Interferenceless Coded Aperture Correlation Holography Research Articles

Point spread function engineering enable resolution enhanced imaging for Interferenceless coded aperture correlation holography

The point spread function (PSF) of an optical system could characterize the resolving ability of the whole optical system for point light sources. Therefore, the imaging performance of the system could be significantly improved by regulating and optimizing the PSF. In this paper, we innovatively propose a single-exposure hologram resolution enhanced cross-correlation (RECC) method for Interferenceless coded aperture holography(I-COACH) system, circumventing the necessity to obtain the point spread hologram (PSH) of an ideal point object. The RECC method firstly acquires an approximate image of a large-size point object by Lucy-Richardson (LR) algorithm in lens imaging mode, and takes it as a PSF to acquire a PSH with ideal size of the I-COACH system by LR algorithm again, and finally acquires a reconstructed image by the single-exposure hologram RECC method. In the RECC method, the approximate ideal PSHs at different axial positions of the system are acquired by offline operation, therefore, it has a high imaging temporal resolution, and the imaging transverse resolution is not affected by the size of the point objects at the time of recording the PSH, which provides a high imaging signal-to-noise ratio and stable resolution. The proposed method provides powerful technical support for further extending the application field of the I-COACH system, and provides technical reference for other incoherent imaging.

Multiple images simultaneous encryption and decryption via deep-learning assisted interferenceless coded aperture correlation holography

Optical encryption based on interferenceless coding aperture correlation holography (I-COACH) is one of the holographic encryption technologies. I-COACH with dual-channel has been employed to encrypt two plaintexts, not only is the encryption capacity limited, but when the two plaintexts are horizontally overlapped, the crosstalk between the two decrypted plaintexts becomes significant. To address these issues, we present an optical multiple images encryption system based on single-channel I-COACH. In our optical encryption system, the multiple images are placed adjacent to each other and encrypted simultaneously through a single-shot I-COACH. The traditional cross-correlation methods fail to decrypt the multiple plaintexts, we propose a decryption scheme based on a novel deep learning framework (M-Net). The multiple plaintexts can be decrypted from a single ciphertext simultaneously, greatly improving the decryption efficiency by our method. Moreover, the crosstalk between the multiple images is avoided. Various experiments are conducted to demonstrate the effectiveness and feasibility of our proposal.

Accelerating quad Airy beams-based point response for interferenceless coded aperture correlation holography.

Interferenceless-coded aperture correlation holography (I-COACH) is a promising single-shot 3D imaging method in which a coded phase mask (CPM) is used to encode 3D information about an object into an intensity distribution. However, conventional CPM encoding methods usually lead to intensity dilution, especially in the recording of point spread holograms (PSHs), resulting in low-resolution reconstruction of I-COACH. Here, we propose accelerating quad Airy beams with four mainlobes as a point response to enable weak diffraction propagation and a sharp maximum intensity in the transverse direction. Moreover, the four mainlobes exhibit lateral acceleration in 3D space, so the PSHs in different axial positions show a unique and concentrated intensity distribution on the image sensor, thereby realizing a high-resolution reconstruction of I-COACH. Compared with conventional CPM encoding methods, the proposed accelerating quad Airy-beam-encoding method has superior performance in improving the resolution of I-COACH reconstruction even in the presence of external interference.

Single shot interferenceless coded aperture correlation holography via a learnable Wiener deconvolution network

One of the challenges in interferenceless coded aperture correlation holography (I-COACH) is high-quality single-shot reconstruction, as conventional cross-correlation reconstruction algorithm requires recording multiple holograms and complex reconstruction operations, resulting in serious background noise. Here, we present a deep learning based single-shot reconstruction by introducing a learnable Wiener deconvolution network in I-COACH. By feeding the point spread hologram (PSH) of I-COACH system and object hologram (OH) into Wiener deconvolution, a mapping relationship between Wiener deconvolution result and ground truth is generated. A Res-UNet is trained to learn optimal filter and noise regularization parameters, thereby achieving high quality reconstruction. Moreover, the training dataset used in our network are simulated using PSH that is obtained through only one experiment acquisition in advance, greatly simplifying experimental OH dataset acquisition. Compared to the conventional correlation reconstruction methods, the proposed Wiener deconvolution network can conveniently realize high-quality single-shot reconstruction in I-COACH, and the axial sensitivity in 3D reconstruction can be demonstrated by varying scattering degree of coded phase mask. Importantly, this Wiener deconvolution solution will provide an enlightening reference for dynamic imaging in I-COACH.

