By embedding thin tapered silica optical fibers in a silica aerogel, researchers at the University of Bath (Bath, England) and the University of Sydney (Sydney, Australia) have created what could become a new class of fiber-optic sensor. Gas-permeable and with a refractive index (1.048 at a wavelength of 633 nm) close to that of air, but with a structure rigid enough to hold a fiber in place and allow normal handling, the aerogel is a stable platform for the potential exploitation of evanescent interactions between the fiber and dopants or gases in the aerogel.
Fibers with 10-mm-long tapers of 10, 2, and 1 µm diameter were embedded in aerogel, showing increasing evanescent interaction with decreasing waist diameter (measured losses of 0.1 dB, 0.3 dB, and 1.1 dB, respectively). In addition to holding the fiber, the aerogel prevented the scattering loss from the fiber from increasing over time due to settling of dust on the fiber. While the experimental aerogel was hygroscopic (water-absorbent, and therefore not stable in many environments), the researchers are investigating aerogels that are chemically altered to make them waterproof. Conversely, the sensitivity to water could be exploited for certain kinds of sensors. Contact Limin Xiao at [email protected].
