Measurements of the cathodoluminescence (CL) and the degree of polarization (DOP) of (CL) from the facet of a GaAs substrate and in the vicinity of a SiN stripe are reported and analyzed. The deformation induced by the SiN stripe is estimated by fitting the measured DOP to 3D finite element method (FEM) simulations. The deformation is found to be more complex than an initial condition of biaxial stress in the SiN. A ratio of fit coefficients suggests that the dependence of DOP on strain is described by equations presented in Appl. Opt. 59, 5506-5520 (2020). These equations give a DOP that is either proportional to a weighted difference of the principal components of strain in the measurement plane, or proportional to the shear strain in the measurement plane, depending on the chosen orientation of the measurement axes.