Coded aperture correlation holographic imaging method based on single exposure point extended hologram

Abstract

The invention discloses a coding aperture correlation holographic imaging method based on a single exposure point extended hologram, and relates to the field of computational optical imaging. According to the method, a conventional coding phase mask and a secondary phase are respectively modulated by using opposite linear phases to obtain an intensity image for simultaneously recording an object and an object hologram, then the intensity image is segmented to obtain the object and the object hologram, and finally the object and the object hologram are subjected to deconvolution to obtain a point expansion hologram for reconstruction. According to the method provided by the invention, the point expansion hologram can be obtained through single exposure, and the reconstruction quality of the interference-free coded aperture-related holography can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to coded aperture related holographic imaging technology, belonging to the field of computational optical imaging, and particularly relates to a coded aperture related holographic imaging method based on single-exposure point spread hologram. Background Art

[0002] In an optical imaging system, it is of great practical significance to simplify the imaging steps and reduce the system complexity. The complexity of traditional imaging technologies often leads to an extended imaging time and difficulties in system integration, thus restricting their application efficiency.

[0003] Interferenceless Coded Aperture Correlation Holography (I-COACH), as a non-coherent digital holographic technology, simplifies the optical system and improves the power efficiency by avoiding the interference of two light waves. However, the existing I-COACH technology has the following limitations: 1. Based on a single-channel imaging system, during the imaging process, it is necessary to replace the pinhole with the object hologram after shooting the object hologram, resulting in multiple operations during the imaging process; 2. Based on a two-channel imaging system, during the imaging process, it is necessary to separately turn on two optical paths to record the pinhole and the object hologram, with high system complexity and low efficiency; 3. For a single-channel imaging system that obtains the point spread hologram through deconvolution, during the imaging process, different coded phase masks (CPMs) are respectively loaded by using a spatial light modulator to record the reference object and its hologram, and the point spread hologram for reconstruction is obtained through deconvolution. This method improves the imaging efficiency on the basis of realizing single-channel imaging, but still requires multiple calibration steps.

[0004] In view of the above problems, the present invention proposes a method for obtaining a point spread hologram based on single exposure, which realizes the synchronous recording of the object and its hologram through linear phase, breaking through the efficiency bottleneck of the traditional I-COACH system. Summary of the Invention

[0005] A coding aperture correlation holographic imaging method based on a single-exposure point spread hologram. The core of the present invention lies in first multiplexing a conventional CPM, a quadratic phase, and a positive linear phase, multiplexing the quadratic phase and the negative linear phase, then combining these two multiplexed phases to generate a complete CPM, and finally placing the complete CPM into an I-COACH system to achieve separate recording of the hologram and the object image through single exposure. The I-COACH system includes a light source, a pinhole, an object, a phase-type spatial light modulator PSLM (Phase Spatial Light Modulator), and an image sensor. The light source uses incoherent light. After diffractive propagation and modulation by the coded phase mask CPM in the PSLM, the intensity image is finally recorded by the image sensor.

[0006] This method includes the following four steps:

[0007] S1, Generation of the complete CPM;

[0008] S11: Generate a conventional CPM based on the Gerchberg-Saxton algorithm and sparse point frequency domain design; This conventional CPM is a random phase with a spectral amplitude of multiple sparse points, denoted as Φ gsp .

[0009] The quadratic phase is expressed as Q(b) = exp{iπb(x 2 +y 2 ) / λ} In the formula, λ is the optical wavelength of the light emitted by the light source, and x and y respectively represent the transverse and longitudinal coordinate axes of any plane perpendicular to the light propagation direction.

[0010] The linear phase function is expressed as

[0011] S12: Multiplex the quadratic phase and the positive linear phase on the conventional CPM;

[0012] Multiplex a quadratic phase on the conventional CPM to determine the focal plane position, z h represents the distance from the CPM plane to the image sensor. Then, multiplex the positive linear phase wherein is the tilt sine angle between the two centers on the image sensor plane of the light wave.

[0013] S13: Multiplex the same quadratic phase and the negative linear phase, and splice to form the complete CPM;

[0014] Use the same quadratic phase and the negative linear phase Reuse. The phases generated after reusing two are spliced into a complete CPM, which is called Φ tp , and its expression is as follows:

[0015] S2, acquisition of the reference image and the unknown image;

[0016] On the CPM plane, the complex amplitude of the light diffracted and propagated from the point light source after passing through the object multiplied by the complete CPM represents the complex amplitude distribution of the light field on the CPM plane. The light with the above complex amplitude distribution is then propagated to the image sensor, and the obtained intensity distribution is the complete intensity image, and its expression is In the formula, x s and y s respectively represent the horizontal and vertical coordinate axes on the image sensor plane, x j and y j respectively represent the horizontal and vertical coordinates of the object on the object plane, U is the horizontal size of the image sensor, and represent two-dimensional Fourier transform.

