Grating coupler strategies for integrated non-linear waveguides based on thin film lithium niobate

In a non-linear photonic chip, the waveguide parameters, critical for an efficient grating coupler, are often dictated by the non-linear process. These limitations could lead to poor coupling of light on and off the chip. Here we propose a flexible design strategy to achieve efficient coupling and polarisation separation on the same grating coupler while working in such a restricted parameter space.