Design and demonstration of a vari-focal optical see-through head-mounted display using freeform Alvarez lenses.

Austin Wilson,Hong Hua

doi:10.1364/oe.27.015627

Abstract

Alvarez lenses offer accurate and high-speed, dynamic tuning of optical power through a lateral shifting of two lens elements, making them an appealing solution to eliminate the inherent decoupling of accommodation and convergence seen in conventional stereoscopic displays. In this paper, we present a design of a compact eyepiece coupled with two lateral-shifting freeform Alvarez lenses to enable a compact, high-resolution, optical see-through head-mounted display (HMD). The proposed design is able to tune its focal depth from 0 to 3 diopters, rendering near-accurate focus cues with high image quality and a large undistorted see-through field of view (FOV). Our design utilizes an 1920x1080 color resolution organic light-emitting diode (OLED) microdisplay to achieve a >30 degree virtual diagonal FOV, with an angular resolution of <0.85 arcminutes and an average optical performance of > 0.4 contrast over the full field. We also experimentally demonstrate a fully functional benchtop prototype using mostly off-the-shelf optics.

Highlights

Conventional head-mounted displays (HMDs) lack the ability to correctly render focus cues, including accommodation and retinal blur effects, because they merely present a pair of stereoscopic images with binocular disparities and other pictorial depth cues on a fixed image plane
These displays force an unnatural decoupling of the accommodation and convergence cues and induce a fundamental problem referred to as the vergenceaccommodation conflict (VAC), which can lead to various visual artifacts, such as distorted depth perception and visual fatigue [1,2,3]
We present a novel design of a high-resolution vari-focal plane optical seethrough HMD (OST-HMD) system using freeform Alvarez lenses coupled with ultra-fast high resolution piezo linear actuators

Summary

Introduction

Conventional head-mounted displays (HMDs) lack the ability to correctly render focus cues, including accommodation and retinal blur effects, because they merely present a pair of stereoscopic images with binocular disparities and other pictorial depth cues on a fixed image plane. A key enabling technology in a vari-focal HMD is an active optical element that is able to dynamically tune the optical power of the system at a high speed and in a large depth range (typically a few diopters) while offering a large, clear aperture. Examples for such an active optical element include: deformable membrane mirror devices (DMMD) [22], electrowetting lenses [23], elastomer-membrane fluidic lenses [24], liquid crystal lenses [25], and digitally switchable multi-focal lenses [26]. Our design utilizes a Sony 0.7” OLED microdisplay for the virtual display path to achieve a 30 degree diagonal FOV and 1920x1080 pixel resolution, with an optical performance greater than 20% modulation contrast at 0.81 arcmins over the full FOV

Optical system design

Conclusion

Findings

Disclosures