HIGH-SPEED ELECTRO-OPTIC WAVEGUIDE GRATING MODULATORS

摘要

An optical waveguide modulator-switch based on an electro-optically induced Bragg phase diffraction grating has been developed that gives over 50% diffraction with pulse rise times less than 3 nsec. Low-loss optical waveguides of single crystal ZnO epitaxially grown on sapphire served as the basis for the waveguide modulator. To study the problem of bulk and surface loss in optical waveguides we have developed a convenient theory and compared it with measured waveguide losses as a function of mode and wavelength. The theory has assisted us in the evaluation and improvement of the processes used to epitaxially grow the waveguides, resulting in dramatic improvement in the ZnO Waveguide properties, from losses on the order of 40 dB/cm to losses below 2 dB/cm and often even below 1 dB/cm. Our study includes a theoretical description useful for the design of modulators and general predictions verified by experiment. Our experimental results were used to empirically modify aspects of the theory to allow accurate quantitative description. Thus, by theoretical and empirical means we predict that an optimized electro-optic grating modulator on epitaxial ZnO waveguides will be capable of 80% diffraction at a drive voltage of 25 V, with pulse rise times less than 1 nsec drive powers of approximately 3 mW/MHz. (Author)