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SUMMARYThis paper theoretically evaluates the leakage loss characteristics of a quasi-phase-matched second-harmonic generation device using a ridge-type MgO:LiNbO 3 / LiNbO 3 waveguide with a gap proposed as an efficient low-loss wave conversion device. The full-vectorial finite element method for an analysis of the anisotropic waveguide is used. The effects of the distance from the MgO:LiNbO 3 surface to the gap and the width and depth of the gap on the leakage loss are studied in detail. Also, it is found that there are cases where the leakage loss of the polarization related to wavelength conversion does not become less than a certain level even if the depth of the gap is made sufficiently deep. Its mechanism is found and a provision for further reduction of such a leakage loss is described.

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