A new publication from
Opto-Electronic Advances;
DOI 10.29026/oea.2025.240181 , discusses high-efficiency achromatic liquid crystal diffractive optical elements.
Augmented reality (AR) and virtual reality (VR) technologies have transformed human-digital interaction, unlocking new opportunities in healthcare, gaming, education, and manufacturing. A key challenge for the widespread adoption of AR and VR, however, lies in developing compact, lightweight, and energy-efficient optical systems that make these devices truly wearable. Liquid crystal (LC)-based Pacharatnam-Berry phase optical elements (PBOEs) (Fig. 1(a)) are a promising solution, offering an ultrathin form factor, high diffraction efficiency, polarization selectivity, and the ability to switch dynamically. Despite their potential, chromatic aberration remains a significant challenge for PBOEs, as shown in Fig. 1(b).
Several strategies have been explored to mitigate chromatic aberration. One approach is to laminate a PBOE film onto a refractive lens, but this adds bulk to the system. A more efficient solution involves planar optical elements, such as switchable PBOEs, which modulate phase retardation for different colors in separate frames. However, this requires high frame rates to avoid color breakup. Another method is digital compensation, where images are pre-processed to correct chromatic aberration, though it comes with high power consumption and computational demands.
Further advancements have focused on enhancing the performance of PBOEs and other optical elements, such as waveplates and holographic films. Techniques like stacking RGB narrowband PBOEs or combining them with half-wave plates or holograms show promise but often result in reduced optical efficiency, ghost images, and color crosstalk. Additionally, fabrication challenges, including the precise control of birefringence and layer thickness, continue to complicate these methods. Despite progress, achieving an optimal balance between performance, complexity, and efficiency remains a critical hurdle for AR/VR optical systems.
The research group led by Prof. Shin-Tson Wu at the University of Central Florida is pioneering advancements in liquid crystal photonics, focusing on applications in AR/VR displays and imaging optics. Recently, they introduced a transformative solution using a multi-twist structure (Fig. 1(c)) to address chromatic aberration (Fig. 1(d)) in liquid crystal polarization-based optics, achieving achromatic PBOEs. This innovation holds significant promise for AR/VR systems, imaging technologies, and display advancements.
To mitigate chromatic aberration in polarization-based lenses (PBLs), the team designed three specialized PBLs tailored to RGB colors with identical focal lengths. While this approach minimizes color distortion, it initially faced challenges such as crosstalk, leading to light loss and ghost images when RGB colors overlap. To overcome this, the researchers developed narrowband PBLs, each exclusively focusing on red, green, or blue light as shown in Fig. 2(a-c). For example, the PBL designed for red light should only focus the red light while not affecting the blue and green lights. In this way, chromatic aberration among the RGB colors can be eliminated, as shown in Fig. 2(d). By employing a multi-twist structure, the team optimized the thickness and twist angles of individual layers to achieve precise phase retardation for each wavelength, effectively eliminating crosstalk and chromatic aberration. Experimental validation using a laser projector confirmed the efficacy of this design, with each narrowband PBL modulating only its target color as shown in Fig. 2(e-g). By stacking the three narrowband PBLs, they merged RGB beams into a near-perfect white image with minimal residual aberration as depicted in Fig. 2(h).
Expanding the scope, the team also explored thicker narrowband PBOEs, achieving a contrast ratio exceeding 500:1 across customizable RGB wavelengths. Using Rigorous Coupled-Wave Analysis and polarization raytracing in OpticStudio, they demonstrated the method’s versatility across laser, LED, and quantum dot light sources, delivering superior chromatic correction as shown in Fig. 3.
Overall, this innovative multi-twist structure not only enhances compactness, optical efficiency, and fabrication simplicity but also opens new avenues for high-performance solutions in AR/VR displays, imaging systems, and advanced photonics.
Keywords: achromatic diffractive optical elements / Pacharatnam-Berry phase optical elements / liquid crystal planar optics / near-eye displays
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Shin-Tson Wu is a Trustee Chair Professor at College of Optics and Photonics, University of Central Florida. He received his PhD in Physics from the University of Southern California and BS in Physics from National Taiwan University. He is a Charter fellow of National Academy of Inventors, and a recipient of Optica Edwin H. Land Medal (2022), SPIE Maria Goeppert-Mayer Award (2022), OSA Esther Hoffman Beller Medal (2014), SID Slottow-Owaki Prize (2011), OSA Joseph Fraunhofer Award (2010), SPIE G. G. Stokes Award (2008), and SID Jan Rajchman Prize (2008). His research group focuses on augmented reality and virtual reality, including light engines (LCOS, mini-LED, micro-LED, and OLED), optical systems (lightguide, diffractive optics, and projection optics), and display materials (liquid crystals, quantum dots, and perovskites).
Currently, there are ten Ph.D. students, and one M.S. student in his group. Students in Prof. Wu’s group have received plenty of awards and scholarships. In 2021, Jianghao (Jasper) Xiong and Kun (Kelly) Yin have received ILCS-FRL Diamond and Platium award, respectively. In 2022, Yannanqi (Nancy) Li has received ILCS-FRL Gold award and En-Lin Hsiang has won the SPIE 2022 scholarship. In 2023, Qian Yang has received the SPIE 2023 scholarship. Recently, Zhenyi Luo also received ILCS-FRL Diamond award.
More information can be found on the group page: https://lcd.creol.ucf.edu/Default.htm
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Ding YQ, Huang XJ, Ma YZY et al. High-efficiency RGB achromatic liquid crystal diffractive optical elements.
Opto-Electron Adv 8, 240181 (2025). doi:
10.29026/oea.2025.240181