Polarization detection analysis of dual-channel surface plasmon resonance sensing for silicone oils based on the D-shaped fiber with a central hole

We present and numerically characterize a dual channel surface plasmon resonance (SPR) sensor based on a D-shaped fiber with a central hole for silicone oil detections. The proposed design incorporates two metalized channels to facilitate the simultaneous detection of one group of silicone oils, which can consist of two different species. It has been demonstrated that the p-polarized input light can induce two peaks among surface plasmon resonance places, which come from the coupling between the core-guided mode and the fundamental surface plasmon polariton (SPP) modes at the D-shaped surface and around the central hole surface. However, the s-polarized input light can only induce one peak among surface plasmon resonance places, which comes from the coupling between the core-guided mode and the fundamental SPP mode around the central hole surface. The simulation results show that the characteristic responses of two channels independently correspond to the refractive index variations in the silicone oils with which they are in contact. A maximum sensitivity of 3500 nm/RIU (refractive index unit) and 4400 nm/RIU are achieved for channel A and B, respectively. This kind of sensor structure and polarization related demodulation method is promising in the simultaneous multi-analytes sensing applications in the future.     

Refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers

We propose refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers. The surface plasmon resonance modes and the sensing properties are theoretically analyzed using finite element method (FEM). In the calculation, Drude–Lorentz model is used to describe the Metal Dielectric constant. The calculation results show that the sensitivity of Ag-metalized SPR sensor can reach 1500 nm/RIU corresponding to a resolution of 6.67 × 10^?5 RIU. Comparing with conventional detecting material-Au under the same structure, the sensitivity and 3 dB bandwidth of our device are better.     

Bi-dipole excited plasmonic modes of an elongated gold nanorod

The first and higher-order longitudinal surface plasmon resonance (SPR) modes of an elongated gold nanorod (GNR) induced by the photoluminescence of two quantum dots (QDs) respectively located at the two ends were studied theoretically. Two configurations of a GNR combined with a symmetric or anti-symmetric bi-dipole were simulated and analyzed using the multiple multipole method. The results show that the local maxima of the radiative and nonradiative powers of the bi-dipole are at these modes. When the aspect ratio (AR) of GNR exceeds a specific value, not only the first mode but also the second, third and even fourth modes are generated. For example, for an elongated GNR (radius: 30 nm, AR=7) in water, the first, second, third and fourth modes are at 1800 nm, 930 nm, 680 nm and 600 nm, respectively. These SPR modes depend on the AR as well as the radius of GNR. The larger the AR is, the more the red-shift of these modes will be. In addition, the red-shift increases as the radius increases. Moreover, the odd modes are induced by the anti-symmetric bi-dipole, but suppressed by the symmetric one. On the contrary, the even modes are induced by the symmetric bi-dipole, but suppressed by the anti-symmetric one. In comparison with the scattering and absorption cross sections of GNR irradiated by a plane wave, the high-order modes, particularly the even modes, can be easily induced by the bi-dipole. Moreover, the mutual excitation rate of the two QDs is also enhanced through these modes of GNR.     

Polarization-insensitive surface plasmon resonance sensor by cross-slit metallic periodic arrays

We propose a plasmonic structure to obtain polarization-insensitive localized surface plasmon resonance (LSPR) sensor, which consists of cross-slit metallic periodic arrays embedded in the background material. Numerical simulation illustrates that the mechanism of the LSPR sensor is based on the shift of the Fabry–Perot cavity mode resonance peak in the spectrum as the change of the dielectric material properties for the near fields. And one of the transmission dips of the structure is very sensitive to the background materials; the structure could gain the sensitivity (nm/RIU) more than 500 nm/RIU. Meanwhile, the structure holds great potential to achieve high-performance sensors in practical application due to polarization-insensitive virtue.     

