ABSTRACT: The electronic structures of Al/RbF/8-hydroxyquinoline aluminium (Alq3) and Al/CaF2/Alq3 interfaces were investigated using x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). For both systems, the UPS showed that a significant valence band shift occurred by evaporating the thin fluoride layer on Alq3. However, the gap state formation and the evolution of N 1s core level spectra showed rather different trends, suggesting that the alkali fluoride and alkali–earth fluoride interlayer have different reaction mechanisms at the interface with the Al cathode. In addition, the deposition of Al has considerably less effect on the valence band shift compared to the deposition of both RbF and CaF2. These results suggest that the complex charge transfer mechanism across the interface has considerably less effect on the enhancement of organic light-emitting device performance than the significant valence band shift as a result of deposition of interlayer materials.
Journal of Physics D Applied Physics 11/2002; 35(24):3171. · 2.54 Impact Factor
ABSTRACT: We report experimental results on the development of residual stress due to OH impurity in optical fibers. The effect of OH impurity on residual stress is demonstrated by direct residual stress measurement. The residual stress at the outer-cladding/jacketing-tube boundary of the fiber drawn at 3.48 N was found to be -61 MPa . The residual compressive stress is attributed to the viscosity decrease induced by a significant OH impurity at the boundary, as measured by a Fourier transform infrared microscope.
Optics Letters 06/2002; 27(10):806-8. · 3.40 Impact Factor
ABSTRACT: The compressive residual stress was found to develop at the outer-cladding/jacketing boundary of the optical fibers during the fiber drawing process. The residual stress of the fiber drawn at 3.48 N was found to be -61 MPa and it was due to the viscosity decrease induced by a significant OH impurity of ∼582 ppm.
Optical Fiber Communication Conference and Exhibit, 2002. OFC 2002; 04/2002
ABSTRACT: We observed residual stress relaxation by CO(2) laser irradiation in the cores of optical fibers by direct stress measurement. It was demonstrated that the mechanical stress was fully relaxed by CO(2) laser irradiation and that the remaining stress in the core was thermal stress that was due to a mismatch of the thermal expansion coefficients of the fiber core and cladding. The net core stresses after relaxation were 17, 68, and 203 MPa in Ge-B-codoped fibers drawn at 0.53, 1.38, and 3.48 N, respectively. Changes in the refractive indices of the cores as a result of residual stress relaxation were also estimated.
Optics Letters 12/2001; 26(21):1657-9. · 3.40 Impact Factor
ABSTRACT: A novel method is demonstrated for determining the photoelastic effect profile as well as the residual stress profile of an optical fiber for the first time. Measurement results of the residual stress profiles and the photoelastic effect profiles of a B-Ge doped fiber and an Er-Al doped fiber are demonstrated by using this technique with its spatial resolution better than 0.8 pm.
Optical Fiber Communication Conference and Exhibit, 2001. OFC 2001; 02/2001
ABSTRACT: Summary form only given. A HeNe laser is used for the light source
with random polarization. A rotating diffuser is used for reducing the
unwanted diffraction effects result from high spatial coherence of the
source light. The light is scattered and collected by lens. The state of
polarization of the weakly focused light is modified by the linear
birefringence device, which includes a rotating polarizer and a quarter
wave plate. The light is focused by condenser and is polarized by an
analyzer through the optical fiber immersed in index matching liquid.
The magnified image of the optical fiber is detected by a CCD camera
through 20X objective lens and is scanned as a line data by a monochrome
frame-grabber. By using this technique we measured the residual stress
and the strain-optic coefficient profiles of an Er-Ge-Al doped fiber
Lasers and Electro-Optics, 2001. CLEO '01. Technical Digest. Summaries of papers presented at the Conference on; 02/2001
ABSTRACT: Thermal and mechanical stresses developed in concentric
three-layered optical fiber-core, and inner and outer cladding, have
been thoroughly studied for various concentrations of dopants and
geometric structures. In order to examine the parametric results of
thermal stresses in preforms, the stresses were measured with a
polariscope. The results agreed well with the theoretical calculations.
The thermal stresses were calculated for three temperature ranges in
which the glass in each layer has a different thermal expansion
coefficient. The mechanical stresses were studied considering the normal
stress in the molten neck down region and its development with time. In
order to include the time dependence of the stress below softening
point, Maxwell's one dimensional viscoelasticity was applied. In a
parametric study, the analyzes were carried out based on the fiber
parameters such as relative index difference, ratio of clad to core, and
depressed relative index difference. With an increase of core index
above the silica, the thermal stresses in core increased linearly, but
the depressed inner clad does not affect the stresses in core. From the
parametric studies and modeling it was found that when the depressed
inner cladding (DIC) layer has a large cross-section or high dopant
concentration, the mechanical stress in core change from compression to
Journal of Lightwave Technology 11/1999; · 2.78 Impact Factor