Second-harmonic generation by off-axis propagation in an anisotropic optical waveguide
Second-harmonic generation (SHG) by means of radiation modes (the Cerenkov-type radiation scheme) in an anisotropic optical waveguide by off-axis propagation has been studied theoretically. If the second-harmonic wave is a leaky wave of the waveguide, the Cerenkov-type SHG efficiency may be comparable with the efficiency of the guided-mode–guided-mode SHG without critical control of the wave-vector-matching condition. The model presented predicts a strong modification of the radiation field by a change of the interaction length. A numerical simulation of the proposed type of SHG in a graded-index waveguide on the X-cut surface of LiNbO3 is made.
This paper deals with robust estimation of states and unknown inputs for a class of non linear system described by Takagi-Sugeno fuzzy models. The proposed approach is developed on the basis of adaptive Luenberger observer theory. A robustness study, using the L 2 technique, is carried out to take in consideration the model uncertainties. Unknown inputs estimation is ensured through a fuzzy proportional integral adaptive law, computed from an accurate observer outputs which allow a fast dynamic estimation. Design conditions are formulated into Linear Matrix Inequalities (LMIs) terms. Numerical example is given to illustrate the efficiency of the proposed techniques.