Cantilever Inverse Taper Coupler With SiO2 Gap for Submicrometer Silicon Waveguides

In this letter, we present a cantilever inverse taper coupler with SiO ₂ gap for coupling optical beam between an optical fiber and a sub-micron Si waveguide. The result shows that the input spot size of 5 μm can be coupled to 500 nm×240 nm silicon waveguide with a coupling loss less than 0.49 dB/facet and a 3-dB misalignment tolerance larger than ± 1.8 μm for both TE and TM modes. The coupling loss for a standard cleaved fibre with the input spot size of 10.5 μm is 3.72 dB/facet (TE) and 2.12 dB/facet (TM). The couplers have shown improvement in misalignment tolerance for the input spot size of 5 μm and in coupling loss for the input spot size of 10.5 μm due to the introduction of SiO ₂ gap in comparison with other reported taper coupler designs. These improvements are achieved without compromising the other performance parameter (coupling loss or misalignment tolerance) and requiring complicated design and fabrication process.