A novel see-through screen is developed for automobiles which reduces the size of the head-up display (HUD) unit considerably. The screen is illuminated by a laser scanning pico-projector and a real image is formed on the screen. The screen has thousands of hexagonally packed microlenses that are partially reflective and embedded in an index matched medium which provides very good see-through capability. Light reflected from the microlenses expand and form a hexagon shaped viewing window. This system is called a direct projection HUD system as the pico projector projects directly onto the screen and forms a real image on it. The system is very compact and does not require any space under the dashboard, which saves on space for the car manufacturers, or allows it to be used immediately as an aftermarket HUD installed in any car.

Head-up display (HUD) systems have been used in recent car models to provide essential information to the drivers while keeping their eyes on the road. Virtual image HUD systems have been the preferred method, but they have the drawback of requiring a large volume of space in order to accommodate the relay optics that creates the virtual image. This is especially significant as the desired field of view increases. Direct projection HUD systems have been developed with a separate stand-alone microlens array (MLA)-based transparent screen on the dashboard, offering a compact solution. In this paper, we propose a direct projection HUD system based on a unique, windshield-embedded see-through screen that uses minimal space under the dashboard, offering an elegant and compact solution to the HUD problem. The screen is based on MLAs with varying surface normal angles such that the light from the projector is directed to the viewer's eyes from all positions across the field of view. Varying tilts provide an efficient relay and high brightness even with a low-lumen output projector. The calculated screen gain is about 69 and the eyebox area is about 30 cm×30 cm.

We present a novel head-mounted display setup that uses the pinhole imaging principle coupled with a low-latency dynamic pupil follower. A transmissive LCD is illuminated by a single LED backlight. LED illumination is focused onto the viewer's pupil to form an eyebox smaller than the average human pupil, thereby creating a pinhole display effect where objects at all distances appear in focus. Since nearly all the light is directed to the viewer's pupil, a single low-power LED for each primary color with 0.42 lumens total output is sufficient to create a bright and full-color display of 360 cd/m 2 luminance. In order to follow the viewer's pupil, the eyebox needs to be steerable. We achieved a dynamic eyebox using an array of LEDs that is coupled with a real-time pupil tracker. The entire system is operated at 11 msec motion-to-photon latency, which meets the demanding requirements of the real-time pupil follower system. Experimental results effectively demonstrated our headmounted pinhole display with 37° FOV and very high light efficiency, equipped with a pupil follower with low motion-to-photon latency.

A microlens array (MLA) based see-through, front projection screen, which can be used in direct projection head-up displays (HUD), color teleprompters and bidirectional interactive smart windows, is evaluated for various performance metrics in transmission mode. The screen structure consists of a partially reflective coated MLA buried between refractive-index-matched layers of epoxy as reported in Ref [1]. The reflected light is expanded by the MLA to create an eyebox for the user. The brightness gain of the screen can be varied by changing the numerical aperture of the microlenses. Thus, using high gain designs, a low-power projector coupled with the screen can produce high-brightness and even 3D images as the polarization is maintained at the screen. The impact of the partially reflective coatings on the transmitted light in terms of resolution and modulation transfer function associated with the screen is studied. A condition similar to the Rayleigh criteria for diffraction-limited imaging is discussed for the microlens arrays and the associated coating layers. The optical path difference between the light transmitted from the center and the edges of each microlens caused by the reflective layer coatings should not exceed λ/4. Furthermore, the crosstalk between the front and rear projected images is found to be less than 1.3%.

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