On-chip silicon based photonic structures : photonic band gap and quasi-photonic band gap materials

Abstract

This thesis focuses on integrated silicon based photonic structures, photonic band gap (PBG) and quasi-photonic band gap (QPX) structures, which are based on high refractive index contrast dielectric layers and CMOS compatibility. We developed a new type of silicon waveguide - Photonic Crystal (PC) cladding waveguide is studied based on PBG principle. The refractive index in the new PC cladding waveguide core therefore has a large flexibility. Low index core (e.g. SiO2) or hollow core waveguide can be realized with our PC cladding waveguide structure. The fabrication of the waveguide is compatible to CMOS process. To demonstrate the PBG guiding mechanism, we utilized prism coupling to the Asymmetric PC cladding waveguide and the effective index of the propagation mode is measured directly. The measured effective mode index is less than both Si and Si3N4 cladding layers, which is clear demonstration of the photonic band gap guiding principle. We also fabricated and measured the PC cladding channel waveguide. Potential applications include high power transmission, low dispersion, thin cladding thickness and nonlinear properties engineering. Secondly, we developed a Si-based multi-channel optical filter with tunability, which is based on omnidirectional reflecting photonic band gap structure with a relatively large air gap defect. Using only one device, multi channel filter with tunability around two telecom wavelength 1.55[mu]m and 1.3[mu]m by electrostatic force is realized. Four widely spaced resonant modes within the photonic band gap are observed, which is in good agreement with numerical simulations.

(cont.) The whole process is compatible with current microelectronics process technology. There are several potential applications of this technology in wavelength division multiplexing (WDM) devices. Thirdly, to further extend the photonic crystal idea, we studied the quasi-photonic crystal structures and their properties, especially for the fractal photonic band gap properties and the transparent resonant transmission states. A-periodic Si/SiO2 Thue-Morse (T-M) multilayer structures have been fabricated, for the first time, to investigate both the scaling properties and the omnidirectional reflectance at the fundamental optical band-gap. Variable angle reflectance data have experimentally demonstrated a large reflectance band-gap in the optical spectrum of a T-M quasicrystal, in agreement with transfer matrix simulations. The physical origin of the T-M omnidirectional band-gap has been explained as a result of periodic spatial correlations in the complex T-M structure. The unprecedented degree of structural flexibility of T-M systems can provide an attractive alternative to photonic crystals for the fabrication of photonic devices.