Tunable Terahertz Topological Photonic Chips Using Silicon/Graphene Heterostructures

Abstract

The emergence of photonic topological insulators (PTIs) in the terahertz band has ushered in a new era for on-chip communication and sensing. To date, most reported terahertz PTIs are based on passive silicon photonic crystals. The development of active PTIs with versatile electrical tunability via novel heterogeneous structures is crucial for the development of multifunctional terahertz photonic chips. Here, electrically tunable terahertz topological photonic chips using a heterogeneous silicon/graphene configuration is demonstrated. Specifically, the graphene and silicon layers are separated by an insulating oxide layer, which functions as a field-effect transistor. The band diagram of the PTIs can be actively tuned by altering the Fermi level of the graphene. It is experimentally demonstrated that both the amplitude and phase of terahertz light can be tuned by controlling its gate voltage. A Mach-Zehnder interferometer device containing two branches of topologically protected waveguides is further developed, which exhibit 36 dB modulation at 277.06 GHz when the same size graphene is used to control one branch. This electrically tuned PTIs have the potential to form a high-rate and large-scale on-chip modulator array. The controllable varied loss characteristics also provide insights into active non-Hermitian topology research for the terahertz band.