PURPOSE: To modulate the intensity of a light beam by an arbitrary frequency by constituting the titled optical modulator, of an acousto-optical medium, the first and the second ultrasonic wave generating means, and an exciting means for generating the same ultrasonic traveling waves whose propagation directions are diametrically opposite to each other by exciting the first and the second ultrasonic wave generating means.

CONSTITUTION: On the upper face of each ultrasonic transducer 1, 2, gold is vapor-deposited. By impressing a high frequency on electrodes 1a, 2a, a longitudinal ultrasonic wave is generated, and in an acoustic medium, ultrasonic beams of USW-1 and USW-2 are formed. Silver pate for forming an absorber layer 3 for preventing a reflection by absorbing the ultrasonic beam USW-1 is applied to a part opposed to the first ultrasonic transducer 1 of the second plane F2. In the same way, silver paste for forming an absorber layer 4 for preventing a reflection by absorbing the ultrasonic beam USW-2 is applied a part opposed to the second ultrasonic transducer 2 of the first plane F1. That is to say, by opposing the absorber layers, an ultrasonic resonator is not constituted between the first plane F1 and the second plane F2.