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

Abstract

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$$\varepsilon $$ ε /$$\sqrt{(}Hz)$$ ( H z ) at 10 Hz and 1 f$$\varepsilon $$ ε /$$\sqrt{(}Hz)$$ ( H z ) 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.

Impact of Soil-Based Insulation on Ultrahigh-Resolution Fiber-Optic Interferometry

“…To this end, we have chosen to use a MZ-FP hybrid fiber interferometer. Details about the characterization of this interferometer have been reported elsewhere [ 17 ]. Here, we only give a brief overview of its operation principle for the convenience of the readers.…”

“…To ensure its proper operation, the interrogating laser must stay on resonance with both FFPIs for extended periods of time. This requires the use of Pound-Drever-Hall (PDH) frequency locking as well as a co-packaging scheme for the two FFPIs [ 17 ]. Figure 1 b shows a schematic of the experimental setup.…”

“…The result clearly indicates a broadband suppression of ambient noises by the soil. Especially, it has been shown that thermal-noise-limited fiber-optic sensing is achieved within a frequency range of 10 1 –10 5 Hz [ 17 ], which highlights the crucial impact of the soil insulation to the operation of the MZ-FP hybrid interferometer.…”

“…These are theoretical predictions of the fundamental limits of interferometric fiber sensors due to intrinsic spontaneous fluctuations inside optical fibers [ 23 ]. The calculations of these noises are detailed elsewhere [ 17 ].…”