We examined the optical properties of <i>a</i>-Si:H/SiO<sub>2</sub> multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between <i>a</i>-Si:H and SiO<sub>2</sub>, the total number of layers of an <i>a</i>-Si:H/SiO<sub>2</sub> multilayer can be relatively small. We obtained an <i>a</i>-Si:H refractive index of 3.6 at λ = 1550 nm and its extinction coefficient <i>k</i> < 1 × 10<sup>−4</sup> and confirmed by Fourier-transform infrared spectroscopy that such small <i>k</i> is influenced by the Si-H bonding in the film. We fabricated <i>a</i>-Si:H/SiO<sub>2</sub> BPFs by using <i>in situ</i> optical monitoring. Thermal tuning of <i>a</i>-Si:H/SiO<sub>2</sub> BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/°C was obtained.
© 2004 Optical Society of America
(060.4230) Fiber optics and optical communications : Multiplexing
(230.4170) Optical devices : Multilayers
(310.1860) Thin films : Deposition and fabrication
(310.3840) Thin films : Materials and process characterization
(310.6860) Thin films : Thin films, optical properties
Hidehiko Yoda, Kazuo Shiraishi, Yuji Hiratani, and Osamu Hanaizumi, "a-Si:H/SiO2 Multilayer Films Fabricated by Radio-Frequency Magnetron Sputtering for Optical Filters," Appl. Opt. 43, 3548-3554 (2004)