Search

A waveguide grating coupler based on a silicon nitride overlay at 1.55 [micro]m for TE polarization is designed with no experimental demonstration. Its coupling efficiency for a fiber is 76%, the 1 dB bandwidth is 75 nm, and the coupling angle is 10[degrees]. The effects of different device parameters on the coupling performance for the grating coupler are discussed. The coupling efficiency of our grating coupler is almost equal, yet the 1 dB spectral bandwidth is around 25 nm broader, as compared with the grating coupler design based on a poly-silicon overlay. The coupling performance of our coupling device could still be further improved. The grating coupler presented in this paper is applicable to the optical coupling in nanophotonic integrated circuits. OCIS codes: 130.0130, 050.0050.

A novel cyanide analyzer based on sensitive cobinamide chemistry relies on simultaneous reagent and sample injection and detection in a 50 cm liquid core waveguide (LCW) flow cell illuminated by a white light emitting diode. 0The transmitted light is read by a fiber-optic charge coupled device (CCD) spectrometer. Alkaline cobinamide (orange, [lambda].sub.max] = 510 nm) changes to violet ([[lambda].sub.max]] = 583 nm) upon reaction with cyanide. Multiwavelength detection permits built-in correction for artifact responses intrinsic to a single-line flow injection system and corrects for drift. With optimum choice of the reaction medium, flow rate, and mixing coil length, the limit of detection (LOD, S/N = 3) is 30 nM and the linear dynamic range extends to 10 [micro]M. The response base width for 1% carryover is this can be corrected for. We demonstrate applicability by analyzing the hydrolytic cyanide extract of apple and pear seeds with orange seeds as control and also measure HCN in breath air samples. Spike recoveries in these sample extracts ranged from 91 to 108%. 10.1021/ac101158d

Switchable waveguiding is investigated in two liquid-crystal-filled photonic crystal fibers with a solid core using the nematic liquid-crystal mixture E7 under planar and homeotropic anchoring conditions. Addressing experiments using ac voltages show polarization-dependent and -independent effects with response times down to a few ms. It is shown that the attenuation spectra of the two liquid-crystal-filled photonic crystal fibers can be changed dramatically by just varying the boundary conditions. Electromagnetic field simulations are presented, which are in good agreement with the experimental findings. OCIS codes: 060.5295, 260.1440, 230.3990, 230.7370, 160.3710, 060.2270.

We report a novel system to analyze atmospheric nitrophenols (NPs). Pain or air sample extracts (1 mL) are pre-concentrated on a narrow bore (2 mm) aliphatic anion exchanger. In the absence of strong retention of NPs exhibited by aromatic ion exchangers, retained NPs are eluted as a plug by injection of 100 [micro]L of 0.1 M [Na.sub.2]S[O.sub.4] on to a short (2 x 50 mm) reverse phase C-18 column packed with 2.2 [micro]m particles. The salt plug passes through the C-18 column unretained while the NPs are separated by an ammonium acetate buffered methanol--water eluent, compatible with mass spectrometry (MS). The eluted NPs are measured with a long path Teflon AF-based liquid core waveguide (0.15 x 1420 mm) illuminated by a 403 nm light emitting diode and detected by a monolithic photodiode-operational amplifier. The waveguide is rendered chemically active by suspending it over concentrated ammonia that permeates into the lumen. The NPs ionize to the yellow anion form ([[lambda].sub.max] ~ 400 nm). The separation of 4-nitrophenol, 2,4-dinitrophenol, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenol, and 2-nitrophenol (these are the dominant NPs, typically in that order, in both rain and air of Houston and Arlington, TX, confirmed by tandem MS) takes just over 5 min with respective S/N = 3 limits of detection (LODs) of 60, 12, 30, 67, and 23 pg/mL compared to MS/MS LODs of 20, 49, 11, 20, and 210 pg/mL. Illustrative air and rain data are presented. 10.1021/ac101015y

