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Abstract: A theoretical investigation of an innovative cascade laser source is performed. The main goal of the work is the design of a continuous-wave (CW) photonic crystal fiber (PCF) laser, based on an erbium-doped chalcogenide glass. Due to the comparable lifetimes of the 4I13/2, 4I11/2 and 4I9/2 erbium energy levels, the simultaneous emissions at the wavelengths close to 2.7μm and 4.5μm are obtained with a pump wavelength close to 806nm (direct pumping into the level 4I9/2). This scheme could be useful to develop high efficiency, high beam-quality and compact Near-IR and Mid-IR oscillators with single-mode output for applications not only in surgery but also in spectroscopy, remote sensing, infrared countermeasures. The feasibility investigation is performed by taking into account the optical and spectroscopic parameters measured on a previously fabricated chalcogenide glass sample. A home made numerical code that solves the multilevel rate equations and the power propagation equations has been ad hoc developed. The obtained results constitute a realistic feasibility investigation of the Mid-IR laser performance by varying the length and the transversal cross section of the fiber, the mirrors reflectivity, the erbium concentration. [ABSTRACT FROM AUTHOR]

The model of rare-earth-doped optical devices based on the rate equations and the power propagation equations can be employed for both the feasibility investigation of innovative challenging devices and the recovering, via an indirect approach, of the rare earth spectroscopic parameters. In this review, different and novel examples of rare-earth-doped device refinements as well as the evaluation of unknown optical parameters are reported. The investigated cases are obtained starting from developed models and computer codes illustrated in recent literature and from measured performance of lasers and amplifiers. • Design of Medium Infrared (Mid-IR) fiber sources. • Optimization of fluoride and chalcogenide glass fibers. • Co-doping with rare-earth for Mid-IR lasing enhancement. • Modeling of rare-earth-doped optical devices based on the rate equations and power propagation equations. • Recovering of the rare earth spectroscopic parameters via an indirect approach. [ABSTRACT FROM AUTHOR]

The design of suitable electromagnetic bandgap (EBG) cavities has been performed by means of a hybrid numerical/analytical approach implemented via a homemade code with the aim of optimizing a novel accelerating structure for proton linear accelerators (linacs). In particular, a 3-GHz proton linac tank with on-axis coupled EBG cavities closed with full-end cells has been optimized. The proton beam input energy is 27 MeV. The performances of the proton linac EBG accelerating cavities have been compared with the performances of 27-MeV 3-GHz side-coupled proton linac accelerating cavities in terms of typical linac figures of merit. The use of EBG cavities allows to increase the transit time factor (by about 8%). Moreover, the peak surface electric field is strongly reduced (by about 65%), paving the way to the design of very high accelerating gradient microwave proton linacs. Furthermore, the wakefields of the EBG structure have been compared with those of the SCL structure, showing that the EBG structure provides effective damping of the transverse wakefields. [ABSTRACT FROM AUTHOR]

We propose a reconfigurable scheme consisting of an antenna loaded by a CVD graphene capacitor. We show how the gated-graphene can actively control the antenna gain by about 2–3 dB and the phase of far-field electric field by about 45°. The proposed idea could be efficiently adapted to antennas with different geometries and operating frequencies becoming transparent with respect to antenna technologies. We believe that these results clear a path toward graphene-based antenna systems for reconfigurable and smart telecommunication systems. [ABSTRACT FROM AUTHOR]

In this paper we report a numerical study of a palladium-based metallo-dielectric photonic band gap structure for the purpose of detecting H2. In particular, and as an example, we will explore applications to the diagnosis of lactose malabsorption, more commonly known as lactose intolerance condition. This pathology occurs as a result of an incomplete absorption or digestion of different substances, causing an increased spontaneous emission of H2 in human breath. Palladium is considered in order to exploit its well known ability to absorb hydrogen spontaneously. The proposed structure is particularly able to detect the lactose malabsorption level of the patient with relatively high sensitivity and rapidity. [ABSTRACT FROM AUTHOR]

