Study on QPSK vector signal generation and transmission based on Turbo equalization

We propose a novel method to generate photonic quadrature-phase-shift-keying (QPSK) vector signal by using only one Mach-Zehnder modulator (MZM). Because of the ?square-law? by the photo-detector, the amplitudes and the phase of the driving radio-frequency (RF) signal changed after detection. So the amplitude and the phase of the driving radio-frequency (RF) signal should be pre-coded before used to drive the MZM. Turbo equalization is investigated in vector signal system to improve the system transmission performance. We experimentally demonstrate and investigate the transmission performance with rates of 1-Gbaud over 40-km single-mode fiber (SMF) transmission. Our experimental results shows that this concept of the generation of QPSK vector signal can be employed in our transmission system architecture based on Turbo equalization. The received sensitivity of QPSK vector signal with code rate 1/2 and 2/3 Turbo equalization at the bit error rate (BER) of 10?4 after 40km SMF transmission are 4dB and 3dB better than the original QPSK signal, respectively. The experimental results show that the QPSK signal with Turbo equalization has better dispersion compensation and error-correcting ability.