Bare optical fiber consists of ultra-thin strands of glass or plastic (typically 125–250 microns in diameter) designed to transmit data via light pulses. Bare fiber refers to the fundamental glass strand of an optical fiber without any protective coatings, buffers, or jackets. Please check your network connection and try again. AFL's optical fiber identifiers (OFIs) are rugged, easy-to-use test instruments that detect the presence of signals on optical fibers. Multimode. Bare Fiber Strands are cladded step index fibers with no sheath manufactured by Coherent and Corning to allow for easy integration in space constrained systems.