Full Complex‐Amplitude Modulation of Second Harmonic Generation with Nonlinear Metasurfaces (original) (raw)
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Nano Letters, 2017
The spin and orbital angular momentum (SAM and OAM) of light is providing a new gateway towards high capacity and robust optical communications. While the generation of light with angular momentum is well studied in linear optics, its further integration into nonlinear optical devices will open new avenues for increasing the capacity of optical communications through additional information channels at new frequencies. However, it has been challenging to manipulate the both SAM and OAM of nonlinear signals in harmonic generation processes with conventional nonlinear materials. Here, we report the generation of spin controlled OAM of light in harmonic generations by using ultrathin photonic metasurfaces. The spin manipulation of OAM mode of harmonic waves is experimentally verified by using second harmonic generation (SHG) from gold meta-atom with threefold rotational symmetry. By introducing nonlinear phase singularity into the metasurface devices, we successfully generate and measure the topological charges of spin-controlled OAM mode of SHG through an on-chip metasurface interferometer. The nonlinear photonic metasurface proposed in this work not only opens new avenues for manipulating the OAM of nonlinear optical signals, but also benefits the understanding of the nonlinear spin-orbit interaction of light in nanoscale devices.
Electrically tunable third-harmonic generation using intersubband polaritonic metasurfaces
2024
Nonlinear intersubband polaritonic metasurfaces, which integrate giant nonlinear responses derived from intersubband transitions of multiple quantum wells (MQWs) with plasmonic nanoresonators, not only facilitate efficient frequency conversion at pump intensities on the order of few tens of kW cm-2 but also enable electrical modulation of nonlinear responses at the individual meta-atom level and dynamic beam manipulation. The electrical modulation characteristics of the magnitude and phase of the nonlinear optical response are realized through the resonant properties of intersubband nonlinearity and Stark tunability. In this study, we report, for the first time, experimental implementations of electrical modulation characteristics of midinfrared third-harmonic generation (THG) using an intersubband polaritonic metasurface based on MQW with Stark-tunable third-order nonlinear response. Experimentally, we achieved a 450% modulation depth of the THG signal, complete suppression of zero-order THG diffraction tuning based on local phase tuning exceeding 180 degrees, and THG beam steering using phase gradients. Our work proposes a new route for electrically tunable flat nonlinear optical elements with versatile functionalities.
Zero-Order Second Harmonic Generation from AlGaAs-on-Insulator Metasurfaces
ACS Photonics, 2019
All-dielectric metasurfaces consist of two-dimensional arrangements of nanoresonators and are of paramount importance for shaping polarization, phase, and amplitude of both fundamental and harmonic optical waves. To date, their reported nonlinear optical properties have been dominated by local features of the individual nanoresonators. However, collective responses typical of either Mie-resonant metamaterials or photonic crystals can potentially boost the control over such optical properties. In this work we demonstrate the generation of a second harmonic optical wave with zero-order diffraction, from a metasurface made out of AlGaAs-on-AlOx nanocylinders arranged with spatial period comparable to the pump telecom wavelength. Upon normal incidence of the pump beam, the modulation of Mie resonances via Bragg scattering at both fundamental and second harmonic frequencies enables paraxial second harmonic light generation by diffraction into the zero order, with a 50-fold increase in detected power within a solid angle of 5°. Exquisite control of a higher harmonic wavefront can be thus achieved in all-dielectric nonlinear metasurfaces, with potential applications for on-axis optical systems.
Direct and cascaded collective third-harmonic generation in metasurfaces
Journal of the Optical Society of America B, 2019
We use collective interactions in plasmonic metasurfaces to manipulate the interplay between direct and cascaded third-harmonic generation. We implement a simple case where in contrast to the direct contribution, which is mainly enhanced by the local plasmonic resonances, the cascaded contribution enhancement may be manipulated using the metasurface's geometry, in addition to the single nanoparticle's electrical response, by enabling the proper nonlocal interactions at the second-harmonic frequency. In addition, an anomalous phase relation of the single nanoparticle's linear polarizability at the second-harmonic region affects the relative phase between the direct and cascaded contributions, which results in a Fano-like asymmetrical line shape of the third-harmonic generation. We demonstrate that this can be used to enhance or contrarily completely eliminate third-harmonic generation from metasurfaces over a very narrow bandwidth. Such a unique fundamental observation of the interplay between direct and cascaded third-harmonic generation in periodic resonant systems may find new applications in sensing and to control nonlinear optical phenomena.
