477 research outputs found
Phase-coherent lightwave communications with frequency combs
No full textFiber-optical networks are a crucial telecommunication infrastructure in society. Wavelength division multiplexing allows for transmitting parallel data streams over the fiber bandwidth, and coherent detection enables the use of sophisticated modulation formats and electronic compensation of signal impairments. Optical frequency combs can replace the multiple lasers used for the different wavelength channels. Beyond multiplexing, it has been suggested that the broadband phase coherence of frequency combs could simplify the receiver scheme by performing joint reception and processing of several wavelength channels, but an experimental validation in a fiber transmission experiment remains elusive. Here we demonstrate and quantify joint reception and processing of several wavelength channels in a full transmission system. We demonstrate two joint processing schemes; one that reduces the phase-tracking complexity and one that increases the transmission performance.\ua0\ua9 2020, The Author(s)
Mechanical overtone frequency combs
No full textMechanical frequency combs are poised to bring the applications and utility
of optical frequency combs into the mechanical domain. So far, their main
challenge has been strict requirements on drive frequencies and power, which
complicate operation. We demonstrate a straightforward mechanism to create a
frequency comb consisting of mechanical overtones (integer multiples) of a
single eigenfrequency, by monolithically integrating a suspended dielectric
membrane with a counter-propagating optical trap. The periodic optical field
modulates the dielectrophoretic force on the membrane at the overtones of a
membrane's motion. These overtones share a fixed frequency and phase relation,
and constitute a mechanical frequency comb. The periodic optical field also
creates an optothermal parametric drive that requires no additional power or
external frequency reference. This combination of effects results in an
easy-to-use mechanical frequency comb platform that requires no precise
alignment, no additional feedback or control electronics, and only uses a
single, mW continuous wave laser beam. This highlights the overtone frequency
comb as the straightforward future for applications in sensing, metrology and
quantum acoustics
Bulletin No. 166 - Sterilization of Brood Combs Infected With American Foulbrood
No full textBulletin No. 166 - Sterilization of Brood Combs Infected With American Foulbroo
Understanding Eastern Kentucky Ecosystems: Three Studies
No full textThree different projects conducted by students working with the Eastern Kentucky Environmental Research Institute at EKU are featured in this poster. “Woody Plant Species Compositional Response to a Timber Harvest in South-Central Kentucky” (Emily Clemons), compared a site logged in 1996 with nearby unlogged control site to examine the regeneration of forest structure post-timbering. Prior to harvest, the logged site was divided into 25 plots, and an unharvested control area was established consisting of 16 plots. This followup ten years after the timber harvest examined forest composition information was collected in the same manner from both the harvested and unharvested plot sites. “GroundTruthing Remotely Sensed Data In a Small Watershed on the Urban/Rural Fringe” (Jill Hunter), tested methods of generating a land coverage at reasonable cost by combining the National Land Cover Dataset (NLCD), the National Agriculture Imagery Program digital orthophotography, and a limited number of field observations to produce a revised polygonal land use layer. While the NLCD is good for GIS applications at the state scale, it much less accurate at the small watershed scale where many land management decisions take place. “The Big Dip (Evan Smith, ,Jeff Combs, and others) was a diagnostic sampling of 917 headwaters streams in Southeastern Kentucky conducted by a team of both EKU students and community members in Letcher county. The geographic distribution of the eight parameters tested and their implications for ecological and community health will be presented
SCALING OF YB-FIBER FREQUENCY COMBS
