Photothermal Switching of SOI Waveguide-Based Mach-Zehnder Interferometer with Integrated Plasmonic Nanoheater

We theoretically and numerically investigated the photothermal switching of a Mach-Zehnder interferometer (MZI) based on two Si waveguides integrated with plasmonic nanoheaters. The nanoheater is a composite nanowire with Au/Al₂O₃/Au three-layer structure, which is designed to have a highly efficient optical absorption peak at wavelength of 1,064 nm. Based on this finding, we further analyze a MZI built with two 40-μm-long symmetric waveguide branches, each integrated with a 20-μm-long nanoheater. The optical switching power of the MZI device is 190 mW (280 mW) for the capped (buried) channel waveguide, when pumped by a circular Gaussian beam with a waist of 10 μm. Alternatively, the switching power can be reduced to 38 mW (56 mW) by using an astigmatic Gaussian beam, with a semi-major axis of 10 μm and an aspect ratio of 5. The switching response time of the MZI is 0.7 μs (1.0 μs) for capped (buried) channel waveguide design. Our design opens a new route for optically driven non-contact optical on-off switching with sub-microsecond time response.     

A Polarization Filter Based on Photonic Crystal Fiber with Symmetry Around Gold-Coated Holes

We propose a modified design for a photonic crystal fiber (PCF) polarization filter based on surface plasmon resonance (SPR). The air holes are arrayed in diamond lattices, and the diameter of the holes around the gold-coated holes are different that can separate the refractive index of the x-polarization and y-polarization second order surface plasmon polariton (SPP) modes. The influences of structural parameters of the photonic crystal fiber (PCF) on the filter characteristics are studied using the finite element method (FEM). Great changes have taken place in the results of numerical simulation by changing the thickness of the gold film and air hole diameter. Simulation results show that the resonance wavelength is communication wavelength 1550 mm, the loss of the y-polarization mode is 43,126.7 dB/m. When the length of the fiber is 500 μm, extinction ratio is more than 20 dB at the communication wavelength, and bandwidth achieve to 190 nm. It is an important property of PCF polarization filter in production.     

A Polarization Filter Based on a Novel Photonic Crystal Fiber with a Gold-Coated Air Hole by Using Surface Plasmon Resonance

A novel design of a polarization filter based on photonic crystal fiber (PCF) is proposed in this paper. With the introduction of a gold-coated air hole, the resonance strength is much stronger in y-polarized direction than in x-polarized direction at some particular wavelengths, which is due to the metal surface plasmon effects. At the wavelength of 1.31 μm, the loss of y-polarized mode is 2138.34 dB/cm while the loss is very low in x polarization. Furthermore, the loss peak can be flexibly adjusted from the wavelength of 1.26 to 1.56 μm by changing the thickness of a gold layer, and the loss in y polarization can be kept above 1200 dB/cm. The significant loss in y polarization makes this PCF a good candidate for developing a polarization filter with high performance.     

Effective Coupling of Incident Light Through an Air Region into an S-Shape Plasmonic Ag Nanowire Waveguide with Relatively Long Propagation Length

Coupling of incident light through an air region into an S-shape silver (Ag) plasmonic nanowire waveguide (SSAPNW) is a highly difficult challenge of light guiding on the surface of metal nanowire. In this paper, we numerically analyze the coupling effect of an SSAPNW which is covered by a dielectric medium using a finite element method. The coupling effect can be modulated by adjusting the Ag nanowire diameter and the covering dielectric medium width and wavelength of incident light, and the propagation length of surface plasmon (SP) coupling can be maximized. Simulation results reveal that the field confinement can be significantly improved and the majority of the electric field can be carried on the surface of a bending Ag nanowire. The effect of electric field transport along an SSAPNW due to SP coupling and Fabry-Perot resonance is investigated for different dimensions and lengths. Accordingly, long propagation lengths of about 41.5 μm for 10?×?SSAPNW at an incident wavelength of 810 nm and longer propagation length can be achieved if more sections of an SSAPNW are used. Simulation results offer an efficient method for optimizing SP coupling into bending metal nanowire waveguides and promote the realization of highly integrated plasmonic devices.     

Choice of Pore Size Can Introduce Artefacts when Filtering Picoeukaryotes for Molecular Biodiversity Studies

Published results of studies based on samples size fractionated by sequential filtration (e.g. 0.2–3 μm) indicate that many ciliate, dinoflagellate and rhizarian phylotypes are found among marine picoeukaryotes. This is somewhat surprising as these protists are typically known as being large organisms (often >10 μm) and no picoplanktonic species have so far been identified. Here, the abundances of ciliate and dinoflagellate phylotypes in published molecular studies of picoeukaryotes are shown to correlate negatively with the pore size chosen for the end filter in the sequential filtrations (i.e. the filter used to collect the microbial biomass). This suggests that extracellular DNA adhering to small particles may be the source of ciliate and dinoflagellate phylotypes in picoplanktonic size fractions. This hypothesis was confirmed using real-time qPCR, which revealed significantly less dinoflagellate 18S rDNA in a 0.8–3-μm size fraction compared to 0.2–3 μm. On average, the abundance of putative extracellular phylotypes decreased by 84–89 % when a 0.8-?μm end filter was used rather than a 0.2-μm end filter. A 0.8-μm filter is, however, not sufficient to retain all picoeukaryotic cells. Thus, selection of filter pore size involves a trade-off between avoiding artefacts generated by extracellular DNA and sampling the entire picoeukaryotic community. In contrast to ciliate and dinoflagellate phylotypes, rhizarian phylotypes in the picoplankton size range do not display a pattern consistent with an extracellular origin. This is likely due to the documented existence of picoplanktonic swarmer cells within this group.     

Fano Resonance Excited All-Optical XOR,XNOR, and NOT Gates with High Contrast Ratio

We have presented all-optical XOR, XNOR, and NOT gates using metal-insulator-metal (MIM)-coupled ring resonator. The performance of the device is evaluated by finite difference in time-domain (FDTD) method. The proposed gate utilizes a unique phenomenon of Fano resonance to excite logic OFF/ON state. Fano resonance has quite asymmetric resonance profile and the transmission spectrum of Fano profile abruptly drops to a minimum value at the resonance condition. Due to this unique resonance phenomenon, a large value of contrast ratio is obtained. The proposed XNOR gate offers a contrast ratio (C.R.) of 20.66 dB while XOR and NOT gates offer C.R. 12.8 and 18.8 dB respectively. The variation of contrast ratio is also studied against different input wavelength and it is reported that the obtained value of contrast ratio is an optimum value for the proposed structure. The device is compact sized with small dimension 0.31 λ₀², where λ₀?=?1.55 μm. The proposed device opens up the avenues for designing on-chip optical gates in the field of high-speed optical communication networks.     

Plasmonically Tunable Blue-Shifted Emission from Coumarin 153 in Ag Nanostructure Random Media: A Demonstration of Fast Dynamic Surface-Enhanced Fluorescence

Enhancement of intensity and wavelength tunability of emission are desirable features for light-emitting device applications. We report on the large and tunable blue shift (60 nm) in emission from an environment-sensitive fluorophore (Coumarin153) embedded in Ag plasmonic random media. Coumarin 153 having emission at 555 nm, show a systematic blue shift (to 542, 503 and 495 nm) upon infiltration into random media fabricated by Ag nanowires of different aspect ratio (hence, surface plasmon resonances at 426, 445 and 464 nm). The blue shift is due to the fast dynamic surface-enhanced fluorescence mechanism and can be tuned by controlling the surface plasmon resonance and hotspot density in random media. Enhanced emission at desired wavelength is achieved by using nanostructures having higher extinction coefficient but same-surface plasmon resonance. Ag nanostructures of different aspect ratio used for fabricating the random media are synthesized by chemical route.     

Effects of various LED light wavelengths and light intensity supply strategies on synthetic high-strength wastewater purification by Chlorella vulgaris

Chemical fertilizer agricultural wastewater is a typical high-strength wastewater that has dramatically triggered numerous environmental problems in China. The Chlorella vulgaris microalgae biological wastewater treatment system used in this study can effectively decontaminate the high-strength carbon and nitrogen wastewater under an optimum light wavelength and light intensity supply strategy. The descending order of both the dry weight for C. vulgaris reproduction and wastewater nutrient removal efficiency is red > white > yellow > purple > blue > green, which indicates that red light is the optimum light wavelength. Furthermore, rather than constant light, optimal light intensity is used for the incremental light intensity strategy. The phases for the optimal light intensity supply strategy are as follows: Phase 1 from 0 to 48 h at 800 μmol m^?2 s^?1; Phase 2 from 48 to 96 h at 1,200 μmol m^?2 s^?1; and Phase 3 from 96 to 144 h at 1,600 μmol m^?2 s^?1. Additionally, the optimal cultivation time is 144 h.     

