Design, Fabrication And Characterization Of Guided-mode Resonance Transmission Filters

Abstract

This dissertation addresses photonic devices enabled by the guided-mode resonance (GMR) effect. As periodic phototonic structures can become highly reflective or transmissive at resonance, this effect has been utilized to design suites of optical elements including reflection filters, transmission filters, broadband mirrors, polarizers, and absorbers with a plethora of possible deployment venues. Even though there has been considerable research on the reflection type GMR elements, attendant transmission filters have less explored experimentally, as there is material limitation to design this kind of filters with simple architecture and they also may require coupling to multiple resonances simultaneously. Apart from the design issues, experimental realization of these filters is challenging. There have not been any experimental reports on optical transmission filters with narrow transmission band and high efficiency and well defined low sidebands. In this Dissertation, we design, fabricate and characterize narrow band guided-mode resonance transmission filters.Initially we study a way to engineer the optical constants of amorphous silicon (a-Si) suitable for different applications. Rapid thermal annealing is applied to induce crystallization of sputtered amorphous silicon deposited on thermally grown oxide layers. The influence of annealing temperatures in the range of 600°C-980°C is systematically investigated. Using scanning-electron microscopy, ellipsometry and x-ray diffraction techniques, the structural and optical properties of the films are determined. An order-of-magnitude reduction of the extinction coefficient is achieved. We show that the optical constants can be tuned for different design requirements by controlling the process parameters. For example, we obtain a refractive index of ~3.66 and an extinction coefficient of ~0.0012 at the 1550-nm wavelength as suitable for GMR transmission filter applications where a high refractive index and low extinction coefficient is desired.We design transmission filters for both transverse electric (TE) and transverse magnetic (TM) polarizations and experimentally demonstrate a simple and geometrically tunable narrowband transmission filter for TM polarization using a one-dimensional silicon grating. We interpret the response in terms of symmetry of the guided modes in a dielectric slab waveguide, with numerical analysis and experimental results. The filter exhibits a 50-nm wide transmission peak with 60% efficiency at off-normal incidence in the telecommunication wavelength region. We can achieve higher efficiency with broader linewidths from larger incidence angles. We also explain the challenges that the experimental realization of these devices entail such as susceptibility to extinction coefficient, mode confinement, and surface irregularities.Moreover, we provide a new principle for optical transmission filters based on the GMR effect cooperating with the Rayleigh anomaly in a subwavelength nanograting. We theoretically and experimentally show that the onset of higher diffraction orders at the Rayleigh anomaly can dramatically sharpen a GMR transmission peak in both spectral and angular domains. There results a unique transmission spectrum that is tightly delimited in angle and wavelength as demonstrated with a precisely fabricated device. Finally, we report experimental research on GMR transmission filters based on a Fabry-Perot cavity. We achieve a resonance linewidth of close to 3 nm with attendant free spectral range (FSR) of 7 nm. Even though the efficiency of the resonance peak is not high, we can improve the results by applying low-loss materials and generate broad low sidebands by decreasing the cavity length with a micro-control translation stage