Ray optics determination of the DFB coupling coefficient in separate confinement and multiquantum-well laser structures

A ray optics technique is used to derive a closed-form expression for the first-order backward coupling coefficient κ in a generic five-layer separate confinement distributed feedback laser configuration with sinusoidal, triangular, or rectangular gratings. The expression is applicable to multiquantum-well structures as well as strong coupling configurations, and can be evaluated without using any numerical techniques. For the weak perturbation configurations normally encountered in such devices, the ray optics κ values are in good agreement with those obtained using the standard overlap integral technique