Blue Phase liquid crystals (BPLCs) offer a sophisticated 3D self-assembled scaffold for templating functional nanomaterials. This study investigates the optical coupling within BPLCs doped with Copper (Cu) nanoparticles (NPs), specifically focusing on the interference between localized plasmonic modes and the 3D photonic lattice. Using dark-field hyperspectral imaging (HSI), we resolve the far-field scattering of individual Cu NPs embedded within the BPLC matrix.

A central finding of this work is the experimental observation of Fano resonance, manifested as a distinct spectral asymmetry with a pronounced shoulder and dip—in the broad scattering profile of the Cu NPs. This spectral feature occurs precisely at the wavelength range corresponding to the narrow selective reflection peak of the BPLC lattice. We attribute this to the interference between the broad plasmonic continuum of the Cu NPs and the discrete Bragg modes of the BPLC scaffold. These results are supported by polarized optical microscopy (POM) and temperature-dependent reflection measurements, which confirm the spatial and spectral correlation between NP scattering and the BPLC’s 3D photonic bandgap. These observations are validated through a finite-element method (FEM) framework, using COMSOL Multiphysics to simulate the reflection and scattering spectra. This multimodal approach demonstrates that Cu-BPLC architectures function as tunable, hybrid metamaterials, offering a pathway for designing responsive chiro-optical devices through precision spectral engineering.