A Mach-Zehnder Fabry-Perot hybrid fiber-optic interferometer operating at the thermal noise limit.

A new type of interferometric fiber sensor based on a Mach-Zehnder Fabry-Perot hybrid scheme has been experimentally demonstrated. The interferometer combines the benefits of both a double-path configuration and an optical resonator, leading to record-high strain and phase resolutions limited only by the intrinsic thermal noise in optical fibers across a broad frequency range. Using only off-the-shelf components, the sensor is able to achieve noise-limited strain resolutions of 40 f[Formula: see text]/[Formula: see text] at 10 Hz and 1 f[Formula: see text]/[Formula: see text] at 100 kHz. With a proper scale-up, atto-strain resolutions are believed to be within reach in the ultrasonic frequency range with such interferometers.