Currently, Mid-Air Display (MAD) technology is of a great interest to practitioners. Potential application in consumer products with large aperture “floating” image displays, like TV, monitor, ATM, vending machine, home appliance, etc., and contactless user interface for remote control increase their attractiveness. In order to obtain enlarged mid-air image size at maintaining large horizontal Field of View (FoV) and high light display efficiency, the following challenges are to be solved: developing high fill-factor Diffractive Optical Elements (DOE) architecture with optimal size of out-coupling aperture and designing custom-made projection optics with specified exit pupil matched to in-coupling DOE. As a possible solution to abovementioned problems, the authors propose a MAD based on commercially available projector source, custom-made projection optics and designed corner DOE waveguide architecture with focusing Fresnel lens. The mid-air image is formed at the back focal plane of the Fresnel lens, between the viewer and the display. For mid-air image with five-inch diagonal and 32° horizontal FoV, we take waveguide out-coupling aperture of 245 x 145 mm2 and Fresnel lens with back focal length of 220 mm and obtain image brightness ~1000 cd/m2 due to custom projection optics. Basic contactless user interaction was also implemented.
Mid-air display (MAD) technology is attractive to practitioners nowadays. The interest is due to the potential application in consumer products with embedded floating image displays, like smartphones, smartwatches and dock-stations, and as a part of new holographic user interfaces for safe and contactless control. Some of the problems to solve on the way to compact and light efficient MAD include small field of view, small image size, low image resolution, low image contrast, absence of image magnification, low perceived sense of depth, etc. In order to overcome these challenges, the authors propose a MAD based on a DMD pico-projector and a DOE waveguide with a positive Fresnel lens, placed near the out coupling aperture of the DOE waveguide. The developed MAD forms a real image with a positive relief from the display surface so that the viewer perceives this image floating in front of it, at the back focal plane of the Fresnel lens. For mid air image with ≥ 1-inch diagonal with 57 mm image relief horizontal field of view was 35 degrees, with image brightness 100 cd/m2 . The proposed mid-air image display has a compact form factor with dimensions 100 mm × 50 mm × 3 mm, without dimensions of the DMD pico-projector. It can be used in consumer products to provide a new kind of experience including contactless holographic user interaction
The mismatch between positions of virtual images and a see-through view constitute a serious problem in virtual and augmented reality optical systems with a single projection plane. These issues may lead to a user’s discomfort: eye fatigue, headache and nausea. In order to solve these problems a tunable lens forming several projection planes at different locations can be used. Developed varifocal lens consists of two tunable liquid crystal cells. The first cell for fine adjustment varies optical power from 1 D to 3 D, the second cell for coarse adjustment varies power from 0.25 D to 1 D. The total dioptric range is -4 D … +4 D with an equidistant step of 0.25 D that forms 33 projection planes. Electrode pattern made of indium zinc oxide consists of rings corresponding to Fresnel zones, each zone is divided to multiple subzones. In order to minimize the number of control electrodes (bus lines) and keep high diffraction efficiency, the bus lines shunt together all of the corresponding sub-zones in all of the zones. Developed lens is tested with AR glasses based on a holographic waveguide. Displacement of virtual image from 250 mm to 1 meter is demonstrated.
Augmented reality (AR) systems are of huge interest for last decade since they are predicted to be the next generation of mobile devices for consumers. One of the key parameters in terms of AR systems properties is the field of view. The best performance in this regard is shown by DOE/HOE-based planar-waveguides systems since they can provide the widest field of view among other approaches even with the simplest architecture. However it is still not wide enough for consumers, so more complex architectures are created. In this work, a novel approach for reaching wide field of view is proposed. It is based on the eyebox magnification in two directions by two different waveguides systems. The first system provides magnification along the axis with wider field of view and consists of waveguides inclined along the field of view central beam with HOE-based 1D gratings, providing the TIR diffraction in both +1 and -1 orders. The TIR condition in this case is reached more easily because of inclination, so the wider angular spectrum can be transferred. The second system provides magnification along the axis with narrower field of view and consists of conventional HOE-based periscope system with in-coupling and out-coupling zones. The system working principle, HOEs specifications, main advantages, challenges and solutions are discussed. The proposed system allow 60-degrees diagonal field of view for the white (RGB) color.
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