Angular random walk improvement of a fiber-optic gyroscope using an active fiber ring resonator

High precision fiber-optic gyroscopes (FOGs) interrogated with broadband light have angular random walk (ARW) limited by the source relative intensity noise (RIN). A passive fiber ring resonator (passive FRR) reduces the RIN and improves the ARW, but the low power transmission results in a low signal-to-noise ratio at the detection. For a great ARW improvement, the fiber ring resonator should have not only a great RIN reduction but also a large power transmission. An erbium-doped fiber amplifier (EDFA) is inserted in the passive resonator to construct an active fiber ring resonator (active FRR). The EDFA compensates for the loss of the resonator and leads to a high finesse and a greater reduction in the RIN. The coupling ratios of the couplers in the active FRR are both 50%-50% tap. By adjusting the EDFA gain properly, a 17-dB decrease in the RIN is demonstrated, which reduces the standard deviation by 8.5 dB. Adding the active FRR between the Sagnac interferometer and the broadband light, the detected power reaches 150 μW with the FOG at rest and without modulation, which is about one hundred times of the detected power when using a passive FRR. The phase noise is reduced by 6 dB at the proper frequency. The ARW is improved by 4.9 dB from 1.40 to 0.45  mdeg/hour^1/2.