Optimized Si_3N_4 grating couplers for relaxed alignment requirements under flood illumination
Grating couplers are essential building blocks to integrated photonic circuits, as they allow surface access to the photonic chip. They are most commonly used in combination with an optical fiber, requiring precise alignment, resulting in a high instrumentation cost. In this paper, an alternate use is proposed: by flood illuminating part of the chip surface, the alignment conditions can be relaxed. The grating coupler parameters were optimized for this coupling method. The novel grating couplers were fabricated in Si3N4 and characterized through flood illumination measurements. At peak wavelength as well as within a 20 nm interval, the coupled power was increased considerably over a smaller coupler, by a factor of 6 and 4.5, respectively. The influence on bandwidth and the required precision of coupling angle were also investigated. These optimized designs for flood illumination can provide a cost-efficient coupling mechanism for numerous applications.