次波長週期結構之濾波特性與等效光學參數之研究

Abstract

Subwavelength periodic structures provide two attractive capabilities: controllable filtering effects and synthesis of effective parameters supporting extraordinary physical properties not seen usually in nature; therefore they have been the subject of tremendous research in recent years. The variety of features in subwavelength arrays, such as extraordinary transmission, reflection, and absorption, polarization steering, and nonlinear effects are attributed to resonances. Besides intrinsic material resonances from light-matter interactions, geometrical confinements of electromagnetic waves in a unit cell of arrays support new pathways to excite various site resonances involving geometrical resonance, surface plasmon resonance, guided mode resonance, and Fabry-Perot resonance. In another aspect, the collective behavior contributed from the periodicity of subwavelength arrays provides lattice resonances, which can be tuned by lattice arrangements. In particular, the coupling between these resonances, which is related to Fano resonances, brings about lots of degree of freedoms in design, and possesses a great number of potential applications. In this thesis, multiple Fano resonances in asymmetric multi-stripe arrays with two-dimensional rectangular grid, which have potential applications in multi-band filters, are investigated first. The underlying mechanism is illustrated by analyzing field pattens. Another fascinating filtering feature, extraordinary absorption related to Fano resonances, is studied next. We propose one-dimensional compound gratings with anomalous optical absorption associated with bounding, antibounding, and semibounding surface plasmon modes. The demonstrated structures can be applied to photodetectors. In contrast to subwavelength arrays with conducing materials, those made of dielectrics with high permittivity are also investigated, and we finally study the other important capability of subwavelength arrays: effective optical parameters, by means of homogenization. Negative effective permittivity and effective permeability occur simultaneously in the feasible wavelength region for s-polarized incidence, and give rise to negative index of refraction.