  We demonstrate passive harmonic mode-locking of a quantum well laser diode
designed to support a discrete comb of Fabry-Perot modes. Spectral filtering of
the mode spectrum was achieved using a non-periodic patterning of the cavity
effective index. By selecting six modes spaced at twice the fundamental mode
spacing, near-transform limited pulsed output with 2 ps pulse duration was
obtained at a repetition rate of 100 GHz.
