Photophoretic separation of particles using two tapered optical fibers

Abstract

Particle separation is of great importance for a wide range of applications, such as biochemistry and biomedicine, and has been demonstrated using various techniques. Generally, these techniques necessitate carefully microfabricated devices and the assistance of microfluidics, thus making the separation difficult to accomplish. Here, we report a flexible, handy, and highly efficient optical method for particle separation using two tapered optical fibers, avoiding the use of complicated devices. By launching a laser beam with a power of 80 mW and wavelength of 1.55 μm into the first tapered fiber, particles of SiO2 with a size of 3.14 μm and poly(methyl methacrylate) (PMMA) with a size of 10 μm were trapped and collected. As the laser (330 mW) was switched to the second fiber for 29 s, SiO2 and PMMA particles were separated with separation efficiencies of 89.1% and 92.4%, respectively, because of their different photophoretic velocities. The separation performance was further demonstrated using different mixtures, with all separation efficiencies higher than 78%. The separation mechanism was explained by numerical simulations.