Dielectric Metamaterials with Toroidal Dipolar Response

Toroidal multipoles are the terms missing in the standard multipole expansion; they are usually overlooked due to their relatively weak coupling to the electromagnetic fields. Here we propose and theoretically study all-dielectric metamaterials of a special class that represent a simple electromagnetic system supporting toroidal dipolar excitations in the THz part of the spectrum. We show that resonant transmission and reflection of such metamaterials is dominated by toroidal dipole scattering, the neglect of which would result in a misunderstanding interpretation of the metamaterials macroscopic response. Due to the unique field configuration of the toroidal mode the proposed metamaterials could serve as a platform for sensing, or enhancement of light absorption and optical nonlinearities

Demonstrating Elusive Toroidal Dipolar Response in Metamaterials

Toroidal moments are fundamental electromagnetic excitations that cannot be represented in terms of the standard multipole expansion [1]. They were first considered by Zel’dovich back in 1957 [2], but only recently have become the subject of growing interest owing to their peculiar electromagnetic properties. Electromagnetic interactions with toroidal currents were predicted to disobey such widely accepted principle as the action-reaction equality. Toroidal currents can also form charge-current configurations generating vector potential fields in the absence of radiated electromagnetic waves. Although toroidal moments are held responsible for parity violation in nuclear and particle physics, no direct evidence of their importance for classical electrodynamics has been reported so far. This is because effects associated with toroidal moments in naturally available materials are extremely weak and usually masked by much stronger effects due to conventional electric and magnetic dipole and quadrupole moments

Merging metamaterial and fiber technologies

We report on integration of plasmonic and all-dielectric metamaterials into active photonic devices on the fiber platform. These include all-optical and electro-optical phase change and nano-opto-mechanical switching devices, dispersion control solution and coherent control metadevices

Super-resolution imaging beyond the near-field

We report a new technique for sub-wavelength imaging of complex objects in the far-field using a quasiperiodic nanohole array as an imaging lens. Nanohole arrays in metal screens have exhibited many interesting optical properties, including extraordinary transmission of light through periodic and quasiperiodic nanoholes and optical energy concentration [1,2]. We have demonstrated that a quasiperiodic array of nanoholes in a metal screen can concentrate optical energy into hot spots and form sub-wavelength spots in the far-field of the array [1,2] and can be used to image multiple point sources [3]. Here we extend that demonstration to show that a quasiperiodic nanohole array can be used to image more complex structures, such as an array of slits, in the far-field and with sub-wavelength resolution. Figure 1 (a) shows the imaging arrangement, using a quasiperiodic hole array in the place of a conventional lens. The object structure consists of an array of 10 slits, each 300nm x 1.5µm, with a pitch of 600nm and a wavelength of 660nm. The object is 13.5µm away from the quasiperiodic nanohole array and an image is formed 13.5µm behind the array. Assuming the grating lines are incoherent, as would be the case in a biological experiment using fluorescence imaging, the grating can be clearly resolved, with a measured average period of 603.6nm.This shows the use of a quasiperiodic hole array as a far-field sub-wavelength imaging device, in a form that is simple to manufacture and include in a realistic imaging system

Coherent metamaterial absorption of two-photon states with 40% efficiency

Multiphoton absorption processes have a nonlinear dependence on the amplitude of the incident optical field, i.e., the number of photons. However, multiphoton absorption is generally weak and multiphoton events occur with extremely low probability. Consequently, it is extremely challenging to engineer quantum nonlinear devices that operate at the single photon level and the majority of quantum technologies have to rely on single photon interactions. Here we demonstrate experimentally and theoretically that exploiting coherent absorption of N = 2 NOON states makes it possible to enhance the number of two-photon states that are absorbed by at most a factor of 2 with respect to a linear absorption process. An absorbing metasurface placed inside a Sagnac-style interferometer into which we inject an N = 2 NOON state, exhibits two-photon absorption with 40.5 % efficiency, close to the theoretical maximum. This high probability of simultaneous absorption of two photons holds the promise for applications in fields that require multiphoton upconversion but are hindered by high peak intensities

Fibre-coupled photonic metadevices

We report on metadevices realised by integration of functional metamaterials with single-mode telecoms fibres. These include plasmonic and all-dielectric nonlinear, nano-opto-mechanical and phase-change switching, dispersion manipulation and coherent absorber metadevices

Novel toroidal and superconducting metamaterials

This thesis reports on new solutions for sensing and controlling the electromagnetic radiation, and explores some novel effects of electrodynamics, using metamaterials.I have demonstrated the first superconducting metamaterial-based electro-optical modulator controlled by passing current through the network of meta-molecules. The meta- material, fabricated out of thin niobium film, modulated the sub-terahertz radiation through magnetic-field-induced suppression of superconductivity as well as through thermal effect. Transmission modulation up to 45% has been observed and main mechanisms of modulation have been studied.I have demonstrated a resonant radiation-harvesting bolometer for the sub-terahertz frequency range using a superconducting metamaterial fabricated out of thin niobium film. The strong electromagnetic interactions between the meta-molecules allowed harnessing of the radiation incident on the metamaterial and channeling it into a small radiation sensor, thus boosting the device sensitivity and selectivity. Bolometer sensitivity band-width of 1% has been achieved.I have suggested and experimentally demonstrated a new type of quantum metamaterial that engages the quantization of magnetic flux trapped in the meta-molecules. The metamaterial, fabricated out of high-temperature superconductor YBCO, has been designed to display nonlinear response associated with switching between the magnetic flux states. Although switching experiments have not been performed, a detailed characterization of the metamaterial, including the study of superconducting metamaterial structures that model different switching states, has been conducted.I have, for the first time, investigated highly nonlinear superconducting sub-terahertz metamaterial that exploits critical current and thermal nonlinearity. The metamaterial was fabricated out of thin niobium film with every meta-molecule containing wire segments of nanoscale thickness. The transmission change of up to 13% has been observed in response to ramping up the intensity of incident radiation to 8 W/m2.I have developed a novel analytical formalism that, for the first time, linked the reflection and the transmission of the metamaterial with the microscopic multipole excitations taking into account the electric, magnetic and toroidal multipoles of the constituent meta-molecules. A planar superconducting metamaterial with strong toroidal dipole response has been fabricated to test the formalism experimentally, and a very good agreement between the experiment and the analytical predictions has been observed.I have, for the first time, numerically and analytically studied the non-radiating configuration observed in the microwave experiment with the toroidal void metamaterial. It has been found that the non-radiating configuration is non-trivial and results from the destructive interference between the co-located electric and toroidal dipoles. Such non-radiating configurations shall allow designing high-Q metamaterial resonances and the generation of oscillating vector-potential for the study of the time-dependent Aharonov-Bohm effect

Light emission by accelerated electric, toroidal, and anapole dipolar sources DATASET

Data set for the paper &quot;Light emission by accelerated electric, toroidal, and anapole dipolar sources&quot;. As the paper is nearly entirely analytical, the data set consists only of data for the polygonal files of the radiation patterns in fig 3. Data is in PLY format, essentially this is a text file with all the vertices and faces.The names of the files are anaDip_aOc_1.000e+000_fine.plyanaDip (eDip, tDip) = anapole (electric, toroidal) dipole aOc_1.000e+00 = a/(\omega c)=1 (see fig 3)</span