Experimental demonstration of second-harmonic generation in high χ2 metasurfaces
Optics Letters, 2021
Metasurfaces able to concentrate light at various wavelengths are promising for enhancing nonlinear interactions. In this Letter, we experimentally demonstrate infrared second-harmonic generation (SHG) by a multi-resonant nanostructure. A 100 GaAs layer embedded in a metal-insulator-metal waveguide is shown to support various localized resonances. One resonance enhances the nonlinear polarization due to the transverse magnetic (TM)-polarized pump wavelength near 3.2 µ m , while another is set near the TE-polarized generated wavelength ( 1.6 µ m ). The measured SHG efficiency is higher than 10 − 9 W − 1 for pump wavelengths ranging from 2.9 to 3.3 µ m , which agrees with theoretical computations. This is typically 4 orders of magnitude higher than the equivalent GaAs membrane.
Controlling the phase of optical nonlinearity with plasmonic metasurfaces
Nanophotonics, 2018
Metasurfaces are ultrathin structured surfaces that are capable of manipulating the propagation of light in an arbitrary manner. It has been endowed with various functionalities ranging from imaging to holography. In contrast to linear optical processes, the control of wave propagation and diffraction over nonlinear optical processes such as harmonic generations had been much more limited until recently, when the concept of metasurfaces was extended from linear optics to the nonlinear optical regime for manipulating the generation of harmonic signals in an unprecedented level. The key to this recent development lies in the local control over the phase and/or the amplitude of nonlinear polarizability. This new development has led to an array of interesting optical phenomena and nonlinear optical devices that went beyond what had been achieved with traditional nonlinear optical elements. In this review, we summarize the latest progress in controlling the local phase of nonlinearity with plasmonic metasurfaces, with a focus on nonlinear geometric Berry phase and wavefront engineering, and various device applications with nonlinear metasurfaces.
Second Harmonic Generation from Phase-Engineered Metasurfaces of Nanoprisms
Micromachines, 2020
Metasurfaces of gold (Au) nanoparticles on a SiO2-Si substrate were fabricated for the enhancement of second harmonic generation (SHG) using electron beam lithography and lift-off. Triangular Au nanoprisms which are non-centro-symmetric and support second-order nonlinearity were examined for SHG. The thickness of the SiO2 spacer is shown to be an effective parameter to tune for maximising SHG. Electrical field enhancement at the fundamental wavelength was shown to define the SHG intensity. Numerical modeling of light enhancement was verified by experimental measurements of SHG and reflectivity spectra at the normal incidence. At the plasmonic resonance, SHG is enhanced up to ∼3.5 × 103 times for the optimised conditions.
Third-Harmonic Generation in Photonic Topological Metasurfaces
Physical Review Letters
We study nonlinear effects in two-dimensional photonic metasurfaces supporting topologicallyprotected helical edge states at the nanoscale. We observe strong third-harmonic generation mediated by optical nonlinearities boosted by multipolar Mie resonances of silicon nanoparticles. Variation of the pump-beam wavelength enables independent high-contrast imaging of either bulk modes or spin-momentum-locked edge states. We demonstrate topology-driven tunable localization of the generated harmonic fields and map the pseudospin-dependent unidirectional waveguiding of the edge states bypassing sharp corners. Our observations establish dielectric metasurfaces as a promising platform for the robust generation and transport of photons in topological photonic nanostructures.
Phase-matched nonlinear second-harmonic generation in plasmonic metasurfaces
Nanophotonics
The phase matching between the propagating fundamental and nonlinearly generated waves plays an important role in the efficiency of the nonlinear frequency conversion in macroscopic crystals. However, in nanoscale samples, such as nanoplasmonic structures, the phase-matching condition is often ignored due to the sub-wavelength nature of the materials. Here, we first show that the phase matching of the lattice plasmon modes at the fundamental and second-harmonic frequencies in a plasmonic nanoantenna array can effectively enhance the surface-enhanced second-harmonic generation. Additionally, a significant enhancement of the second-harmonic generation is demonstrated using stationary band-edge lattice plasmon modes with zero phase.
Wavevector-Selective Nonlinear Plasmonic Metasurfaces
Nano letters, 2017
Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear ...