Abstract
The understanding of free-carrier dynamics in silicon photonic nano-waveguides and micro-cavities is fundamental to several nonlinear optical phenomena. Through time-resolved pump and probe experiments, a complex and nonlinear carrier recombination dynamics is revealed. Our results show that the carrier lifetime varies as the recombination evolves, with faster decay rates at the initial stages (with lifetime of ∼800 ps) and much slower lifetimes at later stages (up to ∼300 ns). The large surface-to-volume ratio in nano-waveguides enables clear observation of the effect of carrier trapping, manifesting as a decay curve that is highly dependent on the initial carrier density. Further, we demonstrate faster recombination rates by operating at high carrier density. Our results, along with a theoretical framework based on trap-assisted recombination statistics applied to nano-waveguides, can impact the dynamics of several nonlinear nanophotonic devices in which free carriers play a critical role, and open further opportunities to enhance the performance of all-optical silicon-based devices.
Highlights
Free-carrier effects have a critical role in future silicon photonic circuits [1,2,3,4]
Both the dispersion and attenuation of optical modes in waveguides and cavities are modified in the presence of excess electron-hole pairs in the silicon core region, effects referred respectively as Free-Carrier Dispersion (FCD) and Free-Carrier Absorption (FCA) [5, 6]
Two regimes can be identified: within the pump pulse duration, the nonlinear loss is dominated by instantaneous non-degenerate Two-Photon Absorption (TPA), while after the pulse the nonlinear loss arises solely from FCA [25,26,27]
Summary
Free-carrier effects have a critical role in future silicon photonic circuits [1,2,3,4] Both the dispersion and attenuation of optical modes in waveguides and cavities are modified in the presence of excess electron-hole pairs in the silicon core region, effects referred respectively as Free-Carrier Dispersion (FCD) and Free-Carrier Absorption (FCA) [5, 6]. These two basic phenomena have been extensively explored in a variety of silicon-based photonic devices and applications. There are a number of nonlinear phenomena impacted by free-carriers in micro-cavities [15, 16]
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