Abstract
In order to enhance microalgal growth in photobioreactors (PBRs), light requirement is one of the most important parameters to be addressed; light should indeed be provided at the appropriate intensity, duration, and wavelength. Excessive intensity may lead to photo-oxidation and -inhibition, whereas low light levels will become growth-limiting. The constraint of light saturation may be overcome via either of two approaches: increasing photosynthetic efficiency by genetic engineering, aimed at changing the chlorophyll antenna size; or increasing flux tolerance, via tailoring the photonic spectrum, coupled with its intensity and temporal characteristics. These approaches will allow an increased control over the illumination features, leading to maximization of microalgal biomass and metabolite productivity. This minireview briefly introduces the nature of light, and describes its harvesting and transformation by microalgae, as well as its metabolic effects under excessively low or high supply. Optimization of the photosynthetic efficiency is discussed under the two approaches referred to above; the selection of light sources, coupled with recent improvements in light handling by PBRs, are chronologically reviewed and critically compared.

Abstract

Abstract
In this work an all optical hot-wire flowmeter based on a silver coated fibre incorporating a long period grating and a Bragg grating is demonstrated. Optical energy at 1480 nm propagating down the fibre is coupled by the long period grating into the fibre cladding and absorbed by the metallic coating deposited on the fibre surface over the Bragg grating position. This absorption acts like a hot-wire raising locally the fibre temperature, which is effectively detected by the FBG resonance shift. The temperature raise depends on the flow speed of the surrounding air that has the effect to cool the fibre. In this way, the FBG Bragg wavelength shift can be related with the flow speed. Results obtained demonstrate the working principle and a flow speed resolution of 0.08 m/s is demonstrated.

Abstract
We propose and theoretically study a novel surface-plasmon-resonance sensor based on an H-shaped, elliptical-core optical fibre. The two grooves of the H-fibre are coated with a thin, uniform metal layer that in turn is covered with a high-index dielectric layer to allow broad spectral tunability. The sensor maintains linear polarization and facilitates effortless splicing. Electromagnetic mode analysis indicates a sensitivity of 1800 nm/RIU (refractive-index unit) for aqueous analytes.

Abstract
In this work, the authors present an alternative Sagnac interferometer based on a suspended twin-core fibre. Using the suspended twin-core fibre, the pattern fringe is due to the different optical paths of the light in the two cores. In this case, the value of the refractive index difference between the two cores is 10(-3), which indicates an advantage of this approach, namely the possibility to use a small length of the suspended twin-core fibre. The sensing configuration was characterized for strain, temperature, curvature and torsion, respectively.

Abstract
In this work, we propose to take advantage of properties of a Bragg fibre for optical sensing. The Bragg fibre exhibits three concentric high refractive index layers embedded in pure silica and surrounding a 35 mu m diameter core. A short (0.3 m long) piece of Bragg fibre slightly multimode, is used to elaborate an intermodal interferometer, the spectral response of which exhibits a fringe pattern that depends on the operating wavelength, which can therefore be used as a sensor. The two modes considered were found to be the fundamental LP(01) and the high-order mode LP(02). The sensor has been characterized in strain and temperature and presents a sensitivity of - 1.09 pm/mu epsilon and 14.1 pm/degrees C respectively. The sensor demonstrated insensitivity to curvature thanks to well known Bragg fibre properties.