Poincaré Beams for Magnetic Field Sensing

Poincaré beams (PB), carrying spin angular momentum (SAM) and orbital angular momentum (OAM), play a significant role in a wide range of optical applications. The inhomogeneous polarization distribution of PB can be represented as a point on the surface of hybrid-order Poincaré sphere (HyOPS). Here, we have investigated the properties of PB propagation in a magnetic fluid under an applied magnetic field. The PB consists of a Gaussian and a vortex beam, which are in orthogonally linear polarization. The Stokes parameters of PB are measured in the experiment to build the Stokes phase profile. Besides, one of the phase contours is marked to analyze the changes of the phase profile. The results show that the phase contours rotate, and the rotation angle is well linearly to magnetic field strength with sensitivity of 0.934°/mT in the range of 2.42 to 27.79 mT, which is consistent with the expectation of the theoretical formula. Our results may contribute to the effort of exploring potential optical sensing at the onset of PB.