Abstract
High-resolution strain sensing based on long, high-finesse fiber Fabry–Perot interferometers (FFPIs) has been demonstrated with a special focus on the infrasonic frequency range. A novel dual-FFPI scheme allows the large environment-induced background at low frequencies to be suppressed, permitting high strain resolution limited only by excess electronic noise. Noise-equivalent strain resolution of ${{257}}\;{{{\rm p}\unicode{x03B5} /}}\surd {\rm{Hz}}$ has been achieved at 6 mHz, and the resolution improves to ${\sim}{{200}}\;{{{\rm f}\unicode{x03B5} /}}\surd {\rm{Hz}}$ between 4–20 Hz. Without the use of any additional optical frequency references and with only off-the shelf commercial components, these resolutions are much better than most in the prior reports. Especially, an improvement of a factor of 1.8 is achieved in comparison with the highest resolution reported so far near 5 Hz. The limiting factors of the current scheme have been analyzed in detail, and the application prospects have been demonstrated using an acoustic transducer. The work lays out the potential of using long FFPIs with high finesse for high-resolution fiber-optic sensing in the infrasonic frequency range.
© 2020 Optical Society of America
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