Nonlinearity and in-line residual dispersion tolerance of π-AP-RZ and CS-RZ modulation formats in 40-Gb/s transmission over standard single-mode fiber

We achieved a 40% increase in 40-Gb/s transmission distance in links with exact dispersion compensation through suppression of nonlinear distortion by using the alternate-phase return-to-zero (AP-RZ) modulation format. A novel experimental technique was used to compare in-line residual dispersion tolerances, and it was found that AP-RZ is less dispersion tolerant than conventional RZ and carrier-suppressed RZ (CS-RZ) when both linear and nonlinear transmission are considered. Maximum dispersion tolerance of ±50 ps/nm over 300 km was shown to be possible using CS-RZ.