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.

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 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.

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.

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.

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.

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.

The Mach-Zehnder interferometer (MZI) is a common structure for integrated all-optical switches. We proposed and designed an all-optical 2 x 2 switch that is based on the MZI, multimode interference, and a nonlinear two-mode interference waveguide. The beam propagation method is used to simulate and analyze the device. The results show that the switching action is done properly. OCIS codes: 230.1150, 130.0130, 130.3120, 190.3270, 230.4320, 060.1810.

We analyze two basic aspects of a scanning near-field optical microscope (SNOM) probe's operation: (i) spot-size evolution of the electric field along the probe with and without a metal layer, and (ii) a modal analysis of the SNOM probe, particularly in close proximity to the aperture. A slab waveguide model is utilized to minimize the analytical complexity, yet provides useful quantitative results--including losses associated with the metal coating--which can then be used as design rules. OCIS codes: 060.2340, 060.2350, 110.0180, 170.5810.

The anisotropic dependence of the formation of one-dimensional (1-D) spatial dark solitons on the orientation of intensity gradients in lithium niobate crystal is numerically specified. Based on this, we propose an approach to fabricate channel waveguides by employing 1-D spatial dark solitons. By exposure of two 1-D dark solitons with different orientations, channel waveguides can be created. The structures of the channel waveguides can be tuned by adjustment of the widths of the solitons and/or the angles between the two exposures. A square channel waveguide is experimentally demonstrated in an iron-doped lithium niobate crystal by exposure of two orthogonal 1-D dark solitons in sequence. OCIS codes: 190.5330, 230.7380, 130.3730.

A coarse wavelength division multiplexer is designed on a silicon-on-insulator waveguide using the Mach-Zehnder interferometers with novel multimode interface-periodically segmented waveguide couplers and segmented waveguide arms. It is viable for metro and access applications, since it can be inexpensive and provide easy fabrication, compact size, and good output performance. As a design example, the channel spacing of the demultiplexer is chosen to be 24.5 nm for applications to the 10-Gigabit Ethernet. The simulation results show that the wide-passband demultiplexer can have insertion loss less than 2.3 dB and crosstalk better than 18 dB. OCIS codes: 130.0130, 130.2790, 130.3120, 060.4510.

A fiber optic system for water analysis with high transparency in the deep-UV region ([Lambda] [greater than or equal to] 190 nm) is presented. The system consists of special UV-improved silica fibers and a liquid-core waveguide (LCW) as an optical cell. The apertures of both light guides, the silica fiber and the LCW, are matched. The optical losses of the device are investigated experimentally and compared with theory, especially with a standard free-space geometry. The performance of the system with respect to UV absorption spectroscopy is demonstrated for nitrate and chlorine pollution in pure water. For a 203-mm-long LCW the detection limits have been determined to be as low as 22 [[micro]gram]/L for nitrate and 26 [[micro]gram]/L for chlorine.

Hollow cylindrical waveguide sensors permit conventional capillary injection techniques for flowing precise volumes of a liquid sample through the sensor while exciting and collecting fluorescence by use of evanescent fields. Both a ray-optics model and experimental data show that fluorescence collected from bulk or thin-layer fluorescent samples increases strongly as the numerical aperture (N.A.) increases and is maximized when the N.A. of the excitation-collection optics matches the waveguide N.A. The dependence of fluorescence on N.A. closely resembled that reported previously for solid cylindrical waveguides. Mode mixing reduced the strength of this dependence and should be minimized to increase collected fluorescence. Key words: Fluorescence sensors, hollow cylindrical waveguide, capillary.

High peak power transverse excitation atmospheric CO2 laser pulses are transmitted through flexible hollow sapphire waveguides with losses of 0.84 dB/m and no damage to the waveguides.

Gaussian beams have been widely used for propagating electromagnetic waves in free space and in certain other optical systems. It has been suggested that recurring forms of such beams might also be useful for propagation in planar or rectangular metal waveguides. Experimental verification of the recurrence of the Gaussian field distribution in metal waveguides is reported here. OCIS codes: 230.0230, 230.7370, 230.7390, 350.5500.

We demonstrate what we believe is the first application of the recently developed electrically pumped GaAs/A1GaAs quantum-cascade lasers in a spectroscopic gas-sensing system by use of hollow waveguides. Laser light with an emission maximum at 10.009 [micro]m is used to investigate the mid-infrared absorption of ethene at atmospheric pressure. We used a 434-mm-long silver-coated silica hollow waveguide as a sensing element, which served as a gas absorption cell. Different mixtures of helium and ethene with known concentrations are flushed through the waveguide while the laser radiation that passes through the waveguide is analyzed with a Fourier-transform infrared spectrometer. The experimentally obtained discrete ethene spectrum agrees well with the calculated spectrum. A detection threshold of 250 parts per million is achieved with the current setup. [C] 2000 Optical Society of America OCIS codes: 300.1030, 300.6260, 140.3600, 000.2107, 060.2370, 300.6390.

The confusion apparently stems from the fact that our paper [Appl. Opt. 44, 5937 (2005)] dealt with modulated pulses, modulated at terahertz frequency, while Mendis' paper [Appl. Opt. 47, 4231 (2008)] dealt with narrow-baseband pulses that may contain a very large (terahertz) spectral width. Therefore, the criticism given by Mendis is erroneous, since his analysis is for baseband pulses only. OCIS codes: 230.7370, 230.7390, 230.7400, 130.2790.