| 摘要 |
PURPOSE:To increase an extinction ratio by disposing a clad layer having the refractive index smaller than the refractive index of optical waveguide layers to at least one of the optical waveguide layers and controlling the refractive index of the optical waveguide layers so as to attain the refractive index approximately equal to the refractive index of the clad layer by changing external modulating energy. CONSTITUTION:The refractive index of the InGaAsP waveguide layer is high and therefore the mode in which light propagates is a waveguide mode and the propagation less thereof is small. The refractive index of the InGaAsP waveguide layer attains n1=3.22 with respect to light having 1.5mum and can be approximated to the refractive index n2=3.18 of InP if said layer is constituted with the compsn. (In1-xGaxAsyP1-y and 0<x<=0.1, 0<y<=0.2) approximate to the compsn. of the InP clad layer, for example, the compsn. of which the wavelength lambdag corresponding to the forbidden band width is 1.0mum. The refractive index of the InGaAsP waveguide layer decreases and can be approximated to the refractive index of InP if a p-n junction is preliminarily formed along said InGaAsP waveguide layer and a carrier is injected there in. More specifically, the incident light transmits said layer as it is when no current is injected and the transmission is suppressed when the current is injected thereto. The element is therefore made to function as the optical modulation element of high speed having the large extinction ratio. |
