A multi-mode super-fano mechanism for enhanced third harmonic generation in silicon metasurfaces

We present strong enhancement of third harmonic generation in an amorphous silicon metasurface consisting of elliptical nano resonators.We show that this enhancement originates from a new type of multi-mode Fano mechanism.These‘Super-Fano’resonances are investigated numerically in great detail using full-wave simulations.The theoretically predicted behavior of the metasurface is experimentally verified by linear and nonlinear transmission spectroscopy.Moreover,quantitative nonlinear measurements are performed,in which an absolute conversion efficiency as high as η_(max)≈2.8×10^(-7) a peak power intensity of 1.2 GW cm^(-2) is found.Compared to an unpatterned silicon film of the same thickness amplification factors of up to ~900 are demonstrated.Our results pave the way to exploiting a strong Fano-type multi-mode coupling in metasurfaces for high THG in potential applications.

Beam switching and bifocal zoom lensing using active plasmonic metasurfaces

Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators.While the larger counterparts typically rely on mechanical actuation,this can be undesirable in some cases on a microscopic scale due to inherent space restrictions.Here,we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge3Sb2Te6.In particular,we demonstrate beam switching and bifocal lensing,thus,paving the way for a plethora of active optical elements employing plasmonic metasurfaces,which follow the same design principles.

Multichannel vectorial holographic display and encryption

Since its invention,holography has emerged as a powerful tool to fully reconstruct the wavefronts of light including all the fundamental properties(amplitude,phase,polarization,wave vector,and frequency).For exploring the full capability for information storage/display and enhancing the encryption security of metasurface holograms,smart multiplexing techniques together with suitable metasurface designs are highly demanded.Here,we integrate multiple polarization manipulation channels for various spatial phase profiles into a single birefringent vectorial hologram by completely avoiding unwanted cross-talk.Multiple independent target phase profiles with quantified phase relations that can process significantly different information in different polarization states are realized within a single metasurface.For our metasurface holograms,we demonstrate high fidelity,large efficiency,broadband operation,and a total of twelve polarization channels.Such multichannel polarization multiplexing can be used for dynamic vectorial holographic display and can provide triple protection for optical security.The concept is appealing for applications of arbitrary spin to angular momentum conversion and various phase modulation/beam shaping elements.

Helicity dependent directional surface plasmon polariton excitation using a metasurface with interfacial phase discontinuity

Surface plasmon polaritons(SPPs)have been widely exploited in various scientific communities,ranging from physics,chemistry to biology,due to the strong confinement of light to the metal surface.For many applications,it is important that the free space photon can be coupled to SPPs in a controllable manner.In this Letter,we apply the concept of interfacial phase discontinuity for circularly polarizations on a metasurface to the design of a novel type of polarization-dependent SPP unidirectional excitation at normal incidence.Selective unidirectional excitation of SPPs along opposite directions is experimentally demonstrated at optical frequencies by simply switching the helicity of the incident light.This approach,in conjunction with dynamic polarization modulation techniques,opens gateway towards integrated plasmonic circuits with electrically reconfigurable functionalities.

Metasurface interferometry toward quantum sensors

Optical metasurfaces open new avenues for the precise wavefront control of light for integrated quantum technology.Here,we demonstrate a hybrid integrated quantum photonic system that is capable of entangling and disentangling two-photon spin states at a dielectric metasurface.Via the interference of single-photon pairs at a nanostructured dielectric metasurface,a path-entangled two-photon NOON state with circular polarization that exhibits a quantum HOM interference visibility of 86±4% is generated.Furthermore,we demonstrate nonclassicality andphase sensitivity in a metasurface-based interferometer with a fringe visibility of 86.8±1.1%in the coincidence counts.This high visibility proves the metasurface-induced path entanglement inside the interferometer.Our findings provide a promising way to develop hybrid-integrated quantum technology operating in the high-dimensional mode space in various applications,such as imaging,sensing,and computing.

Nonlinear optics in all-dielectric nanoantennas and metasurfaces:a review

Free from phase-matching constraints,plasmonic metasurfaces have contributed significantly to the control of optical nonlinearity and enhancement of nonlinear generation efficiency by engineering subwavelength meta-atoms.However,high dissipative losses and inevitable thermal heating limit their applicability in nonlinear nanophotonics.All-dielectric metasurfaces,supporting both electric and magnetic Mie-type resonances in their nanostructures,have appeared as a promising alternative to nonlinear plasmonics.High-index dielectric nanostructures,allowing additional magnetic resonances,can induce magnetic nonlinear effects,which,along with electric nonlinearities,increase the nonlinear conversion efficiency.In addition,low dissipative losses and high damage thresholds provide an extra degree of freedom for operating at high pump intensities,resulting in a considerable enhancement of the nonlinear processes.We discuss the current state of the art in the intensely developing area of all-dielectric nonlinear nanostructures and metasurfaces,including the role of Mie modes,Fano resonances,and anapole moments for harmonic generation,wave mixing,and ultrafast optical switching.Furthermore,we review the recent progress in the nonlinear phase and wavefront control using all-dielectric metasurfaces.We discuss techniques to realize alldielectric metasurfaces for multifunctional applications and generation of second-order nonlinear processes from complementary metal–oxide–semiconductor-compatible materials.

Metasurfaces help lasers to mode-lock

Metasurface saturable absorbers may result in versatile mode-locking that allows one to obtain stable ultrashort laser pulses with high repetition rates and peak powers,along with broadband operation,within fiber to solid-state laser cavities.