Ultra-stable waveguides for on-chip integration of hBN emitters

Integrating a quantum light source with photonic circuits is crucial for reliable quantum photonics. Layered hexagonal boron nitride (hBN) has gained considerable interest as an excellent room-temperature quantum light emitter. However, high-temperature (> 900 °C) thermal annealing is generally necessary to create defect emission in layered hBN, which poses a great challenge for photonic integration. Here, we report ultra-stable optical waveguides (Type T) fabricated by ultrafast laser direct writing within glass. The laser-induced local densification relying on the temperature gradient and pressure wave propagation, endows waveguides with ultra-high stability against high-temperature up to 1100 °C, which provides a fascinating platform for integration of hBN emitters. We develop a waveguide/hBN butt-coupling integrated device. Efficient emissive defects are created in the integrated hBN with single pulse ultrafast laser irradiation a and the subsequent high temperature annealing at 950 °C, and the emission can propagate through the waveguide due to the strong coupling between waveguide and hBN. These findings present a promising pathway towards scalable photonic chips for applications in integrated quantum photonics.