Carrier injection type topological edge state electro-optic Mach-Zehnder modulator based on valley photonic crystals.

Valley photonic crystals (VPCs) and their topological edge states have been widely studied and applied to many passive devices. However, reconfigurable topological photonic devices remain to be further explored. In this work, we propose a Mach-Zehnder modulator (MZM) structure based on silicon VPCs. One arm of the proposed VPC-MZM is doped and driven by forward-biased voltage to achieve intensity modulation. Theoretically, it is demonstrated that the phase-shifting efficiency of the edge state mode is 1.31 times that of traditional strip waveguides. A theoretical model combined with numerical simulations is used to analyze the effects of heavily doped region width and doping concentration on the half-wave voltage-length product V_π · L, extinction ratio (ER), and the modulation bandwidth f_3dB of the VPC-MZM. With appropriate parameters, the V_π · L can reach 0.0036 V·cm, the ER is 20.7 dB, and the modulation bandwidth is 340.18 MHz. The phase shifter length is only 21.1 µm, and the overall size is approximately 16 × 33.9 µm. The proposed modulator shows high modulation efficiency and an extremely small footprint with acceptable modulation speed, which can enable the practical application of reconfigurable topological photonic devices in future optical communication systems.