A light source that includes first and second waveguides and a passive resonator for coupling light between the waveguides. The waveguides include a gain region for amplifying light of a desired wavelength, a transparent region, and an absorption region. The passive resonator couples light of the desired wavelength between the first and second transparent regions of the first and second waveguides and has a resonance at that wavelength. The resonator is preferably a microdisk resonator. The index of refraction of the microdisk resonator can be altered to select the desired wavelength. A second microdisk resonator having a different radius may be incorporated to increase the tuning range of the light source. The resonator is preferably constructed over the waveguides with an air gap between the resonator and the substrate in which the waveguides are constructed.
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