Broadband Mode Coupling with Record‐High Fabrication Tolerance Using the Stimulated Raman Adiabatic Passage Technique

Abstract

Coupled‐waveguide structures are fundamental in photonic integrated circuits for their wide applications in basic optical functions such as directional coupling, polarization handling, and mode manipulation. However, the couplings between waveguides usually suffer from high wavelength and structure sensitivity, which hinders the development of broadband and fabrication‐tolerant devices. Here, a new method based on the stimulated Raman adiabatic passage (STIRAP) procedure is proposed for various kinds of on‐chip mode manipulation such as mode conversion and multiplexing. The coupling process of the STIRAP system is thoroughly explored to reveal the topological nature of STIRAP. The experimental results prove that the mode‐division multiplexer employing the STIRAP scheme has low insertion losses of < 1.8 dB and intermodal crosstalk of < −17.3 dB for all four mode channels over a 100‐nm wavelength range (1480–1580 nm). Thanks to the topological protection of the mode coupling, the proposed multiplexer exhibits unprecedented fabrication tolerance (−80–100 nm) to the structural deviations in waveguide width and gap distance. This work provides an intriguing approach to expanding the working bandwidth and improving the fabrication tolerance of coupled‐waveguide devices, which may find applications in diverse fields including optical communications, optical computing, quantum information processing and beyond.