.png){kind=icon}
.png){kind=icon}
Return
Efficient Construction Method of Vector Vortex Beams Based on Birefringent Metasurfaces
.png){kind=icon}
PRE
AI
DOI：10.3788/LOP251198.png)
.png){kind=icon}
Original request for help.png){kind=icon}
Share.png){kind=icon}
Save
Abstract
En 中文
Objective Vector vortex beams, characterized by helical phase fronts, complex spatial structures, and anisotropic polarization distributions, have broad applications in super-resolution imaging, long-distance transmission in atmospheric or underwater environments, and laser micro/nano-processing. Conventional vector vortex polarization converters are predominantly based on natural birefringent crystals. However, their bulky size, challenging fabrication and integration, and severe chromatic dispersion limit their applicability in integrated optical systems. To address these limitations, this study proposes a design method for an all-dielectric transmissive optical metasurface-based vector vortex polarization converter, leveraging the birefringent effects of locally engineered generalized waveplate (GWP) and quarter-wave plate (QWP). Methods The proposed approach employs meta-atom structures with waveplate-like functionalities to construct vector vortex beams via geometric phase modulation. The meta-atom unit consists of a silicon dioxide (SiO2) substrate and an amorphous silicon (alpha-Si) nanostructure. By optimizing the dimensions of the meta-atoms, GWP-and QWP-type units are designed to achieve desired polarization conversion. The metasurface is fabricated by arranging these meta-atoms on the substrate, and its polarization conversion properties are systematically investigated. The operational bandwidth and robustness of the device are further validated by varying the incident light source and introducing intentional structural deviations in the meta-atom dimensions. Results and Discussions Under left circularly polarized (LCP) illumination at lambda =632.8 nm, optimized GWP and QWP meta-atoms are designed (Fig. 4). Based on geometric phase principles, polarization converters for generating radial polarized vortex (RPV) and LCP beams are constructed (Fig. 7). Experimental results demonstrate that the generated RPV and LCP beams exhibit doughnut-shaped intensity profiles, uniform polarization states, and helical phase distributions ranging from-180 degrees to 180 degrees, consistent with the properties of vector vortex beams (Fig. 8). The polarization conversion efficiencies for RPV and azimuthally polarized vortex (APV) beams reach 94.13 degrees o and 91.41 degrees o for GWP-type devices, and 80.18 degrees o and 82.78 degrees o for QWP-type devices, respectively. Broadband characterization is conducted at wavelengths A1=600 nm, A2=610 nm, A3=620 nm, A4=640 nm, and A5=650 nm. The GWP-type device exhibits polarization angles with less than 17 degrees deviation from theoretical predictions at 632.8 nm and 640 nm, while demonstrating gradient variations at 620 nm. The QWP-type device maintains polarization angles within 17 degrees deviation across 620-650 nm, with consistent gradient behavior (Fig. 10). These results indicate operational bandwidths of 610-640 nm for GWP-type devices and 620-650 nm for QWP-type devices.Robustness analysis is performed by introducing +/- 5 nm deviations in the length (L), width (W), and height (H) of the meta-atoms (Fig. 11). The device maintains stable beam intensity, polarization, and phase distributions, confirming its tolerance to fabrication tolerances within +/- 5 nm. Conclusions To overcome the limitations of conventional bulky and complex vector vortex polarization converters, this study presents an all-dielectric metasurface-based design for transmissive vector vortex beam generation. Jones matrix analysis confirms the theoretical polarization conversion efficiencies of 99 degrees 0 and 98 degrees 0 for GWP and QWP-type devices, respectively. Finite-difference time-domain (FDTD) simulations demonstrate experimentally achievable efficiencies of 94.13 degrees 0 (GWP-type, operational bandwidth: 610- 640 nm) and 80.18 degrees 0 (QWP-type, operational bandwidth: 620-650 nm), with fabrication tolerances within +/- 5 nm. Although the nano-scale meta-atoms require high precision, their simplified structural constraints and strong robustness significantly reduce practical fabrication challenges. This metasurface-based approach offers a compact, high-performance solution for vector vortex beam generation, with promising applications in optical microscopy and biomedical imaging.
Keywords:
optical metasurface
vector vortex beam
polarization conversion
birefringence effect
general waveplate
quarter-wave plate
Journal
L
IF:
1
Papers:
596
Citations:
0