Neutral density filter-based catadioptric optical design for thin virtual reality head-mounted device

Virtual reality (VR) has been a popular trending technology affecting the lifestyles of humans. Especially for near-eye displays, VR head-mounted devices (HMDs) are designed accordingly and widely used in different fields. Nowadays, small structure size is a challenge and an urgent need for the VR HMD, while catadioptric optics is an effective and promising approach to solving this problem. Thus, this paper develops three kinds of catadioptric optical systems for thin VR HMDs by adjusting the configuration positions of the light refraction module created by the aspheric lens and the light partial reflection module formed by the neutral density (ND) filter. The comparison results of the three designs in terms of structure size and imaging quality show that multiple reflections during the light divergence process can effectively reduce the thickness of the optical structure. Reasonable transmission during the reflection process is also favorable for size reduction. Based on the designed catadioptric optical module, a varifocal VR HMD is developed to mitigate the vergence-accommodation conflict, thereby improving the image quality and the sensory experience of users.