Dispersion-engineered silicon nitride waveguides for mid-infrared supercontinuum generation covering the wavelength range 0.8-6.5 mu m

We numerically demonstrate the generation of a mid-infrared supercontinuum (SC) through the design of an on-chip complementary metal oxide semiconductor (CMOS) compatible 10-mm-long air-clad rectangular waveguide made using stoichiometric silicon nitride (Si 3 N 4 ) as the core and MgF 2 glass as its lower cladding. The proposed waveguide is optimized for pumping in both the anomalous and all-normal dispersion regimes. A number of waveguide geometries are optimized for pumping at 1.55 μ m with ultrashort pulses of 50-fs duration and a peak power of 5 kW. By initially keeping the thickness constant at 0.8 μ m, four different structures are engineered with varying widths between 3 μ m and 6 μ m. The largest SC spectral evolution covering a region of 0.8 μ m to beyond 6.5 μ m could be realized by a waveguide geometry with a width of 3 μ m. Numerical analysis shows that increasing width beyond 3 μ m by fixing thickness at 0.8 μ m results in a reduction of the SC extension in the long wavelength side. However, the SC spectrum can be enhanced beyond 6.5 μ m by increasing the waveguide thickness beyond 0.9 μ m with the same peak power and pump source. To the best of our knowledge, this is first time report of a broad SC spectral evolution through numerical demonstration in the mid-infrared region by the silicon nitride waveguide. In the case of all-normal dispersion pumping, a flatter SC spectra can be predicted with the same power and pump pulse but with a reduced bandwidth spanning 950–2100 nm

"On some definitions in matrix algebra"

Many definitions in matrix algebra are not standardized. This notediscusses some of thepitfalls associated with undesirable orwrong definitions, anddealswith central conceptslikesymmetry, orthogonality, square root, Hermitian and quadratic forms, and matrix derivatives.

Demonstration of fine pitch FCOB (Flip Chip on Board) assembly based on solder bumps at Fermilab

Bump bonding is a superior assembly alternative compared to conventional wire bond techniques. It offers a highly reliable connection with greatly reduced parasitic properties. The Flip Chip on Board (FCOB) procedure is an especially attractive packaging method for applications requiring a large number of connections at moderate pitch. This paper reports on the successful demonstration of FCOB assembly based on solder bumps down to 250um pitch using a SUESS MA8 flip chip bonder at Fermilab. The assembly procedure will be described, microscopic cross sections of the connections are shown, and first measurements on the contact resistance are presented.Comment: 4 pages, 8 figure

Ultra-broadband mid-infrared supercontinuum generation using chalcogenide rib waveguide

The ultrabroadband mid-infrared (MIR) supercontinuum (SC) generation using dispersion-tailored Ge11.5As24Se64.5 chalcogenide (ChG) glass rib-waveguide has been investigated numerically. An air-clad 1-cm-long rib-waveguide employing MgF2 glass for its lower cladding shows that an ultrabroadband MIR SC spanning from 1.8 to 8 μm and extending over more than 2 octave could be generated with a relatively low peak power of 0.5 kW pumped at a wavelength of 3.1 μm. Our estimated bandwidth is the largest reported so far for SC generated using ChG rib-waveguide pumped at a wavelength of 3.1 μm with a low peak power of 0.5 kW. We carry out simulations by varying peak power ranges between 0.1 and 3 kW. Our analysis through rigorous numerical simulations show that SC can be extended further into the MIR up to 10 μm using the same pump pulses with a relatively modest peak power of 3 kW

Estimating the amount of vorticity generated by cosmological perturbations in the early universe

We estimate the amount of vorticity generated at second order in cosmological perturbation theory from the coupling between first order energy density and non-adiabatic pressure, or entropy, perturbations. Assuming power law input spectra for the source terms, and working in a radiation background, we calculate the wave number dependence of the vorticity power spectrum and its amplitude. We show that the vorticity generated by this mechanism is non-negligible on small scales, and hence should be taken into consideration in current and future CMB experiments.Comment: 9 pages, revtex4, 1 figure; v2: typos and minor error corrected, result unchange

SIMILARITY AND NONSIMILARITY SOLUTIONS ON FLOW AND HEAT TRANSFER OVER A WEDGE WITH POWER LAW STREAM CONDITION

The similarity and non-similarity analysis are presented to investigate the effect of buoyancy force on the steady flow and heat transfer of fluid past a heated wedge. The fluid is assumed to be a Newtonian, viscous and incompressible. The wall of the wedge is an impermeable with power law free stream velocity and a wall temperature. Due to the effect of a buoyancy force, a power law of free stream velocity and wall temperature, then the flow field is similar when n = 2m - 1, otherwise is non-similar when n ≠ 2m - 1. The governing boundary layer equations are written into dimensionless forms of ordinary differential equations by means of Falkner-Skan transformation. The resulting ordinary differential equations are solved by Runge-Kutta Gill with shooting method for finding a skin friction and a rate of heat transfer. The effects of buoyancy force and non-uniform wall temperature parameters on the dimensionless velocity and temperature profiles are shown graphically. Comparisons with previously published works are performed and excellent agreement between the results is obtained. The conclusion is drawn that the flow field and temperature profiles are significantly influenced by these parameters

