An optical source is described. This optical source includes a semiconductor optical amplifier, with a semiconductor other than silicon, which provides an optical gain medium. In addition, a photonic chip, optically coupled to the semiconductor optical amplifier, includes: a first optical waveguide that conveys at least a portion of the optical signal, and a second optical waveguide that conveys at least another portion of the optical signal. Moreover, the photonic chip includes a distributed-Bragg-reflector (DBR) ring resonator that is optically coupled to the first optical waveguide and the second optical waveguide, and that reflects a tunable wavelength in the optical signal. Furthermore, a monitor on the photonic chip measures at least the other portion of the optical signal, and control logic on the photonic chip thermally tunes the tunable wavelength of the DBR ring resonator based on the measurement of at least the other portion of the optical signal.