Photonic crystal fiber sensor based on hybrid mechanisms: Plasmonic and directional resonance coupling

We propose a special refractive index sensor design based on a photonic crystal fiber. Two analyte channels are introduced, with one analyte channel coated with gold layer and the other one without gold layer. A hybrid resonance method is used in the sensor to achieve a large dynamic index range, where surface plasmon resonance occurs when the analyte index is lower than that of the fiber material, while the core mode couples with the resonant mode of the adjacent analyte-filled cylinder when the analyte index is larger than the fiber material. When considering fluorinated polymer fibers, a broad index range of analyte refractive index from 1.25 to 1.45 with high sensitivity can be achieved. The maximal sensitivities reach 1.4 × 10⁴ nm/RIU and 2.7 × 10⁴ nm/RIU respectively when refractive index is in the range of 1.25 to 1.383 and 1.383 to 1.45. The sensor characteristics, make this simple sensor very interesting for detecting a wide range of fluid's refractive index or chemical agent concentration.     

Characterization of NiO–yttria stabilised zirconia (YSZ) hollow fibres for use as SOFC anodes

NiO–yttria stabilised zirconia (YSZ) hollow fibres with varying NiO content and a desired microstructure were prepared using a phase inversion technique and sintering. By controlling the fabrication parameters, microstructures with predominately finger-like pores near the inner and outer surfaces and a denser central layer with sponge-like pores were produced, for use as substrates for anode-supported hollow fibre solid oxide fuel cells (HF-SOFC). The NiO–YSZ fibres were reduced to Ni–YSZ at 250–700 °C in hydrogen flowing at 20 cm³ min^? 1 to produce Ni–YSZ hollow fibres, the mechanical and electrical properties of which were determined subsequently, reduction to Ni being verified by X-ray diffraction. The effects of NiO concentration and sintering temperature of the fibre precursors on the conductivity, strength and porosity of the reduced hollow fibres were investigated to assess their suitability for use as anode substrates. As expected, increasing Ni concentration increased electrical conductivities and decreased mechanical strength. Sintering temperature had a critical effect in producing axially conductive hollow fibres of sufficient mechanical strength for use as SOFC anodes. The hollow fibres retained their initial microstructure through the reduction process, though ca. 41% volume contraction is predicted on reduction of NiO to Ni, producing increased porosity in the reduced fibres. The mean porosity of the Ni–YSZ hollow fibres was ca. 60% and ca. 40% after sintered at 1250 °C and 1400 °C, respectively. The mean pore sizes for all the fibres after reduction varied between ca. 0.3 and 1 µm. The hollow fibres produced with 60% NiO, of length ca. 300 mm, electrical conductivities of ca. (1–2.25) × 10⁵ S m^? 1 and a porosity of ca. 43% are being used currently to construct and test the electrical behaviour of an anode-supported HF-SOFC.     

Wideband slow light achievement in MIM plasmonic waveguide by controlling Fano resonance

In this paper, we have investigated the characteristics of an asymmetric shaped Fano line in a metal–insulator–metal (MIM) plasmonic waveguide side coupled to two resonating stub structures. The spectral properties of Fano resonance are quite distinct due to the destructive interference between a two propagating plasmon modes. Two structural parameters are carefully adjusted: physical separation between both the resonating stubs and length of resonating stubs. By tailoring the separation between both the resonating structures, coupling between both the plasmon modes is controlled, and hence asymmetric nature of Fano line can be shaped accordingly. Resonance condition of Fano line can be tuned by scaling the length of stubs. A strong red shift in resonating wavelength with varying degree of asymmetry is observed, when length of resonating structures is increased. The sharp resonant peak, due to an asymmetric shaped Fano resonance is generally accompanied by large dispersion that results in reduction of group velocity of light near Fano resonance. By controlling the coupling between resonating stub, or by scaling the length of lower resonating stub, large value of group index (n_g = 75) and delay bandwidth product (DBP = 0.2533) is obtained. The structure can be modified to suit different applications in optical buffers, optical switches and nonlinear optics devices.     

Enhanced transmittance of a dual pass-band metamaterial filter

A broad pass-band metamaterial-based optical filter is experimentally and numerically studied. The designed structure consists of periodically arranged composite metallic arrays and dielectric layer that exhibits transmission responses composed of two flat pass-bands. The coupling of localized surface plasmon (LSP) modes results in the low-frequency pass-band, while the internal surface plasmon polaritons (ISPPs) between the upper and lower metal layers leads to the high-frequency pass-band. Structural parameters (L and R) are experimentally considered from the viewpoint of exploiting their effects on the pass-bands and resonance frequencies. The bandwidths of these pass-bands both can reach to maximums by optimization of these structural parameters. In addition, the two pass-bands can be modulated to be a single pass-band with a bandwidth of 10.7 THz by optimizing L and R simultaneously.     

