Authentication labels based on guided-mode resonant filters.
A guided-mode resonance (GMR) filter with wide angular tolerances is experimentally demonstrated as an authentication label illuminated with unpolarized white light. The proposed filter, based on a free-standing silicon nitride membrane suspended on a silicon substrate, is fabricated by using anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both grating and waveguide structures without a lower cladding layer, i.e., a substrate, are fabricated simultaneously on a silicon nitride membrane. Since the silicon nitride is transparent within the spectra of visible and infrared light, such suspended-membrane-type GMR filters are well suited for applications within the visible spectrum. Moreover, the high refractive index of silicon nitride allows the proposed filters to have strongly modulated gratings and an immunity to high angular deviation. The measured reflection resonance has an angular tolerance up to +/-5 degrees under normal incidence for the wavelength of 629.5 nm.
Wu
Mount-Learn
ML
Department of Optics and Photonics, National Central University, Jhongli, Taiwan. mlwu@dop.ncu.edu.tw
Hsu
Che-Lung
CL
Lan
Hsiao-Chin
HC
Huang
Hung-I
HI
Liu
Yung-Chih
YC
Tu
Zong-Ru
ZR
Lee
Chien-Chieh
CC
Lin
Jian-Shian
JS
Su
Chih-Chieh
CC
Chang
Jenq-Yang
JY