An optical measuring device for measuring a measurement region, the optical device comprising a photonic chip with an interferometer defined on said chip, said interferometer comprising first and second waveguides on said photonic chip and an interference region, wherein the first and second waveguides carry signals from the interference region to the sample region and back to the interference region, the device further comprising a phase adjusting unit configured to vary a phase difference between the signals in the first and second waveguides reflected by the measurement region.