The Extraordinary Optical Absorption Effects in Subwavelength Periodic Structures
Date Issued
2012
Date
2012
Author(s)
Shue, Yu-Shuan
Abstract
Subwavelength periodic structure plays an important role in the electromagnetic science. Caused by periodic arrangement of structures, structures themselves are equipped with tunable resonance. Because the period of subwavelength structure is less than the incident wavelength, it can explore to the physical phenomena by the way of effective medium concept. With these properties, the design objects possess high degrees of freedom which can create physical characteristics that cannot be found in nature material, including the negative index of refraction and backward wave. These are called metamaterial. Subwavelength periodic structures have many interesting optical phenomena, such as extraordinary optical transmission and extraordinary optical absorption, and these properties are caused by resonance.
This thesis aims to investigate the behavior of extraordinary optical absorption of the subwavelength periodic structure, and focus on the resonance mechanism. It lets the metal which does not absorb easily have extraordinary high absorption by resonance. The investigation has three parts. First, it is fixed at the groove height and varies the groove period to investigate the absorption situation in the different periods. Due to the cavity resonance, the electric field strength is significantly enhanced inside the groove. The structure with shallow grooves has abnormally total absorption, and it tries to use the effective medium theory to explain these anomalies. When the groove height is fixed at 30 nm, the wavelength of the high absorption is first blue-shift then red-shift with increasing of the groove period. Second, it is fixed at the groove period(d=600 nm and d=10 nm) and varies the groove height to investigate the absorption situation in the different heights. Found that when the wavelength is greater than 600 nm there is high absorption caused by Fabry-Perot resonance. In the greater period it tries to use MIM waveguide to approximate the absorption curve. Particularly, there is a Wood anomaly caused by absorption in the greater cycle. In the smaller period, we successfully use effective medium to simulate the same phenomenon. Third, it changes the groove shape from rectangle to sinusoidal surface. It investigates to absorption effect by changing period and height. It found that if one wants to have total absorption, the ratio of period and height must be precise in the different materials.
Subjects
subwavelength periodic structures
metamaterial
effective medium theory
Wood anomalies
Fabry-Perot resonance
Extraordinary optical absorption
Type
thesis
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