1.6 Tbit/s (40/spl times/40 Gbit/s) DPSK transmission over 3/spl times/100 km of TeraLight fibre with direct detection

By transmitting 40 channels over 300 km of TeraLight fibre, it is shown that optical differential phase shift keying can be used in 100 GHz-spaced 40 Gbit/s systems, with direct detection and a simple receiving filter. Chromatic dispersion tolerance around 300 ps/nm is also measured, compared to 70 ps/nm for NRZ.     

Programmable group-delay module using binary polarization switching

We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.     

Positively Thermo‐Sensitive Monodisperse Core–Shell Microspheres

In this paper, we report on a novel family of monodisperse thermo‐sensitive core–shell hydrogel microspheres that is featured with high monodispersity and positively thermo‐responsive volume phase transition characteristics with tunable swelling kinetics, i.e., the particle swelling is induced by an increase rather than a decrease in temperature. The microspheres were fabricated in a three‐step process. In the first step, monodisperse poly(acrylamide‐co‐styrene) seeds were prepared by emulsifier‐free emulsion polymerization. In the second step, poly(acrylamide) or poly[acrylamide‐co‐(butyl methacrylate)] shells were fabricated on the microsphere seeds by free radical polymerization. In the third step, the core–shell microspheres with poly‐ (acrylamide)/poly(acrylic acid) based interpenetrating polymer network (IPN) shells were finished by a method of sequential IPN synthesis. The proposed monodisperse core–shell microspheres provide a new mode of the phase transition behavior for thermo‐sensitive “smart” or “intelligent” monodisperse micro‐actuators that is highly attractive for targeting drug delivery systems, chemical separations, sensors, and so on.     

Formation of C49-TiSi2 in flash memories: a nucleation controlled phenomenon?

The formation of Ti silicides has been examined in flash memories with 0.25 μm linewidth by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It has been observed that, after the first rapid thermal process and the selective metal etch, there is no silicide on the source and on a majority of drain contacts while C49-TiSi₂ is found on the gate. A pre-amorphisation implant increases drastically the formation of C49-TiSi₂ in the drain zone while modifications of annealing conditions have little impact. These results indicate that the formation of C49-TiSi₂ is most likely controlled by nucleation and that this nucleation is sensitive to both the width and the length of the reaction zone. The formation of a Ti rich silicide may play an important role in this nucleation by decreasing the driving force for the formation of C49-TiSi₂. Curiously enough, the formation of C49-TiSi₂ appears thus as a major concern for the salicide process in flash memories.     

Power combining characteristics of backed-off traveling wave tubes for communications applications

Traveling wave tubes (TWTs) used in multi-tone and digital communications applications are typically operated backed off from saturation in order to improve the amplifier linearity. This reduces the bit error rate (BER), decreases intermodulation distortion and lowers adjacent channel power; all at the expense of reducing the average output power. For emerging telecommunications applications, the average power requirement is increasing to provide higher bit rates and lower BER, and often exceeds the power obtainable from backed-off space or telecommunications TWTs. One solution is to power combine TWTs that are operated 3 to 10 dB backed off from saturation. Efficient power combining requires that the phase and gain of the signal from each TWT be closely matched. To understand the variation in these parameters across a build-set of tubes, the phase and gain versus drive of 35 Boeing S-band 5525H TWTs were measured. The standard deviation in the phase about the mean phase shift measured at saturation was found to be 2.6/spl deg/, with a related standard deviation of the gain compression at saturation of 0.22 dB. These levels result in small power combining losses and small errors in phased-array fed multi-beam antennas in broadband multi-tone applications.     

Minimal, rigid foliations by curves on ℂℙ n

We prove the existence of minimal and rigid singular holomorphic foliations by curves on the projective space ℂℙ ⁿ for every dimension n≥2 and every degree d≥2. Precisely, we construct a foliation ℱ which is induced by a homogeneous vector field of degree d, has a finite singular set and all the regular leaves are dense in the whole of ℂℙ ⁿ . Moreover, ℱ satisfies many additional properties expected from chaotic dynamics and is rigid in the following sense: if ℱ is conjugate to another holomorphic foliation by a homeomorphism sufficiently close to the identity, then these foliations are also conjugate by a projective transformation. Finally, all these properties are persistent for small perturbations of ℱ.?This is done by considering pseudo-groups generated on the unit ball 𝔹 ⁿ ⊆ℂ ⁿ by small perturbations of elements in Diff(ℂ ⁿ ,0). Under open conditions on the generators, we prove the existence of many pseudo-flows in their closure (for the C ⁰-topology) acting transitively on the ball. Dynamical features as minimality, ergodicity, positive entropy and rigidity may easily be derived from this approach. Finally, some of these pseudo-groups are realized in the transverse dynamics of polynomial vector fields in ℂℙ ⁿ . Received March 7, 2002 / final version received November 26, 2002?Published online February 7, 2003 Most of this work has been carried out during a visit of the first author to IMPA/RJ and a visit of the second author to the University of Lille 1. We would like to thank these institutes for hospitality and express our gratitude to CNPq-Brazil and CNRS-France for the financial support which made these visits possible. We are also indebted to Paulo Sad, Marcel Nicolau and the referee whose comments helped us to improve on the preliminary version. Finally, the second author has partially conducted this research for the Clay Mathematics Institute.     

Considerations for polarization insensitive optical switching and modulation using strained InGaAs/InAlAs quantum well structure

It is shown that In/sub 1-x/Ga/sub x/As/In/sub 0.52/Al/sub 0.48/As MQW structures with the wells under tensile strain obtained by the appropriate selection of the Ga mole fraction and well size can achieve polarization-insensitive optical switching and modulation for a wide range of wavelengths between 1.0 and 1.6 mu m. For example, a change in refractive index of -0.5% at about 1.55 mu m will facilitate an intersectional angle of more than 10 degrees in a total internal reflection switch which can be readily fabricated. Hence, this material system is promising for long-wavelength polarization-insensitive semiconductor optoelectronic devices.<>     

Circuit techniques for large CSEA SRAMs

The CMOS-storage emitter-access (CSEA) memory cell offers faster access than the MOS cells used in conventional BiCMOS SRAMs but using it in large memory arrays poses several problems. Novel BiCMOS circuit approaches to address the problems of decoding power, electronic noise, level translation, and write disturbance are described. Results on a 64-kb CSEA SRAM using these techniques are reported. The device, fabricated in an 0.8-μm BiCMOS technology, achieves read access and write pulse time of less than 4 ns while dissipating 1.7 W at a case temperature of 70°C     

Methodologies for characterizing traffic in wide area networks: Analysis and benchmarking

Since computer networks play an important role in distributed computing environments, an application's performance depends heavily on the quality of service provided by the communication networks. To ensure a high performance, the characteristics of wide area networks, WANs, must be well understood. This paper presents methodologies to characterize WAN traffic based on real measurements from Bellcore's backbone network that connects remote sites using dedicated T1 links. This paper also suggests some workload models that can be used for wide area network sizing and performance evaluation studies. It is found that the inter-site traffic pattern depends on the time of the day and the day of the week. Furthermore, the traffic between two sites is found to be reasonably symmetric, except for those sites designated as back-up sites. The coefficient of variation is used as a measure for the traffic burstiness and it is found to be 1·5 degree during working hours. The methods presented here are easy to use and cost-effective.