Adaptive coded phase mask design and high-quality image reconstruction for interference-less coded aperture correlation holography.

The interference-less coded aperture correlation holography is a non-scanning, motionless, and incoherent technique for imaging three-dimensional objects without two-wave interference. Nevertheless, a challenge lies in that the coded phase mask encodes the system noise, while traditional reconstruction algorithms often introduce unwanted surplus background components during reconstruction. A deep learning-based method is proposed to mitigate system noise and background components simultaneously. Specifically, this method involves two sub-networks: a coded phase mask design sub-network and an image reconstruction sub-network. The former leverages the object's frequency distribution to generate an adaptive coded phase mask that encodes the object wave-front precisely without being affected by the superfluous system noise. The latter establishes a mapping between the autocorrelations of the hologram and the object, effectively suppresses the background components by embedding a prior physical knowledge and improves the neural network's adaptability and interpretability. Experimental results demonstrate the effectiveness of the proposed method in suppressing system noise and background components, thereby significantly improving the signal-to-noise ratio of the reconstructed images.

Resolution-enhanced imaging by interferenceless coded aperture correlation holography with two competing methods of phase mask synthesis

Introducing a scattering phase mask between an object and an objective lens can improve the imaging resolution of a maskless system. The resolution enhancement is achieved using the technique of interferenceless coded aperture correlation holography with a point spread hologram (PSH) of N randomly distributed dots. For the same PSH type, there is more than one way to synthesize the phase mask. In this study, we suggest a new method of synthesizing masks and compare it with the previous method. The new method is random multiplexing of linear phase functions, each of which is responsible for a single dot on the camera plane. The previous method is based on the well-known iterative Gerchberg-Saxton algorithm with the constraints of a randomly chosen dot pattern on the camera plane and a pure phase function on the mask plane. In terms of the signal-to-noise ratio of the reconstructed image, the iterative algorithm is better for high N but worse for low N, as expected. This article has also answered the question of which method is preferred to synthesize the phase mask.

Single viewpoint tomography using point spread functions of tilted pseudo-nondiffracting beams in interferenceless coded aperture correlation holography with nonlinear reconstruction

Single viewpoint tomography using point spread functions of tilted pseudo-nondiffracting beams in interferenceless coded aperture correlation holography with nonlinear reconstruction

Non-iterative reconstruction of interferenceless coded aperture correlation holography enabled high quality three-dimensional imaging

Interferenceless coded aperture correlation holography (I-COACH) is a rapidly developing indirect three-dimensional (3D) imaging technique. However the ideal point spread function of imaging system is not obtained in most cases, the object hologram is usually correlated with the system response of a limited-size pinhole during the reconstruction process. As a result, the quality of reconstructed images is contaminated by noise. In this paper, the system response of a limited-size pinhole is regarded as the convolution of the pinhole (as an object) intensity and the ideal point spread function of I-COACH, a mathematical analysis of the background noise is conducted and a general high-quality reconstruction mathematic model of I-COACH system is derived when a limited-size pinhole is used to record point spread hologram, in which the reconstructions and noise is separated. Then a non-iterative cross-correlation reconstruction algorithm has been developed here to achieve high-quality 3D reconstruction. The proposed method has been implemented on a regular I-COACH system in both transmission as well as reflection illumination modes to demonstrate the imaging ability of our method. The experimental results show that high quality reconstructions can be achieved by our proposal with a single-exposure object hologram.

Optical 3D information encryption and rapid decryption via interferenceless coded aperture correlation holography

Holographic encryption has obvious advantages in large key space and anti-attack ability, but the corresponding coherent noise and optical alignment requirement greatly affect the encryption efficiency and decryption quality. Here, we present an optical 3D information encryption method based on the interferenceless coded aperture correlation holography (I-COACH), which consists of a coded phase mask and a lens. The speckle pattern, which is the convolution of the point spread hologram (PSH) with the object intensity distribution recorded in the image sensor plane, is used as the ciphertext, and these pre-recorded PSH are utilized as the decryption key. Due to the spatial decorrelation characteristics of the PSH at different axial positions, the plaintext can be decrypted only when the ciphertext is cross-correlated with the PSH of its corresponding axial position. Therefore, a 3D object composed of multiple 2D planes can only be decrypted by the PSH of its corresponding depth. For rapid and efficient decryption, we introduce the space division multiplexing technology. By multiplexing coded phase masks at different positions, the PSH at two positions can be simultaneously recorded in single-shot. In addition to improving the encryption efficiency and decryption quality, both numerical simulation and experimental results demonstrate the excellent security and robustness of the proposed I-COACH based 3D information encryption method.

