Thermally Tunable Reflective Colors of Cholesteric Liquid Crystal for Near‐Infrared Planar Optics

Abstract Manipulating the transmission and reflection characteristics of materials or structures is a pivotal area in optical research. This pursuit is crucial for advancing micro‐nano planar optics, groundbreaking display technologies, and sophisticated optoelectronic devices. Despite these advancements, the challenge of achieving dynamic, broadband control over reflective colors, as well as broadening their applications in planar optics covering visible and near‐infrared (NIR) regions, persists as a critical issue to solve. To address this challenge, this study presents a method for dynamically controlling reflecting colors across broadband using a simple binary cholesteric liquid crystal (CLC) system composed of E7 and R811. Through thermal modulation, the CLC's selective reflection can be reversibly adjusted between the visible (at 463 nm) and NIR (at 967 nm) ranges. Leveraging this capability, planar optics capable of dynamically tunable gratings and holography spanning from the visible to the NIR range are successfully developed. This research offers novel perspectives for the development of dynamically tunable LCs and is poised to accelerate the use of LCs in the domain of NIR planar optics.