Though often taken for granted because of their relative invisibility, optical coatings are an indispensible element of almost all of today’s optical components. From spectacles and camera lenses in the consumer world to optical filters and laser mirrors in research labs, thin-film coatings are essential to obtaining the desired performance of an optical system. Modern thin-film technology dates back to the 1930s when vacuum technology developed sufficiently to enable coating deposition. It received a big boost during the 1940s because of World War II and the military’s need for better optical performance of, for instance, binoculars and bombsights. And since then–driven by the rapidly evolving number of applications–constant improvement in vacuum and deposition technology combined with new techniques and materials has put thin-film coating performance at the forefront of optical design. Despite such advances, however, cost-effective volume production of coated optics is just as important to long-term commercial success as coating performance. Novel techniques aimed at higher throughput and better yields in precision coating production include advanced plasma reactive sputtering, which is highlighted on this month’s cover (see p. 41).
New materials systems are at the center of many photonics advances, especially the advent of new laser wavelengths. Fiber lasers based on ytterbium-doped fiber are now in the commercial mainstream, producing 1 µm output at kilowatt levels. More recently, similar lasers using thulium-doped fiber that emit at 2 µm are delivering increasingly higher output powers (see p. 51). Meanwhile, research groups around the globe are racing to produce a semiconductor laser that emits green light. From Japan to Germany, a variety of approaches includes devices based on indium gallium nitride and others using different II-VI compounds on indium phosphide substrates (see p. 30).
No doubt results from this research and that based on other materials systems will be presented at the Conference on Lasers and Electro-Optics (CLEO; Baltimore, MD) next month (see p. 25). And you can expect to find papers about the use of thin-film coatings in photovoltaics and LED lighting at the upcoming “green” photonics conference–OPTOmism–in Santa Clara, CA. That’s also next month (see p. 19).