  A high reflectivity and polarization selective high contrast grating mirror
has been designed with the use of an automated optimization algorithm. Through
a precise study of the tolerance of the different lengths of the structure, the
robustness with respect to the fabrication errors has been enhanced to high
tolerance values between 5 % and 210 %. This adjustment of the dimensions of
the structure leads to a 250 nm large bandwidth mirror well adapted for a VCSEL
application at \lambda = 2.65 $\mu$m and can easily be scaled for other
wavelengths.