We demonstrate the use of both optical extinction and phase measurements for probing the interactions between DNA and small molecules by dual polarization interferometry. On binding to DNA at the interface, mitoxantrone (MTX) and methylene blue (MB) induced reversible concentration-dependent optical extinction due to light absorption, which clearly revealed the association end dissociation of small molecules with DNA in real time. The binding constants of MTX--DNA and MB--DNA determined from the masses derived from optical extinction are 1.8 x [10.sup.5] and 4.2 x [10.sup.4] [M.sup.-1], respectively, and shown to be buffer salt concentration-dependent. Apart from optical extinction, phase measurements reflected the overall change of the interaction; namely, a combined result of the binding of small molecules and any changes in DNA structure. The masses derived from phase could be very different from those derived from optical extinction. The structural changes detected by phase measurements showed a contraction and densification of DNA upon intercalation by MTX or MB. The combination of optical extinction and phase measurements allows a detailed understanding of the interaction process. 10.1021/ac9027164

This paper reports a fully integrated hand-held photometer based on the liquid-core waveguide (LCW) detection principle for nanoliter-scale samples. All components of the photometer including fight-emitting diode (LED) light source, LCW flow cell, photodiode detector, dropper pump, electronic circuit, liquid-crystal display screen, and battery were fully integrated into a small-sized (12 x 4.5 x 2.1 cm) instrument. A bent optical coupler was developed to conduct the detection light into or out of the LCW flow cell through its sidewall. This design allowed the sampling probe, input and output optical couplers, and LCW flow cell to be integrated in a single Teflon AF capillary, which significantly simplified system structure, improved working reliability, and reduced sample consumption. Two UV--LEDs were used as light source in the photometer to achieve dual wavelength detection at 260 and 280 nm, which was applied to assess on-site the quality and quantity of DNA samples. The effective optical path length of the photometer was ~15 mm with a sample consumption of only 350 nL. The potential of the photometer applied in point of care testing was also demonstrated in the measurement of total cholesterol in serum samples. 10.1021/ac100257z

We analyzed and experimentally tested a metal--dielectric composite waveguide structure. After coating the surface of the metal layer in the Kretschmann attenuated total internal reflection configuration with a dielectric layer, we explain the coupling of incident light into the coated layer. After finding the dispersion relationships for the layered media including the metal--dielectric composite waveguide, we can determine a solution for its existance in a complex domain. By inscribing a periodic grating structure in the dielectric layer of the metal--dielectric composite waveguide, we experimentally verify the coupling of incident light on the metal--dielectric composite waveguide structure and propose its application for use as a wavelength-band selection filter. OCIS codes: 240.6680, 230.7400, 230.7408.

No single biomarker can accurately predict disease. An ideal biodetection technology should be capable of the quantitative, reproducible, and sensitive detection of a limited suite of such molecules. To this end, we have developed a multiplex biomarker assay for protective antigen and lethal factor of the Bacillus anthracis lethal toxin using semiconductor quantum dots as the fluorescence reporters on our waveguide-based biosensor platform. The platform is extendable to a wide array of biomarkers, facilitating rapid, quantitative, sensitive, and multiplex detection, better than achievable by conventional immunoassay. Our assay allows for the sensitive (limit of detection 1 pM each), specific (minimal nonspecific binding), and rapid (15 min) detection of these biomarkers in complex biological samples (e.g., serum). To address the issue of reproducibility in measurement and to increase our sample throughput, we have incorporated multichannel waveguides capable of simultaneous multiplex detection of biomarkers in three samples in quadruplicate. In this paper, we present the design, fabrication, and development of multichannel waveguides for the simultaneous detection of lethal factor and protective antigen in serum. Evaluation of the multichannel waveguide shows an excellent concordance with single-channel data and effective, simultaneous, and reproducible measurement of lethal toxins in three samples. 10.1021/ac901497g

Metallic nanoscale structures are capable of supporting surface plasmon polaritons (SPPs), propagating collective electron oscillations with tight spatial confinement at the metal surface. SPPs represent one of the most promising structures to beat the diffraction limit imposed by conventional dielectric optics. Ag nanowires have drawn increasing research attention due to 2D sub-100 nm mode confinement and lower losses as compared with fabricated metal structures. However, rational and versatile integration of Ag nanowires with other active and passive optical components, as well as Ag nanowire based optical routing networks, has yet to be achieved. Here, we demonstrate that SPPs can be excited simply by contacting a silver nanowire with a Sn[O.sub.2] nanoribbon that serves both as an unpolarized light source and a dielectric waveguide. The efficient coupling makes it possible to measure the propagation-distance-dependent waveguide spectra and frequency-dependent propagation length on a single Ag nanowire. Furthermore, we have demonstrated prototypical photonic-plasmonic routing devices, which are essential for incorporating low-loss Ag nanowire waveguides as practical components into high-capacity photonic circuits. waveguides | subwavelength | Ag nanowires | Sn[O.sub.2] nanoribbons | propagation length doi/10.1073/pnas.0902064106

