Rigorous assessment of small-signal analysis for linear and dispersive optical communication systems operating near zero-dispersion wavelength

Abstract

This paper presents a rigorous small-signal theory for linear single-mode fibers taking into account the first- and second-order fiber dispersion. From this theory, exact small signal intensity modulation (IM) and frequency modulation (FM) fiber transfer functions are presented. Exact expressions of the intensity and frequency noise spectra at fiber output due to laser noise taking into account all Langevin noise terms are also derived. Accurate numerical simulations of the IM and FM fiber transfer functions, and intensity and frequency noise spectra after linear transmission along single-mode fiber are compared with theoretical predictions and very good agreement is achieved. In addition, the theoretical predictions are compared with other author's results and the discrepancies are thoroughly explained. A new expression for the transmission distance which can lead to further significant reduction of intensity noise spectrum in systems using single-mode lasers with reduced linewidth enhancement factor is presented. The theoretical and simulation results show that the magnitude of the small-signal IM and FM fiber transfer functions, and the intensity and frequency noise spectra after linear single-mode fiber transmission are not affected by second-order fiber dispersion. The theory indicates that second-order fiber dispersion solely introduces delay distortion in the IM and PM fiber transfer functions. So, with linear transmission second-order dispersion effects on the intensity and frequency noise have proved to be irrelevant even for very long broad-band fiber systems.