Optical Density Tuning through Refractive Index Contrast in Periodic and Quasi-Periodic 1D Photonic Crystals

This study investigates the optical density (OD) characteristics of one-dimensional photonic crystals (1D PCs) deposited on a polycarbonate substrate, focusing on the comparative performance of periodic and quasi-periodic architectures. Using the transfer matrix method (TMM), four material pairs with varying refractive index contrasts as SiO₂/ZrO₂, TiO₂/MgF₂, Si/Al₂O₃, and Nb₂O₅/CYTOP were analyzed under transverse electric (TE) and transverse magnetic (TM) polarizations across a broad spectral range. The results demonstrate that periodic structures exhibit a single, well-defined photonic bandgap, with its width and strength strongly dependent on refractive index contrast, incident angle, and polarization. By contrast, quasi-periodic configurations significantly enrich the spectral response: the Double-Period sequence fragments the broad bandgap into multiple, narrower mini-gaps, while the Thue–Morse arrangement produces an even denser distribution of ultra-narrow resonances. These findings highlight the critical role of structural complexity in tailoring wave attenuation, offering enhanced spectral selectivity, multi-channel filtering, and high sensitivity to angular and polarization variations. Owing to these features, the proposed designs are well-suited for applications in optical filtering, protective coatings, biochemical sensing, and photonic devices requiring tunable light management. Overall, this work establishes the effectiveness of quasi-periodic stacking as a powerful design strategy for engineering next-generation photonic crystal systems.