Optimum cavity length for high conversion efficiency quantum well diode lasers

Optimum cavity length for high conversion efficiency quantum well diode lasers D. P. Bour and A. Rosen, J. Appl. Phys. 66, 2813 (1989), DOI:10.1063/1.344209The cavity length which maximizes the peak power conversion efficiency is determined for quantum well diode lasers. These calculations are based upon simple models of the diode injection laser's electrical and optical behaviors, including saturation in the quantum well gain current characteristic. Here the influences of the distributed optical cavity loss, electrical resistivity, and facet reflectivity on the optimum cavity length are described. Although a lower facet reflectivity results in increased threshold current, there are advantages to longer devices, as the peak conversion efficiency is not reduced. Since the optimum cavity length is greater for low reflectivity, the diode series resistance is smaller. Furthermore, when operating at the point where conversion efficiency is a maximum, the power output of the device with low facet reflectivity exceeds that of the device with higher facet reflectivity. Therein lies the principle advantage of reduced front-facet reflectivities in high power, high efficiency quantum well diode lasers. Good agreement results when these predictions are applied to a strained InGaAs/AlGaAs single quantum well laser (A = 0.93 f./m)

Exploiting ballistic electrons in a uni-traveling carrier traveling wave photo-detector for efficient generation of sub-MM waves

International Topical Meeting on Microwave Photonics, MWP 2005, pp. 133-136.The Generation of microwave signals by heterodyning two optical signals has been demonstrated in the past. However, so far this approach is limited in bandwidth, power and efficiency. In this paper we present an analysis of optical heterodyning in the uni-traveling carrier traveling wave photo detector taking into account the effect of ballistic electrons. The analysis is validated by comparison to measurement of an existing device made at the University of California, San Diego. Based on the above analysis a new photodiode design is made, which is expected to have a bandwidth well into the sub-MM wave region. The device exploiting the ballistic electrons effect can reach a bandwidth 2-3 times larger compared to device using velocity-saturated electrons

Coherent, phase modulated (PM) fiber-optic link design

2006 IEEE MTT-S International Microwave Symposium Digest: pp. 1943-1946.This paper is concerned with a coherent, phase modulated optical link for microwave applications, such as antenna remoting. The optical transmitter employs a low noise high power solid state laser and a sensitive phase modulator. The demodulator/detector in the optical receiver utilizes a newly developed and tested photonic phased locked loop (PPLL). All signal processing, including down-conversion to intermediate frequency (IF) range, is executed in the optical domain. The link design predicts a spurious free dynamic range up to 157 dBHz2/3 and noise figure below 3dB. The requirements on key photonic components to attain these results are described in detail

Silicon as a Millimeter-Wave Monolithically Integrated Substrate - A New Look

Materials suitable for use as monolithic substrates are summarized. A study of the properties of silicon substrates as transmission line media shows that serious consideration should be given to them for use at mm-wave frequencies. It is concluded that for silicon resistivities of 2000 ohm-cm or greater, microstrip loss in silicon at mm-wave frequencies is only slightly higher than that in GaAs or alumina. The cross section width of a transmission line represents an appreciable part of a wavelength when microstrip is used as an impedance transformer at mm-wave frequencies. Therefore, substrate thickness (using the latest dispersion characteristics) is especially considered in circuit design. These effects on the design of 3-dB interdigitated and branch-line couplers are demonstrated. Fabrication of silicon IMPATT diodes operating up to 200 GHz has been ac­complished by novel techniques that maintain the silicon\u27s high resistivity. We report on diodes yielding 25 mW cw at 102 GHz, 16 mW cw at 132 GHz, and 1 mW at 195 GHz. The techniques described are ion implantation, laser annealing, unique secondary-ion mass spectrometry (SIMS) profile diagnostics, and novel wafer thinning. The utilization of these technologies paves the way for the pro­cessing of silicon monolithic mm-wave integrated circuits

Receiver for a coherent fiber-optic link with high dynamic range and low noise figure

International Topical Meeting on Microwave Photonics, MWP 2005, pp: 273-276.Phase modulated coherent fiberoptic links can potentially provide exceptionally high spurious free dynamic range (SFDR) and low noise figure (NF). Critical issue is the development of a strictly linear phase demodulator. In this paper we describe a phase demodulator employing a phase locked loop discriminator. Implementing the PPLL on a single substrate using the state-of-the-art components could yield an SFDR better than 145 dB/Hz2/3 and NF lower than 3dB

