Near-field scanning optical microscopy of standing waves in fiber Bragg gratings

Near-field scanning optical microscopy (NSOM) can provide direct information about the electric fields inside optoelectronic devices with subwavelength resolution. This letter describes direct, wavelength-resolved measurements of the amplitude and phase of the standing waves within a fiber Bragg grating, using a heterodyne interference variant of NSOM that works at telecommunications wavelengths. The amplitudes of forward- and backward-going components of the standing wave can be measured separately, and the position shift of the standing wave antinodes as the wavelength varies across the stop band is imaged directly