Highly Efficient and Tunable Linear-to-Circular Polarization Conversion Enabled by Topological Unidirectional Guided Resonance

The absence of natural sources of circularly polarized light has created a critical demand for high-performance polarization converters in emerging technologies such as quantum information processing, biomedical diagnostics, and advanced magneto-optical recording systems. Despite significant efforts, linear-to-circular polarization converters that combine high efficiency with tunability remain scarce. In this paper, we present a multifunctional and tunable device with 99.9% efficiency for converting linear to circular polarization in the telecom wavelength range. It can also function as a phase-only compensator with a controllable phase range of 1.93π while maintaining a reflectance above 99%. The angular sensitivity analysis indicates that the device can tolerate incidence angles ranging from 8 to 10.4 degrees. This high-efficiency polarization conversion device offers significant advantages in integrated optics due to its multifunctionality and tunability and has promising applications in optical phased-array radars and quantum communication.