Tuning optical fibers with microfluidics

Optical fibers are a fundamental part of optical sensing, optical telecommunications, and many medical applications. One way to make the fibers even more efficient and versatile is to hand over some of the switching, tuning, and reconfiguring chores to the fibers themselves, rather than to rely on separate devices. Researchers at OFS Laboratories in Murray Hill, New Jersey, have now developed a tunable optical grating in a microstructured optical fiber. Their fiber has a hexagonal array of tiny air holes running its length, surrounding the 8-μm core where the light actually propagates. They created a tapered region, about 7 cm long, in the fiber so that the light field could expand beyond the core and interact with the air holes. With a vacuum applied at one end of the fiber, they alternately drew fluid plugs and air into the microchannels in the tapered region. The resulting periodic structure of fluid plugs was, in effect, a photonic crystal that caused resonant coupling of modes and wavelength-dependent attenuation. (C. Kerbage, B. J. Eggleton, Appl. Phys. Lett. 82, 1338, 2003 http://dx.doi.org/10.1063/1.1557334 .)