Low-loss coupler between fiber and waveguide based on silicon-on-insulator slot waveguides

We propose a novel optical fiber-to-waveguide coupler for integrated optical circuits. The proper materials and structural parameters of the coupler, which is based on a slot waveguide, are carefully analyzed using a full-vectorial three-dimensional mode solver. Because the effective refractive index of the mode in a silicon-on-insulator-based slot waveguide can be extremely close to that of the fiber, a highly efficient fiber-to-waveguide coupling application can be realized. For a TE-like mode, the calculated minimum mismatch loss is approximately 1.8 dB at 1550 nm, and the mode conversion loss can be less than 0.5 dB. The discussion of the present state of the art is also involved. The proposed coupler can be used in chip-to-chip communication.