Polarization switching characteristics of birefringent vertical cavity surface emitting lasers (VCSELs) subject to polarized optical injection are investigated experimentally. The role of the suppressed mode of VCSELs in reducing the injected optical power required for polarization switching (PS) has been identified. For orthogonal optical injection, the minimum optical injection power (Pinj) to induce PS is found to occur at a frequency detuning (FD) of -11 GHz corresponding to the VCSEL birefringence. The value of the minimum Pinj reduced significantly with increasing bias current. The FD for PS is independent of the VCSEL bias current, injected power level, and a defined range of polarization angles of the injected light. However, for parallel optical injection, the minimum FD for PS is normally found to be positive and dependent on the VCSEL bias current and injected optical power.