Multi-variable focal lens system for extended depth of field in augmented reality display

In augmented reality (AR), focal accommodation for real objects and augmented imagery is essential for comfortable viewing, and this requires a depth of field (DoF) in AR displays. Wide DoFs have been achieved in various display systems, but these systems are often bulky, highly power-consuming, and computationally complex. Hence, we propose a simple and effective optical method to extend the DoF in AR displays. The proposed method harnesses a focus tuning block consisting of a multifocal lens (MFL) and a focus tunable lens. Through the multi-variable focusing unit, virtual imagery is displayed at spatially separated focal depths using the MFL; then, the focus tunable lens dynamically tunes the foci. This enables the individual virtual objects to be sequentially focused on the same image plane, helping to register them with the real objects in the user’s eye accommodation. The proposed approach was numerically simulated, and its performance was experimentally evaluated with an AR display equipped with the focusing unit, which extended the DoF from 0.3 m (3.3 diopters) to 2 m (0.5 diopters).