A Robust Method for Characterization of Optical Waveguides and Couplers

We propose a simple yet powerful method to characterize waveguide propagation loss and 2 × 2 waveguide coupler's coupling coefficient simultaneously. The method, based on the spectrum analysis of transmission through an unbalanced Mach-Zehnder interferometer, requires only a single test structure and is insensitive to variation of input coupling losses. We show that, in most general cases, it is possible to determine both the propagation loss and the coupling of both couplers that can have different coupling coefficients.