Vertical-cavity surface-emitting lasers (VCSELs) are widely used in automotive systems, sensors, short and long-range communications. However, emerging applications like polarization LIDARs, atomic clocks and atomic magnetometers require stable circular polarization in the laser beam. This thesis explores potential designs for circularly-polarized (CP) VCSELs and identifies key parameters that influence CP performance. CP VCSELs have been analysed by means of our in-house VCSEL ELectroMagnetic Suite (VELMS), serving as optical mode solver of Maxwell's equations, based on the mathematical framework of coupled mode theory. In particular, this thesis is focused on engineering optical anisotropies, investigating the impact of their orientation on the polarization features of the emitted light.