Optical Linearization of Silicon Photonic Ring-Assisted Mach-Zehnder Modulator

Abstract: In high-performance RF photonic systems, the Electro-Optic (EO) modulators play a critical role as a key component, requiring low SWaP-C and high linearity. While traditional lithium niobate (LiNbO$_3$) Mach-Zehnder Modulators (MZMs) have been extensively utilized due to their superior linearity, silicon-based EO modulators have lagged behind in achieving comparable performance. This paper presents an experimental demonstration of a Ring Assisted Mach Zehnder Modulator (RAMZM) fabricated using a silicon photonic foundry process, addressing the performance gap. The proposed RAMZM modulator enables linearization in the optical domain and can be dynamically reconfigured to linearize around user-specified center frequency and bias conditions, even in the presence of process variations and thermal crosstalk. An automatic reconfiguration algorithm, empowered by Digital-to-Analog Converters (DACs), Analog-to-Digital Converters (ADCs), Trans-Impedance Amplifiers (TIAs), and a digital configuration engine, is developed to achieve linearization, resulting in a spurious-free dynamic range (SFDR) exceeding 113 dB.Hz$^{2/3}$. Furthermore, a biasing scheme is introduced for RAMZMs, significantly enhancing the modulation slope efficiency, which in turn yields a tone gain of over 13 dB compared to its standard operation. This reconfigurable electro-optic modulator can be seamlessly integrated into integrated RF photonic System-on-Chips (SoCs), leveraging the advantages of integration and cost-effectiveness.