Design of a SOI-based quantum interferometer with ultralow fiber-to-fiber insertion loss

Based on the standard silicon-on-insulator platform, we design an on-chip interferometer at the telecom spectral range, with ultra-low fiber-to-fiber insertion loss. Special attention is given to beams splitters with waveguide tapers instead of single-mode waveguides as input ports. By carefully designing the dimension of the waveguide taper, the multimode mode waveguide and the multi-mode interferometer, the structures can achieve the highest intermode conversion efficiency We numerically demonstrate that the proposed ladder-shaped waveguide taper achieves a high transmission of more than 80%, with an ultra-short length of only 20 mu m. The total insertion loss from the input fiber to output fiber can be reduced down to 1.07 dB. This work holds a great potential in various application, especially for the on-chip quantum interferometer that highly desires the low-loss property.