In this review paper some recent advances on optical sensors based on photonic crystal fibres are reported. The different strategies successfully applied in order to obtain feasible and reliable monitoring systems in several application fields, including medicine, biology, environment sustainability, communications systems are highlighted. Emphasis is given to the exploitation of integrated systems and/or single elements based on photonic crystal fibers employing Bragg gratings (FBGs), long period gratings (LPGs), interferometers, plasmon propagation, off-set spliced fibers, evanescent field and hollow core geometries. Examples of recent optical fiber sensors for the measurement of strain, temperature, displacement, air flow, pressure, liquid-level, magnetic field, and hydrocarbon detection are briefly described.

A cavity-backed microstrip patch antenna array was optimized in the Ku band. The backing cavity was designed under each patch antenna of the array in order to increase the bandwidth and minimize the intercoupling among the radiating elements. Substrate integrated waveguide (SIW) technology was employed to fabricate the above-mentioned cavity below the radiating patch. More precisely, four microstrip array antennas, made by 2 × 2, 4 × 4, 8 × 8, and 16 × 16 elements were designed, fabricated, and characterized. The measured maximum gain was G = 13 dBi, G = 18.7 dBi, G = 23.8 dBi, and G = 29.2 dBi, respectively. The performance of the proposed antenna arrays was evaluated in terms of radiation pattern and bandwidth. An extensive feasibility investigation was performed even from the point of different materials/costs in order to state the potential of the engineered antennas in actual applications. The obtained results indicate that a cavity-backed microstrip patch antenna is a feasible solution for broadband digital radio and other satellite communication overall for niche applications.

In this article, for the first time, an efficient multiwavelength fiber laser based on a Tm:Er:Yb:Ho co-doped germanate glass, optically pumped at 980 nm wavelength and simultaneously emitting at 1550 nm, 1800 nm and 2050 nm wavelengths, is designed and optimized. An exhaustive model, taking into account the energy transfer phenomena between different rare earths, is developed. The device behavior is investigated by means of several parametric sweeps with respect to the input pump power, the fiber length, the dopant concentrations and the output mirrors reflectivities. Four optimal concentrations have been found by means of a home-made computer code based on particle swarm optimization (PSO) approach, allowing a global solution search. These concentrations allow levels of output powers very close to each other, equal to 20 mW ± 0.1% at 1550 nm, 1800 nm and 2050 nm, respectively. These results predict the possibility of tailoring the dopant concentrations in order to construct broadband optical sources with similar emission powers at multiple wavelengths and broadband amplifiers.

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