PROCEEDINGS ARTICLE | May 21, 2018
Proc. SPIE. 10676, Digital Optics for Immersive Displays
KEYWORDS: Polarization, Polarizers, Distortion, Lens design, Aspheric lenses, Fresnel lenses, Head-mounted displays
The contradiction between large field of view, big exit pupil and large eye relief in immersive virtual reality (VR) head- mounted displays limits the probability that such bulky device would be accepted by the most consumers. Typical of the wide field of view optical systems, Oculus CV1 adopts the Fresnel lens as the eyepiece to display the magnified virtual image. However, complexity in fabricating the Fresnel lens makes the commercial VR products with it cost-inefficient, especially when both surfaces employ the Fresnel surface. A wide field of view coaxial catadioptric system is proposed to serve as the magnified optics in this paper, which consists of a wire grid polarizer, two quarter-wave plates and a powered lens, making the optics thinner and fabrication easier. Note that coated on the surface of one quarter-wave plate is a partially reflecting coating. The powered lens takes the role of imaging, while the wire grid polarizer and the quarter- wave plates work together to adjust the polarization orientation so as to suppress direct transmission. The resulting monocular optical system yields the field of view as large as 110°, with virtual image exhibited 5 meters away from the observer. Exit pupil diameter and eye relief of the designed system are 9 mm and 15 mm, respectively. Considerable distortion will appear inevitably when field of view approaches 100°, which could be tackled via electronic correction. With evaluation in the CODEV, weight of the whole monocular optics is about 35 grams and the distance from the element near the observer to the image source is as thin as 30 mm, showing that the suggested design is superior to the ones in the form of singlet, doublet and the singlet using aspheric surface or Fresnel, in terms of the weight, compactness and fabricating cost. With this monocular optical system, an HMD binocular optical system can be achieved in the form of partially overlapping field of view. The present design offers a solution to acquiring the light-weight and small- volume VR optics and making cost of the commercial VR products acceptable to the public at the same time.
