Optical engineering of nanoporous photonic crystals by Gaussian-like pulse anodization

Abstract

A new class of nanoporous anodic alumina photonic crystals (NAA–PCs) are optically engineered by four distinct forms of Gaussian-like pulse anodization (GLPA) – Gaussian, Lorentzian, logarithmic normal, and Laplacian. NAA–PCs produced by GLPA under current density control conditions show well-resolved, spectrally tunable photonic stopbands (PSBs), the features of which – central wavelength, full width at half maximum, intensity, and quality factor – can be precisely tuned across the UV–visible spectrum by the input Gaussian-like current density pulses. Effects of type, width, and period of Gaussian-like current density pulses on the structural and optical properties of NAA–PCs are systematically assessed. Comprehensive electrochemical, structural, and optical characterizations allow us to elucidate the interplay of input GLPA profile and structural features in determining forbidden light propagation within these NAA–PCs. Sensitivity of these PC structures toward changes in their effective medium are determined by quantifying spectral shifts in their characteristic PSB upon infiltration of their nanoporous structure with analytical solutions of alcohol mixtures with varying refractive index, from 1.362 to 1.383 RIU. It is found that, at fixed anodization period, NAA–PCs produced by Laplacian current density pulses achieve the highest sensitivity (105 ± 4 nm RIU⁻¹) and, for a given type of GLPA, NAA–PCs produced with longer anodization period achieve higher sensitivity (123 ± 10 nm RIU⁻¹ for NAA–PCs fabricated by Gaussian pulses with a 1400 s-period). Our advances provide exciting new opportunities for future developments of high-quality NAA–PCs with broad applicability across various photonic technologies, including optical sensing, photocatalysis, lasing, and optical encoding.