A fundamental formulation of plasmonic nanolasers from Fermi's Golden rule is developed by considering the inhomogeneity and dispersion of the cavity media. A Fabry-Perot nanolaser based on the plasmonic slab waveguide is used as an example and the studies have shown that the power confinement is inappropriate for plasmonic cavity modes.

A mask programmable technology to implement RF and microwave integrated circuits using an array of standard 90-nm CMOS transistors is presented. Using this technology, three wideband amplifiers with more than 15-dB forward transmission gain operating in different frequency bands inside a 4-22-GHz range are implemented. The amplifiers achieve high gain-bandwidth products (79-96 GHz) despite their standard multistage designs. These amplifiers are based on an identical transistor array interconnected with application specific coplanar waveguide (CPW) transmission lines and on-chip capacitors and resistors. CPW lines are implemented using a one-metal-layer post-processing technology over a thick Parylene-N (15 [micro]m) dielectric layer that enables very low loss lines (~0.6 dB/mm at 20 GHz) and high-performance CMOS amplifiers. The proposed integration approach has the potential for implementing cost-efficient and high-performance RF and microwave circuits with a short turnaround time. Index Terms--Amplifiers, coplanar waveguide (CPW), gain-bandwidth product, mask programmable technology, Parylene-N, Si CMOS, transmission line, wideband circuits.

A reconfigurable miniaturized-element frequency-selective surface (FSS) is presented in this paper. A standard wave-guide measurement setup is used to evaluate the performance of the design. The proposed FSS consists of two periodic arrays of metallic loops, with the same periodicity, on either side of a very thin dielectric substrate. The tuning of the reconfigurable surface is shown numerically to be possible by incorporating tuning varactors into the structure. Using varactors on both layers, a reconfigurable frequency response is achieved, which has two modes of operation: bandstop and bandpass. In addition to two completely different modes of operation, the center frequency, as well as the bandwidth of the response can be tuned independently. Frequency tunability with a constant bandwidth over 3-3.5 GHz is shown. A bandwidth tuning at a fixed center frequency is also demonstrated. Simulation results are verified experimentally by fabricating prototypes of the design at S-band loaded with lumped capacitors. To demonstrate the tunability, different pairs of fixed-valued capacitors, as opposed to varactors, are used in a waveguide measurement setup to avoid difficulties associated with biasing varactors in the waveguide. Index Terms--Electronic tuning, miniaturized-element frequency-selective surface (FSS), reconfigurable.

This paper presents a modified [theta]-scanning technique for first/third-order probes for spherical near-field antenna measurements. Unlike the traditional [theta]-scanning technique, this new scanning technique gives a possibility, due to the cutoff property of the azimuthal spherical modes, to filter out the influence of the undesired third-order azimuthal modes of the probe near the poles of the measurement sphere. Without increasing the measurement time, the technique allows reducing the errors caused by the application of the computationally efficient first-order probe correction technique (incorrectly) to first/third-order probes. The technique is optimal for spherical near-field systems, that employ, for example, an open-ended rectangular (or square) waveguide probe, that closely approximates a first/third-order probe, and apply the well-known first-order probe correction technique. In such systems, compared to the traditional [theta]-scanning technique, the modified [theta]-scanning technique can be used to significantly reduce the errors caused by the incomplete probe correction. Index Terms--Antenna measurements.

We study cross-slot waveguides for polarization diversity schemes that simultaneously offer strong confinement in the slot region for both TE and TM polarizations. A symmetric configuration is initially presented to demonstrate that the same strong confinement and propagation constants can be obtained for both polarizations and slot thicknesses down to 50 nm. To make easier further realization of these waveguides, an asymmetric waveguide configuration with a vertical slot height of up to 120 nm is proposed. The waveguide parameters are then optimized taking into account a 220 nm silicon thickness. Our simulation results show that no beating issues between TE and TM modes is observed for beating lengths under 6.68 [micro]m, thus opening the way to efficient implementations of polarization diversity approaches. OCIS codes: 130.2790, 130.3120, 230.7370.

