We present the studies of Terahertz (THz) Semiconductor-Insulator-Semiconductor (SIS) Planar Plasmonic waveguide of Indium Antimonide (InSb) with cavities along the waveguide acting as resonator. The Surface Plasmon Polariton (SPP) modes were confined in the SI interface and resonance behavior and filtering functionality of the device were demonstrated. The transmission characteristic of the structure depends on the interference effects between the SPP mode passing through the cavity and the one returning from the cavity. These effects were observed by studying the transmission from the SIS waveguide as a function of frequency and cavity length and proving analytically using the analogy with microwave transmission line network. Furthermore, we present the SIS cavity resonator’s transmission characteristics which vary with changes in the dielectric constant of the insulator region. Such a study was proposed to incorporate in the structure for sensing of biomolecules in THz region.

Metallic nanostructures can exhibit different optical properties compared to bulk materials mainly depending on their shape, size, and separation. We present the results of an optical modeling study on ordered arrays of aluminum (Al) nanorods with a hexagonal periodic geometry placed on an Al thin film. We used a finite-difference time-domain (FDTD) method to solve the Maxwell's equations and predict the reflectance of the nanorod arrays. The thickness of the base Al film was set to 100 nm, and diameter, height and nanorod center-to-center periodicity were varied. Incident light in the FDTD simulations was an EM-circular polarized plane wave and reflectance profiles were calculated in the wavelength range 200-1800 nm. In addition, we calculated spatial electric field intensity distributions around the nanorods for wavelengths 300, 500, and 700 nm. Our results show that average reflectance of Al nanorods can drop down to as low as ∼50%, which is significantly lower than the ∼90% reflectance of conventional flat Al film at similar wavelengths. In addition to the overall decrease in reflectance, Al nanorod arrays manifest multiple resonant modes (higher-order modes) indicated by several dips in their reflectance spectrums (i.e. multiple attenuation peaks in their absorption profiles). Positions of these dips in the reflectance spectrum and spatial EM field distribution vary with nanorod height and diameter. Multiple reflectance peaks are explained by cavity resonator effects. Spatial EM field distribution profiles indicate enhanced light trapping among the nanorods, which can be useful especially in optoelectronic and solar cell applications.

Localized surface plasmon resonance (LSPR) is a label-free biosensing technique employing plasmonic nanostructures to detect local refractive index change induced by biomolecules in the vicinity of these nanostructures. In analogy to surface plasmon resonance (SPR) sensor in a cuvette, LSPR is resistant to bulk refractive index fluctuation yet remains comparably sensitive for biosensing purpose. LSPR has the advantage over SPR in that the overall system size is smaller, and not affected by normal temperature fluctuations during measurement. However, mass production of a cheap but effective LSPR substrate remains challenging. In this paper, a self-assembly gold nanoisland structure was synthesized on transparent glass substrate by a simple two-step deposition-growth process. The first step involved depositing an ultra thin film of gold with nominal thickness of 5 nm by thermal evaporation at 1× 10-7 torr. Then the gold coated substrate was placed into a high temperature oven and annealed at 450°C for 10 hours. By first observation, the annealed substrate turned from pale green to dark pink. Upon scanning with atomic force microscopy, it was revealed that nanoislands of about 100 nm to 150 nm wide with average height of 60 nm were formed. Optical extinction measurements showed that the absorption peak was about 560 nm with fullwidth-half-maximum of 100 nm, so dark pink color was observed. For the biosensing demonstration, Bovine serum albumin (BSA) and Anti-BSA bio-affinity interaction was measured using the self-assembly gold nanoisland LSPR sensor. Anti-BSA was functionalized onto the sensing site and BSA of known concentrations, i.e. 1 ug/ml was injected. The results showed LSPR spectral intensity change of 650 counts at the resonance slope of 634 nm. With standard deviation of spectral intensity fluctuation at 7 counts, the detection limit of BSA was estimated at about 0.5 nM which was comparable with that of LSPR systems with more elaborate nanostructures. The limit of detection of the present system can be further improved by implementing phase measurement and further nanostructure improvement.

We demonstrate and analyze a highly efficient on-chip 3D metal-insulator-metal (MIM) nanofocusing structure. Here, we show the in-depth theoretical design, analysis and discussion to provide a detailed picture of the highly efficient, on-chip nanofocusing process which is linearly tapered in 3D.