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

Abstract

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 $1.8\text{\hspace{0.17em} dB}$ at $1550\text{\hspace{0.17em} nm}$, and the mode conversion loss can be less than $0.5\text{\hspace{0.17em} dB}$. The discussion of the present state of the art is also involved. The proposed coupler can be used in chip-to-chip communication.