A system comprising: a resonator fiber optic gyroscope (RFOG) including: a resonator having an optical fiber loop; a light source configured to generate a light beam; and an intensity modulation circuit coupled between the light source and the resonator, the intensity modulation circuit configured to modulate the intensity of the light beam from the light source to output an intensity modulated signal to the resonator, characterised in that: the intensity modulation circuit is configured to produce the intensity modulated signal such that harmonics of the intensity modulated signal which overlap a primary wave of a counter-propagating light beam in the resonator have an amplitude below a predetermined threshold, wherein amplitudes below the predetermined threshold have a negligible effect on counter-propagating signals at the same frequency in the presence of optical backscatter; wherein the intensity modulation circuit comprises: a modulation signal generator configured to generate a signal at a predetermined frequency; and an intensity modulator configured to modulate the intensity of the light beam from the light source based on the generated signal output from the modulation signal generator. a resonator fiber optic gyroscope (RFOG) including: a resonator having an optical fiber loop; a light source configured to generate a light beam; and an intensity modulation circuit coupled between the light source and the resonator, the intensity modulation circuit configured to modulate the intensity of the light beam from the light source to output an intensity modulated signal to the resonator, characterised in that: the intensity modulation circuit is configured to produce the intensity modulated signal such that harmonics of the intensity modulated signal which overlap a primary wave of a counter-propagating light beam in the resonator have an amplitude below a predetermined threshold, wherein amplitudes below the predetermined threshold have a negligible effect on counter-propagating signals at the same frequency in the presence of optical backscatter; wherein the intensity modulation circuit comprises: a modulation signal generator configured to generate a signal at a predetermined frequency; and an intensity modulator configured to modulate the intensity of the light beam from the light source based on the generated signal output from the modulation signal generator. a resonator having an optical fiber loop; a light source configured to generate a light beam; and an intensity modulation circuit coupled between the light source and the resonator, the intensity modulation circuit configured to modulate the intensity of the light beam from the light source to output an intensity modulated signal to the resonator, characterised in that: the intensity modulation circuit is configured to produce the intensity modulated signal such that harmonics of the intensity modulated signal which overlap a primary wave of a counter-propagating light beam in the resonator have an amplitude below a predetermined threshold, wherein amplitudes below the predetermined threshold have a negligible effect on counter-propagating signals at the same frequency in the presence of optical backscatter; the intensity modulation circuit is configured to produce the intensity modulated signal such that harmonics of the intensity modulated signal which overlap a primary wave of a counter-propagating light beam in the resonator have an amplitude below a predetermined threshold, wherein amplitudes below the predetermined threshold have a negligible effect on counter-propagating signals at the same frequency in the presence of optical backscatter; a modulation signal generator configured to generate a signal at a predetermined frequency; and an intensity modulator configured to modulate the intensity of the light beam from the light source based on the generated signal output from the modulation signal generator.