Several subwavelength grating mirrors have been designed for VCSEL application in mid-infrared wavelength range (λ = 2.3 µm). These mirrors are automatically optimized thanks to a global algorithm which maximizes a specially defined quality factor for VCSEL top mirrors. Three different designs based on Si/SiO2, AlGaSb/GaSb and GaAs/AlOx are simulated and exhibit bandwidth as large as 206 nm. Also, the bandwidth is polarisation selective with a TM reflection coefficient higher than 99.9 % while TE coefficient is kept below 90 %. These reflectors present several fabrication solutions with a trade off between technological limitations, tolerances in regard to the fabrication error and mirror quality.