Abstract: An integrated optics device has a substrate of lithium niobate (LiNbO.sub.3) with at least one optical waveguide. A slot formed in the edge of the substrate has end wall that exposes an end surface of the optical waveguide formed at an end surface angle with the optical axis of propagation to reduce reflected light in the optical waveguide. A length of optical fiber. The optical fiber has an end face formed at an end face angle with the direction of the propagation of light in the optical fiber. The slot is formed to receive the optical fiber. The optical fiber is positioned in the slot with the end face butt-coupled to the end surface of the optical waveguide to form an interface such that light may propagate between the optical waveguide and the optical fiber. A means for mounting the substrate. The optical waveguide is extended to an input junction with a center wave guide and with an sense waveguide.