Silicon-Photonic Electro-Optic Phase Modulators Integrating Transparent Conducting Oxides

Higher-order digital modulation formats are demonstrated by electrically inducing free-carrier concentration changes in thin films of transparent conducting oxides, integrated into well-established silicon-photonic waveguiding architectures. The proposed near-infrared modulators employ as physical platforms the silicon-rib and silicon-slot waveguides, exploiting the highly dispersive and carrier-dependent epsilon-near-zero behavior of transparent conducting oxides to modulate the optical carrier. Advancing the existing studies on conventional amplitude modulation, phase-shift keying formats are investigated in this paper, using a rigorous and physically consistent modeling framework that seamlessly combines solid-state physics with Maxwell wave theory through carrier-dependent material models. The designed in-line modulators achieve Vπ L products in the order of 0.1 Vmm, two orders of magnitude lower than their respective all-silicon or lithium niobate counterparts, accompanied by an insertion loss of about 3 dB/π. Switching speeds in the order of 50 GHz are feasible along with a potential for sub-pJ/symbol energy consumption, meeting the demands for on-chip optical modulation.