Optical bistability and set-reset operation of a Fabry-Perotsemiconductor laser amplifier with two detuned light injections

Optical bistability in a Fabry-Perot semiconductor laser amplifier when two optical inputs detuned from the resonant wavelength of a semiconductor laser amplifier are injected is discussed. A split branch is found in the optical output versus input characteristics in addition to conventional optical bistability behavior. It is shown analytically and experimentally that set and reset can be achieved in the optical output of the semiconductor laser amplifier for each wavelength by applying two detuned optical pulses and using the split branch     

Local dimming light‐guiding plate type backlight system using alignment‐controlled polymer‐dispersed liquid crystals

A new technology which enables a local brightness control according to the displayed images has been expected in the thin and lightweight backlight systems to improve a contrast ratio and power consumption of the liquid crystal displays (LCDs). In this paper, we have proposed a novel local‐dimming backlight system using alignment‐controlled polymer‐dispersed liquid crystals as a light‐guiding plate and investigated the forming conditions of polymer‐dispersed liquid crystals to achieve both a high‐luminance ratio and a fast response speed. As a result, we found that a luminance ratio and response speed of the backlight system can be improved by using bifunctional LC monomer materials and forming fine and rigid polymer network in the LCs, and achieved high luminance ratio of 16:1 and fast response time less than 0.5 ms. In addition, we fabricated the twisted nematic‐mode LCD using the local dimming light‐guiding plate‐type backlight based on this design, and successfully realized eight times higher contrast ratio than that of the traditional twisted nematic‐mode LCD.     

Alignment control of liquid crystals in a 1.0‐μm‐pitch spatial light modulator by lattice‐shaped dielectric wall structure

We achieved uniform liquid crystal (LC) alignment in lattice‐shaped dielectric walls 1 μm in pitch; this is a prerequisite when driving the individual pixels of spatial light modulators, facilitating the development of practical electronic holographic displays with a wide field of view. In lattice‐shaped dielectric walls, LC alignment becomes unstable, particularly on the bottom and the walls; the LC directors tend to align parallel to the walls. To overcome this problem, we created lattice‐shaped walls featuring partition plates that allow uniform LC alignment. When the plates confine LCs to small regions exhibiting spatial anisotropy, the LC elastic effect and wall anchoring forces align the LC directors parallel to the long anisotropic axis. We found that pixels 0.5 μm × 1.0 μm in pitch formed if the partition plates were sufficiently thick to allow shielding of electric field leakage.     

The effects of a detuned optical input on bistable laser diodeswith inhomogeneous current injection

The effects of an external optical input on a bistable laser diode (BLD) with inhomogeneous current injection are discussed. The bistable behavior of optical output versus injection current is shown to be variously modified, depending on the wavelength and power of the optical input. Optical set and reset operations and optical logic achieved by optical input pulses can be explained by these characteristics of a BLD modified by an external optical signal. Analysis using rate equations is also offered to help interpretation of experimental results, as well as the optical output and the bias current injected into the BLD     

Automatic color-temperature compensator with guest-host liquid-crystal filter for video image sensing

A color-temperature compensating system with an electrically controllable liquid-crystal filter and a color sensor mounted on a video camera has been developed for color image sensing. The filter contains two guest-host liquid-crystal devices with dichroic dyes that have strong light absorption for shorter-wavelength light; two devices are necessary because of the spectral difference between the sun and an incandescent lamp as light sources. The filter's absorption is continuously controlled by the voltage applied to the filter. Because the filter is driven according to spectral information about the illumination detected by the color sensor, the color balance of the video image to be sensed can be compensated automatically and rapidly. This is especially useful for video image shooting in which a video camera experiences changes in illumination color temperatures.     

The nitrogen gas tension test of concrete. Part 1: effect of boundary conditions and axial strain response

In this study, the surface and internal strain response of a specimen subjected to the nitrogen gas tension test was examined. The effect of the restraining force acting on the cylindrical specimen due to the rubber “O” ring seal was also determined. It was found that the effect of the restraining force was vanishingly small, and that the specimen was uniformly deformed in the axial direction. The effect of moisture content was also studied, and was found to have a considerable influence on the results. It was concluded that the concrete specimen should be considered as a two-phase system, consisting of a solid phase and a fluid phase.     

Spatial light modulators for projection displays

Spatial light modulators (SLM's) consisting of a polymer-dispersed liquid crystal (PDLC) film and a Bi(12)SiO(20) photoconductor are discussed and demonstrated. This device, which uses light scattering in the PDLC film, has several advantages including no polarizer, a low optical loss, and video-rate operation. The device was designed by use of an electrical-image method. High-definition SLM's with a limiting resolution (36-50 line pairs/mm) were fabricated by stacking of an optimized mirror and the PDLC film. The device, which was incorporated into a Schlieren system with a 1-kW xenon lamp, provided high-contrast video images and a total luminous flux of 1000 lm.     

A 5‐in. flexible ferroelectric liquid‐crystal display driven by organic thin‐film transistors

Abstract— An organic thin‐film‐transistor (OTFT) driven color flexible ferroelectric‐liquid‐crystal (FLC) display with 160 × 120 pixels and a resolution of 50 ppi has been developed. The flexible FLC was fabricated on a pentacene‐OTFT array using printing and lamination techniques. To drive the display at a fast driving speed, an OTFT was developed with a short channel length having a large current output. The fabricated OTFT array with a channel length of 5 μm exhibits a carrier mobility of 0.3 cm²/V‐sec and an ON/OFF ratio of over 10⁷ at a low drain voltage of ?6 V. A field‐sequential‐color system with a flexible backlight unit was also developed and used to drive the display. Color moving images were successively shown on the 5‐in. display using an active‐matrix driving technique of the OTFT.     

High-definition imaging system based on spatial light modulators with light-scattering mode

We have developed a prototype high-definition imaging system using polymer-dispersed liquid-crystal (PDLC) light valves, which can modulate unpolarized light with high spatial resolution and exhibit a high optical efficiency, based on the light-scattering effect. We fabricated high-definition light valves with a fine polymer-matrix structure in a PDLC film by controlling the curing conditions used during the photopolymerization-induced phase separation and formation process. This device has excellent characteristics, such as a high resolution, with 50 lp/mm for a limiting resolution and greater than 20 lp/mm at the 50% modulation transfer function point, and a reflectivity of greater than 60%. An optically addressable full-color projection display was designed, consisting of three PDLC light valves, a schlieren optical system based on shift-decentralization optics with a xenon lamp illumination and input-image sources with 1.5 million pixels, including electrical image compensation of the gamma characteristics. We succeeded in displaying pictures on a 110-inch screen with a resolution of 810 TV lines and a luminous flux of 1900-2100 American National Standards Institute lumens.     

Anthracene derivatives as efficient emitting hosts for blue organic light-emitting diodes utilizing triplet–triplet annihilation

The molecular design strategies for the host materials suitable for highly efficient, blue fluorescent organic light-emitting diodes (OLEDs) are demonstrated. The device characteristics of blue fluorescent OLEDs are compared with different host materials. Some devices exhibit a highly efficient blue electroluminescence with a high external quantum efficiency of more than 7%. The correlation between OLED efficiency and triplet–triplet annihilation is characterized by measuring the up-conversion of triplet excited states into singlet ones. The host materials require an anthracene unit and a bulky molecular structure to prevent the overlap of anthracene units between adjacent molecules in the film.