As one of optical wireless Orthogonal Frequency Division Multiplexing (OFDM) systems, there is Flip-OFDM, which separates an OFDM signal into positive and negative parts and transmits them. It has good power efficiency and low hardware complexity. However, the system halves transmission efficiency compared with Direct Current-biased Optical OFDM. In this paper, Circular Polarized Optical OFDM (CPO-OFDM) is presented. This system separates OFDM signals into positive and negative parts, and it converts these signals into left-handed and right-handed polarization, and it multiplexes these signals. CPO-OFDM is analyzed with an intensity modulation/direct detection channel model which considers the change of the state of polarization owing to free space propagation. As a result of the analysis, it is shown that CPO-OFDM is a flexible system like the conventional systems by using circular polarization and it has the equivalent bit error rate (BER) and the double transmission efficiency compared with Flip-OFDM. The IM/DD channel model which considers the degree of polarization (DOP) is also shown. As for the DOP, it improves by the increase of the propagation distance. Thus, we can achieve the equivalent BER obtained with a high DOP laser even if we use a low DOP laser.