Goethe, University of Central Florida research team showcases light and thin achromatic diffractive liquid crystal optical systems

Headdisplay devices such as Apple Vision Pro, Meta Quest, and PICO are expected to completely change the way we perceive and interact with various digital information. By providing more direct interaction with digital information, MR has become one of the key driving forces for the metaverse, spatial computing, and digital twins, and has begun to be widely applied in fields such as intelligent tourism, intelligent healthcare, intelligent manufacturing, and intelligent buildings.

But in order to further enhance the ergonomics of MR, the industry must improve the overall user experience, especially long-term wear comfort. To achieve this goal, ultra compact and lightweight devices are key targets.

Recently, a team composed of Goethe Corporation and the University of Central Florida showcased an achromatic diffractive liquid crystal optical system with an ultra-thin and lightweight appearance.

The team pointed out that diffractive liquid crystal optical devices have the advantages of ultra-thin, lightweight, high diffraction efficiency (nearly 100%), easy manufacturing, polarization selectivity, and dynamic switching, making them highly promising optical components in the fields of virtual reality and hybrid reality.

Unlike refractive index optics that use optical path difference to generate phase maps, diffractive liquid crystal optical elements generate the required phase map by satisfying the half wave condition along the thickness direction. However, the diffraction angle of liquid crystal optical elements depends on the wavelength, which in turn leads to severe color difference and cannot be used for imaging purposes.

In order to overcome this long-standing color difference problem while maintaining an ultra-thin appearance, a team composed of Goethe Corporation and the University of Central Florida has proposed an achromatic liquid crystal optical system. The device consists of three stacked diffractive liquid crystal optical elements, which have specially designed spectral response and polarization selectivity.

In other words, in order to control the polarization state and correct color difference, the transmission spectrum and phase diagram of each optical element are carefully designed.

Among them, for the achromatic liquid crystal lens system that eliminates the focal shift between blue and red light, the first component is a broadband lens that displays high efficiency in the visible spectrum region; The second component is a half wave plate designed to switch the polarization state of blue light; The final component is an LC lens with a specially designed transmission spectrum, which is only effective for blue and red light.

The achromatic liquid crystal lens system can be achieved by simply stacking these three components together, and both achromatic grating and deflector systems can be constructed based on the same principle.

This concept has been validated through two different types of light engines: laser projectors and organic light-emitting diode display panels. The image of a single liquid crystal lens exhibits severe color difference, which is caused by the wavelength dependence of diffractive optical devices on optical power.

However, the achromatic lens system significantly improves color performance and greatly suppresses color difference. The experimental results indicate that two types of light engines, laser projectors and organic light-emitting diode display panels, have significantly improved imaging performance. In addition, simulation results show that compared to traditional broadband diffractive liquid crystal lenses, the lateral color shift is reduced by about 100 times.

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The team pointed out that by appropriately controlling the polarization state, this method can be extended to other types of diffractive optical devices, potentially achieving more compact optical components.

Source: Sohu