Wavelength tunable laser apparatus and wavelength control method

A wavelength control method for a wavelength tunable laser apparatus including:

• a semiconductor substrate having:
• a region which emits light when a current is applied thereto and having a first semiconductor composition, and a phase control region including a pn junction section having a second semiconductor composition;
• a gain chip in which the light-emitting region and the phase control region are connected to each other with a waveguide;
• and a wavelength selective mirror constituting a cavity between itself and an optical output end surface of the gain chip, the method comprising the steps of:
• causing a positive current to flow to the pn junction section of the phase control region when a laser wavelength is to be shifted to a shorter wavelength side from a wavelength with no phase control signal being applied to the phase control region;
• and
• applying a voltage with a negative bias to the pn junction section of the phase control region when a laser wavelength is to be shifted to a longer wavelength side from a wavelength with no phase control signal being applied to the phase control region;
• wherein the first semiconductor composition of the light-emitting region and the second semiconductor composition of the phase control region are different from each other.