arXiv:1102.5641v1 [cs.IT] 28 Feb 2011 fgwang@inc.cuhk.edu.hk, wangx@ee.columbia.edu New York, NY 10027 Columbia University Electrical Engineering Dept. Fanggang Wang, Xiaodong Wang Coherent Optical DFT-Spread OFDM Abstract We consider application of the discrete Fourier transform-spread orthogonal frequency-division multiplexing (DFT-spread OFDM) tech- nique to high-speed fiber optic communications. The DFT-spread OFDM is a form of single-carrier technique that possesses almost all advantages of the multicarrier OFDM technique (such as high spec- tral efficiency, flexible bandwidth allocation, low sampling rate and low-complexity equalization). In particular, we consider the optical DFT-spread OFDM system with polarization division multiplexing (PDM) that employs a tone-by-tone linear minimum mean square er- ror (MMSE) equalizer. We show that such a system offers a much 1