Impact of Free Carriers on Modulational Instability in Silicon-on-insulator Nanowaveguides

TL;DR

This study numerically investigates how free carriers influence modulational instability in silicon-on-insulator nanowaveguides, revealing new gain phenomena in normal dispersion regimes and ways to control MI gain through free carrier lifetime adjustments.

Contribution

It reports the first observation of MI gain in normal SOI nanowaveguides without higher order dispersion, highlighting free carriers' role and methods to modulate MI gain.

Findings

Free carriers affect MI gain spectra at low powers.

MI gain occurs in normal dispersion SOI nanowaveguides without higher order dispersion.

Reducing free carrier lifetime suppresses MI gain in anomalous waveguides.

Abstract

We have numerically studied the effect of free-carrier-induced loss and dispersion on the modulational instability (MI) gain at low input powers in silicon-on-insulator (SOI) nanowaveguides with normal and anomalous second-order dispersion. We have shown that the free carriers affect the gain spectra even at low input powers. First time we have reported the gain in normal SOI nanowaveguides even in the absence of higher order dispersion parameters, which is due to the interaction of free-carrier-induced dispersion and nonlinearity. The MI gain in an anomalous SOI nanowaveguide vanishes even at a few milliwatt range of input power due to this interaction. We have shown that the gain could be achieved in an anomalous nanowaveguides by reducing the free carrier lifetime.