All-dielectric metasurf ace beam deflector at the visible frequencies

摘要

Beam deflectors, which are able to change or control the propagation direction of the beam in free space, are important optical components in integrated optical circuit and optical communication systems. However, with the de-velopment of miniaturization of the optical systems, conventional reflector-based mechanical beam deflectors confront a huge challenge due to their large size and incompatible to the device integration. Recently, metasurfaces, also known as two-dimensional metamaterials, have attracted significant attentions due to their ultrathin thicknesses and perfect con-trolling of amplitude, phase and polarization of the beams. On account of full 2p phase control, metasurfaces are widely used in lensing, holograms, wave plates and other applications. The original metasurfaces are mainly designed using metallic resonant structures. However, metallic metasurfaces always have large ohmic losses, which are similar to the plasmonic structures. To overcome the loss issue, metasurfaces using dielectrics, such as silicon and titanium dioxide (TiO2), appear and are widely employed in the novel optical devices’ design. Here we propose and design an all-dielectric flat metasurface beam deflector which is composed of a single layer array of TiO2 nanoantennas resting on a fused-silica substrate. The TiO2 nanoantennas are considered as birefringent elements and the Jones transfer matrix can be used to model electrometric response of each TiO2 nanoantenna. Based on the phase discontinuity principle, we design the beam deflectors that operate at the wavelengths of 450 nm, 532 nm, and 633 nm, respectively. For the circularly polarized in-cident light, the polarization conversion efficiencies of the designed beam deflectors are all higher than 90% at the oper-ation wavelength. Numerical simulations based on the finite-difference time-domain (FDTD) algorithm show that de-flecting behaviors of the proposed devices with deflection angles of 15°, 30° and 45° are all in excellent agreement with our theoretical predictions. The simulated optical transmissions of the designed deflectors are 88.2%, 86.8% and 71.3% for 15°, 30° and 45° at wavelength of 450nm; 86.7%, 86.4%, 69.7% for 15°, 30° and 45° at wavelength of 532nm and 89.3%, 80.6%, 62.0% for 15°, 30° and 45° at wavelength of 633nm, respectively. Compared with other thin-film plasmonic beam deflectors using metallic nanoslits, the transmission efficiencies of the metasurface beam deflectors are much higher. The all-dielectric metasurface beam deflector may have potential applications for manipulation of the light propagation in the high-integration optical systems.