Dielectric Chiral Metasurfaces for Second‐Harmonic Generation with Strong Circular Dichroism

Abstract

Dielectric chiral metasurfaces can generate harmonic waves with high efficiency and strong circular dichroism (CD), when they are supported by metallic substrates. Numerical results show that the second-harmonic generation (SHG) efficiency of about 10 −3 % for a peak pump intensity of about 5 GW cm −2 can be achieved in the blue-UV, and the SHG CD reaches up to about 1.8, from a metasurface of Z-shaped lithium niobate nanoantenna array supported by gold substrate. Highly efficient and strong circular dichroic nonlinear responses are attributed to the plasmon-assisted local field enhancement in the dielectric chiral nanoantennae adjacent to the metallic substrate.

Giant Nonlinear Circular Dichroism from High Q‐Factor Asymmetric Lithium Niobate Metasurfaces

“…Figure 6b shows the wavelength dependence of the SHG conversion efficiency (𝜂) for RCP and LCP, which is calculated as 𝜂 = P SH ∕P FH . The efficiency can reach ≈1.35 × 10 −2 % for RCP pumping at 1.334 μm, which is larger than the efficiency that was previously reported, [15] and the peak position is consistent with (E y /E 0 ) 2 in Figure 3d. For LCP pumping, the SHG efficiency is only 8 × 10 −4 % which is attributed to the effective suppression of the quasi-BICs and low internal field enhancement.…”

“…For the RCP incident, although the maximum field enhancement occurs in the vicinity of the bar tips, there is still an enhancement of nearly 20 times inside the elliptical LN bars, which is significantly higher than that reported in the literature. [15] Moreover, by comparing Figure 4a,c and Figure 4b,d, it can be observed that the field enhancement effect is close to 0 for LCP incidence, which indicates that the metasurface field enhancement strongly depends on the handedness of the incident light polarization owing to the strongly polarization-dependent strength quasi-BIC modes excited on the LN metasurface, and also provides a method for the strong nonlinear CD implementation.…”

“…Recently, chiral metamaterials have attracted much attention because of their unique circular dichroism (CD), [1][2][3][4][5][6][7][8][9] i.e., incident lights with different polarization states have different responses, which can be used for polarimetric detection, [10] biosensors, [11][12][13] optical communications, chiral nonlinearity, [14][15][16][17][18] and chiral meta-holography. [19][20][21][22] Compared with 3D bulk materials, metamaterials and metasurfaces have sub-wavelength scale volume, which is more conducive to the integration of ultra-compact optical elements, and can effectively reduce the requirements for phase matching.…”

“…Recently, LN metasurfaces with excellent photoelectric properties have been reported. Note that LN has a high second-order nonlinear polarization coefficient and low optical loss in the UV to mid-infrared spectral regions, [15,[30][31][32] which make it suitable for the study of the second harmonic. [33][34][35] Many methods have been employed to improve the second-harmonic generation (SHG) efficiency of LN, such as plasmonic resonance and anapole mode, [15,36] however, they still experience low efficiency.…”

Quasi-bound states in the continuum with high Q-factors in metasurfaces of lower-index dielectrics supported by metallic substrates

“…8). Ensuring high index contrast between the nanoparticles and substrates 8 or using metallic substrates [9][10][11] prevent the mode leakage and support strong eld connement even with the lower-index materials.…”