Compact and broadband dual-polarization waveguide crossing utilizing subwavelength-hole-assisted MMI couplers

In this Letter, an ultracompact silicon-based waveguide crossing for dual polarizations is proposed and experimentally demonstrated using subwavelength-hole-assisted multimode interference couplers. Thanks to the flexible and easy dispersion engineering in the introduced subwavelength-hole-assisted multimode interference couplers, the reduced and equal beat lengths for dual polarizations are accessible via careful parametric optimization, consequently enabling a substantially reduced device size. Experimental results indicate that the proposed crossing (13.6 × 13.6 µm in size) features a low insertion loss of 1.03 dB (0.76 dB) and low crosstalk of -32.5 dB (-37.8 dB) at a central wavelength of 1550 nm for TE (TM) mode, with a broad bandwidth of ∼80 nm for crosstalk of