Geometry of a self-pumped passive ring mirror in crystals with strong fanning

Most photorefractive crystals that are suitable for self-pumped four-wave-mixing phase-conjugation and mutual-conjugation geometries are characterized by significant levels of fanning. In some cases this may mean that the nonlinearity in these crystals is already too large to be good, and a decrease in the value of the nonlinear coupling coefficient may result in an improvement in the performance of these geometries. We illustrate this point, using the geometry of a self-pumped ring mirror as an example.