We present experimental evidence for the spontaneous formation of discrete X waves in AlGaAs waveguide arrays. This new family of optical waves has been excited, for the first time, by using the interplay between discrete diffraction and normal temporal dispersion, in the presence of Kerr nonlinearity. Our experimental results are in good agreement with theoretical predictions.

Sensing molecular chirality at the nanoscale has been a long-standing challenge due to the inherently weak nature of chiroptical signals, and nanophotonic approaches have proven fruitful in accessing these signals. However, in most cases, complete sensing of the chiral part of the molecule’s refractive index (magnitude and sign of both its real and imaginary part) has not been possible, while the strong inherent signals from the nanostructures themselves obscure the weak chiroptical signals. Here, we propose a dielectric metamaterial system that overcomes these limitations and allows for complete measurements of the total chirality and discrimination of the effects of its real and imaginary part, possible also in an absolute manner via the application of a crucial signal reversal (excitation with reversed polarization) that enables chirality measurements without the need for sample removal. As proof of principle, we demonstrate signal enhancements by a factor of 200 for ultrathin, subwavelength, chiral samples over a uniform and accessible area.

No abstract

A theory of thermotropic nematic liquid crystals in which molecules form internally ordered clusters is presented. The formulation is based on the same molecular-field approximation and form of the anisotropic potential used in the Maier-Saupe theory. One uniaxial nematic and two macroscopically isotropic phases are predicted. The lowertemperature isotropic phase consists of thermodynamically stable clusters with internal orientational order. The transition from this phase to the nematic phase is characterised by the divergence of cluster size whilst the entropy and the order parameter change continuously.

A circular array of optical waveguides collectively coupled with a central core is investigated. Nonlinear losses, both linear and nonlinear coupling as well as energy transfer between neighboring array elements and between the array and the core are allowed. The concept is ideal for the design of high power stable amplifiers as well as of all-optical data processing devices in optical communications. The existence of stable steady-state continuous wave modes as well as of localized solitary and breathing type modes is demonstrated. These properties render the proposed system functionally rich, far more controllable than a planar one and easier to stabilize.

By using a discrete-dipole approximation for two-dimensional periodic lattices of scatterers, we show that three-dimensional layer-by-layer metamaterials consisting of twisted arrays of metal-nanoparticle chains exhibit giant circular dichroism spanning over the entire visible regime. The evident broad-band circular dichroism of the metamaterial is not a result of the intrinsic handeness of the constituent meta-atoms as in mainstream chiral designs but arises from the combined action of the anisotropy of each array of chains of nanoparticles, the gradual rotational twist of the metamaterial, and the strong electromagnetic coupling between adjacent layers of nanoparticle chains. As such, it is shown numerically that the degree of circular dichroism of the twisted metamaterial under study depends strongly on the twist angle between two successive lattices of nanoparticle chains and on the degree of anisotropy of each lattice.

We theoretically demonstrate that optical discrete X-waves are possible in normally dispersive nonlinear waveguide arrays. We show that such X-waves can be effectively excited for a wide range of initial conditions and in certain occasions can be generated in cascade. The possibility of observing this family of waves in AlGaAs array systems is investigated in terms of pertinent examples.

Recently, our group proposed a metamaterial laser design based on explicitly-coupled dark resonant states in low-loss dielectrics, which conceptually separates the gain-coupled resonant photonic state responsible for macroscopic stimulated emission from the coupling to specific free-space propagating modes, allowing independent adjustment of the lasing state and its coherent radiation output. Due to this functionality, it is now possible to make lasers that can overcome the trade-off between system dimensions and Q factor, especially for surface emitting lasers with deeply sub-wavelength thickness. Here, we give a detailed discussion of the keyfunctionality and benefits of this design, such as radiation damping tunability, directionality, subwavelength integration, and simple layer-by-layer fabrication. We examine in detail the fundamental design trade-offs that establish the principle of operation and must be taken into account and give guidance for realistic implementations.