Orthogonal two-wave vector interaction in a gyrotropic photorefractive crystal

We propose a novel scheme of a polarisation-independent (PI) adaptive interferometer based on orthogonal geometry of vectorial two-wave mixing in a gyrotropic photorefractive crystal. A mathematical model that allows the efficiency of two-wave mixing to be calculated in a gyrotropic photorefractive crystal in orthogonal geometry is developed. Using this model, conditions are found under which the PI regime of an adaptive interferometer is implemented. It is shown that the PI regime is due to optical gyrotropy-induced natural rotation of the polarisation plane of light waves in a crystal. A key feature of this approach is that the PI regime is achieved by using only a single reference wave in contrast to other similar techniques where two reference waves are required. As a result it allows a significant simplification of the PI-adaptive interferometer scheme.