Volume 96, Issue 5, 01 September 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
96(2004); http://dx.doi.org/10.1063/1.1775051View Description Hide Description
Interface reactions in thin-film bilayered structures were examined for applications to optical recordingmaterials. Decreases in the reflectance of the structures caused by temperature elevation were observed and were attributed to (i) coloration of the layers, and (ii) decreases in the reflectance of the metal layers resulting from redox reactions between the and the metals. The reflectance spectra of the structures before temperature elevation showed moderate wavelength dependence over a wide range, from the visible to the near infrared. Decreases in the reflectance due to temperature elevation occurred over a wide wavelength range. Examination of the bilayered structures as potential optical disk memories revealed that the redox reactions occurred within submicrosecond time periods during irradiation with the recording laser. The results indicate that these structures possess promising properties for applications to optical recordingmaterials that can be used over a wide wavelength range.
96(2004); http://dx.doi.org/10.1063/1.1775302View Description Hide Description
Both the reflectivity and the reflection delay of a quarter wave mirror (QWM) can be controlled by choosing the outermost layer of the QWM appropriately. For a QWM, depositing a Si layer as the incoming outermost layer decreases the reflectivity to the same degree as removing 19.6 layers, and increases the reflection delay by 12.0 times. Likewise, when using a layer, the reflectivity decreases to a level similar to the removal of 16.1 layers while the reflection delay is 7.9 times longer. Therefore, an efficient method to fabricate resonant cavity enhanced photodetectors for bidirectional optical interconnects is proposed. This method needs no subsequent etching process while giving a quantum efficiency of approximately using currently available deposition techniques. Furthermore, the tunable wavelength and bandwidth ranges of microelectromechanical system tunable filters can be controlled separately by the outermost layer, thereby allowing filters with different bandwidths to be fabricated on the same wafer.
Holographic method for a direct growth of three-dimensional photonic crystals by chemical vapor deposition96(2004); http://dx.doi.org/10.1063/1.1776322View Description Hide Description
A method to obtain three-dimensional (3D) photonic crystals by chemical vapor deposition(CVD) is presented. Campbell et al. [N. Campbell, N. Sharp, M. T. Harrison, R. G. Denning, and A. J. Tuberfield, Nature404, 53 (2000)] have developed a method of holographic lithography for producing 3D periodic structures with photoresists. Their method is adapted in two main directions. First, we optimize the geometry of the interferometer with respect to polarizations and relative intensities of the beams. The construction of an interferometer adapted to a ultraviolet laser source at 355 nm is described and direct observations of the interference field obtained by a video camera are presented. Second, we show that a laser source with short pulses could induce a suitable thermal contrast on a convenient substrate in order to grow a 3D photonic crystal by CVD.
96(2004); http://dx.doi.org/10.1063/1.1772890View Description Hide Description
The structure of technologically important tellurite glasses has been studied by Raman spectroscopy. The present investigation revealed the presence of trigonal bipyramid, trigonal pyramid, and octahedra in these glasses. The influence of a gradual addition of the modifier oxides on the glass structure has been elucidated. The evolution of units with the modifier addition was different from the earlier reports on the tellurite glasses. Even at higher modifier concentrations units were dominating in the glass network compared to , though octahedra also come into the picture. The ratio of structural units was discussed for different series of glass compositions. An attempt has been made based on these structural details obtained via Raman studies to explain the origin of the greatly improved thermal stabilities and refractive indices of these glass compositions.
Nonlocal photopolymerization effect in the formation of reflective holographic polymer-dispersed liquid crystals96(2004); http://dx.doi.org/10.1063/1.1778480View Description Hide Description
The optical performance of reflective holographicpolymer-dispersed liquid crystals (H-PDLCs) is investigated as a function of sample thickness and laser exposure intensity, and, the data are analyzed in terms of a nonlocal photopolymerization model. The intensity of laser exposure is proven to have a strong influence on the reflection efficiency of H-PDLCs. We have found that the experimental results cannot be completely interpreted by the previous local diffusion model. Combined with transfer matrix analysis, a modified diffusion model with a nonlocal photopolymerization term is proposed herein, which qualitatively describes our experimental observations. The experimental data demonstrates our assertion that the nonlocal effect is strongly correlated to the exposure conditions. Under the low exposure condition, the diffusion effect is screened by this nonlocal effect, and effectively a small diffusion constant is observed. Under the high exposure condition, the nonlocal effect can be suppressed and the modified diffusion model can be deduced to the original local diffusion model. Also, within the framework of this nonlocal model, overexposure can be properly explained.