This paper reports recent progress in resonator fiber optic gyroscope (RFOG) development towards realization of a next generation compact device for commercial navigation applications by incorporation of a novel signal processing technique to reduce error terms from backscattered light and producing a miniature a compact three-laser source for optical sensing. We have recently presented progress towards compact RFOGs using phase locked diode lasers and miniaturized optics on a silicon optical bench (SiOB), as well as demonstrating navigation-grade angle random walk performance with that architecture [1]. However, the most challenging technical barrier has been achieving the requisite bias stability for civil navigation applications (0.003 deg/hr drift). A major issue has been that error terms that cause bias drift have heretofore been addressed by competing, or mutually exclusive, countermeasures. The error mechanisms which have typically driven designs in different directions are (1) optical backscatter and (2) imperfections in the optical frequency modulation used to determine the resonance line center. We report updates to a modulation technique that has been demonstrated [2] to simultaneously solve these issues, resulting in the best performing RFOG to our knowledge. We illustrate its ability to reduce the drift due to optical backscatter while retaining a common modulation for cw and ccw resonance detection. Further improvements (achieved in a Honeywell partnership with TeraXion) to performance and size of a compact three-laser source previously reported [3] for the RFOG is also presented. It is based on a low-noise implementation of the Pound-Drever-Hall method and comprises high-bandwidth optical phase-locked loops. The outputs from three semiconductor distributed feedback lasers, mounted on thermo-electric coolers (TEC), are coupled with micro-lenses into a silicon photonics (SiP) chip that performs beat note detection and several other functions. The chip comprises phase modulators, variable optical attenuators, multi-mode-interference couplers, variable ratio tap couplers, integrated photodiodes and optical fiber butt-couplers. Electrical connections between a metallized ceramic and the TECs, lasers and SiP chip are achieved by wirebonds. All these components stand within a 35 mm by 35 mm package which is interfaced with 90 electrical pins and two fiber pigtails. One pigtail carries the signals from a master and slave lasers, while another carries that from a second slave laser. The pins are soldered to a printed circuit board featuring a micro-processor that controls and monitors the system to ensure stable operation over fluctuating environmental conditions. This work demonstrates a further step in the development of a compact RFOG with improved SWaP, ARW and Bias Stability.
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