Interferometric modulator with phase-modulating and cavity-modulating components (IMPACC) for high linearity microwave applications: technology review

In this invited paper, we review the theoretical model and performance of an Interferometric Modulator with Phase modulating And Cavity-modulating Components (IMPACC). IMPACC has the highest reported SFDR (e.g., 132 dB-Hz) and offers additional advantages compared to other Mach-Zehnder Interferometer (MZI) based electro-optic modulators (e.g., MZI, ring-assisted MZI or RAMZI). The modulator is based on a unique combination of a RF driven phase-modulator (PM) and a ring resonator (RR) within a MZI interferometer. Both the PM and RR in the IMPACC are simultaneously driven by a RF signal of the same frequency, but not necessarily the same amplitude and phase. Here, we summarize the non-ideal and oftentimes detrimental effects such as: (1) RF bandwidth limitation due to free spectral range (FSR) of the RR, (2) RR waveguide loss, (3) deviation of RR coupling ratio from the ideal value, and (4) unbalanced MZ splitter/coupler on the performance of both IMPACC and RAMZI. We show that proper choice of RF power split ratio and RF phase for IMPACC compensate these negative effects and recover IMPACC’s ideal performance. Unlike RAMZI, this translates to higher device tolerance, added manufacturing flexibility, and superior modulator performance.