Photonic page buffer based on GaAs multiple-quantum-well modulators bonded directly over active silicon complementary-metal-oxide-semiconductor (CMOS) circuits

We present a 2-kbit, 50-Mpage/s, photonic first-in, first-out page buffer based on gallium arsenide/aluminium-gallium arsenide multiple-quantum-well diodes that are flip-chip bonded to submicrometer silicon complementary-metal-oxide-semiconductor circuits. This photonic chip provides nonvolatile storage (buffering), asynchronous-to-synchronous conversion, bandwidth smoothing, tolerance to jitter or skew, spatial format conversion, wavelength conversion, and independent flow control for the input and the output channels. It serves as an interface chip for parallel-accessed optical bit-plane data. It represents the first smart-pixel array that accomplishes the vertical integration of multiple-quantum-well modulators and detectors directly over active silicon VLSI circuits and provides over 340 transistors per optical input-output. Results from high-speed single-channel testing and real-time array operation of the photonic page buffer are reported.     

Interference-based micromechanical spectral equalizers

Dynamic gain equalization filters (DGEFs) are important for high-performance wavelength division multiplexed (WDM) communications. One of the first demonstrated DGEF used a micromechanical etalon filter array illuminated with free-space spectral demultiplexing optics. Here, we present subsequent research on etalon-based dynamic spectral filters, including vertical device structures which linearize and reduce the drive voltage from 70 to 40 V, and spatially-segmented etalons which allow channelized spectral equalization and further reduce drive voltage. We describe a prototype using a simplified cylindrical optomechanical package with a 104-nm broadband spectral response, 7.5-dB insertion loss and less than 16-V operation voltage. Finally, we show the use of a 42-nm bandwidth DGEF prototype with feedback stabilization to more than double the number of channels and operating bandwidth of a conventional Erbium-doped fiber amplifier while maintaining < 1-dB power uniformity.     

Assessing quality of rural areas in the Netherlands: finding the most important indicators for recreation

Quality is a major topic in most Western societies, not only for products, but also for land. This is especially true in the Netherlands, a country with 15.6 million people living on 33 900 km² of land, with a huge demand for land for agriculture, urban development, nature, infrastructure, recreation, etc. The Dutch Ministry of Agriculture, Nature and Fishery has asked the Winand Staring Centre to find out if it is possible to measure the quality of rural areas for recreational purposes.In a survey about quality, it is important to interview the recreationists themselves. So, in-home interviews were made with cyclists, walkers, swimmers, sailors and fishermen. The survey tried to assess the relative importance of some quality indicators of rural areas for recreational purposes. Dutch researchers usually divide quality into utilisation quality and perception quality. Utilisation quality is defined as fitness for use, while perception quality is that quality of the environment which people notice or experience (such as the beauty of the landscape or tranquillity) when they engage in recreational activities. Tranquillity, accessibility, water quality and nuisance value were the most important quality indicators. On the basis of the importance of some quality indicators, maps were prepared showing the attractiveness of various areas in the Netherlands for swimming and cycling, as an example what can be done with the results. It was found that 75% of the swimming locations were quite attractive or even extremely attractive. About 12% of the rural areas were good for cycling, and 56% were reasonable.     

Micromechanical fiber-optic attenuator with 3 μs response

Optomechanical fiber-optic attenuators are bulky and slow. The mechanical antireflection switch (MARS) modulator offers a high-speed alternative for applications including dynamic gain control in fiber amplifiers. This paper describes a compact electrically controlled variable attenuator using a micromechanical device where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a variable reflectivity mirror. This device is packaged with two fibers in one ceramic ferrule placed in contact with a gradient index (GRIN) collimation lens, so that the input light reflects from the modulator in the collimated beam plane and couples into the output fiber. Using a 300 μm diameter MARS attenuator and a 500 μm diameter collimation lens, the total insertion loss at 1550 nm was 3.0 dB with no applied voltage, increasing to 31 dB at 35.2 V. The polarization dependent loss was less than 0.06 dB. Full attenuation with more than 100 mW input power produced no damage. The response time was 2.8 μs to move from maximum to minimum transmission and 1.1 μs to return to maximum transmission     

