An optical source, comprising: a semiconductor optical amplifier defined in a semiconductor other than silicon, wherein the semiconductor optical amplifier has a first edge and a second edge, includes a reflective coating on the first edge, and, during operation, provides an optical signal at the second edge; and a photonic chip optically coupled to the semiconductor optical amplifier, wherein the photonic chip includes: a first optical waveguide having a third edge, optically coupled to the second edge of the semiconductor optical amplifier, and a fourth edge; a first ring resonator optically coupled to the first optical waveguide; a second optical waveguide, optically coupled to the first ring resonator, having a fifth edge and a sixth edge optically coupled to a first termination; a second ring resonator optically coupled to the second optical waveguide; a common thermal-tuning mechanism thermally coupled to the first ring resonator and the second ring resonator; a first thermal-tuning mechanism thermally coupled to the first ring resonator; a second thermal-tuning mechanism thermally coupled to the second ring resonator; a monitoring device optically coupled to the fourth edge and the fifth edge; and control logic, electrically coupled to the monitoring device, the common thermal-tuning mechanism, the first thermal-tuning mechanism and the second thermal-tuning mechanism, that, during operation, tunes the first ring resonator and the second ring resonator. a semiconductor optical amplifier defined in a semiconductor other than silicon, wherein the semiconductor optical amplifier has a first edge and a second edge, includes a reflective coating on the first edge, and, during operation, provides an optical signal at the second edge; and a photonic chip optically coupled to the semiconductor optical amplifier, wherein the photonic chip includes: a first optical waveguide having a third edge, optically coupled to the second edge of the semiconductor optical amplifier, and a fourth edge; a first ring resonator optically coupled to the first optical waveguide; a second optical waveguide, optically coupled to the first ring resonator, having a fifth edge and a sixth edge optically coupled to a first termination; a second ring resonator optically coupled to the second optical waveguide; a common thermal-tuning mechanism thermally coupled to the first ring resonator and the second ring resonator; a first thermal-tuning mechanism thermally coupled to the first ring resonator; a second thermal-tuning mechanism thermally coupled to the second ring resonator; a monitoring device optically coupled to the fourth edge and the fifth edge; and control logic, electrically coupled to the monitoring device, the common thermal-tuning mechanism, the first thermal-tuning mechanism and the second thermal-tuning mechanism, that, during operation, tunes the first ring resonator and the second ring resonator. a first optical waveguide having a third edge, optically coupled to the second edge of the semiconductor optical amplifier, and a fourth edge; a first ring resonator optically coupled to the first optical waveguide; a second optical waveguide, optically coupled to the first ring resonator, having a fifth edge and a sixth edge optically coupled to a first termination; a second ring resonator optically coupled to the second optical waveguide; a common thermal-tuning mechanism thermally coupled to the first ring resonator and the second ring resonator; a first thermal-tuning mechanism thermally coupled to the first ring resonator; a second thermal-tuning mechanism thermally coupled to the second ring resonator; a monitoring device optically coupled to the fourth edge and the fifth edge; and control logic, electrically coupled to the monitoring device, the common thermal-tuning mechanism, the first thermal-tuning mechanism and the second thermal-tuning mechanism, that, during operation, tunes the first ring resonator and the second ring resonator.