Supermode suppression to below-130 dBc/Hz in a 10 GHz harmonically mode-locked external sigma cavity semiconductor laser

We demonstrate supermode suppression to levels below - 125 dBc/Hz and - 132 dBc/Hz using Fabry-Perot etalons with finesse values of 180 and 650, respectively, for a 10 GHz harmonically mode-locked external sigma cavity semiconductor laser. The laser was hybridly mode-locked using direct electrical modulation in a compact package without the need for an external modulator

Classifying and scoring of molecules with the NGN: new datasets, significance tests, and generalization

<p>Abstract</p> <p/> <p>This paper demonstrates how a Neural Grammar Network learns to classify and score molecules for a variety of tasks in chemistry and toxicology. In addition to a more detailed analysis on datasets previously studied, we introduce three new datasets (BBB, FXa, and toxicology) to show the generality of the approach. A new experimental methodology is developed and applied to both the new datasets as well as previously studied datasets. This methodology is rigorous and statistically grounded, and ultimately culminates in a Wilcoxon significance test that proves the effectiveness of the system. We further include a complete generalization of the specific technique to arbitrary grammars and datasets using a mathematical abstraction that allows researchers in different domains to apply the method to their own work.</p> <p>Background</p> <p>Our work can be viewed as an alternative to existing methods to solve the quantitative structure-activity relationship (QSAR) problem. To this end, we review a number approaches both from a methodological and also a performance perspective. In addition to these approaches, we also examined a number of chemical properties that can be used by generic classifier systems, such as feed-forward artificial neural networks. In studying these approaches, we identified a set of interesting benchmark problem sets to which many of the above approaches had been applied. These included: ACE, AChE, AR, BBB, BZR, Cox2, DHFR, ER, FXa, GPB, Therm, and Thr. Finally, we developed our own benchmark set by collecting data on toxicology.</p> <p>Results</p> <p>Our results show that our system performs better than, or comparatively to, the existing methods over a broad range of problem types. Our method does not require the expert knowledge that is necessary to apply the other methods to novel problems.</p> <p>Conclusions</p> <p>We conclude that our success is due to the ability of our system to: 1) encode molecules losslessly before presentation to the learning system, and 2) leverage the design of molecular description languages to facilitate the identification of relevant structural attributes of the molecules over different problem domains.</p

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Chloroplast genomes as a tool to resolve red algal phylogenies: a case study in the Nemaliales

Obtaining strongly supported phylogenies that permit confident taxonomic and evolutionary interpretations has been a challenge in algal biology. High-throughput sequencing has improved the capacity to generate data and yields more informative datasets. We sequenced and analysed the chloroplast genomes of 22 species of the order Nemaliales as a case study in the use of phylogenomics as an approach to achieve well-supported phylogenies of red algae.Australian Research Council/[FT110100585]/ARC/AustraliaAustralian Biological Resources Study/[RFL213-08]/ABRS/AustraliaMillennium Scientific Initiative/[NC120030]/MSI/Nueva JerseyUniversity of Melbourne///AustraliaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

External-Cavity Semiconductor Diode Ring Laser For Application In Hybrid Optoelectronic Analog-To-Digital Converter

Current state-of-the-art electronic analog-to-digital converters (ADCs) operating at multigigahertz sampling frequencies are known to exhibit fairly limited resolution (∼4 bits at room temperature and ∼6 bits when superconducting). These high-frequency restrictions stem primarily from the response time of the constituent transistors that make up the ADC\u27s comparators (also known as comparator ambiguity). In an effort to improve the resolution of ADCs operating at ultrahigh sampling frequencies, several areas of investigation are currently underway regarding the capabilities of hybrid optoelectronic systems. High-power optical pulses can be used as sampling windows and high-bandwidth electro-optic modulators as voltage-to-intensity transducers to provide a means for digitizing ultrafast voltage waveforms with much greater accuracy than conventional (purely electronic) ADCs. When optical sampling is employed, the primary limiting factors determining ADC conversion accuracy (now that comparator ambiguity is no longer an issue) become the noise in the sampling pulsetrain and the extent of the sampling time (optical pulsewidth). Detrimental pulsetrain noise is associated with either phase modulation (PM noise) or amplitude modulation (AM noise), and recent measurements of AM and residual PM noise on our 10 Ghz ring laser show the best results to date for an actively-modelocked semiconductor diode system. Carrier offset integration bands extending from 10 Hz to 10 MHz exhibit RMS levels of AM and PM noise as low as 0.12% and 43 fs, respectively. In addition, linear dispersion compensation has successfully reduced the optical pulsewidth from 13 ps to 1.2 ps. Based on these experimental numbers, this laser could form the front end for an optoelectronic ADC capable of a theoretical resolution as high as 8.6 bits (10 Ghz sample rate)

Ultralow Noise And Supermode Suppression In An Actively Modelocked External-Cavity Semiconductor Diode Ring Laser

The lowest noise characteristics for an actively-modelocked external-cavity semiconductor diode laser were achieved by the use of active harmonic modelocking at 10 GHz with extensive polarization control in a mirror-less ring geometry. Residual RMS jitter as low as 18 fs and 94 fs were measured, as well as RMS amplitude noise as low as 0.05% and 0.74%. Nearly complete supermode suppression out to the Nyquist limit was demonstrated while favorably retaining a low-offset noise knee

Pm Noise Measurements Of An Actively Modelocked External Cavity Semiconductor Ring Laser At 10 Ghz

A novel approach to residual jitter measurement examines the intensity crosscorrelation generated by two optical pulses with various relative delays. A relative delay of 25 pulses produces a residual jitter value of 26 fsec RMS for a 10 GHz actively modelocked ring laser. The phase noise measurement carried out to the Nyquist frequency (5 GHz) offset gives 47 fsec RMS pulse-to-pulse timing jitter. The field correlation measurement obtains a 10 asec RMS pulse-to-pulse optical carder jitter

Complete Noise Characterisation Of External Cavity Semiconductor Laser Hybridly Modelocked At 10 Ghz

The measurements of amplitude modulation (AM) and residual phase modulation (PM) noise for a 10 GHz modelocked laser out to Nyquist frequency offsets were presented. The peak values of the spurs around the harmonics of modelocking frequency were measured to determine whether the cavity harmonic spurs represented AM or PM noise. It was found that the quadratic dependence of spur-to-carrier ratio on harmonic number suggested that the noise in the spurs was predominantly PM noise

Modelocked Semiconductor Laser Comb Stabilization Using The Pound-Drever-Hall Scheme

We report optical frequency comb drift stabilization of an external cavity semiconductor laser modelocked at 10 GHz using the Pound-Drever-Hall scheme. The peak-to-peak 2.4 GHz frequency drift was reduced to a RMS fluctuation of 30 MHz. © 2002 Optical Society of America

Ultralow Noise And Supermode Suppression For High-Speed Photonic Sampling With A Semiconductor Diode Ring Laser

Ultralow noise and supermode suppression for high-speed photonic sampling with a semiconductor diode ring laser were discussed. High dynamic range measurements out to Nyquist offsets were presented which show strong supermode suppression to levels below -140 dBc/Hz. The loss-modulated laser geometry is such that the free-space section contains extensive isolation and polarization-controlling optics surrounding an InGaAsP SOA. For supermode suppression, a high-finesse fiber Fabry-Perot filter and 3-ring polarization controller are inserted before the Mach-Zehnder modulator