Abstract: An environment-proof fiber optic coupler couples two optical fibers to one another at a coupled region. The optical fibers on each side of the coupled region are bonded to a central receiving substrate of a substrate part which together with a cover part bonded thereto forms a sleeve with open sleeve ends. The volume between the sleeve ends is then evacuated, and the sleeve returned to atmospheric pressure with the sleeve ends filled respectively with a cured and an uncured sleeve sealant. Air is drawn through the uncured sleeve sealant during evacuation, and thereafter the uncured sleeve sealant is drawn into the sleeve before curing such that the coupled region is protected by the sealed sleeve. Next, a tube is placed around the sealed sleeve which tube extends beyond the sealed sleeve ends thereof. With at least one of the tube ends filled with an uncured tube sealant, the volume between the tube ends is evacuated so that air is drawn through the uncured sealant which is thereafter drawn into the tube.

Abstract: Fiber optic couplers formed of at least two single mode optical fibers, at least one of which is an input fiber, are shown, the fibers constructed and arranged in the manner that coupling between the input fiber and the other fibers limits antisymmetric modal energy to substantially less than 50% of the input energy, the coupling region of said coupler being fused and drawn to an extended length sufficient to cause cutoff of the antisymmetric mode energy, whereby the coupler exhibits coupling ratio stability over an extended range of wavelengths and an excess loss of substantially less than 50%. Numerous fiber couplers of various construction, all employing cut-off of the antisymmetric mode to achieve wideband response or wavelength insensitivity are shown along with their method of manufacture.