We propose a novel multiple-input-multiple-output (MIMO) optical modulation method that combines binary polarization shift keying (BPOLSK) with pulse position modulation (PPM). The proposed approach, denoted BPOLSK-PPM, offers a good promise between power and spectral efficiencies compared to standard uses of PPM and BPOLSK. We provide a theoretical analysis to evaluate the performance of BPOLSK-PPM over free space optical (FSO) atmospheric turbulence channels and provide average bit error probability (ABEP) bounds for both uncoded and coded performances. The theoretical derivations are also corroborated via extensive simulation results and comparisons with conventional modulation approaches.