High precision planar waveguide propagation loss measurement technique using a Fabry-Perot cavity

A high precision measurement technique for characterizing the propagation loss in silica low-loss optical waveguides, based on measuring the contrast of a Fabry-Perot cavity, is demonstrated. The cavity consists of the waveguide coupled to two polarization-maintaining fibers, each end facet coated with dielectric mirrors, leaving the reflectivity as an adjustable parameter. The contrast is measured by modulating the cavity length without influence on the waveguide characteristics and the coupling efficiency. A double modulation of the cavity length reduces the measurement uncertainty, and provides a measurement precision better than 0.1 dB, corresponding to 0.02 dB/cm in case of a 5 cm long waveguide.<>