A light source[50, 90] that includes first and second waveguides[21, 22] and a passive resonator[30] for coupling light between the waveguides. The waveguides include a gain region[23] for amplifying light of a desired wavelength, a transparent region[25], and an absorption region[27]. 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[30] 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[101] 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[132] between the resonator and the substrate[20] in which the waveguides are constructed.
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