Evaluation of antireflection coatings for optical waveguides

A simple new technique is presented for evaluating the structural parameters of antireflection coating films formed on optical waveguide facets. SiO(x)/MgF(2) double layer AR coatings are fabricated on silica based optical waveguide facets by the thermal evaporation method. The transmission properties of the waveguides are measured in the 0.5-1.7-microm wavelength region. The structural parameters (refractive index and thickness) of the SiO(x) and MgF(2) films are determined by fitting the theoretical transmission properties to the experimental results by iteratively changing the parameters for calculation. The calculated reflectivity is in good agreement with the value measured with an optical time domain reflectometer. A graphic method for the simple determination of the parameters is also discussed.