39 research outputs found
Optical Frequency Mixing Through Nanoantenna Enhanced Difference Frequency Generation: Metatronic Mixer
A design for a subwavelength all-optical frequency mixer is proposed. The method relies on enhanced difference-frequency generation, which is achieved in two steps with the help of plasmonic nanoantennas. The interaction of the two input signals with the nonlinear material is increased through the use of input nanoantennas, which focus the incident energy of two different frequencies onto the nanoparticle formed by a nonlinear material. Next, the difference-frequency emission is enhanced through the Purcell effect by the use of a separate output nanoantenna that is resonant at the difference frequency. The application of this twofold approach allows for a significant enhancement in the difference-frequency generation efficiency. Simulation results are presented highlighting the features of the method. This multi-element nanostructure is indeed an optical mixer circuit element in the metatronic paradigm
Negative index metamaterial combining magnetic resonators with metal films
We present simulation results of a design for negative index materials that
uses magnetic resonators to provide negative permeability and metal film for
negative permittivity. We also discuss the possibility of using semicontinuous
metal films to achieve better manufacturability and enhanced impedance
matching.Comment: 6 pages, 3 figure
Tunable magnetic response of metamaterials
We demonstrate a thermally tunable optical metamaterial with negative
permeability working in the visible range. By covering coupled metallic
nanostrips with aligned nematic liquid crystals (NLCs), the magnetic response
wavelength of the metamaterial is effectively tuned through control of the
ambient temperature, changing the refractive index of LC via phase transitions.
By increasing the ambient temperature from 20 degree to 50 degree, the magnetic
response wavelength shifts from 650nm to 632nm. Numerical simulations confirm
our tests and match the experimental observations well
Dual-Band Negative Index Metamaterial: Double-Negative at 813 nm and Single-Negative at 772 nm
This work is concerned with the experimental demonstration of a dual-band
negative index metamaterial. The sample is double-negative (showing both a
negative effective permeability and a negative effective permittivity) for
wavelengths between 799 and 818 nm of linearly polarized light with a real part
of refractive index of about -1.0 at 813 nm; the ratio -Re(n)/Im(n) is close to
1.3 at that wavelength. For an orthogonal polarization, the same sample also
exhibits a negative refractive index in the visible (at 772 nm). The
spectroscopic measurements of the material are in good agreement with the
results obtained from a finite element electromagnetic solver for the actual
geometry of the fabricated sample at both polarizations.Comment: 3 pages, 4 figure
Comment on "Negative Refractive Index in Artificial Metamaterials" [A. N. Grigorenko, Opt. Lett., 31, 2483 (2006)]
A key optical parameter characterizing the existence of negative refraction
in a thin layer of a composite material is the effective refractive index of an
equivalent, homogenized layer with the same physical thickness as the initial
inhomogeneous composite. Measuring the complex transmission and reflection
coefficients is one of the most rigorous ways to obtain this parameter. We
dispute Grigorenko's statement (Optics Letters 31, 2483 (2006)) that measuring
only the reflection intensity spectrum is sufficient for determining the
effective refractive index. We discuss fundamental drawbacks of Grigorenko's
technique of using a best-fit approximation with an a priori prescribed
dispersive behavior for a given metamaterial and an 'effective optical
thickness' that is smaller than the actual thickness of the sample. Our
simulations do not confirm the Grigorenko paper conclusions regarding the
negative refractive index and the negative permeability of the nanopillar
sample in the visible spectral range.Comment: 18 pages, 7 figure
Negative Refractive Index in Optics of Metal-Dielectric Composites
Specially designed metal-dielectric composites can have a negative refractive
index in the optical range. Specifically, it is shown that arrays of single and
paired nanorods can provide such negative refraction. For pairs of metal rods,
a negative refractive index has been observed at 1.5 micrometer. The inverted
structure of paired voids in metal films may also exhibit a negative refractive
index. A similar effect can be accomplished with metal strips in which the
refractive index can reach -2. The refractive index retrieval procedure and the
critical role of light phases in determining the refractive index is discussed.Comment: 39 pages, 17 figures, 24 equation
Negative Index of Refraction in Optical Metamaterials
An array of pairs of parallel gold nanorods is shown to have a negative
refractive index n'=-0.3 at the optical communication wavelength of 1.5 micron.
This effect results from the plasmon resonance in the pairs of nanorods for
both the electric and magnetic components of light. The refractive index is
retrieved from the direct phase and amplitude measurements for transmission and
reflection, which are all in excellent agreement with our finite difference
time domain simulations. The refraction critically depends on the phase of the
transmitted wave, which emphasizes the importance of phase measurements in
finding n'.Comment: an improved version (17 pages, 5 figures) with a new sample and
additional measurement