Design and characterization of resonant devices for optical applications

Periodic structures have attracted huge research interest over the past many years due to their interesting electromagnetic properties. There are lots of useful applications in the fields of photonics and microwave engineering that come from periodic structures. Examples of periodic structures include diffraction gratings, photonic crystals, phased array antennas, frequency selective surfaces, and metamaterials. A diffraction grating is composed of diffracting elements arranged periodically. The spacing between these elements is comparable to the wavelength of the incident light. The amplitude, or phase, or both, of the diffracted electromagnetic radiation from a diffraction grating, can be modified in a controlled and predictable manner. Another interesting phenomenon is the presence of sharp resonant features in the optical spectra of the gratings such as Guided-Mode Resonances (GMR). GMR gratings have been employed in wide-ranging applications such as sensors for biosensing, optical absorbers, efficient photodetectors and tunable filters for optical communication systems, reflection mirrors for lasers, and spectrometers. The first part of this work focuses on the design, fabrication, and characterization of resonant pillar gratings. This is further split into two parts. The first part describes the graphene-based pillar grating for optical absorber applications. The performance of the proposed periodic structure is investigated through numerical simulations. The proposed design exploits the guided mode resonances of the structure to achieve enhanced absorption in the monolayer graphene. In the second part, a phase change material vanadium-dioxide (VO2) is integrated with the pillar grating structure to achieve the thermal tuning of the optical response exploiting the phase change properties of VO2. The grating has been fabricated utilizing a nanoimprint lithography system exploiting a silicon mold. VO2 nano-powders have been deposited by spin-coating. In addition to the experimental tests, the proposed structure is simulated using the RCWA method. Next, plasmonic grating structures on planar as well curved surfaces are designed and analyzed through numerical simulations for sensing and Surface Enhanced Raman Spectroscopy (SERS) applications. The work related to plasmonic structures has also been further split into two parts. In the first part, a planar plasmonic grating is designed and synthesized for sensing applications in the transmission domain exploiting Extraordinary Transmittance (EOT) properties of the plasmonic modes as well as the sensitivity of these modes to the changes in the refractive index of the surrounding media. A Finite Difference Time Domain (FDTD) model of the finite set of nanoplatelets has been developed to theoretically investigate and optimize the nanostructure as well as validate the experimental results. Plasmonic modes can concentrate light to much smaller locations creating field hotspots. This makes plasmonic structures a suitable platform for SERS. In the second part of the work, plasmonic gratings on planar and curved surfaces are investigated as SERS platforms.