A rotation detection apparatus, including: a beam source for emitting a beam of polarized light; a decohering arrangement for eliminating or reducing the degree of coherence between first and second independent polarization components of the polarized light to produce a decohered beam of polarized light; a detector for outputting a signal in dependence on the intensity of light incident thereupon, the detector arranged so that the decohered beam of polarized light is incident upon it; a polarizer for location in the path of the decohered beam of polarized light such that rotation of the polarizer relative to the decohered beam of polarized light results in a variation of the intensity of light incident upon the detector from the beam source and a corresponding variation in the signal output from the detector; and a processor for detecting the relative rotation based on the variation of the signal output from the detector.