Nonlocal resonances in pedestal high-index-contrast metasurfaces based on a silicon-on-insulator platform

Abstract

Subwavelength control of the electromagnetic field distribution represents one of the current challenges in photonics research. In this field, diffractive metasurfaces with spatially extended (i.e., nonlocal) resonant modes have recently gained great interest for their versatility in molding the electromagnetic field beyond the approximation of independent resonators. In this framework, we design a high-contrast nonlocal metasurface featuring modes situated in the third operating spectral window of optical communications. The optical properties of the fabricated metasurface are investigated by linear spectroscopy and numerical simulations. Our analysis allows to discern the magnetic and electric nature of the bounded modes by means of polarization-resolved reflectance measurements. Our results represent a step toward integrated nano-photonics in the telecom regime and open promising opportunities for the development of compact nonlinear optical devices.

Giant photoinduced reflectivity modulation of nonlocal resonances in silicon metasurfaces

“…We employ an NLM, which we previously demonstrated 29 to feature sharp spectral resonance with large amplitude in the third operating window of optical communications, to unveil the pivotal role of the photonic structure to achieve large amplitude modulation with smaller fluence compared to bulk materials. The high-index-contrast NLM under analysis, shown in Fig.…”

“…S3 in the Supplementary Material), which is mediated by a leaky mode propagating along the grating periodicity direction (y axis). 29 The leaky nature of the GMR can be deduced by looking at the spatial distribution of the mode in Fig. 1…”

“…30 Discrepancy in the spectra may originate from the dispersion of the geometrical parameters (due to fabrication tolerances) or minimum differences of the pedestal profile within the sample area detected by the probe beam (see Ref. [29] for more details). Nevertheless, the model reveals the collective (i.e., nonlocal) nature of the resonance and the eigenmode analysis allows one to correctly locate its spectral position at λ eq Γ ≃ 1375 nm.…”

“…2 highlight a nonnegligible difference regarding the order of magnitude between the optical response of the structure (ΔR∕R ∼ 50% at maximum) and the modulation of the material properties (Δε∕ε ∼ 0.4% and Δλ∕λ ∼ 0.1%) following the moderate excitation of 180 μJ∕cm 2 . Therefore, in order to better investigate the role of the photonic structure in the interplay between the optical response and material properties variation, we report excitation-dependent pump-probe measurements on the NLM, and we compare the results to those obtained from a multilayer thin-film-like platform, consisting in a uniform Si (500 nm)/SiO 2 (1160 nm) bilayer 29 deposited on the Si substrate. [We underline that the thickness of the Si (SiO 2 ) layer in the thin-film-like sample is the same as d (h) in the NLM (see Appendix D).]…”

“…Further details about the fabrication process are provided elsewhere. 29,57 5 Appendix B: Equilibrium Linear Spectroscopy…”