We design, fabricate and experimentally demonstrate a highly efficientadiabatic mode converter for coupling light into a silicon slot waveguide witha slot width as large as 320nm. This strip-to-slot mode converter is optimizedto provide a measured insertion loss as low as 0.08dB. Our mode converterprovides 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 slotphotonic crystal waveguide, and it is experimentally shown to improve thecoupling efficiency up to 3.5dB compared to the V-shape mode converter, overthe slow-light wavelength region.
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