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Researchers at EPFL have developed a technology that can amplify light in the latest hollow-core optical fibers. The work was carried out at the lab of Luc Thévenaz, the head of the Fiber Optics Group in EPFL’s School of Engineering. This could be a promising breakthrough for the future of communications, according to experts. The findings have been published in Nature Photonics.
Squaring the Circle
Today’s optical fibers usually have a solid glass core, so there’s no air inside. Light can travel along the fibers but loses half of its intensity after 15 kilometers. It keeps weakening until it can hardly be detected at 300 kilometers. So to keep the light moving, it has to be amplified at regular intervals. Thévenaz’s approach is based on new hollow-core optical fibers that are filled with either air or gas. The air means there’s less attenuation, so the light can travel over a longer distance. That’s a real advantage, explains the professor. But in a thin substance like air, the light is harder to amplify. That’s the crux of the problem: light travels faster when there’s less resistance, but at the same time it’s harder to act on. Luckily, the new discovery has squared that circle, added Thévenaz.
From Infrared to Ultraviolet
So what did the researchers do? They just added pressure to the air in the fiber to get some controlled resistance, explained Fan Yang, a postdoctoral student. According to him, it works in a similar way to optical tweezers – the air molecules are compressed and form into regularly spaced clusters. This creates a sound wave that increases in amplitude and effectively diffracts the light from a powerful source towards the weakened beam so that it is amplified up to 100,000 times. This technique therefore makes the light considerably more powerful. The technology can be applied to any type of light, from infrared to ultraviolet, and to any gas, Fan Yang added.
An Extremely Accurate Thermometer
Going forward, the technology could serve other purposes in addition to light amplification. Hollow-core or compressed-gas optical fibers could, for instance, be used to make extremely accurate thermometers. According to Flavien Gyger, PhD student, they will be able to measure temperature distribution at any point along the fiber. So if a fire starts along a tunnel, they’ll know exactly where it began based on the increased temperature at a given point. According to Flavien Gyger, PhD student. The technology could also be used to create a temporary optical memory by stopping the light in the fiber for a microsecond – that’s ten times longer than is currently possible.
Click here to read the published paper.
