Microparticle manipulation using modal superpositions in air-filled hollow-core photonic crystal fiber

Higher order Bessel, Airy and Laguerre-Gaussian beams have recently been used to manipulate micrometer-sized objects in free space. In this paper, the authors used a coherent superposition of the two lowest order forward-propagating modes of a soft glass hollow-core photonic crystal fiber (HC-PCF) to control the axial and radial trapping position of particles inside the core. Because each fiber mode propagates at a different phase velocity, the transverse intensity distribution varies periodically along the propagation direction. A counter-propagating fundamental mode (FM) is then used to create a series of trapping positions along the fiber. The trapping sites are slightly off-axis, spaced by half the intermodal beat length L_B, and can be moved simply by changing the phase Δφ between the two forward-propagating modes.