A 16×1 wavelength division multiplexer with integrateddistributed Bragg reflector lasers and electroabsorption modulators

The integrated operation of a 16×1 wavelength-division-multiplexed (WDM) source with distributed Bragg reflector (DBR) lasers and electroabsorption modulators has been demonstrated. By using repeated holographic exposures and wet chemical etching, 16 different wavelengths from 1.544 to 1.553 μm with an average channel spacing of 6 Å are obtained. A high-performance combiner is used to obtain a very uniform coupling into the single-output waveguide, and with the integration of an optical amplifier an average optical power of -8 dBm per channel is coupled into a single-mode fiber     

On the effect of floorplanning on the yield of large areaintegrated circuits

Until recently, VLSI designers rarely considered yield issues when selecting a floorplan for a newly designed chip. This paper demonstrates that for large area VLSI chips, especially those that incorporate some fault tolerance, changes in the floorplan can affect the projected yield. We study several general floorplan structures, make some specific recommendations, and apply them to actual VLSI chips. We conclude that the floorplan of a chip can affect its projected yield in a nonnegligible way, for chips with or without fault-tolerance     

Measurement of the stimulated carrier lifetime in semiconductor optical amplifiers by four-wave mixing of polarized ASE noise

We present a simple experiment aimed at measuring the stimulated carrier lifetime in semiconductor optical amplifiers (SOA's). The technique relies on polarization-resolved nearly degenerate four-wave mixing (FWM) of a laser source with an amplified spontaneous emission (ASE) noise source. The method can quickly characterize the bandwidth performance of active layers for application in a cross-gain or cross-phase wavelength converter.     

Benzodiazepine use in pregnancy and major malformations or oral cleft: meta-analysis of cohort and case-control studies

OBJECTIVE: To determine if exposure to benzodiazepines during the first trimester of pregnancy increases risk of major malformations or cleft lip or palate. DESIGN: Meta-analysis. SETTING: Studies from 1966 to present. SUBJECTS: Studies were located with Medline, Embase, Reprotox, and from references of textbooks, reviews, and included articles. Included studies were original, concurrently controlled studies in any language. INTERVENTIONS: Data extraction and quality assessment were done independently and in duplicate. MAIN OUTCOME MEASURES: Maternal exposure to benzodiazepines in at least the first trimester; incidence of major malformations or oral cleft alone, measured as odds ratios and 95% confidence intervals with a random effects model. RESULTS: Of over 1400 studies reviewed, 74 were retrieved and 23 included. In the analysis of cohort studies fetal exposure to benzodiazepine was not associated with major malformations (odds ratio 0.90; 95% confidence interval 0.61 to 1. 35) or oral cleft (1.19; 0.34 to 4.15). Analysis of case-control studies showed an association between exposure to benzodiazepines and development of major malformations (3.01; 1.32 to 6.84) or oral cleft alone (1.79; 1.13 to 2.82). CONCLUSIONS: Pooled data from cohort studies showed no association between fetal exposure to benzodiazepines and the risk of major malformations or oral cleft. On the basis of pooled data from case-control studies, however, there was a significant increased risk for major malformations or oral cleft alone. Until more research is reported, level 2 ultrasonography should be used to rule out visible forms of cleft lip.     

Optoelectronic properties of InGaAs/InGaAsP multiple-quantum-wellwaveguide detectors

The performance of InGaAs/InGaAsP multiple-quantum-well material as the absorbing medium in waveguide detectors is discussed. No deleterious saturation effects were observed up to an absorbed power of ~1 mW, with strong enough absorption for a four-well separate confinement heterostructure to provide ⩾80% quantum efficiency for lengths at least as short as 114 μm. The frequency response up to 5 GHz shows only a simple parasitic-limited rolloff which matches the measured impedance. These results provide sound evidence that the carrier trapping problem in this quantum-well material combination is much less serious than that in other material systems. This has important consequences not only for quantum-well field effect optical devices, but also for photonic integration, since the same quantum-well layers can simultaneously serve as a gain medium and as a detecting medium     

Topological fisheye views for visualizing large graphs

Graph drawing is a basic visualization tool that works well for graphs having up to hundreds of nodes and edges. At greater scale, data density and occlusion problems often negate its effectiveness. Conventional pan-and-zoom, multiscale, and geometric fisheye views are not fully satisfactory solutions to this problem. As an alternative, we propose a topological zooming method. It precomputes a hierarchy of coarsened graphs that are combined on-the-fly into renderings, with the level of detail dependent on distance from one or more foci. A related geometric distortion method yields constant information density displays from these renderings.     

Miniature Mach-Zehnder InGaAsP quantum well waveguideinterferometers for 1.3 μm

Electrooptic Mach-Zehnder interferometers with active lengths as small as 350 μm are discussed. These strip-loaded waveguide devices utilize the electrooptic effect in InGaAsP/InP quantum wells to achieve pi phase shift with single arm drive voltages of 12 V and 6 V drive in push-pull operation     

The onset of coherence collapse in DBR lasers

A study of the dependence of the onset of coherence collapse on laser output power is discussed. Three-section multiquantum-well-distributed-Bragg-reflector (MQW-DBR) lasers were used. The fraction of light reflected back into the lasing mode was varied, and the point at which the transition to coherence collapse occurred was measured. This feedback level varies approximately linearly with laser output power. For these lasers, when the output power is 1 mW, the transition to coherence collapse begins when the optical feedback into the lasing mode is below -40 dBm; when the feedback power is -35 dBm, the laser line is completely collapsed     

The Detection of Parallel Reactions by the Temperature-Jump Method

When a reaction of the type A ? 2B (I) is accompanied by a parallel, autocatalytic reaction A + B ? 3B (II), the expression for the reciprocal relaxation time contains one concentration-independent term, derived from reaction (I) in the forward direction, and two terms linear in [B], one derived from reaction (I) in the reverse direction, and one derived from reaction (II) in the forward direction (in addition to a quadratic term). In such a case, the equilibrium constant for the reaction cannot be determined from relaxation experiments. It is suggested that the experimental results obtained in the acid hydrolysis of the dichromate ion can be explained on this basis.