0057] Where * represents the conjugate symbol, and α is a constant 0.01;

[0058] (g) Repeat steps (b)-(f) until the expected result is obtained [e.g.] Figure 4 (c) is shown.

Claims

1. A single-pixel diffraction imaging method, characterized in that, It includes two processes: optical field modulation detection and computational demodulation reconstruction; (1) Light field modulation detection process: In single-pixel diffraction imaging, monochromatic plane light is used as the illumination source for detection, and digital micromirror devices are used. and spatial light modulator The amplitude and phase of the incident light field were modulated respectively, and in Modulation matrices are loaded on top respectively The incident light field, after amplitude and phase modulation, is emitted onto the target scene, then transmitted through the target scene to a converging lens behind it. Finally, the converging lens focuses the light onto a single-pixel detector placed at the focal point behind the lens, thus obtaining the light field intensity sequence of the target scene. ; (2) Calculation demodulation and reconstruction process: Input the light field intensity sequence and the corresponding modulation matrix into the reconstruction algorithm respectively. Set the initial guess of the target scene reconstruction to random distribution. Transform back and forth between the target scene plane and the recording plane, as well as between the spatial domain and the frequency domain. Alternately iterate and calculate to reconstruct the target scene. Stop the calculation when the result of the iterative calculation meets the expectations. The reconstruction algorithm comprises the following steps: Set an initial guess for the target scenario. Input the corresponding amplitude modulation matrix and phase modulation matrix ; The lighting distribution of the target scene is represented as The initial guess is that the emitted beam from the target scene is ; The light field intensity of the recording surface of a single-pixel detector is expressed as: in, For diffraction propagation symbols; The intensity value of the recorded light field is used to constrain the predicted light field of the recording surface; that is, the square root of the recorded intensity value is used as the amplitude of the constrained region in the light field to obtain a new light field. in, It is the aperture function associated with the surface element of a single-pixel detector. ; The replaced light field is then transmitted back to the target scene plane, resulting in: ； Right now: in, This is the symbol for reverse diffraction propagation; Then update the light field on the target scene plane: Where * represents the conjugate symbol. It is a constant of 0.01; Repeat steps Until the reconstruction results that match expectations are obtained.

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