Polarized 3D: High-Quality Depth Sensing with Polarization Cues

Coarse depth maps can be enhanced by using the shape information from polarization cues. We propose a framework to combine surface normals from polarization (hereafter polarization normals) with an aligned depth map. Polarization normals have not been used for depth enhancement before. This is because polarization normals suffer from physics-based artifacts, such as azimuthal ambiguity, refractive distortion and fronto-parallel signal degradation. We propose a framework to overcome these key challenges, allowing the benefits of polarization to be used to enhance depth maps. Our results demonstrate improvement with respect to state-of-the-art 3D reconstruction techniques.Charles Stark Draper Laboratory (Doctoral Fellowship)Singapore. Ministry of Education (Academic Research Foundation MOE2013-T2-1-159)Singapore. National Research Foundation (Singapore University of Technology and Design

Multiplexed photography : single-exposure capture of multiple camera settings

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 115-124).The space of camera settings is large and individual settings can vary dramatically from scene to scene. This thesis explores methods for capturing and manipulating multiple camera settings in a single exposure. Multiplexing multiple camera settings in a single exposure can allow post-exposure control and improve the quality of photographs taken in challenging lighting environments (e.g. low light or high motion). We first describe the design and implementation of a prototype optical system and associated algorithms to capture four images of a scene in a single exposure, each taken with a different aperture setting. Our system can be used with commercially available DSLR cameras and photographic lenses without modification to either. We demonstrate several applications of our multi-aperture camera, such as post-exposure depth of field control, synthetic refocusing, and depth-guided deconvolution. Next we describe multiplexed flash illumination to recover both flash and ambient light information as well as extract depth information in a single exposure. Traditional photographic flashes illuminate the scene with a spatially-constant light beam. By adding a mask and optics to a flash, we can project a spatially varying illumination onto the scene which allows us to spatially multiplex the flash and ambient illuminations onto the imager. We apply flash multiplexing to enable single exposure flash/no-flash image fusion, in particular, performing flash/no-flash relighting on dynamic scenes with moving objects. Finally, we propose spatio-temporal multiplexing, a novel image sensor feature that enables simultaneous capture of flash and ambient illumination.(cont.) We describe two possible applications of spatio-temporal multiplexing: single-image flash/no-flash relighting and white balancing scenes containing two distinct illuminants (e.g. flash and fluorescent lighting).by Paul Elijah Green.Ph.D

Development of Holographic Phase Masks for Wavefront Shaping

This dissertation explores a new method for creating holographic phase masks (HPMs), which are phase transforming optical elements holographically recorded in photosensitive glass. This novel hologram recording method allows for the fast production of HPMs of any complexity, as opposed to the traditional multistep process, which includes the design and fabrication of a master phase mask operating in the UV region before the holographic recording step. We holographically recorded transmissive HPMs that are physically robust (they are recorded in a silicate glass volume), can handle tens of kilowatts of continuous wave (CW) laser power, are un-erasable, user defined, require no power to operate, can work over a wavelength band ranging from 350 to 2500 nm, and can modify the wavefront of narrow line or broad band coherent sources. The HPMs can be wavelength-tunable by angular adjustment over tens or even hundreds of nanometers. The HPMs incorporate the phase information in the bulk of a volume Bragg grating (VBG) resulting in only a single diffraction order and up to 100% diffraction efficiency. Recording in thick photosensitive medium also enables the multiplexing of HPMs in a single monolithic element. While these HPMs are physically overlapped in the space, they provide independent phase profiles, efficiencies, spectral and angular acceptances. Multiplexing HPMs allows splitting or combining of multiple beams while affecting their wavefronts individually. We also developed a new holographic phase mask of reflective-type. This device provides us the ability of recording RBGs with transversely shifted parts in the larger aperture which upon reconstruction will produce different phases to different parts of the diffracted beam. RBG\u27s diffraction spectrum possesses a very narrow bandwidth, and the holographic recording technique allows to multiplex multiple gratings into a single volume of PTR glass. If each of these Bragg wavelengths is assigned with a specific spatial mode, it can be achieved simultaneous spatial and spectral multiplexing. As a separate research topic, we look at how holographic optical elements (HOEs) can be used for improving the capabilities of the existing generation of head-up displays (HUDs), resulting in smaller, lighter units with a larger eye-box. Currently, surface relief gratings recorded in photosensitive polymers that are susceptible to the environmental conditions are used in HOE-based HUDs. This has an impact on their reliability and overall lifespan. We investigated a specific holographically recorded in the volume of photo-thermo-refractive glass transmissive gratings that generated multiple diffracted beams due to their operation in Raman-Nath regime. The Raman Nath gratings were successfully used to create an array of images because in augmented reality systems, this approach can be used to enhance the size of the exit pupil. These image splitting elements, due to the features of PTR glass, have a great resistance to temperature gradients, mechanical shocks, vibrations, and laser radiation

