Abstract
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.
© 2010 IEEE
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