Broadband directional coupling in aluminum nitride nanophotonic circuits

TL;DR

This paper demonstrates broadband, low-loss directional couplers in aluminum nitride nanophotonic circuits, enabling efficient on-chip optical routing with high extinction ratios and extended bandwidth for advanced photonic applications.

Contribution

The work introduces optimized AlN nanophotonic directional couplers with broad bandwidth and low insertion loss, advancing integrated photonics capabilities.

Findings

Achieved high extinction ratio (>33dB) in Mach-Zehnder Interferometers.

Extended coupling bandwidth by nearly an order of magnitude compared to traditional devices.

Demonstrated variable splitting ratios in three-waveguide couplers.

Abstract

Aluminum nitride (AlN)-on-insulator has emerged as a promising platform for the realization of linear and non-linear integrated photonic circuits. In order to efficiently route optical signals on-chip, precise control over the interaction and polarization of evanescently coupled waveguide modes is required. Here we employ nanophotonic AlN waveguides to realize directional couplers with a broad coupling bandwidth and low insertion loss. We achieve uniform splitting of incoming modes, confirmed by high extinction-ratio exceeding 33dB in integrated Mach-Zehnder Interferometers. Optimized three-waveguide couplers furthermore allow for extending the coupling bandwidth over traditional side-coupled devices by almost an order of magnitude, with variable splitting ratio. Our work illustrates the potential of AlN circuits for coupled waveguide optics, DWDM applications and integrated polarization diversity schemes.