SIMILARITY AND NONSIMILARITY SOLUTIONS ON FLOW AND HEAT TRANSFER OVER A WEDGE WITH POWER LAW STREAM CONDITION

The similarity and non-similarity analysis are presented to investigate the effect of buoyancy force on the steady flow and heat transfer of fluid past a heated wedge. The fluid is assumed to be a Newtonian, viscous and incompressible. The wall of the wedge is an impermeable with power law free stream velocity and a wall temperature. Due to the effect of a buoyancy force, a power law of free stream velocity and wall temperature, then the flow field is similar when n = 2m - 1, otherwise is non-similar when n ≠ 2m - 1. The governing boundary layer equations are written into dimensionless forms of ordinary differential equations by means of Falkner-Skan transformation. The resulting ordinary differential equations are solved by Runge-Kutta Gill with shooting method for finding a skin friction and a rate of heat transfer. The effects of buoyancy force and non-uniform wall temperature parameters on the dimensionless velocity and temperature profiles are shown graphically. Comparisons with previously published works are performed and excellent agreement between the results is obtained. The conclusion is drawn that the flow field and temperature profiles are significantly influenced by these parameters

All-Normal Dispersion Chalcogenide PCF for Ultraflat Mid-Infrared Supercontinuum Generation

We numerically study the dispersion-engineered chalcogenide photonic crystal fiber (PCF), which allows us to generate ultraflat broadband supercontinuum (SC) spectra in all-normal dispersion regime. A 1-cm-long chalcogenide hexagonal PCF made using Ge11.5As24Se64.5 glass pumped at 1.55 μm produced an SC bandwidth 700 nm at a peak power of 1 kW. By shifting pump at 2 μm, SC spectra can be extended with a bandwidth of 1900 nm at the same peak power level. In both cases, nonuniform spectral power distribution observes over the entire output bandwidth owing to the lower dispersion slop on the long wavelength side of the dispersion curve. To spanning SC further in the mid-infrared as well as to reduce the spectral asymmetry, we optimize another design for pumping at 3.1 μm in such a way that the pump source can be employed vicinity to the peak of the dispersion curve. Employing the largest pump peak power up to 5 kW, SC can be extended up to 6 μm (1.5 octaves), and the power distribution among the spectral components over the entire SC bandwidth can be improved significantly by this design. To enhance the spectral flatness, we optimize a second PCF geometry by reducing its pitch length, and it is possible to obtain ultraflat coherent SC spanning from 2 to 5.5 μm (>1 octave) by this structure maintaining nearly symmetric power distribution between both side of its spectral components

All-Normal-Dispersion Chalcogenide Waveguides for Ultraflat Supercontinuum Generation in the Mid-Infrared Region

We show numerically, how a chalcogenide planar waveguide designed to exhibit normal dispersion over a wide spectral range around the pump wavelength can produce relatively flat supercontinuum in the mid-infrared regime. A 1-cm-long channel waveguide, made using Ge11.5As24Se64.5 glass and pumped at 1.55 gm using short optical pulses with only 25 W peak power, produced a supercontinuum that was nearly 600 nm wide. Employing the same pump source with a peak power of 100 W, the supercontinuum could be extended to beyond 2.2 gm with a bandwidth of 1000 nm. By shifting the pump wavelength to 3.1 gm and using pulses with peak powers of up to 3 kW, the resulting ultraflat supercontinuum extended from 2 to 5.5 gm. Even a wider spectral range (1.8-6 gm) can be realized if MgF2 glass is used for the lower cladding while maintaining power variations below 5 dB over the entire bandwidth

An experimental study of the dual-fuel performance of a small compression ignition diesel engine operating with three gaseous fuels

A dual-fuel engine is a compression ignition (CI) engine where the primary gaseous fuel source is premixed with air as it enters the combustion chamber. This homogenous mixture is ignited by a small quantity of diesel, the ‘pilot’, that is injected towards the end of the compression stroke. In the present study, a direct-injection CI engine, was fuelled with three different gaseous fuels: methane, propane, and butane. The engine performance at various gaseous concentrations was recorded at 1500 r/min and quarter, half, and three-quarters relative to full a load of 18.7 kW. In order to investigate the combustion performance, a novel three-zone heat release rate analysis was applied to the data. The resulting heat release rate data are used to aid understanding of the performance characteristics of the engine in dual-fuel mode. Data are presented for the heat release rates, effects of engine load and speed, brake specific energy consumption of the engine, and combustion phasing of the three different primary gaseous fuels. Methane permitted the maximum energy substitution, relative to diesel, and yielded the most significant reductions in CO2. However, propane also had significant reductions in CO2 but had an increased diffusional combustion stage which may lend itself to the modern high-speed direct-injection engine