Coherent Optical OFDM Systems Based on the Fractional Fourier Transform

An innovative Orthogonal Frequency Division Multiplexing (OFDM) scheme based on orthogonal chirped subcarriers is proposed. We show that the fractional Fourier transform (FrFT) of the input signal can be electronically implemented with a complexity equivalent to the conventional fast Fourier transform (FFT); on the other hand, the planar device that implements the FrFT in the optical domain is similar to the passive arrayed waveguide grating (AWG) device that performs the FFT. We analyze the spectral efficiency, the peak-to-average power ratio (PAPR) and the frequency offset sensitivity of a FrFT-based optical OFDM system, and make an accurate comparison with the standard FFT-based implementation.