Distributed Polarization Measurement for Fiber Sensing Coils: A Review

Distributed polarization measurement is a significant way to evaluate polarization-maintaining fiber. It can assess the fiber's polarization preserving ability and locate internal defects and external perturbations of a long-distance PM fiber. Distributed polarization crosstalk of a fiber-optic polarization device accurately describes its time-dependent optical performance. Therefore, distributed polarization measurement technology can be used to predict and prevent the performance degradation and failure. However, the remaining shortcomings of existing measurement methods are low dynamic range, short measurement length, inadequate spatial resolution, and low diagnostic ability. This paper reviews recent advances in solving the above issues and presents ways to obtain high performances: a dynamic range > 90 dB, a measurement length > 10 km, a full range spatial resolution < 10 cm, and developments in time domain, frequency domain, and time-frequency domain diagnosis methods. All these high-performance techniques have led to more effective diagnosis of fiber optic sensing coils. This can be demonstrated by a series of comparative measurements and analysis of three PM fiber optic sensing coils in various configurations such as a randomly-wound spool of fiber and a free-standing coil quadrupole-pattern-wound from it, a second coil with and without a flange at various temperatures, and a third coil spliced to a Y waveguide. Each is one of the key configurations during the production processes or the application of the fiber sensing coil. The technical progress reviewed here will greatly promote the development, production, and application of fiber sensing coils.