This PDF file contains the front matter associated with SPIE Proceedings Volume 12445, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

We will discuss diffractive optical networks designed by deep learning to all-optically implement various complex functions as the input light diffracts through spatially-engineered surfaces. These diffractive processors complete their computational task at the speed of light propagation through thin, passive optical layers and have various applications, e.g., all-optical image analysis, feature detection, object classification, computational imaging and seeing through diffusers. They also enable task-specific camera designs and new optical components for, e.g., spatial, spectral and temporal beam shaping, polarization engineering and spatially-controlled wavelength division multiplexing. These deep learning-designed diffractive networks broadly impact (1) all-optical statistical inference engines, (2) computational cameras and microscopes, and (3) inverse design of optical systems that are task-specific.

Bayfol® HX photopolymer films prove themselves as easy-to-process recording materials for volume holographic optical elements (vHOEs) and are available in customized grade at industrial scale. Their full-color (RGB) recording and replay capabilities are two of their major advantages. Moreover, the adjustable diffraction efficiency, tunable angular and spectral selectivity of vHOEs recorded into Bayfol® HX as well as their unmatched optical clarity enables superior invisible “off Bragg” optical functionality. As a film product, the replication of vHOEs in Bayfol® HX can be carried out in a highly cost-efficient and purely photonic roll-to-roll (R2R) process. Utilizing thermoplastic substrates, Bayfol® HX was demonstrated to be compatible to state-of-the-art plastic processing techniques like thermoforming, film insert molding and casting, which opened up using a variety of industry-proven integration technologies for vHOEs. Therefore, Bayfol® HX makes its way in applications in the field of augmented reality such as Head-up-Displays (HUD) and Head-mountedDisplays (HMD), in free-space combiners, in plastic optical waveguides, and in transparent screens. Also, vHOEs made from Bayfol® HX are utilized in highly sophisticated spectrometers in astronomy as well as in narrow band notch filters for eyeglasses against laser strikes. See through applications such as, HMD and HUD, have demanding performance requirements on combiner and imaging technologies such as efficiency, optical function, and clarity. The properties of Bayfol® HX make it well suited to solve these challenges in primary display, and near-infrared imaging applications such as eye-tracking, while maintaining the requirements on optical performance. We demonstrate practical examples of Bayfol® HX vHOE’s using novel holography techniques for spatially varying diffraction efficiency.

In this work we report an improved platform for testing and comparing particles for use in optical trap displays. We constructed seven prototypes, and deployed them to five different locations where they were successfully used to perform comparative optical particle trap tests. This improved rig makes it possible to expand optical trap display research by a decentralized group of citizen scientists.

Holographic Optical Elements (HOE) are well known optical devices which can be used as for example light focusing and/or directing the light to desired areas. Until now, there have been no manufacturing facilities capable to manufacture substantial quantities of volume holographic optical elements with in-application stable properties devoted to being used as taillights or head-up displays in a relatively harsh automotive environment. We describe in this article the working principles of an industrial manufacturing process of holographic optical elements targeting automotive industry needs.

Working in the full-parallax digital format with the CHIMERA holography technology, which offers a 250 micrometre hogel size ensuring a clear image, this project explores anatomical imaging from an artist’s perspective. A completed hologram visualises anatomical MRI scans, adapted from a 3D printable model of the Bulbo-clitoral organ, building on studies in urology. A collage approach has been taken to include structural detail and creative vision. The work takes advantage of the available colour representation offered through continuous wave RGB laser technology. Transparent modelling options are explored. A Practice-Based Research method has been adopted to investigate creative possibilities in display holography.

We present an interactive aerial-3D-touch user interface enabled by a holographic light-field display consisting of a holographic screen and a projector. 3D images are reproduced midair between the screen and a user, and the user can interact with the aerial 3D image. A technique to automatically align the 3D image and gesture sensing is developed to achieve direct-3D-touch interaction. It can be combined with a conventional 2D display thanks to the see-through capability of the volume holographic optical element. Some examples of 3D-touch interactions are demonstrated, such as 3D swipe, grabbing, object moving, and free-drawing. The experimental result of the usability evaluation is also reported.

The double-phase hologram adapts a complex wavefront for phase-type devices, but the reconstruction is plagued by the noise caused by spatial-shifting errors. To suppress the spatial-shifting noise, a spectral-envelope modulated approach is proposed. With this way, the capability of double-phase holograms is extended to encoding complex holograms generated with random phase, which is verified here with a colored holographic display of 2D photographs.

