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The magnetic field sensing properties based on the slow light effect of magneto-photonic crystals are studied. The nonreciprocal slow light effect of the magneto-photonic crystal immersed into an applied magnetic field is deduced by the scattering matrix method. A Sagnac interferometer is designed to enhance the sensitivity coefficient to the magnetic field and suppress the influences of reciprocal disturbances. Numerical results show that the sensitivity coefficient of a MPC slow light sensor is about 50 times that of the sensor made of bulk magneto-optic material with the same thickness. The influences of structural parameters of the magneto-photonic crystal, such as the number of periods, the duty ratio and the chirp, on the sensitivity coefficient are discussed.

The influence of the spin rate profiles on the stability of polarization transformations of all-fiber polarization transformers (AFPTs), which behave as a broad-band all-fiber quarter-wave plate, is analyzed by the super-mode theory. Huang firstly proposed and demonstrated these AFPTs, and suggested qualitatively that to perform a stable polarization transformation, the variation of the spin rate from zero to fast of the AFPT should be slow. However a compact fiber structure is desirable for an optical current transformers (OCT) system, and bending or wrapping AFPTs will weaken their abilities to hold the output SOPs. A first-order analytical approximation describing the coupling between the two local eigen-modes in the AFPT is derived, and two more detail suggestions for the spin rate profiles design of AFPTs are proposed. A random orthogonal axial gradient method (ROAGM) is developed to optimize the spin rate profiles. Numerical simulations show that for an AFPT with a shorter length, the stable transformation can also be obtained by a carefully designed spin rate profile according the two suggestions.