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17 Jun 2002
A tunable distributed-feedback waveguide laser gears up to target the telecoms market.
Researchers at the Chinese University of Hong Kong have fabricated a tunable distributed-feedback (DFB) laser from a thin-film sol-gel glass waveguide, (App.Phys.Lett. 80 917). Dennis Lo and Xiao-lei Zhu say the laser is a versatile tunable light source for today's polymer optical fiber and also has huge potential in long-distance transmissions.
To form the waveguide, the researchers deposited a dye-doped titania-silica thin-film onto a glass substrate via a low-temperature sol-gel technique. A 6 ns pulsed Nd:YAG laser was diffracted through a beamsplitter and recombined at the thin-film surface to create the periodic gain modulation of a DFB structure.
According to Lo, at a threshold of 3.7 µJ the sol-gel waveguide lased with a peak power of 1 kW. The researchers went on to tune the output wavelength between 576 and 614 nm by changing the angle at which the Nd:YAG pump hit the thin-film surface.
Lo believes that when it comes to transmission in the ultraviolet and infrared, sol-gel glass is better than its optical polymer rivals. "Sol-gel is more chemically stable, which is important for the sol-gel matrix to host luminescent phosphors," he added. "[I believe] that the thermal properties of sol-gel glass are superior."
Lo also says that he and his colleague did not encounter any fabrication problems with their sol gel technique, and they are now working on the quality of the glass waveguide to improve the optical confinement. "This will reduce the lasing threshold to a fraction of a micro Joule and boost power," Lo explained.
Although a prototype could be up to 5 years away, Lo is optimistic about the future of sol-gel devices in telecoms applications. "The immediate application for the laser is to couple it with polymer optical fiber," he said. "But for the sol-gel DFB laser to work in the near infrared - for long-distance communications - we need to dope the sol-gel glass with rare-earth elements such as erbium," he said.
Research in this area has yet to be successful, but Lo is confident that he and his colleague will make progress here. "We will soon study infrared emission in the sol-gel waveguide which will hopefully lead to DFB lasing," he said. "The potential of [these] sol-gel glass DFB lasers in long distance telecoms is huge."
Author
Rebecca Pool is news editor on Optics.org and Opto & Laser Europe magazine.
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