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.