In this paper, the ‘terahertz gap’ has been addressed by designing a novel THz metasurface for potential use in biosensing applications. The metasurface sensor employs Surface Plasmon Resonance (SPR). It operates in the 0 - 1 THz band. Two sharp reflection dips are provided by the sensor, which serve as indicators of analyte refractive index variations. Geometrical as well as compositional parameters of the biosensor design have been studied to optimize the performance in the targeted frequency band. The sensor design shows compatibility with different metals. The performance of the metasurface with gold, copper and aluminum has been investigated. The metasurface geometry is decently resilient to fabrication tolerances. The sensor maintains its resonance conditions when the angle of incidence is changed with minor deviations in the spectral response, but the polarization state of the incident terahertz beam clearly disturbs the absorption peak. Therefore, the sensing performance is restricted to a maximum allowable incidence angle of 20 degrees and circularly polarized terahertz beams. The resonance conditions for the metasurface appear around 0.4 and 0.7 THz. Both resonances have been investigated with respect to changes in the analyte refractive index. The chosen refractive index range is 1 to 1.5. The sensor response is calibrated by plotting the resonance frequency versus the refractive index. Least squares regression technique has been used to extract a data model for sensor response. Comparison of the proposed design with contemporary works has been incorporated into the paper. The sensor provides sensitivities of 0.1614 THz/ RIU and 0.23 THz/ RIU. The electromagnetic simulations have been carried out through the Finite Element Method (FEM).

This paper proposes an optical sensor based on nanoscale metamaterial structures. The design of the sensor has been explored with respect to biosensing applications through numerical modeling and analysis. The sensor comprises silica substrate and diamond nanostructures, both of which represent dielectrics. The sensing principle is based on the detection of ambient refractive index change. As the analyte properties change, the refractive index changes, as well. The refractive index change has been detected by striking electromagnetic waves onto the structure and noting the spectral response. Ultraviolet waves have been utilized for recording spectral responses and evaluating sensor performance. The sensor displays multiple sharp resonance peaks in the reflected beam. By altering the refractive index of the analyte present around the sensor, the peaks can be seen choosing different wavelengths. The resonance peaks have been investigated to observe electric and magnetic field dipoles in the sensor structure. The spectrum peaks have also been studied to understand fabrication tolerances. The sensor displays a linear response, along with a large Quality (Q) factor. The maximum value of the achieved Quality (Q) factor for the proposed sensor is 1229 while operating across the refractive index range of 1.4–1.45. The claim has been supported by comparison with contemporary works on similar platforms. A range of other sensing parameters have also been calculated and benchmarked. Metamaterial-based optical sensors can provide smaller device sizes, faster response times and label-free detection.

As the limitations of integrated electronics start to appear, it becomes important to look for potential alternatives. Silicon photonics holds a lot of promise in this regard. It cannot only provide superior performance to traditional integrated electronics in many aspects, but also co-exist in harmony with it through the realization of electro-optic devices. The focus of this paper is on Photonic Integrated Circuits (PICs) only. A theoretical understanding of Mach-Zehnder Interferometer (MZI) circuits has been developed. Computational design tools have been employed to model photonic waveguides. The design of optical waveguides has been numerically investigated in MATLAB through the Effective Index Method (EIM). The material properties of silicon and silicon dioxide, used in the simulations, have been presented. The properties include the refractive indices, group refractive indices and effective indices. Waveguide geometrical parameters have been explored and a 500 nm x 220 nm silicon waveguide structure has been finalized for experimental work. The schematics for four MZI optical circuits have been prepared in KLayout. Interoperability of KLayout and Ansys Lumerical Interconnect allows for spectral response to be obtained through simulations. The circuits consist of grating couplers, Y-branch splitters and bidirectional couplers. The input signal is split into two waveguide paths. Both waveguide paths culminate into grating couplers connected to photodetectors. The signals from both the channels have been recorded. The fabrication of the chip has been carried out at Applied Nanotools Inc. through Electron Beam Lithography (EBL). The characterization of the devices has been done at 25oC. A decent conformity can be observed between simulation and experimental results.

Plasmonic nano-antennas are widely accepted as suitable platforms for biosensing tasks because Surface Plasmon Resonance (SPR) is very sensitive to changes in its environment. However, recent studies suggest that SPRs may have limited Quality (Q) factors, especially in comparison with their dielectric counterparts. Therefore, this paper attempts to innovate the design of plasmonic nano-antennas to achieve high Q factors through Surface Lattice Resonance (SLR) in the visible frequency band. This resonance is linked with plasmonic nanostructures organized in arrays. The structure consists of a metal-dielectric-metal configuration at the base with metallic nanopillars protruding upward. The nanophotonic device has been investigated for refractometric sensing applications. The maximum Q factor achieved as a result of this work is 245, which has been compared with contemporary plasmonic metasurface Q factors. The simulation framework has been implemented in COMSOL Multiphysics, which employs the Finite Element Method (FEM). Regression analysis has been used to formulate the calibration curve for the sensor. High Q factors provide better selectivity for biosensing applications.