Computational Light Transport for Forward and Inverse Problems.

El transporte de luz computacional comprende todas las técnicas usadas para calcular el flujo de luz en una escena virtual. Su uso es ubicuo en distintas aplicaciones, desde entretenimiento y publicidad, hasta diseño de producto, ingeniería y arquitectura, incluyendo el generar datos validados para técnicas basadas en imagen por ordenador. Sin embargo, simular el transporte de luz de manera precisa es un proceso costoso. Como consecuencia, hay que establecer un balance entre la fidelidad de la simulación física y su coste computacional. Por ejemplo, es común asumir óptica geométrica o una velocidad de propagación de la luz infinita, o simplificar los modelos de reflectancia ignorando ciertos fenómenos. En esta tesis introducimos varias contribuciones a la simulación del transporte de luz, dirigidas tanto a mejorar la eficiencia del cálculo de la misma, como a expandir el rango de sus aplicaciones prácticas. Prestamos especial atención a remover la asunción de una velocidad de propagación infinita, generalizando el transporte de luz a su estado transitorio. Respecto a la mejora de eficiencia, presentamos un método para calcular el flujo de luz que incide directamente desde luminarias en un sistema de generación de imágenes por Monte Carlo, reduciendo significativamente la variancia de las imágenes resultantes usando el mismo tiempo de ejecución. Asimismo, introducimos una técnica basada en estimación de densidad en el estado transitorio, que permite reusar mejor las muestras temporales en un medio parcipativo. En el dominio de las aplicaciones, también introducimos dos nuevos usos del transporte de luz: Un modelo para simular un tipo especial de pigmentos gonicromáticos que exhiben apariencia perlescente, con el objetivo de proveer una forma de edición intuitiva para manufactura, y una técnica de imagen sin línea de visión directa usando información del tiempo de vuelo de la luz, construida sobre un modelo de propagación de la luz basado en ondas.<br /

Towards a unified treatment of 3D display using partially coherent light

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 111-120).This thesis develops a novel method of decomposing a 3D phase space description of light into multiple partially coherent modes, and applies this decomposition to the creation of a more flexible 3D display format. Any type of light, whether it is completely coherent, partially coherent or incoherent, can be modeled either as a sum of coherent waves or as rays. A set of functions, known as phase space functions, provide an intuitive model for these waves or rays as they pass through a 3D volume to a display viewer's eyes. First, this thesis uses phase space functions to mathematically demonstrate the limitations of two popular 3D display setups: parallax barriers and coherent holograms. Second, this thesis develops a 3D image design algorithm based in phase space. The "mode-selection" algorithm can find an optimal holographic display setup to create any desired 3D image. It is based on an iterative algebraic-rank restriction process, and can be extended to model light with an arbitrary degree of partial coherence. Third, insights gained from partially coherent phase space representations lead to the suggestion of a new form of 3D display, implemented with multiple time-sequential diffracting screens. The mode-selection algorithm determines an optimal set of diffracting screens to display within the flicker-fusion rate of a viewer's eye. It is demonstrated both through simulation and experiment that this time-sequential display offers improved performance over a fixed holographic display, creating 3D images with increased intensity variation along depth. Finally, this thesis investigates the tradeoffs involved with multiplexing a holographic display over time with well-known strategies of multiplexing over space, illumination angle and wavelength. The examination of multiplexing tradeoffs is extended into the incoherent realm, where comparisons to ray-based 3D displays can hopefully offer a more unified summary of the limitations of controlling light within a volume.by Roarke Horstmeyer.S.M

