Variable Focal Length Near-Eye Display Reducing Eye Strain

The patent applies the dynamics principle by replacing the fixed focal length with a variable focal length imaging lens group. The lens group can dynamically adjust its focal length to match different depths of virtual images, allowing the imaging system to adapt to varying display requirements. This dynamic adjustment capability resolves the contradiction by enabling both structural simplicity (through a single lens group) and reduced eye fatigue (through variable focal length matching).

The patent implements parameter changes by modifying the focal length parameter of the imaging lens group based on the depth of virtual images. When the virtual image depth changes, the lens group's focal length is adjusted accordingly through optical path control. This parameter adaptation allows the system to maintain optimal imaging conditions for different display scenarios, thereby reducing convergence conflicts and eye fatigue while keeping the overall structure relatively simple.

The patent applies the universality principle by designing the imaging lens group to serve multiple functions: it acts as both the primary imaging element and the variable focal length adjustment mechanism. The lens group can handle different virtual image depths and display scenarios without requiring separate optical systems for each function. This multi-functionality approach reduces device complexity while achieving the three-dimensional display effect and reducing eye fatigue.

The patent introduces a semi-transparent and semi-reflective layer as an intermediary element that facilitates the variable focal length function. This layer works in conjunction with the liquid crystal lens to control the optical path and adjust the focal length. By using this intermediary mechanism, the system achieves variable focal length capability without requiring a completely complex reconfiguration of the optical system, thus balancing the three-dimensional display effect with acceptable device complexity.

The patent implements parameter changes by controlling the phase retardation of the liquid crystal lens to vary between 0 and π/2 (or odd multiples of π/2). This controlled parameter variation enables the system to achieve different light path configurations and depth of field effects. By defining specific phase retardation ranges, the patent balances the adaptability for depth of field improvement with manageable manufacturing precision requirements.

The patent utilizes polarization state changes (analogous to color changes in the broader sense of optical property changes) to control the light path. The liquid crystal lens modifies the polarization state of light by introducing variable phase retardation, which interacts with the reflective polarized layer to achieve different light path configurations. This approach allows for depth of field improvement through optical property modulation rather than mechanical adjustment, thereby reducing manufacturing precision requirements.