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Overview
Mixed reality (MR) devices such as Apple Vision Pro and Meta Quest Pro are candidates for next-generation mobile platforms. By enabling more direct interaction with digital information, MR supports applications in the metaverse, spatial computing, and digital twins across smart tourism, smart healthcare, smart manufacturing, and smart buildings. Improving long-term wear comfort requires more compact and lighter-weight near-eye displays.
Diffractive liquid-crystal optics
In contrast to refractive optics that create a phase profile via optical path differences, diffractive liquid-crystal (LC) optics generate the required phase by meeting a half-wave condition along the thickness direction, typically only a few micrometers for visible wavelengths. LC diffractive elements offer several advantages, including high diffraction efficiency (near 100%), manufacturability, polarization selectivity, and dynamic switching, making them promising candidates for near-eye displays. However, diffraction angles depend on wavelength, which causes significant chromatic aberration and prevents their direct use for imaging.
Achromatic LC system design
To address this chromatic aberration while maintaining an ultrathin form factor, Shin-Tson Wu and colleagues at the College of Optics and Photonics, University of Central Florida, proposed an achromatic LC optical system composed of three stacked LC components that exploit polarization selectivity. Each element's transmission spectrum and phase profile are engineered to control polarization and correct chromatic dispersion.
Specifically, the achromatic LC lens system uses a first component that acts as a broadband lens with high efficiency across the visible spectrum, a second component that functions as a half-wave plate to switch the polarization state of blue light, and a final LC lens whose transmission spectrum is designed to act selectively on blue and red wavelengths. By stacking these three LC elements, achromatic behavior is achieved. The same principle can be applied to build achromatic gratings and beam-steering systems.
Experimental validation
The concept was validated with two light engines: a laser projector and an organic light-emitting diode (OLED) display panel. Imaging with a single LC lens showed severe chromatic aberration due to the wavelength dependence of diffractive optical power. The achromatic lens system markedly suppressed chromatic errors and produced substantially improved color performance. By appropriately controlling polarization states, the approach can be extended to other diffractive optical devices to realize more compact optical modules for MR-enabled applications.
