F. Di Pasquale
University College London
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Publication
Featured researches published by F. Di Pasquale.
IEEE Photonics Technology Letters | 1995
M. Federighi; F. Di Pasquale
High-concentration Er/sup 3+//Yb/sup 3+/ co-doped silica waveguide amplifiers are numerically analyzed. With optimized rare-earth concentrations the effect of Er/sup 3+//Er/sup 3+/ ion-pairs can be neglected and each Er/sup 3+/ ion can be assumed to be paired only to the surrounding Yb/sup 3+/ ions. The rate-equations model includes uniform upconversion mechanisms from /sup 4/I/sub 13/2/ and /sup 4/I/sub 11/2/ erbium levels and an Yb/sup 3+/ to Er/sup 3+/ pair-induced energy transfer process. Numerical results demonstrate the possibility of fabricating short- and high-gain integrated optical amplifiers; it is shown that net gain as high as 3 dB/cm can be obtained.<<ETX>>
IEEE Journal of Selected Topics in Quantum Electronics | 2000
C. E. Chryssou; F. Di Pasquale; C.W. Pitt
Er/sup 3+/-doped tellurite and Er/sup 3+/-doped alumina optical waveguide amplifiers are analyzed both as single amplifiers and as elements of 16-channel wavelength-division multiplexing (WDM) systems; their performances are compared with that from Er/sup 3+/-doped Al/P silica waveguide amplifiers. The amplifier model is based on propagation and population-rate equations and includes both uniform and pair-induced up-conversion mechanisms. It is solved numerically by combining finite elements and the Runge-Kutta algorithm. The analysis predicts that Er/sup 3+/-doped tellurite waveguides exhibit improved gain characteristics compared with alumina and Al/P silica waveguides. Using Er/sup 3+/-doped tellurite waveguide amplifiers, it is suggested that 16 WDM channels may be transmitted to a maximum distance of 4250 km. By using in-line notch gain equalizing filters, the maximum transmission distance can be increased to 5250 km.
IEEE Journal of Quantum Electronics | 1996
F. Di Pasquale
The continuous wave operations of highly-efficient Er/sup 3+//Yb/sup 3+/ co-doped fiber lasers pumped at 980 nm are numerically analyzed. The model, based on propagation-rate equations, includes uniform upconversion from the /sup 4/I/sub 13/2/ and /sup 4/I/sub 11/2/ erbium levels and a pair-induced energy transfer process from Yb/sup 3+/ to Er/sup 3+/; it allows the description of both single-mode and multimode laser operations. Numerical results show that slope efficiencies close to the quantum limit, with threshold pump powers of few mW, can be achieved in short single-frequency fiber lasers using grating Bragg reflectors. Moreover, we demonstrate the possibility of performing equispaced multiwavelength laser emissions in high-concentration Fabry-Perot fiber microlasers.
IEEE Transactions on Electron Devices | 1999
F. Di Pasquale; Huifang Deng; F. Anibal Fernandez; Se Day; Jb Davies; Mark Thomas Johnson; A.A. van der Put; J.M.A. van de Eerenbeemd; J.A.M.M. van Haaren; Jeffrey A. Chapman
In this paper a two-dimensional (2-D) dynamic model, based on a tensor formulation and solved numerically by combining finite elements and finite differences, is proposed and used for analyzing nematic liquid crystal (LC) test cells with interdigital electrodes. We compare theoretical and experimental results concerning the switching behavior, response mechanism, and viewing angle characteristics of nematic LC pixel structures which use the in-plane-switching (IPS) mode. The good agreement observed between theory and experiment in terms of electro-optical properties validates our modeling and demonstrates its potential for design optimization. We show that the proposed LC test cells, using the in-plane-switching mode, ensure switching-ON and -OFF response times of 22 and 28 ms, respectively, and excellent viewing angle characteristics.
IEEE Journal of Selected Topics in Quantum Electronics | 1996
F. Di Pasquale; Fa Fernandez; Se Day; Jb Davies
A two-dimensional finite-element code is presented for the steady-state analysis of liquid crystal structures in nonuniform electric fields. It is based on a free-energy formulation which includes all three elastic constants and can deal with pure nematic, twisted nematic, and cholesteric liquid crystal materials. The enhanced capabilities of our code allow the design of composite structures made of both dielectric and liquid crystal materials and with arbitrary configuration of electrodes. Unwanted effects, such as the formation of disclination lines in the director orientation, can be accurately predicted. The method has been applied for analyzing pure nematic liquid crystal microlenses with variable focal length and twisted nematic liquid crystal cells for display applications. Numerical results show that a careful choice of the device structures can avoid the formation of defects and improve their performance.
IEEE Photonics Technology Letters | 1995
F. Di Pasquale; M. Federighi
Continuous wave laser operations of silica-based Er/sup 3+/-Yb/sup 3+/ co-doped waveguides have been numerically analyzed by means of a finite-element method. The theoretical model, based on propagation-rate equations, describes uniform upconversion by a dipole-dipole interaction between Er/sup 3+/ ions, and includes a pair-induced energy transfer process from Yb/sup 3+/-Er/sup 3+/ Numerical results show that single-frequency operation with slope efficiency higher than 50% and threshold pump powers of few mW can be achieved in short and heavily doped waveguides equipped with input dielectric mirrors and output distributed Bragg reflectors.<<ETX>>
lasers and electro optics society meeting | 1998
M. Federighi; N. Othman; F. Di Pasquale
We show that, if the limited gain of Er-doped waveguides makes them unsuitable as a replacement for EDFAs in straight amplifier roles, the very low threshold achievable with Yb co-doping allow their use in integrated configurations where gains of a few dB/cm are adequate, with the possibility of pumping several waveguides from a single 980 nm laser diode.
Electronics Letters | 1995
F. Di Pasquale; Polina Bayvel; J.E. Midwinter
Electronics Letters | 1996
Jb Davies; Se Day; F. Di Pasquale; Fa Fernandez
ECOC | 2007
T. Rogowski; S. Faralli; G. Bolognini; F. Di Pasquale; R. Di Muro; B. Nayar