Glen A. Sanders

Theory of polarization evolution in interferometric fiber-optic depolarized gyros

Single-mode (SM) fiber which is used in the sensing coil of depolarized interferometric fiber-optic gyroscopes (IFOGs) does not maintain the polarization state of light. As a consequence, the state of polarization evolves freely over the length of the sensing coil and over environment. The polarization evolution is induced by birefringence within the SM coil. Variations of this birefringence may lead to nonreciprocal errors whose treatment is presented in this paper together with signal fading and the mean wavelength stability. Thus, this treatment provides a relatively comprehensive analysis of polarization evolution in depolarized gyroscopes. The analysis leads to the conclusion that the depolarized gyro architecture with two depolarizers on the opposite sides of the gyro loop must be used to obtain low-drift behaviour.

Novel Polarization-Rotating Fiber Resonator For Rotation Sensing Applications

A novel fiber resonator architecture is presented, employing a 90 deg rotation of the polarization within the birefringent fiber ring. In principle, this concept provides a temperature-independent separation of the resonance dips corresponding to the two resonant polarization states in the ring. The technique thus avoids gross thermally driven errors encountered in the use of ordinary polarization-maintaining rings for resonator fiber-optic gyros. Data from an experimental polarization-rotating ring at 1.3 μm wavelength demonstrates greatly improved thermal stability in the presence of typical imperfections of a practical device.

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.