Photo-written waveguides in iron-doped lithium niobate crystal employing binary optical masks

Photo-written waveguides employing binary optical masks are investigated in an iron-doped lithium niobate crystal. Planar and Y-branch waveguides are experimentally demonstrated. The index variations along the propagation direction of the writing beam in the crystal are experimentally measured and theoretically analyzed. The influence of the diffraction from the optical masks, which imposes a limitation for the applications of the waveguide fabrication method, is numerically specified. Additionally, the asymmetry of the index distribution in the waveguide region, which is related to the transport process of the photoexcited charge carriers, is revealed and qualitatively explained.