Analysis modulation formats of DQPSK in WDM-PON system

In the modulation and demodulation methods of the optical differential quadrature phase shift key (DQPSK) and the different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) are introduced, studying the different optical signals in the 40 Gb/s high speed transmission system. The system is simulated in 200 km optical fiber by way of dispersion compensation. It is showed that the ability of anti-dispersion and anti-PMD (polarization mode dispersion) is better in the CS-RZ–DQPSK modulation format, and this format has the smallest eye-opening penalty (EOP) with a wider range of power into the optical fiber.