Silicon-Nitride-Integrated Hybrid Optical Fibers: A New Platform for Functional Photonics

Hybrid optical fibers that integrate exotic materials within more traditional silica glass architectures open a route for the development of highly functional all-fiber photonic systems. Here, a compact hybrid optical fiber platform is reported formed by depositing a silicon nitride (SiN_x - nitride-rich) nanolayer onto the surface of fused-silica microfibers via plasma-enhanced chemical vapor deposition. The SiN_x thickness can be precisely tuned over a range of tens of nanometers, while maintaining an ultra-smooth deposition surface, allowing for tunable coupling between the modes guided predominantly in the nanolayer and the fiber core. The effective indices of the hybrid modes display an anti-crossing behavior under resonant conditions, resulting in a rich dispersion landscape that can be tailored via adjusting the SiN_x thickness. By fabricating a SiN_x-silica hybrid microfiber with precise dispersion engineering and a low insertion loss, a flat supercontinuum spectrum spanning >1.5 octaves (−20 dB level) has been generated. The results demonstrate that SiN_x-silica hybrid microfibers can offer a unique combination of broadband transmission and wide tunablity of the mode properties, while still retaining the benefits of robust integration with conventional silica glass fiber networks, providing a rich playground for hybrid fiber-based photonic systems.