Picostrain-resolution fiber-optic sensing down to sub-10  mHz infrasonic frequencies

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 p ε / √ H z has been achieved at 6 mHz, and the resolution improves to ∼ 200 f ε / √ H z 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.

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.…”

“…The high-frequency peak at 58 kHz is introduced by the PDH lockbox. It is worth mentioning here that a similar effort based on a single meter-long FFPI sensor has also been carried out but has failed to reach the thermal noise limit due to the dominance of laser noise 22 , 23 . This highlights the advantage of the MZ-FP hybrid scheme as it greatly mitigates the impact of the laser noise.…”

“…The first goal can be accomplished by using interferometric schemes featuring sharp phase/frequency discrimination. Over the years, several ultra-sensitive IFS techniques have been demonstrated, including -phase shifted fiber Bragg gratings ( -FBG) 10 – 13 , slow-light FBG 14 – 17 , and long fiber Fabry-Perot interferometers 18 – 23 . Meanwhile, considerable effort has also been dedicated to lowering the noise.…”

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

“…As a result, FOI is often highly susceptible to external perturbations such as temperature fluctuations and acoustic noises, which tend to mask the signals under investigation. This limits the resolutions of FOI in an array of applications including strain sensing [ 6 ], quantum optics [ 7 ], and remote clock distribution [ 8 , 9 ]. To overcome this barrier, high-quality thermal and acoustic insulations are frequently required.…”

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

“…[1][2][3][4] Among them, as a critical branch of optical fiber sensing, fiber-optic strain sensing is widely used for dynamic deformation measurement, structural health monitoring, and underwater acoustic detection. [5][6][7][8] Particularly, for frontier research areas involving nanotechnology, biophotonics, seismology, and geophysics, [9][10][11][12] a high resolution (typically pε or sub-pε) is demanded of the strain sensor. 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.…”