A Review of Two-Dimensional Liquid Crystal Polarization Gratings

Design of two-dimensional multilevel optical anisotropic diffraction gratings with a generative adversarial network

This study uses a generative adversarial network to design multilevel optical anisotropic diffraction gratings with specific customizable characteristics. As input, this method uses the far electric field of polarization and intensity in each diffracted light through the gratings to design. Using the finite-difference time-domain method, the designed structures are numerically evaluated, confirming that they can be created with the intended parameters. Multilevel optical anisotropic diffraction gratings created this way can be used in various fields to develop improved optical elements.

Research on laser target dynamic tracking system with rotating polarization grating

A micromechanical target tracking system based on polarization grating (PG) is designed to meet the conformal design of laser communication systems and to realize the lightweight and miniaturization of space laser communication networking. The rotating dual PGs are applied to the dynamic tracking of laser targets for the first time, the relationship between the target position and the dual polarization gratings (PGs) angles is defined, and the PG beam deflection multi-coordinate construction and decoupling are carried out. A dual PGs mathematical model was established, and a controller based on the dual PGs system loop was designed. After calibration and dynamic verification of the dual PGs, the unmanned aerial vehicle (UAV) tracking experiment is conducted for the first time, and the dual axis closed-loop tracking error of the dynamic target is within 300µrad (RMSE). The feasibility of dual PGs tracking formula, the feasibility of laser target fixed-point closed-loop control, and the dynamic closed-loop tracking performance are verified. In engineering applications, the dual PGs tracking system has guiding significance for realizing the lightweight and miniaturization of system integration, as well as the possibility to replace the traditional tracking control system.

Diffraction characteristics of orthogonal gratings analysis based on a spatial light modulator

The diffraction characteristics of orthogonal gratings with variable duty cycles and phase modulation depths are analyzed by using a spatial light modulator. The calculation methods of the transmission function, far-field diffraction light field, and diffraction efficiency of orthogonal gratings are deduced in theory. Meanwhile, the influences of the duty cycle and phase modulation depth on the diffraction characteristics of the orthogonal grating are discussed. The simulation and experimental results verify the correctness of the theoretical derivation. This method can be widely used in the fields of an optical vortex array, laser parallel processing, optical computing, optical communication, and optoelectronic hybrid processing.

Diffraction characteristics of a non-mechanical beam steering system with liquid crystal polarization gratings

The non-mechanical beam steering system is composed of multiple liquid crystal polarization gratings (LCPGs) cascaded by binary or ternary technologies. However, cascading multiple LCPGs cause the beam from one LCPG to obliquely enter the subsequent LCPGs, changing their diffraction efficiency and working voltage at different steering angles. This paper uses the elastic continuum theory of liquid crystals to simulate the tilt angle of liquid crystal molecules under different voltages. The transmission process of the beam in the system at oblique incidence is described with an extended Jones matrix, and the highest diffraction efficiency and working voltage of each LCPG at different steering angles are calculated using vector diffraction theory. It is convenient to calibrate the LCPGs' working voltage and analyze the system's diffraction characteristics. In addition, we used an improved binary cascade technology to design a LCPG non-mechanical beam steering system with a steering angle of ±10° and an angular resolution of 0.67°. Compared with binary cascade, this technology can effectively reduce the number of cascaded devices and increase the system throughput under the same maximum beam steering angle and angular resolution.