Contradirectional two-beam coupling was achieved using a single laser beam incident on fibers grown from congruent iron doped lithium niobate using the laser heated pedestal growth technique. To our knowledge, this is the first time that a grating has been written in a fiber using a single laser beam and its Fresnel reflection in a 180 degree(s) contradirectional two-beam coupling geometry. Beam-coupling efficiencies were compared as a function of beam spot size for fibers and bulk crystals. At small spot sizes, the fibers outperformed the bulk crystals by reducing the diffraction effect.
In this work we present the experimental results of contradirectional two-beam coupling in a bulk crystal and single crystal fibers of iron-doped lithium niobate. Results of a reduction of the grating writing instability, a comparison of the two-beam coupling efficiency of the fibers and bulk crystal as a function of focusing geometry, as well as a comparison of theoretical and experimental results of the two-beam coupling efficiency are presented.