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Orthogonal frequency division multiplexing (OFDM) is a candidate technique to provide high-speed data transmissions for optical communication systems. For intensity modulation and direct detection (IM/DD) optical communication systems, only real and non-negative valued signals can be transmitted due to the natural properties of the transmitters and receivers. This paper proposes a technique called magnitude-phase optical OFDM (MPO-OFDM) that transmits the magnitude and phase of the conventional complex valued OFDM signal successively, similar to polar-based OFDM. Unlike polar-based OFDM, however, the proposed MPO-OFDM quantizes, encodes, and transmits the phase information using pulse amplitude modulation (PAM) to reduce the interference introduced by the additive noise on the phase. Considering the peak radiation power constraint of optical devices, the magnitude component of the MPO-OFDM signal experiences clipping distortion. In this paper, we optimally adjust the modulation index to control the scale of the magnitude component and achieve the highest signal to noise ratio (SNR). For the same transmitted data rate, the proposed MPO-OFDM can achieve a lower bit error rate than previously proposed techniques. For a similar BER performance, MPO-OFDM can support a higher throughput than the other techniques tested. 

Orthogonal frequency division multiplexing (OFDM) is a candidate technique to provide high-speed data transmissions for optical communication systems. For intensity modulation and direct detection (IM/DD) optical communication systems, the peak transmitted power limitation of light sources and nonnegative transmitted signal constraints can result in nonlinear distortions from clipping. In this paper, we propose a clipping enhanced optical OFDM (CEO-OFDM) for IM/DD communication systems to reduce the clipping effects. CEO-OFDM transmits the information that results from clipping the peak power, which allows the use of a higher modulation index to improve the signal to noise ratio in exchange for a larger bandwidth. For the same transmitted data rate, CEO-OFDM can achieve a lower bit error rate than DC-biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM) and unipolar OFDM (U-OFDM). By using a larger modulation constellation size, the proposed CEO-OFDM can support a higher throughput than other techniques when the same bit error rate is achieved.