Systematic identification of crosstalk and bandwidth upper limit in highly cascaded Mach–Zehnder lattice optical filters

Abstract

Crosstalk among channels in wavelength division multiplexing (WDM) filters must be suppressed to enhance receiver sensitivity in direct-detection-based optical communication systems. We present a systematic method to identify the maximum crosstalk and upper limit of the transmission spectrum bandwidth of a highly multi-staged Mach-Zehnder interference (MZI) lattice optical filter with a number of cascade N (N=1,2,…,∞). The scattering matrix including the wafer-level-measurement-based coupling coefficients of directional couplers is used to calculate the transmittance from the input to each output channel and the result is exactly extrapolated to infinite N. This method can be used to design, characterize, and evaluate $N$-cascaded MZI lattice optical filters that must meet strict WDM specifications.