A fibre-optic interferometric measurement device (100; 200; 300) intended to measure a physical parameter (Ω R) and including: - a wide-spectrum light source emitting a source light signal, - a fibre-optic SAGNAC interferometer (110; 210; 310), in which propagate a first light wave and a second light wave, which are counter-propagating, said SAGNAC interferometer (110; 210; 310) comprising: - an input port receiving, in a forward direction, an input light signal (110 IN), - a splitter connected, on the one hand, to said input port and, on the other hand, to a first arm and to a second arm of said SAGNAC interferometer (110; 210; 310), - measurement means (1140; 2140; 3140) sensitive to said physical parameter (Ω R) to be measured, said physical parameter (Ω R) generating a non-reciprocal phase difference Δφ p, which is function of said physical parameter (Ω R), between said two counter-propagating light waves (101, 102), and - an output port, common with said input port, transmitting, in a return direction opposite to the forward direction, an output light signal (110 OUT) having an output light power P OUT that is function of the total phase difference Δφ t between said two counter-propagating light waves (101, 102), - an optical radiation detector, receiving said output light power P OUT exiting from said SAGNAC interferometer (110; 210; 310) and delivering an electric signal representative of the output light power P OUT and of the physical parameter (Ω R) to be measured, and - a source coupler that couples, in said forward direction, said light source to said input port of the SAGNAC interferometer (110; 210; 310), and in said return direction, to said output port of the SAGNAC interferometer (110; 210; 310) to said detector, said interferometric measurement device (100; 200; 300) being characterized in that said measurement means (1140; 2140; 3140) of the SAGNAC interferometer (110; 210; 310) include a transmission-mode fibre-optic ring resonator, said ring resonator comprising a first coupler, respectively a second coupler, which couples the first arm, respectively the second arm, of said SAGNAC interferometer (110; 210; 310) to said ring resonator, so that said first and second light waves (101, 102) in said ring resonator circulate in opposite directions of circulation (1143H, 1143AH). - a wide-spectrum light source emitting a source light signal, - a fibre-optic SAGNAC interferometer (110; 210; 310), in which propagate a first light wave and a second light wave, which are counter-propagating, said SAGNAC interferometer (110; 210; 310) comprising: - an input port receiving, in a forward direction, an input light signal (110 IN), - a splitter connected, on the one hand, to said input port and, on the other hand, to a first arm and to a second arm of said SAGNAC interferometer (110; 210; 310), - measurement means (1140; 2140; 3140) sensitive to said physical parameter (Ω R) to be measured, said physical parameter (Ω R) generating a non-reciprocal phase difference Δφ p, which is function of said physical parameter (Ω R), between said two counter-propagating light waves (101, 102), and - an output port, common with said input port, transmitting, in a return direction opposite to the forward direction, an output light signal (110 OUT) having an output light power P OUT that is function of the total phase difference Δφ t between said two counter-propagating light waves (101, 102), - an input port receiving, in a forward direction, an input light signal (110 IN), - a splitter connected, on the one hand, to said input port and, on the other hand, to a first arm and to a second arm of said SAGNAC interferometer (110; 210; 310), - measurement means (1140; 2140; 3140) sensitive to said physical parameter (Ω R) to be measured, said physical parameter (Ω R) generating a non-reciprocal phase difference Δφ p, which is function of said physical parameter (Ω R), between said two counter-propagating light waves (101, 102), and - an output port, common with said input port, transmitting, in a return direction opposite to the forward direction, an output light signal (110 OUT) having an output light power P OUT that is function of the total phase difference Δφ t between said two counter-propagating light waves (101, 102), - an optical radiation detector, receiving said output light power P OUT exiting from said SAGNAC interferometer (110; 210; 310) and delivering an electric signal representative of the output light power P OUT and of the physical parameter (Ω R) to be measured, and - a source coupler that couples, in said forward direction, said light source to said input port of the SAGNAC interferometer (110; 210; 310), and in said return direction, to said output port of the SAGNAC interferometer (110; 210; 310) to said detector,