Random Lasing in an Optical Fiber

The research team fabricated a new type of optical fiber that is capable of controlling these random lasers. (Source: UNM)

At its most basic level, a random laser is precisely what its name implies; random. It’s random in the spectrum of light it produces and in the way that light is emitted, making what could be an extremely versatile laser source, nearly useless for most practical appli­cations. So, how do you control some of the random­ness to make useful devices? It’s a question that’s led a team of researchers at The Uni­versity of New Mexico to a disco­very that’s taking laser tech­nology to the next level.

“It’s been incredible to see how this project has progressed,” said Behnam Abaie, a Ph.D. student at UNM’s Center for High Tech­nology Materials (CHTM). “When I first came to work with Pro­fessor Mafi, I knew this project had the potential to be very success­ful but I never expected this.” Abaie provides in his work a technical analysis of how they are able to reliably control these extremely powerful, but previously uncon­trollable, lasers. “Our success in being able to control these random lasers addresses decade-old issues that have prevented these lasers from becoming main­stream devices,” said Mafi, who is also an asso­ciate professor in UNM’s Dept. of Physics & Astronomy. “It’s a very exciting contri­bution.”

Tradi­tional lasers consist of three main components: an energy source, gain medium and optical cavity. The energy source is provided through pumping and can be supplied through an electrical current or another light source. That energy then passes through the gain medium which contains proper­ties that amplify the light. The optical cavity ­– a pair of mirrors on either side of the gain medium – bounce the light back and forth through the medium, ampli­fying it each time. The result is a directed, intense beam of light.

Random lasers, by compa­rison, perform using a pump, a highly-disor­dered gain medium but no optical cavity. They are extremely useful due to their simplicity and broad spectral features, meaning a single random laser can produce a beam of light containing multiple spectra, a very beneficial property for certain appli­cations like bio­medical imaging. However, given their nature, random lasers are difficult to reliably control due to their multi-direc­tional output and chaotic fluc­tuation. The UNM team, in colla­boration with researchers at Clemson Uni­versity and the Univer­sity of Cali­fornia San Diego, has been able to overcome these obstacles in an effi­cient way – a victory they hope will continue to push the use of random lasers forward.

“Our device has all the great qua­lities of a random laser, plus spectral stabi­lity and it is highly directional,” said Mafi. “It’s a wonderful develop­ment.” Researchers are able to achieve these results through the fabri­cation and use of a unique glass Anderson loca­lizing optical fiber. The fiber is made of a satin quartz, an extremely porous artisan glass that is typically only used to calibrate the machinery that draws fiber optics. When pulled into long rods, the porous material forms dozens of micro­scopic air channels in each fiber.

“The glass that we’re using for these fiber optics is actually material that we would typi­cally throw away because it is very porous,” said Abaie. “But, it’s those holes in the glass that are actually creating the channels that control the laser.” Once filled with a gain medium and pumped using a single-colored green laser, the random laser becomes less random and highly control­lable, thanks to a pheno­menon known as Anderson Loca­lization.

“There is still a lot to learn about Anderson Loca­lization but it’s exciting for us to be part of this develop­ment,” said Mafi. “To be able to actually make devices that utilize this pheno­menon, it’s taking the science to yet another level.” Moving forward, Mafi says they hope to broaden the spectrum of this new device and make it more effi­cient, creating a broad spectrum illu­mination source that can be uti­lized around the world. (Source: UNM)

Reference: B. Abaie et al.: Random lasing in an Anderson localizing optical fiber, Light: Sci. & App. 6, e17041 (2017); DOI: 10.1038/lsa.2017.41

Link: Center for High Technology Materials, University of New Mexico, Albuquerque, USA

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