A portable near infrared spectroscopy system for bedside monitoring of newborn brain

BACKGROUND: Newborns with critical health conditions are monitored in neonatal intensive care units (NICU). In NICU, one of the most important problems that they face is the risk of brain injury. There is a need for continuous monitoring of newborn's brain function to prevent any potential brain injury. This type of monitoring should not interfere with intensive care of the newborn. Therefore, it should be non-invasive and portable. METHODS: In this paper, a low-cost, battery operated, dual wavelength, continuous wave near infrared spectroscopy system for continuous bedside hemodynamic monitoring of neonatal brain is presented. The system has been designed to optimize SNR by optimizing the wavelength-multiplexing parameters with special emphasis on safety issues concerning burn injuries. SNR improvement by utilizing the entire dynamic range has been satisfied with modifications in analog circuitry. RESULTS AND CONCLUSION: As a result, a shot-limited SNR of 67 dB has been achieved for 10 Hz temporal resolution. The system can operate more than 30 hours without recharging when an off-the-shelf 1850 mAh-7.2 V battery is used. Laboratory tests with optical phantoms and preliminary data recorded in NICU demonstrate the potential of the system as a reliable clinical tool to be employed in the bedside regional monitoring of newborn brain metabolism under intensive care

GIFtS: annotation landscape analysis with GeneCards

<p>Abstract</p> <p>Background</p> <p>Gene annotation is a pivotal component in computational genomics, encompassing prediction of gene function, expression analysis, and sequence scrutiny. Hence, quantitative measures of the annotation landscape constitute a pertinent bioinformatics tool. GeneCards^®is a gene-centric compendium of rich annotative information for over 50,000 human gene entries, building upon 68 data sources, including Gene Ontology (GO), pathways, interactions, phenotypes, publications and many more.</p> <p>Results</p> <p>We present the GeneCards Inferred Functionality Score (GIFtS) which allows a quantitative assessment of a gene's annotation status, by exploiting the unique wealth and diversity of GeneCards information. The GIFtS tool, linked from the GeneCards home page, facilitates browsing the human genome by searching for the annotation level of a specified gene, retrieving a list of genes within a specified range of GIFtS value, obtaining random genes with a specific GIFtS value, and experimenting with the GIFtS weighting algorithm for a variety of annotation categories. The bimodal shape of the GIFtS distribution suggests a division of the human gene repertoire into two main groups: the high-GIFtS peak consists almost entirely of protein-coding genes; the low-GIFtS peak consists of genes from all of the categories. Cluster analysis of GIFtS annotation vectors provides the classification of gene groups by detailed positioning in the annotation arena. GIFtS also provide measures which enable the evaluation of the databases that serve as GeneCards sources. An inverse correlation is found (for GIFtS>25) between the number of genes annotated by each source, and the average GIFtS value of genes associated with that source. Three typical source prototypes are revealed by their GIFtS distribution: genome-wide sources, sources comprising mainly highly annotated genes, and sources comprising mainly poorly annotated genes. The degree of accumulated knowledge for a given gene measured by GIFtS was correlated (for GIFtS>30) with the number of publications for a gene, and with the seniority of this entry in the HGNC database.</p> <p>Conclusion</p> <p>GIFtS can be a valuable tool for computational procedures which analyze lists of large set of genes resulting from wet-lab or computational research. GIFtS may also assist the scientific community with identification of groups of uncharacterized genes for diverse applications, such as delineation of novel functions and charting unexplored areas of the human genome.</p

Silicon as a millimeter-wave monolithically integrated substrate - A new look

An important goal of microwave research has now been attained with the development of the technologies needed to fabricate monolithic microwave (mm-wave) integrated circuits. Questions regarding the use of monolithic versus hybrid circuits are investigated. Attention is given to the pros and cons of materials considered for use as monolithic substrates at mm-wave frequencies, the properties of the microstrip, and the effects of shorter wavelengths as the wavelengths become comparable with the microstrip cross section. A novel technology is considered for the fabrication of mm-wave devices utilizing ion-implantation, laser annealing, and unique secondary-ion mass spectrometry diagnostics

Microwaves treat heart disease

IEEE Microwave Magazine, 8(1): pp. 70-75. DOI: http://dx.doi.org/10.1109/MMW.2007.28907