Shcherbakov, Maxim R.; Liu, Sheng L.; Zubyuk, Varvara V.; Vaskin, Aleksandr; Vabishchevich, Polina P.; Keeler, Gordon A.; Pertsch, Thomas; Dolgova, Tatyana V.; Staude, Isabelle; Brener, Igal B.; Fedyanin, Andrey A.
Optical metasurfaces are regular quasi-planar nanopatterns that can apply diverse spatial and spectral transformations to light waves. However, metasurfaces are no longer adjustable after fabrication, and a critical challenge is to realise a technique of tuning their optical properties that is both fast and efficient. We experimentally realise an ultrafast tunable metasurface consisting of subwavelength gallium arsenide nanoparticles supporting Mie-type resonances in the near infrared. Using transient reflectance spectroscopy, we demonstrate a picosecond-scale absolute reflectance modulation of up to 0.35 at the magnetic dipole resonance of the metasurfaces and a spectral shift of the resonance by 30 nm, both achieved at unprecedentedly low pump fluences of less than 400 μJ cm-2. Our findings thereby enable a versatile tool for ultrafast and efficient control of light using light.
We experimentally demonstrate resonantly enhanced nonlinear optical processes such as 2nd-, 3rd-, and 4th-harmonic generations, sum-frequency generation, four-wave mixing processes, etc., in the visible and near-IR using GaAs dielectric metasurfaces.
We demonstrate the active tuning of all-dielectric metasurfaces exhibiting high-quality factor (high-Q) resonances. The active control is provided by embedding the asymmetric silicon meta-atoms with liquid crystals, which allows the relative index of refraction to be controlled through heating. It is found that high quality factor resonances (Q = 270 ± 30) can be tuned over more than three resonance widths. Our results demonstrate the feasibility of using all-dielectric metasurfaces to construct tunable narrow-band filters.
Dielectric metasurfaces that exploit the different Mie resonances of nanoscale dielectric resonators are a powerful platform for manipulating electromagnetic fields and can provide novel optical behavior. In this work, we experimentally demonstrate independent tuning of the magnetic dipole resonances relative to the electric dipole resonances of split dielectric resonators (SDRs). By increasing the split dimension, we observe a blue shift of the magnetic dipole resonance toward the electric dipole resonance. Therefore, SDRs provide the ability to directly control the interaction between the two dipole resonances within the same resonator. For example, we achieve the first Kerker condition by spectrally overlapping the electric and magnetic dipole resonances and observe significantly suppressed backward scattering. Moreover, we show that a single SDR can be used as an optical nanoantenna that provides strong unidirectional emission from an electric dipole source.
We experimentally demonstrate ultrahigh extinction ratio (>65 dB) amplitude modulators (AMs) that can be electrically tuned to operate across a broad spectral range of 160 nm from 1480-1640 nm and 95 nm from 1280-1375 nm. Our on-chip AMs employ one extra coupler compared with conventional Mach-Zehnder interferometers (MZI), thus form a cascaded MZI (CMZI) structure. Either directional or adiabatic couplers are used to compose the CMZI AMs and experimental comparisons are made between these two different structures. We investigate the performance of CMZI AMs under extreme conditions such as using 95:5 split ratio couplers and unbalanced waveguide losses. Electro-optic phase shifters are also integrated in the CMZI AMs for high-speed operation. Finally, we investigate the output optical phase when the amplitude is modulated, which provides us valuable information when both amplitude and phase are to be controlled. Our demonstration not only paves the road to applications such as quantum information processing that requires high extinction ratio AMs but also significantly alleviates the tight fabrication tolerance needed for large-scale integrated photonics.
