Patent ID: 7633984

Claim:
An optical semiconductor device, comprising: a semiconductor substrate; a structure formed on one surface of the semiconductor substrate and including at least a diffraction grating, an active layer generating light by a current injection, and a refractive index control layer whose refractive index is allowed to be changed by a current injection; and a laser element including an electrode for the active layer, an electrode for the refractive index control layer, and an electrode for switching, the electrodes being formed independently of each other and formed any one of above the structure and on an other surface of the semiconductor substrate, wherein, in a state of not supplying a switching current for generating a laser light from the electrode for switching to a part of the active layer, a pre-bias current for the active layer is supplied from the electrode for the active layer to the active layer, and a pre-bias current for the refractive index control layer is supplied from the electrode for the refractive index control layer to the refractive index control layer in advance, and then while a current for activation is supplied from the electrode for the active layer to the active layer, the switching current is supplied from the electrode for switching to a part of the active layer, thus turning on the laser element, and supply of the switching current is halted, thus turning off the laser element.