This paper describes the design of embedded-grating [n.sup.+]-i-[n.sup.+] traveling-wave photodetectors (TWPDs). In the ideal case of perfect electrically matched photodetectors, the TWPD bandwidth is determined by the velocity mismatch between the group velocity of the optical beam and the phase velocity of the electrical photogenerated signal, as well as by the attenuation of the RF signal propagating along the electrodes. Since the group velocity is determined once the layer's thickness is selected, which, in turn, is optimized for coupling the light into the photodetector, only an accurate electrode design allows for the velocity matching. In this paper, we propose a new structure that utilizes a grating integrated within a single-mode waveguide in order to tailor the optical group velocity and match it to the phase velocity of the photogenerated signal. Index Terms--Bandwidth, grating, photodiode, semiconductor device, traveling-wave photodetector (TWPD).

We present a photonic-crystal (PC) channel-drop filter (CDF) design based on 3 x 3 PC ring resonators. The normalized transmission spectra for single-ring and dual-ring configurations have been investigated using two-dimensional finite-difference time-domain (FDTD) technique in a square-lattice dielectric-rod PC structure. First, we investigate a single ring and we show that backward and forward dropping is possible in the third communication window. Then we add another ring and waveguide to develop a new CDF. This filter consists of an input and three outputs. Our FDTD simulation yields more than 85% efficiency over each output port. OCIS codes: 230.5298, 230.3120.

Coupling the high specificity of the immunoanalytical reaction with the high sensitivity of optical waveguide light-mode spectroscopy (OWLS) detection gives the possibility to develop immunosensors with in most cases a definitely lower detection limit than traditionally used immunoassays. Measurements were performed on the sensitized surface of optical waveguide grating coupler sensors (2400 lines/mm grating). The OWLS technique is based on the precise measurement of the resonance angle of a polarized laser light (632.8 nm), diffracted by a grating and incoupled into a thin waveguide. The effective refractive index, determined from the resonance incoupling angle detected at high accuracy, allows determination of layer thickness and coverage (or mass) of the adsorbed or bound material with ultrahigh sensitivity. OWLS immunosensors were developed as label-free immunosensors with an amino group modified Si[O.sub.2]-Ti[O.sub.2] sensor surface on which the immunoreactants could be anchored. One of the components of the antibody-antigen complex was chemically bound on the sensor surface, allowing noncompetitive or competitive detection of the analytes. To illustrate that the resulting immunosensors are suitable for the determination of small and large molecular weight analytes, OWLS sensor formats were applied for quantitative detection of a herbicide active ingredient trifluralin, a Fusarium mycotoxin zear-alenone, and an egg yolk protein of key importance in endocrine regulation, vitellogenin. OCIS codes: 120.4820, 130.2755, 130.6010, 230.7370, 280.4788, 350.2770.

A 30-mm-long multimode waveguide, 40 [micro]m wide and 40 [micro]m high, is fabricated on a silicon wafer using polymer SU-8 as the core and liquid buffer as the cladding. Antibodies are successfully immobilized on the SU-8 surface designated for binding target antigens dispersed in the buffer solution. Evanescent-wave spectroscopy is performed by exciting the fluorescently labeled antigens, bound to the waveguide surface within its evanescence field, and measuring the emission light intensity. This evanescent-wave biosensor detects specific molecular interaction. The optical output as a function of the antigen concentration can be described by Langmuir equation. Antigen concentration as low as 1.5 [micro]g/mL is detected; concentrations higher than 100 [micro]g/mL lead to sensor saturation. [2008-0058] Index Terms--Antibody immobilization, biomolecule binding, evanescent wave, SU-8 waveguide.

We point out an important fundamental limitation associated with the dielectric ribbon waveguide described by Yeh et al. [Appl. Opt. 44, 5937 (2005)], which would restrict its practical use in ultrahigh- or terahertz-speed guided-wave applications, contrary to their underlying prediction, and we additionally point out a noteworthy inaccuracy in their introductory discussion. OCIS codes: 230.7390, 320.5390, 350.4010, 320.5550, 350.5500.

