Engineering nonlinear optical absorption through slow-photon effects in calix[4]resorcinarene-based nonlinear distributed Bragg reflectors.

Periodic dielectric nanophotonic structures provide an effective platform for enhancing light-matter interactions and tailoring nonlinear optical responses at low excitation powers. In this work, we demonstrate enhanced nonlinear optical absorption and improved optical limiting behaviour of C-4 methoxyphenylcalix[4]resorcinarene (CMPCR) using a nonlinear distributed Bragg reflector (NDBR) fabricated by alternate spin coating of poly(9-vinylcarbazole) (PVK) and CMPCR-incorporated cellulose acetate (CA) layers. The NDBR was designed such that its short-wavelength photonic band edge coincides with the 532 nm excitation wavelength of an Nd:YAG laser, enabling slow-photon effects and enhanced local electromagnetic field confinement near the band edge. Owing to this enhanced photon confinement, the embedded CMPCR exhibits significantly amplified nonlinear optical absorption and improved optical limiting performance compared to the reference film. The device shows efficient optical limiting with a low limiting threshold of 0.49 J cm-2 at an input intensity of 0.18 GW cm-2. These results demonstrate that photonic band-edge engineering is an effective strategy for amplifying nonlinear optical responses in organic materials and highlight the potential of CMPCR-based NDBRs for compact, low-cost, and energy-efficient all-optical limiting applications.