Design And Optical Characterization Of Anodic Aluminum Oxide Planar Waveguide By Spectroscopic Ellipsometry

AAO has been applied to various areas performing in the role of photoniccrystal, mask of nanoscale microstructure and dielectric waveguide etc.. The smallextinction coefficient within the range from IR to UV makes the considerableimportance to be taken for application of slab waveguide and label free bio-detection.However, optical characters(refractive index) and structural parameters of AAO, thewaveguide layer at the same time should be known preliminarily before its usage inlight scattering enhancement and bio-sensing (RI sensing)or related fields. Thus anexact characterization of AAO film is strictly necessary. Methods to determine RI ofthin film are listed as spectroscopic ellipsometry, prism coupling and interferometryetc.. The latter two always need rigorous treatment to ensure small surface roughnessand can’t provide surface roughness and porosity of porous membrane additionally.In this paper, we made a meticulous research of the porous AAO for its optical andstructural properties making use of the spectroscopic ellipsometry(UviselⅡ,HORIBA).AAO has been fabricated to kinds of forms for the advantages ofconvenient production, inert chemical property, high physical intensity and easycontrol of porosity and pore configuration. Such as cylindric vertical pores formedafter two times oxidation and multilevel structure executed by plasma etchingmasked by polystyrene microspheres. Nevertheless, a plain and ordinary way ofAAO manufacture in waveguide-related field is: thin Al film is anodized inelectrolyte just for once and the thickness of the remain Al film is estimated on thebasis of oxidation rate. Another advantage of this method is: we can obtain thewaveguide layer and index-matching layer at the same time omitting the transfer ofwaveguide in case of use of other metals. Additionally the two layers are closeenough to satisfy theoretical simulation by scientific software and performs good physical strength as well. A good analysis of the aforementioned structure providesimportant information for AAO manufacture and waveguide-related area. Wecalculated the existed mode in waveguide through Fresnel equation under theconditions as below: sandwich structure, wavelength of incident light is532nm,dielectrics close to waveguide are separately Ag film and water. The electric fieldintensity in standing wave becomes the maximum when reflectivity is the lowest.However, the maximum of electric field intensity ordinarily doesn’t appear at theinterface of waveguide and water. But we can move the maximum to the place wherewe want it to be through changing related parameters. We did this by software ofMathematic and we simulated the electric field intensity in waveguide by FDTD toensure the result was reached. Therefor we continued to make the wanted AAO filmand we had done much work about characterization of it. We had got the expected RIthat we needed through controlling anodizing time of thin Al membrane,temperature and concentration of electrolyte. Finally we found RI of AAO film isdetermined by both porosity and anodizing extent.