Measurements of the Thermal Resistivity of InAlAs, InGaAs, and InAlAs/InGaAs Superlattices.

Thermal management efforts in nanoscale devices must consider both the thermal properties of the constituent materials and the interfaces connecting them. It is currently unclear whether alloy/alloy semiconductor superlattices such as InAlAs/InGaAs have lower thermal conductivities than their constituent alloys. We report measurements of the crossplane thermal resistivity of InAlAs/InGaAs superlattices at room temperature, showing that the superlattice resistivities are larger by a factor of 1.2-1.6 than that of the constituent bulk materials, depending on the strain state and composition. We show that the additional resistance present in these superlattices can be tuned by a factor of 2.5 by altering the lattice mismatch and thereby the phonon-mode mismatch at the interfaces, a principle that is commonly assumed for superlattices but has not been experimentally verified without adding new elements to the layers. We find that the additional resistance in superlattices does not increase significantly when the layer thickness is decreased from 4 to 2 nm. We also report measurements of 250-1000 nm thick films of undoped InGaAs and InAlAs lattice-matched to InP substrates, for there is no published thermal conductivity value for the latter, and we find it to be 2.24 ± 0.09 at 22 °C, which is ∼2.7 times smaller than the widely used estimates.

Simple design of an edge-emitting diode laser for preventing spatial multimoding via thermal lensing.

The parameters of a diode-laser structure composed of a pair of built-in high-index regions for providing stable, single-spatial-mode operation to high cw powers are numerically found. A three-dimensional numerical code has been implemented that takes into account carrier diffusion in the quantum well and thermal lensing. The laser characteristics are calculated as functions of the above-threshold drive level. Within the simulation, higher-order optical modes on a "frozen background" are computed via the Arnoldi algorithm. Then, for a 6-µm-wide low-index core and 2-3-mm-long devices, stable single-mode operation up to multiwatt-level (2-3 W) cw output power is predicted.

Confined modes in dual-state two-dimensional waveguides.

We consider the confined modes in dual-state two-dimensional waveguides in which each slab segment of waveguides can support two vertically confined modes with different effective indices. A matrix formulation is developed to extend the conventional effective-index method to investigate the two-dimensional confinement in multistate waveguides. The results are presented and discussed.

Nonlinear restrictions of Talbot-like spatial filters in semiconductor laser arrays.

We consider the operation of an active Talbot spatial filter in semiconductor laser arrays. High linearity of filtering can be achieved in lasers with separate driving systems for the array and filter regions by the use of a constant driving current in the filter region. If the regions are pumped equally, then lasers with high threshold current will show nonlinear light-current characteristics.

Optical properties of dual-state Fabry-Perot talons.

We consider the optical properties of dual-state Fabry-Perot étalons where both the cavity and the external media can support two eigenmodes with different refractive indices. A matrix formulation is developed to analyze resonant transmission of such étalons. The results are presented and discussed. In particular, the results can be employed to explain the resonances of phase-locked arrays of antiguides.

Ureaplasma urealyticum serotypes isolated from cases of female sterility.

Ureaplasma strains isolated from vagina, cervix, endometrium or urine of 45 infertile women (121 strains) and 54 fertile women (145 strains) were tested using the growth inhibition test with standard Ureaplasma sera (types 1 through 8). Serotypes 3, 4 and 6 were more frequently recovered. Predominance of serotype 3 (35.5% of cases) over serotype 6 (22.2% of cases) in the infertile group, and conversely, predominance of serotype 6 (33.3%) over serotype 3 (20.3%) in the fertile women were noted. Serotype 4 was present in 15.5% of infertile subjects and 14.8% of the fertile ones. Serotypes 1, 2, 7 and 8 were found in proportions ranging between 1.8 and 11.1% of the positive Ureaplasma subjects. Serotypes 5 was never isolated. The predominant frequency of serotype 3 in infertile women and of serotype 6 in fertile women was observed regardless of the samples from which the strains were isolated. The proportion of non-typable strains amounted to 1.6% of strains isolated from the infertile group and to 5.5% of those isolated from the fertile group. The authors suggest the utilization of the serotyping scheme with 8 serotypes (Black and Shepard) for epidemiological studies including the transmissibility of genital Ureaplasma infection.

Preferential chemical etching of blazed gratings in (110)-oriented GaAs.

Blazed gratings with a theoretical blaze angle of 35 degrees 16' are etched into (110) GaAs surfaces by preferential chemical etching, using a photoresist mask. A maximum total diffraction efficiency of 15% was measured at 6328 A from a blazed grating with a 2.23-microm period, and the diffracted light was concentrated in a single order. To demonstrate the applicability of such gratings in integrated optics, gratings with periods in a 3000- to 5000-A range were made, and epitaxial growth on (110) GaAs substrates was carried out using a method of growth that deposits high-quality, nearly defect-free layers on such substrates.

[Comparative study of 2 serological methods of diagnosis of acute respiratory Mycoplasma pneumoniae infections]. / Studiu comparativ a doua metode serologice de diagnostic în infectiile respiratorii acute cu Mycoplasma pneumoniae.

Complement fixation (CF) and haemagglutination (HAP) with M. pneumoniae antigen have proved valuable methods for the etiological diagnosis of acute respiratory infections. Both methods are sensitive and specific, provided purified antigens are used, of the Kenny and Grayston lipid antigen type for CF and the antigen treated by ultrasound and purified by centrifugation for HAP. Concomitant and repeated use of both tests is recommended, following the taking of paired serum samples at 7 to 10 day intervals the first samples being taken within the first ten days of the disease. A single test can only be used for a presumptive serologic diagnosis of acute infection with M. pneumoniae and only if the minimal diagnostic titre is taken into consideration, i.e. 1/64 for CF and 1/160 for HAP.