Resonant fiber-optic strain and temperature sensor achieving thermal-noise-limit resolution

Abstract

In the area of fiber-optic sensors (FOSs), the past decade witnessed great efforts to challenge the thermal-noise-level sensing resolution for passive FOS. Several attempts were reported claiming the arrival of thermal-noise-level resolution, while the realization of thermal-noise-level resolution for passive FOSs is still controversial and challenging. In this paper, an ultrahigh-resolution FOS system is presented with a sensing resolution better than existing high-resolution passive FOSs. A fiber Fabry-Perot interferometer as the sensing element is interrogated with an ultra-stable probe laser by using the Pound-Drever-Hall technique. Both strain and temperature measurements are carried out to validate the performance of the sensor. The measured noise floor agrees with the theoretical thermal noise level very well.

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

“…With the noise floor of the MZ-FP interferometer approaching the limit set by the fiber thermal noise, record-high strain resolutions have been achieved. Table 1 lists the measured strain resolutions at six decadal frequencies between 1 Hz and 100 kHz (top row) as well as the best results previously reported at these frequencies 23 , 37 , 38 . Note that some of the prior records are estimated based on graphical results because exact values of the strain resolution at these frequencies are not given in these reports.…”

“…Achieving thermal noise-limited fiber-optic sensing is both attractive and challenging: attractive because it represents the maximum resolving power a sensor can possibly achieve; challenging because reaching the minuscule thermal noise requires a sensing system to have both an extremely high sensitivity and a very low system noise 30 – 32 . Over the last three decades, there has been a continued effort to develop fiber-optic sensors that can operate at the thermal noise level 1 , 33 – 38 . Generally, two distinctive approaches have been taken to accomplish this goal: i) frequency discrimination and ii) phase discrimination.…”

“…Generally, two distinctive approaches have been taken to accomplish this goal: i) frequency discrimination and ii) phase discrimination. In a frequency-discrimination scheme, an optic resonator such as a fiber Bragg grating (FBG) 37 or a fiber Fabry-Perot interferometer (FFPI) 38 is employed to create a sharp spectral feature (i.e., a resonance peak) that can be used as a highly sensitive optical-frequency discriminator. The advantage of this approach is that the sensor itself can be very compact, typically on the order of a meter or less.…”

“…The disadvantage, however, lies in their inability to distinguish the sensing signal from laser noise, which often makes the interrogating laser the greatest liability of the overall sensor resolution 39 . As a result, in order to attain thermal-noise-limited operation with a frequency-discrimination scheme, either an ultralow-noise laser 37 or a highly sophisticated laser frequency-stabilization system 30 , 38 has to be deployed. Meanwhile, a phase-discrimination scheme leverages the phase sensitivity of a traditional double-path interferometer, such as the Michelson 36 , the Mach-Zehnder 35 , or the Sagnac configuration 33 .…”

Ultralow‐Noise Single‐Frequency Fiber Laser and Application in High‐Resolution Fiber‐Optic Dynamic Strain Sensing

“…With the development of photonics technologies and the gradual reduction of other noises, the noise characteristics of the single-frequency laser source have become the key factors limiting the increase of strain sensing resolution, especially for weak strain signals in the low-frequency range. [13][14][15][16] Consequently, the realization of an ultralow-noise singlefrequency laser source, to satisfy the increasing demand for high-resolution fiber-optic dynamic strain sensing, has become a matter of intense interest.The suppression of phase noise, especially in the lowfrequency range, is still technically challenging. As known, Pound-Drever-Hall (PDH) technology provides a reliable solution, and the error signal representing phase fluctuation is usually extracted through the ultrahigh-finesse Fabry-Pérot…”