Design, fabrication, linear and nonlinear optical properties of metal-dielectric photonic bandgap structures

The linear and the nonlinear optical properties of metallodielectric photonic bandgap (MD-PBG) structures were studied by using linear absorption spectroscopy and a femtosecond nonlinear transmission method. The MD-PBG structure consisted of three bilayers of MgF₂(250 nm)/Ag(30 nm). It was prepared by evaporating MgF₂ and Ag layers alternatively onto a glass plate. The optical transmission spectrum of the prepared MD-PBG structure was found to exhibit several pass bands and a broad photonic bandgap. The photonic bandgap extended throughout most of the visible region from 475 nm to 780 nm. Interestingly, there existed transmissive pass bands corresponding to the Bragg resonances: λ₂ = 410 nm (T = 53.9%), λ₂ = 449 nm (T = 42.9 %), λ₃ = 802 nm (T = 39.6 %) and λ₄ = 878 nm (T = 16.9%). The observed transmission spectra could be described by applying the optical transfer matrix formalism to the periodic metallodielectric multilayer. The number of pass bands was found to increase with increasing number of metal-dielectric pairs, and the band width of PBG was found to increase with increasing dielectric layer thickness. At high laser intensity, the MD-PBG structure exhibited a large nonlinear absorption. The enhanced optical nonlinearity is thought to be due to a bathochromic shift of the low-energy band edge of PBG by the saturable absorption of each metallic layer.