We theoretically demonstrate high efficiency broadband vector beams generation with polarization rotation metasurfaces composed of L-shaped silver antenna array, silica spacer, and silver ground plane. 0° to 90° arbitrary optical rotation with high degree of linear polarization (DoLP) over a broadband can be achieved readily by adjusting arm length of the L-shaped antenna. And through turning the L-shaped antennas upside down, the 0° to 90° optical rotation can be turned into 0° to -90°. Reflected phase can be shift by π after a 90° rotation of the L-shaped or Γ-shaped antennas, while optical rotation angle remains the same. Then six discrete units are designed to realize 0° to 360° polarization rotation with a step of 60°. With the combination of these units, we proposed metamaterial structures for highly efficient generation of radially polarized and azimuthally polarized vector beams.
We present a quarter-wave plate composed of two pairs of cross-shaped elliptical nanoatennas. This setup can transform linearly polarized incident light to circular polarized light at a wavelength of 862nm. The cross-shaped elliptical configuration can control the amplitude and phase of incident light. By the modulation of the elliptical size, equal amplitude and specific phase difference can be obtained in orthogonal directions. Furthermore, as a quarter-wave plate, this configuration is not sensitive to the polarized direction of the linearly polarized incident beam. In order to verify the designed metasurface, numerical simulation were performed using the finite difference time domain method. Our results may benefit novel photonics devices design such as polarization manipulation, optical sensing, optical detecting, and photonic integration.
The trade-off between the enhanced signal-to-noise ratio and reduced light absorption in thin-film photodetectors is
the main issue for improving device performance. Nanoscale patterning of metal/dielectric interface can couple incident
light into surface plasmon polaritons (SPPs) modes, leading to the enhanced absorption. However, due to the nature of
resonant excitation of SPPs, it is difficult to realize broadband absorption enhancement. In this study, we propose a novel
device structure to achieve absorption enhancement over the whole spectral response range of the thin-film In0.53Ga0.47As
photodetector. Numerical simulation shows that both the preferential forward scattering of InP cylinder and grating
coupled waveguide modes contribute to the broadband absorption enhancement.
In this paper, metallic back structure with one dimensional periodic nano-ridge is attached to the capping layer of the In<sub>0.53</sub>Ga<sub>0.47</sub>As photodetector with 100 nm absorption layer. We present finite difference time domain (FDTD) simulation to analyze the optical absorption enhancement of the photodetector. By comparing with the photodetector with planar metallic film, simulation results show that by introducing the nanostructure a 2.8 times and a 3 times absorption enhancements can be achieved under transverse magnetic (TM) and transverse electric (TE) polarized plane wave illuminations, respectively. Increasing the period of the nanostructure, the absorption enhancement peak positions exhibit a red shift. In addition, the optimization of the metal grating height and width is also crucial for maximizing the absorption enhancement. The absorption enhancements are well explained by surface plasmon polaritons and Rayleigh Anomalies phenomena. Solid simulation and theoretical results are both presented with good agreement with each other.