Research published in Nanomaterials proposed geometric metasurface-based multifunctional polarizers which can simultaneously generate several polarization states, notably hybrid polarization. Due to the compact design and capability to generate multiple polarization states, these polarizers are extremely valuable to biomedical sensing, optical imaging, and material processing applications.
Significance of Polarization
Polarization is the fundamental property of a light beam and refers to the direction in which its electric field oscillates. Polarization of light is typically random, meaning that the electric field's orientation varies from one wave to the next. However, a polarizer can polarize light in any specific direction.
Polarization has various applications in our everyday lives, such as polarization cameras, polarized sunglasses, and 3D cinema.
Most optical imaging and processing applications use uniformly polarized beams such as elliptically polarized, linearly polarized, or circularly polarized light beams.
In recent years, non-uniform polarized light beams, i.e. vector beams with spatially variable polarization states, have garnered great interest as they exhibit significant advantages in high-resolution imaging, optical trapping, optical microscopy, and particle acceleration because of their precise focusing.
Metasurfaces for Generation of Polarized Light Beams
Diffraction and refraction elements can produce uniformly polarized light beams. Some standard techniques to generate vector beams are orientation-tailored liquid crystal, subwavelength grating, interferometer, fiber laser, and laser in-cavity device. However, generating polarized light beams through these techniques is quite challenging.
Metasurfaces, thin 2D layers of metamaterials, have significant potential for generating polarized light and manipulating vector beams. Due to the inexpensive fabrication, ultra-thin thickness, quick integration, and light modulation on the nano-scale, metasurfaces have seen widespread application in the design of optical devices such as polarization converters, circular polarization analyzers, and optical vortices.
The metasurface structures used to convert the polarization states include rectangular antenna arrays, high-contrast dielectric elliptical nanoposts, U-shaped aperture antennas, V-shaped antennas, and orthogonal nanoslits.
The polarization transition from a uniform to a hybrid polarization state has been realized using compact metasurfaces structure. This demonstrates that metasurfaces can manipulate the polarization of light beams.
Metasurface integrated polarizers have not been researched much, but their potential to generate multiple polarization states holds significant value in practical photonics applications.
Using Geometric Metasurfaces Polarizers for Multiple Uniform and the Non-uniform Polarization States
In this study, researchers worked on designing versatile polarizers based on optical geometric metasurfaces employing an L-shaped hole array imprinted on a silver film.
The finite-difference time-domain approach helped optimize the parameters of an L-shaped nanohole.
Integrating quarter-wave plates with varying rotation angles with a plane allows several polarization states of desired polarization light illumination to be generated simultaneously.
Metasurface polarizer for multiple uniform polarization states
Researchers designed a metasurface polarizer, with four sets of nanoholes positioned in four positions and variable rotation angles for each set of nanoholes.
The designed metasurface can generate four different polarization states when the incident polarization is vertical, horizontally linear, left-handed circular, and right-handed circular polarized.
Due to the fixed rotation angles of nanoholes in different partitions, the polarization state at each region is uniform.
Metasurface polarizer for the non-uniform polarization states
When the rotation angles of nanoholes change with their orientation, the metasurface integrated polarizer generates non-uniform polarization states, including circular, linear, and elliptical polarization.
Since the polarization state is inherently non-uniform, these polarized beams are often referred to as vector beams or vector vortex beams due to the presence of a unique spiral phase.
Important Findings of the Study
Yue et al. designed two versatile integrated polarizers based on optical geometric metasurfaces that could successfully generate multiple polarization states simultaneously.
One can produce multiple uniform polarization states with unique partitions, and these partitions across the polarizer can be modified by adjusting the nanoholes' orientation angle. The other can generate the vector vortex beam or vector beam under the circularly polarized light illumination.
The metasurface polarizer can generate circular, elliptic, linear, and even hybrid polarization states. Depending on the illumination conditions, the same integrated polarizer can generate a unique combination of vector beam polarization.
The transmission field's linear polarization in these polarizers constantly changes along the azimuthal axis. The theoretical and simulated findings validate the polarization performance of the proposed integrated metasurface polarizers.
The compact architecture of the proposed metasurface polarizer and the production of multiple integrated polarization states are advantageous in polarized light applications.
Yue, Z., Xu, J., Lu, P., & Teng, S. (2022). Versatile Integrated Polarizers Based on Geometric Metasurfaces. Nanomaterials, 12, 2816. https://www.mdpi.com/2079-4991/12/16/2816/htm