A Theoretical Sub-0.1 dB Loss Single Mode Fiber-To-Chip Edge Coupler for Silicon Nitride Waveguides

A low loss optical interconnection between optical fibers and photonic integrated circuits is critical for high performance photonic systems. In the past decade, spot size converters, subwavelength waveguide grating (SWG) structures, and different refractive index materials have been applied to allow efficient coupling between the fiber and the photonic chips. However, it is still challenging to achieve low-loss coupling when interfacing high index contrast waveguides such as SiN with SMF-28 fibers. In this work, we report a multilayer edge-coupler using SiOxN materials with different indices to allow for efficient edge coupling between SMF-28 fiber and SiN single mode waveguides. A coupling loss of 0.068 dB for the TM mode was achieved theoretically at a 1550 nm wavelength, with a 1 dB alignment tolerance offset of 2.4 μm.