A new method of coupling from a single-mode fiber to a thin-film waveguide through a coupling fiber is reported. This method provides high coupling efficiency, whereby the coupling fiber helps to match the coupling conditions. Experimentally the maximum coupling efficiency of 78% was obtained by use of a polymeric thin-film waveguide, in which propagation loss of the film and other coupling losses were excluded. The system also provides the means to measure characteristics of the polymeric films.
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