The first self-assembled InAs quantum dash lasers grown by molecular beam e
pitaxy on InP (001) substrates are reported. Pulsed room-temperature operat
ion demonstrates wavelengths from 1.60 to 1.66 mum for one-, three-, and fi
ve-stack designs, a threshold current density as low as 410 A/cm(2) for sin
gle-stack uncoated lasers, and a distinctly quantum-wire-like dependence of
the threshold current an the laser cavity orientation. The maximal modal g
ains for lasing in the ground-state with the cavity perpendicular to the da
sh direction are determined to be 15 em(-1) for single-stack and 22 cm(-1)
for five-stack lasers.