C.G. Someda

Planar, Compact Dual-Band Antenna for Wireless LAN Applications

A compact, printed dual-band antenna for WLAN applications is proposed. The radiating elements consist of a combination of a printed dipole for the lower resonant frequency and a bow-tie antenna for the upper resonant frequency. The operation on two separate bands is guaranteed by the use of two surface-mounted-device inductors. The antenna has been manufactured in antipodal configuration. Measurement results show good omnidirectionality and low cross-polarization levels.

Polarization mode dispersion in long single-mode-fiber links: A review

Abstract Polarization mode dispersion (PMD) is the interplay of birefringence (both systematic and random) and coupling between orthogonal polarizations, in a single-mode fiber. PMD will set the ultimate limit to the fiber length × capacity product, when all the deterministic causes of dispersion are under control. We review the state of the art in this field, with emphasis on experiments, which demonstrate that the behavior of long links can be predicted with full confidence, in a statistical sense, from factory-based tests on individual cables. Successful application of the same experimental technique to detecting fiber stresses is also demonstrated.

On the modelling of non-linear guided-wave optics for all-optical signal processing

The application of a reduced variational formalism, to model guided-wave optical signal processing devices is reviewed. The focus is mainly on second-order non-linearities. First, approximate analytical solutions (solitary waves) are derived for propagation in second-order non-linear media. Next, these analytical results are validated through numerical simulation of the governing equations. To show the potential of this formalism by means of a practical example, the analytical results are applied to a soliton-based LiNbO3 non-linear directional coupler exploiting second-order non-linear effects.

Variational analysis of nonlinear channel waveguides

The dynamics of a two-dimensional optical beam propagating in a nonlinear channel waveguide is investigated by means of a variational technique. Through this analysis, one can determine the eigenmodes (self-trapped modes) of the structure. Their stability has also been checked numerically. >

Directional couplers and de-couplers in photonic crystal waveguides: simulations and theory

Numerical simulations indicate that photonic crystals are excellent candidates to build high-performance directional couplers (or de-couplers). Theoretical explanations for these results, in physical terms, are provided as well.

SELF-TRAPPED, STABLE SOLUTIONS IN NONLINEAR CHANNEL WAVEGUIDES

It is well known that a 2-D optical beam propagating along a given direction (say z) in a homogeneous nonlinear medium (HNLM) will either spread out or collapse within a finite distance, depending on whether its power is below or above a critical value, PC [1] . The next question then is whether or not it is possible to obtain stable, stationary (i.e., z-independent) beams by adding a linearly guiding structure, like for example a channel-waveguide. The linear refractive index has to decrease monotonically as a function of distance from the z axis.

Prediction of second harmonic generation efficiency in real periodically poled lithium niobate structures grown by the off-center Czochralski technique

The work focuses on periodically poled lithium niobate crystals grown by the off-center Czochralski technique and exhibiting an appreciable second harmonic generation efficiency. Several samples have been characterized through experimental measurements of domains periods in order to find out the real period values and drifts of the border domains positions. By means of the nonlinear bidirectional beam propagation method (NL Bi-BPM), the governing equations describing the interaction between the wave at fundamental frequency and the wave at second harmonic have been integrated and the theoretical SHG efficiency was numerically determined. In order to take into account the border domain effects, the normalized efficiency was used to rescale the calculated value furnishing the real SHG efficiency. As an interesting result an efficiency of 0.5% in forward QPM SHG has been predicted for a reference structure of 0.5 mm length.

Bidirectional beam propagation method for the modeling of microstructured waveguides for second harmonic generation

We discuss the application of the bidirectional beam propagation method for the analysis of nonlinear microstructured waveguides. We review two different formulations of the nonlinear algorithm, and demonstrate, also by comparison with experimental data taken from the literature, that the method is a valuable tool for the design of devices for second harmonic generation.

Modelling of photonic crystal devices

Recent advancements in the theoretical analysis of photonic crystal planar waveguides and devices will be reviewed. A new design principle, that we proposed recently, will be illustrated, and compared with numerical techniques in current use. Examples of applications will be also provided.