Passive Mode-Locking of 3.25 μm GaSb-Based Cascade Diode Lasers

Abstract

Passively mode-locked type-I quantum well cascade diode lasers emitting near 3.25 μm were designed, fabricated, and characterized. The deep etched ∼5.5-μm-wide single spatial mode ridge waveguide design utilizing split-contact architecture was implemented. The epi-side-up mounted 3-mm-long ridge lasers with both 2.7-mm-long gain and 300-μm-long absorber sections forward biased operated in the continuous wave regime with above 12 mW of output power at 20 °C. The devices with a reverse-biased absorber section generated ∼10 ps pulses at the repetition rate of ∼13.2 GHz with average power exceeding 1 mW. The laser emission spectrum in the mode-locked regime comprised a smooth bell-shape-like frequency comb covering about a 20 nm range at the full-width at half-maximum level. Second-order interferometric autocorrelation studies revealed a strong spectral chirp in the pulse. The intermodal beat note of the Lorentzian shape with a 180 kHz line width was observed, corresponding to pulse-to-pulse timing jitter of ...