We study surface plasmon polariton (SPP) guiding structures, which are a modification of the Metal-Insulator-Metal (MIM) waveguide. The designs are constructed by introducing a periodic modulation in a MIM waveguide, with a glass core and silver claddings. This periodic modulation is created either by causing periodic indentations in the silver slabs encompassing the glass core, or by increasing the glass spacer material in certain periodic locations. Our objective is to achieve long range sub-wavelength waveguiding with vast dispersion engineering capabilities. We employ the Finite Difference Time Domain Method (FDTD) with the Auxiliary Differential Equation method (ADE) for the calculation of the dispersion relation of the guided modes, as well as the real time propagation suggests that the guiding mechnism in the examined structures is based on the electromagnetic (EM) couping between the slit plasmon modes. These - depending on the design - exist in the grooves between the silver plates or in the larger areas of the glass core spacer. Put it different, the guiding mechanism in the examined SPP waveguide designs is analogous to the EM energy transfer along metallic nanoparticle chains.
We present a review of recent achievements in nanoscale optical devices based on energy transport with surface
plasmon-polaritons and localized surface plasmons. Chains of metal subwavelength-size particles and stripes are used to
build straight waveguides, s-bends, y-junctions and beam shaping devices. Strong enhancement of near-field in
nanogaps between particles leads to efficient light emission from such nanoantennas. Development of surface plasmon
nanoptics stimulates further progress in near-field imaging. To improve resolution of scanning near-field optical
microscope (SNOM) it is necessary to improve light throughput in tapered metal-coated SNOM probes. This is
achievable due to resonant surface plasmons that propagate in corrugated probes.
We present FDTD simulations of light interaction with two dimensional silver structure made of the tip forming array of channel plasmon-polariton waveguides, that confines light to a small width beam or focus. The flat end of triangle formed plasmon-polariton waveguides array is illuminated with the optical range H-polarized Gaussian beam or plane wave. Light is transported through the structure with plasmon-polariton waves on surface of metal. At sloped planes energy from plasmon-polariton modes is refracted at an angle defined by propagation constants of modes. Propagation constants of excited plasmon-polaritons modes in waveguides array are predicted by semi-analytical calculations. Choosing canal widths, their separation and slop angle, we can couple energy from waveguides array to both free space propagation beams and to surface waves of the whole tip structure, which have propagation constants greater than free space waves. Combined effects of refraction, diffraction on the narrow end of the structure and the plasmon-polaritons like properties of surface waves on the whole structure lead to significant local enhancement of the field, high directivity of the output energy and focusing with resolution below diffraction limit for free space.
We propose two dimensional waveguide composed of silver rods in hexagonal lattice where coupling of surface
plasmons is responsible for transport of energy. We examine guiding properties of this structure for lattice constant 200
nm, diameter of rods 100 nm and wavelength λ = 500 nm using Finite Difference Time Domain method.
Electromagnetic wave is guided for transverse magnetic mode (light polarized perpendiculary to rods). Estimated
attenuation factor is a = 5.63 dB/μm and group velocity of the signal is v<sub>g</sub>=0.86 c. Interference pattern observed along
the waveguide can be explained as standing wave created by reflection from edge of the structure. From period of this
standing wave we calculate that phase velocity is v<sub>p</sub> = (6.4 ± 0.1) c. Transverse electric mode when light is polarized
parallel to rods is not guided in the structure.
The idea of a substance with simultaneously negative values of dielectric permittivity ε and magnetic permeability μ
presented by Veselago in 1968 has been brought to reality. Firstly, negative permittivity ε(ω) of a three dimensional
photonic structure composed of thin metal wires was experimentally demonstrated in the GHz range. Secondly, a
concept of split ring resonator has appeared and a structure composed of such metal resonators was shown to have
negative permeability μ. Consequently, in a so called double negative, both ε(ω) and μ(ω) < 0, composite material made
of cells consisting of a split ring resonator and a wire unnatural phenomenon of negative refraction was experimentally
observed in the microwave spectral region. Recently, perfect lenses made of metamaterial with negative refraction index,
photonic crystal or metal slabs were used to focus light below the diffraction limit of resolution. Electromagnetic
transport of energy in plasmon waveguides made of subwavelength metallic elements offers a great potential value for
nanoscale photonic devices of the future.
We examine the propagation of energy along chains of silver nanoelements oriented perpendicularly to the flow of light
and ordered in several ways. The first chain is composed ofvertical silver nanorods arranged in a hexagonal lattice. The
second one consists of vertical elongated nanoplates that form a herring-bone pattern. In the third, distribution of
vertically oriented nanoplates recalls footsteps. The chains are embedded in a medium with refractive index <i>n</i> = 1 and
1.5. Incident polarized Gaussian beams propagate along chains of nanoelements and have electric field components
oriented transversally with respect to the vertical nanoelements. Transport of energy is investigated with the Finite
Difference Time Domain (FDTD) method for visible and infrared range ofwavelengths, where the Drude model is valid.
Propagation constants and attenuation factors are calculated. Losses are due to absorption in metal and light scattering on
structure elements. In the analyzed structures, energy is transported due to localized surface plasmons-polaritons, where
the amplitude of optical fields is locally enhanced by orders of magnitude. This property might be useful in the
construction of nanoscale photonic devices. The smaller the metallic elements are, the stronger is the concentration of
energy. Waveguides of that form may be used for creating a medium with novel effective electromagnetic properties.
