  That light propagating in a gravitational field gets frequency-shifted is one
of the basic consequences of any metric theory of gravity rooted in the
equivalence principle. At the same time, also a time dependent material's
refractive index can frequency-shift light propagating in it. The mathematical
analogy between the two effects is such that the latter has been used to study
the optical analogue of a black-hole spacetime. Here, we combine these two
effects by showing that light propagation in non-linear media in the presence
of a moving refractive index perturbation can lead to a gravity-dependent
blueshift. We find that the predicted blueshift surpasses the gravitational
redshift even if the medium is considered to be perfectly stiff. In realistic
scenarios, by far the strongest frequency shift arises due to the deformation
of the dielectric medium and the corresponding photoelastic change of
refractive index. This has the potential to facilitate optical sensing of small
gravity gradients.
