Pasi Saarikko

Exit pupil expander with a large field of view based on diffractive optics

Abstract— The field of view is an important parameter of a near-to-eye display. To achieve an immersive viewing experience, the field of view should be as high as possible. Presently, in most of the commercially available devices the field of view is between 15° and 30°. In this paper, a large-field-of-view exit pupil expander that is based on diffractive optics was demonstrated. Usually these types of diffractive expanders cannot have a field of view much more than 25°. Here, an exit pupil expander with an extended field of view, based on two stacked plates, was demonstrated. The expander is designed for green light and it achieves a field of view of more than 40°.

A novel diffractive backlight concept for mobile displays

efficiency demands on mobile communication device displays have become severe with the emergence of full video capable phones and mobile telephony services such as the third- generation networks (3G). One way of reducing the power dissipation of a mobile liquid-crystal display (LCD) is to efficiently distribute and outcouple the light available in the backlight unit (BLU) to direct the light in a spectrum-specific fashion through the respective color pixels. This paper describes a diffractive optics approach to realize a novel backlight unit. A model grating structure was fabricated and the outcoupled distribution of light was studied. The results verify that the new BLU concept based on an array of spectrum-specific gratings is possible.

Diffractive exit-pupil expander for spherical light guide virtual displays designed for near-distance viewing

In this paper the use of diffractive exit-pupil expanders (EPEs) for implementation of compact and ergonomically friendly head-worn virtual displays is studied. We show that exit-pupil expansion of a virtual display designed for near-distance viewing is possible with a diffractive EPE having spherical shape. An analytical model for ray propagation through the proposed EPE is derived. The resulting expressions are used to characterize the geometrical distortions and the lateral color introduced in the pupil expansion process. Moreover, the resolution properties of the EPE are calculated using numerical simulations and compared with the acuity of the human eye. The results show that pupil expansion ratios enabling natural eye movements in typical near-to-eye display applications can be achieved while maintaining the information content of a virtual display.

Diffractive exit-pupil expander with a large field of view

A concept of asymmetric exit-pupil expansion for head-worn virtual displays is introduced. Expression for the achievable field of view (FOV) of a stack of asymmetric pupil expanders is derived. Comparison with the symmetric case indicates a possibility for doubling the horizontal FOV for given material parameters and spectral bandwidth. Using the parameter values of readily available plastics, the horizontal field of view approaching the viewing conditions of typical desktop monitors should be possible. Moreover, improvement of the illumination uniformity can be achieved through optimized positioning of the out-coupling diffraction gratings.

5-2: A Novel Diffractive Backlight Concept for Mobile Displays

Power efficiency demands on mobile communication device displays have become severe with the emergence of full video capable phones and mobile telephony services such as the third-generation networks (3G). One way of reducing the power dissipation of a mobile liquid-crystal display (LCD) is to efficiently distribute and outcouple the light available in the backlight unit (BLU) to direct the light in a spectrum-specific fashion through the respective color pixels. This paper describes a diffractive optics approach to realize a novel backlight unit. A model grating structure was fabricated and the outcoupled distribution of light was studied. The results verify that the new BLU concept based on an array of spectrum-specific gratings is possible.

Efficiency optimization of blazed effective-medium gratings in the resonance domain

Three types of subwavelength-structured grating for efficient beam deflection in the non-paraxial domain are considered. The first-order efficiency is optimized by first designing an index-modulated grating and then encoding the optimized values of refractive index in the form of surface-relief profiles using effective-medium theory. Comparison with direct parametric optimization shows the feasibility of the approach in finding nearly optimum designs with greatly reduced computational effort.

Near-to-eye display based on retinal scanning and a diffractive exit-pupil expander

In this paper, we propose a novel design to construct a near-to-eye display with an appearance resembling that of a regular eye wear. Our design combines a scanning display engine with a diffractive exit pupil expander. Both of these components have been used separately earlier, but we propose to combine them in a single device. This allows the construction of a smaller and lighter display system, as well as a more power efficient design as compared to traditional micro display based systems. In our design the light source can be moved away from the display to decrease the weight and size. An exit-pupil expander based on diffractive optics allows a size and weight efficient way to build a near-to-eye display with a large exit pupil. A large exit pupil is desired in near-to-eye displays to accommodate the eye movements and to improve the comfort and ease of the use. The diffractive exit-pupil expander also allows a switchable see-through feature; enabling the viewer the see the surroundings together with the displayed information. In the paper the operation and the design of the proposed near-to-eye display are described. We also present modeling results that support the validity of the design, and finally some preliminary measurement results are given.

64.3: Vertical Expansion Problem in Light Guide Type Near to Eye Displays

A Near to Eye Display that uses a light guide is a compact optical system for viewing virtual images. The light guide expands the exit pupil in one dimension, far away from the imaging optics, but lacks the ability to expand the exit pupil in the other direction. In this paper we present vertical expansion methods that can be imbedded in the light guide and introduce a new optical method for the vertical expansion. Simulations and experiments are discussed.