Ultracompact and Broadband Silicon-Based Strip-to-Slot Mode Converter

An ultracompact and broadband strip-to-slot mode converter based on subwavelength grating (SWG) structures is proposed and analyzed, where an SWG multimode waveguide combined with two SWG-wire tapered transitions at its both ends is used to connect the input strip and output slot waveguides. In this SWG multimode waveguide, a twofold image can be easily formed based on the symmetric interference for the central input, and then this image can be further converted into the output slot mode due to similarity of their field distributions. Based on this mechanism, we optimize the structural parameters and obtain a device length of ~4.3 μm (SWG multimode waveguide length is only 1.4 μm) with an insertion loss (IL) and a reflection loss (RL) below 0.36 and -20 dB, respectively, in an ultra-wide wavelength range covering the O, E, S, C, L, and U bands (IL = 0.19 dB and RL = -28.72 dB at 1.55 μm).