  A GaAs/AlOx high contrast grating structure design which exhibits a 99.5%
high reflectivity for a 425nm large bandwidth is reported. The high contrast
grating (HCG) structure has been designed in order to enhance the properties of
mid-infrared VCSEL devices by replacing the top Bragg mirror of the cavity. A
robust optimization algorithm has been implemented to design the HCG structure
not only as an efficient mirror but also as a robust structure against the
imperfections of fabrication. The design method presented here can be easily
adapted for other HCG applications at different wavelengths.
