Precise topological transition and negative refraction of a wave vector in a symmetrically arranged Al2O3/Ag/Al2O3 multilayer.

The topological transition of a symmetrically arranged Al2O3/Ag/Al2O3 multilayer is precisely estimated by the product of characteristic film matrixes instead of treating the multilayer as an anisotropic medium with effective medium approximation. The variation of the iso-frequency curve among a type I hyperbolic metamaterial, a type II hyperbolic metamaterial, a dielectric-like medium, and a metal-like medium of such a multilayer with wavelength and the filling fraction of the metal is investigated. The estimated negative refraction of wave vector in a type II hyperbolic metamaterial is demonstrated with near field simulation.

Silver split nano-tube array as a meta-atomic monolayer for high-reflection band.

In this work, an ultra-thin silver film-coated grating as a split silver nanotube array exhibits not only high TE polarized reflectance as a conventional subwavelength grating but also high TM polarized reflectance that is close to or higher than TE reflectance at certain wavelength range. The TM reflectance peak shifts with the morphology of the silver covering. The near-field analysis reveals that the silver nanotube array is an ultra-thin optical double negative metamaterial. The negative permeability associated magnetic field reversal is induced within the grating that is surrounded by a split current loop at the TM reflectance peak wavelength. The near field simulation is used to retrieve the equivalent electromagnetic parameters and optical constants that cause the anomalous TM high reflection. It is demonstrated that the TM impedances have a low magnitude and high magnitude with respect to unity for light incident onto the top and bottom of the grating at the peak wavelength, respectively.

Deposited ultra-thin titanium nitride nanorod array as a plasmonic near-perfect light absorber.

The transmittance, reflectance, and extinctance that correspond to the localized plasmonic resonance within TiN nanorods were investigated. The obliquely deposited TiN nanorod array shows polarization-independent admittance matching to air. Unlike noble metal nanorods, the near-field localized longitudinal and transverse plasmonic resonance of TiN nanorod arrays present polarization-dependent light extinction in the far field. The longitudinal plasmonic mode presents stronger extinction than transverse plasmonic mode. In order to have high efficient light absorption, an ultra-thin two-layered TiN nanorod array was fabricated with orthogonal deposition planes for upper layer and bottom layer to absorb different polarized light energy. The measured spectrum shows broadband and wide-angle light extinction.

Bideposited silver nanocolloid arrays with strong plasmon-induced birefringence for SERS application.

Silver nano-rod, nano-zigzag, nano-saw, and nano-particle arrays are fabricated with glancing angle bideposition. The structure-dependent anisotropic optical properties of those bideposited nanostructured arrays are measured and investigated. The equivalent birefringence values of nano-rod and nano-zigzag arrays are much larger than crystals found in nature and liquid crystal used in display products. The fact that induced localized plasmon-magnetic field between nanorods dominates the strong phase retardation between p-polarized and s-polarized transmitted wave. For the nano-saw, the strong localized electric field induced between the saw teeth leads to strong SERS signals. Although the bideposited nanoparticles own weak morphological anisotropy, strong optical phase retardation is still detected at wavelengths near 400 nm.

Obliquely Deposited Titanium Nitride Nanorod Arrays as Surface-Enhanced Raman Scattering Substrates.

In this work, titanium nitride (TiN) nanorod arrays were prepared as surface-enhanced Raman scattering (SERS) substrates using glancing angle deposition (GLAD) in a magnetron sputtering system. The nitrogen flow rate was varied from RN2 = 1 to 3 sccm, yielding five TiN uniform thin films and five TiN nanorod arrays. The figure of merit (FOM) of each TiN uniform film was measured and compared with the SERS signal of each TiN nanorod array. Rhodamine 6G (R6G) was used as the analyte in SERS measurement. For an R6G concentration of 10-6 M, the analytical enhancement factor (AEF) of the TiN nanorod array that was prepared at RN2 = 1.5 sccm was 104. The time-durable SERS performance of TiN nanorod arrays was also investigated.

Capping metallic nanohelixes with SiO2 nanohelixes to enhance broadband and wide-angle light extinction.

In this work, an SiO2 nanohelix array is obliquely deposited upon a metal nanohelix array as an index matching layer to enhance light extinction. Firstly, an SiO2-Ag nanohelix array is fabricated with stronger light extinction than the Ag nanohelix array over wavelengths from 300 nm to 1000 nm at normal incidence. Next, the SiO2-Al-Ag nanohelix array is fabricated; it exhibits broadband and wide-angle light extinction that is stronger that reported for the Al-Ag nanohelix array. The unpolarized extinctance exceeds 90% over wavelengths from 400 nm to 2000 nm and angles of incidence from 0° to 70°.

Metamaterial-inspired compact optical coating for broadband polarization beam splitting.

