Horizontal Slot Research Articles

Hydrodynamic characteristics of double permeable breakwater under regular waves

The wave transmission, reflection, and energy dissipation of the double vertical wall with permeable lower part (horizontal slots) were experimentally and theoretically studied under normal regular waves. The effect of different wave and structural parameters on the hydrodynamic characteristics was investigated e.g. the wave length, the upper part drafts, the lower part porosities, and the space between the double walls. Also, the theoretical model based on an EigenFunction Expansion Method was developed to study the hydrodynamic breakwater performance. In order to examine the validity of the theoretical model, the theoretical results were compared with the present experimental results. Comparison between experiments and predictions showed that theoretical model provides a good estimate to the wave transmission, reflection, and energy dissipation coefficients when the friction factor f = 3. The hydrodynamic efficiency of the proposed breakwater is strongly affected by changing the following: (1) The two upper part drafts together, (2) The upper part draft of the first barrier, (3) The two lower part porosities together, (4) The lower part porosity of the first barrier.

Effects of supply air temperature and inlet location on particle dispersion in displacement ventilation rooms

The effects of supply temperature and vertical location of inlet air on particle dispersion in a displacement ventilated (DV) room were numerically modeled with validation by experimental data from the literature. The results indicate that the temperature and vertical location of inlet supply air did not greatly affect the air distribution in the upper parts of a DV room, but could significantly influence the airflow pattern in the lower parts of the room, thus affecting the indoor air quality with contaminant sources located at the lower level, such as particles from working activities in an office. The numerical results also show that the inlet location would slightly influence the relative ventilation efficiency for the same air supply volume, but particle concentration in the breathing zone would be slightly lower with a low horizontal wall slot than a rectangular diffuser. Comparison of the results for two different supply temperatures in a DV room shows that, although lower supply temperature means less incoming air volume, since the indoor flow is mainly driven by buoyancy, lower supply temperature air could more efficiently remove passive sources (such as particles released from work activities in an office). However, in the breathing zone it gives higher concentration as compared to higher supply air temperature. To obtain good indoor air quality, low supply air temperature should be avoided because concentration in the breathing zone has a stronger and more direct impact on human health.

Silicon-based horizontal nanoplasmonic slot waveguides for on-chip integration

Horizontal metal/insulator/Si/insulator/metal nanoplasmonic slot waveguide (PWG), which is inserted in a conventional Si wire waveguide, is fabricated using the standard Si-CMOS technology. A thin insulator between the metal and the Si core plays a key role: it not only increases the propagation distance as the theoretical prediction, but also prevents metal diffusion and/or metal-Si reaction. Cu-PWGs with the Si core width of ~134-21 nm and ~12-nm-thick SiO2 on each side exhibit a relatively low propagation loss of ~0.37-0.63 dB/µm around the telecommunication wavelength of 1550 nm, which is ~2.6 times smaller than the Al-counterparts. A simple tapered coupler can provide an effective coupling between the PWG and the conventional Si wire waveguide. The coupling efficiency as high as ~0.1-0.4 dB per facet is measured. The PWG allows a sharp bending. The pure bending loss of a Cu-PWG direct 90° bend is measured to be ~0.6-1.0 dB. These results indicate the potential for seamless integration of various functional nanoplasmonic devices in existing Si electronic photonic integrated circuits (Si-EPICs).

Soret-driven convection and separation of binary mixtures in a porous horizontal slot submitted to a heat flux

The onset of Soret-driven convection in a shallow porous horizontal layer filled with a binary mixture and submitted to a vertical heat flux on the two horizontal walls is investigated. We study the species separation between the two vertical ends of the cell, which appears for low values of the Rayleigh number and for positive separation ratio. An analytical solution is performed and the separation is expressed in terms of thermal Rayleigh number, Lewis number, separation ratio and aspect ratio of the cell. These analytical results are corroborated by direct non-linear numerical simulations. Then, the results are compared with those obtained in a differentially heated vertical cavity.

Radiation field computation of leaky coaxial cables by finite-difference time domain in cylindrical coordinates and equivalent source integration

A combined scheme involving a conventional perfectly matched layer and lossy material is proposed for absorbing both the radiating and evanescent waves of leaky coaxial cables (LCX) efficiently. After parameter optimisation and correctness verification, the combined absorbing boundary is used to calculate the near field of LCX with horizontal triangle slots. The radiation field is then obtained by integrating the near field on an equivalent surface surrounding the cable. The LCX with horizontal triangle slots is desired to have advantages in generating smoother field distribution around the cable, especially for the vertical component.

