Volume 98, Issue 12, 15 December 2005
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS
98(2005); http://dx.doi.org/10.1063/1.2149163View Description Hide Description
An analysis of the optical properties of photonic woodpile structures is presented. We demonstrate large superprism phenomena inside polymeric woodpile structures having a refractive index of less than . Due to the low contrast in refractive indices the structures investigated do not possess a complete photonic band gap. Nevertheless, their photonicband structures show strong anisotropy at frequencies slightly above the band gap in the direction, leading to an extreme sensitivity to the angle and the frequency of the incident light in the propagation direction inside the crystal. Furthermore, if the woodpile structure is arranged in a prism-like shape, the transmitted beam outside the crystal shows a strong sensitivity to the frequency and angle of the incident light.
98(2005); http://dx.doi.org/10.1063/1.2146075View Description Hide Description
A method of patterningsurfaces for liquid-crystal alignment using a polarizationholography exposure on a linear photopolymerizable polymer alignment layer is demonstrated. Three configurations are demonstrated which include registered planar-periodic surface boundary conditions on both surfaces (true polarizationgratings), planar-periodic and uniform planary surface boundary conditions, and planar-periodic and homeotropic boundary conditions. Two-dimensional polarizationgratings are also demonstrated by orientating planar-periodic alignment layers orthogonally. Passive polarizationgratings are also demonstrated using reactive mesogens to capture the periodic order indefinitely. The underlying structure of the configuration is discussed, including the nature of their switching transition (threshold or thresholdless), for all three configurations. A simple phenomenological model is presented to describe the Freedericksz transition for the registered planar-periodic boundary condition case.
Three-dimensional optical modeling and optimizations of color filter liquid-crystal-on-silicon microdisplays98(2005); http://dx.doi.org/10.1063/1.2149494View Description Hide Description
We have developed a three-dimensional (3D) optical modeling of small color pixels in color filter liquid-crystal-on-silicon (CF-LCOS) microdisplays. The 3D optical modeling includes a LC electromechanical analysis of color LC cells, a calculation of optical reflectance using the extended Jones matrix, and a standard RGB (sRGB) representation of the optical reflectance in the pixel array. The simulated optical reflectance agreed well with the experiments. With this 3D optical analysis as a tool, the relation of the lateral color fringing field with pixel size and thickness of color filter were studied. Minimizations of the fringing field in the CF-LCOS microdisplays were obtained by pixel arrangement, rubbing direction, and LC mode. The color purity of the CF-LCOS microdisplays could attain 63% National Television System Committee (NTSC) level for a typical pixel size of . With an optimized LC mode, the color purity could still be maintained at 54% NTSC level even when the pixel size was reduced to . This enabled the feasibility of the CF-LCOS microdisplays for very high-resolution display applications.
98(2005); http://dx.doi.org/10.1063/1.2138797View Description Hide Description
Powders embedded in a plastic matrix could exhibit attractive optical properties as flexible emissivity modulator. The choice of the materials to obtain significant contrasts in reflectivity and consequently in emissivity is discussed using a two-flux model to simulate qualitatively the performance of high- and low-absorptive materials. For high-absorptive compounds, such as metallic powders, high reflectivity values can be obtained with a large particle size of a highly conductive metal. The reflectivity value for spherical copper particles at about (about 70%) could be enhanced by 20% in the case of platelet-shaped particles. For low-absorptive compounds, reflection increases with decreasing absorption. For these compounds, larger particles do not lead to higher reflectivity values. An optimum size of the particles has to be found in order to obtain a maximum reflectivity value. Additional considerations on the electronic delocalization are also presented.
98(2005); http://dx.doi.org/10.1063/1.2149499View Description Hide Description
Coherent diffractionmicroscopy requires a well-defined illumination wave such as a plane wave on a specimen. Experimentally, a small pinhole or a focused beam is often used to reduce the illumination area but they unavoidably distort the waves. The distortion of the illumination wave causes artifacts in the phase retrieval of oversampled diffraction patterns. Using computer simulations, we searched for the conditions where strong artifacts arise by changing the Fresnel number, pinhole size, alignment error and photon statistics. The experimental setup with Fresnel number of around 1 and smaller than 1 realized a small reconstruction error when the pinhole radius is larger than a few times the specimen size. These conditions are suitable for the rotation of specimens for the three-dimensional (3D) observations. Such investigation will have an impact in the design of coherent diffraction microscopes for the 3D characterization of nanoscale materials and biological systems using the third generation synchrotron radiation and future x-ray free-electron lasers.