Interest in photonic nanodevices motivates search for efficient transport of energy in plasmon waveguides. Chains of silver nanoelements guide light in channels of below-the-diffraction-limit size due to surface plasmon coupling. We calculate attenuation factors in chains with several geometries of nanoplates using the Finite Difference Time Domain (FDTD) method for visible and near infrared range of wavelengths, where the Drude model of dispersion is valid. Nanoplates considered in simulations are 1 micrometer high, 50 nm thick and 380 nm long and are embedded in a medium with refractive index reaching n = 1.5. Advantages of proposed waveguides are connected with their small size and possible tuneability by adjustment of geometrical parameters. However, the waveguides highly attenuate signals due to radiation into the far field and internal damping. For the optimum considered geometry and 595 nm wavelength, the energy transmission of 2 micrometers long chain of parallel nanoplates reaches 39%.
Most works on photonic crystal fibers with a photonic bandgap are concerned with structures made of silica glass with a hexagonal lattice. However, there are many other possible choices for the crystal structure of the fiber. In this paper, we study the optical properties of photonic bandgaps in a hollow-core photonic crystal fiber with a square lattice fabricated from multi-component glass. A composition of oxides was chosen to obtain a refractive index contrast higher than in fused silica fibers. The core size of the fiber is 11 microns and the cladding is made of an array of 17 x 17 air capillaries. A full-vector mode solver using the biorthonormal basis method is employed to analyze the modal properties of the fiber. We verify the guiding properties of the fiber by FDTD simulations. The transmission properties for several lengths of the fiber were measured by using broadband light from a nanosecond-pulse supercontinuum source and an optical spectrum analyzer. Preliminary results show that light is guided around 1650 nm. Possible modifications of the structure and potential applications will be discussed.
A metal-in-dielectric metamaterial structure different from that composed of split-ring-resonators and wire units was proposed. The metamaterial layer is composed of randomly distributed parallel pairs of nanowires of subwavelength size that form electromagnetically active units. It was predicted that the metamaterial should exhibit macroscopic negative refraction. In a recent paper fabrication of the metamaterial in the form of periodic array of parallel golden nanorods with trapezoidal cross section was reported and a negative refractive index of <i>n</i> = -0.3 was observed at a wavelength 1.5 μm (200 THz).
In this paper we simulate response of a single pair of nanowires to near-infrared illumination and observe surface plasmon resonances using FDTD method. We simulate light propagation through the metamaterial slab made of one, two and three layers. In each layer the nanowires cover 10% of the surface. In simulations made for a single layer medium, negative refraction is observed for wavelengths from 1.55 to 2.1 μm, with Δλ/λ ≈ 0.3. When the number of layers increases, the range of negatively refracted wavelengths becomes narrower. For a narrow range of wavelengths that are close to the resonant frequency the intensity transmission of three layers reaches −7dB for the angle of incidence of 10°. Then layers with two orientations of nanowires are considered. In the first stack of layers all nanowires are oriented in parallel. This configuration assures plasmon resonances for both the electric and magnetic components of electromagnetic wave in all layers. In the second stack, nanowires in two subsequent layers are oriented perpendicularly. In the second layer, the plasmon resonance for the electric component of light is due to the oblique incidence of light. For a small angle of incidence of a near infrared narrow Gaussian beam we calculate two characteristics: the attenuation vs. wavelength and the lateral shift of the beam on the plane-parallel slab vs. wavelength. For a narrow range of wavelengths simulations show negative refraction of a beam incident the plane of the nanowires and a corresponding shift in the far field.
In this paper we examine properties of plasmon-polariton waveguide made of five rows of silver nanorods arranged in the hexagonal lattice. Electromagnetic wave illuminating metal structures generates surface plasmons. In nanoscale structures plasmons locally enhance near field and light propagates in modes confined below the diffraction limit. We present results of simulations using Finite Difference Time Domain (FDTD) method, which illustrate guiding visible light in the examined waveguide. We calculate modal properties of the waveguide. Propagation of two groups of modes with different symmetry with respect to the waveguide axis is observed. When the monochromatic light source is located on the waveguide axis both groups of modes are excited independently due to source symmetry. We assess that in the symmetric mode wavelengths longer than 500 nm are guided. For the antisymmetric mode that value is equal 450 nm. For off-axis illumination modes propagate together and form a snake-like beat pattern. Interference of modes from the first and second Brillouin zones (BZ) is also observed for a few wavelengths. To analyze the dispersion properties of the waveguide we assume Bloch type and absorbing boundary conditions in a single cell of the waveguide and make calculations on complex fields. FDTD equations work as a sieve that extracts modes with a given wavenumber from the initial field distribution. Then the guided frequency is found from spectrum. Group and phase velocities of modes are obtained from the dispersion relations.
The properties of photonic crystal fibers are determined by the structure of photonic cladding: filling factor, type of lattice and shape of air holes. The dispersion and modal characteristics of the fiber can be modified by adding an additional lattice of glass micro-rods with a refractive index higher than the glass substrate. We have fabricated a solid-core photonic crystal fiber with a double photonic cladding composed of air holes and glass micro-rods, where a high index multicomponent glass is used for the micro-rods. As a reference a fiber with similar parameters and a single lattice of air holes is fabricated. The fiber cladding is composed of 17 x 17 air holes and micro-rods ordered in square lattice. In this paper, we study the optical properties of photonic crystal fiber with single and double lattices. FDTD method and a full-vector mode solver based on biorthonormal basis method are used for fiber analysis. Possible modifications of the structure and potential applications will be discussed.