Generate multi-Bottle beam using the structure of single mode fiber-multi mode fiber

A novel method for generating muti-Bottle beam based on the property of multimode interference in multimode fiber was proposed. The structure of single mode fiber-multi mode fiber was a multi-mode fiber (MMF) spliced onto a piece of single-mode fiber (SMF). When input field propagated to MMF, only linearly polarized (LP0,n) modes were excited. As a consequence of the superposition of multimode interference, multi-Bottle beam can be generated at certain axial regions in free space. In this paper, the theory of propagation process was analyzed and numerically simulated using Matlab software. The result indicates that the size of multi-Bottle beam about 400 m20 m can be obtained in free space. 45 m, 60 m, 90 m diameter MMF are selected, the size of Bottle beams obtained from them are almost the same, but both side relative intensity of axial region of dark space are 0.62, 0.41, 0.11 respectively. Therefore, the larger diameter of MMF, the more similar intensity is on both side of dark spot. It can work better for trapping particles.