For two decades, extraordinary optical transmission (EOT) has amplified exploration into subwavelength systems. Researchers have previously suggested exploiting the spectrally selective electromagnetic field confinement of subwavelength cavities for multispectral detectors. Utilizing the finite-difference frequency domain (FDFD) method, we examine electromagnetic field confinement in both 2-dimensional and 3-dimensional scenarios from 2.5 to 6 microns (i.e., mid-wave infrared or MWIR). We explore the trade space of deep subwavelength cavities and its impact on resonant enhancement of the electromagnetic field. The studies provide fundamental understanding of the coupling mechanisms allowing for prediction of resonant spectral behavior based on cavity geometry and material properties. In addition to work on spectral response due to geometric parameters for subwavelength cavities, we investigate the spectral response with the inclusion of an absorber on the output in the mid-wave infrared. The placement of an absorbing layer causes a dramatic increase on the effective index within the subwavelength cavity while causing the cavity to become energetically leaky. We have found this broadens the spectral response of the cavity. To mitigate this undesired effect for spectral filter applications, we investigate modulation of the absorber-cavity field coupling by addition of an isolation layer; we show this layer decreases the spatial overlap of the cavity mode with the lossy absorber. In addition, we examine the effect of these layers on the quantum efficiency of the system. We also explore changing the material environment both within and surrounding the cavity to increase quality factors of designed cavities. We examine and quantify such systems by the trade-off that occurs between the quality factor and quantum efficiency. This trade-off occurs due to the spatial extent of fields in the propagating direction. The lateral spatial extent of the cavity is also examined by changing the lateral subwavelength spacing of a periodic array of cavities. The cavities are found to be sensitive to fields extending ~10x larger than the physical extent of the cavity. This phenomenon is indicative of the funneling effect. In addition, fabrication techniques were examined and found to be successful in creating the subwavelength features necessary for creation of such systems. The spectral response of fabricated devices was found to be in excellent agreement with simulation. This dissertation sets the groundwork for development of a novel multispectral detector in the MWIR by examining the spectral relationship of subwavelength cavities coupled to an absorber.


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Graduation Date





Renshaw, Kyle


Doctor of Philosophy (Ph.D.)


College of Optics and Photonics


Optics and Photonics

Degree Program

Optics and Photonics




CFE0008839; DP0026118



Release Date

December 2021

Length of Campus-only Access


Access Status

Doctoral Dissertation (Open Access)