Robust, ultralow-loss, and broadband light-recycling for a nanophotonic delay line

The optical delay line is a key building block for applications in photonics. It requires low loss, wide bandwidth, and small footprint. In this work, we adopt the light recycling approach based on spatial-mode multiplexing, and achieve high performance with a Mach-Zehnder interferometer (MZI)-based design, which significantly increases the fabrication error tolerance. The proposed nanophotonic delay lines allow fabrication errors of ±10 nm over the broad bandwidth of 100 nm while maintaining the excess insertion loss below 0.5 dB. It will enable power-efficient, ultralow-loss, small-footprint, and broadband optical information processing capabilities in diverse applications.