Volume 92, Issue 1, 01 July 2002
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Estimate of spontaneous emission coupling factor for GaAs quantum well embedded in planar microcavities with Bragg mirrors92(2002); http://dx.doi.org/10.1063/1.1479748View Description Hide Description
This article presents the spontaneous emissionspectra for a single quantum well embedded in a planar microcavity with Bragg mirrors at 300 K. The confinements of vacuum fields and electrons are considered together in the microcavity. An estimate of the spontaneous emission coupling factor is given. We find that the maximum scaling of the spontaneous emission coupling factor is 0.0055.
92(2002); http://dx.doi.org/10.1063/1.1481774View Description Hide Description
The purpose of this article is to study the materials physics behind dye-doped polymethyl metharcylate (PMMA) that is important for the optical fiber drawing process. We report effects of the fabrication process on the mechanical properties of the final fiber. The qualitative degree of polymer chain alignment is found to increase with the drawing force, which in turn decreases with the drawing temperature and increases with the drawing ratio. The chain alignment relaxes when the fibers are annealed at with a commensurate decrease in fiber length and increase in diameter. The annealed fiber has higher ductility but lower strength than the unannealed fiber. Both the yield and tensile strengths are dependent on the strain rate. The relationship between tensile strength, and fiber diameter, is found empirically to be The yield strength appears to be less sensitive to the fiber diameter than the tensile strength. For PMMA doped with disperse red 1 azo dye, the yield strength, tensile strength, and Young’s modulus peak at a dye concentration of 0.0094 wt %. These results are useful for designing polymeroptical fibers with well-defined mechanical properties.
92(2002); http://dx.doi.org/10.1063/1.1481211View Description Hide Description
Studies carried out on gallium nitride showed that they have a high defect density in their band gap. These defects have direct influence on the electrical characteristics of the devices, by contributing leakage currents and the trap assisted tunnel currents. In this article, we carried out numerical calculations based on the experimental data, in order to study the contribution of each component of the current. A comparison has been made between the devices based on GaN and on AlGaN. We study also the capacitance–frequency characteristics, which enable us to locate defects in the band gap. We discuss the effect of the series resistance on the current–voltage characteristics, as well as the influence of defects on the photodetector response time and on the rejection ratio.
Fully leaky guided mode study of the flexoelectric effect and surface polarization in hybrid aligned nematic cells92(2002); http://dx.doi.org/10.1063/1.1483392View Description Hide Description
The fully leaky guided-mode optical-waveguide technique has been used to characterize the tilt profiles in two E7-filled hybrid-aligned nematic cells. The director distortion was measured with ac and dc voltages applied perpendicular to the substrates. By comparing the tilt profiles with model profiles produced using a free-energy minimization program, the flexoelectric coefficient of E7 at 20 °C has been measured as The effect of surfacepolarization in the cells has also been observed. This surfacepolarization is attributed to the influence of the homeotropic surface. The dipole alignment imbalance of the liquid crystal at the homeotropic surface has then been estimated.