Multichannel High-Bandwidth Coupling of Ultradense Silicon Photonic Waveguide Array to Standard-Pitch Fiber Array

摘要

A multichannel tapered coupler interfacing standard 250- $mu$m-pitch low-numerical-aperture (NA) polarization-maintaining fiber arrays with ultradense 20- $mu$m-pitch high-NA silicon waveguides is designed and fabricated. The coupler is based on an array of 12 dual-core glass waveguides on 250-$mu$ m pitch that are tapered to a 20- $mu$m pitch, simultaneously providing both pitch and spot-size conversion. At the wide end, the inner core matches the NA and mode profile of standard single-mode fiber. When drawn and tapered, the inner core “vanishes” and the outer core, surrounded by the clad, matches the NA and mode profile of the on-chip photonic waveguide. Ultradense high-efficiency coupling to an array of Si photonic waveguides is demonstrated using a 12-channel polarization-maintaining-fiber pigtailed tapered coupler. Coupling to Si waveguides is facilitated using SiON spot-size converters integrated into the Si photonic IC to provide 2-3-$mu$m mode field diameters compatible with the tapered coupler. The tapered coupler achieves ${<}1$ dB coupling losses to photonic waveguides. Furthermore, eight-channel coupling is shown with less than ${-}35$ dB crosstalk between channels. Finally, a 640-Gb/s wavelength-division-multiplexing signal is coupled into four waveguides occupying 80 $mu$m of chip edge, providing 160-Gb/s per-channel bandwidths.