JPS6461072A - Light modulator - Google Patents

Abstract

PURPOSE:To lessen the loss in an ON condition even if the length of wave guide is enlarged and increase the ON/OFF ratio by applying a multiple quantum well structure, whose absorption is small when an electric field is not applied, to a wave guide layer. CONSTITUTION:A wave guide layer 13 is a multiple quantum well structure which alternately laminates a first semiconductor layer 131 having a first conductivity type, a second semiconductor layer 132 of intrinsic semiconductors, a third semiconductor layer 133 having a conductivity type different from the semiconductor layer 131, and a fourth semiconductor layer 134 of intrinsic semiconductors having the different thickness from the semiconductor layer 132. When a electric field is not applied, wave functions 23, 24 of electrons and holes are not nearly overlapped, oscillator strength of excitons is also small and the loss in the ON condition is small. When the electric field is applied, the functions 23, 24 are exuded in respective neighbor layers, their overlaps are large and transmittance of light is quickly reduced by the increase of absorption by the wave guide layer 13 to be an OFF condition. Therefore, the ON/OFF ratio is large.