Phase Retrieval of Complex OFDM Signal by Solving Temporal Transport-of-Intensity Equation

We simulate the complex signal reconstruction by solving the temporal transport-of-intensity equation (TIE) in a direct detection orthogonal frequency division multiplexing (OFDM) system. At the receiver, by measuring two intensities before and after a dispersive element, we construct a TIE and retrieve the phase information of the complex OFDM signal by solving it. We investigate the influence of the carrier-signal power ratio (CSPR), the value of the dispersion, signal baud rate, sampling rate, laser linewidth, and frequency offset on the performance of phase retrieval (PR). In a 20 Gbaud 16 quadrature-amplitude-modulation (16QAM) OFDM system, the TIE-based direct-detection requires a 12 dB CSPR, which is comparable to Kramers–Kronig (KK)-based receiver and the single carrier TIE scheme. A proof-of-concept adaptive modulation scheme has also been applied to the TIE-based OFDM system.