In this paper, color optimization of a full-color holographic stereogram printing system using a single SLM based on iterative exposure is proposed. First, an array of sub-holograms (hogels) is generated effectively within fast computergenerated integral imaging, and fully analyzed phase-modulation for red, green, and blue (RGB) channels of hogel. Then, the generated hogels are recorded into holographic material sequentially where SLM displays the R, G, and B channels of a single hogel via effectual exposure under synchronized control with three electrical shutters for RGB laser illumination to obtain verified color optimization. Numerical simulation and optical reconstructions are implemented.

Our team works on a disruptive concept of Near Eye Display for Augmented Reality (AR) applications. This device requires distributions of holographic elements described as Emissive Points Distributions (EPDs) to create a composite planar wavefront emitted towards the eye. The crystalline lens focuses this signal onto the retina in a mix of diffraction and refraction processes, to form the pixels of an image. We experimentally recorded an image of the letter “R” with pixelated holograms. At the reading of this image, we observe speckle that partially alters the image. Using image processing on the experimental results, we can suppress this speckle and recover the initial “R”, which validates our concept. We develop a simulation tool based on Fourier optics to better understand the emergence of this speckle noise. With the knowledge of the recording process and the form of the hologram given by microscopy, we simulate the electric field 𝐸𝑛 reflected by the different holographic elements from a unique collimated laser. Each field 𝐸𝑛 encodes an angular pixel of the recorded image. The sum of these optical beams in field and/or in intensity allows us to analyze the role of the different optical elements in the generation of a speckle. In particular, the role of the cross interferences between different EPDs is questioned. The experimental analysis is brought for periodic EPDs but can be extended to the case of random EPDs. It gives some insights into some possible evolutions of our concept in terms of optical implementation.

Holographic near-eye displays have the potential to overcome many long-standing challenges for virtual and augmented reality (VR/AR) systems; they can reproduce full 3D depth cues, improve power efficiency, enable compact display systems, and correct for optical aberrations. Despite these remarkable benefits, this technology has been held back from widespread usage due to the limited image quality achieved by traditional holographic displays, the slow algorithms for computer-generated holography (CGH), and current bulky optical setups. Here, we review recent advances in CGH that utilize artificial intelligence (AI) techniques to solve these challenges.

Holographic displays based on spatial light modulators suffer from limited ´etendue, defined as the product of the display’s size and angular range and bounded by the number of pixel units. In this work, we suggest that rather than excessively increasing the pixel count, etendue can be expanded by augmenting the display units with tilting capabilities. We built a prototype constructed of multiple binary tilt layers and demonstrated applications of the device.

CHIMERA is the third generation of digital holographic printing system based on three low-power continuous lasers combined with Ultimate U04 silver-halide holographic glass plates. This holoprinter prints at 50 Hz, 120° full-parallax, and full-color digital reflection holograms or holographic optical elements with a size of up to 60×80 cm and a 250 μm hogel size. An in-house scanner was designed to record full-parallax CHIMERA holograms of still object scenes. This scanner can automatically record a still object scene from 10×13 cm to 60×80 cm with a 4K camera and a controlled turning table. The scanner records a still object scene in 2 hours with 768 horizontal images, 192 elevation levels, and a 180 degrees rotation. From the obtained perspective images, in-house software calculates all the hogels for the CHIMERA printing. This paper discusses the different characteristics of this in-house scanner and analyzes its advantages, benefits, and limitations for applications such as museums, art, education, architecture, and advertising.

Modern touch control infotainment systems in vehicles present distractions to drivers and endanger road safety. Current industrial head-up displays (HUDs) require the driver to shift the gaze from the road towards a region on the 2D windscreen. Panoramic augmented reality holographic color projections in could prevent driver distraction. This is an inclusive tool to incorporate all members of society into the transportation sector. A 4k color augmented reality holographic automotive head-up display was developed to project road obstacles in 360° in the driver’s field of view. This technology could be useful for drivers, including elderly and disabled populations.

Micro Mechanical Electronics System based Spatial Light Modulators (MEMS-SLM) enables unique capability “Just in time photon delivery” or steering beam images to where and when they are needed. The beam and image steering solves challenges commonly found in both lidar and AR optical engines dominated by classical tradeoffs, such as image FOV, resolution and SLM size or form factor of optical engine. As a novel beam and image steering device, we transformed Texas Instruments Digital Micromirror Device (TI-DMD) into a diffractive beam and image steering device. TI-DMD is known as a binary spatial light modulator. Micromirros’ tilt re-directs light into on- or off-states. Without modifying TIDMD, but with employing a nano-second pulse illumination synchronized to the transitional movement of micromirrors between the of- and off-states turns DMD into a diffractive beam and image steering device.

