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.

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.

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.

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.

Plasma-Etched Black GaAs Nanoarrays with Gradient Refractive Index Profile for Broadband, Omnidirectional, and Polarization-Independent Antireflection.

Black GaAs nanotip arrays (NTs) with 3300 nm lengths were fabricated via self-masked plasma etching. We show, both experimentally and numerically, that these NTs, with three gradient refractive index layers, effectively suppress Fresnel reflections at the air-GaAs interface over a broad range of wavelengths. These NTs exhibit exceptional UV-Vis light absorption (up to 99%) and maintain high NIR absorption (33-60%) compared to bare GaAs. Moreover, possessing a graded layer with a low refractive index (n = 1.01 to 1.12), they achieve angular and polarization-independent antireflection properties exceeding 80° at 632.8 nm, aligning with perfect antireflective coating theory predictions. This approach is anticipated to enhance the performance of optoelectronic devices across a wide range of applications.

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.

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.

Giant optical anisotropy of oblique-aligned ZnO nanowire arrays.

A combined method of modified oblique-angle deposition and hydrothermal growth was adopted to grow an optically anisotropic nanomaterial based on single crystalline ZnO nanowire arrays (NWAs) with highly oblique angles (75°-85°), exhibiting giant in-plane birefringence and optical polarization degree in emission. The in-plane birefringence of oblique-aligned ZnO NWAs is almost one order of magnitude higher than that of natural quartz. The strong optical anisotropy in emission due to the optical confinement was observed. The oblique-aligned NWAs not only allow important technological applications in passive photonic components but also benefit the development of the optoelectronic devices in polarized light sensing and emission.

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.

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 metamaterial thin film with negative refractive index and permeability in the visible regime.

Thin films are fabricated from arrays of silver nanorods with thicknesses of 160 nm and 200 nm, to function as a metamaterial. The negative refractive index and negative permeability are retrieved from measured reflection and transmission coefficients using walk-off interferometer in the visible regime. A negative-index-material thin film with negative permittivity or (and) permeability can be produced by glancing angle deposition.

Optical configuration for unpolarized ultra-long-range surface-plasmon-polariton waves.

Multilayered structures were designed on both sides of a thin silver film to let both transverse-magnetic- and transverse-electric-polarized electromagnetic waves propagate along a thin metal film simultaneously in the same configuration, as so-called long-range surface-plasmon-polariton (LRSPP) waves. Based on the admittance analysis and design, the propagation length of an unpolarized LRSPP wave can be extended by more than 1 order of magnitude compared with previous results.

Effects of the equivalent coupling layer on ultra-long-range surface-plasmon-polariton waves.

The mechanism and design of p- and s- polarized ultra-long-range surface-plasmon-polariton (SPP) propagation in the configuration {prism/ equivalent coupling layer (ECL)/ silver film (20 nm)/ equivalent substrate (ES)} are investigated using a normalized admittance diagram (NAD). The excitation of ultra-long-range SPP waves is characterized as a huge open loop of the NAD of the metal film at a designated angle of incidence. We propose three kinds of ECLs to complete the multilayer ultra-long-range SPP design: the normalized admittance of the ECL is (i) real (ii) infinite (iii) imaginary. The ultra-long propagation lengths in the three designs are compared at a wavelength of 632.8 nm for p- and s-polarization states.

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.

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.

Vapor-deposited thin films with negative real refractive index in the visible regime.

A thin film comprising parallel tilted nanorods was deposited by directing silver vapor obliquely towards a plane substrate. The reflection and transmission coefficients of the thin film were measured at three wavelengths in the visible regime for normal-illumination conditions, using ellipsometry and walk-off interferometry. The thin film was found to display a negative real refractive index. Since vapor deposition is a well-established industrial technique to deposit thin films, this finding is promising for large-scale production of negatively refracting metamaterials.

Multilayered structures for p- and s-polarized long-range surface-plasmon-polariton propagation.

A normalized admittance diagram assists in describing and designing multilayered structures to excite long-range surface-plasmon-polariton (LRSPP) waves of either the p- or the s-polarization state. These structures comprise symmetric periodic multilayers on one or both sides of a metal thin film in either the Kretschmann or the Sarid configuration. The normalized admittance diagram even assists in designing structures that can be used to excite LRSPP waves of both polarization states simultaneously.

Anisotropic optical thin films finely sculptured by substrate sweep technology.

In this paper, we have fabricated for the first time films with different orientations of principal axes but similar principal indices and also films with different principal refractive indices but the same orientations of principal axes. During deposition, the deposition angle and the substrate sweep angle are varied to control separately the porosity (refractive principal indices) and column tilt angle (orientations of principal axes) of a birefringent thin film.