  Efficient fiber-to-waveguide light coupling has been a key issue in
integrated photonics for many years. The main challenge lies in the huge mode
mismatch between an optical fiber and a single mode waveguide. Herein, we
present a novel fiber-to-waveguide coupler, named "L-coupler", through which
the light fed from the top of a chip can bend 90{\deg} with low reflection and
is then efficiently coupled into an on-chip Si waveguide within a short
propagation distance (<20{\mu}m). The key element is a bent metal-clad
waveguide with a big matched input port. According to our finite-difference
time-domain (FDTD) simulation, the coupling efficiency is over 80% within a
broad range of working wavelengths in the near-infrared regime for a transverse
electric input Gaussian wave. The coupler is polarization-dependent, with very
low coupling efficiency (6%-9%) for transverse magnetic waves. The coupler can
also be used for three-dimensional (3D) chip-to-chip optical interconnection by
efficiently coupling light into an integrated photonic chip from a
vertical-cavity surface-emitting laser (VCSEL), or Si waveguide on another
chip. The work presented in this Arxiv article has been filed as a patent.
Detailed description of this work may be published in future papers.
