Compact photonic-crystal superabsorbers from strongly absorbing media

Copyright © 2013 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Applied Physics, Volume 114 (3), article 033504, and may be found at http://dx.doi.org/10.1063/1.4811521We present a route to near-perfect absorption in compact photonic-crystal (PC) structures constructed from strongly absorbing media that are typically highly reflective in bulk form. Our analysis suggests that the key underlying mechanism in such PC superabsorbers is the existence of a PC-band-edge reflectionless condition. Although the latter is by default uncharacteristic in photonic crystals, we propose here a clear recipe on how such condition can be met by tuning the structural characteristics of one-dimensional lossy PC structures. Based on this recipe, we constructed a realizable three-layer SiC- BaF2 -SiC PC operating within the Reststrahlen band of SiC. We demonstrate near-perfect absorption in this prototype of total thickness smaller than λ/3 , where more than 90% of the impinging light is absorbed by the top deep-subwavelength layer of thickness ∼λ/1100 . We believe our study will inspire new photonic-crystal-based designs for extreme absorption harnessing across the electromagnetic spectrum.University of Exete

Simulation and analysis of grating-integrated quantum dot infrared detectors for spectral response control and performance enhancement

We propose and analyze a novel detector structure for pixel-level multispectral infrared imaging. More specifically, we investigate the device performance of a grating-integrated quantum dots-in-a-well photodetector under backside illumination. Our design uses 1-dimensional grating patterns fabricated directly on a semiconductor contact layer and, thus, adds a minimal amount of additional effort to conventional detector fabrication flows. We show that we can gain wide-range control of spectral response as well as large overall detection enhancement by adjusting grating parameters. For small grating periods, the spectral responsivity gradually changes with parameters. We explain this spectral tuning using the Fabry-Perot resonance and effective medium theory. For larger grating periods, the responsivity spectra get complicated due to increased diffraction into the active region, but we find that we can obtain large enhancement of the overall detector performance. In our design, the spectral tuning range can be larger than 1 mu m, and, compared to the unpatterned detector, the detection enhancement can be greater than 92% and 148% for parallel and perpendicular polarizations. Our work can pave the way for practical, easy-to-fabricate detectors, which are highly useful for many infrared imaging applications. (C) 2014 AIP Publishing LLCopen1

Evaluation Of Quantization Effects On The Frequency Response Of Digital Filters.

An optimum non-real time algorithm for evaluating the frequency response of real time digital filters, which includes quantization affects, is formulated. After showing that pulse responses are not suitable, an algorithm based on the step response is derived. Then this algorithmic formulation is validated by using it to design a computer simulation that reveals the digital quantization affects in an Intel 2920 real time digital filter implementation