Varifocal Pancake Lens Assembly for HMD Vergence-Accommodation Conflict

The patent applies a varifocal lens that can dynamically adjust its focal length to match the user's accommodation state. The lens transitions from a fixed focal length design to a dynamic one, allowing the optical system to adapt to different viewing distances and reduce vergence-accommodation conflict, thereby decreasing eye strain during prolonged VR/AR/MR usage.

The patent changes the optical parameter of the lens by introducing a varifocal lens with adjustable focal length. This parameter change allows the lens to adapt its focusing capability to match the user's eye accommodation state, resolving the mismatch between vergence and accommodation that causes eye strain and headaches.

The varifocal lens serves multiple functions: it provides focus adjustment to match accommodation state, maintains compact form factor, and preserves optical quality. By integrating these functions into a single lens element, the patent reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving eye strain reduction.

The patent introduces dynamic adjustability to the optical system through the varifocal lens, allowing real-time adaptation to user accommodation needs. This dynamic capability addresses the vergence-accommodation conflict without requiring complex multi-element systems, as the single varifocal lens handles focus adjustment, field curvature correction, and optical power variation.

The patent employs a nested cavity configuration where optical elements are arranged in a compact, nested structure. The first and second optical elements form a cavity that houses additional components, allowing the optical path to be folded within a small volume. This nesting approach reduces HMD size while distributing alignment requirements across multiple standardized interfaces rather than requiring single-point precision.

The patent folds the optical path by introducing a cavity configuration that utilizes three-dimensional space more efficiently. By arranging optical elements in a nested, multi-dimensional configuration rather than a linear sequence, the system achieves compact HMD size. The cavity structure provides built-in alignment references that reduce the stringency of manufacturing precision requirements compared to traditional folded-optic designs.