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.

Deep-learning-based cross-talk free and high-security compressive encryption with spatially incoherent illumination.

Incoherent optical cryptosystem is promising for its immunity against coherent noise and insensitivity to misalignment, and compressive encryption is desirable considering the increasingly demand on the exchange of encrypted data via Internet. In this paper, we propose a novel optical compressive encryption approach with spatially incoherent illumination based on deep learning (DL) and space multiplexing. For encryption, the plaintexts are individually sent to the scattering-imaging-based encryption (SIBE) scheme where they are transformed to scattering images with noise appearances. Afterwards, these images are randomly sampled and then integrated into a single package (i.e., ciphertext) by space multiplexing. The decryption is basically the inverse of the encryption, while it involves an ill-posed problem (i.e., recovering the noise-like scattering image from its randomly sampled version). We demonstrated that such a problem can be well resolved by DL. The proposal is radically free from the cross-talk noise existing in many current multiple-image encryption schemes. Also, it gets rid of the linearity bothering the SIBE and is hence robust against the ciphertext-only attack based on phase retrieval algorithm. We present a series of experimental results to confirm the effectiveness and feasibility of the proposal.

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.

Computational adaptive holographic fluorescence microscopy based on the stochastic parallel gradient descent algorithm.

Optical aberrations introduced by sample or system elements usually degrade the image quality of a microscopic imaging system. Computational adaptive optics has unique advantages for 3D biological imaging since neither bulky wavefront sensors nor complicated indirect wavefront sensing procedures are required. In this paper, a stochastic parallel gradient descent computational adaptive optics method is proposed for high-efficiency aberration correction in the fluorescent incoherent digital holographic microscope. The proposed algorithm possesses the advantage of parallelly estimating various aberrations with fast convergence during the iteration; thus, the wavefront aberration is corrected quickly, and the original object image is retrieved accurately. Owing to its high-efficiency adaptive optimization, the proposed method exhibits better performances for a 3D sample with complex and anisotropic optical aberration. The proposed method can be a powerful tool for the visualization of dynamic events that happen inside cells or thick tissues.

Incoherent coded aperture correlation holographic imaging with fast adaptive and noise-suppressed reconstruction.

Fast and noise-suppressed incoherent coded aperture correlation holographic imaging is proposed, which is utilized by employing an annular sparse coded phase mask together with adaptive phase-filter cross-correlation reconstruction method. Thus the proposed technique here is coined as adaptive interferenceless coded aperture correlation holography (AI-COACH). In AI-COACH, an annular sparse coded phase mask is first designed and generated by the Gerchberg-Saxton algorithm for suppressing background noise during reconstruction. In order to demonstrate the three-dimensional and sectional imaging capabilities of the AI-COACH system, the imaging experiments of 3D objects are designed and implemented by dual-channel optical configuration. One resolution target is placed in the focal plane of the system as input plane and ensured Fourier transform configuration, which is employed as reference imaging plane, and moved the other resolution target to simulate different planes of a three-dimensional object. One point spread hologram (PSH) and multiple object-holograms without phase-shift at different axial positions are captured by single-exposure sequentially with the annular sparse CPMs. A complex-reconstruction method is developed to obtain adaptively high-quality reconstructed images by employing the cross-correlation of PSH and OH with optimized phase filter. The imaging performance of AI-COACH is investigated by imaging various type of objects. The research results show that AI-COACH is adaptive to different experimental conditions in the sense of autonomously finding optimal parameters during reconstruction procedure and possesses the advantages of fast and adaptive imaging with high-quality reconstructions.

Direct and accurate phase unwrapping with deep neural network.

In this paper a novel, to the best of our knowledge, deep neural network (DNN), VUR-Net, is proposed to realize direct and accurate phase unwrapping. The VUR-Net employs a relatively large number of filters in each layer and adopts alternately two types of residual blocks throughout the network, distinguishing it from the previously reported ones. The proposed method enables the wrapped phase map to be unwrapped precisely without any preprocessing or postprocessing operations, even though the map has been degraded by various adverse factors, such as noise, undersampling, deforming, and so on. We compared the VUR-Net with another two state-of-the-art phase unwrapping DNNs, and the corresponding results manifest that our proposal markedly outperforms its counterparts in both accuracy and robustness. In addition, we also developed two new indices to evaluate the phase unwrapping. These indices are proved to be effective and powerful as good candidates for estimating the quality of phase unwrapping.

Optimized reconstruction with noise suppression for interferenceless coded aperture correlation holography.

A modified nonlinear reconstruction technique with a noise modulation parameter is proposed for interferenceless coded aperture correlation holography (I-COACH), and thus the signal-to-noise ratio of a reconstructed image is improved without sacrifice of the field of view and temporal resolution of the system. In order to obtain the optimal reconstructed image, no-reference structural sharpness (NRSS) is introduced as the evaluation metric of reconstructed image quality during nonlinear reconstruction. On the other hand, the noise modulation function is built in order to analyze the effect of phase on noise when the amplitude of the point spread hologram and object hologram is unity of 1. Both the NRSS and noise modulation functions are combined with nonlinear reconstruction in I-COACH for improving imaging performance. The validities of the proposed method under different experimental conditions have been demonstrated by experiments.

Adaptive optics via self-interference digital holography for non-scanning three-dimensional imaging in biological samples.

Three-dimensional imaging in biological samples usually suffers from performance degradation caused by optical inhomogeneities. Here we proposed an approach to adaptive optics in fluorescence microscopy where the aberrations are measured by self-interference holographic recording and then corrected by a post-processing optimization procedure. In our approach, only one complex-value hologram is sufficient to measure and then correct the aberrations, which results in fast acquisition speed, lower exposure time, and the ability to image in three-dimensions without the need to scan the sample or any other element in the system. We show proof-of-principle experiments on a tissue phantom containing fluorescence particles. Furthermore, we present three-dimensional reconstructions of actin-labeled MCF7 breast cancer cells, showing improved resolution after the correction of aberrations. Both experiments demonstrate the validity of our method and show the great potential of non-scanning adaptive three-dimensional microscopy in imaging biological samples with improved resolution and signal-to-noise ratio.

Self-interference compressive digital holography with improved axial resolution and signal-to-noise ratio.

Fresnel incoherent correlation holography (FINCH) was proposed to break the barrier of spatial incoherent digital holographic imaging and show the potential of super-resolution imaging preferences. We developed FINCH as a compressive sensing modality and reconstruction procedure as an inverse problem in order to realize 3D tomographic imaging. Improved axial resolution is obtained via compressive reconstruction. Reconstruction guarantees and accuracy of the proposed method are discussed. Compared with the real-valued signal operation, the signal-to-noise ratio of the results is increased when reconstructing from the complex-valued hologram obtained from the FINCH system.

Incoherent off-axis Fourier triangular color holography.

We present a new method for recording off-axis digital Fourier holograms of three-dimensional objects under spatially incoherent illumination. The method is implemented by modifying the optical configuration of triangular interferometer. The recording properties and 3D reconstruction ability of the proposed method are investigated theoretically and experimentally. Multicolor holographic recording and reconstruction of spatially incoherent illuminated object are achieved by using the proposed off-axis Fourier triangular interferometer and monochromatic digital camera. Only three holograms are sufficient to rebuild a color image without zero-order and twin image disturbing effect. Combining with some image fusion skills during reconstruction, the reconstructed color images with satisfied quality are demonstrated.