When Light Loses Symmetry, it can Hold Particles

Optical tweezers use light to immobilize microscopic particles as small as a single atom in 3D space. The principle behind the tweezers is the momentum transfer between light and the object held. Light pushes onto objects that make the light bend. This force can be designed to point to a specific location in space where the particle will be held. This optical trapping technique has, to date, won two Nobel Prizes.

Researchers at Huazhong University of Science and Technology (HUST) in China are studying fiber optical tweezers, where light and the particles are manipulated at the tip of an optical fiber. This eliminates conventional, bulky optical accessories, including microscope objectives, lenses, and mirrors.

They begin with a perfectly annular symmetric light mode that can only transmit in the optical fiber and not leak into the surrounding space through the fiber tip. By changing the symmetry and the momentum of the light, the particle receives a reactive force that holds it at the fiber tip. Researchers predict such potential applications as performing an in-vivo single bioparticle manipulating experiment by using the fiber optical tweezer as an endoscope in the interior of a living animal.

The work, “Optical trapping using transverse electromagnetic (TEM)-like mode in a coaxial nanowaveguide” was featured in Frontiers of Optoelectronics.