High-Q dielectric optical whispering-gallery (WG) microresonators with narrow-band wavelength selectivity and enhanced mode intensity due to the total internal reflection based confinement have long been investigated for applications like wavelength agile filtering in optical communications and sensing in bio-photonics. It is well known that light can be evanescently coupled in and out of the microresonator using prism-coupling, tapered fiber-coupling or integrated waveguide-coupling. For practical applications, it is important to effectively in- and out- couple light in order to obtain superior microresonator-based devices....[ Read more ]

High-Q dielectric optical whispering-gallery (WG) microresonators with narrow-band wavelength selectivity and enhanced mode intensity due to the total internal reflection based confinement have long been investigated for applications like wavelength agile filtering in optical communications and sensing in bio-photonics. It is well known that light can be evanescently coupled in and out of the microresonator using prism-coupling, tapered fiber-coupling or integrated waveguide-coupling. For practical applications, it is important to effectively in- and out- couple light in order to obtain superior microresonator-based devices.

In this thesis, we propose a novel coupling method through surface plasmon resonance (SPR). Surface plasmon resonance enhances evanescent wave which improves the optical coupling to microresonators. We experimental demonstrate the SPR-assisted coupling to WG modes using a laser-illuminated gold-coated glass prism with a 125-μm-diameter silica micropillar WG resonator. We observe resonance extinction ratio (ER) enhancement near the SPR angle with SPR-assisted coupling. The improved ER is relevant to various wavelength agile applications. By optimizing the laser incident angle and the gold film thickness, we obtain a maximum ER enhancement factor of ~12 using a ~50-nm-thick gold-film coated glass-prism compared with plain prism-coupling.

Apart from passive devices, active microresonator switches and modulators based on resonance wavelength shift through refractive index tuning are potentially essential components for next generation optical communications. Over the past five years, silicon-based optical devices with the merit of compatibility with silicon microelectronics have raised lots of research interest and technological breakthrough. In this thesis, we also propose and numerically investigate a silicon depletion-type electrooptic (EO) microdisk modulator by integrating a waveguide-coupled microdisk resonator with reverse-biased PN⁺ or Schottky diodes. Our calculations suggest that the proposed silicon 5-μm-diameter microdisk modulator can have an electrical rise time of ~3 ps and fall time of ~2 ps using an 5 V reverse bias to obtain a refractive index change of ~ 0.7x10^-4. Although the modulation speed may be limited by the cavity lifetime, the proposed silicon microdisk modulator offers bandwidth of ~40 Gbps using carrier-depletion induced refractive index change in silicon. We also discuss initial device fabrication and characterizations.