A detailed description of the non-linear effects in silicon is needed when designing ring resonators in the silicon platform. The optical field propagating in the ring waveguide is strongly absorbed due to two-photon-absorption (TPA) and free-carrier-absorption (FCA), which become more prominent with increasing the input power in the ring. We present a new approach for the modelling of non-linear effects in silicon based ring resonators. We have numerically solved the non-linear problem coupling the variation of refractive index and loss due to TPA, FCA , self-heating and Shockley-Read-Hall (SRH) theory for trap-assisted recombination process. The model is validated by reproducing experimental measurements on a ring and a racetrack resonator having different Q-factors and waveguide cross-sections. As a result, we show that the SRH recombination is the origin of the dependence of free carrier lifetime on the power circulating in the ring and how this dependence is affected by the surface trap density and trap energy level. The model is then applied to the calculation of the maximum power that can incident the silicon rings designed for the Si PIC mirror of a hybrid III-V/Si widely tunable laser.

In this paper we discuss the influence of war as a metaphor in the context of the COVID-19 pandemic. After an introduction on the traditional analysis of the war metaphor, we address the social consequences of using this metaphor, a topic that has been widely debated with regard to public communication in the context of COVID-19. We pay particular attention to a theory that many intellectuals have raised: the possibility that the use of the metaphor in this context is harmful to a democratic society because it may lead citizens to accept limited civil liberties and authoritarian policies. After presenting the extensive literature on the use of the war metaphor before and during the COVID-19 pandemic, in the final section of the paper, we analyse experimental evidence of the effects of this metaphor. In the conclusion, we hint at open questions and suggest that the current evidence does not support claims of direct liberticidal influence.

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.

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