Light can be coupled into propagating electromagnetic surface waves at a metal-dielectric interface known as surface plasmon polaritons (SPPs). This process has traditionally faced challenges in the polarization sensitivity of the coupling efficiency and in controlling the directionality of the SPPs. We designed and demonstrated plasmonic couplers that overcome these limits using polarization-sensitive apertures in a gold film. Our devices enable polarization-controlled tunable directional coupling with polarization-invariant total conversion efficiency and preserve the incident polarization information. Both bidirectional and unidirectional launching of SPPs are demonstrated. The design is further applied to circular structures that create radially convergent and divergent SPPs, illustrating that this concept can be extended to a broad range of applications.

Photonic components with adjustable parameters, such as variable-focal-length lenses or spectral filters, that can change functionality upon optical stimulation, could offer numerous useful applications. Tuning of such components is conventionally achieved by either micro-or nano-mechanical actuation of their constitutive parts, by stretching or heating. Here we report a new type of dielectric metasurface for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion. Such components are written, erased and re-written as two-dimensional binary or grey-scale patterns into a nanoscale film of phase change material by inducing a refractive-index-changing phase-transition with tailored trains of femtosecond pulses. We combine germanium-antimony-tellurium-based films with a sub-wavelength-resolution optical writing process to demonstrate a variety of devices: visible-range reconfigurable bi-chromatic and multi-focus Fresnel zone-plates, a super-oscillatory lens with sub-wavelength focus, a grey-scale hologram and a dielectric metamaterial with on-demand reflection and transmission resonances.A metasurface made of carefully designed discrete metallic or dielectric elements can exhibit interesting abilities for directing the flow of electromagnetic radiation across the entire electromagnetic spectrum with similar capabilities to planar holograms in optics 1,2,3,4,5,6,7,8,9,10 . As substantial efforts are now focused on developing metamaterials with switchable 11, 12 and reconfigurable metadevices 13 driven by thermal 14,15 , electrostatic 16 and magnetic forces 17,18 and stretching 19 , and we are witnessing the emergence of concepts of randomly accessible reconfigurable metamaterials in the microwave 20,21,22 and optical regions of the spectrum 23, 24 thus making reconfigurable photonic devices 2 controllable by external signals a realistic possibility. Here we introduce and demonstrate dynamic photonic components written into a dielectric film that can be randomly and reversibly reconfigured with light. Recent work demonstrated control of a metamaterial with light 25 . In contrast, the technique reported here allows random and non-volatile two-dimensional control of optical properties of the film with diffraction-limited resolution and in a femtosecond (fs) time-frame. This provides much more flexibility and allows the creation of various photonic functions difficult or impossible with the above mentioned technologies. The randomly reconfigurable metasurface uses phase-change material and is written, erased and re-written as a two-dimensional binary or grey-scale pattern into a nanoscale thin film by inducing a refractive-index-changing phase-transition with tailored trains of femtosecond pulses.We use phase-change medium, the chalcogenide compound Ge 2 Sb 2 Te 5 (GST), which is widely exploited in rewritable optical disk storage technology and non-volatile electronic memories due to its good thermal stability, high switching speed and large number of achievable rewr...

Scattering forces in focused light beams push away metallic particles. Thus, trapping metallic particles with conventional optical tweezers, especially those of Mie particle size, is difficult. Here we investigate a mechanism by which metallic particles are attracted and trapped by plasmonic tweezers when surface plasmons are excited and focused by a radially polarized beam in a high-numerical-aperture microscopic configuration. This contrasts the repulsion exerted in optical tweezers with the same configuration. We believe that different types of forces exerted on particles are responsible for this contrary trapping behaviour. Further, trapping with plasmonic tweezers is found not to be due to a gradient force balancing an opposing scattering force but results from the sum of both gradient and scattering forces acting in the same direction established by the strong coupling between the metallic particle and the highly focused plasmonic field. Theoretical analysis and simulations yield good agreement with experimental results.

No abstract

No abstract