Abstract
Bi-core optical fiber structures are studied for applications in sensing. In this paper, an analysis is performed on the spectral characteristics of light propagating in these fibers with central launching core illumination from a standard single mode fiber. Reflective and transmissive configurations are addressed. The characteristics of a reflective bi-core fiber structure for measurement of strain, temperature and absolute value of torsion are investigated and highlights for further research are presented.

Abstract
This article presents a review of the numerical techniques employed in simulating plasmonic optical sensors based on metal-dielectric nanostructures, including examples, ranging from conventional D-type fiber sensors, to those based on photonic crystal D-type fibers and incorporating metamaterials, nanowires, among other new materials and components, results and applications. We start from the fundamental physical processes, such as optical and plasmonic mode coupling, and discuss the implementation of the numerical model, optical response customization and their impact in sensor performance. Finally, we examine future perspectives.

Abstract
This paper explores and compares three different plasmonic optical fibre sensor configurations, based on D-type and suspended core fibres combined with metallic nanowires, and investigates how their different geometrical parameters can affect the coupling between the guided optical mode supported by fibres and the localized plasmonic modes, and how that ultimately results in improved sensor performance. Fibre optical sensors based on plasmonic resonances with metallic nanostructures have revolutionized the field of optical sensing because they have permitted to obtain sharper and fine-tuned resonances with higher sensitivity. The essence for exploring the properties of localized plasmonic modes and their coupling with the optical guided mode depends not only on the choice of the materials employed in the device, but also on the geometry of the different components and their relative position, which ultimately determines the spatial distributions of optical power of the different modes and consequently their overlap and coupling. In this work, we use numerical simulations based on finite element methods to demonstrate the importance of shaping the features of the guided optical mode to promote the coupling with the localized modes, in the two types of fibres considered. The results clarify some of the fundamental aspects behind the operation of these devices and provide novel proposals for enhanced refractive index sensors. © 2019 SPIE.

Abstract
The introduction of metallic nanostructures in optical fibers has revolutionized the field of plasmonic sensors since they produce sharper and fine-tuned resonances resulting in higher sensitivities and resolutions. This article evaluates the performance of three different plasmonic optical fiber sensors based on D-type and suspended core fibers with metallic nanowires. It addresses how their different materials, geometry of the components, and their relative position can influence the coupling between the localized plasmonic modes and the guided optical mode. It also evaluates how that affects the spatial distributions of optical power of the different modes and consequently their overlap and coupling, which ultimately impacts the sensor performance. In this work, we use numerical simulations based on finite element methods to validate the importance of tailoring the features of the guided optical mode to promote an enhanced coupling with the localized modes. The results in terms of sensitivity and resolution demonstrate the advantages of using suspended core fibers with metallic nanowires.

Abstract
We present the design, fabrication and optical characterization of functional metamaterials for optical sensing of Hydrogen based on inexpensive self-assembly processes of metallic nanowires integrated in nanoporous alumina templates[37-42]. The optical properties of these materials strongly depend on the environmental concentration or partial pressure of hydrogen and can be used to develop fully optical sensors that reduce the danger of explosion. Optical metamaterials are artificial media, usually combining metallic and dielectric sub-wavelength structures, that exhibit optical properties that cannot be found in naturally occurring materials. Among these, functional metamaterials offer the added possibility of altering or controlling these properties externally after fabrication, in our case by contact with a hydrogen rich atmosphere. This dependency can be used to design[43-45]and develop optical sensors that respond to this gas or to chemical compounds that contain or release hydrogen. In this paper we present some designs for hydrogen functional metamaterials and discuss the main parameters relevant in the optimization of their response. © 2019 SPIE.

Abstract