Environmentally stable fiber optic polarization maintaining couplers

Abstract

The invention features a fiber optic coupler package including a rigid substrate and at least two side-by-side optical fibers joined in a coupler region. The substrate has a coefficient of thermal expansion substantially matched to that of the fibers. Each fiber extends axially to opposite sides of the coupler region to a primary and secondary regions of fixation, at each side of the coupler region. In the primary region of fixation, each fiber is separately bonded in close proximity to a rigid mounting surface of the substrate using a small amount of adhesive contiguously disposed on opposite sides of the line of tangency formed by the fiber and the mounting surface. The adhesive is distributed to form a pair of substantially identical masses with mirror symmetry relative to a plane defined by the central fiber axis and the line of tangency. In the secondary region of fixation, extended outward from the coupling region beyond the primary regions of fixation, each fiber has a buffer coating and the fiber is bonded through the buffer coating to the substrate. The coupling region may be formed by the biconically tapered laterally fused process or by bonding the fibers together. The fibers of the coupler may be PM fibers, single mode fibers, multimode fibers, or their combination.