Abstract

Fiber connection losses are affected by intrinsic fiber parameter mismatch, by extrinsic misalignment such as off-set, tilt, and end-separation; by the end-face polishing quality, and by the modal power distribution existing at the connection point. The modal power distribution itself depends on the fiber transmission characteristics, i.e. differential mode attenuation and mode coupling, the location of the connector or splice, and the launch conditions. Unique, steady-state losses are only obtained for an equilibrium mode distribution (EMD) at the splice point^1,2 which establishes itself, in general, after a few kilometers, or which can be created within a much shorter distance by controlled-beam excitation, or with mode filters^1-4. Recently, the EMD losses of graded-index fibers have been measured with high accuracy using a simple, mandrel-wrap (MW) mode filter.^1,3. The main function of this filter, which consists of five turns of fiber wound around a 1.2-cm diameter mandrel (as optimized for 50µm-core, 0.23-NA, graded-index fibers), is to eliminate excess higher-order and leaky modes inadvertently launched by typical excitation conditions. Since, in general, the MW filter does not generate the EMD exactly, the question arises as to the accuracy of connector loss measurements performed with this filter.