A model for diffraction-limited high-power multimode fiberamplifiers using seeded stimulated Brillouin scattering phaseconjugation

Diffraction-limited polarized stimulated Brillouin scattering (SBS) Stokes output from a multimode fiber is possible when the Stokes beam is the phase conjugate of diffraction-limited polarized pump light from a narrow-band master oscillator. Net amplification can be obtained by interposing a gain medium, such as a fiber amplifier between the master oscillator and the region of SBS generation. This paper proposes and studies numerically a model which describes the space-time dynamics of SBS generation, including phase conjugation, attenuation, phonon decay, thermal noise, inhomogeneous broadening, and amplifier gain. Noise reduction and phase locking are obtained by seeding the low-power end of the fiber at the Stokes frequency. Simulations are described for the case of 1.064 μm light amplification in a dual-clad Yb-doped multimode fiber amplifier     

A 15-mW fully integrated I/Q synthesizer for Bluetooth in 0.18-/spl mu/m CMOS

A low-power fully integrated synthesizer for Bluetooth applications is presented. The circuit with quadrature output signals at 2.45 GHz and 15-mW power dissipation has been designed in a digital 0.18-/spl mu/m CMOS process with 1.8-V supply voltage. The only external component is a 64-MHz crystal. Measurements have been performed on packaged samples mounted on an FR-4 board and show that the Bluetooth requirements are met. The measured phase noise is below -120 dBc/Hz at 3-MHz offset, and the resulting residual frequency modulation is 7.4-kHz rms. The tuning range consists of an analog and digital tuning mechanism, resulting in more than 15% overall tuning range.     

Elemental Powder Approaches to Ni3Al-Matrix Composites

Reactive sintering and hot isostatic compaction of mixed elemental powders have been combined to fabricate full density NiAl intermetallic-matrix composites. This process involves the formation of the matrix compound from its elemental constituents through an exothermic reaction. Dispersed ceramic phases inhibit direct consolidation, necessitating superposition of external pressure via hot isostatic compaction to obtain full density. The latter process is termed reactive hot isostatic pressing (RHIP). Because of its flexibility and low cost, this fabrication process merits attention as a means of preparing monolithic compounds and intermetallic-matrix composites.     

Spectral analysis of waiting time jitter in the presence of stuff threshold modulation

The Fourier transform of waiting time jitter in the presence of stuff threshold modulation is derived. Comparisons are made between power spectral densities and RMS jitter obtained analytically and by simulation. The Fourier transform enables the jitter performance to be evaluated in the presence of alternative stuff threshold modulation waveforms, required for example, in some SONET applications.<>     

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Synchronized External Pulsation for Improved Tolerance to Acceleration Stress: Model Studies and Preliminary Experiments

Synchronized external pulsation is proposed as a method to improve tolerance to acceleration stress. This technique uses a modified anti-G suit which is pressurized and depressurized synchronously with the heart cycle. The feasibility of the procedure has been studied using a computer model of the cardiovascular system which includes the effects of Gz stress, and contains simulations of baroreceptor control of heart rate and venous tone. Model predictions indicate that for unprotected subjects, carotid pressure at eye level (ophthalmic artery pressure) decreases to 20 mmHg (beginning of central light loss) at approximately +3.6 Gz. Applying standard anti-G suit pressure to the model increases this level to 5.3 Gz. When synchronized external pulsation of 2 psi is superimposed on the standard anti-G suit pressure, the tolerance to acceleration stress is further augmented by at least 0.9 G above the protection afforded by the standard anti-G suit alone. A set of preliminary experiments on human subjects to test the feasibility of using the technique in the high-G environment has also been carried out. The results under various protection modes compare favorably to the model predictions. Our results suggest that the computer model presented here is a useful tool for studying cardiovascular responses under +GZ stress. It also indicates that using synchronized external pulsation pressure superimposed on the standard anti-G suit pressure may offer extra protection to acceleration stress.     

Fault-tolerant communications for wafer-scale integration of a processor array

This paper describes schemes for introducing fault-tolerance into a two-dimensional orthogonal array of cells with nearest neighbour communication paths. The schemes are designed to tolerate a large number of faults and are therefore applicable to the yield-enhancement of large-area VLSI circuits. Simulation results are presented which show the superiority of the schemes over previous proposals and indicate that the nearest neighbour interconnections need not be a barrier to the desirable goal of integrating an array computer onto a whole-wafer circuit.