Cavity Q measurements of silica microspheres with nanocluster silicon active layer

Abstract

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) (140 +/- 10 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 650 degrees C to 1100 degrees C. The cavity Q of the spheres with the active layer was measured at 1.56 mu m 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 >= 2 x 10(7) to (2-5) x 10(5). 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.