Fabry-Perot interferometers have found a multitude of scientific and industrial applications ranging from gravitational wave detection, high-resolution spectroscopy, and optical filters to quantum optomechanics. Integrated with optical fiber waveguide technology, the fiber-optic Fabry-Perot interferometers have emerged as a unique candidate for high-sensitivity sensing and have undergone tremendous growth and advancement in the past two decades with their successful applications in an expansive range of fields. The extrinsic cavity-based devices, i.e., the fiber-optic extrinsic Fabry-Perot interferometers (EFPIs), enable great flexibility in the design of the sensitive Fabry-Perot cavity combined with state-of-the-art micromachining and conventional mechanical fabrication, leading to the development of a diverse array of EFPI sensors targeting at different physical quantities. Here, we summarize the recent progress of fiber-optic EFPI sensors, providing an overview of different physical and mechanical sensors based on the Fabry-Perot interferometer principle, with a special focus on displacement-related quantities, such as strain, force, tilt, vibration and acceleration, pressure, and acoustic. The working principle and signal demodulation methods are shown in brief. Perspectives on further advancement of EFPI sensing technologies are also discussed.

Fiber-optic distributed acoustic sensing (DAS) has proven to be a revolutionary technology for the detection of seismic and acoustic waves with ultralarge scale and ultrahigh sensitivity, and is widely used in oil/gas industry and intrusion monitoring. Nowadays, the single-frequency laser source in DAS becomes one of the bottlenecks limiting its advance. Here, we report a dual-comb–based coherently parallel DAS concept, enabling linear superposition of sensing signals scaling with the comb-line number to result in unprecedented sensitivity enhancement, straightforward fading suppression, and high-power Brillouin-free transmission that can extend the detection distance considerably. Leveraging 10-line comb pairs, a world-class detection limit of 560 fε/√Hz@1 kHz with 5 m spatial resolution is achieved. Such a combination of dual-comb metrology and DAS technology may open an era of extremely sensitive DAS at the fε/√Hz level, leading to the creation of next-generation distributed geophones and sonars.

Ultra-high extinction ratio (ER) optical modulation is crucial for achieving high-performance fiber-optic distributed acoustic sensing (DAS) for various applications. Bulky acousto-optical modulators (AOM) as one of the key devices in DAS have been used for many years, but their relatively large volume and high power consumption are becoming the bottlenecks to hinder the development of ultra-compact and energy-efficient DAS systems that are highly demanded in practice. Here, an on-chip silicon electro-optical modulator (EOM) based on multiple coupled microrings is demonstrated with ultra-high ER of up to 68 dB while the device size and power consumption are only 260 × 185 μm²and 3.6 mW, respectively, which are at least two orders of magnitude lower than those of a typical AOM. Such an on-chip EOM is successfully applied to DAS with an ultra-high sensitivity of −71.2 dB rad²/Hz (4 pε/√Hz) and a low spatial crosstalk noise of −68.1 dB rad²/Hz, which are very similar to those using an AOM. This work may pave the way for realization of next-generation ultra-compact DAS systems by integration of on-chip opto-electronic devices and modules with the capability of mass-production.

This article reports a multi-point curvature sensor system based on multiplexed optical fiber Fabry-Perot interferometric (FPI) sensor devices and a microwave photonics interrogation technique. The FPI sensor is fabricated with the assistance of a capillary tube, where a short section of the capillary is sandwiched between two single-mode fibers, forming the air-gap Fabry-Perot cavity. Bending of the FPI device leads to changes in the fringe contrast of its reflection spectrum. Based on the microwave photonics filtering technique, variations of the fringe contrast are encoded into the changes in the peak magnitude of the passband in the frequency response of the FPI device. By multiplexing such FPI devices with different cavity lengths, multi-point measurements of curvature can be realized by tracking changes in corresponding passbands in the frequency response of the system. The FPI curvature sensor is easy-to-manufacture and cost-effective, and the microwave photonics-based system provides an alternative and robust solution to interrogating the multiplexed FPI sensors for multi-point curvature sensing that could be desired in structural health monitoring, human-machine interface sensing, and other related fields.

Distributed acoustic sensing (DAS) system with point-backscattering-enhanced fiber (PBSEF) has the capability of breaking the signal to noise ratio limit of traditional DAS, therefore, it would become one of the most powerful DAS technologies and expand the applications of DAS systems. To optimize the performance when designing DAS system with PBSEF, it is crucial to understand the relationship between the system noise and the reflectance enhancement, which is yet to be systematically studied. In this paper, both experimental investigation and theoretical analysis of a typical 3×3 heterodyne DAS system with PBSEF were carried out. The relationship between system noise level and the reflectance enhancement was studied by both experiments and simulations. And the results, with good agreements between each other, show that the system noise level drops exponentially as the reflectance increases. With 29.7 dB reflectance enhancement, the system noise level decreased from 9.5 pε/√Hz to 0.44 pε/√Hz. The influences of intensity noise and phase noise were also analyzed based on the theoretical model. The findings of the quantitative relationship and the noise influence can be used as a universal guidance for the design of PBSEF-based high performance DAS systems.