Metamaterials have revolutionized the ways we control light and design optical materials. Researchers have been highly successful in designing sub-wavelength “meta-atoms” to achieve new optical functionalities. On the other hand, “meta-atoms” have to be made of natural materials, therefore one can further tune the responses of metamaterials by varying the constituent natural materials and achieve even broader range of optical properties.
In my research lab, we conduct extensive exploration of optical materials beyond the widely used noble metals to achieve novel capabilities of metaphotonic systems. Here I would like to share some of our recent progresses on implementing new material platforms in metaphotonics:
First I will present an all-solid, rewritable metacanvas using phase change materials, on which arbitrary photonic devices can be rapidly and repeatedly written and erased for real-time manipulation of light waves. Different patterns can be written and erased on the same metacanvas with a low-power laser. Dynamic manipulation of optical waves is demonstrated with the metacanvas, specifically light propagation, polarization, and reconstruction. This dynamic optical system without moving parts opens possibilities where photonic elements can be field-programmed to deliver complex, system-level functionalities.
We have also demonstrated a simple bottom-up approach to create self-assembled, nanostructured metamaterials with controllable structural geometry and temperature-tunable optical response from spinodally-decomposed VO2-TiO2 epitaxial thin films. As-grown solid solution films are driven to phase separate upon post-annealing and we demonstrate the ability to deterministically create horizontally- or vertically-aligned lamellae consisting of Ti- and V-rich phases. The optical iso-frequency surface of the self-assembled nanostructures can be made to exhibit a temperature-tunable transition from elliptic to hyperbolic dispersion in the near-infrared range and thus the formation of hyperbolic metamaterial response.
Lastly, I will talk about our recent efforts in achieving functional metasurfaces in the UV range by introducing new material platforms and new light-manipulation mechanisms.