Polished fiber-optic coupler with intermediate planar waveguiding layer. I

Experimental results concerning the characteristics of polished single-mode fiber couplers with an intermediate waveguiding optical layer between the two fiber half-blocks are presented. In order to obtain controlled thickness of the planar layer between the two fibers, half-blocks made from different materials are used. Regions of the parameters of the planar layer exist for which large losses arise. Different theoretical approaches are compared and a suitable equivalent planar geometry is chosen, which is treated in the limits of coupled-mode theory