Single and Dual-Level Minimum Shift Keying Optical Transmission Systems

We present optical transmission systems employing minimum shift keying modulation formats of single and dual-amplitude level under linear, weakly nonlinear, strongly nonlinear variation of the lightwave carrier within a bit-period depending on whether the phase variation within a symbol period is linear or nonlinear. These formats are externally modulated, incoherently and differentially detected based on the Mach-Zehnder delay interferometric optical balanced receiver. Transmission performance of these optical transmission systems is evaluated in terms of receiver sensitivity, amplification stimulated emission noise loading, dispersion tolerances. These performance characteristics are compared with return-to-zero (RZ) differential phase shift keying (DPSK) and carrier-suppressed RZ on-off keying modulation formats. Accurate bit-error ratios are obtained and confirmed by different statistical techniques: Monte Carlo, single-Gaussian or multiple Gaussian distributions and generalized Pareto distribution statistical methods, especially when the eye diagrams are distorted. Among the three minimum shift keying (MSK) types, the weakly nonlinear optical MSK is found to be the most promising because of its robust transmission performance and more importantly, its reduced-complexity of the electrical driving signals for transmitter in modulating the lightwave carrier as compared to the linear MSK counterpart. Transmission performance of dual-level MSK optical transmission systems depends on the intensity-splitting ratio of the two levels. The performance of three ratios: 0.7/0.3,0.8/0.2, and 0.9/0.1 are demonstrated. The spectral attributes of 80 Gb/s dual-level MSK optical signals for these three ratios are similar to each other and compatible with that of 40 Gb/s optical MSK, but narrower than that of 40 Gb/s optical nonreturn-to-zero DPSK, hence high spectral efficiency of the dual-level MSK.