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Optimization Of Optical Coupling In Fiber-Optic Systems By Fiber Etching

A method is described for optimizing the power coupling efficiency between a single fiber or bundle of fibers and either an optical component (such as a detector, coupler, splitter, etc.) or another fiber or fiber bundle. The technique described is to either (i) match the cross sectional areas of the components to be butt-coupled or (ii) decrease the diameter of the active area of the fiber or fiber bundle to be lens-coupled so that the image size and numerical aperture of the lens are optimized. In either case the desired result is accomplished by controlled etching of the ends of each of the appropriate fibers involved in the coupling. We have shown that the loss in optical power associated with pre-etching a fiber before it is epoxied in a resilient ferrule connector is less than 0.5 dB even when the fiber cladding is completely removed in the etching process. Thus, efficient coupling has been demonstrated, for example, between a bundle of seven etched fibers and a single unetched fiber (i.e., a fan-in coupler). Although the technique is primarily of wider application with multi-mode fiber, it has been shown to work equally well for single-mode fiber.