On-chip broadband Mach-Zehnder interferometer based on a broadband taper-section phase shifter

In this paper, we propose a new broadband nulling interferometer based on the Si₃N₄/SiO₂ platform which utilizes a π-phase shifter. This π-phase shift multimode interference Mach-Zehnder interferometer (πPS MMI-MZI) leverages a novel low phase shift error (PSE) and broadband taper-section phase shifter (TSPS). For the TSPS, our simulation predicts an unprecedented PSE from 1450 nm to 1650 nm for the two- and three-section TSPS of 1^o and 0.02^o, respectively. Our experimental results demonstrate a PSE of 1^o within a 190 nm bandwidth for the two-section TSPS. A slightly adjusted TSPS gives an even lower PSE of 0.6^o within a narrower bandwidth of 90 nm. With the help of the TSPS, the πPS MMI-MZI shows a significant improvement in extinction ratio compared to the conventional MMI-MZI. Simulations predict an extinction ratio of 50 dB within a 150 nm bandwidth. Experimental measurements demonstrate a 40 dB extinction ratio within a 100 nm bandwidth. The broadband TSPS, as well as the broadband πPS MMI-MZI, pave the way for novel high performance photonic integrated circuits.