Patent ID: 7773642

Claim:
A tunable laser, comprising: a multiple ring resonator in which a plurality of ring resonators, which are constituted with ring-type waveguides having optical path lengths different from each other, are directly coupled through an optical-coupling device; an LD-side waveguide having a first end connected to one of the plurality of ring resonators through an optical-coupling device; a reflection-side waveguide having a first end connected to other one of the plurality of ring resonators through an optical-coupling device; a single board on which the ring resonator, the LD-side waveguide and the reflection-side waveguide are formed; a reflection film provided to a second end of the reflection-side waveguide, wherein said reflection film comprises a high-reflection film capable of reflecting laser light without regard to a wavelength of a transmission peak of said laser light; a laser diode chip having a low reflection film formed on one of two opposing emission end faces, which is optically coupled to the LD-side waveguide through the low reflection film; and a tuning device comprising a plurality of heaters on each of the ring resonators for changing a resonance wavelength of only the multiple ring resonator, wherein, in the plurality of ring resonators, diameters of the ring waveguides are set so that intervals of reflection peaks appearing periodically become different, and there generates a resonance at a meeting point of the reflection peaks.