548 research outputs found
Spectral line-by-line pulse shaping of on-chip microresonator frequency combs
No full textRecently, on-chip comb generation methods based on nonlinear optical modulation in ultrahigh-quality-factor monolithic microresonators have been demonstrated, where two pump photons are transformed into sideband photons in a four-wave-mixing process mediated by Kerr nonlinearity. Here, we investigate line-by-line pulse shaping of such combs generated in silicon nitride ring resonators. We observe two distinct paths to comb formation that exhibit strikingly different time-domain behaviours. For combs formed as a cascade of sidebands spaced by a single free spectral range that spread from the pump, we are able to compress stably to nearly bandwidth-limited pulses. This indicates high coherence across the spectra and provides new data on the high passive stability of the spectral phase. For combs where the initial sidebands are spaced by multiple free spectral ranges that then fill in to give combs with single free-spectral-range spacing, the time-domain data reveal partially coherent behaviour
TiSapphire frequency combs
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis. Vita.Includes bibliographical references (p. 179-186).Femtosecond mode-locked lasers are a unique laser technology due to their broad optical bandwidth and potential for linking the optical and radio frequency domains when these lasers are configured as frequency combs. Ti:Sapphire based mode-locked lasers offer considerable advantages over other laser systems by generating both the broadest optical spectrum and highest fundamental pulse repetition rates directly from the laser cavity. Recent advances in laser diode technology have reduced the cost of pump lasers for Ti:Sapphire based frequency combs considerably, and the recent demonstration of direct diode pumping of a narrowband mode-locked Ti:Sapphire laser suggests that Ti:Sapphire frequency combs may finally be ready to make the transition from an indispensible research tool to a wider set of industrial applications. In this thesis, several applications and fundamental properties of Ti:Sapphire based mode-locked lasers are investigated. To enable more widespread use of Ti:Sapphire based frequency combs, a frequency comb based on an octave spanning 1 GHz Ti:Sapphire laser is demonstrated. The I GHz Ti:Sapphire laser is referenced to a methane stabilized HeNe laser, resulting in a frequency comb with a fractional frequency stability of its optical spectrum of 2x1 0-14 on a 20 second timescale. A recently identified frequency comb application is the calibration of astronomical spectrographs to enable detection of Earth-like planets which are orbiting Sun-like stars. In support of this application, a second frequency comb system was constructed which ultimately was characterized by a 51 GHz pulse repetition rate and 12 nm bandwidth centered at 410 nm. This "astro-comb" system was deployed to the Fred Lawrence Whipple Observatory where preliminary results indicate a 40-fold increase in the spectrograph stability due to calibration by the astro-comb. Finally, the stability of the optical pulse train emitted from femtosecond mode-locked lasers is expected to exhibit the lowest phase noise of any oscillator, with theoretical predictions of phase noise levels below -190 dBc for offset frequencies exceeding 1 kHz. A comparison between the pulse trains of two nearly identical mode-locked lasers resulted in a measured timing error of less than 13 attoseconds measured over the entire Nyquist bandwidth.by Andrew John Benedick.Ph.D
Data from: "Larger but not louder: bigger honey bee colonies have quieter combs”
No full textCommunication is impossible if the sender’s signal cannot overcome background noise to reach the receiver. This obstacle is present in all communication modalities, forcing organisms to develop diverse mechanisms to overcome noise. Honey bees will modify combs to improve signal efficiency of substrate-borne vibrations, but it is unknown whether, and if so, how, bees compensate for the largest potential source of noise: the bees themselves. The number of bees in a colony changes markedly throughout the year, but the size of the nest cavity does not, forcing workers into high densities on the combs. How, then, do bees communicate via substrate-borne vibrations on combs that are covered in bees? We used accelerometers to measure comb vibrations, while varying the number of workers on the comb. Surprisingly, comb vibrations decreased with increased worker number. Furthermore, inserting freshly killed bees to the comb demonstrated that it is not simply the bees’ collective mass that damps vibrations, but is probably their behavior. We propose that their posture damps vibrations, with each bee linking up
to six neighboring cells with her legs. This collective damping reduces background noise, and improves the landscape for communication. These results demonstrate how living systems, including superorganisms, can overcome physical obstacles with curiously simple and elegant solutions.MLS is supported by the National Science Foundation Graduate Research Fellowship Program (DGE-1144153). This research was funded with a National Science Foundation Doctoral Dissertation Improvement Grant (1600775), an Andrew W. Mellon research grant, and a Centennial Pollinator Fellowship from the Garden Club of America (to MLS)
Robust controllable FD-FWM based Micro-combs
No full textThe FD-FWM is a proven approach to implement coherent Microcomb generation. Comb repetition rates can be finely controlled in a robust way, while maintaining the coherence during the whole process, whereas full-coherent type-I and type-II combs can be accessible. We present our recent advances towards effective control of optical combs exploiting integrated chip-based resonators. © 2018 IEEE.</p
Framework for complex quantum state generation and coherent control based on on-chip frequency combs