Leak detection of hydrogen for medical purposes, based on the monitoring of the optical response of a simple Fabry-Perot microcavity, is proposed to investigate either the occurrence of lactose intolerance, or lactose malabsorption condition. Both pathologic conditions result in bacterial overgrowth in the intestine, which causes increased spontaneous emission of H2 in the human breath. Two sensitivity figures of merit are introduced to inspect changes in the sensor response, and to relate the microcavity response to a pathologic condition, which is strictly related to a different level of exhaled hydrogen. Different sensor configurations using a metal-dielectric microcavity are reported and discussed in order to make the most of the well-known ability of palladium to spontaneously absorb hydrogen. [ABSTRACT FROM AUTHOR]

We study second harmonic generation in a planar dielectric waveguide having a low-index, polymer core layer, bounded by two multilayer stacks. This geometry allows exceptionally strong confinement of the light at the fundamental wavelength inside the core region with virtually zero net propagation losses for distances that exceed several centimeters, provided that material and scattering losses are neglected. A phase-matched configuration of the waveguide is reported in which the pump signal is the lowest-order mode of the waveguide, and the generated second harmonic signal corresponds to the third propagation mode of the waveguide. Using a polymer waveguide core, having χ(2)∼100 pm/V, we predict a conversion efficiency of approximately 90% after a propagation distance of 2 mm, using peak pump intensities inside the core of the waveguide of 1.35 GW/cm2. If the waveguide core contains polymer layers with different glass transition temperatures, the layers can be poled independently to maximize the overlap integral, and similar pump depletions may be achieved over a distance of approximately 500 μm. [ABSTRACT FROM AUTHOR]

A homemade computer code for designing the coupled microwave cavities of a linear accelerator (linac) has been developed. A hybrid approach, based on both analytical investigation and numerical calculation, is exploited. A finite-element method (FEM) based on 2-D/3-D electromagnetic simulation software is used to find the eigenmodes and eigenfrequencies of the accelerator cavities as well as design typical figures of merit. The FEM investigation is integrated with a multiobjective particle swarm optimization approach in order to automatically optimize the geometry of the accelerating tanks. This approach seems very promising and general, allowing the optimization of a wide class of side-coupled resonant structures. The computer code is validated via measurements on a 27-MeV 3-GHz standing-wave side-coupled linac tank of five cavities closed with suitable end cells. The agreement between simulation and experiment is excellent; the displacement between the maxima of the simulated and measured longitudinal electric field modulus is close to 0.2%. [ABSTRACT FROM AUTHOR]

In this paper, we numerically and experimentally demonstrate that few-layer Chemical Vapour Deposition graphene can be employed for the fabrication of fully optical transparent antennas for microwave applications. We show that planar graphene-based antennas, having a size of tens of square centimeters, can achieve relatively high gain over a wide operating bandwidth (>3.5 GHz) simultaneously covering the GPS, WiFi, Bluetooth, and 5G bands. The measured 3D radiation patterns show dipole-, quadruple-, and hexapole-behavior. These findings open up routes for the realization of innovative devices where “invisible and hidden” antennas could be integrated in smart windows or photovoltaic systems, fostering configurations for camouflage, and communications systems. Furthermore, the possibility to handle different radiation patterns could allow the engineering of complex systems such as antenna arrays devoted to beam-steering, beam-forming, and healthcare applications. Finally, combining graphene transparency and flexibility could also pave the way for the realization of wearable devices, demanding invisibility, which operate on the surface of the human body or can be integrated in transparent devices (for example, in contact lenses) reducing their invasiveness. [ABSTRACT FROM AUTHOR]

Praseodymium-doped selenide thin films are deposited by radio frequency magnetron sputtering on thermally oxidized silicon wafers and undoped selenide layers. Ridge waveguides are then processed using photolithography and dry etching techniques. Under optical pumping at 1.55 μm, broadband guided mid-infrared photoluminescence is recorded for the first time for wavelengths above 4 μm from rare earth-doped integrated chalcogenides waveguides. Optical design confirmed that these active waveguides allow single-mode optical propagation at a wavelength of 4.70 μm. [ABSTRACT FROM AUTHOR]

ABSTRACT A substrate integrated waveguide Magic Tee with very compact size and operating over a wide band is proposed. The circuit is made of two stacked substrates connected by cutting a small aperture between them. This solution presents slightly higher complexity compared to a single substrate magic Tee but it avoids the radiation losses because the circuit is completely closed. A simple and effective procedure is used to design the circuit. A prototype is built and experimental results show a good agreement with simulations. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:932-936, 2016 [ABSTRACT FROM AUTHOR]

