OptiDiff: a spectrum-conditioned diffusion framework for inverse design of multilayer structures with asymmetric reflectance and non-intuitive field-distribution exploration

Designing photonic structures with desired optical responses has been a driving force in nanophotonics, as conventional design workflows are inherently iterative, intuition-driven, and limited by predefined structural configurations. Here we introduce OptiDiff, a spectrum-conditioned diffusion framework that directly maps target spectra to manufacturable material sequences and thickness profiles, enabling the efficient generation of diverse multilayer structure designs. A key capability of OptiDiff is asymmetric reflectance spectra design. Unlike nonreciprocal materials such as magneto-optical media and magnetic Weyl semimetals, OptiDiff generates reciprocal multilayer structure designs with asymmetric reflectance spectra, thereby satisfying distinct spectral requirements for bidirectional incidence, including narrowband reflection peaks, narrowband reflection notches, and long-wavelength reflection edges. Notably, OptiDiff exploits the solution-space diversity inherent in diffusion models to generate diverse multilayer designs with non-intuitive electric-field distribution characteristics. These findings demonstrate that OptiDiff can serve as an efficient framework for designing multilayer structures with bidirectional asymmetric reflection spectra and for exploring diverse solutions with non-intuitive electric-field distributions.