Ultra-long-range optical pulling with an optical nanofibre.

As a counterintuitive phenomenon, optical pulling of an object has been attracting increasing attention in recent years, owing to its intriguing underlying physics of light momentum transfer and potential for multi-directional manipulation. Due to the difficulty in engineering wave vectors for long-range optical pulling with a single beam, to date, the pulling range of an object is experimentally limited to hundreds of micrometres. Here, we demonstrate ultra-long-range optical pulling of a micro-droplet with an optical nanofibre based on the Minkowski-photon-momentum engineering. We show that, when a 1552-nm-wavelength light is launched into and guided along a silica nanofibre with a diameter below 1/3 of the vacuum wavelength, it can pull back a micro-droplet (tens of micrometres in diameter) over a distance up to 40 cm. Also, we have succeeded in vertically pulling up a micro-droplet against its own gravity (1 nN). These results pave the way for ultra-long-range optical pulling, with promising applications in nanophotonics, optomechanics, biophotonics and optofluidics.