High-order diffraction gratings for high-power semiconductor lasers

A deep diffraction grating with a large period ($\sim$2 $\mu$m) within one of the cladding layers is proposed for the implementation of selective feedback in a semiconductor laser. Frequency dependences of reflectance in the 12th diffraction order for rectangular, triangular, and trapezoidal diffraction gratings are calculated. It is shown that the maximum reflectance of the waveguide mode is attained using a rectangular or trapezoidal grating $\sim$2 $\mu$m deep in the laser structure. Deep trapezoidal diffraction gratings with large periods are fabricated in the Al$_{0.3}$Ga$_{0.7}$As cladding layer of a GaAs/AlGaAs laser structure using photolithography and reactive ion etching.