Grating couplers in planar polymer waveguides with beam shaping properties

Abstract

Investigations on input and output grating couplers with asymmetric triangular (blazed) profiles for planar polymer waveguides are reported. With blazed gratings a high outcoupling efficiency into one direction, either substrate or superstrate is achieved. The gratings are written directly into the waveguiding polymer layer by electron beam lithography and are replicated by embossing. Electron dose control across every grating period results in asymmetric blazed corrugation of the grating. Additionally, variation of the electron dose across the whole grating leads to a variable corrugation depth along the grating length. Two types of waveguide gratings were designed and produced, blazed corrugated gratings with constant groove depth and with variable groove depth, respectively. Input efficiencies of about 40% for gratings with constant grating depth were measured. The original gratings were replicated into nickel by electroplating. For a replicated grating we attained an efficiency of the outcoupled light into one diffraction order of about 74%. Waveguide grating couplers with blazed profile and variable grating groove depth are investigated. Thus, the intensity distribution of the outcoupled light can be varied and the field profile was matched to a Gaussian like profile.