Broadband wide-view all-dielectric handedness-preserving mirror

Abstract

We report the theoretical design and experimental realization of a wideband, all-dielectric mirror that preserves the handedness of incident light upon reflection in the near-infrared range. The mirror consists of a high-contrast, near-subwavelength, one-dimensional dielectric grating on a Bragg mirror. We optimized this structure using a genetic algorithm and demonstrated its robustness against geometric imperfections and oblique incidence. Experimental reflection spectra measured under normal incidence in a circular polarization basis demonstrate a more than 100-nm-wide reflection band in which more than 98% of the reflected light preserves its handedness. The total reflection coefficient reached 80%. Furthermore, we demonstrate that the fabricated mirror maintains high performance even under oblique incidence for angles up to $\pm 15^\circ$. Owing to these unique characteristics, this mirror can serve as a reflective phase plate, making it an excellent candidate for the creation of a Fabry-Pérot resonator for chiral light.

Figures (12)

• Figure 1: Modeling. (a) The sketch of a wide-band handedness-preserving mirror consisting of the one-dimensional Si grating on a Si/SiO$_2$ multilayered structure. (b) Spectral dependence of $\Delta \phi = \arg(r_{xx})-\arg(r_{yy})$ and $|r_{xx}+r_{yy}|$. (c) Spectral dependencies of cross-polarization reflection coefficients in the basis of linear polarizations. (d) Spectral dependencies of cross-polarization reflection coefficients in the basis of circular polarizations. Parameters used for modeling: thicknesses of the layers was $h_{gr} = 297$ nm (grating), $h_{\text{SiO}_2}^{\text{sub}} = 50$ nm (SiO$_2$ sublayer), $h_{\text{Si}}^{\text{BM}} = 102$ nm (Si layer of the Bragg mirror), $h_{\text{SiO}_2}^{\text{BM}} = 297$ nm (SiO$_2$ layer of the Bragg mirror); the period $p = 503$ nm; the stripes' width $a = 131$ nm the grooves' width $b = 372$ nm.
• Figure 2: Modeling. Reflection coefficient for LH→LH (RH→RH) polarization as a function of the light wavelength and structural parameters: (a) grating period $p$, (b) filling factor $f = a/p$, (c) grating thickness $h_{gr}$, (d) SiO$_2$ sublayer thickness $h_{\text{SiO}_2}^{\text{sub}}$, and (e) Bragg mirror layers thickness $h_{\text{Si}}^{\text{BM}}$, $h_{\text{SiO}_2}^{\text{BM}}$ that was changed simultaneously. Initial parameters used for modeling: $h_{gr} = 297$ nm, $h_{\text{SiO}_2}^{\text{sub}} = 50$ nm, $h_{\text{Si}}^{\text{BM}} = 102$ nm, $h_{\text{SiO}_2}^{\text{BM}} = 297$ nm, $p = 503$ nm, $a = 131$ nm, $b = 372$ nm.
• Figure 3: Modeling. Reflection coefficient for LH→LH (RH→RH) polarization as a function of the light wavelength and incidence angle $\theta$: incidence perpendicular to the grating stripes and parallel to the grating stripes. Parameters used for modeling: $h_{gr} = 297$ nm, $h_{\text{SiO}_2}^{\text{sub}} = 50$ nm, $h_{\text{Si}}^{\text{BM}} = 102$ nm, $h_{\text{SiO}_2}^{\text{BM}} = 297$ nm, $p = 503$ nm, $a = 131$ nm, $b = 372$ nm.
• Figure 4: Experiment. (a) SEM image of the grating fabricated on top of the Si/SiO$_2$ Bragg mirror. (b) SEM image of the side cross section of the unprocessed Bragg mirror. Measured average parameters of fabricated structure: $h_{gr} = 290$ nm, $h_{\text{SiO}_2}^{\text{sub}} = 60$ nm, $h_{\text{Si}}^{\text{BM}} = 110$ nm, $h_{\text{SiO}_2}^{\text{BM}} = 260$ nm, $p = 650$ nm, $a = 150$ nm, $b = 500$ nm. (c) Spectral dependence of the DCP and (d) handedness-preservation coefficient $\eta$ for the bare Bragg mirror (red markers) and the fabricated handedness-preserving mirror (black line). (e) Co- and cross-handed reflectivity spectra for the Bragg mirror (dashed lines) and the fabricated handedness-preserving mirror (solid lines).
• Figure 5: Experiment. Co- and cross-handed reflectivity spectra and the handedness-preservation coefficient $\eta$ for (a,b) normal incidence, (c,d) $\theta = 5^{\circ}$ with the plane of incidence perpendicular to the stripes ($\varphi = 0^{\circ}$), and (e,f) $\theta = 5^{\circ}$ with the plane of incidence parallel to the stripes ($\varphi = 90^{\circ}$). (g,h) Spectral evolution of the handedness-preservation coefficient $\eta$ for different incidence angles in the two incidence geometries: (g) $\varphi = 0^{\circ}$ and (h) $\varphi = 90^{\circ}$.