Two-Step Narrow Ridge Cascade Diode Lasers Emitting Near $2~\mu$ m

Abstract

Nearly diffraction limited GaSb-based type-I quantum well cascade diode lasers emitting in the spectral region 1.95– $2~\mu \text{m}$ were designed and fabricated. Two-step 5.5- $\mu \text{m}$ -wide shallow and 14- $\mu \text{m}$ -wide deep etched ridge waveguide design yielded devices generating stable single lobe beams with 250 mW of continuous wave output power at 20 °C. Quantum well radiative recombination current contributes about 13% to laser threshold as estimated from true spontaneous emission and modal gain analysis. Recombination at etched sidewalls of the 14- $\mu \text{m}$ -wide deep ridges controls about 30% of the threshold.