A metal-dielectric is designed and fabricated as a compact polarization beam splitter. High p-polarized transmission is achieved by admittance matching, which is developed using a normalized admittance diagram. High s-polarized reflection is achieved with a metal-like equivalent s-polarized admittance which real part is much smaller than its imaginary part. An ultra-thin silver film with a thickness of around 11 nm is deposited to form an Ag-SiO2 multilayer. The polarization beam splitter requires only three or five layers of thin films to perform broadband beam splitting over wavelengths from 450 nm to 850 nm.

Obliquely Deposited Gold Nanohelices on Lithography-Free Prepared Nanoseeded Surfaces.

A substrate surface on which gold particles are distributed is prepared by annealing an ultra-thin gold film to enable glancing angle deposition. By cooling the substrate and controlling its spin rate, two spiral-like and one screw-like gold nanohelix arrays are grown upon the seeded surfaces. The mean helix radius and pitch length are reduced to 17 and 55 nm, respectively. The g-factor of the three nanohelix arrays is measured here and associated circular dichroism peak blue shifts occur as the gold helices shrink.

Design and deposition of a metal-like and admittance-matching metamaterial as an ultra-thin perfect absorber.

A stratiform metamaterial, comprising metal and dielectric thin films, exhibits both near-perfect antireflection and strong light extinction to function as a perfect and ultra-thin light absorber. The equivalent admittance and extinction coefficient of the metamaterial are tailored using a visual method that is based on an admittance diagram. A five-layered metamaterial was designed and deposited with a total thickness of 260 nm on a mirror to exhibit strong and wide angle absorption over wavelengths from 400 nm to 2000 nm. A seven-layered metamaterial with a total thickness of less than 200 nm was designed and deposited to have equivalent admittance around unity and an extinction coefficient that is comparable to that of metal. Such a metal-like metamaterial exhibits low reflectivity so couples most visible light energy into the films and dissipates energy with an equivalent skin depth of less than 55 nm over visible wavelengths.

Densely packed aluminum-silver nanohelices as an ultra-thin perfect light absorber.

Metals have been formed into nanostructures to absorb light with high efficiency through surface plasmon resonances. An ultra-thin plasmonic structure that exhibits strong absorption over wide ranges of wavelengths and angles of incidence is sought. In this work, a nearly perfect plasmonic nanostructure is fabricated using glancing angle deposition. The difference between the morphologies of obliquely deposited aluminum and silver nanohelices is exploited to form a novel three-dimensional structure, which is an aluminum-silver nanohelix array on a pattern-free substrate. With a thickness of only 470 nm, densely distributed nanohelices support rod-to-rod localized surface plasmons for broadband and polarization-independent light extinction. The extinctance remains high over wavelengths from 400 nm to 2000 nm and angles of incidence from 0° to 70°.

Tunable tapered waveguide for efficient compression of light to graphene surface plasmons.

Dielectric-graphene-dielectric (DGD) structure has been widely used to construct optical devices at infrared region with features of small footprint and low-energy dissipation. The optical properties of graphene can be manipulated by changing its chemical potential by applying a biased voltage onto graphene. However, the excitation efficiency of surface wave on graphene by end-fire method is very low because of large wavevector mismatch between infrared light and surface wave. In this paper, a dielectric-semiconductor-dielectric (DSD) tapered waveguide with magnetic tunability for efficient excitation of surface waves on DGD at infrared region is proposed and analyzed. Efficient excitation of surface waves on DGD with various chemical potentials in graphene layer and incident frequencies can be attained by merely changing the external magnetic field applied onto the DSD tapered waveguide. The electromagnetic simulations verify the design of the proposed structure. More importantly, the constituent materials used in the proposed structure are available in nature. This work opens the door toward various applications in the field of using surface waves.

Self-Shadowing Deposited Pure Metal Nanohelix Arrays and SERS Application.

In this work, one-step glancing angle deposition is utilized to fabricate gold and silver nanohelix arrays (NHAs) on smooth glass substrates. During deposition, the substrate is cooled using liquid nitrogen and rotated with a tunable spin rate. The substrate spin rate is tuned to match the deposition rate to yield a spiral-like helix structure. The morphologies and optical properties of spiral-like Ag and Au NHAs are measured and compared. The polarization-dependent reflectance of Au NHA leads to a strong g-factor. The three-dimensional nanohelical structures are demonstrated to be a highly sensitive surface-enhanced Raman scattering (SERS) substrate.

Design for approaching Cicada-wing reflectance in low- and high-index biomimetic nanostructures.

Natural nanostructures in low refractive index Cicada wings demonstrate ≤ 1% reflectance over the visible spectrum. We provide design parameters for Cicada-wing-inspired nanotip arrays as efficient light harvesters over a 300-1000 nm spectrum and up to 60° angle of incidence in both low-index, such as silica and indium tin oxide, and high-index, such as silicon and germanium, photovoltaic materials. Biomimicry of the Cicada wing design, demonstrating gradient index, onto these material surfaces, either by real electron cyclotron resonance microwave plasma processing or by modeling, was carried out to achieve a target reflectance of ∼ 1%. Design parameters of spacing/wavelength and length/spacing fitted into a finite difference time domain model could simulate the experimental reflectance values observed in real silicon and germanium or in model silica and indium tin oxide nanotip arrays. A theoretical mapping of the length/spacing and spacing/wavelength space over varied refractive index materials predicts that lengths of ∼ 1.5 µm and spacings of ∼ 200 nm in high-index and lengths of ∼ 200-600 nm and spacings of ∼ 100-400 nm in low-index materials would exhibit ≤ 1% target reflectance and ∼ 99% optical absorption over the entire UV-vis region and angle of incidence up to 60°.

