Determination of spatio-spectral properties of individual modes within multimode waveguides using spectrally resolved near-field scanning optical microscopy

Abstract

Near-field scanning optical microscopy (NSOM) is used to measure the relative group velocity and relative amplitude of modes in a multimode waveguide with an incoherent broadband light source. A spectrally resolving NSOM probe was used to observe localized spectral interference in the multimode waveguide. Fourier analysis was used to identify temporal delays. The modes can be further identified by their temporally discriminated spatial profile which is based on the product of their fields. This data provide the relative amplitude and phases of the modes.