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3 April 2003 Nonconventional optical characterization techniques of planar waveguides for nonlinear processes
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Full optical characterization of planar nonlinear waveguides is of major importance for the assessment of reliable fabrication processes of integrated all-optical devices. A high accuracy in the design of the waveguide parameters fixing the refractive index profile (typically optical depth and index change) and in the knowledge of their wavelength dependence are mandatory for the realization of nonlinear integrated optical devices that meet phase matching conditions and achieve highly efficient interactions. Conventional characterization techniques, such as m-lines spectroscopy, do not always fulfil the accuracy requirements especially in the case of very thin waveguides. Moreover additional preliminary determination of the refractive index of the substrate is often required. In our laboratory we developed different non-conventional optical characterization techniques to overcome the main problems related to nonlinear waveguides and, in particular, to proton-exchanged (PE) waveguides in lithium niobate or lithium tantalate that are the most commonly used waveguides for all-optical devices. Different methods will be presented. In most cases, both radiation and guided modes are exploited in the characterization process. The new techniques proposed allowed a full optical characterization of the ordinary and extraordinary refractive indices of the substrates and index profiles of the exchanged layers for single-mode and multimode PE waveguides and the determination of the Sellmeier dispersion curves. Experimental results on typical waveguides will be presented. A new method, based on prism coupling, for the measurement of waveguide losses will also be discussed.
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Marco Marangoni, Roberto Osellame, and Roberta Ramponi "Nonconventional optical characterization techniques of planar waveguides for nonlinear processes", Proc. SPIE 4944, Integrated Optical Devices: Fabrication and Testing, (3 April 2003);

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