Signal Degradation
Wavefront error sources in polarization-maintaining fibers result from the transfer of optical power between the two orthogonal principal axes of the waveguide. Polarization cross coupling is caused by structural perturbations such as microbends or internal defects. This transfer degrades the polarization extinction ratio and introduces phase noise into the measurement.
Geometric Alignment
Precise orientation of the fiber axes during splicing or assembly is required to minimize the initial coupling. Even a small angular mismatch at a junction leads to significant polarization cross coupling. This effect is cumulative over the length of the fiber.
Metrological Detection
Optical frequency domain reflectometry allows for the localization of coupling points along the fiber. The strength of the coupling is measured in decibels, representing the ratio of the power in the unwanted mode to the power in the primary mode. In a fiber optic gyroscope, this coupling leads to a non-reciprocal phase shift known as the polarization error.
Calibration of the system involves characterizing this error over the full operating temperature range.
System Tolerance
Designers set a maximum allowable level for the extinction ratio to ensure the sensor meets its bias stability targets. Quality control teams verify this parameter during the assembly of the optical circuit.
