Abstract: 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.