Efficient Unidirectional Launching of Surface Plasmons by Multi-Groove Structures

Efficiency is an important criterion in developing a practical surface-plasmon-polariton (SPP) unidirectional launcher. In this paper, we show that multi-groove structures can efficiently launch SPPs by numerically optimizing structural parameters and normal incident light. Experimentally, a high efficiency of 58.4 % is demonstrated in a six-groove structure with a lateral dimension of 3.9 μm. For a three-groove structure with even smaller lateral dimension of 1.35 μm, the efficiency presents a broadband response, which remains higher than 42 % from 720 to 860 nm. The proposed multi-groove structures with high SPP launching efficiency and small size exhibit potential in highly integrated plasmonic circuits.     

The effect of varying LED light sources and influent carbon/nitrogen ratios on treatment of synthetic sanitary sewage using Chlorella vulgaris

Sanitary sewage can create serious environmental problems if discharged directly into natural waters without appropriate treatment. This study showed that red light is the optimum light wavelength for growing microalgae Chlorella vulgaris in microalgae biological wastewater treatment systems, given a harvest time of 144 h. Only moderate light intensities (1,000, 1,500, 2,000, and 2,500 μmol m^?2 s^?1) were able to remove nutrients from synthetic sanitary sewage, but higher light intensity led to better nutrient removal effects. Because of economic considerations, the optimum light intensity range for efficient nutrient removal was determined to be between 1,500 and 2,000 μmol m^?2 s^?1. Furthermore, nutrient removal efficiency was significantly affected by light wavelength, light intensity, the interaction of these two factors, and the interaction among light wavelength, light intensity, and influent carbon/nitrogen (C/N) ratios. Total nitrogen and total phosphorus removal efficiency was also significantly affected by influent C/N ratios. Appropriate control of carbon and nitrogen source concentrations enabled optimal nutrient removal. The optimal influent C/N ratio was determined to be 6:1.     

Infrared Plasmonic Transmission Resonances of Gold Film with Hexagonally Ordered Hole Arrays on ZnSe Substrate

The high fractional open area of metal thin film coatings, with two dimensional, hexagonally ordered, close packed arrays of holes, makes them of interest for the incorporation of plasmonic effects into a variety of optical devices. Gold films with hexagonal patterns of circular holes have been created on ZnSe infrared windows. The films have 2.50 μm diameter holes and a hexagonal lattice parameter of 3.06 μm which places the primary transmission resonances of the ZnSe/gold interface at ~1,400 cm^?1 (7.14 μm) and that of the air/gold interface at ~3,800 cm^?1 (2.63 μm). This geometry produces useful transmission across the whole traditional mid-infrared range. The dispersion of these resonances has been measured by changing the angle of incident light. The data is modeled with explicit momentum matching equations in two different, high symmetry geometries, allowing the effective index of refraction to vary with wavelength. The response of these resonances to the addition of an acetaldehyde coating is described.     

Characterisation and simulation of an active microvalve for glaucoma

Glaucoma drainage device (GDD) has the potential to eliminate hypotony but still suffers from poor flow control and fibrosis. The ideal shunt should change its hydraulic resistance to achieve the desired intraocular pressure (IOP). In this study, the characterisation of a preliminary design of a new GDD is presented. This is activated by means of a diaphragm, which is actuated by conducting polymers. The valve can be manufactured employing microelectromechanical system technology by soft lithography. The characterisation process is performed by numerical simulation using the finite element method, considering the coupling between the fluid and the structure (diaphragm) obtaining the hydraulic resistance for several positions of the diaphragm. To analyse the hydraulic system of the microvalve implanted in a human eye, an equivalent circuit model was used. The parameters of the equivalent circuit model were obtained from numerical simulation. The hydraulic resistance of the designed GDD varies in the range of 13.08–0.36 mmHg min/μl compared with 3.38–0.43 mmHg min/μl for the Ahmed valve. The maximum displacement of the diaphragm in the vertical direction is 18.9 μm, and the strain in the plane is 2%. The proposed preliminary design allows to control the IOP by varying the hydraulic resistance in a greater range than the existing passive valves, and the numerical simulation facilitates the characterisation and the improvement of the design before its construction, reducing time and costs.     

Investigating the Characteristics of a Double Circular Ring Resonators Slow Light Device Based on the Plasmonics-Induced Transparency Coupled with Metal-Dielectric-Metal Waveguide System

