18 research outputs found
Reading Responses To Journal Articles, Computational Emulation Of Published Research
Students responded to sets of journal articles in computational optics and imaging every week. Articles investigated scientific questions, visualization of scientific data, ethical questions, and international collaborative projects (such as the Event Horizon Telescope). Students also completed labs to gain proficiency in computational tools
Computational Optics (ENGR 030) Syllabus
This course provides an introduction to computational optics and imaging, where camera hardware is co-designed with processing algorithms. Topics may include: geometrical and wave optics, PSF engineering, light field imaging, compressed sensing, time-of-flight imaging, Fourier optics, super-resolution, medical imaging, and virtual and augmented reality. Students will also investigate ethical and artistic questions in image collection and processing
Intermediate Mirrors to Reach Theoretical Efficiency Limits of Multi-Bandgap Solar Cells
Creating a single bandgap solar cell that approaches the Shockley-Queisser
limit requires a highly reflective rear mirror. This mirror enhances the
voltage of the solar cell by providing photons with multiple opportunities for
escaping out the front surface. Efficient external luminescence is a
pre-requisite for high voltage. Intermediate mirrors in a multijunction solar
cell can enhance the voltage for each cell in the stack. These intermediate
mirrors need to have the added function of transmitting the below bandgap
photons to the next cell in the stack. In this work, we quantitatively
establish the efficiency increase possible with the use of intermediate
selective reflectors between cells in a tandem stack. The absolute efficiency
increase can be up to ~6% in dual bandgap cells with optimal intermediate and
rear mirrors. A practical implementation of an intermediate selective mirror is
an air gap sandwiched by antireflection coatings. The air gap provides perfect
reflection for angles outside the escape cone, and the antireflection coating
transmits angles inside the escape cone. As the incoming sunlight is within the
escape cone, it is transmitted on to the next cell, while most of the
internally trapped luminescence is reflected
Light Trapping Textures Designed by Electromagnetic Optimization for Sub-Wavelength Thick Solar Cells
Light trapping in solar cells allows for increased current and voltage, as
well as reduced materials cost. It is known that in geometrical optics, a
maximum 4n^2 absorption enhancement factor can be achieved by randomly
texturing the surface of the solar cell, where n is the material refractive
index. This ray-optics absorption enhancement limit only holds when the
thickness of the solar cell is much greater than the optical wavelength. In
sub-wavelength thin films, the fundamental questions remain unanswered: (1)
what is the sub-wavelength absorption enhancement limit and (2) what surface
texture realizes this optimal absorption enhancement? We turn to computational
electromagnetic optimization in order to design nanoscale textures for light
trapping in sub-wavelength thin films. For high-index thin films, in the weakly
absorbing limit, our optimized surface textures yield an angle- and
frequency-averaged enhancement factor ~39. They perform roughly 30% better than
randomly textured structures, but they fall short of the ray optics enhancement
limit of 4n^2 ~ 50
Optimal Physical Preprocessing for Example-Based Super-Resolution
In example-based super-resolution, the function relating low-resolution
images to their high-resolution counterparts is learned from a given dataset.
This data-driven approach to solving the inverse problem of increasing image
resolution has been implemented with deep learning algorithms. In this work, we
explore modifying the imaging hardware in order to collect more informative
low-resolution images for better ultimate high-resolution image reconstruction.
We show that this "physical preprocessing" allows for improved image
reconstruction with deep learning in Fourier ptychographic microscopy.
Fourier ptychographic microscopy is a technique allowing for both high
resolution and high field-of-view at the cost of temporal resolution. In
Fourier ptychographic microscopy, variable illumination patterns are used to
collect multiple low-resolution images. These low-resolution images are then
computationally combined to create an image with resolution exceeding that of
any single image from the microscope. We use deep learning to jointly optimize
the illumination pattern with the post-processing reconstruction algorithm for
a given sample type, allowing for single-shot imaging with both high resolution
and high field-of-view. We demonstrate, with simulated data, that the joint
optimization yields improved image reconstruction as compared with sole
optimization of the post-processing reconstruction algorithm
Illumination Pattern Design With Deep Learning For Single-Shot Fourier Ptychographic Microscopy
Fourier ptychographic microscopy allows for the collection of images with a high space-bandwidth product at the cost of temporal resolution. In Fourier ptychographic microscopy, the light source of a conventional widefield microscope is replaced with a light-emitting diode (LED) matrix, and multiple images are collected with different LED illumination patterns. From these images, a higher-resolution image can be computationally reconstructed without sacrificing field-of-view. We use deep learning to achieve single-shot imaging without sacrificing the space-bandwidth product, reducing the acquisition time in Fourier ptychographic microscopy by a factor of 69. In our deep learning approach, a training dataset of high-resolution images is used to jointly optimize a single LED illumination pattern with the parameters of a reconstruction algorithm. Our work paves the way for high-throughput imaging in biological studies
Ultraefficient Thermophotovoltaic Power Conversion By Band-Edge Spectral Filtering
Thermophotovoltaic power conversion utilizes thermal radiation from a local heat source to generate electricity in a photovoltaic cell. It was shown in recent years that the addition of a highly reflective rear mirror to a solar cell maximizes the extraction of luminescence. This, in turn, boosts the voltage, enabling the creation of record-breaking solar efficiency. Now we report that the rear mirror can be used to create thermophotovoltaic systems with unprecedented high thermophotovoltaic efficiency. This mirror reflects low-energy infrared photons back into the heat source, recovering their energy. Therefore, the rear mirror serves a dual function; boosting the voltage and reusing infrared thermal photons. This allows the possibility of a practical \u3e50% efficient thermophotovoltaic system. Based on this reflective rear mirror concept, we report a thermophotovoltaic efficiency of 29.1 ± 0.4% at an emitter temperature of 1,207 °C