We report the phase locking of an oscillating GaAs/AlGaAs resonant tunneling diode (RTD) to a train of optical pulses. Locking was achieved by direct illumination of a specially designed RTD with a diode laser pulse train. Locking occurs at all rational frequency ratios and with excitation energies as low as 0.1 pJ/pulse for the principle lock.

We use an oscillating resonant tunneling diode as the driver of an external cavity diode laser to produce active mode locked light pulses in the picosecond range. We demonstrate dc voltage-controlled uniform temporal positioning, or time shifting, or the laser pulses with reference to a synthesizer based reference signal. This may be very useful for picosecond time-resolved applications.