Time-domain upconversion measurements of group-velocity dispersion in quantum cascade lasers

A time-resolved mid-infrared upconversion technique based on sum-frequency generation was applied to measure pulse propagation in lambda similar to 5.0 mu m quantum cascade lasers operated in continuous wave at 30 K. The wavelength-dependent propagation delay of femtosecond mid-infrared pulses was measured to determine the total group-velocity dispersion. The material and waveguide dispersion were calculated and their contributions to the total group-velocity dispersion were found to be relatively small and constant. The small-signal gain dispersion was estimated from a measurement of the electroluminescence spectrum without a laser cavity, and was found to be the largest component of the total GVD. A negative group-velocity dispersion of beta(2) ( = d(2)beta/d omega(2)) approximately -4.6 x 10(-6) ps(2)/mu m was observed at the peak emission wavelength, and good agreement was found for the measured and calculated pulse-broadening. (c) 2007 Optical Society of America.