Influence of a Regenerative Amplifier on the Sensitivity of a Resonant Fiber Ring Interferometer to Rotation

Abstract

We consider the possibility of using a regenerative amplifier based on an intracavity active fiber to enhance the rotation sensitivity of the resonant fiber ring interferometer (RFRI) with an external reflector and a low-coherence source. The influence of amplifier noise on the RFRI sensitivity to rotation is discussed. It is shown that the use of a regenerative amplifier makes it possible to obtain the maximum sensitivity with a lower-power source due to compensation for cavity losses. Comparison with the sensitivity of the conventional nonresonant fiber ring interferometer (NFRI) is done.Fiber optical gyroscopes are based on the Sagnac effect which consists in the fact that the phase difference ϕ s of counterpropagating waves in a ring is related to the angular velocity Ω s of the ring aswhere S = πR 2 is the area enclosed by the ring, R is the ring radius, L = 2πRN is the fiber length, N is the number of turns, and λ and c are the wavelength and the speed of light, respectively. To date, physical studies in the field of the conventional fiber gyroscopy based on the Sagnac effect in single-pass fiber ring interferometers (FRIs) are completed in general. However, the problem of increasing sensitivity in optical gyroscopy remains topical. Solution of this problem with the use of resonant fiber ring interferometers (RFRIs), whose amplitude and phase characteristics are fairly sensitive to the appearance of the Sagnac phase difference in the case of a high Q-factor [1-8], encountered a number of difficulties. These difficulties were related to the use of laser radiation sources and the necessity of tuning the laser oscillation frequency to the resonant frequency of a fiber cavity as well as the influence of coherent scattered signals on the measured phase difference, etc. Hence, the study of RFRIs was not as active as the study of the conventional single-pass gyroscopes. The idea of using wideband (femtocorrelated) sources for RFRIs [9,10], which began to be employed much earlier in the conventional FRIs to decrease the backscattering effects, gave a hope for implementation of the potential of the resonance schemes with a considerably higher sensitivity to rotation than in the conventional FRIs. To date, a number of papers studying various RFRI schemes with wideband radiation sources and intracavity amplifiers appeared in the literature [11][12][13][14][15]. However, the problem of increasing sensitivity to rotation in fiber gyroscopy owing to the use of different RFRI schemes, including the use of fiber amplifiers, is far from completion at present, both experimentally and theoretically. The objective of this paper is to study the possibilities of increasing the signal sensitivity at the output of a resonant fiber interferometer with an external reflector and modulator (Fig. 1a) to rotation when using an active-fiber intracavity amplifier as well as to optimize the scheme parameters with allowance for source