The refractive index of the surrounding glass tube is higher than the refractive index of air, which means that normally, the light in a hollow-core fiber would leak from the air into the glass. In contrast, hollow-core fibers are made of glass cladding surrounding an air-filled center. In other words, 1 percent of light entering a 100-kilometer length of such fiber emerges from the other end, which is still good enough for long-distance communications. If the core is pure silicon dioxide, the loss at wavelengths near 1.55 micrometers-the wavelength of choice for fiber-optic signals-is less than 0.2 decibels per kilometer. Light traveling through the fiber is lost only by the scattering and absorption of photons. Any light that hits the cladding boundary is perfectly reflected into the core through total internal reflection. Standard optical fibers-whether they’re being used for communications or machining-work by trapping light aimed along their length inside a solid glass core surrounded by a glass cladding with a lower refractive index. The development marks a big step for precision machining that requires high-power laser beams. Now a hollow-core fiber described in Nature Photonics on 30 May can transport a kilowatt of laser power up to a kilometer away. Recent reductions in loss of hollow-core fibers make them attractive for communication applications.
0 Comments
Leave a Reply. |