How Laser Diode (LD) Intensity Modulation Induced by Current Tuning Affects the Performance of an Open-loop Resonator Fibre Optic Gyro (R-FOG) with Sinusoidal Wave Modulation

We present how the laser diode (LD) current tuning induced intensity modulation affects the performance of an open-loop resonator fibre optic gyro (R-FOG) with sinusoidal wave modulation. The expression for the demodulation curve under intensity modulation caused by the dynamic input rotation angular rate and varied environmental factors induced resonance frequency drift is provided. Numerical investigation shows that under the intensity modulation effect due to dynamic input rotation angular rate, which results in a bending trend for the linear part of demodulation curve, the linearity of R-FOG system is deteriorated, and the scale factor nonlinearity of gyro output increases as the frequency-intensity conversion coefficient of the LD increases. By simulating the demodulation curve with different amount of resonance frequency drift due to varied environmental factors, the slope of the linear part is found to fluctuate under the resonance frequency drift induced intensity modulation, and it causes the scale factor of the practical R-FOG system to fluctuates. This scale factor fluctuation results in a system measurement error, which is proven to increase as the amount of resonance frequency drift or input rotation angular rate increases, and numerical calculation result shows this large system error should be counted for an open-loop R-FOG system.