Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

A method of lensless, single pixel imaging is presented. This method, referred to as MAS-IPSII, is theoretically capable of resolutions as small as one quarter of the wavelength of the imaging light. The resolution is not limited by the aperture of any optic, making high resolutions (including subwavelength) feasible even at very large (greater than a meter) distances. Imaging requires only flat optics and a coherent source, making it a good candidate for imaging with extreme wavelengths in the UV and x-ray regimes. The method is demonstrated by the imaging of various test targets. Both real and complex imaging (i.e. holography) is demonstrated.

Highly coherent light, although beneficial in specific applications, suffers from the formation of speckles, resulting in poor imaging, lighting, and projection/display quality. Moreover, the long coherence length limits the resolution in interference based sensing. This has led to the emergence of edge-emitting semiconductor low coherence light sources (e.g., broadband lasers, superluminescent diodes, etc.), which have been used in display applications, optical coherence tomography, and random bit generation. However, edge emission prevents the ease of fabricating two-dimensional arrays. Conversely, vertical-cavity surface-emitting lasers (VCSELs) have recently been widely used in consumer electronics due to the unique advantages of surface emission. Nevertheless, they still suffer from issues caused by high coherence. The aim of this dissertation is to design low-coherence surface-emitting lasers to push simultaneous illumination and optical wireless communication (OWC) toward reliable implementation with higher speeds. To that end, we demonstrate, for the first time, the use of chaotic cavities to lower the coherence of VCSELs without increasing their emission area, which would lower their speed. Not only did the chaotic cavity result in doubling the number of modes (lowering the coherence) compared to conventional VCSELs, but it also resulted in an increase in the optical power of up to 60%. We also show that chaotic-cavity broad-area VCSELs can achieve significantly broader modulation bandwidths (up to 5 GHz) and higher data rates (up to 12.6 Gb/s) compared to other low-coherence light sources, while achieving a lower speckle contrast. We further report a novel technique of lowering the speckle contrast 2 by carefully designing the AC signal used for communication. We show that the apparent spatial coherence is dramatically decreased by inserting a short chirp signal between symbols. Using this method with a chaotic-cavity VCSEL, the number of apparent modes can be up to 450 modes, compared to 88 modes measured from a conventional broad-area VCSEL. The simplicity of implementing the reported design, which requires no additional fabrication steps, makes it a promising solution for applications that would benefit from the lower speckle density of the emitted light as well as those that rely on lower temporal coherence.

From the twelfth to the nineteenth centuries, a corpus of didactic Persian texts circulated across Central and South Asian courts, functioning as a ‘mirror for princes’ or didactic manuals of ethical comportment. Numerous such manuscripts were embellished with meticulously detailed and laboriously created paintings. But what was the role of manuscript illustrations in shaping ethical and moral transformation? Though we now understand paintings through the frameworks of taxonomy and connoisseurship, how did illustrations make meaning to their intended audience, who read the text and were steeped in textual traditions? Contemporary sources are silent on the role of paintings in didactic texts, but, as my dissertation demonstrates, an in-depth evaluation of paintings and their accompanying text reveals how painted manuscripts engendered specific reading practices. These reading practices involved listening, visualizing mental images, viewing paintings, anticipating, recollecting, confusion and wonder, exercising patience, and even stilling our minds – experiences that made the reader-viewer dwell on the manuscript’s contents for an extended period. Focusing on painted manuscripts commissioned and collected by the Qutb Shahis in sixteenth-century Golconda, this dissertation’s chapters explore how writers, scribes, painters, and illuminators deployed allegory, repetition, and narrative plot, to attract and sustain their intended audience's attention.

The use of light has always been a vehicle of symbolic meaning and spiritual experience in religious spaces. Depending on culture and religion this use differs, but in any case, the connection between the built form, the architecture and the history makes the relationship with light a compelling issue that is worth exploring. This thesis aims to study the role that light played in the designing of St: Eskilskyrkan church in Sweden, and the way it affected the perception of the architecture and its materials. In order to answer this question, a methodology based on both qualitative and quantitative methods, was generated. Evaluation and discussion of literature review, interviews, survey on perception of light, a comparison between two similar buildings, daylight analysis using lighting software and testing lighting design tools are the key elements to create the guidelines for the lighting design proposal that will be generated in the last part of the thesis. This proposal aims to redevelop the existing illumination of the interior of the church, emphasizing on functionality, on the built form and the enhancement of spiritual experience.

