We present the design of a sub-wavelength grating mirror optimized for integration in mid-IR VCSEL. The definition of a quality factor adapted to VCSEL requirements and maximized by an optimization algorithm allowed us to obtain a polarization selective and high reflectivity structure showing several percent of tolerance. The design of the SGM mirror can easily be adapted to the technological constraints of the manufacturers by adjusting the limitations defined for the automated optimization process. Indeed, the comparison between different technological constraints shows that a better accuracy of the etching process results in an increase of the quality of the mirror.