Ultrabroadband and compact 2 × 2 3-dB coupler based on trapezoidal subwavelength gratings

We propose and experimentally demonstrate an ultrabroadband and compact 2 × 2 3-dB coupler based on the trapezoidal subwavelength gratings (SWGs). The adiabatic coupling is achieved between a trapezoidal SWG waveguide and a reversely tapered strip waveguide, which contributes to the ultrabroad operation bandwidth and the compact footprint of the coupler. Numerical results prove that our device has a power splitting imbalance of < ± 0.5 dB and an excess loss of < 0.2 dB in the ultrabroad bandwidth of 300 nm from 1400 nm to 1700nm, with a coupling length of 4.4 µm and a total length of 24.4 µm. The fabricated device is characterized in a 270-nm bandwidth from 1400 nm to 1670 nm, showing a measured power splitting imbalance of < ± 0.7 dB and an excess loss of < 0.5 dB.