Enhanced Coupling to Slow Photon Modes in Three‐Dimensional Graded Colloidal Photonic Crystals

Enhanced coupling to slow photon modes at the band‐edge of graded three‐dimensional, thin‐film polymer colloidal photonic crystals (see Figure) is demonstrated. For the gradation, polystyrene latex is etched by exposure to air plasma, yielding a top‐to‐bottom filling‐fraction gradient. By monitoring transmission and corresponding phase spectra upon etching, spectral blue‐shifts and enhanced mode coupling are observed. Also, surface roughness is reduced, resulting in higher structural and optical quality colloidal photonic crystals.