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International Journal of Optics
Volume 2012 (2012), Article ID 916482, 9 pages
Research Article

Plasmonic Band-Pass Microfilters for LWIR Absorption Spectroscopy

1Department of Physics, Colorado School of Mines, 1500 Illinois Street, Golden, CO 80401, USA
2Thin Film Technologies Division, ITN Energy Systems, Inc., 8130 Shaffer Parkway, Littleton, CO 80127, USA

Received 31 October 2011; Revised 13 January 2012; Accepted 13 January 2012

Academic Editor: K. S. Chiang

Copyright © 2012 J. M. Banks et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Absorption spectroscopy in the long wave infrared provides an effective method for identification of various hazardous chemicals. We present a theoretical design for plasmonic band-pass filters that can be used to provide wavelength selectivity for uncooled microbolometer sensors. The microfilters consist of a pair of input reflection gratings that couple light into a plasmonic waveguide with a central resonant waveguide cavity. An output transmission grating on the other side of the structure pulls light out of the waveguide where it is detected by a closely spaced sensor. Fabrication of the filters can be performed using standard photolithography procedures. A spectral bandpass with a full-width at half-maximum (FWHM) of 100 nm can be obtained with a center wavelength spanning the entire 8–12 μm atmospheric transmission window by simple geometric scaling of only the lateral dimensions. This allows the simultaneous fabrication of all the wavelength filters needed for a full spectrometer on a chip.