Silver nanoparticle in situ growth within crosslinked poly(ester-co-styrene) induced by UV irradiation: aggregation control with exposure time

Silver nanoparticles (NPs) were photogenerated in situ in crosslinked poly(ester-co-styrene) resins (self-standing films and monoliths) by irradiating the samples with UV light. Addition of the silver salt solution did not interfere in the resin curing process and silver reduction was not detected during sample crosslinking. The samples were characterized by absorption spectroscopy and transmission electron microscopy. The initially broad and asymmetric surface plasmon resonance band was narrowed and blue-shifted as the exposure time to UV light was increased. Samples illuminated up to 120 min have an average particle size near 9.0 nm; a decrease to ∼5.0 nm was observed for longer exposure times up to 790 min. The asymmetric surface plasmon resonance band was due to particle aggregation; higher irradiation times led to a uniform particle distribution within the polymer matrix.     

Manganese doping influence on the plasmon energy of nickel films

Manganese doping in nickel films capped with copper have been prepared by evaporation in vacuum. The films are composed of grains with an average diameter of ~ 20 nm from scanning electron microscope scans. Optical absorption is measured over a wavelength range of 190–450 nm. Two plasmon peaks are observed at 3.30 eV and 4.45 eV for a range of concentrations of films. The 4.45 eV peak is a bulk plasmon peak that is enhanced by increasing the manganese in nickel. The 3.30 eV peak is a surface plasmon peak that increases in width or strength of plasmon resonance with increasing concentration of manganese. This may be a combination effect of charge carrier concentration and dielectric screening from the reformed electronic band structure caused by manganese doping. By adding manganese into nickel, the ferromagnetic order is further destroyed as a transition into a spin glass occurs. This spin glass behavior is seen in a coercivity measurement at 4 K where the coercivity drops precipitously as the doping concentration increases.     

Symmetric surface plasmon resonance sensing structure excited by a planar waveguide

In this paper, we describe a novel waveguide surface plasmon resonance sensing structure, which consists of a symmetric structure and a planar waveguide. The core component is the symmetric structure of the metal layer, tested sample, and metal layer. The refractive index matching condition of this structure can be adjusted through the thickness of the sample. The planar waveguide is used to excite the surface plasmon wave, and then the parameters are tested and analyzed. The surface plasmon wave is excited when glycerin solutions with concentrations of 0%–70% are used to detect at thicknesses of 300 and 500 nm. The problem that the effective refractive index of the ion exchange planar waveguide is large and using this index to excite the surface plasmon wave between the metal and dielectric for detection is difficult to achieve can be countered by appropriately choosing the thickness of the dielectric in order to be able to measure different refractive indices.     

Investigations of laser oscillation and switching using a resonance at the band edge crossover in an hetero-structure of one-dimensional photonic crystals

This paper presents a theoretical investigation of a laser oscillator and a laser switch, using a hetero-structure made of two one-dimensional photonic crystals with active materials and a period ratio of r (r > 1). Lasing is achieved near frequencies where the upper and lower band edges of the adjacent photonic crystals overlap (i.e., band edge resonance). Near the band edge resonance, two modes of laser oscillations are found; mode A – the threshold gain increases with r and mode B – the threshold gain decreases with r. By assuming a homogenously broadened gain medium at any particular r, only one of the two modes is able to participate in lasing. We also found the lasing mode is switchable upon a very small alteration in the refractive index of the materials present in the photonic crystal. The results of the paper will be very useful for designing a new class of tunable lasers and high sensitivity sensors.     

