Efficient coupling into polymer waveguides by gratings.

Investigations of highly efficient grating couplers for polymer slab and strip waveguides fabricated by electron-beam lithography are reported. A maximum input efficiency of 67% is achieved. The electron-beam direct-writing technique allows one to replicate the original gratings into polymer substrates by embossing. An all-polymeric optical chip with efficient grating couplers is demonstrated. Waveguide grating couplers with blazed profile and variable grating depth are investigated. Thus, the intensity distribution of the outcoupled light is matched to a Gaussian-like profile. A focusing blazed grating that couples the light with an efficiency of 42% into a polymer strip waveguide is reported. A curvature correction of the grating lines allows one to improve the focusing properties.