Efficient Frequency Conversion with Geometric Phase Control in Optical Metasurfaces

Abstract

Metasurfaces have appeared as a versatile platform for miniaturized functional nonlinear optics due to their design freedom in tailoring wavefronts. The key factor that limits its application in functional devices is the low conversion efficiency. Recently, dielectric metasurfaces governed by either high‐quality factor modes (quasi‐bound states in the continuum) or Mie modes, enabling strong light–matter interaction, have become a prolific route to achieve high nonlinear efficiency. Here, an effective way of spatial nonlinear phase control by using the Pancharatnam–Berry phase principle with a high third harmonic conversion efficiency of 10 −4 W −2 is demonstrated both numerically and experimentally. It is found that the magnetic Mie resonance appears to be the main contributor to the third harmonic response, while the contribution from the quasi‐bound states in the continuum is negligible. This is confirmed by a phenomenological model based on coupled anharmonic oscillators. Besides, the metasurface provides experimentally a high diffraction efficiency (80%–90%) in both polarization channels. A functional application of this approach is shown by experimentally reconstructing an encoded polarization‐multiplexed vortex beam array with different topological charges at the third harmonic frequency with high fidelity. The approach has the potential viability for future on‐chip nonlinear signal processing and wavefront control.

Roadmap for Optical Metasurfaces

“…In contrast, the second approach optimizes a single geometry and enables continuous phase variation by simple structure rotation, but typically requires a smaller footprint that provides very weak conversion efficiencies. However, Matsudo et al have recently addressed this issue and demonstrated geometric phase control with high nonlinear efficiency by utilizing a disk with a noncentered hole as the meta-atom. Realized phase-tailoring functionalities for SHG and THG include beam steering, lensing, optical vortex generation, and nonlinear multiplexing holography .…”

Wavelength-adaptive optical angular momentum recognizer via programmable soft materials

“…Overall, compared to the compact metasurface known for wavefront shaping, 40,41 the flat optics based on soft LCs holds the advantageous characteristics of simple fabrication and convenient modulation via a variety of external stimuli. Significantly, by virtue of the erasable and rewritable photo-sensitive aligning layer, the tailored phase distribution configured in NLCs can be easily erased by uniform irradiation, following a programmed photopatterning process to reconfigure another architecture.…”

Investigation of Multiple High Quality-Factor Fano Resonances in Asymmetric Nanopillar Arrays for Optical Sensing

“…It is necessary to create a radiation channel to the outside by breaking the symmetry of the result or by oblique incidence of the light source [38]. Through this method, the symmetry-protected BIC is switched to the quasi-BIC mode so that the Q-factor of the resonance becomes finite [39,40].…”