Marco De Sario

Design of mid-infrared amplifiers based on fiber taper coupling to erbium-doped microspherical resonator.

A dedicated 3D numerical model based on coupled mode theory and solving the rate equations has been developed to analyse, design and optimize an optical amplifier obtained by using a tapered fiber and a Er³⁺-doped chalcogenide microsphere. The simulation model takes into account 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 taper angle of the optical fiber and the fiber-microsphere gap have been designed 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. In order to reduce the computational time, a detailed investigation of the amplifier performance has been carried out by changing the number of sectors in which the doped area is partitioned. The simulation results highlight that this scheme could be useful to develop high efficiency and compact mid-infrared amplifiers.

Theoretical analysis of a palladium-based one-dimensional metallo-dielectric photonic band gap structure for applications to H2 sensors

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.

Optimization of pump absorption in MOF lasers via multi-long-period gratings: design strategies

Different strategies for designing optical couplers, optimized to enhance the pump absorption in the rare-earth-doped core of microstructured fiber lasers, are illustrated. Three kinds/configurations of optical couplers have been designed and compared as examples of the different design strategies which can be followed. Their effectiveness to enhance the performance of an ytterbium-doped, double cladding, microstructured optical fiber laser has been accurately simulated. They consist of a suitable cascade of multiple long-period gratings (MLPGs) inscribed in the fiber core region. The characteristics of the MLPG couplers have been simulated via a homemade computer code based on both rate equations and an extended coupled mode theory. The proposed MLPG couplers seem particularly useful in the case of low rare-earth concentration but, even for a middle-high ytterbium concentration, as N(Yb)=5×10(25) ions/m(3), the slope efficiency S can be increased up to 20%, depending on the fiber length.

Bidirectional beam propagation method based on the method of lines for the analysis of photonic band gap structures

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.

Effects of thermal annealing on the optical characteristics of K + –Na + waveguides

We present a systematic study of the changes induced in the refractive-index profile of different sets of K(+)-Na(+) ion-exchanged waveguides on soda-lime and BK7 substrates because of thermal annealing in the presence or absence of salt vapors. The concentration of potassium is recovered by secondary ion mass spectrometry, and the propagation losses are measured by means of the three-prism configuration.

Enhancement and inhibition of second-harmonic generation and absorption in a negative index cavity

We study second-harmonic generation in a negative-index material cavity. The transmission spectrum shows a bandgap between the electric and magnetic plasma frequencies. The nonlinear process is made efficient by local phase-matching conditions between a forward-propagating pump and a backward-propagating second-harmonic signal. By simultaneously exciting the cavity with counterpropagating pulses, and by varying their relative phase difference, one is able to enhance or inhibit linear absorption and the second-harmonic conversion efficiency.

Numerical analysis of aperiodic photonic crystal fiber structures for supercontinuum generation

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 Schrodinger 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.

Fabry-Perot microcavity sensor for H2-breath-test analysis

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.

Analysis of second harmonic generation in photonic-crystal-assisted waveguides

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)∼100pm∕V, we predict a conversion efficiency of approximately 90% after a propagation distance of 2mm, using peak pump intensities inside the core of the waveguide of 1.35GW∕cm2. If the waveguide core contains polymer layers with different glass transition temperatures, the layers can be poled independently to maximize the overlap int...

Design and fabrication of praseodymium-doped optical waveguides

The feasibility of a planar channel waveguide amplifier and laser made of praseodymium (Pr3+) doped chalcogenide glass, based on the binary composition GeS2, is investigated by means of an appositely implemented computer code. The buried channel waveguide amplifier, having both core and substrate doped with a dopant concentration Nequals3000 ppm, shows gain close to Gequals7 dB for an input signal power of Psequals1 (mu) W at the wavelength (lambda) sequals1310 nm and a pump power Ppequals 200 mW at the wavelength (lambda) pequals1020 nm. The Fabry-Perot laser, based on the aforesaid buried channel waveguide terminated pump power Pthequals16mW and a slope efficiency Sequals8%.