This invention relates to connectors and, more particularly, to high-precision molding of connectors for single-mode optical fibers.
Optical fibers are being increasingly used for a wide variety of purposes in the communication field. As the use of optical fibers increases, a significant need has arisen for low-cost connectors suitable for joining fiber ends together in a way that results in low transmission loss of the optical signal at the joint.
Several types of losses typically occur when the ends of optical fibers are connected together. Among these are losses which stem from angular misalignment between the fiber ends, from gaps between the fiber ends, and from axial misalignment (lack of concentricity) between the fibers.
A number of types of connectors are known for joining fiber ends together. One such type, commonly called a biconic connector, includes two substantially identical apertured plugs designed to respectively engage, in a mirror-image fashion, the two fiber ends to be joined. In the molding operation described herein, the axis of each plug aperture is intended to be positioned with a prescribed high precision with respect to the axis of the plug profile. When the fiber-containing plugs are brought into contact, the cores of the fibers are intended to be substantially concentric.
The cores of multi-mode optical fibers are large relative to those of single-mode fibers. Thus, establishing axial alignment between the cores of multi-mode fiber ends is far less difficult than it is with single-mode fibers. In practice, low-cost connectors for multi-mode optical fibers have been realized by high-volume forming of plastic parts in a conventional injection molding operation.
For single-mode fibers having, for example, a core diameter (mode field diameter) of only about 8.7-to-10 micrometers (.mu.m), axial alignment of the fiber ends must typically be maintained below one .mu.m to ensure that losses are kept at an acceptable level. The machining of suitable mold details to consistently achieve sufficient precision in a molded single-mode connector to ensure that such high-precision axial alignment is realized is a formidable task. This obstacle has priorly stood in the way of economically fabricating suitable single-mode connectors by conventional injection molding techniques.
Accordingly, considerable efforts have been made by workers skilled in the art aimed at trying to devise improved techniques for molding low-cost connectors suitable for joining single-mode fiber ends together in a low-loss way. It was recognized that these efforts, if successful, would contribute importantly to enhancing the quality and lowering the cost of communication systems that utilize single-mode optical fibers.