Liquid crystal-integrated metasurfaces for an active photonic platform

Metasurfaces have opened the door to next-generation optical devices due to their ability to dramatically modulate electromagnetic waves at will using periodically arranged nanostructures.However,metasurfaces typically have static optical responses with fixed geometries of nanostructures,which poses challenges for implementing transition to technology by replacing conventional optical components.To solve this problem,liquid crystals(LCs)have been actively employed for designing tunable metasurfaces using their adjustable birefringent in real time.Here,we review recent studies on LCpowered tunable metasurfaces,which are categorized as wavefront tuning and spectral tuning.Compared to numerous reviews on tunable metasurfaces,this review intensively explores recent development of LC-integrated metasurfaces.At the end of this review,we briefly introduce the latest research trends on LC-powered metasurfaces and suggest further directions for improving LCs.We hope that this review will accelerate the development of new and innovative LC-powered devices.

Integrated metasurfaces for re-envisioning a near-future disruptive optical platform

Metasurfaces have been continuously garnering attention in both scientific and industrial fields,owing to their unprecedented wavefront manipulation capabilities using arranged subwavelength artificial structures.To date,research has mainly focused on the full control of electromagnetic characteristics,including polarization,phase,amplitude,and even frequencies.Consequently,versatile possibilities of electromagnetic wave control have been achieved,yielding practical optical components such as metalenses,beam-steerers,metaholograms,and sensors.Current research is now focused on integrating the aforementioned metasurfaces with other standard optical components(e.g.,light-emitting diodes,charged-coupled devices,micro-electro-mechanical systems,liquid crystals,heaters,refractive optical elements,planar waveguides,optical fibers,etc.)for commercialization with miniaturization trends of optical devices.Herein,this review describes and classifies metasurface-integrated optical components,and subsequently discusses their promising applications with metasurface-integrated optical platforms including those of augmented/virtual reality,light detection and ranging,and sensors.In conclusion,this review presents several challenges and prospects that are prevalent in the field in order to accelerate the commercialization of metasurfaces-integrated optical platforms.