  We demonstrate that the spatial profiles of both propagating and evanescent
Bloch-modes in a periodic structure can be extracted from a single measurement
of electric field at the specified optical wavelength. We develop a systematic
extraction procedure by extending the concepts of high-resolution spectral
methods previously developed for temporal data series to take into account the
symmetry properties of Bloch-modes simultaneously at all spatial locations. We
apply our method to a photonic crystal waveguide interface and confirm its
robustness in the presence of noise.
