Efficient Fiber-to-Slot-Waveguide Grating Couplers Based on a Double-Strip Waveguide

We propose and experimentally demonstrate a fiber-to-slot-waveguide grating coupler based on a double-strip waveguide, together with a double-strip-to-slot waveguide mode converter. By employing the double-strip waveguide, we improve the coupling efficiency from a fiber to the slot waveguide by ~ 1.2 dB, compared with previous grating-based two-stage schemes. In addition, the double-strip-to-slot waveguide mode converter, consisting of two S bends and a taper pair, occupies a short conversion length of only 4 μm. Parameters, including taper length and S-bend length are numerically optimized. Bandwidth and fabrication error tolerance are also analyzed. Experimental results verify the feasibility of the proposed scheme.