Backseeded stimulated photorefractive scattering phase conjugation in SBS niobate fibers

Back-seeded stimulated photorefractive scattering phase conjugation is demonstrated in SBN fibers for the first time. A 7 mm long by 0.8 mm diameter 0.01% Ce:SBN fiber oriented with its c-axis along the length of the fiber is used for the measurement. The seed is provided by placing a retroreflecting screen in the path of the beam that is transmitted by the fiber. Reflectivities of 28% and 49%, accounting for reflection losses, are achieved by using light with wavelengths of 515 nm and 638 nm, respectively. Previously seeded stimulated phase conjugation (SSPC) has been demonstrated in bulk photorefractive BaTiO3,1,2 by using retroreflector arrays. Good fidelity of the back-reflected signal is achieved with reflectivities approaching 60%. The geometry for optimum results requires that an index-matching fluid surround the crystal; pixel-based image processing-appears to be difficult to achieve in bulk crystals. In the new approach a synthetic material is constructed by bundling SBN fibers. This allows parallel, pixel-based image processing to be accomplished3 with low-power (milliwatt) laser beams. By employing a polarization beam splitter in conjunction with a wave plate, the reflected light can be coupled out without loss in amplitude. We report on the angular sensitivity, wavelength dependence, and amplitude threshold needed for SSFC to occur in these fibers.