We have numerically investigated an analog of electromagnetically induced transparency (EIT) in a metal-dielectric-metal (MDM) waveguide bend. The geometry consists of two asymmetrical stubs extending parallel to an arm of a straight MDM waveguide bend. Finite-difference time-domain simulations show that a transparent window is located at 1550 nm, which is the phenomenon of plasmonic-induced transparency (PIT). Signal wavelength is assumed to be 820 nm. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. Multiple-peak plasmon-induced transparency can be realized by cascading multiple cavities with different lengths and suitable cavity-cavity separations. Large group index up to 73 can be obtained at the PIT window. Our proposed configuration may thus be applied to storing and stopping light in plasmonic waveguide bends. In addition, the relationship between the transmission characteristics and the geometric parameters including the radius of the nano-ring, the coupling distance, and the deviation length between the stub and the nano-ring is studied in a step further. The velocity of the plasmonic mode can be largely slowed down while propagating along the MDM bends. For indirect coupling, formation of transparency window is determined by resonance detuning, but, evolution of transparency is mainly attributed to the change of the coupling distance. Theoretical results may provide a guideline for control of light in highly integrated optical circuits. The characteristics of our plasmonic system indicate a significant potential application in integrated optical circuits such as optical storage, ultrafast plasmonic switch, highly performance filter, and slow light devices.     

Laboratory Study Comparing Pharmacopeial Testing of Nebulizers with Evaluation Based on Nephele Mixing Inlet Methodology

Determination of fine droplet dose with preparations for nebulization, currently deemed to be the metric most indicative of lung deposition and thus in vivo responses, involves combining two procedures following practice as described in the United States Pharmacopeia and the European Pharmacopeia. Delivered dose (DD) is established by simulating tidal breathing at the nebulizer, collecting the medication on a filter downstream of the nebulizer mouthpiece/facemask. Fine droplet fraction (FDF_<x μm) is determined separately using a cooled cascade impactor operated at 15 L/min. FDD_<x μm is subsequently calculated as the product of DD and FDF_<x μm. Development of the Nephele mixing inlet has allowed cascade impactor-based assessments to be made at a constant flow rate while simultaneously subjecting the nebulizer to the continuously varying flow profile associated with breath simulation. The study purpose was to investigate the feasibility of this approach, termed mixing inlet lung simulation (MILS), for direct determination of FDD_<x μm. An optimal upper size limit for FDF is not given for nebulizers, but 5 μm was chosen since this limit is the European norm when testing other inhalation products. Vibrating membrane nebulizers (eFlow® Rapid) were used to deliver aqueous salbutamol sulfate, simulating an adult tidal-breathing pattern (inspiratory to expiratory ratio = 1:1, tidal volume = 500 mL, 15 breaths per minute, peak inspiratory flow rate = 24 L/min). The two procedures were inequivalent, as FDD_<5 μm by the MILS approach was 72% of that obtained using the compendial “combination” method. Since the MILS methodology more closely mimics clinical use, we infer that the compendial approach likely overestimates the dose reaching the human lung.     

Tunable Surface Plasmon Resonance Sensor Based on Photonic Crystal Fiber Filled with Gold Nanoshells

We present a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor, whose operating wavelength range is tunable. Gold nanoshells, consisting of silica cores coated with thin gold shells, are designed to be the functional material of the sensor because of their attractive optical properties. It is demonstrated that the resonant wavelength of the sensor can be precisely tuned in a broad range, 660 nm to 3.1 μm, across the visible and near-infrared regions of the spectrum by varying the diameter of the core and the thickness of the shell. Furthermore, the effects of structural parameters of the sensor on the sensing properties are systematically analyzed and discussed based on the numerical simulations. It is observed that a high spectral sensitivity of 4111.4 nm/RIU with the resolution of 2.45 × 10^?5 RIU can be achieved in the sensing range of 1.33–1.38. These features make the sensor of great importance for a wide range of applications, especially in biosensing.     

Somatic embryogenesis in banana (Musa acuminata AAA cv. Grand Naine): effect of explant and culture conditions

An improved, rapid, reproducible, and simple protocol has been developed for somatic embryogenesis in banana cv. ‘Grand Naine’ using explants derived from actively growing multiple shoot cultures. Many restrictive factors remain in banana embryogenesis such as long duration, unpredictability, and a high degree of genotype dependence. In the present study, we used split shoot tips from 4-wk-old cultures as explants. Somatic embryos were induced in 15 d directly in Murashige and Skoog (MS) medium supplemented with different combinations of 0–8.28 μM picloram and 0.22–4.44 μM 6-benzylaminopurine (BA) without callus formation. Maximum embryo induction (100%) occurred when 4.14 μM picloram and 0.22 μM BA were used. Conversion of somatic embryos into plantlets occurred sporadically (2–3%) in MS medium containing α-naphthalene acetic acid (NAA; 0.53–2.68 μM) together with BA (2.22–44.39 μM), or thidiazuron (4.54 μM) plus glutamine (200 mg/L). This protocol is far superior to those already reported for fast and high frequency induction of somatic embryo. In liquid agitated culture, individual embryos separated easily and produced a large number of secondary embryos within 10 d which, upon transfer to filter paper overlaid on MS liquid medium supplemented with 4.44 μM BA, resulted in conversion (3%) into plantlets.     

