Wavelength tunable laser device and laser module

A wavelength tunable laser device, comprising:

• a laser cavity formed of a grating and a reflecting mirror optically coupled to the grating, said reflecting mirror including a ring resonator filter;
• a gain portion arranged within the laser cavity;
• and
• a phase adjusting portion arranged within the laser cavity,
• wherein the grating forms a first comb-shaped reflection spectrum,
• wherein the ring resonator filter of the reflecting mirror includes:
• a ring-shaped waveguide;
• and
• two arms that are respectively optically coupled to different points of the ring-shaped waveguide,
• wherein the reflecting mirror further includes a coupler that unites respective ends of said two arms of the ring resonator filter on one end and that is optically coupled to the grating on another end,
• wherein the reflecting mirror forms a second comb-shaped reflection spectrum having peaks of a narrower full width at half maximum than a full width at half maximum of peaks in the first comb-shaped reflection spectrum at a wavelength interval differing from a wavelength interval of the first comb-shaped reflection spectrum,
• wherein the grating and the reflecting mirror are configured such that one of the peaks in the first comb-shaped reflection spectrum and one of the peaks in the second comb-shaped reflection spectrum are overlappable on a wavelength axis,
• wherein the wavelength tunable laser device is configured to adjust a refractive index of the phase adjusting portion such that one of the cavity modes of the laser cavity enters an overlap region in which said one of the peaks in the first comb-shaped reflection spectrum and said one of the peaks in the second comb-shaped reflection spectrum are overlapped, thereby achieving laser oscillation at a wavelength of said one of the cavity modes,
• wherein the laser cavity is configured such that a spacing between cavity modes is narrower than the full width at half maximum of the peaks in the first comb-shaped reflection spectrum, and such that two or more of the cavity modes are included within a peak in the first comb-shaped reflection spectrum, and
• wherein the wavelength tunable laser device is configured to adjust the refractive index of the phase adjusting portion so as to shift said two or more cavity modes on the wavelength axis and align only one of said two or more cavity modes with said overlap region, thereby achieving single mode laser oscillation at said one of said two or more cavity modes.