Measuring the role of surface chemistry in silicon microphotonics

Utilizing a high quality factor $(Q\sim 1.5\times {10}^6)$ optical microresonator to provide sensitivity down to a fractional surface optical loss of ${\alpha }_s^{\prime }\sim {10}^{-7}$ , we show that the optical loss within Si microphotonic components can be dramatically altered by Si surface preparation, with ${\alpha }_s^{\prime }\sim 1\times {10}^{-5}$ measured for chemical oxide surfaces as compared to ${\alpha }_s^{\prime }⩽1\times {10}^{-6}$ for hydrogen-terminated Si surfaces. These results indicate that the optical properties of Si surfaces can be significantly and reversibly altered by standard microelectronic treatments, and that stable, high optical quality surface passivation layers will be critical in future Si micro- and nanophotonic systems.