3D incoherent imaging using an ensemble of sparse self-rotating beams.

Interferenceless coded aperture correlation holography (I-COACH) is one of the simplest incoherent holography techniques. In I-COACH, the light from an object is modulated by a coded mask, and the resulting intensity distribution is recorded. The 3D image of the object is reconstructed by processing the object intensity distribution with the pre-recorded 3D point spread intensity distributions. The first version of I-COACH was implemented using a scattering phase mask, which makes its implementation challenging in light-sensitive experiments. The I-COACH technique gradually evolved with the advancement in the engineering of coded phase masks that retain randomness but improve the concentration of light in smaller areas in the image sensor. In this direction, I-COACH was demonstrated using weakly scattered intensity patterns, dot patterns and recently using accelerating Airy patterns, and the case with accelerating Airy patterns exhibited the highest SNR. In this study, we propose and demonstrate I-COACH with an ensemble of self-rotating beams. Unlike accelerating Airy beams, self-rotating beams exhibit a better energy concentration. In the case of self-rotating beams, the uniqueness of the intensity distributions with depth is attributed to the rotation of the intensity pattern as opposed to the shifts of the Airy patterns, making the intensity distribution stable along depths. A significant improvement in SNR was observed in optical experiments.

Annular multi-focal-phase mask multiplexing based large depth of field imaging by interferenceless coded aperture correlation holography

Extending depth-of-field (DOF) of the imaging system without modifying the structure and sacrificing imaging performances of the optical system is of great significance to broaden the capability and application of the imaging system. In this paper, the interferenceless coded aperture correlation holography(I-COACH) is developed to be a large-depth incoherent imaging system by employing an annular multi-focal coded phase mask (AM-CPM). Based on the analyses of axial defocus characteristics in I-COACH, the defocus compensation function is defined, the AM-CPM is designed and multiplexed on the system optical pupil, which plays the role of a gradual lens. In AM-CPM, multi-annular zones with different focal lengths are used to compensate different axial defocus aberrations and adjacent annular zones have symmetric axial defocus aberration correction capability according to the imaging characteristics of the system. The simulations and experimental results fully demonstrate that the axial point spread function distribution of the system obtained by AM-CPM is continuous and the development method enables the extension of the DOF of the I-COACH system by only single exposure point spread hologram. This solution is expected to provide great potential in the field of microscopic imaging and other fields of that based on I-COACH system.

Multi-wavelength imaging with extended depth of field using coded apertures and radial quartic phase functions

This study demonstrates a new multi-wavelength imaging technique with an extended depth of field. The spatial and spectral information of the objects is encoded into a single bipolar function of sparse dots using coded phase masks (CPMs) and a radial quartic phase function (RQPF). Each wavelength produces an intensity response of sparse dots with a unique set of distances between the dots, enabling the decoding of multispectral information. The RQPF is introduced to extend the depth of focus for different wavelengths. A library of point spread holograms (PSHs) is prerecorded with uniquely designed CPMs by placing the point objects of multiple wavelengths at the system input. For reconstruction, the object hologram is cross-correlated with a PSH corresponding to the wavelength of the object. The results are compared with direct imaging and with the conventional technique of interferenceless coded aperture correlation holography. The method is unique because the number of camera shots required for multi-wavelength imaging is the same as for monochromatic imaging.