Coupled-Resonator-Induced Fano Resonances for Plasmonic Sensing with Ultra-High Figure of Merits

Fano resonances are numerically predicted in an ultracompact plasmonic structure, comprising a metal-isolator-metal (MIM) waveguide side-coupled with two identical stub resonators. This phenomenon can be well explained by the analytic model and the relative phase analysis based on the scattering matrix theory. In sensing applications, the sensitivity of the proposed structure is about 1.1?×?10³ nm/RIU and its figure of merit is as high as 2?×?10⁵ at λ?=?980 nm, which is due to the sharp asymmetric Fano line-shape with an ultra-low transmittance at this wavelength. This plasmonic structure with such high figure of merits and footprints of only about 0.2 μm² may find important applications in the on-chip nano-sensors.     

High-speed sensing of microliter-order whole-blood viscosity using laser-induced capillary wave

The present paper introduces an innovative contact-free optical viscosity measurement technique, laser-induced capillary wave (LiCW) using pulsed YAG laser as a heating source, to measure whole-blood viscosity with only a microliter-order sample volume and measurement time on the millisecond order. In this method, interfering pulsed laser beams heat a whole-blood sample and generate a capillary wave, the amplitude of which is less than 10 nm with wavelength of 80–100 μm in the present experiment, caused by a spatially sinusoidal temperature distribution. The damped oscillation of the capillary wave, which is detected by a diffracted probing laser beam at the heated area, provides information regarding the viscosity and surface tension of the whole blood. To demonstrate the validity of the present laser-induced capillary wave viscometer, the viscosity of human whole blood taken from two healthy donors having different hematocrit values was measured using 90 μl sample volumes at 37°C. To consider the feasibility of the present technique for blood rheological studies, we discuss the characteristics of LiCW regarding the non-Newtonian behavior of blood, the velocity boundary layer, the existence of a free surface, and the temperature increase of the blood, and also demonstrate the capability of the method to sense the temporal evolution of blood viscosity with sampling frequency of 0.25 Hz.     

A Plasmonic Wavelength-Selected Intersection Structure

A subwavelength intersection structure with wavelength filtering functionality is proposed by using an open loop which consists of four slot cavities and four metal-insulator-metal (MIM) drop waveguides. The slot cavities are used as the resonators while the MIM waveguides serve as the input/output ports. The SPPs propagations and the transmission wavelengths in two pairs of matched input/output ports are immune to each other, which satisfy the intersection characters. The results based on finite difference time domain (FDTD) method demonstrate that high transmittance for the expected output port and high isolation for other ports have been achieved. Specifically, the transmittance and isolation is larger than 0.64 and 14 dB, respectively. In addition, a transmission peak, whose wavelength can be modulated by adjusting the length of the slot cavities, is available for the output port. Such a device can find applications in various optical systems, such as the wavelength filtering area and the optical intersection area.     

Analysis of polyamines in biological samples by HPLC involving pre-column derivatization with o-phthalaldehyde and N-acetyl-l-cysteine

Polyamines (putrescine, spermine and spermidine) play a crucial role in the regulation of cell growth, differentiation, death and function. Accurate measurement of these substances is essential for studying their metabolism in cells. This protocol describes detailed procedures for sample preparation and HPLC analysis of polyamines and related molecules (e.g., agmatine and cadaverine) in biological samples. The method is optimized for the deproteinization of samples, including biological fluids (e.g., 10 μl), plant and animal tissues (e.g., 50 mg), and isolated/cultured cells (e.g., 1 × 10⁶ cells). The in-line reaction of polyamines with o-phthalaldehyde and N-acetyl-l-cysteine yields fluorescent derivatives which are separated on a reversed-phase C₁₈ column and detected by a fluorometer at an excitation wavelength of 340 nm and an emission wavelength of 450 nm. The total running time for each sample (including column regeneration on the automated system) is 30 min. The detection limit is 0.5 nmol/ml or 0.1 nmol/mg tissue in biological samples. The assays are linear between 1 and 50 μM for each of the polyamines. The accuracy (the nearness of an experimental value to the true value) and precision (agreement between replicate measurement) of the HPLC method are 2.5–4.2 % and 0.5–1.4 %, respectively, for biological samples, depending on polyamine concentrations and sample type. Our HPLC method is highly sensitive, specific, accurate, easily automated, and capable for the analysis of samples with different characteristics and small volume/amount, and provides a useful research tool for studying the biochemistry, physiology, and pharmacology of polyamines and related substances.