Tunable microdisk resonators vertically coupled to bus waveguides using epitaxial regrowth and wafer bonding techniques

We demonstrate two different types of tunable microdisk resonators vertically coupled to bus waveguides: a microdisk resonator coupled to air-guided rib bus waveguides and the other one built on buried heterostructure bus lines, respectively. The latter type contacts the substrate without relying on an extra supporting structure, which affords more reliable conductive paths toward the substrate. A planarized epitaxial regrowth technology combined with wafer bonding is used to fabricate the structure. The measured transmission spectra indicate improved tuning capability of buried-bus-coupled microdisks, but the overall device performance is limited by optical leakage through the substrate.