Over the past decade, 3M has developed a number of mobile projectors, with a goal towards providing the world’s smallest, most efficient projection systems. Compact size and efficiency are required characteristics for projection systems used in mobile devices and more lately, in augmented reality systems. In this paper we summarize the main generations of 3M light engine optical designs. We present the optical architectures of four light engines, including the rationale behind the illumination designs and the projection systems. In particular, we describe various configurations relating to the 3M polarizing beam splitter (PBS) which is key to enhanced efficiency of the miniature projection systems.
Multilayer polymer interference mirrors are based on hundreds of 10- to 200-nm thick, simultaneously produced layers of high and low index materials. The low absorptivity of the polymers used in these mirrors lead to very high reflectivity and excellent wavelength selectivity. Currently, the mirrors are being applied to reflective polarizers for displays, and cold and hot mirrors for solar control. New products are being developed for applications in laser protection, optical communication, and optical filtering applications. The design of filters based on multilayer polymers has additional degrees of freedom compared to PVD filters, including the ability to specify Brewster's angle from anywhere from 0 to over 90 degree(s), suppressing side-band reflections, and suppressing 2nd, 3rd, and 4th order reflections.
Exposure of oriented, semicrystalline polymers, such as poly(ethylene terephthalate), poly(ethylene naphthalate) and polyimides, to the output of pulsed light sources, such as excimer lasers or short pulse flashlamps, at energy densities less than the ablation threshold can produce an amorphous layer on the polymer surfaces. Time resolved spectroscopy has shown that this amorphous layer is produced by a transient heating of the surface region to temperatures exceeding the polymer melting point (300-500 degree(s)C) resulting in rapid melting and the production of the thin disordered surface layer. Static SIMS, XPS, and infrared spectroscopy measurements have shown that this surface amorphization occurs without any decomposition or crosslinking of the polymer surface. The amorphous layers produced by this rapid thermal process provide increased adhesion of a wide range of coatings and films to the treated polymers due to the increased fracture toughness of their disordered morphology. The amorphous surface layer also can antireflect the polymers, provide increased autoadhesion, and increase coating penetration into the treated polymer substrates. This last characteristic can be exploited to provide photoimaging properties, as negative photoresists, to polyimides. The rapid thermal surface modification technology shows potential for economic industrial implementation, using short pulse flashlamps, provided that reliable, large-scale flashlamp systems can be made available.
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