Angle selective coupler for optical fibers

摘要

There is disclosed an angle selective coupler for coupling optical energy into and/or out of optical fibers. The coupler consists of a section of the optical fiber modified in such a way as to allow optical excitation of a plurality of higher order modes of optical transmission, each mode being defined by a given angle of propagation relative to the fiber axis. In one embodiment the coupling section comprises a single strand of glass fiber waveguide which is tapered along its length. The existence of the tapered section allows coupling of radiation from an external source into a given propagation angle in the fiber. In another embodiment no taper is used, but the fiber cladding is etched down to a thin layer and higher index material is deposited over the thin layer. This allows coherent coupling of radiation into one or more higher order modes in the optical fiber as determined by the angle of the incident light beam with respect to the cladding of the fiber. In either embodiment the device uses total internal reflection to function as an angle selective input or output connector for efficient coupling of optical energy into a given propagation angle within the fiber waveguide. The existence of a plurality of such angles permits the coupler to be used in a modal multiplexing duplexer.