Ultrahigh-Resolution Fiber-Optic Sensing Based on High-Finesse, Meter-Long Fiber Fabry-Perot Resonators

Abstract

Ultrahigh-resolution fiber-optic sensing has found a wide range of potential applications. However, the techniques reported so far are all based on highly specialized fiber structures and interrogation lasers, which are not widely available. In this paper, we report the demonstration of ultrahigh strain resolutions using only off-the-shelf commercial components. Our method leverages the high wavelength discrimination of long, high-finesse fiber Fabry-Perot interferometers (FFPI), using two 1 m-long FFPIs, one as the sensor and the other as a frequency reference. By locking the interrogation laser to the reference interferometer, which is co-packaged with the sensor interferometer, large, environmentinduced sensing background is removed. This allows the laser to reliably probe the strains applied on the sensor with very high resolutions. A nominal, noise-limited strain resolution of 800 fε/ÝHz has been achieved within 1-100 Hz. Strain resolution further improves to 75 fε/ÝHz at 1 kHz, 60 fε/ÝHz at 2 kHz and 40 fε/ÝHz at 23 kHz, demonstrating better resolutions than proven techniques such as π-phase-shifted and slow-light fiber Bragg gratings. The work lays out a cost-effective scheme to achieve ultrahigh-resolution fiber-optic sensing.

Long-Length and Thermally Stable High-Finesse Fabry-Perot Interferometers Made of Hollow Core Optical Fiber

“…SMF-FPs can have long lengths (e.g., 100's of meters) and can be very compact and lightweight. Although the finesse of SMF-FPs [7], [8] does not reach that achievable in free-space FPs (due to the fiber transmission loss), their small FSR enables narrow transmission peaks similar to those of short, high-finesse free-space FPs. Unfortunately, SMF-FPs have several drawbacks that make free-space FPs the preferred approach for many applications, despite free-space FPs larger size and the alignment challenges.…”

“…ABRY-Perot interferometers (FPs) have many unique properties including high wavelength selectivity, high extinction ratios, the capability to enhance light intensity, etc. Their applications include, amongst others: lasers [1]- [3], metrology [4], [5] and sensing [6]- [8]. The full width at half maximum, FWHM of the transmission peaks is the key parameter of a FP, as a narrower peak provide better capability to discriminate frequency [6], of relevance, e.g., in reference cavities [2] or a ultra-high resolution sensors [5].…”

“…Unfortunately, SMF-FPs have several drawbacks that make free-space FPs the preferred approach for many applications, despite free-space FPs larger size and the alignment challenges. The two primary drawbacks are the large sensitivity to temperature variations [8] and unwanted nonlinear effects like stimulated Brillion scattering (SBS) [9], especially in highfinesse FPs where the intra-cavity power is strongly enhanced by the resonant effect. Both of these parasitic effects are mainly due to the interaction of light with the silica glass material in SMFs.…”

Finesse Limits in Hollow Core Fiber based Fabry-Perot interferometers

“…ABRY-PEROT interferometers (FPs) with high finesse, typically formed by enclosing an optical path with two highly reflective mirrors, present many unique properties such as high wavelength selectivity, high extinction ratio, and the ability to enhance light intensity inside the resonant cavity, making them a common device in many applications such as lasers [1], metrology [2], [3], and sensing [4]- [6].…”

“…When FPs are used as filters, the extinction ratio improves with finesse [28]. When used as a frequency reference for laser locking [3] or a frequency discrimination element for strain sensing [6], the frequency discrimination capacity improves with finesse-length product.…”