KEYWORDS: Light emitting diodes, LED backlight, Resistance, LCDs, Temperature metrology, Transmittance, Photography, Blue light emitting diodes, Field effect transistors, Green light emitting diodes
Trichromatic LED backlights render higher color gamut and panel transmittance to liquid crystal displays (LCDs) than
yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical
challenges arise, such as colour shift due to the ambient temperature change, decrease in brightness at elevated
temperature, an enlarged dead zone for colour mixing, minimizing the total number of chips and so on. In this work, we
designed and demonstrated a low-cost driving circuit that stabilizes brightness and colour coordinates of trichromatic
LED backlights using a thermistor as a temperature compensating element. By applying the temperature compensation,
the amounts of the brightness and colour shift were reduced to 54% and 51% of the uncompensated cases, respectively.
KEYWORDS: Light emitting diodes, LED backlight, LCDs, RGB color model, Transmittance, Temperature metrology, Optical filters, Blue light emitting diodes, Green light emitting diodes, Televisions
Trichromatic LED backlights render higher color gamut and panel transmittance to the liquid crystal displays (LCDs) than yellow phosphor-converted white LED backlights can possibly do at their best. In realization, however, several technical challenges arise, such as color mixing, minimizing the total number of chips, and maintaining the color balance. We designed and demonstrated a backlight unit for 2.2 inch TFT LCD using two RGB 3-chip LEDs to assess the feasibility and the technical hurdles to overcome. The average brightness of the backlight is 2509cd/m2 at the input power of 200mW. The power efficiency is lower than but comparable to commercially available white LED backlights. The color gamut of the LC panel is increased from 53% to 78% when its conventional white LED backlight is replaced by the trichromatic LED backlight. Panel transmittance is expected to be enhanced as well by about 8%. The ambient temperature change was found to be the most significant cause of the color shift of the trichromatic LED backlight. The forward bias voltage can be used in the feedback, since it changes linearly with temperature.
High-speed metal-based optical microscanning devices with low production cost and simple fabrication process wre successfully fabricated by direct deposition of piezoelectric materials using the aerosol deposition method (ADM) onto the micro-structured metal scanner frame. Large optical scanning angle of 35° at high resonance frequency of 23.6 kHz was achieved in ambient air without vacuum package. The scanner is applicable to SVGA high-resolution display of 800 x 600 or more. This method is a powerful tool for realizing ceramic integration with metal components.
We demonstrated a magneto-optic spatial light modulator with one-step pattern formation of iron-garnet films on ion-milled substrates by LPE. The one-step pixel growth is based on the combination of a single-crystal epitaxial film growth (pixel area) by LPE and a impeded film growth (pixel gap area) on a substrate whose surface has been locally damaged and milled by ion bombardment before film deposition. This method overcomes the disadvantages associated with groove etching of the conventional MOSLM. The fabricated prototype MOSLM is switched by applying driving currents of 40 mA for the bottom conductor line and 80 mA for the top conductor line under external bias field of 20 Oe, which is over 2 times smaller than that of the conventional MOSLM. These results strongly suggest that the novel MOSLM can provide higher resolution, simpler fabrication process, more compact systems and lower driving current. Also, the selective-area LPE method offers new possibilities for the fabrication of integrated magneto-optic light switch arrays, magnetic waveguides and similar devices.
We demonstrated a flat-surface magneto-optic spatial light modulator (MOSLM) without physically isolated pixels and an external bias coil. The flat-surface MOSLM, which was fabricated by a simple process, was designed as a compact system with a high resolution and very low driving current. Flat-surface pixels for the novel MOSLM were magnetically isolated and produced by the combinatory use of the local annealing effect that reduced magnetization 4πMs of pixel areas and the stress effect that produced sharp variations of magnetic anisotropy in a magnetic garnet film under the edge of a metal layer. The novel MOSLM can provide a higher resolution, a simpler fabrication process, more compact systems and a lower driving current than the conventional MOSLM.
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