Compact and robust 2 x 2 fast quasi-adiabatic 3-dB couplers on SOI strip waveguides

We design and experimentally demonstrate compact and robust fast quasi-adiabatic (FAQUAD) couplers for silicon-on-insulator (SOI) strip waveguides. The mode evolution region of the coupler is optimized by the FAQUAD protocol, achieving shortcuts to adiabatic mode evolution in a short length of 11.7 mu m. 3-dB couplers with measured bandwidths (3 dB +/- 1 dB) larger than 75 nm over temperature range from 20 degrees C to 50 degrees C are designed and fabricated using standard CMOS-compatible optical lithography, with the smallest device footprint of 53.7 x 4 mu m(2) . Devices with longer mode evolution regions are also evaluated by simulations and experiments. 3-dB couplers with a footprint of 87.6 x 4 mu m(2) show larger than 85 nm bandwidths (3 dB +/- 0.5 dB) over the same 30 degrees C range.

Automated summary

The study demonstrates compact and robust fast quasi-adiabatic (FAQUAD) couplers for silicon-on-insulator (SOI) strip waveguides, achieving shortcuts to adiabatic mode evolution in a short length. Couplers with measured bandwidths over a temperature range are designed and fabricated using standard CMOS-compatible optical lithography, showcasing high performance in a small device footprint. Devices with longer mode evolution regions also show promising bandwidths over a temperature range in simulations and experiments.