We examined the optical properties of a-Si:H/SiO_(2) multilayer films fabricated by radio-frequency magnetron sputtering for optical bandpass filters (BPFs). Because of the high refractive-index contrast between a-Si:H and SiO_(2), the total number of layers of an a-Si:H/SiO_(2) multilayer can be relatively small. We obtained an a-Si:H refractive index of 3.6 at λ=1550 nm and its extinction coefficient k<1×10~(-4) and confirmed by Fourier-transform infrared spectroscopy that such small k is influenced by the Si-H bonding in the film. We fabricated a-Si:H/SiO_(2) BPFs by using in situ optical monitoring. Thermal tuning of a-Si:H/SiO_(2) BPF upon a silica substrate was also performed, and a thermal tunability coefficient of 0.07 nm/℃ was obtained.
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