Cavity $Q$ Measurements of Silica Microspheres with Nanocluster Silicon Active Layer

In this paper, the effect of the nanocluster-silicon (nc-Si) active layer on the cavity Q of silica microspheres is investigated. The silicon-rich silicon oxide (SRSO) (140plusmn10 nm thick) films with excess Si content ranging from 5 to 14 at.% were deposited on the silica microspheres formed by the CO₂ laser melting of an optical fiber, and subsequently annealed at temperatures ranging from 650degC to 1100 degC. The cavity Q of the spheres with the active layer was measured at 1.56 mum using a tunable external cavity coupled laser diode and a tapered fiber coupling. We find that the presence of the nc-Si active layer reduces the Q value of the microsphere from ges 2times10⁷ to (2-5) times10⁵. However, we found no correlation between the formation, size, and density of the nc-Si and the cavity Q-factor, indicating that the scattering by the nc-Si does not present the dominant optical loss mechanism in the SRSO film