Many previous studies have suggested that hologram provides natural parallax and an accommodative response. However, objective/quantitative measurement of holographic performance and image quality, standardized standards and methods are still insufficient. In real life, humans continue to look at external objects in parallel with long distances and near distances. Depending on the distance looking at, natural visual activity is achieved through convergence and accomodation accordingly. Besides, blink rate, one of the major visual physiological reactions in humans, is a major visual function factor that directly affects ophthalmic diseases such as corneal inflammation and xerophthalmia. In this paper, we tried to find out the influence on human visual function when watching digital hologram produced from multi-view image data through factors such as accommodative response and blink rate. In the experiment, subjects of 30 people (29.54±3.71 years old) were selected and the accommodative response and blink rate were measured. The accommodative response was measured using N-vision 5001 at a distance of 40 cm and 50 cm, respectively. For the measurement of a hologram, the film was placed at 40 cm and the reconstruction distance was set up at 50 cm to measure the accommodative response to the hologram target. Blink rate was compared and analyzed through four environments (natural state, viewing monitor, viewing VR HMD, and viewing hologram). For data analysis, SPSS' one-way repeated measures analysis of variances was used. As a result of the experiment, there was no difference between the accommodative response of the hologram target (40 cm) and the accommodative response of the physical target (50 cm). In the blink rate, it was confirmed that the normal range of blink rate appeared in the hologram viewing environment. In this study, the safety of watching digital holograms from the perspective of visual function was verified.

We explore a number of diffractive structures for simultaneous trapping of particles in photophoretic traps for free space volumetric displays. Current optical trap displays move a single particle along a complicated path; to scale displays from 1 cm^3 to 100 cm^3 we aim to move multiple particles along a simple path. Preliminary results for two diffractive approaches are reported: i) a low-order binary grating, and ii) a Fresnel lens. Results are given for trap rate (N=50) for carbon particles at standard pressure and temperature.

Deep learning has proven to be an efficient and robust method for many computational imaging systems. The advantages of machine learning, as a rule, are that it is fast—at least in its supervised form after training is complete—and seems exceedingly effective in capturing regularizing priors. Here, we focus the discussion on non-invasive three-dimensional (3D) object reconstruction. One then faces the additional dilemma of choosing the appropriate model of light-matter interaction inside the specimen, i.e. the forward operator. We describe the three stages of approximation that are applicable: weak scattering with weak diffraction (also known as the Radon transform), weak scattering with strong diffraction, and strong scattering. We then overview machine learning approaches for the various models, and glance at the consequences of oversimplifying the forward operator choice.

In this paper, we introduce an electronic speckle pattern interferometry (ESPI) method for rapid assessment of transient deformations on an opaque object. The method records the change in speckle patterns over time, which relate to the change in phase of the reflected light. The system was capable of high-speed recordings enabled by a camera capable of double exposure and external triggering. Experiments were performed on an opaque PDMS phantom to track rapid surface movements from a piezoelectric acoustic driver located at the back of phantom. Acoustic pulses of different period and amplitude were tested. In each double exposure recording cycle, the image pair were digitally subtracted to reveal the change in the speckle pattern, which represented the change in phase of the object beam relative to the reference. We developed custom software to process the data, including an algorithm to unwrap the phase maps. Experiments revealed an ultimate sensitivity to displacements of approximately 1 nm for signals ranging in period from 50 μs to 200 μs. Future work will examine the capabilities of the system with respect to surfaces with different optical absorption and scattering characteristics.

We introduce an open-source toolkit for simulating optics and visual perception. The toolkit offers differentiable functions that ease the optimization process in design. In addition, this toolkit supports applications spanning from calculating holograms for holographic displays to foveation in computer graphics. We believe this toolkit offers a gateway to remove overheads in scientific research related to next-generation displays.

