Coupling efficiency of single mode fiber with photonic integrated circuit based on Si$_3$N$_4$

This work is devoted to edge coupling of optical fibres with waveguides of Si$_3$N$_4$-based photonic integrated circuits. At the edge coupling splicing of single-mode optical fibre with high numerical aperture fibre was utilised to reduce the mode field diameter of optical fibre, and for photonic integrated circuit, a field mode converter based on inverse linear taper was employ. The inverse linear taper is a trapezoidal prism which is in contact with a wider part the waveguide and narrowing to 0.3 $\mu$m to the ends of the crystal of the photonic integrated circuit, the height of the trapezium lying at the base of this prism is 300 $\mu$m. Experimentally demonstrated the possibility to reduce the coupling loss to 0.7 dB per edge.