Multipath interference characterization of bend-insensitive optical fibers and short jumpers.

Multipath interference (MPI) in bend-insensitive optical fibers is investigated by analyzing different aspects, ranging from a review of the theoretical background, through the analysis of measurement issues, to the characterization of short patch cords. Two setups for the characterization of MPI are analyzed, highlighting their advantages and limitations. Then, a number of commercial bend-insensitive fibers are compared, showing that they generally exhibit a level below -30 dB in the range of 1250-1350 nm. The investigation also includes short offset-spliced fiber segments, with lengths to 1 cm, to simulate the behavior of field-installable connectors and isolate their contribution to the MPI. The results show a step-like increment of MPI when two or more cm-long fiber segments are cascaded.

Film-loaded SAW waveguides for integrated acousto-optical polarization converters.

We report on a detailed theoretical and experimental investigation of film-loaded surface acoustic wave (SAW) waveguides in lithium niobate (LiNbO3) for integrated acousto-optical (AO) polarization converters. The numerical analysis is based on both a scalar and a full-vectorial model. Dispersion plots and figures of merit for several structures are given, which lead to design parameters for optimized polarization converters. It is pointed out that very attractive structures are metal/dielectric/LiNbO3 strip waveguides and dielectric/LiNbO3 slot waveguides, in which metal is either gold (Au) or aluminum (Al), and the dielectric film is an optical transparent material such as silicon oxide (SiO2), magnesium oxide (MgO), or aluminium oxide (Al2O3). Polarization converters with the designed acoustical waveguides have been realized and characterized by optical conversion and laser probing measurements.

A fast Green's function method for the analysis of IDT's for acousto-optical devices.

Surface acoustic wave (SAW) interdigital transducers are key components in X-Y LiNbO3 acousto-optical (A-O) devices. SAW interdigital transducers (IDT's) on this substrate exhibit a high spurious resonance that may reduce the A-O efficiency. In this paper we present a detailed analysis of X-Y LiNbO3 IDT's based on a fast Green's function method (GFM). In order to correctly evaluate the spurious effects on IDT's performance, we also considered bulk terms of the Green's function. When the GFM is applied to IDT's with general topology and over a wide frequency range, the required computation time can reach quickly unacceptable values for long IDT structures. We developed a new model order reduction technique based on the singular value decomposition (SVD) for the fast generation of the IDT's frequency response. Numerical results for different configurations of X-Y LiNbO3 IDT's are in good agreement with measured data and a correct interpretation of the spurious resonance is reported. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band IDT's for A-O devices.

Reduced-order model technique for the analysis of anisotropic inhomogeneous media: application to liquid-crystal displays.

Electromagnetic wave propagation in anisotropic inhomogeneous media is computed by a novel reduced-order model technique, which is based on the restriction of the Marcuvitz-Schwinger equations on Krylov subspaces and on the application of the singular-value decomposition. The model is derived from the standard coupled-wave method and includes both wide-angle diffraction and light scattering at dielectric interfaces. The method, currently implemented for two-dimensional problems, was applied to the analysis of different liquid-crystal test cells. Numerical results are compared with those obtained through the application of the coupled-wave method and the Jones method and with experimental microscopic measurements.

Analysis of piezoelectric strip waveguides based on the effective index and pseudospectral element methods.

Integrated acousto-optical circuits in LiNbO3 are attractive devices for applications especially in advanced WDM systems. In order to increase the scale of integration and to reduce the RF driving power of these devices, one promising approach is to use acoustical waveguides with smaller lateral dimensions. In this paper the combination of a pseudospectral elements method (PSEM) and an effective index method (EIM) for the analysis of film-loaded surface acoustic waveguides (SAWG's) is presented. Numerical results demonstrate the exponential rate of convergence of the PSEM and agree with the computations performed via the transverse resonance technique. Due to the exponential rate of convergence of the PSEM and to a mapping transformation in the substrate, the piezoelectric problem in the depth direction of the structures is evaluated by a low number of Legendre polynomials. The method is applied to the analysis of several layered SAWG's of practical interest for AO devices, such as metal/SiO2/X - YLiNbO3, in which the metal is either Au, Al, In, or Ti.