[0017] In the obtained complete intensity image, G1 and G2 are the object hologram and the object image respectively. The reference image and the unknown image are obtained by using the reference object and the unknown object respectively.

[0018] S3, obtaining the point spread hologram by deconvolving the reference image;

[0019] The obtained reference image is split in the middle to obtain G1 and G2. G1 and G2 are used for deconvolution to generate the point spread hologram, and its expression is In the formula, represents two-dimensional inverse Fourier transform.

[0020] S4, object reconstruction using the generated point spread hologram and the unknown image;

[0021] The generated point spread hologram I psf is cross-correlated and reconstructed with the hologram G unknown in the corresponding image of the unknown object, and the expression is as follows In the formula, represents cross-correlation operation. Description of the Drawings

[0022] Figure 1Schematic diagram of the interference-free coded aperture correlation holographic imaging system used in a specific embodiment of the present invention.

[0023] Figure 2 A flow chart of a coded aperture correlation holographic imaging method based on a single exposure point extended hologram.

[0024] Figure 3 Complete CPM synthesis process and the masks used: (a) conventional CPM, (b) quadratic phase, (c) positive linear phase, (d) negative linear phase, and (e) complete CPM.

[0025] Figure 4 Result records of the specific implementation method: (a) reference image, (b) reference object hologram, (c) reference object image, (d) unknown object hologram, (e) unknown object reconstruction result, (f) unknown object conventional reconstruction result.

[0026] Description of reference numerals:

[0027] 1. Monochromatic LED light source, 2. First lens, 3. Pinhole or sample, 4. Second lens, 5. Polarizer, 6. Phase-type spatial light modulator PSLM, 7. CMOS image sensor. DETAILED DESCRIPTION

[0028] In order to better explain the implementation process of the present invention, the present invention will be further described in detail with reference to an embodiment below, but the present invention is not limited to this embodiment.

[0029] Example

[0030] like Figure 1 As shown, the incoherent light from the monochromatic LED light source (1) is focused by the first lens (2) to illuminate the sample slot (3). The distance from the light source to the first lens is d1, and the distance from the first lens to the object is d2. The second lens (4) collects and collimates the light beam transmitted through the object. The distance between the object and the second lens is always maintained at the focal length f of the second lens. The collimated light is modulated by the polarizer (5). The polarization direction of the modulated light beam is consistent with the active axis of the PSLM (6), so that most of the light is incident on the PSLM. The complete CPM is loaded on the PSLM, and the light is subjected to pure phase modulation through the PSLM. The distance between the image sensor (7) and the PSLM is the focal length z corresponding to the secondary phase in the CPM. h , so that the light forms a focused image on the image sensor.

[0031] Will be like Figure 3 (a) shows the conventional CPM, Figure 3 (b) The quadratic phase and Figure 3 (c) shows the positive linear phase multiplexing, Figure 3 (b) The quadratic phase andFigure 3 The negative linear phase multiplexing shown in (d) is then horizontally spliced with the other one to obtain a complete CPM as shown in Figure 3 (e). The complete CPM is loaded onto the PSLM, and the synthesis process is as shown in Figure 3 . The synthesized complete CPM is expressed as where z h represents the distance from the CPM plane to the image sensor, and is the tilt sine angle of the light wave at two centers on the sensor plane.

[0032] The modulated light forms a reference image on the image sensor as shown in Figure 4 (a). It is the imaging result of the reference object and is expressed as where x s and y s respectively represent the horizontal and vertical coordinate axes on the image sensor plane, x j and y j respectively represent the horizontal and vertical coordinates of the object on the object plane, U is the horizontal size of the image sensor, and represent the two-dimensional Fourier transform.

