Digital system for frequency regulation and stabilisation of a four-frequency Zeeman laser gyroscope

We report the results of theoretical and experimental studies of a digital system for regulating and stabilising the frequency of a four-frequency Zeeman laser gyroscope (ZLG), in which generation occurs simultaneously on two longitudinal modes with orthogonal circular polarisations; therefore, four light waves propagate in the optical ring resonator. In contrast to a two-frequency Zeeman laser gyroscope, a four-frequency ZLG does not use the intensity modulation signal of one of the light waves, which appears when an alternating magnetic field is applied to the active medium, to analyse the frequency detuning of longitudinal modes from the centre of the active-medium gain contour. At the same time, it is possible to construct a digital perimeter adjustment system (PAS), which allows the resonator perimeter to be adjusted so that the magnetic components of the zero drift of the gyroscope for two longitudinal generation modes are equal and opposite in sign. Due to this, almost complete compensation for the magnetic component of the zero drift of the gyroscope is realised in a four-frequency ZLG. The use of the digital system makes it possible to provide a higher accuracy of the resonator perimeter adjustment than that in a two-frequency ZLG, even with a relatively small bit capacity of the PAS digital-to-analogue conversion (DAC), and to fully take advantage of the capabilities of a four-frequency ZLG to reduce the magnetic sensitivity.