All-Optical Diode Action through Enhanced Nonlinear Response from Polymeric Photonic Crystal Microcavity

The search for materials for nanophotonic devices needs a way to overcome the limitations of weak nonlinear optical response due to reduced size. The requirement of a high-power excitation source for inducing nonlinear effects in the active medium poses a hurdle in realizing all-optical and integrated optoelectronic systems. Nanosized optical materials can be embedded in photonic cavities to enhance its optical nonlinear responses through confinement effects. This report systematically investigates the linear and nonlinear optical properties of polymeric 1D-photonic crystals (PhC) with a defect layer incorporated with an imidazo-thiadiazole derivative small molecule. The nonlinear optical studies were carried out by means of a z-scan technique under nanosecond pulse using a Q-switched Nd:YAG laser operating at 532 nm. The resonant excitation creates strong confinement of light in the photonic microcavity and facilitates strong light-matter interaction that induces nonlinear response at low input intensities. A giant enhancement in the nonlinear absorption and optical limiting action was observed for PhC comparing to the bare sample. The significant enhancement in the absorptive nonlinearity is utilized for realizing a practical, on-chip, passive, all-optical diode with a PhC/Au hybrid structure. The asymmetrical nonlinear absorption of the hybrid structure exhibits nonreciprocal light transmission in the nonlinear regime. The high transmittance contrast ratio for forward/reverse bias operation and cost-effective fabrication methods makes our system a potential candidate toward the realization of compact photonic integrated devices.