Optical phased arrays (OPAs) are crucial in beam-steering applications, particularly as transmitters in light detection and ranging and free-space communication systems. In this paper, we demonstrate a on-chip OPA that emits multiple orbital angular momentum (OAM) beams in different directions, each carrying unique topological charges. By superimposing a forked 1×3 Dammann grating on the grating array, six OAM beams with topological charges of ±3, ±4, and ±5 can be radiated from the OPA region. The OPA chip was fabricated on a silicon-on-insulator platform, and the simultaneous generation of multiple OAM beams was realized experimentally. The directions of these vortices can be steered by adjusting the wavelength of the input light and the bias voltages of the phase shifters, enabling a remarkable field of view (FOV) of 140 deg×40 deg within a 120-nm wavelength range. We pave the way for developing systems with ultrawide FOVs, improving the resolution of remote sensing and broadening the possibilities of free-space communications.
Augmented reality (AR) has attracted great attention from academia and industry for its potential applications in diversified fields. In order to eliminate the accommodation-vergence conflict in AR display systems, which causes 3D visual fatigue after prolonged use, several approaches have been proposed. This paper presented three types of true three-dimensional (3D) AR display techniques. The first is multi-plane volumetric display based on liquid crystal (LC) devices. We utilized fast switching polymer stabilized LC (PSLC) scattering films and polarization selective cholesteric LC (CLC) reflective films, respectively, realizing magnified 3D images augmented on the real world. The second is holographic display based on two holographic optical elements (HOEs), functioning as an optical combiner, an ocular lens and a beam expander simultaneously. For the third technique, we proposed two super-multi-view display approaches based on polarizing glasses and geometry phase optical elements (GPOEs), respectively.
Augmented reality (AR) technology, which integrates virtual computer-generated information into the real world scene, is believed to be the next-generation human-machine interface. However, most AR products adopt stereoscopic 3D display technique, which causes the accommodation-vergence conflict. To solve this problem, we have proposed two approaches. The first is a multi-planar volumetric display using fast switching polymer-stabilized liquid crystal (PSLC) films. By rapidly switching the films between scattering and transparent states while synchronizing with a high-speed projector, the 2D slices of a 3D volume could be displayed in time sequence. We delved into the research on developing high-performance PSLC films in both normal mode and reverse mode; moreover, we also realized the demonstration of four-depth AR images with correct accommodation cues. For the second approach, we realized a holographic AR display using digital blazed gratings and a 4f system to eliminate zero-order and higher-order noise. With a 4k liquid crystal on silicon device, we achieved a field of view (FOV) of 32 deg. Moreover, we designed a compact waveguidebased holographic 3D display. In the design, there are two holographic optical elements (HOEs), each of which functions as a diffractive grating and a Fresnel lens. Because of the grating effect, holographic 3D image light is coupled into and decoupled out of the waveguide by modifying incident angles. Because of the lens effect, the collimated zero order light is focused at a point, and got filtered out. The optical power of the second HOE also helps enlarge FOV.
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