Abstract: An optical device having a large extinction ratio and being suitable for the digital operation including first and second electrodes (7, 8) formed on both sides of a waveguide structure, respectively such that a carrier-injection region (3a) and a non-carrier injection regions (3b) are formed adjacent to each other in the waveguide structure. When mass carriers are stored in the carrier injection region, its refractive index is reduced lower than the non-carrier-injection regions. In this state, when a light wave with low optical power propagates through the carrier-injection region, since an amount of carriers consumed thereby is small, the refractive index of this region is still lower than the non-carrier-injection regions, and the input light wave is emitted sideways through the non-carrier-injection region.

Abstract: An optical wavelength converter, including first and second semiconductor optical amplifiers, in which an input optical pulse signal having a first wavelength &lgr;1 and a non-modulated optical signal having a second wavelength &lgr;2 are made incident upon the first semiconductor optical amplifier. Propagation constants of the first and second semiconductor optical amplifiers are determined such that a propagation constant difference &Dgr;&bgr; between the first and the second semiconductor optical amplifiers when only the optical signal having the second wavelength &lgr;2 propagates along the first semiconductor optical amplifier is smaller than a propagation constant difference &Dgr;&bgr; when both the input optical pulse signal and non-modulated optical signal propagate along the first semiconductor optical amplifier.