THz guided-mode resonance notch filter with variable filtering strength

In this paper, we propose a terahertz (THz) guided-mode resonance (GMR) notch filter made of a monolithic polyethylene terephthalate (PET) film, which has a monolayer grating structure. The proposed configuration shows both polarization-dependent and polarization-independent notch filter characteristics for the incident THz wave depending on the rotation angle of the second grating film. When the rotation angle is 0°, the filtering strength (transmittance) at resonance frequency changes from 0.4 (0.996) to 99.0% (0.010) according to the incident polarization. The transmittance continuously decreases with increasing rotation angle until 90°. When the rotation angle is 90°, the transmittance converges to 0.065 (± 0.015) independent of the incident wave polarization. When the incident polarization angle ranges from 90° to 180°, paradoxically, the transmittance through the two GMR grating films is greater than the transmittance through only the first GMR grating film due to the enhancement of the vertical component of the THz wave. These results agree well with a calculation using a polar coordinate system.

Characterization of the koch fractal hexagonal loop frequency selective surface for X-band application

<p>This paper presented the bandstop Koch fractal hexagonal loop frequency selective surface (FSS) for the X-band application. The simulated transmission coefficient response (S_21) had been obtained by using CST software. The proposed Koch fractal hexagonal loop FSS structure is highly insensitive towards angular stability and also incident polarization up to 60 degree , with deviation of resonant frequency, f_r below than 1%. The parametric analysis on the effect of the periodicity, width, and height of the fractal FSS structure on the S_21 has been illustrated and discussed thoroughly.</p>

Polarization-encrypted high-resolution full-color images exploiting hydrogenated amorphous silicon nanogratings

As a prominent alternative to toxic dyes/pigments, nanostructural color pixels have garnered tremendous attention in applications related to display/imaging devices and color printings. However, current color pixels mostly offer static color responses. In relation to this, dynamic color tuning properties must be investigated in order to expand their functionalities and promote their use in the fields of encryption and anti-counterfeiting. In this study, a simple array of hydrogenated amorphous silicon nanogratings is proposed to realize polarization-encrypted full-color images via the coupling of incident light into different leaky mode resonances within the nanogratings. The proposed pixels can readily switch from vivid full colors to indistinguishable orange color by altering the incident polarization state. Hence, unlike the reported polarization-tuned color generation schemes that merely allow for the color variation of the image or require complicated designs to hide the color information, the proposed approach can encrypt arbitrary full-color images via a simple tuning of the incident polarization state. Owing to the localized leaky mode resonances supported by the nanogratings, the pixel can still implement the polarization-encrypted functionality even when it contains only four gratings, thus enabling a remarkably high resolution. The proposed simple scheme may provide a credible new pathway for accelerating the practical applications of high-resolution encryption and anti-counterfeiting.

Crystalline Orientation Identification of Phosphorene Using Polarized Raman Spectroscopy without Analyzer

The unique photoelectric properties of phosphorene typically include anisotropy, hence the nondestructive and rapid identification of its crystal orientation is a key point to the investigation and application of phosphorene. Currently, the orientation identification by analyzing the Ag1 mode based on parallel-polarized Raman has severe requirements for the applicable Raman system. Therefore, it is necessary to develop a more general, convenient, and accurate method for determining the crystal orientation of phosphorene. In this paper, a method of orientation identification was proposed by using a Raman system without an analyzer and quantifying the correlation between the intensities of Ag1 and Ag2 modes with the change of the incident polarization direction. By using mechanically peeled phosphorene as specimens, Raman measurements were carried out under the Raman configurations of both parallel polarization and with no analyzer. The results show that the crystal orientation of phosphorene can be accurately identified by quantifying the Raman intensities of both Ag1 and Ag2 modes using the Raman system without an analyzer.

Controlling the interference between localized and delocalized surface plasmons via incident polarization for optical switching

Surface plasmons supported by various metallic nanostructures have given rise to several significant breakthroughs in the field of integrated photonic devices due to its ability to effectively confine and enhance optical field in subwavelength volume. In particular, the demand to actively control optical responses of plasmonic systems becomes urgent for the miniaturization of signal processing devices, surface-enhanced Raman scattering (SERS) substrates and biochemical sensors. In this paper, we systematically investigate the plasmon modes as well as their interaction in a layered nanostructure composed of a periodically-arranged radiative nanoring and a metallic ground plane, as well as a thin insulating spacer. A tunable transparent peak on the background of the broadband plasmon resonance emerges in the reflection spectrum as changing the periodicity of nanoparticle array, a plasmonic analogue of electromagnetically induced transparency (EIT). Owing to the structural symmetry of the rings, we demonstrate a new scheme of controlling the interference between localized and delocalized plasmons by means of incident polarization and believe that the proposed metasurface may find applications in optical switching if the polarization-controlled components are introduced.

The polarization-dependent anisotropic Raman response of few-layer and bulk WTe2under different excitation wavelengths

WTe2, which is an orthorhombic semimetal crystallized in Td phase, exhibts distinct in-plane anisotropy. The Raman modes depict different anisotropic response by rotating the incident polarization under different excitation wavelengths.