Orthogonal time-frequency-space (OTFS) modulation is a promising two-dimensional (2D) signal technique to tackle high mobility time-varying wireless channels. However, its good performance on time-frequency plane multiplexing for optical-wireless communications (OWC) has never been fully investigated. In this article, we take advantage of OTFS and propose a new orthogonal time-frequency multiplexing (OTFM) scheme for DC-biased OWC. We first design a 2D Hermitian symmetry in the DC-biased optical OTFM (DCO-OTFM) system to generate the real-valued signal. The bit error rate (BER) of a DCO-OTFM system is studied on the OWC channel. Numerical results demonstrate that the proposed scheme outperforms the conventional DC-biased optical orthogonal frequency division multiplexing scheme.