Polarization properties of two-dimensional slot waveguides

We propose and study slot waveguide geometries where both quasi-TE and quasi-TM modes may propagate highly confined within the same low-index slot region. Conventional horizontal and vertical slot waveguides can only provide high slot confinement for either the quasi-TM or quasi-TE modes, respectively. Different two-dimensional slot waveguide structures are analyzed in terms of their mode characteristics, such as the effective index, the confinement factor, and the overlap of quasi-TE and -TM modes within the slot. Attention is also paid to practical manufacturability. Various waveguide structures can be tailored to have zero birefringence or equal confinement at both polarizations. Values for the confinement factors and the overlap of the two polarizations, in the slot region, can reach 0.4 to 0.5.

High performance nanophotonic circuits based on partially buried horizontal slot waveguides

We present a novel platform to construct high-performance nanophotonic devices in low refractive index dielectric films at telecoms wavelengths. The formation of horizontal slots by PECVD deposition of high index amorphous silicon provides a convenient and low-cost way to tailor nanophotonic devices to application needs. Low propagation loss of less than 2 dB/cm is obtained allowing us to fabricate optical resonators with measured high optical quality factors exceeding 10(5). We design and experimentally demonstrate on-chip grating couplers to efficiently couple light into integrated circuitry with coupling loss of 4 dB and optical bandwidth exceeding 110 nm. The entire on-chip circuitry consisting of input/output couplers, Mach-Zehnder interferometers with high extinction ratio and ring, racetrack resonators are designed, fabricated and characterized.

Numerical Study of Supersonic Combustion Processes with Central Strut Injection

The combustion chamber is shown in Fig. 1. It has a rectangular cross section with width w 40 mm and constant isolator height h 35:4 mm. Downstream distance, x, is measured from the Laval nozzle throat where x 0. Air enters the chamber from the left at a Mach number of M 2:1 at isolator entry. The combustor and diverging sections open at angles 1 1 and 2 2 , respectively. The outflow static pressure is p1 0:96 bar. The facility operates continuously at stagnation conditions T0;air 1400 K and p0;air 4 bar. For brevity, in the following, wall pressures in the symmetry plane are only shown for the upper wall. Our injector is shown in Fig. 1b. Chun et al. [1] provide further details about the facility and Gerlinger et al. [2,3] provide further details on the injector. Because of exploitation of symmetry, only half the channel width is modeled. H2 is injected through the horizontal slots (see Fig. 1b). At design conditions, the injection Mach number is MH2 2:6. However, in practice, this is probably not achieved, due to geometric deformation. As a conservative estimate we chose MH2 1:0. The validity of this choice is checked in Sec. V.E. Four combustion modes, i.e., blowoff, weak combustion, strong combustion, and thermal choking were observed. Because of flow overexpansion, all modes feature a shock train in proximity of the channel outflow. Another shock train develops in the isolator, due to injector displacement effects. In flight, strong combustion is desired. Here, the injector acts as the flame holder and heat release is high. For weak combustion the fuel–air mixture is ignited in the outflow shock train. The flame is detached from the injector and heat release is significantly lower. If, in these conditions, the exit pressure is lowered sufficiently, the outflow shock train disappears, and combustion ceases (blowoff). For excessive fuel injection, the flow becomes thermally choked. The combustion mode is determined by the geometry, stagnation conditions, ambient pressure, and the global equivalence ratio (see also Scheuermann et al. [4]).

Adiabatic embedment of nanomechanical resonators in photonic microring cavities

We report a circuit cavity optomechanical system in which a nanomechanical resonator is adiabatically embedded inside an optical ring resonator with ultralow transition loss. The nanomechanical device forms part of the top layer of a horizontal silicon slot ring resonator, which enables dispersive coupling to the dielectric substrate via a tapered nanogap. Our measurements show nearly uncompromised optical quality factors (Q) after the release of mechanical beam.

