A Chip of Pulse-Laser-Assisted Dual-Beam Fiber-Optic Trap

Abstract

Compared with the single-beam gradient optical trap, the dual-beam optical trap based on micro-structure eliminates the need for complex optical alignment and offers intrinsic benefits of miniaturization and stabilization, which are crucial for developing a practical sensor. We design a monolithic chip of dual-beam fiber-optic trap which allows extremely accurate alignment of submicron scale between two counter-propagating fiber beams. Based on micromachining technology, the chip featured a V-shaped groove to align the fibers and a rectangular channel to load the particles is experimentally realized. Recent studies have demonstrated that micro-scale particles can be removed effectively from substrate by focused pulse laser beam. To acquire high trapping efficiency and better trapping stability, we propose a new loading method that combinates pulse laser with dual-beam fiber-optic trap. We have fabricated a silica miniature operating rod for initial storage of the microspheres and moved a targeted particle into the effective trapping area of the fiber-optic trap. Optical loading and trapping of a $10 \mu \mathrm{m}$ polystyrene particle in air are demonstrated and the controllable capturing process avoids any contamination on fiber ends, which ensures the reliability of optical path. We use a microscopic imaging system and image processing method to test the static stability of the captured particle. The static stability of the microspheres is submicron, which is clearly superior to the test results in liquid environment. The rapid loading and manipulation of microspheres in optical trap is significant for its applications in optomechanics and precision force sensing. Our results pave the way for a new class of monolithic and portable optical sensor for inertial measurement.