F. Prudenzano

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.

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.

Erbium-doped hole-assisted optical fiber amplifier: design and optimization

An erbium-doped hole-assisted optical fiber amplifier, to be employed in the third band of the optical communications, is designed and optimized via a tailor made computer code. The finite element method is used for the electromagnetic investigation of the microstructured fiber section. The simulation model takes into account all the rare earth physical phenomena, i.e., the pump and signal propagation, the amplified spontaneous emission, the secondary transitions pertaining to the ion-ion interactions, and so on. The device feasibility is tested via a number of simulations, realistically performed by taking into account the actual parameters pertaining to the dispersion of the germania/silica glass, the erbium emission and absorption cross sections, the propagation losses. By simulation, in the small signal operation, a gain close to 42.8 dB is demonstrated for a fiber 13-m long, using a pump power of 50 mW at the signal wavelength /spl lambda//sub s/=1536 nm, the pump and the signal being copropagating.

Plasma-assisted pulsed laser deposition for the improvement of the film growth process

In this paper, results are reported on the characterization of thin films of titanium dioxide and chalcogenide glass doped with praseodymium by the technique of plasma-assisted pulsed laser deposition (PA-PLD) with biased substrate. This technique is shown to be able to prevent contamination of deposited films by particles ejected and to improve the pulsed laser deposition process for stoichiometry, morphology and optical properties of the films produced.

Design of an Efficient Pumping Scheme for Mid-IR Dy 3+ :Ga 5 Ge 20 Sb 10 S 65 PCF Fiber Laser

This letter illustrates the design of a novel medium infrared (Mid-IR) laser based on a photonic crystal fiber made of dysprosium-doped chalcogenide glass, Dy3+:Ga5Ge20Sb10S65. In order to perform a realistic investigation, the simulation is performed by taking into account the spectroscopic parameters measured on the rare earth-doped glass sample. The simulated results show that an optical beam emission close to 4400-nm wavelength can be obtained by employing two pump beams at 2850 nm (pump #1) and 4092 nm (pump #2) wavelengths. The pump beams can be provided by commercial quantum cascade lasers. As example, for the pump powers of 50 mW (pump #1) and 1 W (pump #2), the input mirror reflectivity of 99%, the output mirror reflectivity of 30%, and the optical cavity length of 50 cm, a signal power close to 350 mW at the wavelength of 4384 nm can be generated. This result indicates that the designed source configuration is feasible for high beam quality Mid-IR light generation and it is efficient enough to find applications in optical free propagation links, optical remote sensing, and medicine.

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.

Second harmonic generation from nanoslits in metal substrates: applications to palladium-based H2 sensor

We conducted a theoretical investigation of second harmonic generation and other nonlinear features that result from the magnetic Lorentz force, when a single aperture is cut on a thick, opaque palladium substrate. We studied the dependences of linear pump transmission and second harmonic generation near resonance conditions, and explored the different physical mechanisms and their dependences, for example, geometrical features. We found that it is possible to exploit field localization and surface plasmon generation to enhance second harmonic generation in the regime of extraordinary transmittance of the pump field. Both transmitted and backward second harmonic generation conversion efficiencies were investigated. The results reveal that it may be possible to access several potential new applications. In particular, we demonstrated that the exploitation of a combination of nonlinear effects and enhanced transmission makes possible a palladium-based device suitable for H 2 -leak-detection.

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.