Measuring the Orbital Angular Momentum of Light for Astronomy

While the story of optical orbital angular momentum (OAM) dates back to the development of Maxwell's equations, the study of photon OAM by the physics community begins in earnest in the 1990s, led in part by a paper by Allen et al. describing the independent control of spin and orbital angular momentum in paraxial modes of light. The recognition of the orbital angular momentum of light in astronomy is a much more recent affair. This thesis explores the role of the OAM of light in astronomy and attempts to make the case for the measurement of photon OAM as a new tool in astronomy. Two contributions are made in order to prepare the groundwork for future endeavours: a laboratory assessment of the effectiveness of adaptive optics (AO) systems on atmospheric turbulence when measuring optical OAM, and an initial field test of an instrument measuring the optical OAM spectrum of the sun. Regarding the first study, the author finds that realistic atmospheric turbulence (1'' seeing) severely corrupts any incoming OAM signal at visible wavelengths, in spite of AO correction (<10% power recovered), however results suggest adequate correction at IR wavelengths. In the second study, an instrument to measure the OAM spectrum of a source is constructed and employed to measure the OAM spectrum of local regions of the sun. It represents the first measurement of its kind, distinguishing sunspots by analyzing their OAM spectrum and in addition, demonstrates the improvement of OAM measurements by implementing a lucky imaging routine. Finally, this thesis highlights a new avenue for further study into the measurement of OAM for observational astronomy. A new type of OAM measurement is proposed, capable of measuring rotations in the plane orthogonal to the line of sight. This measurement takes advantage of the rotational Doppler shift, an analogue of the translational Doppler shift, and an OAM interferometer designed to measure the associated phase shift is outlined. A future instrument is also proposed by combining the OAM interferometer with a high resolution spectrograph. This would allow for measurements of both the rotational and translational Doppler shifts, providing information about the three dimensional motion of an object

Ultrafast manipulation of single photons using dispersion and sum-frequency generation

Single photons provide a natural platform for quantum communication and quantum networking, as they can be entangled in many degrees of freedom and maintain coherence over long-distance links. However, while their minimal interactions with the environment isolate them from detrimental noise, it can make them difficult to measure and manipulate. In particular, manipulation on the ultrafast timescale is necessary to fully exploit the energy-time (or spectral) photonic degree of freedom. Full control over the spectral properties of single photons is key to many quantum technologies and opens the door to natural high-dimensional quantum encodings. In this thesis, we theoretically and experimentally examine the use of nonlinear optical processes mediated by strong laser pulses as a method to control the spectral properties of ultrafast single photons. By mixing single-photon pulses with strong escort pulses that have been shaped through dispersion in a nonlinear crystal, the shape of the escort is imprinted on the photon, resulting in a custom-tailored upconverted pulse. We theoretically examine this process for quadratic spectral phases and show that it has the potential to be simultaneously effective and efficient for the customization of single-photon spectral waveforms, and can be performed in an entanglement-conserving manner. We then experimentally demonstrate the range of this technique through three applications. First, we show that sum-frequency generation with shaped pulses can be used to coherently measure time-bin encoded photons with bin separations on the order of picoseconds, well below the timing resolution of our detectors. Secondly, we show that this technique can be adapted to convert a train of pulses to a frequency comb, which can be read out in a straightforward manner using diffraction-based spectrometry. We also show here that this process can be performed in a polarization-maintaining fashion, and demonstrate that entanglement with a partner photon is conserved with high fidelity. Finally, we show that this process can be viewed as a time lens, which modulates a temporal waveform in an analogous fashion to a lens focusing a beam of light. We apply the time lens to a photon from an energy-time entangled pair, and show negative magnification of the joint spectrum through a reversal of the spectral correlations. Such processes could find application in quantum state engineering and high-speed single-photon measurement