Inert Liquid Paraffin Speeds Preparation of Large, Crack-Free Mesostructured Silica Monoliths
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fluorinated resins ZPU-1279 and ZPU-1215 for the cladding and passive core regions, respectively. The EO (active) polymer was a guest–host complex of CLD-1 chromophore and amorphous polycarbonate (APC). The device was constructed by spincoating the lower cladding and the passive core layers of the device onto a silicon substrate. A layer of the EO polymer was then deposited on top of the passive layer, the nonessential areas removed by reactive ion etching, and vertical tapers etched to reduce the loss as the light couples from the passive to the EO waveguides. The active structure was then covered with the upper passive core and cladding layers. Standard photolithography was used to create the waveguide patterns and gold electrodes were formed by vacuum evaporation and photolithography inside both cladding layers. The arms of the modulator were poled, that is, the CLD-1 chromophores were aligned, by application of 500 V poling voltage with the modulator held at 145°C in N2 atmosphere. The modulator efficiency was measured by coupling 1.55-µm transverse-magneticpolarized light into the device and focusing the output signal onto a photodetector. The measured EO coefficient was 20% smaller than the best values exhibited by the researchers’ conventional modulators utilizing the same EO polymer. The researchers believe that the low efficiency is the result of incomplete poling due to the high resistivity of the passive core
polymer, and will improve if different materials are used. Mode profile studies, on the other hand, showed a tenfold reduction in fiber-waveguide coupling loss and a reduced chip loss when an EO polymer was replaced by the passive material used in this study. GREG KHITROV
Inert Liquid Paraffin Speeds Preparation of Large, Crack-Free Mesostructured Silica Monoliths Bulk mesostructured materials with a high orientation order at the macrolevel are attracting current interest, in particular for developing novel sensors, micro- and optoelectronics, and separation devices. However, industrial applications are limited because of the absence of an adequate route for the preparation of large-sized, crack-free silica monoliths. Researchers from the Department of Chemistry of Fudan University, Shanghai, China, have demonstrated a fast way to prepare mesoporous silica monoliths by using solvent evaporation and a liquid paraffin medium as a morphology protector, as reported in the January issue of Chemistry of Materials. Dongyuan Zhao and co-workers synthesized mesostructured silica monoliths through solvent evaporation from the silica gel by using tetraethoxysilane as a silica source and poly-(ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) (EO 20 PO 70 EO 20 ) amphiphilic block copolymer as a template. They removed
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