No full textAuthor Institution: IMRA America Inc., 1044 Woodridge Avenue, Ann Arbor, Mi 48105-9774, USAImmediately after their introduction in 1999, femtosecond laser frequency combs revolutionized the field of precision optical frequency metrology and are key elements in many experiments. Frequency combs based on femtosecond Er-fiber lasers based were demonstrated in 2005, allowing additionally rugged, compact set-ups and reliable unattended long-term operation. The introduction of Yb-fiber technology led to an dramatic improvement in fiber-comb performance in various aspects. Low-noise Yb-fiber femtosecond oscillators enabled a reduction of relative comb tooth linewidth to the sub-Hz level 355 (2008).} as well as scaling of the fundamental comb spacings up to 1 GHz. This is beneficial for any frequency-domain comb application due to the higher power per comb-mode. Many spectroscopic applications require, however, frequency combs way beyond the wavelength range accessible with broad band laser materials, so nonlinear conversion and hence higher peak intensity is required. We demonstrated power scaling of Yb-fiber frequency combs up to 80 W average power in a strictly linear chirped-pulse amplification schemes compatible with low-noise phase control. These high-power Yb-fiber-frequency combs facilitated not only the extension to the mid-IR spectral region 1330 (2009).}. When coupled to a passive enhancement cavity, the average power can be further scaled to the kW-level opening new capabilities for XUV frequency combs via high-harmonic generation 815 (2009).}. All these advances of fiber-based frequency combs will trigger many novel applications both in fundamental and applied sciences
LASER FREQUENCY COMBS FOR PRECISION RADIAL VELOCITY MEASUREMENTS IN ASTROPHYSICS
No full textAuthor Institution: Harvard-Smithsonian, Cambridge, MALaser frequency combs adapted to serve as wavelength calibrators for astrophysical spectrographs (astro-combs) may greatly advance precision astrophysical spectroscopy, and thus provide a crucial tool for cosmology and the search for Earth-like exoplanets. I will discuss recent progress in developing astro-comb calibrators and bringing them into practice at observatories, with an emphasis on their utility for improving radial velocity precision in exoplanet studies
Experimental Investigation of Tunable Acousto-Optic Frequency Combs
No full textWe demonstrate novel approach for generation of optical combs in frequency shifting loop based on acousto-optic interaction. This approach provides comb multiplication with different line spacing and generation of dual-comb for spectroscopy applications. (c) 2021 The Author(s
Blackout: The Continuing Assault Against Black Bodies
No full textBlackness in a society built largely on anti-Black sentiments simultaneously renders Black bodies both a heightened sense of visibility and invisibility in society. In this talk, Combs shares insights from her new book, Bodies out of Place: Theorizing Anti-Blackness in US Society, which examines practices of racial entrenchment as they have manifested in post-Obama expressions of anti Blackness in discursive, legal, interactional, and extralegal contexts. Combs examines recent incidents of everyday racism against Black persons (the killing of Ahmaud Arbery, the Central Park birding incident, various cases on college campuses, among others) to arrive at a theorization of what expectations about bodies, space, and belonging tell us about the way racism is perpetuated in US society. Barbara Harris Combs is professor of sociology and chair of the Department of Sociology and Criminal Justice at Kennesaw State University. Combs is also the author of From Selma to Montgomery: The Long March to Freedom. Her forthcoming book, Black Places and Spaces of Political Empowerment, with coauthors Todd C. Shaw and Kirk Foster, is under contract with Oxford University Press
Symmetry-Breaking-Induced Frequency Combs in Graphene Resonators
No full text[Image: see text] Nonlinearities are inherent to the dynamics of two-dimensional materials. Phenomena-like intermodal coupling already arise at amplitudes of only a few nanometers, and a range of unexplored effects still awaits to be harnessed. Here, we demonstrate a route for generating mechanical frequency combs in graphene resonators undergoing symmetry-breaking forces. We use electrostatic force to break the membrane’s out-of-plane symmetry and tune its resonance frequency toward a one-to-two internal resonance, thus achieving strong coupling between two of its mechanical modes. When increasing the drive level, we observe splitting of the fundamental resonance peak, followed by the emergence of a frequency comb regime. We attribute the observed physics to a nonsymmetric restoring potential and show that the frequency comb regime is mediated by Neimark bifurcation of the periodic solution. These results demonstrate that mechanical frequency combs and chaotic dynamics in 2D material resonators can emerge near internal resonances due to symmetry-breaking
Integrated Photonic Interposers for Processing Octave-Spanning Microresonator Frequency Combs
No full textWe demonstrate multiple silicon-nitride nanophotonic elements for on-chip processing of octave-spanning microresonator frequency combs. Dichroic filters, multimode interferometers, and tunable add-drop microring filters are shown along with soliton microcombs generated on a bilayer photonic chip. (C) 2020 The Author(s)LSMLPQ
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