Pulse reshaping in photonic crystal waveguides and microcavities with Kerr nonlinearity: Critical issues for all-optical switching

We delineate critical issues for “controlling light with light” in photonic crystal PC waveguides coupled to Kerr-nonlinear microresonators. These arise from a fundamental trade-off between switching speed and switching intensity threshold inherent in high-quality Q-factor cavities and b the dynamical nonlinear oscillation of such cavities in response to incident light pulses. Using finite-difference time-domain simulations of electromagnetic pulse propagation, we consider both i a nonlinear Fabry-Perot microresonator embedded within a PC waveguide exhibiting a narrow transmission resonance and ii a nonlinear point defect sidecoupled to a PC waveguide exhibiting a narrow reflection spectrum. We describe self-induced switching from transmission to reflection induced by pulse intensity tuning as well as control of pulse transmission induced by the secondary, continuous cw laser field propagating through the same PC waveguide. For the Fabry-Perot microresonator, a well-defined self-switching threshold is obtained. However, this is accompanied by considerable temporal and spectral distortion of the pulse caused by the oscillatory nonlinear response of the microresonator. When the quality factor of the microresonator is increased, the switching intensity threshold can be lowered but the pulse transit switching time and the pulse distortion are increased. For the side-coupled microresonator, a gradual not sharp self-switching behavior as a function of incident intensity is obtained. For both the Fabry-Perot and side-coupled nonlinear microresonators, control of pulse transmission can be achieved by means of a secondary cw laser field. The cw power required for switching with realistic Kerr nonlinearities is in excess of 1 W/ m2 and may cause optical damage to the semiconducting PC backbone. Both instantaneous and noninstantaneous Kerr-response models are considered. Our results underscore the limitations and trade-offs inherent in the possible control of light with light using Kerr-nonlinear microresonators.