Coupling. Theory of Coupling Loss of an Ion Exchanged Multimode Channel Waveguide to Optical Fibers

SummaryThe potential applicability of multimode integrated optical branching waveguides and couplers is limited primarily by their coupling loss to optical fibers. To get a reasonably detailed theoretical insight, the fiber-to- fiber coupling loss of a section of a multimode channel waveguide fabricated, e.g., by ion exchange in a glass substrate is calculated using a ray-optic approximation. An approach of the length-averaged coupling loss results in a simple and efficient calculation procedure which enables one to optimize the parameters of a channel waveguide for minimum coupling loss. Coupling losses as low as 2 dB and 0.25 dB can be obtained for single channel and sandwich structures, respectively, coupled to standard graded-index fibers.