Tunable Optical Fibers

Optical fibers regularly carry billions of phone conversations and other data transmissions every day and are a fundamental part of optical sensing and numerous medical applications. The photonic devices responsible for all this traffic are being made even more efficient and versatile by handing over some of the switching and reconfiguring chores to the fibers themselves---the trunk lines linking all the optical nodes. An active optical fiber, which can tunably filter light at different frequencies, has been created by infusing microfluidic plugs, spaced at characteristic (periodic) intervals along the fiber, into air holes running parallel to the passageway for the light at the center of the fiber (see figure). The arrays of microfluidic plugs along the light path serves as a diffraction grating for producing the photonic-crystal effect. In other words, the presence of the fluids is used to change the refractive index periodically, and hence the transmission properties, of the fiber. The creators of this new microstructured optical fiber (MOF), Charles Kerbage (OFS Laboratories in Murray Hill, NJ) and Ben Eggleton (University of Sydney, say that this is the first time a tunable grating has been achieved with microfluids, and that this provides (in addition to the switchability) a very high index of refraction when compared to conventional gratings. (Applied Physics Letters, 3 March 2003)