2, Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Jena, , Germany
3, Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, New Mexico, United States
The recent approach to utilize metasurfaces made from resonant nanostructures has been revolutionizing our perception of nonlinear optical processes. Due to the relaxed phase-matching requirements, simultaneous generation of various nonlinear optical processes can be expected from them. In this work, we show that seven nonlinear processes, including fourth-harmonic generation, four-wave mixing (FWM), and six-wave mixing (SWM) processes can occur simultaneously in GaAs dielectric metasurfaces.
The dielectric metasurfaces used in this work consist of a square array of GaAs nanocylinder resonators that are spatially separated from a GaAs substrate by AlGaO. The nanocylinders have diameters of ~420 nm and support magnetic and electric dipole resonances at ~1520 nm and ~1250 nm, respectively. To explore frequency mixing processes, the GaAs metasurface sample was pumped by two near-infrared femtosecond beams. The optimization of the frequency-mixing signal was achieved by overlapping the pumps’ wavelengths with the two dipole resonances of the nanoresonators. When the two pump pulses spatially and temporally overlap, eleven spectral peaks are observed spanning from UV to near-infrared wavelengths. We divide the newly generated frequencies into two groups: those relying on only one of the two pump beams such as second-, third- and fourth-harmonic generation and two-photon absorption induced photoluminescence; and those relying on both pump beams such as sum-frequency generation, three types of FWM processes, and SWM process. We identify these mechanisms by measuring the power dependence, as well as by matching the photon energy. For example, the observed fifth-order nonlinear effect, SWM, was verified by tunning the wavelengths of the two pumps. To confirm the resonantly enhanced behavior, we also measured the generated nonlinear spectra on an unpatterned sample and observed at least two orders of magnitude smaller signal intensities for most the spectral peaks.
Our demonstration of frequency-mixing in dielectric metasurfaces combines strong material nonlinearities of GaAs, enhanced electromagnetic fields in resonators, and relaxed phase-matching conditions in nanostructures, to allow simultaneously generate of eleven new frequencies. Use of III-V metasurfaces paves a road for realizing ultra-compact optical frequency-mixer for various applications, such as telecommunication technologies.
This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering and performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.