Wavelength tunable laser apparatus and wavelength control method

1. A wavelength tunable laser apparatus comprising:

a semiconductor substrate including:

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;

a wavelength selective mirror constituting a cavity between itself and an optical output end surface of the gain chip;

a current source for causing a positive current to flow into the pn junction section in the phase control region;

a voltage source for applying a negative bias to the pn junction section in the phase control region; and

a control unit for selectively driving any one of the current source and the voltage source depending on a direction of wavelength shift;

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.

2. The wavelength tunable laser apparatus as recited in claim 1 , wherein, the control unit drives the current source when a laser wavelength is to be shifted to a shorter wavelength side from a wavelength with the current supply and the voltage supply being turned off, and drives the voltage supply when the laser wavelength is to be shifted to a long wavelength side from the wavelength with the current supply and the voltage supply being turned off.

3. The wavelength tunable laser apparatus as recited in claim 1 , wherein,

V min=(λ ph 0−λmin)/β

where a semiconductor composition wavelength constituting the phase control region is denoted by λ ph0; a wavelength which is the shortest among wavelengths at which the laser operates, λmin; a rate of change of λ ph relative to an applied voltage V ph, −β; and a value representing the smallest one among operating minus voltages, −V min.

4. 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.

5. The wavelength tunable laser apparatus recited in claim 1 , wherein the voltage source applies only the negative bias to the pn junction section in the phase control region.

6. The wavelength control method for a wavelength tunable laser apparatus of claim 4 , wherein the step of applying the voltage includes applying only the negative bias to the pn junction section in the phase control region.