High-Numerical-Aperture Optical Fibers for Low-Loss Coupling with Silicon Photonic Waveguides

摘要

We have developed high-numerical-aperture (NA) single-mode fibers and polarization-maintaining fibers that are suitable for low-loss coupling with silicon photonic waveguides. They have a mode field diameter (MFD) of 4 μm to match those of the edge-coupling spot size converters (SSCs) formed in the silicon photonic waveguides. We utilized the thermally expanded core (TEC) technique to reduce the splice losses between the high-NA fibers and standard fibers with an MFD of 10 μm. Some dopants were co-doped into the inner cladding region of the TEC fibers, increasing the expansion speed of the fiber core. Lower-loss splicing was achieved by increasing the co-doping concentrations. The fiber coupling with the silicon photonic waveguides using an inverted tapered SSC was tested. The measured coupling loss was as low as 3 dB/2 facets using these fibers and it is possible to further reduce this loss.