title: Fine tuning of optical signals in nanoporous anodic alumina photonic crystals by apodized sinusoidal pulse anodisation.
abstract: In this study, we present an advanced nanofabrication approach to produce gradient-index photonic crystal structures based on nanoporous anodic alumina. An apodization strategy is for the first time applied to a sinusoidal pulse anodisation process in order to engineer the photonic stop band of nanoporous anodic alumina (NAA) in depth. Four apodization functions are explored, including linear positive, linear negative, logarithmic positive and logarithmic negative, with the aim of finely tuning the characteristic photonic stop band of these photonic crystal structures. We systematically analyse the effect of the amplitude difference (from 0.105 to 0.840 mA cm-2), the pore widening time (from 0 to 6 min), the anodisation period (from 650 to 950 s) and the anodisation time (from 15 to 30 h) on the quality and the position of the characteristic photonic stop band and the interferometric colour of these photonic crystal structures using the aforementioned apodization functions. Our results reveal that a logarithmic negative apodisation function is the most optimal approach to obtain unprecedented well-resolved and narrow photonic stop bands across the UV-visible-NIR spectrum of NAA-based gradient-index photonic crystals. Our study establishes a fully comprehensive rationale towards the development of unique NAA-based photonic crystal structures with finely engineered optical properties for advanced photonic devices such as ultra-sensitive optical sensors, selective optical filters and all-optical platforms for quantum computing.
authors.affiliation: School of Chemical Engineering, The University of Adelaide, Engineering North Building, 5005 Adelaide, Australia. abel.santos@adelaide.edu.au and Institute for Photonics and Advanced Sensing (IPAS), The University of Adelaide, 5005 Adelaide, Australia and ARC Centre of Excellence for Nanoscale BioPhotonics (CNBP), The University of Adelaide, 5005 Adelaide, Australia.
authors.forename: Abel
authors.initials: A
authors.lastname: Santos
authors.affiliation: School of Chemical Engineering, The University of Adelaide, Engineering North Building, 5005 Adelaide, Australia. abel.santos@adelaide.edu.au and Institute for Photonics and Advanced Sensing (IPAS), The University of Adelaide, 5005 Adelaide, Australia.
authors.forename: Cheryl Suwen
authors.initials: CS
authors.lastname: Law
authors.affiliation: School of Chemical Engineering, The University of Adelaide, Engineering North Building, 5005 Adelaide, Australia. abel.santos@adelaide.edu.au and Temasek Polytechnic, 21 Tampines Avenue 1, 529757 Singapore, Singapore.
authors.forename: Dominique Wong
authors.initials: DW
authors.lastname: Chin Lei
authors.affiliation: School of Chemical Engineering, The University of Adelaide, Engineering North Building, 5005 Adelaide, Australia. abel.santos@adelaide.edu.au.
authors.forename: Taj
authors.initials: T
authors.lastname: Pereira
authors.affiliation: School of Chemical Engineering, The University of Adelaide, Engineering North Building, 5005 Adelaide, Australia. abel.santos@adelaide.edu.au.
authors.forename: Dusan
authors.initials: D
authors.lastname: Losic