Figure 4 shows the measured probe transmission (colored dots) versus pump-probe delay under different pump energies and with two different probe detunings
d, corresponding to switch-on and -off case. We can find a good agreement between measurements and simulations (colored lines) using the coupled mode theory model employing three carrier rate equations [
5]. In all cases, the transmission recovered in a fast and slow step, similar to the previous findings in Ref. [
3]. The time constants do not depend on experimental conditions, but rather intrinsic structural properties. From the comparisons between simulations and experiments, we concluded that thermal effects were negligible at such a low signal repetition rate (the calculated thermal induced resonance red shift was<0.04 nm) thanks to the high thermal conductivity of InP. For the switch-on case (
d<0), the switching contrast increased with the pump power. When the strong pump pulse injected into the nanocavity, the probe transmission first reduced due to the combination of TPA loss and instantaneous Kerr effect, which resulted in red shifts of the resonance. This reduction was relatively small and therefore not noticeable in the experiments unless very large pump powers were used. Following the Kerr effect, free carriers were generated through TPA, causing free carrier dispersion, which dominates over the thermo-optic effect, red shifting of the cavity resonance, hence the probe transmission was increased. For the switch-off case (
d>0), in contrast, the blue-shift of the cavity resonance causes a probe transmission reduction. In Fig. 4, a switching contrast of ~8 dB can be achieved (switch-on case) with an energy of 180 fJ (a lower energy consumption of ~85 fJ was demonstrated for a better switching configuration). According to the simulations, the calculated absorbed energy in the nanocavity was as low as on the order of 20 fJ, showing an efficient light-matter interaction enhancement in the nanocavity.