Maskless nanostructure photolithography by ultrahigh-order modes of a symmetrical metal-cladding waveguide

To fabricate fine patterns beyond the diffraction limit, a nanostructure photolithography technique is required. In this Letter, we present a method that allows sub-100-nm lines to be patterned photolithographically using ultrahigh-order modes from a symmetrical metal-cladding waveguide (SMCW) in the near field, which are excited by continuous-wave visible light without focusing. The etching depth of the nanopattern reaches more than 200 nm. The localized light intensity distribution can be used to map the photoresist exposure pattern, which agrees well with our theoretical model. This technique opens up the possibility of localizing light fields below the diffraction limit using maskless and lower power visible light.