Extraordinary Optical And Acoustic Transmission Though Subwavelength Aperture Arrays

Since Ebbesen etal. reported the extraordinary optical transmission (EOT) through a periodic subwavelength hole array perforated on a metallic film in 1998, the optical properties of subwavelength structures have been the research hotspot and show potential applications in a wide range of areas, such as nanolithography, optical data storage spec-troscopy, bio-chemical sensing, subwavelength imaging, semiconductor light-emitting devices and so on. Accordingly, it has become an very important branch in plasmonics. In recent years, the idea of EOT has been transferred to the acoustic case and extraordinary acoustic transmission (EAT) has been confirmed, which opens a new research direction in acoustic field.We study the EOT through compound subwavelength hole arrays and EAT through compound and double-layer subwavelength hole arrays, respectively. In addition, the modulation of EOT by external magnetic field has been investigated. In these structures, some new optical and acoustic properties and the underlying physics were discovered. The dissertation consists of six chapters:In chapter one, we give an introduction for the related research background, recent development, theoretical methods and so on.In chapter two, we study the enhanced transmission through compound subwave-length rectangular hole arrays in perfect electronically conductive films. It is shown that phase effects become important in the enhanced transmission when extra rectan-gular holes are added per period. There are two types of resonance mechanisms due to the phase effects:one is the localized waveguide mode phase resonance and the other is the surface mode phase resonance. The localized waveguide mode phase resonances, which are related to the number of holes per period and their relative positions, split the waveguide resonance peak into several peaks. The surface mode phase resonances, which appear evidently only for some special arrangements of holes in a unit cell, lead to the suppression of some surface mode resonance peaks.In chapter three, we theoretically investigate the optical transmission through sub-wavelength semiconductor slits in the presence of external magnetic fields. Firstly, the dispersion relations of surface plasmon polaritons (SPPs) propagating in a subwavelength slit are analytically given. We find that the SPPs propagating along the positive and re-verse directions are symmetrical when the external magnetic fields are parallel, but asym-metrical when the external magnetic fields antiparallel. Afterward, the mode expansion technique is used to study the transmission properties of periodic subwavelength slit ar-rays with antiparallel magnetic fields in each unit cell. Two significant transmission char-acteristics can be observed: (i) The resonant peaks are redshifted with increasing the external magnetic fields; (ii) The transmissions in the two opposite directions through the slit arrays are asymmetric. A physical mechanism is proposed to explain the origin of the transmission asymmetry, which is the magnetic-field induced asymmetry of the SPP propagation loss inside the subwavelength slits.In chapter four, we study the resonant acoustic transmission through compound sub-wavelength periodic hole arrays. Fabry-Perot resonance peak splitting is found. We can attribute the phenomenon to phase resonances via calculating the phase difference between adjacent holes in a unit cell. Furthermore, by analyzing the transmission charac-teristics of different kinds of compound hole arrays for normal and non-normal incidence, it can be demonstrated that the phase resonances arise from the coupling between holes in a unit cell. In addition, we also discuss the transmission resonance originating from acoustic surface modes and illustrate the hybridized features of acoustic surface modes and Fabry-Perot modes.In chapter five, we present a theoretical study of acoustic waves passing through double-layer subwavelength hole arrays. The acoustic transmission resonance and sup-pression are observed. There are three mechanisms responsible for the transmission reso- nance:the excitation of geometrically induced acoustic surface waves, the Fabry-Perot resonance in a hole cavity (â… -FP resonance) and the Fabry-Perot resonance between two plates (â…¡-FP resonance). We can differentiate these mechanisms via the dispersion rela-tion of acoustic modes supported by the double-layer structure. It is confirmed that the coupling between two single-layer perforated plates, associated with longitudinal interval and lateral displacement, plays a crucial role in modulating the transmission properties. The strong coupling between two plates can induce the splitting of the transmission peak, while the decoupling between plates leads to the appearance of transmission suppression. By analyzing the criterion derived for transmission suppression, we conclude that it is the destructive interference between the diffracted waves and the direct transmission waves assisted by the I-FP resonance of the first plate that leads to the decoupling between plates and then the transmission suppression.The last chapter presents a summary and then gives some outlook for the future investigation.