Abstract
A vibration sensor based on a distributed Bragg reflector (DBR) is proposed. The gratings that form the cavity are written in erbium-doped fibre using the femtosecond laser technique. In this configuration, one grating of the DBR acts as a sensor whilst the other one acts as a spectral filter. The active sensor, subjected to vibration measurements, exhibits a response of up to similar to 1.5 kHz.

Abstract
Acoustic sensing is nowadays a very demanding field which plays an important role in modern society, with applications spanning from structural health monitoring to medical imaging. Fiber-optics can bring many advantages to this field, and fiber-optic acoustic sensors show already performance levels capable of competing with the standard sensors based on piezoelectric transducers. This review presents the recent advances in the field of fiber-optic dynamic strain sensing, particularly for acoustic detection. Three dominant technologies are identified - fiber Bragg gratings, interferometric Mach-Zehnder, and Fabry-Pérot configurations - and their recent developments are summarized. © 2014 The Author(s).

Abstract
A gas pressure sensor based on an all-fiber Fabry-Perot interferometer (FFPI) is reported. The sensing head consists of a small section of silica rod spliced with a large offset between two single-mode fibers. The silica rod is used only as mechanical support so that an air cavity can be formed between both SMF. It is shown that the FFPI sensor is sensitive to gas pressure variation and when submitted to different gaseous environments, namely carbon dioxide, nitrogen and oxygen - sensitivities of 6.2, 4.1 and 3.6 nm/MPa, respectively, were attained. The refractive index change on nitrogen environment by means of gas pressure variation was also determined and a sensitivity of 1526 nm/RIU was obtained. The response of the sensing device to temperature variations in air was also studied and a sensitivity of -14 pm/degrees C was attained.

Abstract
A sensor based on Fabry-Perot interferometry with a hollow microsphere cavity embedded in a 3D printed structure is proposed. The sensor was tested for lateral loading and temperature, showing promising results. By imprintring the sensor on the structure, the dynamic range of application is severely increased enabling the application of the sensor in harsh environments.

Abstract
A Fabry-Perot based sensor with two coupled hollow microspheres is presented. The sensor was fabricated using fusion splicing techniques, enabling a low-cost, highly reproducible, production. The coupling of the two microspheres gives rise to a highly sensitive strain sensor, reaching a sensitivity of 4.07 pm/mu epsilon. The allsilica composition leads to a low thermal sensitivity, making the proposed structure suitable applications in environments with varying external conditions.

Abstract
Microfiber knot resonators find application in many different fields of action, of which an important one is the optical sensing. The large evanescent field of light can interact and sense the external medium, tuning the resonance conditions of the structure. The resonant property of microfiber knot resonators can also provide, in some cases, an enhancement in the sensing capability. Until nowadays, a wide variety of physical and chemical parameters have been possible to measure with this device. New developments and improvements are still being done in this field. A review on microfiber knot resonators as sensors is presented, with particular emphasis on their application as temperature and refractive index sensors. The properties of these structures are analyzed and different assembling configurations are presented. Important aspects in terms of the sensor stability are discussed, as well as alternatives to increase the sensor robustness. In terms of new advances, an overview on coated microfiber knot resonators is also presented. Finally, other microfiber knot configurations are explored and discussed.