See-through head-worn display (HWD) architectures

Abstract

Over the past three decades, as computer and display technology advanced along the path laid out by Moore’s law of miniaturization and functionality, many writers presented scenarios for augmented reality (AR) displays centered on bringing information to the individual. Initially, the emphasis was on the individual experience, so the technology, which did not pursue a see-through geometry, seemed viable. When the initial solutions - a generation of look-at displays resting on the nose bridge - appeared around 2000, the market did not embrace it. Suddenly now, social media has burst on the scene and wireless access has become ubiquitous. The result is a renewed research interest in a family of see-through head-worn displays (HWDs) enabling real-time interaction throughout the global community. See-through HWD design inherently requires an interdisciplinary approach; optical engineering, opto-mechanics, ergonomics, and psychology are all keys to the design process. The last decade has seen a game-changing technology emerge, the organic light-emitting display (OLED), replacing what was thought to be a game changer, the light-emitting diode (LED) illuminator combined with a liquid crystal display (LCD) or liquid crystal on silicon (LCoS) display, which, in turn, had replaced the initial technology, the mini-CRT. The first HD-format (1920 x 1080) OLED displays have been commercially available for over a year and have opened new doors for HWD applications. The current industry goal is to supply a system that will receive widespread consumer acceptance (meaning millions of units need to be manufactured in a period of months once a design for manufacture point is selected). The system must be low cost (hundreds of dollars to the consumer) and approach an eyeglass format with resolution that approaches that of the human visual system extending into the peripheral FOV. This chapter will first motivate the potential benefits of HWDs, especially in see-through mode, and examine key technology pathways that build on historical highlights. Market barriers to the emergence of eyewear-format HWDs will then be highlighted. We will then review optical architectures for see-through HWDs along with key factors and functions required of a successful see-through HWD. Specifically, building on fundamentals of optical design, the key engineering concepts and constraints will be presented and solutions discussed. Particular emphasis will be placed on differentiating the concept of an eye pupil and an operational eyebox. Next, the Lagrange invariant (LI), which sets fundamental limits in the optical design of HWDs, will be examined. Following the presentation of see-through HWDs, two differentiated solutions will be presented: the head-mounted (worn) projection display (HMPD) and the retinal scanning display (RSD), along with a brief overview of waveguided HWDs. The chapter will conclude with a brief discussion of some of the current research that may affect the solution that the market selects, including freeform optical surfaces.