Proposed optical device is based on counter-propagating optical fields within at least one nested waveguide-cavity loop, where the part of the waveguide loop is fold into the external waveguide loop. The nesting is performed using at least one waveguide crossing section. The invention may be used in Sagnac interferometer to measure various physical parameters, including rotation rate, electric current and mechanical perturbations. The invention also addressed a measurement method of such non-reciprocal parameters of interest. Optionally, the cavity includes a gain element, and the device operation may be switched discretely or gradually between passive and active regimes, thus changing the measurement characteristics.