Nonreciprocal Transmission of Circularly Polarized Light via Photothermal Phase Transition in Cholesteric Liquid Crystals

Abstract Nonreciprocal devices, enabling asymmetric light transmission, are essential for many photonic applications. However, nonreciprocal devices driven by circularly polarized incident light, without relying on optical nonlinearity or magnetic fields, have been rarely reported. This study introduces a novel nonreciprocal device based on a photothermally driven cholesteric‐to‐isotropic phase transition (CIT) in cholesteric liquid crystals (CLCs). The device enables nonreciprocal transmission of circularly polarized light (CPL) without requiring external bias, magnetic fields, or optical nonlinearity. By incorporating a polydopamine (PDA)‐doped polyvinyl acetate (PVA) layer for photothermal conversion, the device achieves self‐biasing through heat generated by the incident signal light. The performance is tunable, with transmission contrast and insertion loss adjustable via the PDA concentration. At 808 nm CPL, the device achieves an isolation ratio of 7.7 dB and an insertion loss of 1.1 dB. Additionally, extending the photonic bandgap of the CLCs allows nonreciprocal performance at 405 nm CPL, with a high isolation ratio of 16.5 dB. The device also functions as an optical switch, enabling low‐power signal light transmission with pump light assistance, and shows promise for applications in digital holography. These capabilities highlight the device's potential for use in all‐optical communication networks and chirality‐based photonic systems.