Simultaneous trapping of low-index and high-index microparticles using a single optical fiber Bessel beam

We propose and experimentally demonstrate a fiber-based Bessel optical trap for the simultaneous trapping of both high-refractive-index particle and a low-refractive-index particle. We obtain the Bessel beam by incident 980 nm beam into the designed integrate fiber structure, which is fabricated by coaxial splice a section of step-index multimode fiber to the single mode fiber. A high refractive index glass microsphere, which is stuck on the tip of multimode fiber, is utilized to converge the Bessel beam to produce a bright focal spot and a dark cage along the axial direction. The high-refractive-index particle and the low-refractive-index particle are trapped in the bright focal spot and the dark cage, respectively. Our simulation verifies the feasibility that particles with high refractive index and low refractive index can be trapped and manipulated at the same time. The proposed optical trap which can simultaneously trap the particles with different refractive index makes it easier to manipulate cells or molecules with different properties and explore the multi-molecule interaction, which can facilitate the research related to biology and chemistry.