Dynamics of Free Carrier Absorption and Refractive Index Dispersion in Si and Si/PolySi Microrings

Abstract

We report pump-probe measurements of time resolved optical transmission spectra of Si and Si/poly-Si microrings after high free carrier densities have been generated by twophoton absorption of the pump pulse. From measurements, we can extract the recovery dynamics of free carrier absorption, refractive index dispersion, generated free carriers and finally the effective initial free carrier lifetimes. The method is validated by comparing modelling and simulations with measurements; the obtained results are in very good agreement with what predicted by the Shockley-Read-Hall recombination model for trap assisted recombination. We also propose a method for determining the empirical relations for free carrier absorption and refractive index dispersion in poly-Si waveguides.

Design of Silicon Photonic Microrings with complex waveguide cross-sections and minimal non-linearity

“…This result arises from the free carriers diffusion and higher trap density associated to the polysilicon material. In all the cases, the carrier lifetime is dependent of the circulating power, as we already analyzed in our previous works [9], [19].…”

“…where α 0 is linear loss, ∆α F C (x, y) is the local variation of the loss due to free-carrier absorption [18], [19] and t is transmission coefficient at the MRR coupler, t = √ 1 − k 2 in which k is MRR coupling coefficient. While I opt accounts for the transverse profile of the guided mode:…”

“…From this expression we can observe that, in the case of a constant carrier distribution over the whole cross-section (as in the Si Strip waveguide), we obtain the simple expression ∆n ef f,F CD = Γ • ∆n F CD [18], [19], where Γ is optical confinement factor in the silicon core. ∆n F CD is defined as [18]:…”