Double-active-layer index-guided InGaAsP-InP laser diode

A buried crescent InGaAsP-InP laser with two active layers was fabricated to study the temperature behavior of the double-carrier-confinement structure. An anomalously high characteristic temperature T₀ was measured, and optical switching behavior was observed. A mode analysis and numerical calculation using a rate equation approach explained qualitatively very well the experimental results. It was revealed that both the Auger recombination in this special double-active-layer configuration and the temperature-dependent leakage current, which leads to uniform carrier distribution in both active regions, are essential to increase T₀     

Automatic control of lesion size in a simulated model of the eye

A multiple-layer phantom consisting of a thin absorbing layer sandwiched between two nonabsorbing layers was created to simulate laser-induced thermal lesions in the eye. The nonabsorbing layers consisted of clear egg white, and the thin (20-40-μm) absorbing layer was created with black spray paint. Heat generated in the absorbing layer during 0.5-10-s argon irradiation was conducted to the adjacent egg white. Sufficient heat produced a region of coagulation that was graphically evidenced by the characteristic whiteness of cooked egg white. Light reflected from the lesion was monitored with a video camera and used as a feedback signal to control irradiation time. The laser irradiation was automatically ended when the diameter of the reflectance parameter related to coagulation thickness reached a preselected value     

Low threshold distributed Bragg reflector surface emitting laser diode with semiconductor air-bridge-supported top mirror

A surface emitting laser diode (SELD) with two distributed Bragg reflectors (DBR) and semiconductor multilayer air-bridge-supported top mirror is fabricated. A low threshold current of 1.5 mA is achieved under room temperature CW operation. The spectrum shows a strong peak at 891 nm with a FWHM of 10 AA. With light emission from the top Bragg reflector instead of from the back side of the substrate, laser arrays are easily formed with this novel structure.<>     

459 km, 2.4 Gbit/s four wavelength multiplexing optical fibre transmission experiment using six Er-doped fibre amplifiers

A 2.4 Gbit/s, four WDM optical fibre transmission experiment over 459 km using six Er-doped fibre amplifiers in the 1.55 mu m wavelength region is presented. The results confirm the possibility of WDM multiple optical amplifier repeater transmission systems.<>     

A single-power-supply 10-b video BiCMOS sample-and-hold IC

A +5-V single-power-supply 10-b video BiCMOS sample-and-hold IC is described. Video speed, low power, and 10-b accuracy sample-and-hold operation have been achieved using a complementary connected buffer format sample switch. A high-speed p-n-p transistor used in the sample switch is formed by a combination of n-p-n and PMOS transistors. The sample-and-hold operation is accomplished by feeding back the hold capacitor voltage to the sample switch inputs, so that the inputs transfer symmetrically for the hold capacitor voltage at any input level. The sample-and-hold IC has been implemented in 1.2-μm BiCMOS technology and evaluated. The following results have been obtained: 185-MHz 3-dB bandwidth at 22-pF hold capacitor, 63-dB signal-to-noise ratio at 8-MHz full-scale input, 20-ns acquisition time at 1-V step input, 15-ns switch setting time, and 0.1% linearity error. Power dissipation is 150 mW     

Top-surface-emitting GaAs four-quantum-well lasers emitting at 0.85 mu m

Room temperature CW and pulsed lasing of top-surface emitting, vertical-cavity, GaAs quantum-well lasers was achieved at approximately 845 nm. The active gain medium was four 100 AA thick GaAs quantum wells. The whole structure was grown by molecular beam epitaxy. Deep H/sup +/-ion implantation followed by annealing as used to control a vertical profile of resistivity for an efficient current injection at the active region. The threshold current was 2.2 mA for CW and pulsed operation using 10 mu m diameter lasers. Differential quantum efficiency was about 20%. Minimum threshold current density per quantum well of 360 A/cm/sup 2/ was obtained.<>     

Elimination of dislocations in heteroepitaxial MBE and RTCVD Ge x Si1-x grown on patterned Si substrates

We have grown Ge _x Si_1-x (0 <x < 0.20,1000–3000Å thick) on small growth areas etched in the Si substrate. Layers were grown using both molecular beam epitaxy (MBE) at 550° C and rapid thermal chemical vapor deposition (RTCVD) at 900° C. Electron beam induced current images (EBIC) (as well as defect etches and transmission electron microscopy) show that 2800Å-thick, MBE Ge_0.19Si_0.81 on 70-μm-wide mesas have zerothreading and nearly zero misfit dislocations. The Ge_0.19Si{0.81} grown on unpatterned, large areas is heavily dislocated. It is also evident from the images that heterogeneous nucleation of misfit dislocations is dominant in this composition range. 1000Å-thick, RTCVD Ge_0.14Si_0.86 films deposited on 70 μm-wide mesas are also nearly dislocation-free as shown by EBIC, whereas unpatterned areas are more heavily dislocated. Thus, despite the high growth temperatures, only heterogeneous nucleation of misfit dislocations occurs and patterning is still effective. Photoluminescence spectra from arrays of GeSi on Si mesas show that even when the interface dislocation density on the mesas is high, growth on small areas results in a lower dislocation density than growth on large areas.     

Crack formation in metallized single crystal silicon substrates

Ball bonding of metallized silicon substrates has been simulated by microindentation, with a hemispherical diamond indentor, of (100) silicon wafers that contained aluminum film layers. The indentation loads varied up to 35N and the thickest aluminum film, composed of four layers, was 100 × 10^-6 m. The radial cracks in the silicon, beneath the aluminum film, were measured as a function of indentation load and aluminum film thickness, and compared to that of unmetallized silicon. The crack lengths have been used to determine the fracture toughness,K _c = 24.4 ± 4.9 MPam^0.5, which is twice the value obtained by Vickers indentation experiments. A model describing the relationship between the film thickness versus the radial crack length is presented.     

Optimal excitation of multiapplicator systems for deep regionalhyperthermia

A method is proposed for determining the excitation amplitudes and phases of the elements of electromagnetic multiapplicator systems for optimizing the specific absorption rate (SAR) distribution around a deep-seated tumor. In this method, the ratio of the power dissipated in the tumor to a weighted summation of the powers supplied to the surrounding regions is optimized. The optimization procedure is combined with a recently proposed effective technique for analysis of various electromagnetic scattering and interaction problems. The general principle is applied to a two-dimensional problem of a piecewise homogeneous cylinder heated by an array of electric current filaments placed outside the cylinder. Numerical simulations are performed to check the effectiveness of the approach. The results demonstrate that using this optimization method, improved SAR distributions can be achieved. The extension to three-dimensional configurations is discussed.     

Multicategory classification of body surface potential maps

A statistical classification method is suggested for body surface potential maps (BSPM). The initial data reduction utilizes the Fourier expansion and time integration, resulting in physiological-oriented features. Based on Fischer's criterion, optimal discriminant vectors are used to map the features to an optimal subdomain. Experimental criteria determine the dimensionality of the subdomain and the number of features to be mapped into it. Classification is performed in two steps. In the first, a k-nearest neighbor (k-NN) rule is used for every two-category problem, the results of which are fed into a voting rule for final classification. The method is tested with 123 patients divided into four categories: normal (NR), ischemia (IS), myocardial infarction (MI), and left bundle branch block (LB) patients. The success is between 88% (for IS) and 100% (for LB) for QRS segment integration. Departure maps were used to explain the misclassified patterns.