Patent ID: 8073033

Claim:
A method of driving an optical semiconductor device, where the 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, and the method comprising the steps of: in a state of supplying no switching current from the electrode for switching to the active layer, supplying a pre-bias current for the active layer from the electrode for the active layer to the active layer, as well as supplying a pre-bias current for the refractive index control layer from the electrode for the refractive index control layer to the refractive index control layer in advance, turning on the laser element by supplying switching current from the electrode for switching to a part of the active layer while supplying a current for activation from the electrode for the active layer to the active layer, and turning off the laser element by halting the supply of the switching current.