Lee K. Strandjord

Fiber optic gyros for space, marine, and aviation applications

Fiber-optic gyroscopes (FOGs) are under development at Honeywell as the primary next generation inertial sensor. The open-loop FOG technology has been successfully transitioned to production for attitude heading reference systems and the results of this effort are reported. New developments in closed-loop FOG technology aimed at high performance space applications and at navigation grade aviation applications, are underway. In the former case, results on a high precision FOG are reported. In the latter case, special emphasis is placed on improvements of depolarized FOG technology, which promises to produce a low cost navigation grade sensor.

Resonator fiber optic gyro employing a polarization-rotating resonator

A novel fiber optic resonator employing a 90 degree polarization rotation was developed to reduce polarization related bias errors of the resonator fiber optic gyro. For the first time, we have fabricated and tested a nearly all guided-wave gyro having a polarization-rotating fiber resonator. Bias stability better than 0.4 deg/hr, random walk of 0.1 deg/root-hr, and day to day absolute bias stability of 10 deg/hr are reported. The major error mechanism of bias instability and other error sources are discussed.

Hollow Core Fiber Optic Ring Resonator for Rotation Sensing

An exciting new fiber optic resonator architecture that addresses performance barriers of the past is presented for applications in rotation sensing. It uses bandgap fiber. Experimental results of first resonators showing encouraging performance are presented.

Effects of imperfect serrodyne phase modulation in resonator fiber optic gyroscopes

In order for the resonator fiber optic gyroscope to achieve navigation grade performance, it must employ an optical frequency shifting technique for high scale factor accuracy. Serrodyne phase modulation commonly used in interferometric fiber optic gyros, has been considered a leading choice of modulation techniques. Here we present theoretical analysis on the effects of imperfect serrodyne phase modulation along with experimental results. A solution for substantially reducing the rotation sensing errors associated with imperfect serrodyne is also presented.

Fiber-optic gyro development for a broad range of applications

Progress in fiber-optic gyroscope development at Honeywell is reported here. The results illustrate the versatility of the technology, showing its potential to meet both the low-cost, small-sized needs of tactical guidance, as well as the very high perfomance needs of inertial navigation and precision applications. In the case of inertial navigation, data is presented that illustrates the possibility of employing a low-cost depolarized design for this use.

Performance improvements of a polarization-rotating resonator fiber optic gyroscope

A novel error compensation technique capable of significantly improving the gyroscope performance by reducing the polarization related bias errors of a polarization-rotating (PR) resonator is presented. It is shown that the PR-resonator has residual errors which depend on the polarization-dependent losses and coupling ratios of the resonator output coupler and on the polarization crosstalk within the ring. A bias error reduction by a factor of 50 or more is achieved by employing the technique which involves periodical switching of the resonance tracking operation between adjacent resonators.

Resonator fiber optic gyro with high backscatter-error suppression using two independent phase-locked lasers

A resonator fiber optic gyro was constructed using separate lasers for counter-rotating waves to overcome interference between optical backscatter and signal light that causes dead-zone behavior and scale factor nonlinearity. This approach enabled a 2 MHz frequency separation between waves in the resonator; eliminating the intended backscatter error. The two lasers were phase-locked to prevent increased gyro noise due to laser frequency noise. Dead-band-free operation near zero-rate, scale factor linearity of 25 ppm and stability of 11 ppm were demonstrated ─ the closest results to navigation-grade performance reported to date. The approach is also free of impractical frequency shifter technology.

Performance of resonator fiber optic gyroscope using external-cavity laser stabilization and optical filtering

A bench-top resonator fiber optic gyroscope (RFOG) was assembled and tested, showing encouraging progress toward navigation grade performance. The gyro employed a fiber length of 19 meters of polarizing fiber for the sensing coil which was wound on an 11.5 cm diameter PZT cylinder. A bias stability of approximately 0.1 deg/hr was observed over a 2 hour timeframe, which is the best bias stability reported to date in an RFOG to our knowledge. Special care was taken to minimize laser phase noise, including stabilization to an optical cavity which was also used for optical filtering, giving angle random walk (ARW) values in the range of 0.008 deg/rt-hr. The ARW performance and bias stability are within 2x and 10x, respectively, of many civil inertial navigation grade requirements.

Resonator fiber optic gyro progress including observation of navigation grade angle random walk

A benchtop experimental resonator fiber optic gyro (RFOG) was assembled and tested. The gyro employed a fiber length of 19 meters of polarizing fiber for the sensing coil which was wound on a 4.5 inch diameter piezoelectric cylinder. Angle random walk (ARW) values in the range of 0.0075 to 0.0085 deg/rt-hr were observed against a calculated shot noise limit of 0.0053 deg/rt.-hr for this experimental arrangement. To our knowledge, this is the first ARW result reported for an RFOG that is consistent with commercial navigation-grade performance.

Passive stabilization of temperature dependent polarization errors of a polarization-rotating resonator fiber optic gyroscope

The polarization-rotating resonator was developed to reduce temperature dependent polarization errors of a resonator fiber optic gyroscope for navigation-grade applications. Residual temperature dependent fluctuation of the symmetry of the resonance features limits the gyroscope performance. We present a fabrication technique, involving white-light interferometry, that yields a passive stabilized resonator. Experimental results show greatly improved resonator thermal stability.