We demonstrate for the first time, continuous frequency tuning >40 MHz using symmetric phase tuning regions in an InGaAsP/InP 18 GHz passively mode-locked ring laser. Frequency tuning is achieved through current injection into passive waveguides, via the free-carrier plasma effect, which is enhanced by the concurrent increase in cavity losses from free-carrier absorption. Stable mode-locking with ~1 ps pulse-width is realized from -2.5 to -7.5 V bias on the saturable absorber and 170 to 290 mA drive current. The average RF power is 50 dB above the noise level over this regime.
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