Fabry-Perot based metal-dielectric multilayered filters and metamaterials.

The traditional three-layered metal-dielectric-metal Fabry-Perot filter is developed as a new metal-dielectric multilayered band-pass filter. Our design method allows metal and dielectric films to be alternatively arranged to achieve a narrow and high transmission peak and the peak height remains unchanged for any number of metal films arranged in the multilayer. Furthermore, the equivalent refractive index of a subwavelength metal-dielectric multilayer could be negative real at the passband of the filter and such metamaterial exhibits stronger figure of merit than a previous result. By choosing a material with high refractive index as the dielectric film, such metamaterial exhibits a pass band that depends weakly on the angle of incidence.

Strong light coupling effect for a glancing-deposited silver nanorod array in the Kretschmann configuration.

In this work, three slanted silver nanorod arrays (NRAs) with different thicknesses are fabricated using the glancing angle deposition method. Each silver NRA in the Kretschmann configuration is arranged to form a prism/NRA/air system. Attenuated total reflection occurs over the visible wavelengths and wide incident angles of both s- and p-polarization states. The extinctance is inversely proportional to the thickness of the Ag NRA. The thinnest NRA, with a thickness of 169 nm, exhibits strong extinctance of more than 80% over the visible wavelengths. The associated forward scatterings from the three NRAs are measured and compared under illumination with a laser beam with a wavelength of 632.8 nm.

Aluminum-jointed silicon dioxide octagon nanohelix array with desired complex refractive index.

In this Letter, glancing angle deposition is used to form an aluminum-jointed silicon dioxide octagon nanohelix array as a 3D nanostructured thin film. As a sculptured metal-dielectric composite, the film exhibits a complex refractive index of near unity with a small imaginary part. This structured film is demonstrated as an efficient light absorber to absorb light in a broad band and over a wide range of angles for both polarization states.

Orthogonal polarization Mirau interferometer using reflective-type waveplate.

This work proposes an orthogonal polarization Mirau interferometry using a reflective-type waveplate to generate different polarization orientations for broadband white light interferometry. The reflective-type half-waveplate is employed as the reference arm of the Mirau interferometer to convert polarization and it generates a reference light with an orientation orthogonal to the object light. An advantage of the proposed interferometer is its ability to control the ratio of light intensity between the object and reference arms to maximize the interferometric fringe contrast. Better, more accurate calibration of standard step height has been achieved by the developed interferometer, which also can measure solder bumps that traditional Mirau interferometers usually cannot measure.

An interference coating of metamaterial as an ultrathin light absorber in the violet-to-infrared regime.

A metamaterial with brief and ultrathin structure performs high efficiency in light absorption. An upright aluminum nanorod array (Al NRA) is obliquely deposited, measured, and analyzed its optical property. The Al NRA performs high efficiency of light absorption and low reflectance simultaneously. Based on the measured refractive index and impedances, the wave propagation through the Al NRA is traced to demonstrate the destructive interference that leads to antireflection. According to the analysis of wave tracing, an Al semicontinuous film with thickness of 15nm is introduced under an Al NRA with thickness of only 245nm as a brief and thin two-layered structure. The broadband and polarization-independent light absorption is measured over the violet-to-infrared regime.

Metal/dielectric/metal sandwich film for broadband reflection reduction.

A film comprising randomly distributed metal/dielectric/metal sandwich nanopillars with a distribution of cross-sectional diameters, displayed extremely low reflectance over the blue-to-red regime, when coated on glass and illuminated normally. When it is illuminated by normally incident light, this sandwich film (SWF) has a low extinction coefficient, its phase thickness is close to a negative wavelength in the blue-to-red spectral regime, and it provides weakly dispersive forward and backward impedances, so that reflected waves from the two faces of the SWF interfere destructively. Broadband reflection-reduction, over a wide range of incidence angles and regardless of the polarization state of the incident light, was observed when the SWF was deposited on polished silicon.

Extended broadband achromatic reflective-type waveplate.

This work demonstrates the feasibility of applying a symmetrical film stack on a silver mirror, resulting in broadband phase retardation. While functioning as a reflective-type achromatic waveplate, the symmetrical film stack comprises at least one anisotropic thin film. Additionally, selecting the birefringence and thickness of the thin film allows for the design of uniform phase retardation in both the passband and stopband. A symmetrical film stack that is composed of an anisotropic Ta(2)O(5) thin film and isotropic Ta(2)O(5) thin film is investigated for its achromatic performance in phase retardation.