We report lasing from nonpolar p-i-n InGaN/GaN multi-quantum well core-shell single-nanowire lasers by optical pumping at room temperature. The nanowire lasers were fabricated using a hybrid approach consisting of a top-down two-step etch process followed by a bottom-up regrowth process, enabling precise geometrical control and high material gain and optical confinement. The modal gain spectra and the gain curves of the core-shell nanowire lasers were measured using micro-photoluminescence and analyzed using the Hakki-Paoli method. Significantly lower lasing thresholds due to high optical gain were measured compared to previously reported semipolar InGaN/GaN core-shell nanowires, despite significantly shorter cavity lengths and reduced active region volume. Mode simulations show that due to the core-shell architecture, annular-shaped modes have higher optical confinement than solid transverse modes. The results show the viability of this p-i-n nonpolar core-shell nanowire architecture, previously investigated for next-generation light-emitting diodes, as low-threshold, coherent UV-visible nanoscale light emitters, and open a route toward monolithic, integrable, electrically injected single-nanowire lasers operating at room temperature.
We demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron− phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to more complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. The platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.
We experimentally demonstrate amplitude modulators (AMs) with >65 dB extinction across over a 160 nm spectral range. The output optical phase response is also characterized when the amplitude is modulated.
We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality factor Fano resonances. Our approach utilizes symmetry breaking of highly symmetric resonator geometries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple "bright" dipole modes to "dark" dipole modes whose radiative decay is suppressed by local field effects in the array. Our approach is widely scalable from the near-infrared to radio frequencies. We first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieves a quality factor of ∼1300 at ∼10.8 μm. Then, we present two experimental demonstrations operating in the near-infrared (∼1 μm): a silicon-based implementation that achieves a quality factor of ∼350; and a gallium arsenide-based structure that achieves a quality factor of ∼600, the highest near-infrared quality factor experimentally demonstrated to date with this kind of metasurface. Importantly, large electromagnetic field enhancements appear within the resonators at the Fano resonant frequencies. We envision that combining high quality factor, high field enhancement resonances with nonlinear and active/gain materials such as gallium arsenide will lead to new classes of active optical devices.
We present all-dielectric 2D and 3D metamaterials that are monolithically fabricated from III-V semiconductor nanostructures. The active/gain and high optical nonlinearity properties of the metamaterials can lead to new classes of active devices.
We experimentally observe large enhancement of second-harmonic generation (SHG) from GaAs metasurfaces. The SHG polarization when excited at the electric and magnetic dipole resonances is orthogonal and can be attributed to different nonlinear generation mechanisms.
Metamaterial dielectric resonators represent a promising path toward low-loss metamaterials at optical frequencies. In this paper we utilize perturbations of high symmetry resonator geometries, such as cubes, either to overlap the electric and magnetic dipole resonances, thereby enabling directional scattering and Huygens' metasurfaces, or to induce couplings between the otherwise orthogonal resonator modes to achieve high-quality factor Fano resonances. Our results are fully scalable across any frequency bands where high-permittivity dielectric materials are available, including microwave, THz, and infrared frequencies.
Nonlinear optical phenomena in nanostructured materials have been challenging our perceptions of nonlinear optical processes that have been explored since the invention of lasers. For example, the ability to control optical field confinement, enhancement, and scattering almost independently allows nonlinear frequency conversion efficiencies to be enhanced by many orders of magnitude compared to bulk materials. Also, the subwavelength length scale renders phase matching issues irrelevant. Compared with plasmonic nanostructures, dielectric resonator metamaterials show great promise for enhanced nonlinear optical processes due to their larger mode volumes. Here, we present, for the first time, resonantly enhanced second-harmonic generation (SHG) using gallium arsenide (GaAs) based dielectric metasurfaces. Using arrays of cylindrical resonators we observe SHG enhancement factors as large as 104 relative to unpatterned GaAs. At the magnetic dipole resonance, we measure an absolute nonlinear conversion efficiency of ∼2 × 10-5 with ∼3.4 GW/cm2 pump intensity. The polarization properties of the SHG reveal that both bulk and surface nonlinearities play important roles in the observed nonlinear process.