Single shot multispectral multidimensional imaging using chaotic waves

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.

Unrolled primal-dual networks for lensless cameras

Conventional models for lensless imaging assume that each measurement results from convolving a given scene with a single experimentally measured point-spread function. These models fail to simulate lensless cameras truthfully, as these models do not account for optical aberrations or scenes with depth variations. Our work shows that learning a supervised primal-dual reconstruction method results in image quality matching state of the art in the literature without demanding a large network capacity. We show that embedding learnable forward and adjoint models improves the reconstruction quality of lensless images (+5dB PSNR) compared to works that assume a fixed point-spread function.

Tuning Axial Resolution Independent of Lateral Resolution in a Computational Imaging System Using Bessel Speckles

Speckle patterns are formed by random interferences of mutually coherent beams. While speckles are often considered as unwanted noise in many areas, they also formed the foundation for the development of numerous speckle-based imaging, holography, and sensing technologies. In the recent years, artificial speckle patterns have been generated with spatially incoherent sources using static and dynamic optical modulators for advanced imaging applications. In this report, a basic study has been carried out with Bessel distribution as the fundamental building block of the speckle pattern (i.e., speckle patterns formed by randomly interfering Bessel beams). In general, Bessel beams have a long focal depth, which in this scenario is counteracted by the increase in randomness enabling tunability of the axial resolution. As a direct imaging method could not be applied when there is more than one Bessel beam, an indirect computational imaging framework has been applied to study the imaging characteristics. This computational imaging process consists of three steps. In the first step, the point spread function (PSF) is calculated, which is the speckle pattern formed by the random interferences of Bessel beams. In the next step, the intensity distribution for an object is obtained by a convolution between the PSF and object function. The object information is reconstructed by processing the PSF and the object intensity distribution using non-linear reconstruction. In the computational imaging framework, the lateral resolution remained a constant, while the axial resolution improved when the randomness in the system was increased. Three-dimensional computational imaging with statistical averaging for different cases of randomness has been synthetically demonstrated for two test objects located at two different distances. The presented study will lead to a new generation of incoherent imaging technologies.

Nonlinear Reconstruction of Images from Patterns Generated by Deterministic or Random Optical Masks-Concepts and Review of Research

Indirect-imaging methods involve at least two steps, namely optical recording and computational reconstruction. The optical-recording process uses an optical modulator that transforms the light from the object into a typical intensity distribution. This distribution is numerically processed to reconstruct the object's image corresponding to different spatial and spectral dimensions. There have been numerous optical-modulation functions and reconstruction methods developed in the past few years for different applications. In most cases, a compatible pair of the optical-modulation function and reconstruction method gives optimal performance. A new reconstruction method, termed nonlinear reconstruction (NLR), was developed in 2017 to reconstruct the object image in the case of optical-scattering modulators. Over the years, it has been revealed that the NLR can reconstruct an object's image modulated by an axicons, bifocal lenses and even exotic spiral diffractive elements, which generate deterministic optical fields. Apparently, NLR seems to be a universal reconstruction method for indirect imaging. In this review, the performance of NLR isinvestigated for many deterministic and stochastic optical fields. Simulation and experimental results for different cases are presented and discussed.

Multidimension-multiplexed full-phase-encoding holography

I propose a multidimension-multiplexed imaging method with which multiple physical quantities of light are simultaneously obtained as interference fringe images. The varieties of light are distinguished by exploiting the proposed phase-encoding technique. Neither measurements of point spread functions in advance, nor iterative calculations to derive multidimensional information, nor a laser light source is required. Multidimensional imaging of an object and simultaneous three-dimensional image recording of self-luminous light and light transmitted from an object are experimentally demonstrated. A palm-sized interferometer based on the proposed holography is developed for the experiments to show its portability and physical-filter-free multidimensional imaging ability without an antivibration structure.

Invasive and Non-Invasive Observation of Occluded Fast Transient Events: Computational Tools

Industrial processes involving thermal plasma such as cutting, welding, laser machining with ultra-short laser pulses (nonequilibrium conditions), high temperature melting using electrical discharge or ion-beams, etc., generate non-repeatable fast transient events which can reveal valuable information about the processes. In such industrial environments containing high temperature and radiation, it is often difficult to install conventional lens-based imaging windows and components to observe such events. In this study, we compare imaging requirements and performances with invasive and non-invasive modes when a fast transient event is occluded by a metal window consisting of numerous holes punched through it. Simulation studies were carried out for metal windows with different types of patterns, reconstructed for both invasive and non-invasive modes and compared. Sparks were generated by rapid electrical discharge behind a metal window consisting of thousands of punched through-holes and the time sequence was recorded using a high-speed camera. The time sequence was reconstructed with and without the spatio-spectral point spread functions and compared. Commented MATLAB codes are provided for both invasive and non-invasive modes of reconstruction.

