18 September 2007 Light sources and output couplers for a backlight with switchable emission angles
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For switching viewing angles of a liquid crystal display, we proposed to place a liquid crystal device between an LED and a light-guide of a backlight. The first key component for this configuration is a light source with electronically-controlled emission angles. Here, we construct such a device by stacking an optical film and a polymer-network liquid crystal (PNLC) cell on top of a chip-type LED. The optical film contains opaque parallel plates that limit the LED output in a narrow angular range. The PNLC cell either transmits or scatters the light emerging from the optical film. Experiment using a 15μm-thick PNLC cell shows that the angular distribution becomes 2.3 times wider by turning off the PNLC cell. We place this light source at one end of a light-guide so that the angular distribution of the light propagating inside is controlled. The second key component is some types of micro-strucrures built on the light-guide to out-couple the propagating light. We first attached various optical films on a light-guide surface. Although the angular distribution of the extracted light was switched successfully, light was mostly emitted into an oblique direction, approximately 60° from the plane normal. Next, we used a half-cylinder in place of the optical films. The curved surface of the cylinder was attached to the light-guide with a small amount of matching oil, which constituted an optical window. We measured that the angular distribution of the extracted light decreased to 35° FWHM from 62° FWHM by turning on the PNLC cell.
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Ichiro Fujieda, Ichiro Fujieda, Keita Imai, Keita Imai, Yoshihiko Takagi, Yoshihiko Takagi, } "Light sources and output couplers for a backlight with switchable emission angles", Proc. SPIE 6670, Nonimaging Optics and Efficient Illumination Systems IV, 66700N (18 September 2007); doi: 10.1117/12.733223; https://doi.org/10.1117/12.733223


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