Ultra-compact and broadband orthogonal coupler between strip and slot silicon waveguides

We propose an ultra-compact and broadband orthogonal coupler between a strip waveguide and a slot waveguide. Numerical simulations show that a 700-nm wide (full width at half maximum) coupling spectrum can be theoretically achieved and a coupling efficiency as high as 73% around 1500-nm wavelength can be obtained. The coupling length is only about 475 nm which makes the coupler very compact. This configuration does not include a tapering section and has a high tolerance to the waveguide height, alleviating the stringent fabrication requirements.