Design, fabrication, and characterization of Mach-Zehnder interferometers

In this paper, the effects of physical parameters on the performance of unbalanced Mach-Zehnder interferometers (MZIs) are numerically studied by solving Maxwell's equations on a cross-section of the waveguide using finite-difference eigenmode method. The MZIs are fabricated by the electron beam lithography with a single etch process on a silicon-on-insulator wafer. The transmission profiles and free spectral ranges (FSRs) of the fabricated MZIs are also measured using a custom-built automated measurement setup and compared with the simulation results of Corner analysis and Monte-Carlo analysis methods. Our comparison reveals that the measured FSRs of the fabricated MZIs are in the range determined by the Monte-Carlo analysis. While all measured FSRs are less than the FSRs indicated by the Corner analysis. Therefore, Monte-Carlo analysis can be used as an accurate numerical method for the study of photonic integrated circuits before fabrication.