Eitan Abraham

Spatiotemporal chaos in broad-area semiconductor lasers

We study the space–time dynamical behavior of broad-area semiconductor lasers, using an extended phenomenological laser model to include transverse diffraction of the counterpropagating optical fields and transverse diffusion of carriers. Numerical results show that the profile of the output intensity exhibits spatiotemporal chaos by way of changing random filaments. A small confinement factor and/or linewidth enhancement factor can prevent instabilities. Simulations also confirm experimental results showing that a half-symmetric unstable resonator with a suitable mirror curvature restores stability.

Failure mechanisms of legacy aircraft wiring and interconnects

This paper presents a comprehensive list of the causes and modes of failure and ageing in legacy aircraft wiring and interconnects. Taxonomies of the electrical, mechanical, chemical and thermal stresses that contribute to the various stages of ageing and/or failure are presented. A failure modes effects and analysis (FMEA) is conducted to categorize the most serious failures. The order of severity in the FMEA is backed up by maintenance data gathered by the Royal Air Force (RAF) base Brize Norton during routine inspection.

Nonlinear optical properties of multilayer graphene in the infrared

A negative value for the nonlinear refraction in graphene is experimentally observed and unambiguously verified by performing a theoretical analysis arising from the conductivity of the graphene monolayer. The nonlinear optical properties of multi-layer graphene are experimentally studied by employing the Z-scan technique. The measurements are carried out at 1150, 1550, 1900 and 2400 nm with a 100-femtosecond laser source. Under laser illumination the multi-layer graphene exhibits a transmittance increase due to saturable absorption, followed by optical limiting due to two-photon absorption. The saturation irradiance Isat and the two-photon absorption coefficient β are measured in the operating wavelength range. Furthermore, an irradiance-dependent nonlinear refraction is observed and discriminated from the conventional nonlinear refraction coefficient n2, which is not irradiance dependent. The values obtained for the irradiance-dependent nonlinear refraction are in the order of ∼10-9 cm2W-1, approximately 8 orders of magnitude larger than any bulk dielectrics.

Critical interpixel separation in nonlinear interference filters

We work out the minimum interpixel separation for independent operation of as many as nine bistable devices forming a two-dimensional array on the same interference filter. This distance diverges as the holding power approaches the switch-up point of the single element and rapidly increases with the number of pixels. In a uniform area of 4 cm(2) approximately 50 pixels would operate independently with holding powers 15% off the single-element threshold.

Simulation of the electrohydrodynamic instability process used in the fabrication of hierarchic and hollow micro/nanostructures

This article demonstrates that the electrohydrodynamic patterning process, a novel technique for the manufacturing of micro- and nano-scale structures, also allows the one-step realization of hierarchical structures and hollow structures. Through numerical simulation, it is shown that multilevel structures can be obtained if process time and applied electric voltage are optimized. As an example, the growth of structures with a width of around 187 nm and depth of 95 nm has been successfully simulated alongside structures with width of around 0.4 μm and depth of 0.8 μm. The width of the protrusive mask patterns is shown to determine whether hollow structures with single or multiple shapes can be formed using electric field assisted capillarity. The numerical simulation process effectively demonstrates that the realization of micro/nano-structures with hierarchic and multilevel shapes can be considered as an innovative manufacturing process for MEMS or micro/nanofluidic structures.

Regenerative pulsations in an InSb bistable etalon

Abstract Observations are presented of regenerative pulsation in an InSb etalon using a cw CO laser. The pulsations are consistent with competition between thermal and electronic nonlinearities and are governed by thermal time constants which are analysed. The role of noise in the system is also discussed.

Modelling of cross talk in 2-D bistable arrays with carrier diffusion

Abstract We present results for a two-dimensional model of arrays of optically bistable elements. We find that coupling is short-ranged and we show through a heuristic argument that only nearest-neighbour interaction occurs. This result is in marked constrast with the long range coupling between elements in nonlinear interference filters. We also compare a previously studied one-dimensional model for linear arrays with our results. It turns out that the 1-D model overstimates the coupling viz-a-viz the 2-D one in linear arrays but gives comparable results to those for square arrays.

A model for pixellation of nonlinear interference filters

We present a theoretical model for the effect of material pixellation on the operating characteristics of optical logic elements using nonlinear interference filters. From our calculations we predict pixel packing densities of 250×250 per cm2 (an increase of three orders of magnitude over optical pixellation) and power levels of 100 μW. We define a figure of merit which describes the effects of pixellation of thermo‐optic logic elements. We also show numerically the effect on cooling rate.

Cross talk in nonlinear interference filters: loop narrowing and critical slowing down

We study theoretically static and dynamic effects of cross talk between two bistable elements in the same interference filter. The nonlinearity is assumed to be thermal. In the steady state we find that an element in the ON state causes a thermal detuning in another in the OFF state, thereby decreasing its threshold power and narrowing its bistable region. We discuss various ON/OFF combinations in terms of interpixel separation. Starting with two elements in the OFF state, transients are studied by switching one of them with a pulse while the other one remains unaddressed. As the separation approaches a critical value from below, the switching time of the second element diverges. We interpret this effect as critical slowing down. Extension of these results to any array is also discussed.

Fabrication and Characterization of a Low-Cost, Wafer-Scale Radial Microchannel Cooling Plate

The modeling, simulation, fabrication, and testing of a microchannel cooling plate for microelectronic packaging applications are described in this paper. The cooling component uses forced convection of gas injected inside 128 microchannels of 100-mu m width and 70-mu m height. The nickel-based plate is fabricated on a glass substrate using a two-layer electroforming process using UV-LIGA technology. The thermal behavior of the microchannel cooling device is investigated by using the measurement of partial thermal resistances through the use of the structure functions method. Heat transfer coefficient values of 300 W/m2 K have been measured for a nitrogen flow rate of 120 l/h.