Gain assisted nanocomposite multilayers with near zero permittivity modulus at visible frequencies

We have fabricated a layered nano-composite by alternating metal and gain medium layers, the gain dielectric consisting of a polymer incorporating optically pumped dye molecules. Exploiting an improved version of the effective medium theory, we have chosen the layers thicknesses for achieving a very small value of the real part of the permittivity epsilon_\| (parallel to the layers plane) at a prescribed visible wavelength. From standard reflection-transmission experiments on the optically pumped sample we show that, at a visible wavelength, both the real and the imaginary parts of the permittivity epsilon_\ attain very small values and we measure | \epsilon_\| | = 0.04 at lambda = 604 nm, amounting to a 21.5-percent decrease of the minimum | \epsilon_\| | in the absence of optical pumping. Our investigation thus proves that a medium with a dielectric permittivity with very small modulus, a key condition which should provide efficient subwavelength optical steering, can be actually synthesized.Comment: Submitted for publication on Applied Physics Letter

Flexible metamaterials at visible wavelengths

We report on the fabrication and characterization of plasmonic structures on flexible substrates (Metaflex) and demonstrate the optical properties of a single layer of Metaflex. The layer exhibits a plasmonic resonance in the visible region around 620 nm. We show experimental and numerical results for both nano-antennas and fishnet geometries. We anticipate the use of Metaflex as a building block for flexible metamaterials in the visible range.Publisher PDFPeer reviewe

One-dimensional chirality: strong optical activity in epsilon-near-zero metamaterials

We suggest that electromagnetic chirality, generally displayed by 3D or 2D complex chiral structures, can occur in 1D patterned composites whose components are achiral. This feature is highly unexpected in a 1D system which is geometrically achiral since its mirror image can always be superposed onto it by a 180 deg rotation. We analytically evaluate from first principles the bi-anisotropic response of multilayered metamaterials and we show that the chiral tensor is not vanishing if the system is geometrically one-dimensional chiral, i.e. its mirror image can not be superposed onto it by using translations without resorting to rotations. As a signature of 1D chirality, we show that 1D chiral metamaterials support optical activity and we prove that this phenomenon undergoes a dramatic non-resonant enhancement in the epsilon-near-zero regime where the magneto-electric coupling can become dominant in the constitutive relations.Comment: 5 pages, 4 figures. Accepted for publication on Physical Review Letter

Diffuse reflectance measurement tool for laparoscopic surgery

Continuous-wave diffuse reflectance or Near Infrared Spectroscopy (NIRS) offers the possibility to perform a preliminary screening of tissue for ischemia or other tissue anomalies. A tool for intracavity NIRS measurements during laparoscopic surgery, developed within the framework of the FP7-IP ARAKNES (Array of Robots Augmenting the KiNematics of Endoluminal Surgery) project, is described. It consists of a probe, that is located on the tip of an appropriately shaped laparoscopic manipulator and then applied to the tissue. Such a probe employs an array of incoherent semiconductor light sources (LEDs) frequency-multiplexed on a single detector using a lock-in technique. The resulting overall tool structure is simple and compact, and allows efficient coupling of the emitted light towards the tissue. The tool has high responsivity and enables fast and accurate measurements. A dataset gathered from in-vivo tissue is presented. The performance both indicates direct applicability of the tool to significant surgical issues (ischemia detection), and clearly indicates the possibility of further miniaturizing the probe head towards catheterized approaches

Impedance matching in photonic crystal microcavities for Second Harmonic Generation

By numerically integrating the three-dimensional Maxwell equations in the time domain with reference to a dispersive quadratically nonlinear material, we study second harmonic generation in planar photonic crystal microresonators. The proposed scheme allows efficient coupling of the pump radiation to the defect resonant mode. The out-coupled generated second harmonic is maximized by impedance matching the photonic crystal cavity to the output waveguide.Comment: 4 pages, 4 figures. To be published in Optics Letter

Photonics based perfect secrecy cryptography : toward fully classical implementations

Funding: A.D.F. acknowledges support from UK EPSRC (EP/L017008/1).Developing an unbreakable cryptography is a longstanding question and a global challenge in the internet era. Photonics technologies are at the frontline of research, aiming at providing the ultimate system capable of ending the cybercrime industry by changing the way information is treated and protected now and in the long run. Such perspective discusses some of the current challenges as well as opportunities that classical and quantum systems open in the field of cryptography as both a science and an engineering.PostprintPeer reviewe

Ultrafast all-optical order-to-chaos transition in silicon photonic crystal chips

ADF acknowledges support from EPSRC (EP/L017008/1).The interaction of light with nanostructured materials provides exciting new opportunities for investigating classical wave analogies of quantum phenomena. A topic of particular interest forms the interplay between wave physics and chaos in systems where a small perturbation can drive the behavior from the classical to chaotic regime. Here, we report an all-optical laser-driven transition from order to chaos in integrated chips on a silicon photonics platform. A square photonic crystal microcavity at telecom wavelengths is tuned from an ordered into a chaotic regime through a perturbation induced by ultrafast laser pulses in the ultraviolet range. The chaotic dynamics of weak probe pulses in the near infrared is characterized for different pump-probe delay times and at various positions in the cavity, with high spatial accuracy. Our experimental analysis, confirmed by numerical modelling based on random matrices, demonstrates that nonlinear optics can be used to control reversibly the chaotic behavior of light in optical resonators.PostprintPeer reviewe