64QAM Vector Radio-Frequency Signal Generation Based on Phase Precoding and Optical Carrier Suppression Modulation

We propose a 64-quadrature-amplitude-modulation (QAM) vector radio-frequency (RF) signal generation and detection via one intensity Mach-Zehnder modulator (MZM) by using optical carrier suppression modulation. In order to obtain an ordinary QAM modulated RF signal after the square-law detection of the photodiode, amplitude preequalization and phase precoding technique are employed. The 1Gbaud 64QAM vector signals performed on various RF carrier frequencies from 20 to 444 GHz are experimentally demonstrated. The bit-error-rate (BER) performance of unbalanced phase precoding adopting 64QAM modulation is investigated. The digital filter based on blind Decision-Directed Least-Mean-Squares (DD-LMS) algorithm is the key digital-signal-processing, which is used to improve system performance. This concept of the generation of 64QAM-modulated vector signal can be employed in the radio-over-fiber (ROF) system.