Measuring the above-threshold group-velocity dispersion and gain curvature of a semiconductor laser by pulse-propagation techniques

The dispersive broadening of a single optical pulse traveling within a Fabry–Perot semiconductor laser was measured for propagation over 58 round trips of the cavity, a distance of 352 mm. The interference between two copropagating pulses with variable relative phase (stabilized to within 2π×0.02 rad) was used to relate the group-velocity dispersion to the gain curvature. With both single- and double-pulse propagation measurements, the complex group-velocity dispersion (including gain curvature) was found to be 8.7+5.9i ps2/m at twice the laser-threshold bias current. When the laser bias was increased from 1.4 to 2 times the laser threshold, the gain curvature decreased by 2.8%, and the group-velocity dispersion showed less than 0.1% variation.