Actively tunable wideband terahertz topological power splitter with customizable splitting ratio

Abstract Development of robust, efficient, and dynamically-reconfigurable terahertz (THz) photonic circuits can benefit the emerging 6G communication technologies by harnessing the potential of THz spectrum. One essential component of integrated photonic circuits is a power splitter, which enables precise distribution of guided signals needed for routing, multiplexing, and scalability of on-chip networks. Traditional power splitters employing conventional photonic crystal designs are often limited by significant transmission losses and sensitivity to fabrication imperfections. These factors limit their integration in densely layered and multifunctional photonic circuits. In this paper, a dynamically-reconfigurable power splitter (operating between 320 and 350 GHz), based on THz topological valley photonic crystals (VPC) with a bearded interface, is presented. Replacing the conventional domain boundary between two VPCs with a bearded interface improves the input coupling efficiency, thereby facilitating enhanced power flow into the structure due to superior mode spacing. Filling of polyethylene terephthalate into the voids of the bearded interface reduces the insertion loss of the power splitter by ∼ 1.5 dB due to superior impedance matching. Combining slow-light effects with optically induced changes in silicon conductivity allows dynamic reconfigurability of the splitting ratio. This tuning is achieved by illuminating a selected portion (a circular spot of radius 485 μ m ) of the bearded-interface propagation path leading to one of the output ports with a Gaussian profile laser pump. Increasing the pump intensity from 4 to 40 kW m − 2 changes the splitting ratio from 50:50 to 66:34. At sub- THz free-space wavelength ( ∼ 0.9 mm at 330 GHz), the total footprint of the power splitter is approximately 1 cm 2 ( 11 λ × 11 λ ) . This confirms its high integration density and compactness relative to conventional sub-THz photonic circuits and provides a platform for developing highly integrated, reconfigurable photonic circuits necessary for next generation 6G technologies.