728 research outputs found
Enhancement of multioctave dynamic range in a push-pull modulated analog photonic link
We demonstrate an analog photonic link with a high multioctave spurious-free dynamic range (SFDR) using a push-pull modulation technique of laser diodes combined with a balanced detection scheme. SFDR enhancements ranging from 5 dB to 18 dB, relative to the case of a single arm link, have been obtained in a frequency range of 2.5 GHz to 3.2 GHz
Ring resonator-based Tunable Optical Delay Line in LPCVD Waveguide Technology
Optical circuits providing a time delay to signals modulated on optical carriers are considered important for optical communication systems and phased array antennas. A continuously tunable optical delay line is demonstrated in low-cost CMOS compatible LPCVD planar waveguide technology. The device consists of three cascaded ringresonator all-pass filters with fixed circumference of 2 cm (delay of 0.12 ns and FSR of 8.4 GHz). The measured group delay ranges from 0 ns up to 1.2 ns with a bandwidth of 500 MHz and delay ripple smaller than 1 ps, which is in accordance with the calculations
Ring resonator-based single-chip 1x8 optical beam forming network in LPCVD waveguide technology
Optical ring resonators (ORRs) are good candidates to provide continuously tunable delay in beam forming networks (BFNs) for phased array antenna systems. \ud
Delay and splitting/combining elements can be integrated on a single optical chip to form an OBFN. A state-of-the-art 1×8 OBFN chip has been fabricated in LPCVD waveguide technology.\ud
It is designed with 1 input and 8 outputs, between which a binary-tree topology is used. A different number of ORRs (up to 7) are cascaded for each output.\ud
In this paper, the principle of operation is explained and demonstrated by presenting measurements on the 1×8 OBFN chip
Optical beam forming for phased-array antennas
The activities of the Telecommunication Engineering (TE) group span the communications spectrum from copper cables, optical fibres, microwaves, radio and electromagnetic compatibility. Our research concentrates on optical signal processing and networks, mobile communications, microwave techniques and radiation from ICs and PCBs [1]. A considerable (and particularly interesting) part of it is related to optical beam forming for phased array antennas, using optical ring resonators.\ud
In this article the theoretical basics and practical challenges of this interesting research topic will be summarized.\u
Phased array antenna steering using a ring resonator-based optical beam forming network
A novel beam steering mechanism for a phased array antenna receiver system is introduced. The core of the system is a ring resonator-based integrated optical beam forming network chip. Its principles are explained and demonstrated by presenting some measurement results. The system architecture around the chip is based on a combination of frequency down conversion, filter-based optical single sideband modulation and balanced coherent detection. It is proven that such an architecture has significant advantages with respect to a straightforward architecture using double sideband modulation and direct detection, namely relaxed bandwidth requirements on the optical modulators and detectors, reduced complexity and optical losses of the beam forming chip, and enhanced dynamic range
A Chandra Proper Motion for PSR J1809-2332
We report on a new Chandra exposure of PSR J1809-2332, the recently
discovered pulsar powering the bright EGRET source 3EG J1809-2328. By
registration of field X-ray sources in an archival exposure, we measure a
significant proper motion for the pulsar point source over an ~11 year
baseline. The shift of 0.30+/-0.06" (at PA= 153.3+/-18.4) supports an
association with proposed SNR parent G7.5-1.7. Spectral analysis of diffuse
emission in the region also supports the interpretation as a hard wind nebula
trail pointing back toward the SNR.Comment: To Appear in the Astrophysical Journal, Sept 1 (v. 756
Rings and Jets around PSR J2021+3651: the `Dragonfly Nebula'
We describe recent Chandra ACIS observations of the Vela-like pulsar PSR
J2021+3651 and its pulsar wind nebula (PWN). This `Dragonfly Nebula' displays
an axisymmetric morphology, with bright inner jets, a double-ridged inner
nebula, and a ~30" polar jet. The PWN is embedded in faint diffuse emission: a
bow shock-like structure with standoff ~1' brackets the pulsar to the east and
emission trails off westward for 3-4'. Thermal (kT=0.16 +/-0.02 keV) and power
law emission are detected from the pulsar. The nebular X-rays show spectral
steepening from Gamma=1.5 in the equatorial torus to Gamma=1.9 in the outer
nebula, suggesting synchrotron burn-off. A fit to the `Dragonfly' structure
suggests a large (86 +/-1 degree) inclination with a double equatorial torus.
Vela is currently the only other PWN showing such double structure. The >12 kpc
distance implied by the pulsar dispersion measure is not supported by the X-ray
data; spectral, scale and efficiency arguments suggest a more modest 3-4 kpc.Comment: 22 pages, 5 figures, 3 tables, Accepted to Ap
Optical phase synchronization in coherent optical beamformers for phased array receive antennas
An optical phase synchronization system using a power feedback loop technique is experimentally demonstrated. The system allows coherent combining of signals modulated on the same optical carrier in a hybrid optical beam forming system setup
The \u3ci\u3ePhycodnaviridae\u3c/i\u3e: The Story of How Tiny Giants Rule the World
The family Phycodnaviridae encompasses a diverse and rapidly expanding collection of large icosahedral, dsDNA viruses that infect algae. These lytic and lysogenic viruses have genomes ranging from 160 to 560 kb. The family consists of six genera based initially on host range and supported by sequence comparisons. The family is monophyletic with branches for each genus, but the phycodnaviruses have evolutionary roots that connect them with several other families of large DNA viruses, referred to as the nucleocytoplasmic large DNA viruses (NCLDV).The phycodnaviruses have diverse genome structures, some with large regions of noncoding sequence and others with regions of ssDNA. The genomes of members in three genera in the Phycodnaviridae have been sequenced. The genome analyses have revealed more than 1000 unique genes, with only 14 homologous genes in common among the three genera of phycodnaviruses sequenced to date. Thus, their gene diversity far exceeds the number of so-called core genes. Not much is known about the replication of these viruses, but the consequences of these infections on phytoplankton have global affects, including influencing geochemical cycling and weather patterns
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