Optical radiation force points to the same direction as the photon flux, while the direction reversal is quite challenging and necessitates special efforts. Herein, we present the observation of a photonic nanojet-mediated backaction of dielectric particles owing to the local heating of solvent molecules inside the nanojet in a purely dielectric system. Such backaction has been verified to be photothermal, without the influence from thermally induced turbulence. Our findings have been theoretically corroborated by statistical analysis on the size-dependent force and speed. In addition to the increase with laser power, the backaction force is a competing effect between the absorption and thermal conductivity of the immersion medium and is also affected by the photothermally raised background temperature. The backaction force exerts on dielectric particles with a broad size range. Since most biological particles are dielectric, with a refractive index greater than that for the surrounding medium, this work could inspire applications in biophotonics, such as cell sorting and classification.
In this Letter, we theoretically and experimentally demonstrate a new method to generate tunable orbital angular momentum (OAM) by continuously changing the angle of linear polarization of the input light. We use the Fourier series of left- and right-hand projections to prove that the average OAM smoothly varied from l=-1 to l=1 with the angle of LP of input light changing from 0 to π, which is fulfilled by an electrical polarization controller.
Optical non-reciprocity, which breaks the symmetry between forward and backward propagating optical waves, has become vital in photonic systems and enables many key devices, such as optical isolators, circulators and optical routers. Most conventional optical isolators involve magneto-optic materials, but devices based on optical nonlinearities, optomechanically induced transparency and stimulated Brillouin scattering (SBS) have also been demonstrated. So far, however, they have only been implemented for linearly or randomly polarized LP 01 -like fundamental modes. Here we report a light-driven nonreciprocal isolator for optical vortex modes, based on topology-selective SBS in chiral photonic crystal fibre. The device can be reconfigured as an amplifier or an isolator by adjusting the frequency of the control signal. The experimental results show vortex isolation of 22 dB, which is at the state-of-the-art in fundamental mode isolators using SBS. This unique device may find applications in optical communications, fibre lasers, quantum information processing and optical tweezers.
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