Two wave mixing in photorefractive materials has been widely investigated in the last decade. In particulor it has been shown that noneciprocal transmission may be obtained using the reflection geometry". and it has been proposed o that nonreciprocal phase shift should be achievable.
"Nonreciprocal Effects In Photorefractive Materials", Proc. SPIE 0813, Optics and the Information Age, (1 January 1987); doi: 10.1117/12.967367; https://doi.org/10.1117/12.967367