Thermo-optical dynamics of a nonlinear GaInP photonic crystal nanocavity depend on the optical mode profile

Abstract

We measure the dynamics of the thermo-optical nonlinearity of both a mode-gap nanocavity and a delocalized mode in a Ga0.51In0.49P photonic crystal membrane. We model these results in terms of heat transport and thermo-optical response in the material. By step-modulating the optical input power we push the nonlinear resonance to jump between stable branches of its response curve, causing bistable switching. An overshoot of the intensity followed by a relaxation tail is observed upon bistable switching. In this way, the thermal relaxation of both the localized resonance and the delocalized resonance is measured. Significant difference in decay time is observed and related to the optical mode profile of the resonance. We reproduce the observed transient behavior with our thermo-optical model, implementing a non-instantaneous nonlinearity, and taking into account the optical mode profile of the resonance, as experimentally measured.

Mode mapping Q > 500 000 photonic crystal nanocavities using free carrier absorption

“…This probe absorption is the origin of the TO nonlinearity which causes the wellknown hysteresis behavior shown in Fig. 2(b) [30,34]. Secondly, Fig.…”

“…A pump beam is used to locally heat the PhC, and the resulting thermal change in refractive index leads to a shift in resonance frequency. Previously, our group has shown that with local thermal tuning the mode profile of a high-Q cavity can be recovered with a resolution that is limited by thermal diffusion [28][29][30]. The effective spot size depends on the surrounding medium and it is generally much larger than the optical pump spot, so that even after deconvolution a moderate resolution remains [31].…”

Mode Mapping Photonic Crystal Nanocavities with Q>5×105 Using Free-Carrier Absorption

“…This probe absorption is the origin of the TO nonlinearity which causes the well-known hysteresis behavior shown in Fig. 2(b) [31,36]. Figures 2(c) and 2(d) show how direct heating by the pump causes a redshift of the cold cavity resonance λ 0 when the thermal profile overlaps with the optical mode profile of the resonance [29].…”

“…A pump beam is used to locally heat the PhC, and the resulting thermal change in refractive index leads to a shift in resonance frequency. Previously, our group has shown that with local thermal tuning the mode profile of a high-Q cavity can be recovered with a resolution that is limited by thermal diffusion [29][30][31]. The effective spot size depends on the surrounding medium and is generally much larger than the optical pump spot, so that even after deconvolution a moderate resolution remains [32].…”