Impact of initial pulse characteristics on the mitigation of self-phase modulation by sinusoidally time varying phase

Abstract

A simple and efficient approach to suppress undesirable self-phase modulation (SPM) of optical pulses propagating in fiber-optic systems is based on imposing a sinusoidal temporal phase modulation on the pulses to offset the chirp generated by SPM . Here, we present a detailed analysis of this method. We derive an exact formula for the reduction of the SPM-induced rms spectrum broadening of an initially Gaussian pulse enabled by the sinusoidal compensation, and we assess the effects of the initial pulse shape and duration on the effectiveness of the technique by means of numerical simulation. The differences between pre-and postpropagation compensation schemes are also discussed.

Offsetting Self-Phase Modulation in Optical Fibre by Sinusoidally Time-Varying Phase

“…The same trend is observed in the evolution of the spectral Strehl ratio, defined as the ratio of the maximum power spectral density (PSD) of the actual pulse to the PSD obtained assuming a transform-limited pulse and, thus, providing a measure of how close a pulse is to its Fourier transform limit. Following the calculation described in [13] and used by us in [14], we have derived an exact closed formula for the rms spectral width of an initially Gaussian pulse after undergoing SPM and with the corrective phase applied [11]. The rms spectral width evolution predicted by this equation is in perfect agreement with the numerical simulation results [ Fig.…”

“…To corroborate this statement, we have illustrated the case of a hyperbolic secant pulse like those delivered by soliton lasers. Following the same idea of reducing the chirp in the central region of the pulse, one may derive the analogue of the formulae for ω C and A C given in the previous section, for a hyperbolic secant intensity profile [11]. However, we have observed that while this choice of modulation parameters achieves fairly good chirp cancellation near the pulse centre, the deviations from perfect phase compensation on the pulse wings are rather strong, and these result in strong side lobes in the spectrum.…”

“…However, we have observed that while this choice of modulation parameters achieves fairly good chirp cancellation near the pulse centre, the deviations from perfect phase compensation on the pulse wings are rather strong, and these result in strong side lobes in the spectrum. On the other hand, for such pulse shape, optimisation of the parameters of the modulating sinusoid through a scan of the amplitude-frequency space outperforms the parameter choice based on the analytic guidelines, by triggering a threefold decrease in the rms spectrum broadening generated from SPM compared to the analytically calculated modulation and maintaining a high Strehl ratio at large B values [11]. .…”

“…Further, we present an in-depth characterisation of the SPM-mitigation method based on analytic results and numerical simulation of the governing equation. We assess the effects of the initial pulse shape and duration on the effectiveness of the technique, and we highlight the differences between pre-and post-propagation compensation schemes [11].…”