Interferenceless coded aperture correlation holography based on Deep-learning reconstruction of Single-shot object hologram

In interferenceless coded aperture correlation holography with incoherent illumination(I-COACH), point spread hologram(PSH) is important and it is usually necessary to record the PSH library priori. However, the recording of PSH library is time-consuming and basiclly difficult to obtain ideal PSH. The reconstructions correspondingly suffer from some noise which results from the cross-correlation reconstruction of nonideal PSH and object hologram (OH). Here a deep-learning-based interferenceless coded aperture correlation holographic imaging technique (DP-based I-COACH) is developed, in which the object can be reconstructed directly from a single-shot object hologram (OH) without any point spread hologram priori. In DP-based I-COACH, a convolutional neural network (CNN) composed of five encoders and four decoders which follows the encoder-decoder “U-net” architecture is employed. Different object intensity patterns recorded by single-shot together with their associated ground truth form data pairs, are used to train the CNN. In order to demonstrate the reliability of our proposed method, the imaging performances of our proposal is investigated under different experimental conditions, the reconstruction image quality is obviously improved compared with other reconstruction algorithms. The depth of field extension of our proposal without sacrificing the imaging quality and increasing the complexity of system is also described, which will drive the application of I-COACH in some potential scenarios, such as endoscopic application.

3D single shot lensless incoherent optical imaging using coded phase aperture system with point response of scattered airy beams

Interferenceless coded aperture correlation holography (I-COACH) techniques have revolutionized the field of incoherent imaging, offering multidimensional imaging capabilities with a high temporal resolution in a simple optical configuration and at a low cost. The I-COACH method uses phase modulators (PMs) between the object and the image sensor, which encode the 3D location information of a point into a unique spatial intensity distribution. The system usually requires a one-time calibration procedure in which the point spread functions (PSFs) at different depths and/or wavelengths are recorded. When an object is recorded under identical conditions as the PSF, the multidimensional image of the object is reconstructed by processing the object intensity with the PSFs. In the previous versions of I-COACH, the PM mapped every object point to a scattered intensity distribution or random dot array pattern. The scattered intensity distribution results in a low SNR compared to a direct imaging system due to optical power dilution. Due to the limited focal depth, the dot pattern reduces the imaging resolution beyond the depth of focus if further multiplexing of phase masks is not performed. In this study, I-COACH has been realized using a PM that maps every object point into a sparse random array of Airy beams. Airy beams during propagation exhibit a relatively high focal depth with sharp intensity maxima that shift laterally following a curved path in 3D space. Therefore, sparse, randomly distributed diverse Airy beams exhibit random shifts with respect to one another during propagation, generating unique intensity distributions at different distances while retaining optical power concentrations in small areas on the detector. The phase-only mask displayed on the modulator was designed by random phase multiplexing of Airy beam generators. The simulation and experimental results obtained for the proposed method are significantly better in SNR than in the previous versions of I-COACH.

Enhancement of Imaging Quality of Interferenceless Coded Aperture Correlation Holography Based on Physics-Informed Deep Learning

Interferenceless coded aperture correlation holography (I-COACH) was recently introduced for recording incoherent holograms without two-wave interference. In I-COACH, the light radiated from an object is modulated by a pseudo-randomly-coded phase mask and recorded as a hologram by a digital camera without interfering with any other beams. The image reconstruction is conducted by correlating the object hologram with the point spread hologram. However, the image reconstructed by the conventional correlation algorithm suffers from serious background noise, which leads to poor imaging quality. In this work, via an effective combination of the speckle correlation and neural network, we propose a high-quality reconstruction strategy based on physics-informed deep learning. Specifically, this method takes the autocorrelation of the speckle image as the input of the network, and switches from establishing a direct mapping between the object and the image into a mapping between the autocorrelations of the two. This method improves the interpretability of neural networks through prior physics knowledge, thereby remedying the data dependence and computational cost. In addition, once a final model is obtained, the image reconstruction can be completed by one camera exposure. Experimental results demonstrate that the background noise can be effectively suppressed, and the resolution of the reconstructed images can be enhanced by three times.

Interferenceless coded aperture correlation holography\xa0with\xa0point spread\xa0holograms\xa0of isolated chaotic islands for 3D imaging

Interferenceless coded aperture correlation holography (I-COACH) is an incoherent digital holographic technique with lateral and axial resolution similar to a regular lens-based imaging system. The properties of I-COACH are dictated by the shape of the system’s point response termed point spread hologram (PSH). As previously shown, chaotic PSHs which are continuous over some area on the image sensor enable the system to perform three-dimensional (3D) holographic imaging. We also showed that a PSH of an ensemble of sparse dots improves the system’s signal-to-noise ratio (SNR) but reduces the dimensionality of the imaging from three to two dimensions. In this study, we test the midway shape of PSH, an ensemble of sparse islands distributed over the sensor plane. A PSH of isolated chaotic islands improves the SNR of the system compared to continuous chaotic PSH without losing the capability to perform 3D imaging. Reconstructed images of this new system are compared with images of continuous PSH, dot-based PSH, and direct images of a lens-based system. Visibility, SNR, and the product of visibility with SNR are the parameters used in the study. We also demonstrate the imaging capability of a system with partial annular apertures. The reconstruction results have better SNR and visibility than lens-based imaging systems with the same annular apertures.

