Silicon chip-integrated fiber couplers with sub-decibel loss

Silicon nanophotonics represents a scalable route to deploy complex optical integrated circuits for multifold applications, markets, and end-users. Most recently, applications such as optical communications and interconnects, sensing, as well as quantum-based technologies, among others, present additional opportunities for integrated silicon nanophotonics to expand its frontiers from laboratories to industrial product development. Within a wide set of functionalities that silicon nanophotonic chips can afford, the availability of low-loss optical input/output interfaces has been regarded as a major practical obstacle that hampers long-term success of integrated photonic platforms. Indeed, fiber-chip interfaces based on diffraction gratings are an attractive solution to resonantly couple the light between planar waveguide circuits and standard single-mode optical fibers. Surface grating couplers provide much more alignment tolerance in fiber attach compared with most conventional edge-coupled alternatives, while retaining the much-needed control of the fiber placement on the chip surface and wafer-level-test capability that the in-plane convertors lack. Here, we report on our recent advances in the development of high-performance fiber-chip grating couplers that exploit the blazing effect. This is achieved with well-established dual-etch processing in interleaved teeth-trench arrangements or using L-shaped grating-teeth-profile geometries. The first demonstration of the L-shaped-based grating coupler yielded a coupling loss of -2.7 dB, seamlessly fabricated into a 300-mm foundry manufacturing process using 193-nm deep-ultraviolet stepper lithography. Moreover, silicon metamaterial L-shaped fiber couplers may promote robust sub-decibel coupling of light, reaching a simulated coupling loss of -0.25 dB, while featuring device layouts (>120 nm) compatible with lithographic technologies in silicon semiconductor foundries.