Traditional computer vision (CV) approaches are the norm when attempting to extract edge information from an imaged object. These discrete approaches are almost always performed on 2D intensity imagery and at times can be computationally expensive depending on the algorithm. Digital holography (DH) provides access to the 3D object information. By manipulation of the Fourier transform of the hologram, which is also needed for isolating the real or virtual image in off-axis DH, edge information can be extracted by high pass spatial filtering of the pertinent cropped and centered spectrum. We show simple simulations utilizing 2-D and 3-D objects to show edge enhancement qualities using this approach, and compare its performance to conventional CV techniques. The same technique can be used to perform other image processing functions, such as image sharpening, blurring, and others so long as the correct filters are applied. Developments in ultra-high definition displays have either incorporated DH or have overlapping areas of interest currently, including 3-D television and augmented reality.

We propose a holographic printing technology for head-mounted display through practical design in hologram recording and reconstruction. Most head-mounted displays are designed based on waveguide type and analog holographic optical elements, resulting in disruption of the uniformity of the image because of the difference between the initial recording conditions and the source image. This problem can be solved using holographic printing technology to modulate different diffraction efficiencies for each holographic element. This study uses a digital holographic screen that can fabricate and reconstruct augmented reality images of 1.17”, 1.76”, and 2.35” in a field of view of 28.07°, 41.11°, and 53.13°, respectively, at a distance of 53.33 mm from the eye. Moreover, augmented images are realized with higher diffraction efficiency than conventional methods, simplifying the design and facilitating mass production of uniformed products using digital holographic printing technology.

Spatial light modulator (SLM) technology forms the centerpiece of digital holographic displays. However, an inherent limitation of these devices is that their ´etendue, defined as the product of the display’s eye box and field of view (FoV), is bounded by the number of pixel units. As a consequence, current SLMs are far from meeting the required FoV and eye box for the human visual system, which would require scaling the number of display units by a few orders of magnitude. Existing strategies for ´etendue-expansion rely on introducing a diffractive optical element (DOE), a fixed random phase mask whose pitch is much smaller than that of the original display, thereby spreading light over a wider angle. Displayed content is then optimized under perceptual constraints on the generated image. However, since the phase mask is fixed, the number of degrees of freedom does not increase and hence, the expansion in ´etendue necessarily comes with a loss of image quality. The trade-offs involved with such phase masks are not well understood. This paper studies the space of phase masks that can be attached to an SLM to increase its angular range. It attempts to characterize what trade-offs are involved in ´etendue-expansion, and whatever specific phase mask designs would support better holograms. We show that while pseudo random masks support wide-´etendue, they involve an inherent loss of contrast. Perhaps surprisingly, simple commonly-available phase masks like lenslet arrays provide near-optimal results that can largely outperform random masks.

Distance estimation is an important yet challenging part of any tracking system, as being able to quickly locate an object in 3D space allows for the automated targeting of communication, delivery, and interception systems, as well as providing important telemetry about fast moving objects. A monocular passive ranging system is defined as that which only requires one observation point through which it measures some outside signal to estimate range. The approach presented here simultaneously observes the intensity of light emitted by the target at three wavelength bands with ~10nm FWHM, centered at 750, 762, and 780 nm. The light is separated using a PQ:PMMA holographic optical element (HOE) configured as a wavelength division demultiplexer. Light at the two outer bands experiences negligible absorption in the atmosphere, while light at ~762 nm is strongly absorbed by O₂. By comparing the intensity of the two unabsorbed bands, we may interpolate the expected intensity of the 762 nm band if there is no O₂ in the path. This is then used in conjunction with the 762 nm band measurement to approximate the total O₂ transmissivity. Finally, Beer’s law and the HITRAN database provide us with the tools to convert a transmissivity into a distance estimation. The use of an HOE is pivotal in the practicality of such a system, as it allows us to measure all three signals simultaneously, thus eliminating the effects of turbulence and reducing overall noise.

Volume holographic optical elements (HOEs) are of great interest for dense information storage and optical processing such as wavelength division multiplexing (WDM) and angle multiplexing. There are numerous theoretical frameworks that attempt to model and test diffraction from a holographic grating, among the most prominent of which is Kogelnik’s coupled-wave theory, which applies to thick holograms. However, diffraction from grating geometries resulting from interference among more than two wave-vectors is difficult to model mathematically. In particular, gratings formed from converging or diverging beams present curved profiles that vary with the position inside the material. One approach to analyze these types of holographic gratings is to use a finite element method (FEM) to search for a steady-state solution for the wave equation of a beam propagating through, and diffracting from, the grating. Such a method will necessarily be computationally intensive given that the simulation will require a resolution smaller than the reading wavelength but will encompass a large volume, as is required for a thick hologram. Current technology has enabled this approach to be a viable alternative to traditional modeling. Here, we present the results of an FEM analysis using the COMSOL Multiphysics 6.0 computer program to simulate the diffraction of holographic gratings with non-trivial profiles. The results enable us to more accurately design volume HOEs with non-planar profiles such as lenses, WDM, etc., to achieve better Bragg selectivity and overall higher performance.