Compressive Interferenceless Coded Aperture Correlation Holography With High Imaging Quality

Interferenceless coded aperture correlation holography (I-COACH) provides an alternative way for the 3D imaging of spatial incoherent illuminated or fluorescent sample. However, the low imaging signal-to-noise ratio (SNR) is one of the bottlenecks that restrict the application of I-COACH. The limitation is mainly originated from the strong bias level that presents in the recorded holograms. Phase shifting methods were implemented in I-COACH to eliminate the background noise while the multiple-exposures recording mechanism significantly reduces the temporal resolution of the system. In this paper, we proposed a compressive I-COACH imaging method with high reconstruction quality and without the sacrifice of the imaging speed. The 3D holographic image reconstruction was implemented under compressive sensing framework while only one single-exposure object hologram and one point spread hologram are necessary. High quality reconstructions were obtained using the proposed method, even for the down-sampled holograms. The imaging SNR of the I-COACH system was improved by a factor of more than 16.5% when comparing with the imaging SNR obtained by the conventional cross-correlation reconstruction method. The proposed method provides a fast and high-fidelity imaging method that can potentially benefit the imaging through scattering medium, partial aperture imaging, and other fields.

Recording point spread functions by wavefront modulation for interferenceless coded aperture correlation holography.

Coded aperture correlation holography (COACH) needs the point spread function (PSF) for image reconstruction. Utilizing a pinhole to generate a point light source is the most frequently adopted method for measuring PSF, which, however, has significant issues to resolve. One of the problems is that the resolution of the reconstructed result is limited by the cutoff frequency of the pinhole. The other is that the far-field PSF is undetectable because the amount of light illuminance decreases with the distance. In this work, we present a method for recording the PSF based on wavefront modulation. By modulating a plane wave with both the carrier spherical wave and the coded phase mask, we obtain a virtual point spread function (VPSF) that is used for image reconstruction. It is shown that the resolution of reconstructed results is not limited by the pinhole. We experimentally demonstrate high-resolution reconstruction by the VPSF.

High-quality interferenceless coded aperture correlation holography with optimized high SNR holograms.

Motivated by the key role of point spread function in an imaging system, we propose an interferenceless coded aperture correlation holographic (I-COACH) technology with low speckle and high energy efficiency annular sparse coded phase mask (CPM) as system pupil to improve imaging performance. In the proposed method, a modified Gerchberg-Saxton (GS) algorithm is proposed to obtain a low speckle and high energy efficiency annular sparse CPM and to suppress speckle and increase the intensity of the holograms. Therefore, the randomly distributed amplitude in the bandwidth of the GS algorithm is replaced by the annular amplitude to determine the spatial position, and the band-limited random phase and quadratic phase are used as the initial phase to approximately meet band-limited conditions; meanwhile, in the iterative process of the algorithm, appropriate constraints are imposed on the information within and outside the band limit. All are used for obtaining the CPM with low speckle and high energy efficiency. Therefore, the proposed technique here is coined as low speckle I-COACH owing to the characteristics of CPM and imaging performances. The experimental results show that, under the same experimental conditions, the proposed method can obtain holograms with low speckle and intensity enhancement of about 8%, and further improve the quality of reconstructed images due to the improvement signal-to-noise ratio (SNR) of the holograms. The proposed method provides a powerful reference method for further expanding the I-COACH system to the field of low-intensity optical signals detection and imaging.

Single Viewpoint Tomography Using Point Spread Functions of Tilted Pseudo-Nondiffracting Beams in Interferenceless Coded Aperture Correlation Holography with Nonlinear Reconstruction

Single Viewpoint Tomography Using Point Spread Functions of Tilted Pseudo-Nondiffracting Beams in Interferenceless Coded Aperture Correlation Holography with Nonlinear Reconstruction