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.
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/m<sup>2</sup> 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.
Unlike other Micro Electro Mechanical System (MEMS) type devices packaging, MEMS type optical devices require higher standard of packaging technique and careful material selection than any other MEMS type products. A number of attempts and a lot of efforts have been devoted to achieve a reliable MEMS type optical device. In this
paper, we have achieved highly reliable MEMS type variable optical attenuator (VOA), which passed the Telcordia reliability standard for optical components, by our advanced packaging process and careful reliability considerations in the initial product design step. Our advanced packaging process includes, ultra fine optical fibre alignment on the MEMS chip, securing the aligned optical fibre and hermetic sealing technique. This paper will discuss above advanced packaging issues in detail and reliability test result of the device fabricated according to the developed packaging method.
MEMS technologies have been applied to a lot of areas, such as optical communications, Gyroscopes and Bio-medical components and so on. In terms of the applications in the optical communication field, MEMS technologies are essential, especially, in multi dimensional optical switches and Variable Optical Attenuators(VOAs). This paper describes the process for the development of MEMS type VOAs with good optical performance and improved reliability. Generally, MEMS VOAs have been fabricated by silicon micro-machining process, precise fibre alignment and sophisticated packaging process. Because, it is composed of many structures with various materials, it is difficult to make devices reliable. We have developed MEMS type VOSs with many failure mode considerations (FMEA: Failure Mode Effect Analysis) in the initial design step, predicted critical failure factors and revised the design, and confirmed the reliability by preliminary test. These predicted failure factors were moisture, bonding strength of the wire, which wired between the MEMS chip and TO-CAN and instability of supplied signals. Statistical quality control tools (ANOVA, T-test and so on) were used to control these potential failure factors and produce optimum manufacturing conditions. To sum up, we have successfully developed reliable MEMS type VOAs with good optical performances by controlling potential failure factors and using statistical quality control tools. As a result, developed VOAs passed international reliability standards (Telcodia GR-1221-CORE).