Non‐Hermitian Loss‐driven Broadband Low‐Loss on‐Chip Terahertz Photonic SPDT Switch

Abstract Terahertz photonic single‐pole double‐throw (SPDT) switches, which facilitate on‐chip channel control and signal routing, serve as the key components of future terahertz communication and sensing systems. However, broadband and low‐loss on‐chip photonic SPDT switches still present a formidable challenge due to the restricted capability of manipulating terahertz waves in photonic circuits. Here, a non‐Hermitian loss‐driven solution is proposed for achieving broadband and low‐loss terahertz on‐chip photonic SPDT switches. As proof of concept, an all‐silicon terahertz SPDT switching chip is experimentally demonstrated around the center frequency of 125 GHz with a relative bandwidth of 7.2%. The two paths are driven by external optical pumping and evolve adiabatically around an exceptional point (EP) in the unbroken and broken PT‐symmetric phases. Interestingly, the strong non‐Hermitian loss instead enforces the photonic modes to the low‐loss energy level and thereby keeps the switch working at the low‐loss transmission status. As a result, the minimum optical powers require for the ultrafast terahertz communications are only −2 and 1 dBm. Both channels of the SPDT switch support on‐chip 16‐QAM streams with a 36‐Gbit s −1 data rate. The design as a basic building block is anticipated for a myriad of on‐chip applications, including 6G communications, detection, and sensing.