Large area sub-wavelength azo-polymer gratings by waveguide modes interference lithography

Except for the commonly used surface plasmon polaritons (SPPs), in this letter we demonstrate that waveguide modes (WMs) can realize the large area sub-wavelength gratings. Both transverse-magnetic (TM) and transverse-electric polarized beams can be used in this method, while for the lithography based on SPPs only TM polarized beam is applicable. The WMs interference lithography has the advantages of low heat loss and much suitable for thick photo-resist films. Large area gratings were inscribed on the azo polymer film at period of 187 nm and 189 nm, which are smaller than the half wavelength of the incident beam.