Open AccessNovel grating design approach by radiation modes coupling in nonlinear optical waveguides
Author(s) -
Alessandro Massaro,
R. Congolani,
Massimo De Vittorio,
A. Passaseo
Publication year - 2009
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.17.006982
Subject(s) - grating , optics , coupled mode theory , coupling (piping) , waveguide , harmonic , physics , nonlinear optics , guided mode resonance , second harmonic generation , nonlinear system , radiation mode , radiation , diffraction grating , materials science , single mode optical fiber , refractive index , optical fiber , acoustics , laser , quantum mechanics , metallurgy
In integrated optics the radiation modes represent a negative aspect regarding the propagation of guided modes. They characterize the losses of the substrate region but can contribute to enhance the guided modes by considering the coupling through properly designed gratings arranged at the core/substrate interface. By tailored gratings, the radiation modes become propagating modes and increase the guided power inside the waveguide guiding region. This enhancement is useful especially in low intensity processes such as second harmonic chi(2) conversion process. For this purpose, we analyze accurately the radiation modes contribution in a chi(2) GaAs/AlGaAs nonlinear waveguide where second harmonic signal is characterized by a low power intensity. This analysis considers a new design approach of multiple grating which enhances a fundamental guided mode at lambda(FU) =1.55 microm and a codirectional second harmonic guided mode at lambda(SH) =0.775 microm. In particular we analyze the second harmonic conversion efficiency by studying the coupling effect of three gratings. The combined effects of the gratings provide an efficient second harmonic field conversion. Design considerations, based on the coupled mode equations analysis, are theoretically discussed. A good agreement between analytical and numerical results is observed.