Measuring propagation loss in a multimode semiconductor waveguide

The measurement of propagation loss based on the Fabry-Pérot transmission fringes is a powerful tool for the characterization of single-mode optical waveguides. This method is well established for lithium niobate waveguides, but its implementation with semiconductor devices is more delicate. A method to extend this technique to the case of multimode semiconductor waveguides is presented. Our procedure involves Fabry-Pérot measurements on a large spectral range, in order to find an interval where multimode effects do not alter the loss measurement. Two experimental examples are given, showing also the domain of validity of this approach.