Localized in situ cladding annealing for post-fabrication trimming of silicon photonic integrated circuits.

We report the use of localized annealing via in situ heaters to induce a semi-permanent change in the refractive index of the cladding in ring resonator filters. When compared to other methods for post-fabrication trimming, this method has the advantage that no additional equipment, other than a supply of electrical power, is necessary to cause the index change. Two cladding materials were used: hydrogen silsesquioxane (HSQ) for samples that were externally annealed, and PECVD oxide for samples that were annealed with in situ heaters. The resonant wavelengths could be adjusted by as much as 3.0 nm and 1.7 nm for the HSQ and PECVD cladded filters, respectively. The trimming of a 5 channel, single ring filter bank, and a single, double ring filter is demonstrated.

Photonic ADC: overcoming the bottleneck of electronic jitter.

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20-channel silicon filter bank has been demonstrated.

Laboratory diagnosis of tuberculosis in resource-poor countries: challenges and opportunities.

With an estimated 9.4 million new cases globally, tuberculosis (TB) continues to be a major public health concern. Eighty percent of all cases worldwide occur in 22 high-burden, mainly resource-poor settings. This devastating impact of tuberculosis on vulnerable populations is also driven by its deadly synergy with HIV. Therefore, building capacity and enhancing universal access to rapid and accurate laboratory diagnostics are necessary to control TB and HIV-TB coinfections in resource-limited countries. The present review describes several new and established methods as well as the issues and challenges associated with implementing quality tuberculosis laboratory services in such countries. Recently, the WHO has endorsed some of these novel methods, and they have been made available at discounted prices for procurement by the public health sector of high-burden countries. In addition, international and national laboratory partners and donors are currently evaluating other new diagnostics that will allow further and more rapid testing in point-of-care settings. While some techniques are simple, others have complex requirements, and therefore, it is important to carefully determine how to link these new tests and incorporate them within a country's national diagnostic algorithm. Finally, the successful implementation of these methods is dependent on key partnerships in the international laboratory community and ensuring that adequate quality assurance programs are inherent in each country's laboratory network.

Effect of carrier lifetime on forward-biased silicon Mach-Zehnder modulators.

We present a systematic study of Mach-Zehnder silicon optical modulators based on carrier-injection. Detailed comparisons between modeling and measurement results are made with good agreement obtained for both DC and AC characteristics. A figure of merit, static VpiL, as low as 0.24Vmm is achieved. The effect of carrier lifetime variation with doping concentration is explored and found to be important for the modulator characteristics.

Antibody responses to hepatitis A virus vaccine in HIV-infected children with evidence of immunologic reconstitution while receiving highly active antiretroviral therapy.

BACKGROUND: Human immunodeficiency virus (HIV)-infected patients have weak responses to vaccines and may require revised immunization regimens. We investigated the safety and immunogenicity of 2 doses of hepatitis A virus (HAV) vaccine followed by a booster dose in HIV-infected children receiving stable highly active antiretroviral therapy. METHODS: A total of 235 children with CD4+ T cell percentages > or = 20% received 2 vaccine doses 24 weeks apart, and 117 received a third vaccine dose after 104 weeks. Anti-HAV antibody titers were measured at baseline and at 32, 104, and 112 weeks after the first vaccination. Subjects with antibody titers > or = 20 mIU/mL were defined as being seropositive. High and low antibody responses were defined as titers > or = 250 and <250 mIU/mL, respectively. RESULTS: Of 151 subjects who were HAV seronegative at baseline, 97% seroconverted after 2 vaccine doses, and 47% had low antibody responses. At 104 weeks, 90% of subjects had antibody titers > or = 20 mIU/mL, and those with low antibody responses were more likely to lose protective antibody titers. A third vaccine dose generated significantly higher antibody titers than those observed after the second vaccine dose. Undetectable HIV RNA at baseline was associated with higher anti-HAV antibody titers after the second vaccine dose. Antibody titers after the second and third vaccine doses were weakly correlated with CD4+ T cell percentages at the time when each vaccine dose was administered. In the 45 subjects who were HAV seropositive at baseline, responses to 2 and 3 vaccine doses were higher than those in subjects who were HAV seronegative at baseline, but the responses showed similar correlations. There were no serious adverse events associated with the vaccine. CONCLUSIONS: HIV-infected children with CD4+ T cell percentages > or = 20% responded better to the HAV vaccine if they had undetectable HIV RNA. The standard 2-dose immunization regimen generated low antibody titers with limited persistence. A third vaccine dose was safe and increased the antibody titers, suggesting that an increase in immunizations may be warranted in this population.

Effects of development on olanzapine-associated adverse events.

OBJECTIVE: Atypical antipsychotic medications are increasingly prescribed for child and adolescent patients. Relatively little information on adverse events (AEs), specifically in children or adolescents taking atypical antipsychotics, is available. METHOD: The Food and Drug Administration spontaneous AE reporting postmarketing surveillance database was queried for olanzapine until March 31, 2000. Patient exposure estimates as of the same date were provided by the manufacturer. AE complaints and exposure estimates were divided by age: children (birth-9 years), adolescents (10-19), and adults (20+). AE complaint risks per 10,000 patients exposed were calculated along with risk ratios across age groups and their 95% confidence intervals. RESULTS: Extrapyramidal syndrome complaint risks were similar across development, and tardive dyskinesia complaint risks were comparable in adolescents and adults. Overrepresented AE complaints in children included sedation, weight gain, liver function abnormalities, and tardive dyskinesia. Overrepresented AE complaints in adolescents included sedation, weight gain, liver function abnormalities, and prolactin increase. CONCLUSIONS: Extrapyramidal syndromes may be no more common in children and adolescents with olanzapine than in adults. The frequency of some other AEs may differ across development. Caution is warranted because of the likelihood of reporting bias. Similar analyses should be conducted with other atypical antipsychotics.