Novel algorithm for Clos-type networks

A new routing algorithm for controlling nonblocking Clos-type permutation networks is presented. Unlike previous algorithms based on matrix decomposition and looping techniques, the algorithm uses a new method called scheduling, does not use iterations, and has execution time 0(Nr/sup 1/2/) where N is the total number of ports, and r is the number of first-stage switches.<>     

Inside Vertical-Cavity Surface-Emitting Lasers: Extracting the Refractive Index From Spatial-Spectral Mode Images

We present a method to extract the internal effective refractive index of a vertical-cavity surface-emitting laser (VCSEL) from its transverse mode images. High spatial and spectral resolution mode images of an oxide-guided VCSEL were obtained using an etalon filter and an imaging spectrometer. The refractive index and the oxide radius were extracted from the field intensity distribution and the spectral wavelength of the laser modes. The procedure was repeated at two different currents and both gave a refractive index step of 0.046 plusmn 0.006 with a 14.1-mum oxide diameter. With several degrees of freedom for error available in the refractive index extraction, this method may be extended to ion-implanted, photonic crystal, and noncircular devices     

Effects of ultra‐high flux and intensity distribution in multi‐junction solar cells

We report results of high‐flux experiments on tandem solar cells, with a real‐sun probe predicated on mini‐dish fiber‐optic concentrators. Experimental results and their interpretation focus on: (a) a striking insensitivity of cell efficiency to flux map; (b) the predictability of the flux values at which cell efficiency peaks; and (c) performance of the same cell architecture at markedly smaller cell area. Copyright © 2006 John Wiley & Sons, Ltd.     

Liquid–Liquid Diffusion‐Assisted Crystallization: A Fast and Versatile Approach Toward High Quality Mixed Quantum Dot‐Salt Crystals

Here, a new, fast, and versatile method for the incorporation of colloidal quantum dots (QDs) into ionic matrices enabled by liquid–liquid diffusion is demonstrated. QDs bear a huge potential for numerous applications thanks to their unique chemical and physical properties. However, stability and processability are essential for their successful use in these applications. Incorporating QDs into a tight and chemically robust ionic matrix is one possible approach to increase both their stability and processability. With the proposed liquid–liquid diffusion‐assisted crystallization (LLDC), substantially accelerated ionic crystallization of the QDs is shown, reducing the crystallization time needed by one order of magnitude. This fast process allows to incorporate even the less stable colloids including initially oil‐based ligand‐exchanged QDs into salt matrices. Furthermore, in a modified two‐step approach, the seed‐mediated LLDC provides the ability to incorporate oil‐based QDs directly into ionic matrices without a prior phase transfer. Finally, making use of their processability, a proof‐of‐concept white light emitting diode with LLDC‐based mixed QD‐salt films as an excellent color‐conversion layer is demonstrated. These findings suggest that the LLDC offers a robust, adaptable, and rapid technique for obtaining high quality QD‐salts.     

Strain relief in epitaxial HgCdTe by growth on a reticulated substrate

In nearly all cases when an epitaxial layer of HgCdTe is grown on a CdZnTe substrate, there will be a finite lattice mismatch due to the lack of precise control over the ZnTe mole fraction. This leads to strains in the layer, which can be manifested in one or more ways: (1) as misfit dislocations near the interface, (2) as threading dislocations, (3) as surface topographical textures, and (4) as cross-hatch lines seen by x-ray topography. We have found that much of the strain can be relieved by growing on a reticulated substrate. Specifically, when the substrate has been etched to form mesas prior to growth of the layer, the resulting layer on the tops of the mesas shows evidence of significantly reduced strain. CdZnTe substrates oriented (111)A were prepared with two sets of mesas on 125 μm centers and 60 μm centers, and with other planar areas remaining for comparison. From a Hg melt, a layer of LWIR HgCdTe was grown about 16 μm thick on each substrate. Nomarski microscopy showed that the layers on the mesa tops were extremely flat, showing no sign of curvature or surface texture. X-ray topography showed no cross hatch on the mesa tops, while the usual cross hatch appeared in the planar regions. The LPE layer extended laterally beyond the edges of the original mesa because of faster growth in non-(111) directions. Samples were cleaved and examined in cross section. The linear density of etch pits seen in the cross section near the substrate, which represent misfit dislocations, was three times lower in the layer on the mesas than in the layer in the unpatterned region, although both regions have the same layer/substrate lattice mismatch. When an epilayer is grown on an unpatterned wafer (the conventional approach), the growth in any small region is confined laterally by the growing layer in the neighboring regions. However, when growth occurs on a reticulated surface, the lateral confinement is removed, providing strain relief and fewer defects.     

A substrate-dependent CAD model for ceramic multilayer capacitors

In this paper, a substrate-dependent lumped-element model for ceramic multilayer capacitors is presented. The height and dielectric constant of a substrate have a significant impact on the frequency response of a chip capacitor, and these effects cannot be treated independently from the capacitor model. Rather, the equivalent-circuit parameters in the model must be made to vary in accordance with changes in the substrate. The model presented in this paper is suitable for microstrip-mounted components, and has been applied up to 10 GHz for values from 0.5 pF to 0.47 μF, and for FR-4 substrates ranging in height from 5 to 62 mil. The modeling and extraction procedure is demonstrated for 0805- and 1206-style capacitors