Abstract: The present invention relates to a multi-wavelength multi-stage fiber amplifier exhibiting high power output with a flat balanced gain spectrum. The input stage exhibits a given passive loss and a flattened gain spectrum. The output stage exhibits a passive loss that is lower than the given passive loss and a gain spectrum that is less flat than the gain spectrum of the input stage. In a system utilizing erbium-based gain fibers, the input stage gain fiber can contain an amount of alumina sufficient to provide the desired gain spectrum flatness, while the output stage gain fiber has an alumina concentration sufficiently low to render that stage essentially lossless.

Abstract: Overclad fiber optic couplers typically include an elongated glass body having a solid midregion through which at least two glass optical fibers extend in optical signal coupling relationship. At each end of the midregion is an end region containing a bore from which optical fiber pigtails extend. In accordance with the invention, each end region includes a first projecting portion, one surface of which forms a ledge. That end of each bore opposite the midregion terminates at a recessed face that intersects the respective ledge. One end of at least the first fiber extends from the first bore. That portion of the first fiber outside the first bore has a coating that extends along the ledge, the coating terminating outside the first bore. A mass of glue extends between the ledge and the recessed face and encompasses the bare portion of the first fiber that extends along the first ledge and at least a portion of the first coating that extends along the first ledge.

Abstract: The present invention relates to a multi-stage fiber amplifier in which the first and stages are connected by means including a filter for attenuating the amplified spontaneous emission. The pump source consists of a pair of light sources that are connected to a coupler that splits the power equally to two output legs. All of the pump power from the second coupler output leg is supplied to the second stage. A portion of the pump power from the second coupler output leg is converted in the first stage to amplified signal and amplified spontaneous emission, and the remainder of the power from that leg is supplied to the second stage.

Abstract: Methods for deteting defects, such as, holes or voids, in optical waveguide fibers are provided. The methods employ far-field interference patterns produced by transversely illuminating the fiber with a laser beam. Holes in the fiber produce a characteristic peak in the spatial frequency spectrum of the interference pattern which subdivides into two peaks which migrate in opposite directions as a hole grows in size. Holes also produce a characteristic increase in the total power of the interference pattern, the amount of the increase being a linear function of the size of the hole for holes having a diameter less than about 60% of the diameter of the fiber. The hole detection methods are incorporated in an overall system for controlling the drawing of optical waveguide fibers.