Gupta-Bleuler quantization of optical fibers in weak gravitational fields

The theory of gauge-fixed Maxwell equations in linear isotropic dielectrics is developed using a generalisation of the standard $R_\xi$ gauge-fixing term. In static space-times, the theory can be quantised using the Gupta-Bleuler method, which is worked out explicitly for optical fibres either in flat space-time or at a constant gravitational potential. This yields a consistent first-principles description of gravitational fibre-optic interferometry at the single-photon level within the framework of quantum field theory in curved space-times.