Review of Optical Transmission Using Rapidly-Dispersed Signals

Abstract

As the operating bit rate of a system increases, the signal-to-noise ratio (SNR) requirement increases, necessitating higher launched signal power, which can increase signal degradation from fiber nonlinearities such as self-phase modulation (SPM). The short-pulse return-to-zero (RZ) [1-8] modulation format offers significant advantages for transmission at 40 Gb/s and beyond in dispersive fibers. The idea is to disperse the pulses as quickly as possible, thereby creating an intensity pattern due to overlapping pulses that varies rapidly with fiber position. The accumulated effect of the fiber nonlinearity is averaged out over many bit slots and the overall signal degradation is reduced. This concept is distinctly different from soliton or standard dispersion-managed approaches, which attempt to control the nonlinear degradation by reducing pulse interactions. In fact, in order to differentiate it from other approaches, it has been called “pseudo-linear transmission” [3] or “tedon transmission” [7] after the verb “to ted,” meaning “to scatter; to dissipate”. In this paper, we review the theoretical and experimental work that has been done in this area. We also report computer simulations showing the effectiveness of the short-pulse RZ format in mitigating nonlinear effects.