Off-axis holographic augmented reality displays with HOE-empowered and camera-calibrated propagation

Xinxing Xia1, Daqiang Ma1, Xiangyu Meng2, Feifan Qu2, Huadong Zheng1, Yingjie Yu1, Yifan Peng2*
1Shanghai University ,2The University of Hong Kong
Photonics Research, Optica Publishing Group, 2025
*Corresponding author
Paper

Abstract

Holographic near-eye augmented reality (AR) displays featuring tilted inbound/outbound angles on compact optical combiners hold significant potential yet often struggle to deliver satisfying image quality. This is primarily attributed to two reasons: the lack of a robust off-axis-supported phase hologram generation algorithm; and the suboptimal performance of ill-tuned hardware parts such as imperfect holographic optical elements (HOEs). To address these issues, we incorporate a gradient descent-based phase retrieval algorithm with spectrum remapping, allowing for precise hologram generation with wave propagation between nonparallel planes. Further, we apply a camera-calibrated propagation scheme to iteratively optimize holograms, mitigating imperfections arising from the defects in the HOE fabrication process and other hardware parts, thereby significantly lifting the holographic image quality. We build an off-axis holographic near-eye display prototype using off-the-shelf light engine parts and a customized full-color HOE, demonstrating state-of-the-art virtual reality and AR display results.

Method

We extend the vanilla SGD-ASM by modifying the propagation model and introduce the CITL framework to further improve imaging quality in off-axis configurations.


MY ALT TEXT
Overview of tilt-SGD and tilt-CITL. (a) Hologram generation with the tilted plane setting. The initial phase hologram loaded on the SLM is a random phase to avoid getting stuck in local optimum during iteration. The reference plane is parallel to the SLM and set for propagation between two parallel planes. Two coordinate systems are used in the propagation model: one is the SLM coordinate, while the other one is the reference coordinate. Note that the tilted plane can either rotate the reference plane around the axis or the axis. (b) Camera-calibrated hologram optimization. The phase is represented by a green frame and the amplitude is represented by a black frame. The initial hologram loaded on the SLM is also a random phase. Similar to the pipeline of tilt-SGD, the reference plane field can be obtained through the propagation of the SLM field by ASM, and the tilted plane field is obtained by applying the transformation matrix into the reference plane field. Note that tilt-CITL needs to capture the virtual imagery in a dark environment.
MY ALT TEXT
Schematic diagram of the proposed HOE (a) fabrication and (b) reconstruction procedure. The (x, y, z) HOE coordinate is established to analyze the fabrication and reconstruction process better. (c) Fabricated HOE by a 532 nm laser. The HOE consists of a layer of photopolymer and a glass substrate. The glass substrate size is about 50mm * 40mm, and the thickness is 1 to 2 mm. (d) The viewpoint was formed by illuminating the HOE with a 532 nm laser.

Results

We present the reconstruction results of holograms captured with the off-axis HOE display prototype, which supports a flexible switch between virtual reality (VR) and augment reality (AR) modes.

  1. VR-Mode Holographic Display: Tilt-CITL significantly improves brightness uniformity compared to tilt-SGD, eliminating uneven diffraction artifacts. PSNR metrics validate enhanced image quality with reduced speckle noise and preserved detail/contrast;
  2. AR-Mode Holographic Display: The system demonstrates adaptive depth rendering across 30cm (physical cube interaction) and 150cm (virtual signage) focal planes. Monochrome/color results confirm robustness under varying conditions, with uniform clarity and high-fidelity imaging validated through experimental demonstrations.

BibTeX

@article{xia2025off,
        title={Off-axis holographic augmented reality displays with HOE-empowered and camera-calibrated propagation},
        author={Xia, Xinxing and Ma, Daqiang and Meng, Xiangyu and Qu, Feifan and Zheng, Huadong and Yu, Yingjie and Peng, Yifan},
        journal={Photonics Research},
        volume={13},
        number={3},
        pages={687--697},
        year={2025},
        publisher={Optica Publishing Group}
      }