OPTICAL MODULATING ELEMENT

摘要

PURPOSE:To provide the wide-band optical modulating element which has neither a decrease in characteristic impedance nor an increase in the propagation loss of a microwave and no rise in driving voltage and completely matches the speeds of the microwave and light with each other. CONSTITUTION:A substrate part is so structured as to have a projection by etching and digging part of a substrate 1 in an area where the intensity of a microwave electric field propagated in a traveling signal electrode is intense; and the thickness of the traveling wave electrode, the depth of the etching, and the thickness of a buffer layer are properly determined so that the effective refractive index of the microwave propagated in the traveling wave electrode approximates the effective refractive index of light propagated in a light guide 2 and the characteristic impedance of the traveling wave electrode approximates the characteristic impedance of an external circuit. When this optical modulating element constituted as mentioned above is equipped with a shield conductor, the thickness of its overlay is considered for said determination. Further, the buffer layer at the etched part is preferably hollowed.