Double plasmonic profile of tryptophan–silver nano-crystals—Temperature sensing and laser induced antimicrobial activity

Surface plasmon resonance (SPR) for spherical shaped silver nanoparticles showing double maxima at ～390 nm and ～520 nm respectively is reported. Self assembly of silver nanoparticles grown on tryptophan template leads to emergence of equal intensity double plasmon resonance (EIDPR). While for rod shaped nano-forms such double plasmon is explainable but for spherical shaped forms, such double plasmon can be explained on the basis of bidirectional formation of silver cluster in which attachment of silver at two nitrogen atom locations of tryptophan molecule seems to be obligatory. The absence of double resonance in case of silver nanoclusters formed with other amino acids or N-acetyl l-tryptophanamide (NATA), where bidirectional NH₂ attachment is not possible, validates the proposed EIDPR mechanism. Electron micrograph of EIDPR particle indicates a bi-periodic fringe pattern indicating unusual crystalline property. Apart from sensing tryptophan, the double plasmon peaks are sensitive to temperature. Furthermore, the particle can be used as a smart killing agent showing bactericidal activity only upon exposure to low power laser.     

Inherently gain flattened S-band erbium doped fiber amplifier based on dual core resonant leaky fiber

A co-axial dual core resonant leaky optical fiber (DCRLF) is designed for inherent gain equalization of S-band erbium doped fiber amplifier (EDFA). Resonance tail of leakage loss of the fiber into the S-band region is utilized to flatten the gain. We have numerically studied the effect of various design parameters and their fabrication tolerances on gain flattening. We show 23.5 dB flat gain with ± 0.9 dB ripple over 30 nm bandwidth (1490–1520 nm) using 120 mW pump. The study should be useful in designing optical fiber amplifiers for optical communication system employing wavelength division multiplexing.     

Study of resonant modes in a 700 nm pitch macroporous silicon photonic crystal

In this study the modes produced by a defect inserted in a macroporous silicon (MP) photonic crystal (PC) have been studied theoretical and experimentally. In particular, the transmitted and reflected spectra have been analyzed for variations in the defect’s length and width. The performed simulations show that the resonant frequency is more easily adjusted for the fabricated samples by length tuning rather than width. The optimum resonance peak results when centered in the PC bandgap. The changes in the defect geometry result in small variations of the optical response of the PC. The resonance frequency is most sensitive to length variations, while the mode linewidth shows greater change with the defect width variation. Several MPS photonic crystals were fabricated by the electrochemical etching (EE) process with optical response in the range of 5.8 μm to 6.5 μm. Results of the characterization are in good agreement with simulations. Further samples were fabricated consisting of ordered modulated pores with a pitch of 700 nm. This allowed to reduce the vertical periodicity and therefore to have the optical response in the range of 4.4 μm to 4.8 μm. To our knowledge, modes working in this range of wavelengths have not been previously reported in 3-d MPS structures. Experimental results match with simulations, showing a linear relationship between the defect’s length and working frequency inside the bandgap. We demonstrate the possibility of tailoring the resonance peak in both ranges of wavelengths, where the principal absorption lines of different gases in the mid infrared are placed. This makes these structures very promising for their application to compact gas sensors.     

Interferometric profiling of microcantilevers in liquid

Silicon micro cantilevers are used as highly sensitive transducers for a wide range of physical, chemical and biochemical stimuli. Vibrating the cantilevers at higher-order resonant modes can achieve extra sensitivity, but the difficulty lies in determining exactly which modes are excited in the cantilever. This problem is exacerbated for cantilever sensors operating in liquid where the computational analysis of the resonance modes is very challenging. Using strobed interferometric microscopy, we are able to image the dynamic behavior of individual (100×500×1 μm³) cantilevers in an eight cantilever array over frequencies from 0–1 MHz. We show how some modifications to the interferometric microscope allow for the spatial visualization of 16 longitudinal modes of cantilevers working in liquid with nanometer-scale amplitudes. We also compare the shift in frequency response and reduction in quality factor for cantilevers resonating in liquid versus in air and simulations in vacuum. Because the resonant frequency spectrum is fairly complex and does not follow simple intuition, our work maps the actual behavior of cantilevers without having any specific knowledge of the sample and environment parameters and without the necessity of involved simulations and calculations.     

