To obtain a novel and useful optical modulator which is adequate for using as light flickering element of, for example, an optical communication system.

A substrate 11 which defines an optical waveguide 14 and consists of a ferroelectric is provided with an ultrasonic generator 12 which emits a surface acoustic wave along the progression direction of the polarized light progressing in the optical waveguide 14 in order to change the mode of the polarized light by interacting on the polarized light guided to the optical waveguide 14. The optical waveguide 14 is provided with a filter 16 which permits the passage of the polarized light selectively according to the mode of the polarized light. Further, the progressing route of the surface acoustic wave from the ultrasonic generator 12 to the optical waveguide 14 is provided with a semiconductor structure 13 which induces a two-dimensional electron gas for absorbing the surface acoustic wave. The semiconductor structure is provided with a modulating means for increasing or decreasing the two-dimensional electron gas of the semiconductor structure in order to increase or decrease the absorption quantity of the surface acoustic wave.