WAVE-GUIDE CONFINEMENT OF CERENKOV 2ND-HARMONIC GENERATION THROUGH A GRADED-INDEX GRATING COUPLER - ELECTROMAGNETIC OPTIMIZATION

The feasibility of making a frequency doubler for integrated optics is studied with the electromagnetic theory of gratings and graded-index waveguides as a tool. The device consists of a first waveguide filled with a sol-gel nonlinear material doped or grafted with a nonlinear ch romophore whose thickness is chosen to generate a second-harmonic Cere nkov radiation in a dispersive glass substrate. The Cerenkov radiation is coupled into a second waveguide through a graded-index layer produ ced by ion exchange into glass, lying on top of an ion-etched grating coupler. The aim of the study is to optimize the optogeometrical param eters of the device in order to obtain a resonance line of the second waveguide modes that has an angular width large enough to match the ex perimental constraints, and which leads to a good enough coupling coef ficient. The electromagnetic theory of grating couplers is developed i nto an S-matrix propagation algorithm form in order to be combined wit h the electromagnetic analysis of the thick graded-index waveguide wit h a view to analysing the device.