Self-imaging grating couplers for silicon photonics

Abstract Fiber-to-chip coupling often limits the practical performance of photonic integrated devices. In selecting a coupling strategy, designers balance coupling efficiency, optical bandwidth, fiber-array compatibility, polarization-dependent loss, fabrication complexity, footprint, etc. Recently, self-imaging grating-coupler schemes have been reported on silicon nitride and lithium niobate platforms. Here, we adapt and experimentally evaluate this concept on a silicon photonics platform. Our measurements show moderate coupling efficiency and a clear dependence on the coupling distance. These results indicate that distant-coupled gratings are a viable option for interfaces where physical separation is advantageous, such as coupling to a fiber array with a 45-degree total-internal-reflection end-facet and to free-space optical components.