Dual rf-optical slot waveguide for ultrabroadband modulation with a subvolt Vπ

In this letter, we propose a high speed and ultralow driving voltage traveling wave electro-optic (EO) modulator based on a dual horizontal slot waveguide. The proposed design harnesses the unique properties of ferroelectric materials such as LiNBO3 and exotic, organic EO polymers to tightly confine both the optical and rf modes in a nanoscale slot maximizing the nonlinear interaction with the electric field. Larger electrode separation allows for significant reduction in rf propagation loss. Simulations of the half-wavelength voltage-length product and electro-optic response of the proposed device reveal ultrabroadband operation, up to 250 GHz, and subvolt driving voltage for a 1 cm long modulator.

Hydraulic performance of vertical walls with horizontal slots used as breakwater

The hydrodynamic performance of a vertical wall with permeable lower part (horizontal slots) was experimentally and theoretically studied under normal regular waves. The effect of different wave and structural parameters was investigated e.g. the wave length, the upper part draft, and the lower part porosity. Also, the theoretical model based on an Eigen Function Expansion Method and a Least Square Technique was developed. In order to examine the validity of the theoretical model, the theoretical results were compared with the present experimental results and with the results obtained from different previous studies. Comparison between experiments and predictions showed that the theoretical model provides a good estimate of the wave transmission, reflection, and energy dissipation coefficients when the friction factor f = 5.5. In general, the tested model gives transmission coefficients less than 0.5 and reflection coefficients larger than 0.5 when the relative wave length h/ L is larger than 0.3, the relative upper part draft D/ h larger than 0.36, and lower part porosity ε less than 0.5. Also, the tested model dissipates about 50% of the incident wave energy when the relative wave length h/ L is in the range of 0.25 to 0.35.

Ultrafast All-Optical Switching in a Silicon-Nanocrystal-Based Silicon Slot Waveguide at Telecom Wavelengths

We demonstrate experimentally all-optical switching on a silicon chip at telecom wavelengths. The switching device comprises a compact ring resonator formed by horizontal silicon slot waveguides filled with highly nonlinear silicon nanocrystals in silica. When pumping at power levels about 100 mW using 10 ps pulses, more than 50% modulation depth is observed at the switch output. The switch performs about 1 order of magnitude faster than previous approaches on silicon and is fully fabricated using complementary metal oxide semiconductor technologies.

Experimental realization of subwavelength plasmonic slot waveguides on a silicon platform

We report the experimental realization of horizontal plasmonic slot waveguides capable of subdiffraction modal confinement at IR wavelengths. These waveguides have a propagation length of approximately 6 lambda(g) and are monolithically integrated with conventional silicon photonic waveguides on the same silicon-on-insulator platform. Direct coupling of light from the silicon waveguides to the plasmonic waveguides was achieved with an efficiency of 30% using taper-funnel couplers to obtain mode matching between the two waveguide systems.

NanoSi low loss horizontal slot waveguides coupled to high Q ring resonators

Si-based horizontal slot waveguides coupled to ring resonators have been fabricated and characterised. The central layer of the slot has been filled by Silicon nanocrystals (Si-nc) obtained by deposition of silicon rich silicon oxide and then thermal annealing. A comparison of various deposition and annealing parameters to form the Si-nc is performed. Propagation losses as low as 3 dB/cm and ring resonator quality factor of 30,000 have been achieved at 1550 nm.

Electromagnetic Analysis of Ring-Cavity-Assisted Amplified Spontaneous Emission in Er:SiO$_{2}$/a-Si Horizontal Slot Waveguides

In this paper, we present an electromagnetic analysis of ring-cavity-assisted amplified spontaneous emission in Er <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -doped SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (Er:SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ). A horizontal slot geometry, consisting of a low-index Er:SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer embedded between high-index a-Si layers, allows for a planar ring-cavity design which maintains high optical confinement in the active Er:SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> material. The simulations are performed within the auxiliary differential equation-finite-difference time-domain (ADE-FDTD) scheme which couples the quantum mechanical light emission and amplification behavior of the Er:SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> with the electromagnetic device behavior. We present the enhanced spontaneous emission in waveguide-coupled ring cavities with varying coupling gaps. We provide an analysis of the relationship between cavity quality factor, coupling coefficient, and enhanced spontaneous emission.

