Akihiro Funamoto

LED backlight system with double-prism pattern

— A LED backlight system with a double-prism pattern for use in mobile phones to achieve thin and high luminance LED backlight systems is proposed. The double-prism pattern is formed on the light guide of the proposed LED backlight system and simultaneously exhibited two optical functions: shifting of the light from the direction of the guided light toward the radiated light and controlling the directivity of the radiated light. Therefore, using the double-prism pattern eliminates two prism sheets and a diffusive sheet, which are indispensable optical elements to exhibit the optical function that controls the directivity of light in conventional LED backlight systems. Consequently, the thickness of the proposed LED backlight system is reduced to 0.75 mm compared to that of the conventional system. A luminance of 3115 nits and a full-width half maximum of 35° for radiated light, which are comparable to conventional LED backlight systems, were obtained.

Hybrid normal-reverse prism coupler for light-emitting diode backlight systems

For the first time to our knowledge, a hybrid normal-reverse prism coupler was formed on the bottom surface of a light guide in a LED backlight system to achieve a thin, lightweight, LED backlight system. The hybrid prism coupler (HPC) simultaneously exhibits two functions: extraction of guided light from the light guide and focusing the radiated light from the light guide, corresponding to the optical functions of the prism and diffusive sheets used in conventional LED backlight systems. Therefore, using a HPC eliminates the prism and diffusive sheets that have been indispensable optical elements in conventional LED backlight systems, which consequently reduces the thickness of the LED backlight system by 40% compared with conventional systems.

Nanohot embossing using curved stage to replicate antireflection nanostructures onto light guide

Abstract A nanohot embossing using a curved stage is proposed to improve the replication ratio of nanostructures at near the edge of a thick (sub-mm-order thickness) polymer substrate. The lower replication ratio at near the edge resulting from a conventional hot embossing is due to lower compressive stress, which is simulated by the finite-element method (FEM). The height of the proposed curved stage is gradually increased from the center to the edge to bring the levels of compressive stress at the center and at the edge closer. Here, we demonstrate replications of antireflection nanostructures, which have both pitch and height of 200 nm, onto the 0.75-mm-thick light guide for the light emitting diode (LED) frontlight systems used in mobile phones. It was found that a cutting depth of 14 mm on the curved stage is necessary to achieve a high uniformity of the replication ratio at near the edge. The replication ratio at near the edge is improved from 65% to 94%. The reflectance of the antireflection structures is 0.6%, which is a high enough quality for use in LED frontlight systems.