Design and fabrication of ultra-compact, low-loss waveguide crossings utilizing subwavelength perforated metamaterial waveguides

This work numerically proposed and experimentally demonstrated ultra-compact, low-loss waveguide crossings utilizing subwavelength perforated metamaterial waveguides (SPMW). By inserting a double-row subwavelength hole array within MMI couplers to generate the SPMWs, more key geometrical parameters can be flexibly and synergistically optimized to more readily implement waveguide crossings with compact size and high performance, e.g., a dual-polarization crossing with ultra-low loss and a multimode one supporting four modes (TE₀, TE₁, TM₀, and TM₁). Simulation results showcase that at a wavelength of 1550 nm, the insertion losses (ILs) are 0.05 dB, 0.58 dB, 0.07 dB, and 0.8 dB for the four-mode crossing, with a compact footprint of 14 μm × 14 μm. The dual-polarization crossing exhibits an ultra-low IL of 0.08 dB (0.07 dB) for the TE₀ (TM₀) mode, respectively, within a size of only 10.8 μm × 10.8 μm. Experimental findings confirm the good performance of the two types of crossings, demonstrating that over a wide wavelength range of ∼90 nm, the ILs of the four-mode one are below 0.57 dB and 1.15 dB for the fundamental and first-order modes, while the dual-polarization one exhibits low ILs of less than 0.28 dB. The design adaptability, low insertion loss, broad bandwidth, multimode operation, and small size underscore the present devices' promising applications in sophisticated hybrid multiplexing systems and others.