Three-Channel Terahertz Orbital Angular Momentum Beam Generator Based on Polarization Multiplexing Metasurface

Literature Overview

The paper by Li Pengxuan et al., published in Chinese Journal of Lasers in 2026, presents a three-channel terahertz orbital angular momentum (OAM) beam generator based on a single-layer all-dielectric polarization-multiplexed metasurface. The design involves constructing near-field phase distributions for different channels, solving the Jones matrix elements of meta-atoms, and optimizing unit structures using a particle swarm optimization algorithm. Experimental results demonstrate that at approximately 0.55 THz, when 45°, 90°, and 135° linearly polarized plane waves are incident on the metasurface, the transmitted co-polarization components form 0th, +1st, and +2nd order focused OAM beams at different spatial positions on the 7 cm focal plane. All OAM modes exhibit good linear polarization characteristics, with measured degrees of polarization exceeding 0.7, reaching a maximum of 0.99.

Core Technical Points

The polarization-multiplexing approach allows a single metasurface layer to generate three distinct OAM modes simultaneously by encoding different phase distributions for different polarization states. This is a significant advancement in compact terahertz device design, as it eliminates the need for multiple separate optical elements. The particle swarm optimization algorithm plays a crucial role in determining the optimal geometric parameters of each meta-atom to achieve the desired Jones matrix response.

The use of all-dielectric metasurfaces avoids the absorption losses associated with metallic structures, which is particularly important at terahertz frequencies where metal conductivity is reduced due to increased surface roughness scattering. The experimental verification at the focal plane demonstrates that the generated OAM beams maintain their spatial mode purity over propagation distances of several centimeters.

Technical Parameters and Performance

Study Insights and Implications

While this work belongs to the field of terahertz photonics rather than pipe fitting engineering, the underlying design philosophy offers valuable parallels. The concept of encoding multiple functional responses into a single structural layer through careful geometric optimization is analogous to how we design multi-functional pipe fittings that must simultaneously satisfy strength, corrosion resistance, and weldability requirements. The optimization methodology, which systematically searches for optimal structural parameters to achieve a target response, mirrors the finite element-based design optimization approaches used in fitting design, where geometric parameters such as fillet radii, wall thicknesses, and transition angles are optimized to minimize stress concentrations and weight.

The achievement of high polarization purity across multiple channels also reflects the importance of mode control and interference management, concepts that are directly relevant to managing stress wave propagation and vibration modes in piping systems subjected to dynamic loading.