Active Mode Locking of Broadband Quantum Cascade Lasers

Active mode-locking in broadband Quantum Cascade (QC) lasers with a repetition rate of about 14.3 GHz has been achieved through the modulation of the laser bias current. At low driving currents the active mode-locking in the broadband (QC) lasers resemble the active mode-locking in the single wavelength of QC lasers, when at high driving currents the mode-locking properties are governed by the broad spectral gain of these lasers. At high bias currents the active modulation can excite and phase-locks Fabry-Perot modes across the entire gain spectrum in the spectral range between 6.7 and 7.4 mum. The broad spectral width of the actively mode-locked lasers (delta v > 2 THz) demonstrates the potential for generating subpicosecond pulses, and the variation of the spectra with modulation frequency allows a direct measurement of the group refractive index dispersion as +9x10-3 mum-1.