Free-space coupling to ultra-high-Q microtoroid resonators

Whispering gallery mode (WGM) microtoroid resonators are ultra-sensitive biochemical sensors. Traditional coupling using tapered optical fibers is fragile and requires precise alignment. Here we demonstrate free-space coupling using a digital micromirror device and an objective lens. Using this approach, we are able to achieve ultra-high Q-factors in excess of 100 million. This innovation paves the way for the creation of a robust, portable, ultra-sensitive biological and chemical sensing platform.