Abstract: The optical device provides dispersion adjustment or compensation using resonant coupling between a first waveguide and a second waveguide which has a variable thickness and a significantly different index of refraction. The two waveguides are optically coupled about a lateral coupling surface, and as light propagates down the waveguide, it passes from one waveguide to the other at a predetermined position along the propagation axis depending on the thickness of the second waveguide. Mode converters are used at the input and output of the device to provide for more efficient operation. The first waveguide can be made of silica and the second waveguide of silicon, thus providing a differential in the index of refraction of about 2. For dispersion compensation, in which shorter wavelengths need to be retarded with respect to longer wavelengths, the profile of the thickness of the second waveguide is such that shorter wavelengths spend more time in the silicon than do longer wavelengths.