Generation of focal pattern with controllable polarization and intensity for laser beam passing through a multi-mode...

Similar to coherent light passing through a scattering medium, the propagation of coherent light through a multi-mode fiber (MMF) will result in a random speckle field. For a non-polarization maintaining MMF, the randomization can be observed not only in the intensity distribution, but also in the polarization state. In this paper, we propose a new technique known as phase combination to control the optical field for the light passing through the MMF. We show that, based on this new technique, the random speckle pattern can be modulated into an intensity distribution of two bright focal spots with mutually perpendicular polarization by only one polarizer. In particular, the intensity distribution of these two focal spots can be quantitatively controlled. This technique may find applications in medical imaging, nonlinear optics and optical communication etc.