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Detecting faint sound by lightNon-contact sound measurement by precision interferometry 
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Optical measurement methods have been attracting attention to realize various sound measurements that are difficult to achieve with microphones. In this research, in collaboration with the Quantum Optical Physics Research Group of the NTT Basic Research Laboratories, we have developed a sound field measurement technique with much lower noise than conventional methods using precision optical measurement technology. Focusing on the difference in physical characteristics between sound and noise components, we proposed a sound measurement technique using a differential midfringe locked interferometer that reduces noise while maximizing sensitivity to sound. By combining this technology with high-stability laser technology, the amplitude of measurement noise has been reduced to 1/30 compared to conventional methods. By applying the precision measurement technology cultivated in optics, we will realize the next-generation sound measurements such as 3D sound-field measurement, remote sensing, and ultra-high precision measurement.
[1] K. Ishikawa, Y. Shiraki, T. Moriya, A. Ishizawa, K. Hitachi, K. Oguri, “Reducing noise of mid-fringe locked interferometer by optical differential detection,” in Proc. Acoust. Soc. Jpn., 2021. (in Japanese)
[2] K. Ishikawa, Y. Shiraki, T. Moriya, A. Ishizawa, K. Hitachi, K. Oguri, “Simple and low-noise optical measurement of sound using mid-fringe locked interferometer,” in Proc. Acoust. Soc. Jpn., 2020. (in Japanese)
Kenji Ishikawa / Computing Theory Research Group, Media Information Laboratory
Email: cs-openhouse-ml@hco.ntt.co.jp