title: Subwavelength-grating-assisted broadband polarization-independent directional coupler.
abstract: This Letter presents both numerical and experimental results of a polarization-independent directional coupler based on slot waveguides with a subwavelength grating. The measured coupling efficiency is 97.4% for TE and 96.7% for TM polarization at a wavelength of 1550 nm. Further analysis shows that the proposed subwavelength grating directional coupler has a fabrication tolerance of ±20  nm for the grating structure and that the coupling efficiencies for the two polarizations are both higher than -0.5  dB (∼89%), exceeding the entire C-band (1525-1570 nm) experimentally.
authors.forename: Lu
authors.initials: L
authors.lastname: Liu
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Deng
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Zhou