Volume 86, Issue 8, 15 October 1999
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Transparent stacked organic light emitting devices. I. Design principles and transparent compound electrodes86(1999); http://dx.doi.org/10.1063/1.371331View Description Hide Description
Vertical stacking of organic light emitting devices(OLEDs) that emit the three primary colors is a means for achieving full-color flat panel displays. The physics, performance, and applications of stacked OLEDs (SOLEDs) are discussed in this and the following paper (Papers I and II, respectively). In Paper I, we analyze optical microcavity effects that can distort the emission colors of SOLEDs if not properly controlled, and describe design principles to minimize these parasitic effects. We also describe the fabrication and operating characteristics of transparent contacts that are an integral part of SOLEDs. We demonstrate that both metal-containing and metal-free transparent electrodes can serve as efficient electron and hole injectors into the stacked organic semiconductor layers. Two different transparent SOLED structures (metal-containing and metal-free) that exhibit sufficient performance for many full-color display applications will be discussed in Paper II.
Transparent stacked organic light emitting devices. II. Device performance and applications to displays86(1999); http://dx.doi.org/10.1063/1.371428View Description Hide Description
Vertical stacking of organic light emitting devices(OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L’Éclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow for independent grounding of all color emitters in the stack. At operating voltages of 12–14 V, video display brightnesses were achieved with luminous efficiencies of 0.35, 1.36, and 1.05 cd/A for the R, G, and B subpixels, respectively. The respective CIE coordinates for R, G, and B emissions are (0.72, 0.28), (0.26, 0.63), and (0.17, 0.28) in the normal viewing direction, shifting inperceptibly as the viewing angle is increased to as large as 60°. Finally, we discuss addressing schemes of SOLED displays, and compare them with other strategies for achieving full-color, OLED-based displays.
86(1999); http://dx.doi.org/10.1063/1.371332View Description Hide Description
The thermal stresses in double-coated optical fibers are analyzed by the viscoelastictheory. A closed form solution of the thermal stresses is obtained. The thermal stresses are proportional to the temperature change, and are a function of the material’s properties of the polymericcoatings and their thicknesses. The material’s properties of the polymericcoatings include the Young’s modulus, thermal expansion coefficient, Poisson’s ratio, and relaxation time. The relaxation of thermal stresses is strongly dependent on the relaxation time of the polymericcoating. If the relaxation time of the polymericcoating is very long, the viscous behavior of the polymericcoatings will not appear, and the thermal stresses solved by the viscoelastictheory are the same as those solved by the elastic theory. On the other hand, if the relaxation time of the polymericcoating is very short, the relaxation of thermal stresses is very apparent. A compressive radial stress at the interface of the glass fiber and primary coating will result in an increase of the microbending losses, and a tensile interfacial radial stress will possibly produce the debond at the interface of the glass fiber and primary coating. To minimize this interfacial radial stress, the radii, Young’s moduli, thermal expansion coefficients, and Poisson’s ratios of polymericcoatings should be appropriately selected, and the relaxation time of the primary coating should be decreased. Finally, the thermal stresses in single- and double-coated optical fibers are discussed.
86(1999); http://dx.doi.org/10.1063/1.371333View Description Hide Description
We have modeled the switching behavior of a twisted nematic cell using the one-dimensional Ericksen–Leslie equations of nematodynamics. We compare the modeling results with experimental data on transmission versus time. Excellent agreement between experiment and model is achieved at all voltages and viewing angles. To achieve this agreement, only two viscosity parameters are required; these are combinations of the Leslie viscosity coefficients, namely, (the rotational viscosity) and A fast and stable adaptive numerical algorithm, based on an effective viscosity parameter, is developed for solving the equations of motion. The viscosity parameters obtained from fitting the flow experiments are in good agreement with those obtained from dynamic light-scattering measurements.
Fast polarization switching with memory effect in a vertical cavity surface emitting laser subject to modulated optical injection86(1999); http://dx.doi.org/10.1063/1.371429View Description Hide Description
The polarization state of a vertical cavity surface emitting laser(VCSEL) output was driven by means of optical injection from another VCSEL. The bistability inherent to polarization locking allowed us to generate a memory effect. The control parameter was the modulated bias current of the maser laser and effects were shown to exist at frequencies up to 1 GHz.