A circuit for generating a clock or sampling signal, the circuit
including: a semiconductor quantum dot laser element including a region
of quantum dots, wherein the region of quantum dots is characterized by
an emission distribution having a half-width of at least about 10 meV;
and drive circuitry connected to the quantum dot laser element for
operating the quantum dot laser element as a mode-locked laser that
outputs a periodic, uniformly spaced sequence of pulses, wherein the
clock or sampling signal is derived from the sequence of pulses.