An accurate design of an innovative fiber optic temperature sensor is developed. The sensor is based on a cascade of three microstructured optical fibers (MOFs). In the first one a suitable cascade of long period gratings is designed into the core. A single mode intermediate and a rare-earth activated Fabry-Perot optical cavity are the other two sensor MOF sections. An exhaustive theoretic feasibility investigation is performed employing computer code. The complete set-up for temperature monitoring can be obtained by utilizing only a low cost pump diode laser at 980 nm wavelength and a commercial optical power detector. The simulated sensitivity S = 315.1 μW/°C and the operation range ΔT = 100 °C is good enough for actual applications. [ABSTRACT FROM AUTHOR]

ABSTRACT A substrate integrated waveguide six-port directional coupler is designed and characterized. The circuit exploits a very compact size and good reflection and transmission characteristics, as it exhibits both return loss and isolation higher than 15 dB over a 13% bandwidth. The device is made by connecting all ports to a single junction which mixes all signals. Some prototypes have been built and experimental results show a very good agreement with simulations. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2589-2592, 2015 [ABSTRACT FROM AUTHOR]

The influence of high energy radiations on the performance of silicon-on-insulator photonic devices, such as straight waveguides, ring resonators and Raman lasers based on resonant microcavities, has been investigated theoretically in the near infrared. The modeling is based on a generalized full-vectorial wave equation system which also includes deep defect rate equations. Simulation results are compared with the state-of-the-art, demonstrating a very good agreement between theoretical predictions and experiments reported in literature in the case of both ionizing and nonionizing events. Moreover, a parametric analysis is presented in order to investigate the degradation mechanisms of photonic device performance that occur under the influence of radiation bombardment. [ABSTRACT FROM AUTHOR]

This work describes a computational approach for the optical characterization of an opal photonic crystal (PC). We intend, in particular, to validate our approach by comparing the transmittance of a crystal model, as obtained by numerical simulation, with the transmittance of the same crystal, as measured over 400- to 700-nm wavelength range. We consider an opal PC with a face-centered cubic lattice structure of spherical particles made of polystyrene (a nonabsorptive material with constant relative dielectric permittivity). Light-crystal interaction is simulated by numerically solving Maxwell's equations via the finite-difference time-domain method and by using the Kirchhoff formula to calculate the far field. A method to study the propagating Bloch modes inside the crystal bulk is also sketched. [ABSTRACT FROM AUTHOR]

A mid-IR amplifier consisting of a tapered chalcogenide fiber coupled to an Er3+-doped chalcogenide microsphere has been optimized via a particle swarm optimization (PSO) approach. More precisely, a dedicated three-dimensional numerical model, based on the coupled mode theory and solving the rate equations, has been integrated with the PSO procedure. The rate equations have included the main transitions among the erbium energy levels, the amplified spontaneous emission, and the most important secondary transitions pertaining to the ion-ion interactions. The PSO has allowed the optimal choice of the microsphere and fiber radius, taper angle, and fiber-microsphere gap in order to maximize the amplifier gain. The taper angle and the fiber-microsphere gap have been optimized to efficiently inject into the microsphere both the pump and the signal beams and to improve their spatial overlapping with the rare-earth-doped region. The employment of the PSO approach shows different attractive features, especially when many parameters have to be optimized. The numerical results demonstrate the effectiveness of the proposed approach for the design of amplifying systems. The PSO-based optimization approach has allowed the design of a microsphere-based amplifying system more efficient than a similar device designed by using a deterministic optimization method. In fact, the amplifier designed via the PSO exhibits a simulated gain G = 33.7 dB, which is higher than the gain G = 6.9 dB of the amplifier designed via the deterministic method. [ABSTRACT FROM AUTHOR]

