Modal symmetries at the nanoscale: A route toward a complete vectorial near-field mapping

We use symmetry considerations to understand and unravel near-field measurements, ultimately showing that we can spatially map three distinct fields using only two detectors. As an example, we create 2D field maps of the outof- plane magnetic field and two in-plane fields for a silicon ridge waveguide. Furthermore, we are able to identify and remove polarization mixing of less than 1?30 of our experimental signals. Since symmetries are prevalent in nanophotonic structures and their near-fields, our method can have an impact on many future near-field measurements.