  We design, fabricate and experimentally demonstrate a highly efficient
adiabatic mode converter for coupling light into a silicon slot waveguide with
a slot width as large as 320nm. This strip-to-slot mode converter is optimized
to provide a measured insertion loss as low as 0.08dB. Our mode converter
provides 0.1dB lower loss compared to a conventional V-shape mode converter.
This mode converter is used to couple light into and out of a 320nm slot
photonic crystal waveguide, and it is experimentally shown to improve the
coupling efficiency up to 3.5dB compared to the V-shape mode converter, over
the slow-light wavelength region.
