Electronically Controlled Multi-color Optical Shutter with Metallic Nanostructure

Abstract

Electrically tunable multi-color optical filter structure has been studied employing asymmetrical nanohole array design and a twisted nematic (TN) mode of liquid crystal (LC). Recently, some researches have been reported to get various color states in one unit cell structure, since it can be one of the most important solution for ultra-high integration density of some opto-electrical devices such as a semiconductor based image sensor or a display device. Nanometer level size hole arrays on metal film have shown extraordinary phenomenon, filtering effect on visible light due to surface plasmonic effect mainly. The filtering color can be changed by the control of environmental factors such as a refractive index, a dielectric constant or incident polarization direction. However, most of these control principle is not electrical methods, but the change of material property or mechanical principle, so that it is hard to apply this structure to various opto-electrical devices. In this thesis, in order to solve these limitations, 2-dimensional (2D) asymmetric nanohole array design with electrical polarization rotator function employing a twisted nematic (TN) mode of liquid crystal (LC) has been suggested. Nanohole arrays having different structure factors of x and y axis were fabricated on aluminum film. This asymmetric nanohole array design allows to get two different principle colors and mixed states with modulation of incident light polarization, even if it is a structural fixed design. The polarization state is tuned electrically by TN-LC structure combined with the asymmetrically designed nanohole layer. The color tuning shift is larger than 100nm depended on the design layout of nanohole array. It is not easy to get this wide range color change by a control of refractive index of surrounding materials, generally. The functional ability as electrode of nanohole array on metal film and low driving voltage of TN cell mode can open high probability to apply to various electronic device concepts, such as dynamic display, variable information encoding, anti-counterfeiting. ⓒ 2017 DGIST