Monolithic photonic integrated circuit for optical performance monitoring of silicon Mach-Zehnder modulator in C and L bands

Monolithic photonic integrated circuit consisting of first-order mode splitter and Ge photodiode is designed, fabricated and characterized for optical performance monitoring of Si Mach-Zehnder modulator. First-order mode splitter is Si waveguide directional coupler with coupling length as short as 16 μm, allowing efficient transfer of first-order mode from main waveguide to sub waveguide. Evanescent-coupling Ge photodiode is fabricated on the sub waveguide. Optical performance monitoring is confirmed with responsivity higher than 50 mA/W in C and L bands.