Assessing Performance of Silicon Photonic Modulators for Pulse Amplitude Modulation

Silicon photonic (SiP) electro-optic modulators are a key component in cost-efficient and integrated optical transmitters. Modulator design traditionally uses figure of merits (FOMs) that characterize modulation efficiency and propagation loss of light, which underestimate the modulator-induced power penalty due to intersymbol interference, as they do not consider the electro-optic bandwidth limitation. We show that in the presence of limited electro-optic bandwidth of the SiP modulator, the conventional FOMs, such as VπL and V παL, are unable to predict the minimum transmitter power penalty (TPP). Normalized optical modulation amplitude (OMAN) is proved through simulation to be a reliable tool to predict the minimal TPP point. Then, we introduce a new FOM that includes not only the efficiency of the modulator, but also the bandwidth limitation from the SiP electro-optic modulator. The new FOM that is derived from OMAN translates the system-level requirements of a PAM-M optical link to the device-level design parameters. This FOM can be hired to optimize driving voltage swing, bias voltage, and phase-shifter length or to simply choose a SiP modulator with minimal imposed TPP.