M. De Sario

Photonic Crystal Sensors

The paper deals with the possibility of using photonic crystals for sensing purpose. The optical properties of photonic crystals allow to realize sensing devices characterized by a high degree of compactness and a good resolution of the quantity to detect. A particular attention is devoted to force/pressure sensors and the design of a PhC microcavity pressure sensor is reported

Photonic band gap filter for wavelength division multiplexer

An optical multiplexer-demultiplexer based on an index-confined photonic band gap waveguide is proposed. The dropping of electromagnetic waves having a given frequency or a certain frequency band is obtained via a phase-shifted grating obtained by breaking the uniform period sequence to include a defect layer. The selective filtering properties of the proposed structure are simulated by means of a computer code relying on a bi-directional beam propagation method based on the method of lines.

Tunability of Photonic Band Gap Notch Filters

A notch filter based on an index confined photonic band gap waveguide is proposed. The dropping of an electromagnetic wave having a specific wavelength is obtained by opportunely designing a periodically corrugated overlay. The selective filtering properties of the proposed structure are identified by using a computer code based on the bidirectional beam propagation method with the aid of the method of lines. The optimized design of a notch filter, characterized by a full-width half-maximum (FWHM) bandwidth of 2 nm, is given. The tunability is reached by exploiting the electroclinic effect of smectic-A * liquid crystals.

Optimization and Characterization of Rare-Earth-Doped Photonic-Crystal-Fiber Amplifier Using Genetic Algorithm

A genetic-algorithm (GA) procedure has been ad hoc implemented to obtain a tool for both design and characterization of rare-earth-doped optical amplifiers and lasers. In particular, the routines performing the selection, crossover, mutation, and elitism operations have been written with the aim to investigate the optimal erbium-doped amplifier or laser configuration. Conversely, the GA can be employed in device characterization to identify those parameters of the erbium-energy-level transitions, which are not directly measurable, e.g., the cross-relaxation and up-conversion coefficients. The GA appears intriguing because of its efficiency and versatility. Its operation strategy is noticeably for the capability to identify solutions in complex multidimensional spaces. In this paper, the GA application for modeling and characterizing erbium-doped photonic-crystal-fiber amplifiers is described in detail.

Refinement of Er3+-doped hole-assisted optical fiber amplifier.

This paper deals with design and refinement criteria of erbium doped hole-assisted optical fiber amplifiers for applications in the third band of fiber optical communication. The amplifier performance is simulated via a model which takes into account the ion population rate equations and the optical power propagation. The electromagnetic field profile of the propagating modes is carried out by a finite element method solver. The effects of the number of cladding air holes on the amplifier performance are investigated. To this aim, four different erbium doped hole-assisted lightguide fiber amplifiers having a different number of cladding air holes are designed and compared. The simulated optimal gain, optimal length, and optimal noise fig. are discussed. The numerical results highlight that, by increasing the number of air holes, the gain can be improved, thus obtaining a shorter amplifier length. For the erbium concentration NEr=1.8x1024 ions/m3, the optimal gain G(Lopt) increases up to ~2dB by increasing the number of the air holes from M=4 to M=10.

Enhanced transmission and second harmonic generation from subwavelength slits on metal substrates

We theoretically investigate second harmonic generation that originates from the nonlinear, magnetic Lorentz force term from single and multiple apertures carved on thick, opaque metal substrates. The linear transmission properties of apertures on metal substrates have been previously studied in the context of the extraordinary transmission of light. The transmission process is driven by a number of physical mechanisms, whose characteristics and relative importance depend on the thickness of the metallic substrate, slit size, and slit separation. In this work we show that a combination of cavity effects and surface plasmon generation gives rise to enhanced second harmonic generation in the regime of extraordinary transmittance of the pump field. We have studied both forward and backward second harmonic generation conversion efficiencies as functions of the geometrical parameters, and how they relate to pump transmission efficiency. The resonance phenomenon is evident in the generated second harmonic signal, as conversion efficiency depends on the duration of incident pump pulse, and hence its bandwidth. Our results show that the excitation of tightly confined modes as well as the combination of enhanced transmission and nonlinear processes can lead to several potential new applications such as photo-lithography, scanning microscopy, and high-density optical data storage devices.

Photonic Crystal Drop Filter Exploiting Resonant Cavity Configuration

Band dropping devices are widely used in WDM application. In this paper the design of a two-dimensional photonic crystal drop filter is proposed. Different from the configuration reported in literature which are realized by means of a photonic bandgap waveguide and one or more resonant cavities, able to select a signal at desired frequency, the proposed drop filters exploits a novel system of point defects. The design is based on the accurate analysis of higher order resonant modes supported by the system and their parities. The temporal and spectral behavior of the device is studied using plane wave expansion (PWE) and FDTD methods.

Design of Er3+ doped SiO2–TiO2 planar waveguide amplifier

Er-doped silica–titania channel waveguide amplifiers are investigated by means of a home-made computer code to test their feasibility. The optical, spectroscopic and geometrical parameters measured on the fabricated slab waveguides, are used in the simulation model, which takes into account the pump and signal propagation, the amplified spontaneous emission, and the secondary transitions pertaining to the ion–ion interactions. By simulation, in the small signal operation, a gain close to 4.6 dB is demonstrated for a channel waveguide 5 cm long, by using a pump power of 200 mW; the signal wavelength being ks ¼ 1533 nm, pump and signal co-propagating.

Time domain analysis of optical amplification in Er3+ doped SiO2-TiO2 planar waveguide.

A time domain analysis of light amplification in an erbium doped silica-titania planar waveguide is reported. The investigation is performed by means of a home-made computer code which exploits the auxiliary differential equation scheme combined with the finite difference time domain technique to solve Maxwells equations and the rate equations. The simulation model takes into account the pump and input signal propagation, the secondary transitions pertaining to the ion-ion interactions and exploits the optical, spectroscopic and geometrical parameters measured on the fabricated waveguide.

Pulsed laser deposition of materials for optoelectronic applications

SiO 2 (silica) and ITO (indium tin oxide) films, SiO 2 /ITO bilayers and multilayers and Pr 3+ -doped chalcogenide glass films were deposited by excimer laser (λ = 308, 248 and 193 nm) ablation. Dense, stoichiometric SiO 2 films, almost droplet-free and with low surface roughness (<5 nm) were deposited with the ArF laser. By using the XeCl laser, ITO electrodes were deposited on optical waveguides and Pr 3+ -doped chalcogenide glass films on microscope slides. The deposited films were investigated by Rutherford backscattering spectrometry, optical thickness probes, atomic force and scanning electron microscopy. The transmittance and reflectance of chalcogenide films were measured in the range 400-2500 nm and the refractive indices were calculated as a function of wavelength.