Noise and Bias Error Due to Polarization Coupling in a Fiber Optic Gyroscope

Abstract

This paper reports a comprehensive model of the noise and drift induced by polarization coupling in a fiber optic gyroscope (FOG) interrogated with a laser of arbitrary linewidth. It includes the effects of dynamic phase biasing, a realistic description of laser phase noise, and polarization-dependent loss. This model yields concise analytical expressions for the noise and drift dependencies on the laser linewidth, the fiber length and holding parameter h, and the fractional power launched into the unwanted polarization at the input to the sensing coil. For all realistic FOG parameter sets the polarization-coupling noise is found to be insignificant. For a 1-km coil, a typical holding parameter (h = 10 -5 ), and push-pull modulation, the drift is only ~1 µrad up to a linewidth of ~100 MHz, which is far lower than previously believed. The drift decreases to even lower values for larger linewidths. Experimental measurements of the noise and drift in a 150-m FOG and their dependence on laser linewidth support these predictions. Birefringence modulation can be brought to bear to reduce this residual drift enough to meet the requirement for aircraft inertial navigation. Ultimately, this analysis shows that low polarization coupling error can be obtained without the use of a broadband source.Index Terms-Fiber optic gyroscope, laser phase noise, optical polarization, polarization nonreciprocity error, Sagnac interferometer 0733-8724 (c)

Low-Drift Closed-Loop Fiber Optic Gyroscope of High Scale Factor Stability Driven by Laser With External Phase Modulation

“…8(b). These results mean that the polarization coupling has been suppressed to the level as other errors [13]. In this way, continuing to improve the spectral width will indeed improve its performance to a certain extent, but the effect diminishes significantly.…”

“…As the scale factor stability directly depends on the performance of the light source, it can be improved by two orders of magnitude with laser instead of the SLD or SFS. However, the laser-driven IFOG reintroduces coherent backscattering, polarization coupling, and Kerr effect because of its narrow linewidth [12,13]. Although the semiconductor lasers with the linewidth of tens of megahertz have been proved that they can drive the IFOG directly, it is still necessary to use broader laser for further improvement [14].…”

Optimizing Coherence Suppression in a Laser Broadened by Phase Modulation With Noise

“…In photonic systems relying on low-coherence light such as LIDAR and FOGs, noise and drift in the measured signal arise from spurious interferometers (e.g., caused by scatterers [4], [7]). To model how the source coherence affects the magnitude of these errors, a spurious interferometer can be modeled as a Mach-Zehnder interferometer (MZI) with an optical-path delay τ = nΔL/c, where ΔL is the length difference between the two arms, n is the index of the arms, and c is the speed of light.…”

“…Fiber-optic gyroscopes (FOGs) measure extremely small path-length differences (10 fm or less) to infer rotation rates as small as a full turn in 2200 years [2]. This superb precision is achieved by probing the FOG with incoherent light, which significantly reduces the noise and drift arising from spurious interference from light backscattered [5], [6] or polarization-coupled [7] along the FOG's fiber coil. Stimulated Brillouin scattering, which can limit power scaling of fiber lasers, can also be mitigated by externally modulating the phase of the laser with noise to reduce its coherence [8], [9].…”

Bias error and its thermal drift due to fiber birefringence in interferometric fiber-optic gyroscopes

“…The bias error, another error source in IFOGs, induced by the thermal stress through photo-elastic effect in SMFs [9,10], was verified by the simulations with the finite element method recently [11,12]. While the bias error induced by the polarization coupling was investigated [13][14][15] for PMFs used in high performance IFOGs [16,17], the effect of stress-induced birefringence (SIB) produced by the stress-applying parts (SAPs) in PMFs were not considered in the previous reports. As a result, the influence of employing PMFs on the performance of IFOGs becomes unclear, leaving the resultant effect due to the phase error of SIB and its thermal fluctuation unanalyzed.…”