Electrically switchable continuous phase liquid crystal Fresnel zone plate

Figure 1: Schematic of two-photon polymerization direct laser writing inside a liquid crystal director. Localized polymerization forms a rigid network that locks the liquid crystal director and defines a smooth phase profile. @Zhiyu Xu et al.

Augmented and virtual reality headsets, compact cameras, and adaptive optical instruments all require lightweight lenses that can refocus without adding bulky moving parts. Existing solutions such as mechanically tunable lenses increase size and complexity, while pixelated light modulators can introduce diffraction artifacts that reduce image quality and efficiency.

In a paper submitted to Light: Science & Applications, a team at the University of Oxford reports a new class of electrically switchable Fresnel zone plates built from a polymerizable nematic liquid crystal. The devices are fabricated by two-photon polymerization direct laser writing, which locally creates a three-dimensional polymer network inside the liquid crystal layer. This printed network locks the molecular orientation in selected regions, producing a smooth, continuous optical phase profile rather than the abrupt steps typical of binary diffractive optics.

Figure 2: Far-field focal-plane images showing a strong focus at 0 V and suppression of the focus at high voltage. Comparison with a binary Fresnel lens of equal size demonstrates approximately 2× higher focal intensity for the continuous-profile design. @Zhiyu Xu et al.

The first device demonstrated uses a 2π rad wrapped continuous profile. In this case. when no voltage is applied, it produces a bright focal spot at the designed focal plane; however, at higher voltages the focus disappears, providing a genuine electrical ON/OFF function. Because the optical phase varies continuously across the lens, it concentrates more light into the main focus. Results from experiments show the focal intensity is about 80% higher than that of a binary Fresnel lens with the same dimensions and focal length.

The second device demonstrated extends the concept to a 4π rad wrapped profile to achieve discrete varifocal operation. At 0 V the lens exhibits a focal length of 24 mm. Increasing the drive voltage reduces the effective phase depth while preserving the zone structure, so that at an intermediate voltage (2.1 V in this case) the same aperture behaves like a 2π rad lens with a focal length of 48 mm. At higher voltages (10 V) the phase modulation is largely suppressed, and the lens is switched OFF, yielding a three-state element: near focus, far focus, and OFF.

Figure 3: A four-pi wrapped phase profile provides two voltage-addressable focal states (24 mm at 0 V and 48 mm at 2.1 V), and an OFF state at higher voltages; example imaging demonstrates the ability to switch focus without mechanical motion. @Zhiyu Xu et al.

"By sculpting a three-dimensional polymer network inside the liquid crystal, we can write a high-fidelity phase profile and then use an applied voltage to reconfigure its optical function," the researchers explain.

The approach combines the low-power electro-optic tunability of liquid crystals with the optical performance of a continuous-profile diffractive lens. Beyond near-eye displays, the same platform could be used for compact beam shaping, lightweight imaging systems, and adaptive optics modules. The authors note that faster switching should be achievable with thinner liquid crystal layers and optimized materials, while scale-up could leverage parallel laser writing processes or replication methods such as nanoimprint lithography.

Reference

lectrically switchable continuous phase liquid crystal Fresnel zone plate

Zhiyu Xu, Camron Nourshargh, Tianxin Wang, Alec Xu, Nathan Spiller, Urban Mur, Martin J. Booth, Steve J. Elston & Stephen M. Morris

https://www.nature.com/articles/s41377-026-02251-3

Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, CAS