The design and characterization of a single-layer wideband substrate integrated waveguide 3-dB standalone directional coupler are described. The device exhibits a bandwidth of 2 GHz, ranging from 10.7 to 12.7 GHz, and both return loss and isolation better than 15 dB. The coupler has been built using a TACONIC RF-35 A2 substrate. A very good agreement between simulations and experimental results is obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1141-1144, 2014 [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an antenna array is designed in order to transform the thermal energy, provided by the Sun and re-emitted from the Earth, in electricity. The proposed antenna array is constituted by four square spirals of gold printed on a low cost dielectric substrate. A microstrip line, embedded into the substrate, is used to feed the array and to collect the thermal radiation. The dispersive behavior of gold at infrared frequencies has been taken into account through the Lorentz–Drude model. Simulations have been conducted in order to investigate the behavior of the antenna array illuminated by a circularly polarized plane wave with an amplitude chosen according to the Stefan–Boltzmann radiation law. An output current of about 3.8 μA has been simulated at 28.3 THz, i.e. at the frequency of the Earth emitted radiation. Moreover, these infrared antennas could be coupled with other components to obtain direct rectification of infrared radiation. As a consequence, these structures further optimized could be a promising alternative to the conventional photovoltaic solar cells. [Copyright &y& Elsevier]

An unconventional photonic crystal fiber (PCF) is designed in order to obtain supercontinuum (SC) generation. The distance of the air hole rings is not constant, but it follows the Thue-Morse (ThMo) aperiodic sequence. The spectral broadening of high power femtosecond (fs) input pulses in anomalous dispersion regime is investigated by means of a homemade computer code, based on the generalized nonlinear Schrödinger equation (GNLSE) and implemented via the symmetrized split-step Fourier method (S-SSF). A lot of ThMo PCF transversal sections are simulated, and the one providing the flattest and the widest spectrum is identified and further refined by varying the operating conditions. Three different peak powers (5, 10, 15 kW) and three different pulse durations (40, 50, 100 fs) are investigated at the pump wavelength λP = 1064 nm. The novel ThMo PCF proposed in this paper exhibits a SC figure of merit Φ = 16, very high with respect to the state of the art pertaining to fs input pulses. [ABSTRACT FROM AUTHOR]

Abstract: A number of numerical and analytical methods with different complexity can be exploited to analyse fibre amplifiers. Conventional approaches make the refinement and design of the devices extremely time consuming, especially when several design parameters have to be simultaneously optimised to obtain the desired performance in terms of gain and noise figure. In order to tackle this issue, a method based on an artificial neural network to perform the refinement and design of erbium doped photonic crystal fibre amplifiers is proposed in this paper. The capability of the neural network to capture the nonlinear functional link among the physical and geometrical characteristics of the fibre amplifier and its gain and noise figure is exploited. In the refinement it is employed to determine the optimal values of the parameters maximising the gain. In the design, it is used to develop an inverse problem solver in order to determine the values of the parameters corresponding to the known values of gain. Numerical results show that the proposed approach finds the refinement/design parameters in good accordance with respect to the conventional one. [Copyright &y& Elsevier]

Abstract: The design of a laser constituted by an ytterbium doped, double-cladding microstructured optical fiber (DCMOF) with an optimized optical coupler inscribed in the doped core region is illustrated. The coupler is constituted by a long-period grating (LPG) which increases the pump power transfer from the inner cladding modes towards the fundamental core mode. A home-made numerical code solving the coupled-mode equations and the rate equations is ad hoc developed to investigate the dependence of the fiber laser performance on the LPG parameters such as the grating period and the length. The simulations highlight that it is possible to transfer a lot of the total input pump power from the inner cladding modes towards the fundamental mode guided into the core, leading to a significant improvement of both the pump power absorption and the output signal power. Moreover, a reduction of the total length of the laser and a minimization of the length-dependent nonlinear effects can be obtained. [ABSTRACT FROM AUTHOR]

A new microwave technique is proposed in order to prevent the growth of and/or eliminate parasites that infest cereals while they are being stocked in the mills. The investigated microwave system is made of a mode-stirred chamber suitably designed in order to be applied in the cereal industrial working chain without a drastic breakpoint. A dedicated computer code, based on the Transmission Line Matrix method, has been suitably implemented in order to design the particular geometry of the stirrers, to evaluate the microwave characteristics of the resonant cavity, and to identify the best conditions for the electromagnetic field uniformity in the region where the cereals run. [ABSTRACT FROM AUTHOR]

The bidirectional beam propagation method based on the method of lines is proposed as an innovative and efficient algorithm to investigate the optical properties of photonic band gap (PBG) structures. A few examples illustrate the application of this technique to the modeling of passive, lossy and active one-dimensional and index confined PBG structures. The algorithm results are validated by comparison with those obtained via the transfer matrix method, the mode-matching method and the finite difference time domain method. With respect to these methods, the present algorithm exhibits accurate results with reduced computer resources. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]