A method of fabricating a reflective notch coupler in an optical fiber has been developed. The coupler consists of a $45°$ microprism that penetrates into the core of a multimode optical fiber. One face, at $90°$ to the fiber axis, is nonreflective, and one face, at $45°$ to the fiber axis, is reflective. Our method of fabricating a notch and selectively mirroring only the $45°$ face is low-cost, precise, and easily scalable. The coupler allows near-100% coupling of light into an optical fiber from the side, while allowing coupling of any desired fraction of light out from the core at a $90°$ angle on the opposite side of the fiber.