Optoelectronic delay-time controller for laser pulses

A dc-voltage-controlled optoelectronic delay line for continuous tuning of the relative delay time of an optical pulse train generated from a gain-switched laser diode is demonstrated. A maximum tunable range delay time of 3.9 ns ($\approx 2$ periods) for optical pulses at a 500-MHz repetition rate is reported, which corresponds to a phase shift of as much as $4\pi$. The tuning responsivity and resolution of the current apparatus are $0.54 \mathrm{ps}/\mathrm{mV}$ and $<0.2 \mathrm{ps}$, respectively. The measured timing fluctuation and long-term drift at any delay time are 0.13 ps and $20 \mathrm{fs}/min$, respectively. This scheme further permits the simultaneous phase tracking of the laser pulse train to unknown signals generated from the device under test.