Local phase measurements of light in a one-dimensional photonic crystal

For the first time the local optical phase evolution in and around a small, one-dimensional photonic crystal has been visualized with a heterodyne interferometric photon scanning tunnelling microscope. The measurements show an exponential decay of the optical intensity inside the crystal, which consists of a periodic array of subwavelength air rods fabricated in a conventional ridge waveguide. In addition it is found that the introduction of the air rods has a counterintuitive effect on the phase development inside the structure. The heterodyne detection scheme allows the detection of low-intensity scattered waves. In the vicinity of the scattering air rods phase singularities are found with a topological charge of plus or minus one.