  We perform phase-sensitive near-field scanning optical microscopy on
photonic-crystal waveguides. The observed intricate field patterns are analyzed
by spatial Fourier transformations, revealing several guided TE- and TM-like
modes. Using the reconstruction algorithm proposed by Ha, et al. (Opt. Lett. 34
(2009)), we decompose the measured two-dimensional field pattern in a
superposition of propagating Bloch modes. This opens new possibilities to study
specific modes in near-field measurements. We apply the method to study the
transverse behavior of a guided TE-like mode, where the mode extends deeper in
the surrounding photonic crystal when the band edge is approached.
