Subwavelength grating slot (SWGS) waveguide on silicon platform

We present a subwavelength grating slot (SWGS) waveguide on silicon platform. The SWGS waveguide is characterized by the merging of a slot structure and a subwavelength grating (SWG) structure. The mode guiding mechanism (SWG slot mode) relies on the combination of surface enhanced supermode (slot mode) in a slot waveguide and Bloch mode (SWG mode) in an SWG waveguide. The mode properties and nonlinearities of silicon-based strip waveguide, slot waveguide, SWG waveguide and SWGS waveguide are studied in detail for comparison. It is found that the designed SWGS waveguide with SiO₂/air cladding features greatly reduced nonlinearity due to the delocalized light from the silicon region. We also optimize the SWGS waveguide with varied geometries (silicon width, slot width, period, duty cycle) using the mode confinement factor and evaluation factor. An ultralow nonlinearity of 3.20 /W/m is obtained. Moreover, we design two types of compatible strip-to-SWGS mode converters, showing favorable performance with broadband high conversion efficiency. The obtained results indicate that the proposed SWGS waveguide with greatly reduced nonlinearity may find potential applications in chip-scale data transmission for optical interconnects. The SWGS waveguide with air cladding or low-refractive-index nonlinear material cladding may also see possible applications in optical sensing and nonlinear optical signal processing.