Control of duty ratio in waveguide gratings using a near-field holographic lithography system with a variable aperture

A waveguide grating coupler has been developed for optical coupling between a planar waveguide and an optical fiber by some researchers. In a waveguide grating coupler, the shape of diffracted output beam profiles and their focusing performance are dependent on the variations of duty ratios. Therefore, a control of duty ratio in waveguide grating is important for more efficient optical coupling. However, the patterning of a non-uniform duty ratio in waveguide grating is generally very difficult to realize. In our experiments, we propose a new simple fabrication method, which is a variable aperture system incorporating to near-field holographic (NFH) lithography system, to realize a non-uniform duty ratio in waveguide gratings.