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Technology Stocks : LUMM - Lumenon Innovative Lightwave Technology Inc. -- Ignore unavailable to you. Want to Upgrade?

To: donpat who wrote (2432)	4/25/2002 2:59:00 PM
From: Kent Rattey	Read Replies (1) \| Respond to of 2484

They're stealing your thunder! Well, actually, they might just be the chorus to the fat lady... Terahertz touts sol-gel capabilities Products based on planar lightwave circuits (PLCs) promise to slash the cost and size of fiber-optic components and enhance functionality. There's just one problem: traditional PLC production processes - chemical vapour deposition and flame hydrolysis - don't come cheap and are difficult to control. Enter Terahertz Photonics of Scotland, which claims to have perfected the use of sol-gel, a low-cost alternative to the gas-based coating techniques, to deposit silica waveguides on silicon wafers. SOLICA process "Sol-gel provides tremendous savings in infrastructure and operational costs and at the same time adds flexibility in terms of what you can incorporate in the glass," said Navin Suyal, Terahertz's director of PLC materials. "For the same wafer capacity per year, you would possibly need 5% of the infrastructure cost." The sol-gel deposition process involves coating a substrate with a suspension of silica polymers or particles. The solvents are evaporated to leave a solid film, which is then densified to a glass layer and etched to form waveguide structures for PLCs. Unfortunately, this drying stage cracks the film, limiting its thickness to about 1 µm. Terahertz claims that its SOLICA process, on the other hand, enables optical-quality glass layers to be made up to 10 µm thick in a single step. The secret lies in the chemistry. A patented silica suspension (the sol) is formed by hydrolysis and polymerization of tetraethoxysilane. Careful chemical control enables Terahertz to synthesize well dispersed silica units with a tailored size distribution. The sol is spin-coated onto a silicon substrate using a commercial spinner, after which it is dried and sintered at 1050 to 1200 ºC. The silica units in the sol are modified with proprietary additives to control their surface properties and prevent them from agglomerating during the drying process. Suyal says that the final silica film does not contain any impurities that could limit device performance. "The glass is superior or comparable to silica made using gas-based techniques," he said. He continued: "There are no other commercial processes based on pure silica sol-gel. A few firms are using sol-gel for PLC manufacturing, but their methods lead to a mixture of organic polymers and inorganic silica that has higher losses and cannot withstand temperatures higher than 200 ºC or so." The properties of the silica layer can be tailored by incorporating extra elements in the sol. Addition of high-refractive-index components such as germanium, titanium and lead alters the refractive index of the glass in the range 1.45-1.50. Phosphorous and boron are used to modify the thermal expansion and flow properties. SOLICA also allows a high concentration of active ions like erbium to be included - a feat that cannot be achieved using gas-based production. By Tami Freeman, Technology Editor, FibreSystems Europe • This article originally appeared in FibreSystems Europe April 2002 p11