Single Mode Thin Film Directional Coupler

Abstract

Coupling between SM polished half coupler block and thin film planar polymer waveguide is shown. Fabricational procedure for half coupler and thin film are discussed. Half coupler is prepared by polishing coupler block when the remaining cladding thickness and the interaction length is controlled by the loss calibration curve. Assuming two identical waveguides, the analysis of the coupled power is made using coupled mode theory following the evanescent interaction between SM fiber and thin film. For matching the propagation constant of the fiber and the thin film, the thickness of the film is set. The problem of severe control of waveguide coupling length for the required coupled power is discussed. A new structure of coupling between one uniform and other tapered waveguide for both dimensional and index-and-dimensional taper is proposed, where the flat coupling response along the coupling length with low radiation loss is shown. Proposed structure can be used as a waveguide type optical power divider by chosing the appropriate taper slope.