Shin-Etsu Chemical develops 'green' technology for lead-free optical isolators
January 22, 2007 -- Shin-Etsu Chemical Co. Ltd. (search for Shin-Etsu) says it has developed a manufacturing technology for lead-free optical isolators, which enables it to comply with the European RoHS Directive (restriction of hazardous substances).
Until now, Faraday rotators, a main component of optical isolators, contained lead; however, the company says this newly developed technology has made it possible to totally eliminate the lead element in optical isolators.
In July 2006, the European Union issued a RoHS Directive on the restriction of the use of certain hazardous substances such as the lead element in electrical and electronic equipment, and in principle, the decision was made to totally abolish its use. Due to technical difficulties in fulfilling this RoHS Directive for some components and processes -- including optical isolators, which are indispensable components for optical fiber communication systems -- an accommodation was made in the RoHS regulations to allow exemptions for such cases and a less absolute standard of regulating lead content to less than 1,000 ppm has been planned for adoption, although it was expected that completely lead-free optical isolators would be developed soon.
Shin-Etsu reports that its technology fulfills the equipment makers' expectation by achieving the total elimination of lead from optical isolators. Going forward, this new technology will enable the optical communications industry to comply with expanding environmental regulations.
Optical isolators, set in devices such as laser modules, permit light emitted by a laser diode to be transmitted in only one direction. They are used to protect laser diodes because they block the adverse effect of return beams that go back to the laser diodes from the optical fiber transmission channels and amplifiers.
Rare-earth iron garnet single crystals with a thickness of several hundred microns, which are grown by the liquid phase epitaxy (LPE) method, are used in Faraday rotators for optical isolators. In the LPE method, an oxide flux is used to melt the crystal component at a lower melting point. Lead oxide was previously considered to be an essential material, and for this purpose, the rare-earth iron garnet single crystals contained about 5,000 ppm of lead oxide.
Shin-Etsu Chemical, by developing its own original LPE method that does not use lead oxide at all, says its has developed the first technology to grow rare-earth iron garnet crystals with a thickness of several hundred microns and reduce to zero ppm the amount of lead in Faraday rotators.
The company says it will also proceed with developing technology for lead-free rare-earth iron garnet crystals for inline isolators and circulators, and plans to increase its production capacity to respond to demand from the optical communication parts market.