Nonlinearity of optimized silicon photonic slot waveguides

In this numerical study, we show that by exploiting the advantages of the horizontal silicon slot wave-guide structure the nonlinear interaction can be significantly increased compared to vertical slot waveguides. The deposition of a 20 nm thin optically nonlinear layer with low refractive index sandwiched between two silicon wires of 220 nm width and 205 nm height could enable a nonlinearity coefficient gamma of more than 2 x 10(7) W(-1)km(-1).

The Effect of Bead Vacuum on Slot Die Coating

Abstract The effect of bead vacuum on the minimum wet thickness obtained on horizontal and vertical slot die coatings was experimentally examined using a flow visualization technique. The commercial software package FLOW3D was used to simulate the two-dimensional coating flow. Macroscopic material balances were applied to estimate the effect of bead vacuum. Applying vacuum on the coating bead was found to reduce the minimum wet thickness and increase the maximum coating speed, with the effect on horizontal slot die coating being more pronounced. Visual observations revealed that with increasing vacuum, the upstream meniscus against the moving web was pulled back significantly for a low-viscosity solution, and the dynamic contact angle was reduced for a high-viscosity solution. The observed upstream wetting length for a low-viscosity solution subject to bead vacuum was consistent with the prediction using macroscopic balances. The sizes of coating beads predicted by FLOW3D were generally larger than those observed from flow visualization. Coating failures caused by high bead vacuum could be predicted with the aid of numerical simulations.

Anti‐Nogo‐A antibody treatment promotes recovery of manual dexterity after unilateral cervical lesion in adult primates – re‐examination and extension of behavioral data

In rodents and nonhuman primates subjected to spinal cord lesion, neutralizing the neurite growth inhibitor Nogo-A has been shown to promote regenerative axonal sprouting and functional recovery. The goal of the present report was to re-examine the data on the recovery of the primate manual dexterity using refined behavioral analyses and further statistical assessments, representing secondary outcome measures from the same manual dexterity test. Thirteen adult monkeys were studied; seven received an anti-Nogo-A antibody whereas a control antibody was infused into the other monkeys. Monkeys were trained to perform the modified Brinkman board task requiring opposition of index finger and thumb to grasp food pellets placed in vertically and horizontally oriented slots. Two parameters were quantified before and following spinal cord injury: (i) the standard ‘score’ as defined by the number of pellets retrieved within 30 s from the two types of slots; (ii) the newly introduced ‘contact time’ as defined by the duration of digit contact with the food pellet before successful retrieval. After lesion the hand was severely impaired in all monkeys; this was followed by progressive functional recovery. Remarkably, anti-Nogo-A antibody-treated monkeys recovered faster and significantly better than control antibody-treated monkeys, considering both the score for vertical and horizontal slots (Mann–Whitney test: P = 0.05 and 0.035, respectively) and the contact time (P = 0.008 and 0.005, respectively). Detailed analysis of the lesions excluded the possibility that this conclusion may have been caused by differences in lesion properties between the two groups of monkeys.

Slot waveguides with polycrystalline silicon for electrical injection

We demonstrate horizontal slot waveguides using high-index layers of polycrystalline and single crystalline silicon separated by a 10 nm layer of silicon dioxide. We measure waveguide propagation loss of 7 dB/cm and a ring resonator intrinsic quality factor of 83,000. The electric field of the optical mode is strongly enhanced in the low-index oxide layer, which can be used to induce a strong modal gain when an active material is embedded in the slot. Both high-index layers are made of electrically conductive silicon which can efficiently transport charge to the slot region. The incorporation of conductive silicon materials with high-Q slot waveguide cavities is a key step for realizing electrical tunneling devices such as electrically pumped silicon-based light sources.

Wafer-bonded single-crystal silicon slot waveguides and ring resonators

We fabricated horizontal Si slot waveguides with a 25 nm SiO2 slot layer by bonding thin Si-on-insulator wafers. After removing the Si substrate and buried oxide from one side of the bonded structure, grating-coupled waveguides and ring resonators were partially etched into the Si/SiO2/Si device layers. The gratings exhibit efficiencies of up to 23% at 1550 nm and the ring resonators were measured to have loaded quality factors near 42 000 for the lowest-order transverse-electric mode, corresponding to a propagation loss of 15 dB/cm. The leaky lowest-order transverse-magnetic mode was also observed with a propagation loss of 44 dB/cm.