Experimental results are presented for 180° contra-directional two-beam coupling (TBC) measurements in a single crystal fiber of LiNbO<sub>3</sub>:Fe using a single incident beam and its Fresnel reflection off the back surface of the fiber. To our knowledge, this is the first time that volume gratings have been written in a fiber using this beam coupling geometry. At small <i>f</i>-numbers, the TBC efficiency has been predicted to decrease in bulk LiNbO<sub>3</sub>:Fe due to the erasure of the weak gratings by the dark conductivity. We present experimental results validating the published theory and show experimentally that confinement of the interfering beams in a fiber geometry overcomes this limitation.
© 2002 Optical Society of America
D. R. Evans, M. A. Saleh, T. J. Bunning, L. Lu, R. S. Meltzer, W. M. Yen, and S. Guha, "Contra-Directional Two-Beam Coupling by use of a Single Input Beam in an Iron-Doped Lithium Niobate Multimode Fiber," Appl. Opt. 41, 6890-6893 (2002)