Metasurfaces, i.e., periodic arrangements of either resonant or non-resonant meta-atoms, enable light management at the subwavelength scale. Flat lenses, ultra-compact beam steerers, polarization converters, angular filters, and frequency-selective filters can be realized by properly engineering the meta-atom. These structures can be designed with dielectrics, metals, or hybrid material systems, at any desired frequency, from radio-frequencies up to optical frequencies. 

Our research mainly deals with plasmonic and dielectric metasurfaces for applications in the optical regime, with emphasis on nonlinear optical functionalities and tunable nanophotonic devices. 

In collaboration with Sandia National Lab., we have recently demonstrated a hybrid approach for realizing strong coupling and efficient second-harmonic generation in ultrathin dielectric-semiconductor metasurfaces. These device shows low losses, high damage threshold, large bandwidth, wavelength scalability, dual mode operation in transmission and reflection, monolithic integrability, and ease of fabrication. We have demonstrated nonlinear conversion factors of ~ 1 mW/W^2 by exploiting high quality factor leaky mode resonances that are coupled to intersubband transitions of semiconductor quantum wells. These results open a new direction for designing low loss, broadband, and efficient ultrathin nonlinear optical devices. Then, in an another design configuration, we have demonstrated strong coupling of Mie-type resonances with intersubband transitions.