Vector beams, enabling spatially dependent polarization states in the radial and azimuthal directions, have been intensively studied for various applications such as imaging, communication, and optical manipulation of magnetic materials. While liquid crystal-based Q-plates have been routinely employed to convert linearly polarized light to vector beams efficiently, their utility diminishes in the terahertz (THz) spectrum due to excessive absorption and large wavelengths. Alternatively, resonant metasurface-based Q-plates have been employed to demonstrate THz-vector beam generation, however, these Q-plates suffer from narrow operational bandwidth. We propose a method to design and fabricate twisted effective media-based Q-plate generating broadband terahertz vector beams. The twisted media consisted of stacked multiple layers of 270-um thick Si substrates with rotated line and space patterns following a specific twisting power- the angle per unit length along the beam propagation direction. By calculating the effective media with Berreman 4x4 method, we obtained the operating bandwidth of 0.5-1.5 THz (0.5-2.5 THz) with the twisting power of 22.5°/mm (4.5°/mm).
We present electrically-driven generation and dynamics of the real-space optical vortices based on the high-dimensional gradient-thickness optical cavity. The structure consists of a metal-dielectric multi-layer that supports non-trivial topological phases, generating optical vortex lines and rings in three-dimensional generalized parameter space. We experimentally demonstrated the high-dimensional gradient-thickness optical cavity by liquid crystal-based multi-layer structure, which bijectively projects a surface slice of generalized parameter space into the real space. By electric control of the alignment of liquid crystal molecules, we successfully spanned the architecture of the high-dimensional optical singularity in real space, which actively generates and manipulates the optical vortex-antivortex pair.
Owing to the Purcell effect, optical micro-structures can control the radiative decay of the quantum emitters in transition metal dichalcogenide (TMDC) media. However, conventional optical microstructures change the local density of optical states (LDOS) not only at the photoluminescence (PL) wavelength of the TMDC quantum emitters and but also at the pump wavelength simultaneously and thus cause an inevitable influence on the excitation conditions. We propose and experimentally demonstrate a reflective metallic metasurface for independently engineering the excitation and radiation of quantum emitters in the TMDC monolayer
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