On the operational and manufacturing tolerances of GaAs-AlAs MQWmodulators

We approach the question of optimization of surface-normal p-i(multiquantum-well, MQW)-n modulators from the viewpoint of investigating their tolerance to variations in wavelength and temperature and errors in manufacture. The reflection characteristics of two high-quality samples are carefully processed to eliminate Fabry-Perot fringes, and then their spectra at any bias are characterized with six phenomenological parameters which depend on λ₀, the zero-field exciton position. The two GaAs-AlAs samples have λ₀'s of 833.8 and 842.3 nm, and so cover a range useful for modulators designed to operate near 850 nm in the normally reflecting condition, i.e., reflection decreases with field. A linear interpolation of the parameters of these two samples is used to predict the behavior of MQW diodes with λ₀'s around this range, and so a fully comprehensive examination of normally reflecting MQW modulators is performed. The performance aspect that is examined is contrast ratio as a function of nonuniformities in the devices or operating conditions given a voltage swing of 3 V. There are two operational modes discussed. If the voltage offset of the bias is allowed to vary via a feedback circuit, a contrast of 2:1 may be maintained over an operating wavelength change (Δλ) of 17 nm with local variations of wavelength of ±1 nm, which corresponds to a temperature variation of 60°C while allowing for variations of laser driver wavelength of ±1 nm. If feedback Is not permitted, we determine that, given tolerances to manufacturing errors, a contrast of 1.5:1 may be maintained over a wavelength range of ~5 nm by either using stacked diode designs or extremely shallow quantum wells     

Interleaved-contact electroabsorption modulator usingdoping-selective electrodes with 25°C to 95°C operating range

A multiple-quantum-well (MQW) modulator with multiple stacked p-i(MQW)-n-i(MQW)-p-regions is demonstrated. Electrodes are deposited such that all the n-layers are connected to one contact and all the p-layers to the other. This allows high fields to be produced in the i-regions with relatively low voltages, since the i-regions may be made thin while retaining large optical interaction because they are stacked. A large usable wavelength range which translates into a large operating temperature range is obtained because of large Stark shifts in the MQWs at high fields. For a 0 to 6 V swing >22% reflectivity change from 25°C to 95°C, or alternatively over a wavelength range of 15 nm at 25°C, is achieved     

Gas composition dependence of silicon nitride used as gallium diffusion barrier during GaAs molecular beam epitaxy growth on Si complementary metal oxide semiconductor

We have measured the effect of deposition parameters upon the utility of plasma enhanced chemical vapor depositon silicon nitride as a gallium diffusions barrier during molecular beam epitaxy growth of gallium arsenide on silicon submicron complementary metal oxide semiconductor electronics. It was found that the conditions under which the silicon nitride is deposited severely impact the ability of these films to be used as a diffusion barrier, with the most critical dependence upon the silane to nitrogen gas ratio.     

Optical bandwidth considerations in p-i-n multiple quantum-wellmodulators

We investigate the optical bandwidth of p-i(multiple quantum well [MQW])-n modulators employing various MQW designs. The optical bandwidth translates directly into an operating temperature range due to the shift of the band gap with temperature. We find that although greater maximum modulation may be obtained with narrow (~90 Å) quantum wells operating below the band edge (absorption increases with field), uniform large performance may be obtained over a larger bandwidth using wider (~110 Å) quantum wells operating at the exciton (absorption decreases with field). We obtain a usable bandwidth of 7.7 nm, which translates into a operating temperature range of 27°C     

Recombinant iron-regulatory factor functions as an iron-responsive-element-binding protein, a translational repressor and an aconitase. A functional assay for translational repression and direct demonstration of the iron switch

The translation of ferritin and erythroid 5-aminolevulinate synthase mRNAs is regulated via a specific high-affinity interaction between an iron-responsive element in the 5' untranslated region of ferritin and erythroid 5-aminolevulinate synthase mRNAs and a 98-kDa cytoplasmic protein, the iron-regulatory factor. Iron-regulatory factor was expressed in vaccinia-virus-infected HeLa cells (hIRFvac) and in Escherichia coli (hIRFeco). An N-terminal histidine tag allowed a rapid one-step purification of large quantities of soluble recombinant protein. Both hIRFvac and hIRFeco bound specifically to iron-responsive elements and were immunoprecipitated by iron-regulatory-factor antibodies. Using in-vitro-transcribed chloramphenicol-acetyltransferase mRNAs bearing an iron-responsive element in the 5' untranslated region, specific repression of chloramphenicol-acetyltransferase translation by hIRFvac and hIRFeco was demonstrated in wheat-germ extract. In addition, hIRFvac and hIRFeco were shown to display aconitase activity. Treatment of hIRFvac and hIRFeco with FeSO4 resulted in a drastic reduction in iron-responsive-element-binding of iron-regulatory factor, but caused a strong stimulation of its aconitase activity. The results establish that recombinant iron-regulatory factor is a bifunctional protein; after purification, it binds to iron-responsive elements and represses translation in vitro. Following iron treatment, iron-responsive-element binding is lost and aconitase activity is gained. No eukaryotic co-factor seems to be required for the conversion of the iron-responsive-element binding to the aconitase form of the protein.