[0033] The reference image includes the hologram G1 of the left half of the reference object as shown in Figure 4 (b) and the reference object image G2 of the right half as shown in Figure 4 (c). By deconvolving the two, the point spread hologram of the system can be obtained, which is called the generated point spread hologram, and the expression is as follows

[0034] The hologram of the unknown object is taken as shown in Figure 4 (d) to verify the accuracy of the generated point spread hologram. The generated point spread hologram I psf and the hologram G of the unknown object unknown are cross-correlated and reconstructed, and the expression is as follows The reconstruction result I of the unknown object as shown in Figure 4 (e) is obtained. It is compared with the conventional reconstruction result of the unknown object reconstructed from the I-COACH point spread hologram obtained by the conventional method as shown in re (f). The image quality is measured by the peak signal-to-noise ratio PSNR of the result, and the PSNR expression is as follows Figure 4 (f). The image quality is measured by the peak signal-to-noise ratio PSNR of the result, and the PSNR expression is as follows Where n is the number of bits of each sampling value, generally taken as 8, that is, the pixel gray level is 256. p and q represent the horizontal and vertical coordinates of the pixel point, X(p,q) represents the measured image, Y(p,q) represents the reference image, and H and W are the number of pixels in the vertical and horizontal directions of the image respectively. The peak signal-to-noise ratio (PSNR) value of the reconstruction result obtained by this method is 31.82 dB, and the PSNR value of the conventional reconstruction result is 13.72 dB. By comparison, this method has achieved a 238% improvement in the peak signal-to-noise ratio.

[0035] It can be seen that this method has obtained a result with a higher signal-to-noise ratio than the conventional reconstruction, and has reduced the number of recordings by one compared with the traditional deconvolution method, proving the feasibility of this method in significantly improving the imaging efficiency and imaging quality of the I-COACH system.

[0036] The embodiments in the specific implementation manners only represent one implementation manner of the present invention. Embodiment 1 is an implementation device and process designed according to the method proposed by the present invention, and all are within the protection scope of the present invention. The implementation device of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present invention.

Claims

1. A coded aperture correlation holographic imaging method based on a single-exposure point expansion hologram, the method first multiplexes a conventional coded phase mask CPM (Coded Phase Mask) with a secondary phase and a positive linear phase, multiplexes the secondary phase with a negative linear phase, and then combines the two multiplexed phases to splice into a complete CPM; finally, the complete CPM is placed in an interferenceless coded aperture correlation holography I-COACH (Interferenceless Coded Aperture Correlation Holography) system to achieve separate recording of a hologram and an object image through a single exposure; the I-COACH includes a light source, a pinhole, an object, a phase spatial light modulator PSLM (Phase Spatial Light Modulator), and an image sensor; the light source uses incoherent light, which is diffracted and propagated, and after being modulated by the CPM, the image sensor records an intensity image; The method comprises the following four steps: S1: Generate complete CPM; S11: Generate conventional CPM by Gerchberg-Saxton algorithm and sparse point frequency domain design; The conventional CPM is a random phase with a spectrum amplitude of multiple sparse points, called Φ gsp ; The secondary phase is expressed as Q(b)=exp{iπb(x 2 +y 2 ) / λ} In the formula, λ is the wavelength of light emitted by the light source, and x and y represent the horizontal and vertical coordinate axes of any plane perpendicular to the direction of light propagation, respectively; The linear phase function is expressed as S12: Multiplexing of quadratic phase and positive linear phase on conventional CPM; Multiplex a secondary phase on the conventional CPM To determine the focal plane position, z h Represents the distance from the CPM plane to the image sensor, and then multiplexes the positive linear phase Among them is the sinusoidal angle at which the light wave is tilted toward the two centers on the image sensor plane; S13: multiplex the same quadratic phase and negative linear phase and splice them to form a complete CPM; With the same quadratic phase and negative linear phase Multiplexing; splicing the two multiplexed generated phases into the complete CPM, called Φ tp , which is expressed as follows: S2: obtain reference image and unknown image; On the CPM plane, the product of the complex amplitude of the light diffracted from the point light source after passing through the object and the complete CPM represents the complex amplitude distribution of the light field on the CPM plane; The light with the complex amplitude distribution is then transmitted to the image sensor, and the intensity distribution obtained is a complete intensity image, which is expressed as follows: In the formula, x s and s Represents the horizontal and vertical axes on the image sensor plane, x j and j They represent the horizontal and vertical coordinates of the object on the object plane, U is the horizontal size of the image sensor, and In the obtained complete intensity image, G1 and G2 are the object hologram and object image respectively. represents a two-dimensional Fourier transform, using a reference object and an unknown object to obtain a reference image and an unknown image respectively; S3: Deconvolute the reference image to obtain the point spread hologram; The reference image is split in the middle to obtain G1 and G2, and deconvolution is performed using G1 and G2 to generate a point expansion hologram, which is expressed as: In the formula, represents the two-dimensional inverse Fourier transform; S4: Reconstruction using generated point spread hologram and unknown image: The point spread hologram thus obtained can be used to reconstruct other unknown objects from the I-COACH system by cross-correlating it with the unknown object hologram in the corresponding image of the unknown object. The expression is as follows In the formula, Represents the cross-correlation operation.

Images