Optical Interaction
Physical interaction mechanisms describe how mechanical stress induces optical anisotropy in a transparent material, leading to changes in light propagation. Photoelastic birefringence coupling occurs when external pressure or thermal expansion creates localized stress fields in an optical fiber. This effect alters the refractive index along specific axes, which can degrade the polarization state of the signal.
Stress Influence
The magnitude of the induced birefringence is proportional to the difference between the principal stresses. In a fiber optic gyro, photoelastic birefringence coupling can arise from the tension used during the winding of the sensing coil. Non-uniformity in the potting compound also contributes to this phenomenon.
Sensor Error
Variations in the stress field lead to drift in the sensor output over time or temperature. The coupling of light between orthogonal polarization modes introduces phase errors that the signal processing electronics cannot easily distinguish from actual rotation. Proper selection of the fiber coating and winding pattern is necessary to minimize these interactions.
Measuring the polarization extinction ratio provides an estimate of the coupling strength.
Control Boundary
Qualification of a sensor design involves thermal shock testing to ensure the stress-induced effects remain within the specified error budget. A stable photoelastic response is required for long-term navigation accuracy.
