Fig. 2From: Stable Single-Mode Operation of Distributed Feedback Quantum Cascade Laser by Optimized Reflectivity Facet Coatingsa The two red curves are the mode loss of high- and low-frequency mode respectively. The black curve is the differential mode loss between the two band-edge modes labeled as Δ. The inset shows the mode profile calculated for the low- and high-frequency modes, for a single period of the grating. b The calculated mode loss spectrum based on transfer matrix simulation with different AR coatingsBack to article page