Performance enhancement and size reduction of near-eye display

• Main Author: Cheng, Qijia
• Other Authors: Zheng Yuanjin
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: https://hdl.handle.net/10356/144165
• Institution: Nanyang Technological University

Near-eye display (NED) paved its way in a variety of applications of modern virtual reality (VR). However, current NEDs have lots of limitations, which lead to compromised user experience and strongly limit their potential in real-world scenarios. Two of the most noticeable features that demanding improvements are resolution and size. On the one hand, applications of modern VR devices introduce more detailed textures and increased field-of-view (FoV), altogether create excessive demand for resolution. On the other hand, more mobile application scenarios of virtual reality and augmented reality (AR) bring the requirement of size reduction. The trend of developing high-resolution NED with small form-factor is with no doubt. During the last several decades, attempts were made to improve the resolution of NED. However, the utilization of eye-tracking and optical tiling adds a fairly amount of complexity to the NED system, which in turn makes the device even bulkier. Thus, a compact near-eye display device that can deliver excellent image quality is still in great demand by society. In this thesis, theory and methods are demonstrated to improve key performance factors in modern NED, including resolution, depth perception, and size. In Chapter 3, to solve the main conflict between resolution and device size, a versatile resolution enhancement method for NED is implemented by overlapping multiple display panel images. Based on display super-resolution, this overlapping method effectively increases the perceived resolution without optical complexity. By investigating the algorithm theory of image generation and calibration, the perceived resolution can be enhanced and overcome the physical resolution of a single display panel. A NED prototype based on a semi-transparent mirror is designed and fabricated. The experiment demonstrated decent results of resolution enhancement. Compare with the conventional method of display tiling, my method offers an equivalent level of performance yet reduces system complexity, brings more flexibility to the design of NED. Free-form optics enable innovative ways of implementing compact size NED. In Chapter 4, a design routine of off-axis near-eye display system is implemented. A compact near-eye display system described by x-y polynomial function is developed with a 4mm diameter exit pupil, a 21.5° diagonal full field-of-view (FoV) and 23 mm eye relief. Freeform surfaces are used to effectively reduce the size of NED while correcting the off-axis aberration. The designed system yields good optical performance yet very compact in terms of size, compared to traditional NED. A prototype is demonstrated with components available from the market. The prototype effectively indicated the feasibility of the design as a compact NED. Light field receives great research attention in recent years as a feasible way to solve convergence-accommodation conflict in NED and stereoscopic display. Based on either microlens or pinhole, light field NED demonstrates an effective size reduction on the longitudinal direction of the device. In chapter 5, a light field NED with random pinhole design is demonstrated with unique viewing zone and optical simplicity. Further research is recommended in chapter 6 to combine the individual technique as a hybrid device, where multiple light field display module can be used for super-resolution, with the design flexibility of free-form optics. My research can act as guidance in the design of future NED to reduce device size, enhance resolution, and incorporate the depth sense of current virtual reality headset, thus further improve virtual reality user experience.