Scientists at the NEC Research Institute in Princeton, N.J., have demonstrated a new type of fiber image guide comprising individual fibers with core diameters as small as 250 nm. By using fibers with a large difference in the index of refraction for the core and cladding materials, the researchers were able to efficiently contain light inside the core without the need for metallization. Such a probe has the potential for use in applications such as inspection and characterization of submicron devices.