Metasurfaces are composed of arrays of subwavelength nanopillars which, owing to their strong form birefringence, provide an innovative platform to realize novel polarization control. Using matrix Fourier optics, phase retrieval principles, and Jones calculus, we propose and implement a general design strategy to enable polarization holograms with user-specified polarization responses, in the far-field. We fabricate these metasurface holograms (for operation at visible wavelengths) and test them with Mueller matrix polarimetry, showing good agreement with designs. This unprecedented polarization control in the far-field should enable applications in many areas, including in digital displays, augmented and virtual reality, structured illumination, and machine vision.

We present highly transparent, wave front printed volume holographic optical elements (vHOEs), realized with a new recording method based on the pre-illumination of incoherent light patterns. The introduced amplitudemodulated pattern illuminates a distinct area on the unexposed, photopolymer-based holographic recording material prior to the hologram recording sequence. The incoherent pre-illumination scheme enables a precise tuning of the material’s local photosensitivity without the formation of a holographic volume diffraction grating. As a consequence, the pre-illumination exposure significantly suppresses the formation of transparency diminishing structures in the material that are formed concurrently with the volume diffraction grating during the hologram recording sequence. The pre-illumination component is integrated in an extended immersion-based wave front printing setup, which realizes vHOEs by sequentially recording single holographic elements in an array-like structure. A wide range of different recording configurations is enabled by our recording setup due to independent modulation of both wave fronts and the possibility to realize large off-axis recording angles. We introduce two hologram characterization methods, based on a diffraction efficiency and a slanted-edge method analysis, which are used to evaluate the implemented pre-illumination method and demonstrate significant improvements to the see-through quality of the presented wave front recorded vHOEs.

The wavefront measurement accuracy of a grating array based zonal wavefront sensor (GAWS) can be affected by the non-uniform focal spot array and unwanted orders in the detector plane. The non-uniform focal spot array is the outcome of the non-uniform nature of the incident illumination beam’s intensity profile. This paper describes a method that dynamically modulates the laser beam’s intensity using computer generated holography, making the focal spot array uniform and eliminating unwanted spots in a detector plane, thereby enhancing the accuracy of the wavefront measurement. Here, we present proof-of-principle simulation results that demonstrate the working of the proposed improvements in GAWS.

To reconstruct three-dimensional (3D) information perfectly, phase and amplitude of incident waves must be controlled simultaneously. However, since the conventional spatial light modulation techniques could control only one component of phase or amplitude, it has very low quality of reconstructed image of its noise. So, the bulky optical filter system is required. We propose novel pixel design for a complex light modulation that can overcome these limitations. This design is based on the principle of the complex value of each pixel by dividing it into three fixed phases and controllable amplitudes. It is implemented to combination of rotated rods and is modulated to a cross polarized component for an incident wave. It has a concept that each amplitude can be controlled by width or length of each rod. In this research, we present the characteristics of the complex spatial light modulation for the proposed metasurface structure by Fourier modal method (FMM) simulation based on the rigorous coupled wave analysis (RCWA) and verify that the proposed design can control the complex light modulation on the higher-order diffraction component. Also, noise-free hologram is verified by the results of reconstructed diffraction patterns using wave optical based simulations to analyze the distribution of complex modulated waves in free space.

Many architectures of near eye display (NED) using a holographic optical element (HOE) come on the market. HOE has already been successfully industrialized due to its easy manufacturing process and small form factor. However, many studies are being conducted to solve degradation effect by the eye glow that the visibility of the user decreases occurred to external light. HOE is generally used as an element of NED for its good angular and wavelength selectivity characteristics. The parameters controlling those characteristics are the refractive index change and the thickness of HOE. Although the selectivity characteristics are optimized by regulating the two parameters, the eye glow occurs because the HOE reacts in parts other than the desired characteristics for sunlight and white light sources. For a fundamental reason, eye glow is further caused by a sudden refractive index change in boundary condition when incident into the HOE from the air. In this study, we figure out that the boundary condition changes continuously by apodization of the refractive index of HOE for eye glow reduction. Also, we calculate the angular and wavelength selectivity efficiency using scalar Fourier modal method (sFMM) based on rigorous coupled-wave analysis (RCWA) according to the thickness and refractive index change, and investigate the relationship between those parameters.

