Mid-IR applications of resonant semiconductor metasurfaces: from "perfect" diffraction gratings to tunable harmonics generation (Conference Presentation)

Abstract

Resonant metasurfaces present an excellent platform for a variety of mid-IR devices, ranging from linear passive to nonlinear active, with everything in between. The key attractions of such metasurfaces are: their ultra-thin (sub-wavelength) format, strong field enhancement, and high-Q response. I will describe three applications currently under development in our group. First, I will demonstrate how a multi-resonant Si metasurface can be used for making perfectly efficient diffraction gratings. We analytically show that at least four independent resonances are required. Experimental realizations of such gratings will be presented, and high-contrast between targeted and parasitic diffraction orders will be demonstrated. Second, I will present an experimental demonstration of a highly nonlinear high-Q Si metasurfaces whose optical properties rapidly change while the pulse is “trapped” by the structure. The metasurfaces were designed to exhibit sharp resonances in the 3–4 μm spectral range. Third harmonic generation spectroscopy and pump–probe spectroscopy revealed the enhancement of coherent nonlinearities and free-carrier-induced by orders of magnitude compared with unpatterned silicon film without compromising the bandwidth. We show that a phenomenon of photon acceleration (PA) manifests in tunable harmonics generation. The PA phenomenon paves the path towards high-efficiency broadband nonlinear photonics. Finally, I will discuss the possibility of making a efficient generator/modulator of the polarization state of light using thermally tunable high-Q metasurfaces. Our experimental results indicate that such photonic structures enable compact polarimeters and ellipsometers.