precision measurements of the optical attenuation profile along the propagation path in thin-film waveguides

An experimental technique for precision measurements of the optical attenuation profile along a propagation path in thin-film waveguides is reported. The method involves a 100% outcoupling of guided light through immersion of the waveguide into a liquid with an index of refraction slightly higher than that of the film. The measurement is simple and nondestructive. The repeatability and accuracy of the measured attenuation per unit length is typically better than 5%, even with losses below 0.1 dB/cm and less than 1-cm-long guiding paths.