Effects of light polarization in photonic nanojet

Illumination plays a key role in getting high resolution imaging. Photonic nanojet is a new lighting system. Since the transverse beam width of the nanojet can reach λ/3, photonic nanojet is usually considered to be the key point for the explanation of the high-resolution microsphere assisted microscopy. However, the polarization of photonic nanojet are usually out of attention. In this work, we investigate the photonic nanojets formed by illuminating a dielectric microcylinder by two plane waves with different linear polarizations. The influences of wavelength and refractive index contrast between the microcylinder and its surrounding, and the cases illuminated by the Gaussian beam are also studied. Numerical results demonstrate that the TM polarization can generate a wider nanojet waist than the TE polarization, and this is produced by the longitudinal component of the TM-polarization illumination. When the Gaussian beam width becomes larger than diameter of the cylinder, the nanojet waists become smaller than that obtained by the cylinder under a plane wave. At last, the reason why the TE polarization has a thinner nanojet waist is given, it is related to the longitudinal component making light transmission far away from optical axis.