Demonstration of ultra-high-Q small mode volume toroid microcavities on a chip

Optical microcavities confine light spatially and temporally and find application in a wide range of fundamental and applied studies. In many areas, the microcavity figure of merit is not only determined by photon lifetime (or the equivalent quality-factor, Q), but also by simultaneous achievement of small mode volume (V). Here we demonstrate ultra-high Q-factor small mode volume toroid microcavities on-a-chip, which exhibit a Q/V factor of more than 10^6 (lambda/n)^–3. These values are the highest reported to date for any chip-based microcavity. A corresponding Purcell factor in excess of 200,000 and a cavity finesse of > 2.8×10^6 is achieved, demonstrating that toroid microcavities are promising candidates for studies of the Purcell effect, cavity QED or biochemical sensing