Abstract: In an integrated optical circuit, light from a light source is polarized and coupled to a first and second strip waveguide. A waveguide coupling element couples the two optical signals from the two strip waveguides to different polarization modes of an optical fiber line. The optical fiber line is connected to a measuring head, which reflects the optical signal and in which a phase difference between the two optical partial signals is modulated in a magnetic field. In the waveguide coupling element, the reflected signal is split into two optical partial signals having the same polarization and the phase difference between the two partial signals is determined. A phase modulator device provides for closed-loop operation. Compared to fiber-optical concepts, the number of splices is reduced.