Extra-narrowband metallic filters with an ultrathin single-layer metallic grating**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0704401, 2017YFF0206103, and 2016YFA0203500), the National Natural Science Foundation of China (Grant Nos. 61922002, 91850103, 11674014, 61475005, 11527901, 11525414, and 91850111), and the Beijing Natural Science Foundation, China (Grant No. Z180015).

Abstract

Narrowband and high-transmission optical filters are extensively used in color display technology, optical information processing, and high-sensitive sensing. Because of large ohmic losses in metallic nanostructures, metallic filters usually exhibit low transmittances and broad bandwidths. By employing both strong field enhancements in metallic nano-slits and the Wood’s anomaly in a periodic metallic grating, an extra-narrowband and high-transmission metallic filter is numerically predicted in an ultrathin single-layer metallic grating. Simulation results show that the Wood’s anomaly in the ultrathin (thickness H = 60 nm) single-layer metallic grating results in large field enhancements in the substrate and low losses in the metallic grating. As a result, the transmission bandwidth (transmittance T > 60%) at λ = 1200 nm is as small as ΔλFWHM = 1.6 nm, which is smaller than 4% of that in the previous thin dielectric and metallic filters. The corresponding quality factor is as high as Q = λ/ΔλFWHM = 750, which is 40 times greater than that in the previous reports. Moreover, the thickness of our metallic filter (H = 60 nm) is smaller than 40% of that in the previous reports, and its maximum transmittance can reach up to 80%. In experiments, a narrowband metallic filter with a bandwidth of about ΔλFWHM = 10 nm, which is smaller than 25% of that in the previous metallic filters, is demonstrated.