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 non-reciprocal 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.

Schematic of the optical limiting action of a novel imidazo[2,1-b][1,3,4]thiadiazole based small molecule (ThITD3), which blocks high irradiance and transmits low-intensity (less harmful) light.

Diagrammatic representation of excited state assisted two-photon absorption (2PA) behavior of a donor–acceptor type conjugated polymer (P2TPy) exhibiting an extremely low optical limiting threshold.

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A set of four symmetric, butterfly‐shaped 4‐(4‐(decyloxy)phenyl)‐2,6‐di(thiophen‐2‐yl)pyridine (TPY) derivatives 2TPA‐TPY (TPY center and triphenylamine end groups), 2CBZ‐TPY (TPY center and N‐ethyl carbazole end groups), 2TPY‐TPA (triphenylamine center and TPY at the periphery) and 2TPY‐CBZ (N‐ethyl carbazole center and TPY at the periphery) was synthesized. The molecules show reverse saturable absorption (RSA) which is consistent with two‐photon absorption (2PA) associated with excited‐state absorption (ESA) when excited using a 532 nm laser beam. The molecules 2TPA‐TPY and 2TPY‐TPA possess extremely low limiting thresholds of 1.73 and 2.68 J cm−2, respectively. An organic light‐emitting diode (OLED) fabricated from 2TPA‐TPY exhibits green emission with a maximum luminance of 207 cd m−2, a current efficiency (ηCE) of 1.51cd A−1, a maximum power efficiency (ηPmax) of 0.46 lm W−1 and an external quantum efficiency (ηEQE) of 0.48 % at 100 cd m−2.