Reflector design stemmed from the need to shape the light emitted by candles or lamps. Over 2,000 years ago people realized that a mirror shaped as a parabola can concentrate light, and thus significantly boosts its intensity, to the point where objects can be set afire. Nowadays many applications require an accurate control of light, such as automotive headlights, streetlights, projection displays, and medical illuminators. In all cases light emitted from a light source can be shaped into a desired target distribution with a reflective surface. Design methods for systems with rotational and translational symmetry were devised in the 1930s. However, the freeform reflector shapes required to illuminate targets with no such symmetries proved to be much more challenging to design. Even when the source is assumed to be a point, the reflector shape is governed by a set of second-order partial non-linear differential equations that cannot be solved with standard numerical integration techniques. An iterative approach to solve the problem for a discrete target, known as the method of supporting ellipsoids, was recently proposed by Oliker. In this research we report several efficient implementations of the method of supporting ellipsoids, based on the point source approximation, and we propose new reflector design techniques that take into account the extent of the source. More specifically, this work has led to three major achievements. First, a thorough analysis of the method of supporting ellipsoids was performed that resulted in two alternative implementations of the algorithm, which enable a fast generation of freeform reflector shapes within the point source approximation. We tailored the algorithm in order to provide control over the parameters of interest to the designers, such as the reflector scale and geometry. Second, the shape generation algorithm was used to analyze how source flux can be mapped onto the target. We derived the condition under which a given source-target mapping can be achieved with a smooth continuous surface, referred as the integrability condition. We proposed a method to derive mappings that satisfy the integrability condition. We then use these mappings to quickly generate reflector shapes that create continuous target distributions as opposed to reflectors generated with the method of supporting ellipsoids that create discrete sets of points on the target. We also show how mappings that do not satisfy the integrability condition can be achieved by introducing step discontinuities in the reflector surface. Third, we investigated two methods to design reflectors with extended sources. The first method uses a compensation approach where the prescribed target distribution is adjusted iteratively. This method is effective for compact sources and systems with rotational or translational symmetry. The second method tiles the source images created by a reflector designed with the method of supporting ellipsoids and then blends the source images together using scattering in order to obtain a continuous target distribution. This latter method is effective for freeform reflectors and target distributions with no sharp variations. Finally, several case studies illustrate how these methods can be successfully applied to design reflectors for general illumination applications such as street lighting or luminaires. We show that the proposed design methods can ease the design of freeform reflectors and provide efficient, cost-effective solutions that avoid unnecessary energy consumption and light pollution.

Creation of visually-pleasing images has always been one of the main goals of computer graphics. Two important components are necessary to achieve this goal --- artists who design visual aspects of an image (such as materials or lighting) and sophisticated algorithms that render the image. Traditionally, rendering has been of greater interest to researchers, while the design part has always been deemed as secondary. This has led to many inefficiencies, as artists, in order to create a stunning image, are often forced to resort to the traditional, creativity-baring, pipelines consisting of repeated rendering and parameter tweaking. Our work shifts the attention away from the rendering problem and focuses on the design. We propose to combine non-physical editing with real-time feedback and provide artists with efficient ways of designing complex visual aspects such as global illumination or all-frequency shadows. We conform to existing pipelines by inserting our editing components into existing stages, hereby making editing of visual aspects an inherent part of the design process. Many of the examples showed in this work have been, until now, extremely hard to achieve. The non-physical aspect of our work enables artists to express themselves in more creative ways, not limited by the physical parameters of current renderers. Real-time feedback allows artists to immediately see the effects of applied modifications and compatibility with existing workflows enables easy integration of our algorithms into production pipelines.

Visible-light communication (VLC) has several advantages over the commonly used radio frequency (RF) spectrum, including high bandwidth and low crosstalk. These features have become of more significance, especially as the proliferation of wireless devices increases and causes spectrum crowding. The white light in VLC systems is typically obtained from blue/violet light-emitting diodes (LEDs) and phosphors partially converting blue light into longer wavelength colors spanning the visible-light band. One phosphor that is frequently used is cerium-doped yttrium aluminum garnet (YAG). However, YAG suffers from a low color-rendering index (CRI) and high correlated color temperature (CCT). Lead halide perovskites provide an alternative to YAG and have been extensively utilized for optoelectronic devices owing to their tunable bandgap and high photoluminescence quantum yield (PLQY). However, their drawbacks, e.g., lead toxicity and instability, hinder their widespread application. Herein, in order to take advantage of a high-performance lead-free tin-based halide perovskite phosphor that has a high absolute PLQY of near unity and a wide spectral emission ranging from 500 to 700 nm, we fabricated ultraviolet (UV) micro light-emitting diodes (micro-LEDs) with a peak wavelength at 365 nm to match the peak of the photoluminescence excitation (PLE) spectra of the material to obtain strong yellow-spectrum emission. Together with a blue LED, white light was obtained with a CRI of 84.9 and 4115-K CCT. Despite the long PL lifetime of the perovskite material, which is in the order of μs, a net data rate of 1.5 Mb/s was achieved using orthogonal frequency-division multiplexing (OFDM) with adaptive bit and power loading to take advantage of the exceptionally high PLQY of the phosphor to improve the data throughput of the VLC system using higher modulation orders. Furthermore, through improvements to the nanostructure of lead-free tin-based halide perovskite phosphor and the use of excitation sources with a higher power, the data rate is expected to be even higher. The lead-free nature of this material, along with its wide spectrum and high conversion efficiency, makes it a promising alternative to conventional toxic perovskite-based phosphors. As the first demonstration of VLC links using lead-free perovskite, this study paves the way for safer, more sustainable VLC systems.

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