We propose and demonstrate a fiber optical trap based on the coexistence of LP01 and LP11 modes for the simultaneous trapping of both high refractive index particles and low refractive index particles. Since different mode beams have different propagation constants, they exhibit different focused light fields. We fabricated a tapered fiber probe using thermal fusion to converge the beam, which generates a strong gradient force field near the fiber tip, as well as a dark trap along the axial direction. High refractive index particles are attracted near the fiber tip by a strong gradient force, and low refractive index particles are trapped in the dark cage along the axial direction. The proposed optical trap, which can simultaneously trap particles with different refractive indices, makes it easier to manipulate cells or molecules with different properties and explore multi-molecule interactions, which can facilitate research related to biology and chemistry.

Pore-throat ratio is a significant parameter expressing the characteristics of reservoir pores. It has an apparent influence on viscoelastic polymer solution flow in micro-pores. In this article, Upper-Convected Maxwell (UCM) equation is adapted to describe the viscoelastic polymer behavior. The contraction channel models of different pore-throat ratio are selected in process of simulation. And contours of stream function and velocity of different Weissenberg number (We) are calculated and drawn by Finite Volume Method. Results show that, vortex will occur at the re-entrant corner caused by the sudden contraction of channel, size and intensity of the corner recirculation vortex. The residual oil region is reduced and the mobile oil region is enlarged. Microscopic sweep efficiency is increased relatively. Vortex will be larger and stronger, and the velocity will be increased for We. Vortex will be lager with the bigger pore-throat ratio. Micro-sweep efficiency will be capitalized by viscoelastic polymer solution to the utmost.

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