Abstract: The invention relates to an interferometer for carrying out an optical coherence tomography. The interferometer has at least one first part (13) and a second part (14) which are arranged or can be arranged in a spatially separated manner, wherein the two parts (13, 14) are optically connected together by at least one optical fiber (8). The aim of the invention is to provide an interferometer comprising parts which are optically connected by at least one fiber and which can be moved relative to each other, said parts and fiber being as insusceptible as possible to polarization changes induced by movement and temperature changes. The invention is characterized in that the optical fiber (8) is designed as a polarizing fiber which prefers the propagation of a first light wave with a set first polarization state or polarization mode and impedes the propagation of second light waves with different polarization states or polarization modes than those of the first light wave.