Polarization-Independent Large Third-Order-Nonlinearity of Orthogonal Nanoantennas Coupled to an Epsilon-Near-Zero Material

Abstract

The nonlinear optical response of common materials is limited by bandwidth and energy consumption, which impedes practical application in all-optical signal processing, light detection, harmonic generation, etc. Additionally, the nonlinear performance is typically sensitive to polarization. To circumvent this constraint, we propose that orthogonal nanoantennas coupled to Al-doped zinc oxide (AZO) epsilon-near-zero (ENZ) material show a broadband (~1000 nm bandwidth) large optical nonlinearity simultaneously for two orthogonal polarization states. The absolute maximum value of the nonlinear refractive index n2 is 7.65 cm2∙GW−1, which is 4 orders of magnitude larger than that of the bare AZO film and 7 orders of magnitude larger than that of silica. The coupled structure not only realizes polarization independence and strong nonlinearity, but also allows the sign of the nonlinear response to be flexibly tailored. It provides a promising platform for the realization of ultracompact, low-power, and highly nonlinear all-optical devices on the nanoscale.

Broadband Enhancement of Optical Nonlinearity in a Plasmonic Nanocavity Coupled with an Epsilon-Near-Zero Film

“…. 29 It is seen that the nonlinear absorption coefficient β for the proposed hybrid structure is negative, representing the saturated absorption, in two wavelength ranges of 1036−1118 and 1184−1837 nm. At other wavelengths, β is positive, indicating the reverse saturable absorption.…”

“…Compared with the main resonance, the nonlinear response around the weak resonance at λ = 1984 nm is relatively weak but the nonlinear refractive index is still three orders of magnitude larger than that of bare ITO and six orders of magnitude larger than that of quartz glass. Figure b shows that the wavelength-dependent nonlinear absorption coefficient obtained from β = 4 π λ [ Im false( normalΔ n / I false) ] . It is seen that the nonlinear absorption coefficient β for the proposed hybrid structure is negative, representing the saturated absorption, in two wavelength ranges of 1036–1118 and 1184–1837 nm.…”

Enhanced nonlinear optical response by strong coupling between plasmonic antenna arrays and epsilon-near-zero film

“…Besides, as the thickness of the FTO film increases, the ENZ mode of the FTO film disappears, and the lower weak resonance is no longer visible. 17) These results provide guidance for the selection of appropriate ENZ material thicknesses to design the coupled structure.…”

“…14,15) Particularly, there have been many research achievements to confirm that the strong coupling between ENZ materials and antenna results in a strong field enhancement inside the ENZ film and can enhance the nonlinear response of metasurface of polarization-independent and sign-tailored. 16,17) An ENZ film supports a longitudinal bulk-plasma mode and surface plasmon-polariton (SPP) modes at both interfaces. The SPP splits into short-range and long-range SPPs when film thickness is comparable to the skin depth.…”