Coupling coefficients for guided modes in distributed feedback quantum cascade lasers

In this paper, we have calculated the coupling coefficients for guided modes in distributed feedback quantum cascade lasers based on the perturbation theory. The coupling coefficients are given as functions of the grating depth g with g ranging from 0 to 400 nm. When the grating depth is about 250 nm the typical coupling coefficient for quantum cascade lasers working at 5–13 μm is ∼30 cm−1.