No full textIntegrated frequency combs introduce a scalable framework for the generation and manipulation of complex quantum states (including multi-photon and high-dimensional states), using only standard silicon chip and fiber telecommunications components. © 2018 The Author(s).</p
Microwave and RF photonic applications of integrated Kerr micro-combs
No full textWe report applications of integrated Kerr micro-combs to RF photonic systems and demonstrate a wide range of advanced functions including a microwave photonic intensity differentiator, filters and true time delays. The on-chip Kerr optical comb is CMOS-compatible and serves as a high-performance multi-wavelength source for transversal filter functions, thus greatly reducing the cost, size, and complexity of the system. © 2018 The Author(s).</p
Differential perceptions of business majors in training of job applicants with disabilities versus non disabled job applicants
No full textPlan BThis research is being conducted to determine if potential business employers have differential perceptions of job applicants with disabilities when compared to a non-disabled job applicant. Research indicates that the unemployment rate for people with disabilities is seventy percent. One possible reason for this may be due to biases in the work place. This study will investigate attitudes of employers-in-training using survey methodology. This research project will be a quasi-experimental design. Prior to research, permission will be gained from Stout Business School faculty to access business students within the business department. Subjects will consist of business students within a specified course at Stout. Participation will be strictly voluntary. Subjects will view information pertaining to a hypothetical job applicant. Confidentiality will be maintained throughout the study. No names will be requested of the subjects. The only identifiers will be which condition the subjects has (i.e. disabled versus non-disabled). Packets will be randomly administered with two conditions of physical disabilities (i.e. carpal tunnel syndrome and lower back injury) and one control condition (non-disabled job applicant). Carpal tunnel syndrome and lower back injury were chosen because research indicates they are the most frequently occurring work-related physical conditions. Within the packets will be a consent form, job description, cover letter, resume, and survey. After viewing one hypothetical job applicant, subjects will then rate the job applicant according to their perceptions of the applicant’s vocational potential, dependability, and competence. The hypothesis of interest will not be disclosed until after the survey is complete. After the data collection, the subjects of this study will be debriefed regarding the primary hypothesis under investigation. Results will be provided to the business school and others who are interested. It is hoped that this study may enhance understanding and awareness of employer selection processes pertaining to applicants with disabilities
Supplemental Material1 - Supplemental material for Evaluation of a novel screening method for fetal aneuploidy using cell-free DNA in maternal plasma
No full textSupplemental material, Supplemental Material1 for Evaluation of a novel screening method for fetal aneuploidy using cell-free DNA in maternal plasma by Richard P Porreco, Matthew Sekedat, Allan Bombard, Thomas J Garite, Kimberly Maurel, Barbara Marusiak, David Adair, April Bleich, C Andrew Combs, Wayne Kramer, Sherri Longo, Michael Nageotte, Amber Samuel, Jeroen Vanderhoeven, Jeff Buis, Kevin B Jacobs and Jay Stoerker in Journal of Medical Screening</p
Supplemental Material2 - Supplemental material for Evaluation of a novel screening method for fetal aneuploidy using cell-free DNA in maternal plasma
No full textSupplemental material, Supplemental Material2 for Evaluation of a novel screening method for fetal aneuploidy using cell-free DNA in maternal plasma by Richard P Porreco, Matthew Sekedat, Allan Bombard, Thomas J Garite, Kimberly Maurel, Barbara Marusiak, David Adair, April Bleich, C Andrew Combs, Wayne Kramer, Sherri Longo, Michael Nageotte, Amber Samuel, Jeroen Vanderhoeven, Jeff Buis, Kevin B Jacobs and Jay Stoerker in Journal of Medical Screening</p
PRECISION FOURIER TRANSFORM SPECTROSCOPY WITH FEMTOSECOND FREQUENCY COMBS
No full textAuthor Institution: Laboratoire de Photophysique Moleculaire, CNRS, Batiment 350, Universite Paris-Sud, 91405 Orsay cedex, France; Max Planck Institut fur Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany\begin{wrapfigure}[13]{r}{6cm} \vspace{1.7cm} \hspace*{-1.00cm} \epsfig{file=H5O2+09.eps,width=7.7cm, height = 5.2cm} \end{wrapfigure} Fourier transform spectrometers play a crucial and intensive role in molecular spectroscopy. However, these instruments, most often based on Michelson interferometers, are presently unable to address some of the new challenges associated with fundamental experiments or optical diagnostic.\\ In recent years, femtosecond frequency combs, which are new laser sources exhibiting an optical spectrum made of very sharp and uniformly spaced lines, have revolutionized the field of frequency metrology. They lead also to the implementation of a new kind of Fourier interferometers, where two frequency combs with slightly different repetition rates beat with each other. These spectrometers may bring remarkable characteristics, amongst which extremely short measurement time.\\ We report on the implementation of an original and simple set-up for frequency comb Fourier transform spectroscopy, which reaches the unprecedented resolution of 1 kHz within 6 s recording time. Moving mirror of equivalent Michelson interferometers should cover 130 km path-difference excursion at 10 km.s velocity. We also record simultaneously Doppler-limited dispersion and absorption spectra within a few tens of microseconds. The comb structure of the light source provides self-calibration of the wavenumber scale. Precision spectroscopy of the overtone spectrum of acetylene, in the 1.5 m range, is reported as a first demonstration
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