Large Diameter Fiber-Optics Tweezers for Escherichia Coli Bacteria Manipulation

Large diameter fiber-optics tweezers are proposed in this paper, and their ability to trap and deliver Escherichia coli (E. coli) bacteria was characterized. The tweezers were formed by tapering four-mode fiber (FMF) with 8.7 μm diameter, allowing the resonance field of the extended high-order modes to be used for manipulating the micro-objects. The diameter of the FMF taper was much larger than that of reported fiber-optic devices with nanoscale diameter, thereby making the device work as sturdier tweezers. The key factor for success is that, along the light transmission axis, the higher order modes have a unique mode field that extends longer and with a larger range around the fiber waist than the fundamental mode. At wavelengths ranging from 1500 to 1600 nm, especially close to 1560 nm, trapping and delivering of E. coli along the fiber was observed. In addition, a further demonstration for operation time shows a larger tapered fiber diameter was able to extend the service life of tweezers. The higher order micro-fiber modes offer a new opportunity for optical manipulation at the single-cell level.