2,186 research outputs found
Broadband lightweight flat lenses for longwave-infrared imaging
We experimentally demonstrate imaging in the longwave-infrared (LWIR)
spectral band (8um to 12um) using a single polymer flat lens based upon
multi-level diffractive optics. The device thickness is only 10{\mu}m, and
chromatic aberrations are corrected over the entire LWIR band with one surface.
Due to the drastic reduction in device thickness, we are able to utilize
polymers with absorption in the LWIR, allowing for inexpensive manufacturing
via imprint lithography. The weight of our lens is less than 100 times those of
comparable refractive lenses. We fabricated and characterized two different
flat lenses. Even with about 25% absorption losses, experiments show that our
flat polymer lenses obtain good imaging with field of view of ~35degrees and
angular resolution less than 0.013 degrees. The flat lenses were characterized
with two different commercial LWIR image sensors. Finally, we show that by
using lossless, higher-refractive-index materials like silicon, focusing
efficiencies in excess of 70% can be achieved over the entire LWIR band. Our
results firmly establish the potential for lightweight, ultra-thin, broadband
lenses for high-quality imaging in the LWIR band
Diffractive sidewall grating coupler: towards 2D free-space optics on chip.
Silicon photonics has been the subject of intense research efforts. In order to implement complex integrated silicon photonic devices and systems, a wide range of robust building blocks is needed. Waveguide couplers are fundamental devices in integrated optics, enabling different functionalities such as power dividers, spot-size converters, coherent hybrids and fiber-chip coupling interfaces, to name a few. In this work we propose a new type of nanophotonic coupler based on sidewall grating (SIGRA) concept. SIGRAs have been used in the Bragg regime, for filtering applications, as well as in the sub-wavelength regime in multimode interference (MMI) couplers. However, the use of SIGRAs in the radiation regime has been very limited. Specifically, a coarse wavelength division multiplexer was proposed and experimentally validated. In this work we study the use of SIGRAs in the diffractive regime as a mean to couple the light between a silicon wire waveguide mode and a continuum of slab waveguide modes. We also propose an original technique for designing SIGRA based couplers, enabling the synthesis of arbitrary radiation field profile by Floquet- Bloch analysis of individual diffracting elements while substantially alleviating computational load. Results are further validated by 3D FDTD simulations which confirm that the radiated field profile closely matches the target design field.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec
Optimization and Design Numerical Modeling and Advances in Fabrication Technologies to Optical Performance
Photonic crystals and Nano photonics have received a great deal of attention over the last decade, largely due to improved numerical modeling and advances in fabrication technologies. To this day, fabrication and optical behavior remain decoupled during the design phase and numerous assumptions are made about “perfect” geometry. As research moves from theory to real devices, predicting device behavior based on realistic geometry becomes critical. In this dissertation, a set of numerical tools was developed to model micro and nano fabrication processes. They were combined with equally capable tools to model optical performance of the simulated structures. Using these tools, it was predicted and demonstrated that 3D nanostructures may be formed on a standard mask aligner. A space-variant photonic crystal filter was designed and optimized based on a simple fabrication method of etching holes through hetero-structured substrates. It was found that hole taper limited their optical performance and a method was developed to compensate. A method was developed to tune the spectral response of guided-mode resonance filters at the time of fabrication using models of etching and deposition. Auto cloning was modeled and shown that it could be used to form extremely high aspect ratio structures to improve performance of form-birefringent devices. Finally, the numerical tools were applied to metallic photonic crystal devices
Phase Retrieval with Application to Optical Imaging
This review article provides a contemporary overview of phase retrieval in
optical imaging, linking the relevant optical physics to the information
processing methods and algorithms. Its purpose is to describe the current state
of the art in this area, identify challenges, and suggest vision and areas
where signal processing methods can have a large impact on optical imaging and
on the world of imaging at large, with applications in a variety of fields
ranging from biology and chemistry to physics and engineering
Juno: a Python-based graphical package for optical system design
This report introduces Juno, a modular Python package for optical design and
simulation. Juno consists of a complete library that includes a graphical user
interface to design and visualise arbitrary optical elements, set up wave
propagation simulations and visualise their results. To ensure an efficient
visualisation of the results, all simulation data are stored in a structured
database that can filter and sort the output. Finally, we present a practical
use case for Juno, where optical design and fabrication are interlaced in a
feedback cycle. The presented data show how to compare the simulated and the
measured propagation; if a difference or unexpected behaviour is found, we show
how to convert and import the optical element profile from a profilometer
measurement. The propagation through the profile can provide immediate feedback
about the quality of the element and a measure of the effects brought by
differences between the idealised and the actual profile, therefore, allowing
to exclude the experimental errors and to weigh every aspect of fabrication
errors.Comment: The software is available at https://github.com/DeMarcoLab/jun
Hector, a fast simulator for the transport of particles in beamlines
Computing the trajectories of particles in generic beamlines is an important
ingredient of experimental particle physics, in particular regarding near-beam
detectors. A new tool, Hector, has been built for such calculations, using the
transfer matrix approach and energy corrections. The limiting aperture effects
are also taken into account. As an illustration, the tool was used to simulate
the LHC beamlines, in particular around the high luminosity interaction points
(IPs), and validated with results of the Mad-X simulator. The LHC beam
profiles, trajectories and beta functions are presented. Assuming certain
forward proton detector scenarios around the IP5, acceptance plots, irradiation
doses and chromaticity grids are produced. Furthermore, the reconstruction of
proton kinematic variables at the IP (energy and angle) is studied as well as
the impact of the misalignment of beamline elements.Comment: 40 pages, 20 figures; added references, corrected typos ; submitted
to JINS
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