Integrated dual-mode waveguide interferometer

A novel type of interferometer with an ultra-small footprint is presented. The functional principle is based on the excitation of the first and the second order modes in an integrated dual-mode strip waveguide. The light is coupled from a single mode fiber to the dual-mode waveguide by a conventional grating coupler followed by a taper. The difference in the mode propagation velocity leads to a phase difference between the fundamental mode and the second order mode. A proof of concept in the silicon on insulator technology shows promising extinction ratios of around 30 dB.