Transmission spectrum modulation using complementary plasmonic structures with nanohole and nanodisk arrays

Abstract

Perception of color in the imaging system totally relies on the color filter integrated on photodetectors. Monochromatic color filters have been exploited for multispectral imaging systems. Recently, plasmonic nanostructures offer high feasibility as a color filter based on extraordinary transmission phenomenon. This extraordinary light transmission can provide high tunability and wide tuning range in ultrathin scale. Diverse plasmonic filters based on geometric or material variation have been reported from 2000s. However, these filters are passive types, and thus have several limits such as multiple fabrication, unneces-sary spatial allocation for each spectrum filters, and lack of variety in colors. On the other hands, nanohole structures have noticeable characteristic which can be applied for actively tunable filters. Surface plasmon resonance (SPR) of nanoholes is gradually red-shifted as the incident angle increases, and thus several band-pass spectra within wide tuning range can be acquired by actively controllable angle of incidence. However high order resonances of nanoholes emerge with increasing incident angle and these are also red-shifted, which can cause spectral ambiguity between first order resonance (i.e. targeted pass band) and high order resonances. This work reports complementary plasmonic nanostructure which has actively tunable SPR by vary-ing incident angle. The complementary plasmonic structure (CPS) consists of glass nanopillar arrays (GNA), nanodisk arrays (NDA), and nanohole arrays (NHA). NDA are complementarily located above the nanohole arrays with same diameter of holes and disks. The CPS facilitate angular sensitivity of NHA by introducing extinction resonance of NDA. The extinction resonance is coupled to high order SPRs and thus, attenuates redundant resonances except for first order SPR of NHA. The attenuation was simulated using finite differ-ence time domain (FDTD) methods, and found to occur in well-controlled structure dimensions. The dimen-sion of CPS is determined by period of arrays, diameter of holes, thickness of metal and height of GNA. Di-ameter and thickness was used to tune the extinction spectra of NDA in order to maximize attenuation rate. Period and height determined the properties of first order SPR such as peak position, angular sensitivity, and bandwidth. Angular sensitivity of NHA maintains even after the NDA is combined and affects NHA spec-trum. The CPS improves the applicability for tunable filters by facilitating angular sensitivity and attenuating redundant resonances.