Abstract
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%.
Highlights
Transparent displays have been of great interest as they create a magical feeling by displaying information as if it were hanging in the air
A partial reflective microlens array (MLA) sandwiched between refractive-index-matched epoxy layers forms the basis of our seethrough screen technology [1]
The screen creates a bright display in the reflection mode while maintaining excellent transparency
Summary
Transparent displays have been of great interest as they create a magical feeling by displaying information as if it were hanging in the air. A partial reflective MLA sandwiched between refractive-index-matched epoxy layers forms the basis of our seethrough screen technology [1]. Due to this structure, the screen creates a bright display in the reflection mode (due to high gain) while maintaining excellent transparency. The transmitted light through the MLA screen passes through the layered media with non-flat microstructures and layers of coatings. The impact of this micro-optical element on the resolution and modulation transfer function (MTF) is studied in detail in Section 3 and a condition similar to Rayleigh criteria for diffraction limited imaging is derived
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