Metasurfaces have gained significant attention due to their outstanding ability to manipulate electromagnetic waves. These artificial structures retain the remarkable optical properties and functionality of metamaterials while compacting nanostructure spatial distribution into a two-dimensional plane. Although metasurfaces offer numerous advantages in optical manipulation, their optical properties and functionalities cannot be modified after fabrication. Therefore, today's primary challenge is introducing tunability using different tunable materials and mechanisms. Such metasurface tunability would allow us to dynamically switch between different functionalities or manipulate the properties of a single metasurface.

This seminar will discuss the physical insights and tunable optical responses of temporal and spatial metasurfaces using two tunable mechanisms: liquid crystal (LC) reorientation and charge excitation in semiconductors. LC reorientation offers a sizeable refractive index tuning range of approximately 0.2 during optical axis rotation. Due to its significant refractive index changes, LC is commonly implemented in traditional optical devices. While some combinations of LC and metasurfaces have been explored during the last several years, further research is still necessary to fully understand their potential limitations and applications. In my work, I proved the possibility of achieving pure phase tuning by combining thermal and electric effects. Additionally, I explored the metasurface resonance tuning through a comprehensive rotation of the LC using a magnetic field. 

Another tunable material, GaAs, is known for its excellent nonlinearity property and is typically applied in nonlinear optics. In my PhD, I explore the GaAs metasurfaces in time-variant modulation, leveraging their ultrafast optical response during the pump-probe process for ultrafast tuning and frequency conversion. Overall, my results open new opportunities for dynamic optical systems and devices.