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9 February 2007 Improvement of the signal-to-noise ratio in a glass-based guided-wave optical microphone
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In this study, the signal-to-noise ratio of a glass-based guided-wave optical microphone was successfully improved by both increasing sensitivity and reducing noise. The optical microphone has a square diaphragm as a pressure-sensitive structure and a straight single-mode waveguide across the diaphragm. Sensitivity of the microphone and resonance frequency of the diaphragm are dependent on the area and thickness of the diaphragm. In this study, in order to increase sensitivity, the diaphragm dimensions were enlarged from 16 mmx16 mmx0.15 mm in the previous study to 20 mmx20 mmx0.15 mm. According to theoretical calculations, the phase sensitivity and resonance frequency were 2.5 mrad/Pa and 3.4 kHz for a 20 mmx20 mmx0.15 mm diaphragm, respectively. The sensitivity was theoretically expected to be twice as high as that in the previous study. To reduce noise, a bandpass filter with passband from 300 Hz to 3 kHz was employed. After fabrication of the optical microphone, sound pressure, ranging from 100 to 122 dB-SPL, was applied to the microphone with a frequency of 1 kHz. The measured output of the optical microphone was almost proportional to the sound pressure, and the minimum detectable sound pressure level of the microphone was experimentally evaluated to be 100 dB-SPL.
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Hiroyuki Nikkuni, Yoshiaki Mogi, Manabu Hayashi, Masashi Ohkawa, Seishi Sekine, and Takashi Sato "Improvement of the signal-to-noise ratio in a glass-based guided-wave optical microphone", Proc. SPIE 6475, Integrated Optics: Devices, Materials, and Technologies XI, 647519 (9 February 2007);

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