Tapered Fibers: An Overview

Fused tapered couplers are typically cladding-mode devices although the effect of the core is not always negligible. Tapers of single fibers may be used as a building-block to their understanding. If the tapering is not slow, then higher-order mode coupling effects occur. This degrades the coupling between fibers in a fused coupler. However such an effect in a single fiber may be usefully exploited as a basis for interferometric type devices. Accordingly, we review the transmission properties of biconically tapered fibers and propagation mechanisms involved therein, giving reference to fused tapered couplers. Furthermore, we consider tapering as a means of field access and manipulation, provide a comparison with polishing and etching, and discuss applications such as simple in-line modulation and filtering.