Incoherent digital holography simulation based on scalar diffraction theory

Incoherent digital holography (IDH) enables passive 3D imaging through the self-interference of incoherent light. IDH imaging properties are dictated by the numerical aperture and optical layout in a complex manner [Opt. Express27, 33634 (2019)OPEXFF1094-408710.1364/OE.27.033634]. We develop an IDH simulation model to provide insight into its basic operation and imaging properties. The simulation is based on the scalar diffraction theory. Incoherent irradiance and self-interference holograms are numerically represented by the intensity-based summation of each propagation through finite aperture optics from independent point sources. By comparing numerical and experimental results, the applicability, accuracy, and limitation of the simulation are discussed. The developed simulation would be useful in optimizing the IDH setup.

Edge and Contrast Enhancement Using Spatially Incoherent Correlation Holography Techniques

Image enhancement techniques (such as edge and contrast enhancement) are essential for many imaging applications. In incoherent holography techniques such as Fresnel incoherent correlation holography (FINCH), the light from an object is split into two, each of which is modulated differently from one another by two different quadratic phase functions and coherently interfered to generate the hologram. The hologram can be reconstructed via a numerical backpropagation. The edge enhancement procedure in FINCH requires the modulation of one of the beams by a spiral phase element and, upon reconstruction, edge-enhanced images are obtained. An optical technique for edge enhancement in coded aperture imaging (CAI) techniques that does not involve two-beam interference has not been established yet. In this study, we propose and demonstrate an iterative algorithm that can yield from the experimentally recorded point spread function (PSF), a synthetic PSF that can generate edge-enhanced reconstructions when processed with the object hologram. The edge-enhanced reconstructions are subtracted from the original reconstructions to obtain contrast enhancement. The technique has been demonstrated on FINCH and CAI methods with different spectral conditions.

White light three-dimensional imaging using a quasi-random lens

Coded aperture imaging (CAI) technology is a rapidly evolving indirect imaging method with extraordinary potential. In recent years, CAI based on chaotic optical waves have been shown to exhibit multidimensional, multispectral, and multimodal imaging capabilities with a signal to noise ratio approaching the range of lens based direct imagers. However, most of the earlier studies used only narrow band illumination. In this study, CAI based on chaotic optical waves is investigated for white light illumination. A numerical study was carried out using scalar diffraction formulation and correlation optics and the lateral and axial resolving power for different spectral width were compared. A binary diffractive quasi-random lens was fabricated using electron beam lithography and the lateral and axial point spread holograms are recorded for white light. Three-dimensional imaging was demonstrated using thick objects consisting of two planes. An integrated sequence of signal processing tools such as non-linear filter, low-pass filter, median filter and correlation filter were applied to reconstruct images with an improved signal to noise ratio. A denoising deep learning neural network (DLNN) was trained using synthetic noisy images generated by the convolution of recorded point spread functions with the virtual object functions under a wide range of aberrations and noises. The trained DLNN was found to reduce further the reconstruction noises.

Comparative study on resolution enhancements in fluorescence-structured illumination Fresnel incoherent correlation holography

Fresnel incoherent correlation holography (FINCH) is a new approach for incoherent holography, which also has enhancement in the transverse resolution. Structured illumination microscopy (SIM) is another promising super-resolution technique. SI-FINCH, the combination of SIM and FINCH, has been demonstrated lately for scattering objects. In this study, we extended the application of SI-FINCH toward fluorescent microscopy. We have built a versatile multimodal microscopy system that can obtain images of four different imaging schemes: conventional fluorescence microscopy, FINCH, SIM, and SI-FINCH. Resolution enhancements were demonstrated by comparing the point spread functions (PSFs) of the four different imaging systems by using fluorescence beads of 1-μm diameter.

Lensless Three-Dimensional Quantitative Phase Imaging Using Phase Retrieval Algorithm

Quantitative phase imaging (QPI) techniques are widely used for the label-free examining of transparent biological samples. QPI techniques can be broadly classified into interference-based and interferenceless methods. The interferometric methods which record the complex amplitude are usually bulky with many optical components and use coherent illumination. The interferenceless approaches which need only the intensity distribution and works using phase retrieval algorithms have gained attention as they require lesser resources, cost, space and can work with incoherent illumination. With rapid developments in computational optical techniques and deep learning, QPI has reached new levels of applications. In this tutorial, we discuss one of the basic optical configurations of a lensless QPI technique based on the phase-retrieval algorithm. Simulative studies on QPI of thin, thick, and greyscale phase objects with assistive pseudo-codes and computational codes in Octave is provided. Binary phase samples with positive and negative resist profiles were fabricated using lithography, and a single plane and two plane phase objects were constructed. Light diffracted from a point object is modulated by phase samples and the corresponding intensity patterns are recorded. The phase retrieval approach is applied for 2D and 3D phase reconstructions. Commented codes in Octave for image acquisition and automation using a web camera in an open source operating system are provided.