Reflective plasmonic waveplates based on metal–insulator–metal subwavelength rectangular annular arrays

We propose and present a quarter-wave plate using metal–insulator–metal (MIM) structure with sub-wavelength rectangular annular arrays (RAA) patterned in the upper Au film. It is found that by manipulating asymmetric width of the annular gaps along two orthogonal directions, the reflected amplitude and phase of the two orthogonal components can be well controlled via the RAA metasurface tuned by the MIM cavity effect, in which the localized surface plasmon resonance dip can be flattened with the cavity length. A quarter-wave plate has been realized through an optimized design at 1.55 μm, in which the phase difference variation of less than 2% of the π/2 between the two orthogonal components can be obtained in an ultra-wide wavelength range of about 130 nm, and the reflectivity is up to ∼90% within the whole working wavelength band. It provides a great potential for applications in advanced nanophotonic devices and integrated photonic systems.     

Surface and core hole effects in X-ray photoelectron spectroscopy

In XPS analysis, two effects, which significantly reduce the measured peak intensity, are usually neglected: the core hole left behind in an XPS process which causes “intrinsic” excitations and excitations as the photoelectron pass through the surface region. We have calculated these effects quantitatively for various energies, geometries, and materials. Instead of considering the two effects separately, we introduce a new parameter, namely the correction parameter for XPS or CP_XPS, which takes into account both effects. We define this CP_XPS as the change in probability for emission of a photoelectron caused by the presence of the surface and the core hole in comparison with the situation where the core hole is neglected and the electron travels the same distance in an infinite medium. The calculations are performed within the dielectric response theory by means of the QUEELS–XPS software determining the energy-differential inelastic electron scattering cross-sections for X-ray photoelectron spectroscopy (XPS) including surface and core hole effects. This study has been carried out for electron energies between 300 eV and 3400 eV, for angles to the surface normal between 0° and 60° and for various materials. We find that the absolute effect is a reduction by 35–45% in peak intensities but that the variation in CP_XPS with material, angle and energy are < ± 10% for emission angle ≤ 60° and photoelectron energy ≤ 1500 eV. This implies that when XPS analysis is done using relative intensities, the combined effect of the surface and of the core hole is typically less than ≈ ± 10% for geometries and energies normally used in XPS. In practice, it is however difficult to determine the bare peak intensity without the intrinsic electrons because the two overlap in energy.     

Luminescence and micro-Raman investigations on inclusions of unusual habit in chrysoprase from Turkey

Chemical analyses performed on chrysoprase from Turkey have shown many trace elements as well as rare earth impurities. Quantitative chemical analyses of inclusions in minerals can improve our understanding of the chemistry of surface. The environmental scanning electron microscope (ESEM) with an attached X-ray energy dispersive system (EDS) is capable of producing rapid and accurate major element chemical analyses of individual inclusions in crystals larger than about 30 μm in diameter. The samples were examined with lifetime-resolved and spatially-resolved cathodoluminescence (CL), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Spatially resolved CL results at room temperature were recorded for two different areas. Bulk area displays with low CL emission and pores contain iron phases such as chromite, hematite and anatase which cause the green color. For the raw data in the lifetime resolved CL spectrum, at least three broad emission bands were detected in a yellow band of the highest intensity at about 550 nm, a weaker orange band at about 650 nm, and a red band at 720 nm. It is assumed that there are links between the CL emissions and the presence of some transition metal and REE elements, but it is obvious that all trace elements do not play a direct role. Micro-Raman measurements were performed on chrysoprase and these showed a characteristic intensive Raman band peaked at 464 cm^?1 which can be inferred to ν₂ doubly symmetric bending mode of [SiO₄/M] centers. Raman spectrum of all inclusions found in the material are also given and discussed in detail.     

Length-dependent effects due to leaky modes on multimode graded-index optical fibres

The radiation losses of tunnelling leaky modes in graded-index optical fibres are calculated theoretically, and it is shown that the near-field intensity profile has a length dependence. Consequently measurements of the near-field intensity distribution do not give the refractive index profile directly, and a correction factor must be applied. We have investigated this factor and find that it depends only on a single normalisation parameter involving fibre length, core radius and normalised frequency. A further use of the correction factor is to determine the total power attenuation due to the loss of leaky modes.