In our previous work, a meta-surface was designed using adjoint-based topology optimization for high-efficiency. However, since the design pattern was complicated and the size of element was small, it was hard to maintain in the actual process and was not appropriate for commercialization. To solve this problem, we use the adjoint inverse design method by applying the local curvature filter algorithm and curvature flow technique in this study. The meta-surface design was conducted using Fourier modal method, based on rigorous coupled-wave analysis. It is assumed that the meta-surface is composed of pixels having a relative dielectric constant of the dielectric material. The dielectric constant distribution in the meta-lattice region is a design variable for optimization, and the dielectric constant of the air layer is converted over the duration. Traditionally, Gaussian filter was used to change to a processable pattern. However, since it does not maintain high efficiency characteristics, we used the local curvature filter (LCF) method. As a result, the results of efficiently finding and filtering small and complex patterns while maintaining characteristics were acquired. The LCF detects it as a local area according to the degree of curvature. The detected area is filtered using a Bernstein filter, and then combined with the global pattern again. In addition, we re-progress filtering for smooth patterns using the curve flow to adjust the curve threshold value to design the meta-surface. Consequently, we propose the method and theory of novel algorithm as a way of maintaining the high efficiency properties of the meta-surface in practice.

Holographic waveguide display takes the advantage of pupil expansion to increase the size of eye-box which can be widely employed into augmented reality (AR) systems. However, the angular selectivity of holographic optical elements (HOEs) used as in- and out-coupler for waveguide display is very limited when reading out by coherent light source like lasers. Here, we propose a method by utilizing broadband light source like LED with multilayer HOEs or multilayer waveguides, each pair of the in- and out-coupling HOEs or waveguides will be angularly separated to construct the specific angular region. Due to its decent spectrum selectivity of holographic couplers and multilayer structure, the field of view (FOV) of the display system can be significantly increased. Large eye-box is realized by employing pupil expansion for allowing the image to interact with out-couplers multiple times.

The near infrared (NIR) part of the infrared synchrotron beam is usually discarded to improve the signal to noise ratio of spectral imaging at the Australian Synchrotron. In this study, NIR synchrotron beam has been extracted and used for three-dimensional (3D) imaging. A Fresnel zone aperture (FZA) was fabricated on barium fluoride windows using femtosecond ablation. The 3D point spread functions (PSFs) were recorded using the FZA mounted between the pinhole and the image sensor. An object is then placed within the boundaries of the PSF library and an object intensity distribution was recorded. Computational reconstruction methods were applied to reconstruct the object information.

A 4D computational incoherent imaging technique using accelerating Airy beams (A²-beams) and nonlinear reconstruction (NLR) has been developed. The phase mask was designed as a binary version for the generation of a sparse random array of A²-beams. The imaging process consist of three steps. In the first step a 4D point spread function (PSF) was recorded at different wavelengths and depths. In the next step, a multicolor, multiplane object was loaded and a single camera shot was recorded. Finally, the 4D information of the object was reconstructed by processing the object intensity distribution and 4D PSFs. The simulation results for the imaging concept are presented.

Interferenceless coded aperture correlation holography (I-COACH) was developed in 2017 to achieve 3D imaging without two-beam interferences. In I-COACH, the imaging process consists of three steps: COACHing, recording and reconstruction. In the COACHing step, the point spread function (PSF) library is recorded. In the recording step, an object mounted within the axial boundaries of the PSF library is recorded, and the recording is processed with the PSF library in a computer to reconstruct the image of the object in the final step. During the past five years, I-COACH evolved rapidly into a significant incoherent holography technique breaking the limits of almost all imaging characteristics such as lateral resolution, axial resolution, spectral resolution and field of view, not to mention, the ability to sense colour with a monochrome sensor. In this invited article, some of the major milestones in the evolution of I-COACH are briefly presented.

The near infrared (NIR) part of the infrared synchrotron beam is usually dumped to improve the signal to noise ratio of spectral imaging. In this study, this NIR synchrotron beam has been extracted and used for three-dimensional (3D) phase imaging. A pinhole was inserted in the path of the fork shaped NIR synchrotron beam and the Airy diffraction pattern was aligned with biochemical samples and the diffracted intensity distribution was captured using an image sensor sensitive to NIR. A phase retrieval algorithm was used to estimate the 3D phase distribution at the object plane from the recorded intensity distribution.