A compact silicon-based mode converter using bricked subwavelength grating

Facing with the increasing capacity requirements of on-chip optical interconnects, mode division multiplexing technology (MDM), which leverages different spatial eigenmodes at same wavelength as independent channels to transmit signals, has attracted tremendous interest. Mode-order converters that can convert fundamental high-order modes are key components in MDM systems. However, it is still very challenging achieve compact mode-order high performances. Subwavelength grating (SWG) be equivalent homogenous material, prominent advantages such control over birefringence, dispersion and anisotropy, enabling photonic devices performance. Wheras conventional SWG only needs single-etch step, but implementation structure usually requires a fabrication resolution order 100 nm below, difficult for current wafer-scale technology. The anisotropic response further engineered by introducing bricked topology structure, providing an additional degree freedom design. Meanwhile, requirement also reduced (>100 nm). In this work, we experimentally demonstrate TE<sub>0</sub>-TE<sub>1</sub> TE<sub>0</sub>-TE<sub>2</sub> using subwavelength (BSWG) based on silicon-on-insulator (SOI) minimum feature size BSWG 145 nm. proposed converter, quasi-TE<sub>0</sub> generated region, regarded effective bridge between two TE converted. Flexible conversion realized choosing appropriate structural parameters specific transitions input/output mode. By combing 3D finite difference time domain (FDTD) particle swarm optimization (PSO) method, optimal designed. It TE<sub>0</sub> into TE<sub>1</sub> TE<sub>2</sub> length 9.39 μm 11.27 μm. simulation results show insertion loss <1 dB crosstalk < <b>‒</b> 15 achieved both converters, corresponding working bandwidth 128 (1511~1639 nm) 126 (1527~1653 nm), respectively. measurement indicate less than 2.5 -10 68 (1512~1580 nm, limited laser tuning range coupler).