Abstract
Long-period gratings is class of fiber gratings, in which the period of the refractive index modulation is such that it satisfies a phase matching condition between the fundamental core mode and forward propagating cladding modes of an optical fiber. Many applications in optical communications and optical fiber sensing have been reported along the last years. In this work we present a simulation tool for determining LPG transmission spectrum and the coupling curve. The simulation tool uses MatLab code. The software produces also estimations of the resonant wavelength displacement due to changes in external parameters like temperature or external refractive index. A simple comparison between the simulation and the experimental result show that exist a good agreement with results obtain.

Abstract
High data rate optical fiber links are usually deployed in core IP networks to transport bulky [...]

Abstract
This paper presents preliminary results of common water thermal conductivity measurements using an all-fiber sensor based in conventional hot-wire method concept. The thermal conductivity of common water at room temperature obtained is 0.699 W/mK. Although the result is relatively distinct, about 14%, from the reference value found in literature, it is promising and indicates the feasibility of using the experimental arrangement for measuring thermal properties of materials with higher accuracy, provided that improvements already foreseen in future work be incorporated. © OSA 2018 © 2018 The Author(s)

Abstract
In this work, a long-period fiber grating (LPG) based sensor was evaluated as a sensing device for micro-force measurement, in the order of micro Newtons. It was used an LPG fabricated by arc-inducted technique in a SMF-28 standard optical fiber. The optical fiber was fixed between two clamps with a separation of 150 mm with the middle of the LPG located at the center. Characterizations were performed in terms of temperature, curvature and strain. The grating was then used as a micro-force sensor by means of both curvature and strain, induced by a hung mass in a stretched fiber. Furthermore, the evaluation of a precurvature LPG was performed to assess if an increase of sensitivity is achieved. Micro-force sensitivity achieved with the stretched LPG was 1.41 nm/mN and it was demonstrated that its sensitivity can be enhanced to 5.14 nm/mN with a pre-curvature of 2.2 m–1 applied to the LPG, achieving a spectral resolution of at least 15.6 µN.

Abstract
A method based on multiple Fiber Bragg Gratings (FBG) and a structure fabricated using a 3D printer for diameter measurement is proposed and experimentally demonstrated. The sensor is easily developed inserting the FBG on the structure and fixing the FBG in two points. Due to this arrangement, when the diameter is reduced a force is applied on the sensor and this causes a wavelength shift. The study is divided in two steps using one experimental setup. At first, each FBG response is independently evaluated concerning the diameter variation and after that, the FBGs are evaluated together. The results demonstrated that the structure can be used as a way to monitor the diameter variation in some applications.

Abstract