A system for tuning a narrow-linewidth semiconductor laser such that the laser produces a laser beam at its output port having a desired frequency. The system includes an optical resonator and an optical system for coupling a portion of the laser beam into the resonator along a feedback optical path. The resonator may comprise a pair of faces, an electro-optic material between the faces, and an electrode for generating an electric field in the electro-optic material in response to a control voltage. The laser beam portion that enters the resonator causes the resonator to produce a feedback beam that is coupled into the input port of the laser, to provide optical feedback that causes the laser to lock to a resonance of the optical resonator. Tuning is accomplished by varying the resonance by applying a voltage to the electrode. The optical feedback also reduces the laser's linewidth. In another embodiment, a fiber-optic cable ring resonator is used to produce the feedback beam.
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