Low-attenuation waveguides based on the propagation of long-range surface plasmon polaritons (LRSPPs) along thin Au stripes embedded in low absorption perfluorocyclobutane (PFCB) polymer are presented. A new low in propagation loss of OCIS codes: 230.7390, 240.6680, 310.6860, 160.5470.

A subwavelength corrugated metal wavegnide is studied and designed to slow down the light at terahertz frequencies. The waveguide consists of two parallel thin metal slabs with periodic corrugations on their inner boundaries. Compared with structures based on engineered surface plasmons, the proposed structure has smaller group velocity dispersion and lower propagation loss. The origin of the slow wave is also explained. OCIS codes: 260.3910, 230.7370, 040.2235, 230.4555.

This paper describes the development of a high-power, coherent radar system at W-band and discusses potential applications of radars with this new capability. Previous radars in this frequency band were limited by available power-amplifier technology to about 500 W of average power; WARLOC radar represents an increase in power, by 20 times, over previous coherent radars at 94 GHz. This performance improvement is possible due to the development of a gyroklystron amplifier specifically for this and future radars in this frequency band. The gyroklystron amplifier tubes deliver 100 kW peak power and 10 kW of average power at a center frequency of approximately 94 GHz. Other novel features of this radar include the use of highly overmoded waveguides and rotary joints for the transmission of power from the final power amplifier (FPA) to the antenna, and a high-power quasi-optical duplexer. The system uses a relatively large 1.8 m diameter (580-wavelength) Cassegrain antenna, which required the development of an antenna with an rms surface accuracy of 0.0025 in, to obtain long-range detection and identification of small objects. Test data show an antenna gain of 62.5 dB, confirming that the needed surface accuracy was achieved. Two mobile shelters house the radar system, permitting relocation to various test sites. WARLOC is presently operational at the Naval Research Laboratory's Chesapeake Bay Detachment facility, Maryland. It is being employed in radar imaging of airborne and surface objects, and in the scientific study of propagation effects and atmospheric physics phenomena.

Supramolecular conformation and molecular orientation was monitored during supported lipid bilayer (SLB) formation using dual polarization interferometry (DPI). DPI was shown to enable real time sensitive determination of birefringence of the lipid bilayer together with thickness or refractive index (with the other a fixed value). This approach removes differences in mass loading due to anisotropy, so the mass becomes solely a function of the lipid dn/dc value. DPI measurements show highly reproducible qualitative and quantitative results for adsorption of liposomes of different lipid compositions and in buffers with or without Ca[Cl.sub.2]. The packing of solvent-free self-assembled SLBs is shown to differ from other preparation methods. Birefringence analysis accompanied by mass and thickness measurements shows characteristic features of vesicle adsorption and SLB formation kinetics previously not demonstrated by evanescent optical techniques, including indications of percolation-type rupture of clusters of liposomes on the surface and correlated adsorption kinetics induced by liposome charge repulsion. Our study demonstrates that understanding of mechanistic details for an adsorption process for which conformational changes and ordering occur can be elucidated using DPI and greatly enhanced by modeling of optical birefringence. The data is in some respects more detailed than what can be obtained with conventional biosensing techniques like surface plasmon resonance and complementary to methods such as the quartz crystal microbalance.

The characteristics of directional couplers and power splitters based on three-guide optical couplers in slot waveguide structures are analyzed in detail by a three-dimensional full-vectorial beam propagation method. The numerical results show the achievement of a compact three-guide directional coupler operating as polarization independent with a length of 58.0 [micro]m and having almost evenly spaced propagation constants of the three lowest order modes for quasi-TE and quasi-TM modes. Thus, a high coupling efficiency from one outside waveguide to the other outside waveguide is demonstrated and is over 99.5% for both polarization states. For a three-guide power splitter, multiple sets of waveguide parameters for achieving polarization-independent operation are presented. Tolerances to operating wavelength and structural parameters are also analyzed, and the evolution of the injected field along the propagation distance through the proposed devices is demonstrated. OCIS codes: 130.3120, 230.7380, 130.2790, 250.5300.