Intensity and Phase Mapping of Guided Light in LiNbO3 Waveguides with an Interferometric Near-Field Scanning Optical Microscope
01 January 2003
The design and implmentation of a phase sensitivie near-field scanning optical microscope incorporating both heterodyne interferometric detection and a phase feedback mechanism are described. Using this microscope we demonstrate a new method for measuring the effective index of the guided mode of a waveguide from the phase images. Two types of LiNbO3 waveguides, defined by Ti diffusion or annealed proton exchange, were studied. Both the profile and the effective index of the mode were measured experimentally. For Ti diffused waveguides, both agree well with values determined from numerical simulation. In annealed proton exchanged waveguides containing periodically poled domains, we find evidence for back-reflection from the boundaries between neighboring regions of opposite pole directions, which could result in transmission loss in this type of waveguides.