Simultaneous Suppression of Thermal Phase Noise and Relative Intensity Noise in a Fiber-Optic Gyroscope

The short-term sensitivity of a several-kilometers long fiber-optic gyroscope (FOG) is limited mainly by thermal phase noise (TPN) and relative intensity noise (RIN). Increasing the phase modulation frequency decreases the TPN but not the RIN since it behaves as white noise. Here, we propose and experimentally demonstrate that the angular random walk (ARW) can be effectively decreased by suppressing RIN at the modulation frequency and its third-order harmonic using direct feedback to the drive current of a superluminescent diode (SLD). Our simultaneous suppression of TPN and RIN yields an ARW of 15 $\mu {\text {deg}}/\sqrt {{\text {h}}}$ and a bias instability of 33 $\mu {\text {deg}}/{\text {h}}$ using a fiber coil with a length of 5 km and an effective area of 280 ${\text {m}}^{{{2}}}$ for a measurement time of 40 h.