OPTICAL-FIBER BEAM TRANSFORMERS

We consider transitions of bundles of coupled optical fibre cores. Iso lated, each core is single-moded. In the bundle, the cores touch each other and their arrangement is gradually changed from a compact to an elongated form. We use the method of Henry and Verbeek to calculate th e propagation constants of bound modes during the transition. We show that, with the parameters of the structure appropriately chosen, the n umber of bound modes in the bundle remains approximately constant duri ng the transition. This means that optical fibre beam transformers of high efficiency are theoretically possible.