PURPOSE: To obtain a small-sized and lightweight optical modulator based on a new principle by forming electrodes at both ends of a laminate of an org. semiconductor and a highly conductive solid electrolyte, and controlling the intensity of the light incident to the org. semiconductor by the voltage applied to said electrodes.

CONSTITUTION: An AC electric power source is applied to electrodes 3, by which voltage is applied to a highly conductive solid electrolyte 2, for example PbCl2, and the chlorine ions in the PbCl2 are taken into hydroxy squlillium 1. At this time, the hydroxy squlillium 1 forms complex with chlorine and has new absorption at 0.89μm. If laser light of 0.85μm is beforehand passed through an optical fiber, the laser light of 0.85μm is attenuated on account of absorption of 0.89μm only when it forms complex with chlorine. On the other hand, when the polarity of the voltage inverts, the chlorine in the org. semiconductor returns into PbCl2, and as a result the absorption of 0.89μm disappears and the intensity of the light is restored.