Ultralow‐Loss Silicon Photonics beyond the Singlemode Regime

Abstract Silicon photonics beyond the singlemode regime is applied for enabling ultralow‐loss waveguide propagation for the fundamental mode even without any special fabrication process. Here a micro‐racetrack resonator is fabricated with a standard 220‐nm‐SOI (silicon‐on‐insulator) multiproject‐wafer foundry and shows a record high intrinsic quality factor of 1.02×10 7 , corresponding to an ultralow propagation loss of only 0.065 dB cm −1 , which is about 20 times less than that of regular 450‐nm‐wide waveguides on the same chip. A state‐of‐the‐art microwave photonic filter on silicon is then realized with an ultranarrow 3‐dB bandwidth of 20.6 MHz and a tuning range of ≈20 GHz for the first time. A 100‐cm‐long delayline employed the broadened waveguides is also demonstrated with compact 90° Euler‐curve bends, and the measured average propagation loss is about 0.14 dB cm −1 . The concept of silicon photonics beyond the singlemode regime helps solve the issue of high propagation loss significantly. In particular, it enables silicon photonic devices with enhanced performances, which paves the way for realizing large‐scale silicon photonic integration. This concept can be extended further to any other material platforms, such as silicon nitride and lithium niobate. This also brings numerous new opportunities for various applications such as nonlinear photonics, large‐scale photonic integration, quantum photonics, microwave photonics, etc.