Use and misuse of end-facet reflections in the characterization of optical waveguide directional couplers.

From an analysis of the effects of end facet reflections on measurements of the characteristics of optical waveguide directional couplers, we show that these reflections can result in uncertainties of almost 6 dB in measurements of coupler extinction ratios. We present methods for estimating and minimizing these uncertainties. We also show that the Fabry-Perot loss measurement technique, which is widely used for measurements of single waveguides, can be used for loss measurements on directional couplers, but only for high extinction ratio devices.