Distributed optical fiber sensors (DOFS) offer unprecedented features, the most unique one of which is the ability of monitoring variations of the physical and chemical parameters with spatial continuity along the fiber. Among all these distributed sensing techniques, optical frequency domain reflectometry (OFDR) has been given tremendous attention because of its high spatial resolution and large dynamic range. In addition, DOFS based on OFDR have been used to sense many parameters. In this review, we will survey the key technologies for improving sensing range, spatial resolution and sensing performance in DOFS based on OFDR. We also introduce the sensing mechanisms and the applications of DOFS based on OFDR including strain, stress, vibration, temperature, 3D shape, flow, refractive index, magnetic field, radiation, gas and so on.

Optical fiber surface plasmon resonance (SPR) sensors point toward promising application potential in the fields of biomarker detection, food allergen screening, and environmental monitoring due to their unique advantages. This review outlines approaches in improving the fiber SPR sensing performance, e.g., sensitivity, detection accuracy, reliability, cross-sensitivity, selectivity, convenience and efficiency, and corresponding sensing applications. The sensing principles of SPR sensors, especially the performance indicators and their influencing factors, have been introduced. Current technologies for improving the fiber SPR performance and their application scenarios are then reviewed from the aspects of fiber substrate, intrinsic layer (metal layer), and surface nanomaterial modification. Reasonable design of the substrate can strengthen the evanescent electromagnetic field and realize the multi-parameter sensing, and can introduce the in situ sensing self-compensation, which allows corrections for errors induced by temperature fluctuation, non-specific binding, and external disturbances. The change of the intrinsic layer can adjust the column number, the penetration depth, and the propagation distance of surface plasmon polaritons. This can thereby promote the capability of sensors to detect the large-size analytes and can reduce the full width at half-maximum of SPR curves. The modification of various-dimensionality nanomaterials on the sensor surfaces can heighten the overlap integral of the electromagnetic field intensity in the analyte region and can strengthen interactions between plasmons and excitons as well as interactions between analyte molecules and metal surfaces. Moreover, future directions of fiber SPR sensors are prospected based on the important and challenging problems in the development of fiber SPR sensors.

The detection of trace biomarkers is an important supplementary approach for early screening and diagnoses of tumors. An optical fiber near‐field enhanced plasmonic resonance immunoprobe is developed for the detection of the hepatocellular carcinoma biomarker, i.e., the alpha‐fetoprotein. Generic principles based on dispersion models and finite element analysis (FEA) models are developed to realize the optimized configuration of spectral characteristics of the immunoprobe. Dispersion models provide theoretical guidance for the design of the multilayer sensing structure from the perspective of the ray optics theory. FEA models provide theoretical guidance for the selection of coating materials from the perspective of the self‐defined dielectric constant ratio, i.e., the ratio of the real part to the imaginary part. The optimized configuration of the antibody coupling further improves the biosensing performance of the immunoprobe. The limit of detection (LOD) can reach down to 0.01 ng mL⁻¹, which is one order of magnitude lower than those relevant reported works. Such a low LOD can more effectively avoid the accuracy degradation of detection results due to measurement errors. Human serum samples have also been detected, with the good precision achieved. This work shows promising prospects in applications of label‐free, low‐cost, rapid, and convenient early screening of tumors.

Pressure-temperature cross-sensitivity and its accompanying temperature-related stability is a nerve-wracking obstruction for pressure sensor performance in a wide temperature range. To solve this problem, we propose a novel (to the best of our knowledge) all-silicon dual-cavity optical Fabry–Perot interferometer (FPI) pressure sensor. The all-silicon structure has high intrinsic reflectivity and is able to eliminate the influence of thermal-expansion-mismatch-induced stress and chemical-reaction-induced gas generation, and therefore, in essence, enhances measurement accuracy. From the experiment results, the pressure-temperature cross-sensitivity is reduced to be ∼ 5.96 Pa / ° C , which presents the lowest pressure-temperature cross-sensitivity among the FPI pressure sensors with the capability of surviving high temperatures up to 700°C thereby opening the way for high-precision pressure monitoring in various harsh and remote environments.

In unmanned monitoring such as perimeter security, pipeline detection, railway security, and so on, it is still a challenging task to accurately locate the irregular vibration events. Compared with traditional vibration detection technologies, distributed optical fiber vibration sensors (DOFVSs) have superior advantages such as high spatial resolution, large monitoring range, good concealment, excellent flexibility, and simple sensing structure. The DOFVS can be mainly classified into two types, i.e., the interferometer-based DOFVS (IDOFVS) and the backscattering-based DOFVS (BDOFVS). In particular, IDOFVS has unique sensing advantages, such as high stability, simple structure, high sensitivity, and wide frequency response. In this article, the development of long-distance IDOFVS in recent years has been summarized. The sensing principle of IDOFVS has been theoretically explained. The specific classification of the IDOFVS and the corresponding sensing structures are described in detail. In addition, the long-distance distributed vibration sensing structure and processing algorithms, such as denoising and locating algorithms, are analyzed. Finally, the performance of recent long-distance IDOFVS has been compared and the development direction has been discussed.

we demonstrate a fiber-optic Fabry-Perot pressure sensor with embedded MEMS micro-cavity for ultra-high pressure detection. The embedded type structure (ETS) is first proposed and analyzed to meet the requirements of ultra-high pressure detection. The geometry parameters of sensor have been optimized by analyzing mechanical and optical characteristics. From the analysis results based on the ETS, an ultra-high pressure sensor is fabricated and experimentally demonstrated for ultra-high pressure detection. The ultra-high pressure experiment illustrated response relationship between the absolute phase and pressure in the range of 2~120MPa, and full-scale errors less than 0.079%F.S. at room temperature. The other characteristics index of sensor, such as pressure sensitivity, hysteresis error, temperature's influence factor are superior to 1.071rad/MPa, 1.397%, 2.665×10 $^-3$ rad/°C. The transient response time of system is 0.27s. The sensor can be used for ultra-high pressure detections, which is necessary in deep-sea and oil exploration.