Waveguide grating couplers permit efficient coupling to planar waveguides, complete with relaxed alignment
tolerances and the possibility of wafer scale device testing without cleaving. To date, most solutions have been
implemented as 1D gratings in high index contrast waveguides (typically SOI) with high coupling strengths
and lateral mode converters. Here, we report the design and optimization of 1D grating couplers in polymer
waveguides with much lower index cores (n = 1.8). Basic parameters from grating theory are used as the basis
for FDTD simulations scanning over etch depth and grating period. Several optimizations are tested, including
top claddings, buried dielectric mirrors, and buried metal mirrors. More than 80% coupling efficiency to air is
predicted for a uniform symmetric grating, 20 periods long, with a carefully positioned buried metal reflector.
The designs are intended for monolithic integration in polymeric planar lightwave circuits mass-produced by a
roll-to-roll nanoimprint lithography process, where metallic mirrors can be safely and successfully incorporated.
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