Improvements of compact resonator fiber optic gyroscopes

Abstract

This paper reports recent progress beyond our initial report [1] in resonator fiber optic gyroscope (RFOG) development towards realization of a next generation compact device for commercial navigation applications by incorporation of silicon optical bench technology to miniaturize resonator and input optics. The resonator fiber optic gyro is being pursued because of its theoretical potential to meet navigation grade performance in a smaller size and lower cost than ring laser gyros (RLGs) and interferometric fiber optic gyros (IFOGs) [2]. This is due to the fact that the RFOG combines sensitivity-increasing signal to noise attributes of recirculating the light like an RLG, in addition to the ability to wind longer path length multi-turn coils like an IFOG, using optical fiber. New architectures realized with relatively small fiber-optic resonators and optics on a silicon optical bench (SIOB) are presented, along with initial bias stability test data. The laser architecture (Figure 1), which uses two phase-locked lasers to probe clockwise and counterclockwise resonances of a ring resonator, has been presented [3,4] at the OFS-24 in 2015 and at the 2016 SPIE 40th Anniversary of Fiber Optic Gyros Conference using all-fiber resonators and components. The all-fiber implementation, however, is less likely to meet the small-size and low-cost demands of the navigation market. The incorporation of the SIOB technology represents an important step forward in the miniaturization of the RFOG technology. In addition, the SIOB technology promises to be compatible with high volume, low-cost manufacturing techniques used for silicon processing, and automated assembly techniques. The operation of the RFOG is presented in this paper, which discusses the implementation with an SIOB. The SIOB plays a critical role in closing the resonator loop by connecting two ends of the coil, as well as providing an input light path into the resonator, and out of the resonator. By laying fibers in opposite ends of a v-groove with ball lenses in between, light is aligned and focused from one end of the loop fiber to the other. In the region between the ball lenses, light is collimated and polarized so that tiny beam-splitters can couple the light into and out of the resonator. The input paths also incorporate circulators on the chip to attenuate feedback to the lasers. Recent results show bias stability <0.02 deg/hr. These very encouraging early results are amongst the best reported for RFOGs, even though they are the first report of introducing an SIOB into the loop. In addition, we addressed the unknown question of temperature stability of the SIOB in this paper by testing an SIOB over a non-condensing temperature range of 20 degree C to 85 degree C (the unit was not packaged or sealed). As depicted in Figure 7, its finesse demonstrates remarkable stability showing negligible change over temperature. This work demonstrates a further step in the development of a compact RFOG along with improved ARW and Bias Stability.