Nonlinear force dependence on optically bound micro-particle arrays in the evanescent fields of fundamental and higher order microfibre modes

Abstract

Particles trapped in the evanescent field of an ultrathin optical fibre interact over very long distances via multiple scattering of the fibre-guided fields. In ultrathin fibres that support higher order modes, these interactions are stronger and exhibit qualitatively new behaviour due to the coupling of different fibre modes, which have different propagation wave-vectors, by the particles. Here, we study one dimensional longitudinal optical binding interactions of chains of 3 μm polystyrene spheres under the influence of the evanescent fields of a two-mode microfibre. The observation of long-range interactions, self-ordering and speed variation of particle chains reveals strong optical binding effects between the particles that can be modelled well by a tritter scattering-matrix approach. The optical forces, optical binding interactions and the velocity of bounded particle chains are calculated using this method. Results show good agreement with finite element numerical simulations. Experimental data and theoretical analysis show that higher order modes in a microfibre offer a promising method to not only obtain stable, multiple particle trapping or faster particle propulsion speeds, but that they also allow for better control over each individual trapped object in particle ensembles near the microfibre surface.

Synthesizing variable particle interaction potentials via spectrally shaped spatially coherent illumination

“…In the case of a single or a few particles a detailed numerical modeling of the setup is possible with good agreement to the experiment. However, as shown recently, the key physics can be already modeled and understood from a much simplified semi-analytical scattering model [15]. We will generalize this model here towards multifrequency illumination and extract the key physics originating from frequency control.…”

“…In this work we consider broadband transverse illumination characterized by the intensities, central frequencies and spectral widths of the incoming beams. of the particles [15], which will give upper limits on the possible illumination powers, but generally do not seriously affect the longitudinal dynamics.…”

Direct observation of multimode interference in rare-earth doped micro/nanofibers

“…Previous studies had demonstrated multiple miniature fiber lasers using rare-earth doped microfibers [10][11][12]. On the other hand, higher order transverse modes with more complex modal properties offer additional dimension of freedom to manipulate optical field for various applications, and thus have attracted wide interest on relevant topics ranging from propagation characteristics [13,14], selective mode excitation/conversion [15,16] to particle trapping [17,18], higher order mode lasers [19,20], optical vortex generation [21,22] and so on. To inspect fiber modes, one common method is direct imaging of modal profiles at a fiber's output end.…”

Optical tweezing using tunable optical lattices along a few-mode silicon waveguide

“…Two main approaches have been investigated heretofore (8). The first one consists in using the light propagating in a waveguide to trap and propel particles as on a conveyor belt (4,5,(9)(10)(11)(12)(13)(14)(15)(16). However, this strategy usually fails whenever trapped particles' propulsion has to be stopped, requiring more complex and restrictive implementation based on irregular waveguide geometries (17), microfluidic channel walls (18), or counter-propagating modes (8,(19)(20)(21)(22)(23)(24).…”