6,748 research outputs found
The coronagraphic Modal Wavefront Sensor: a hybrid focal-plane sensor for the high-contrast imaging of circumstellar environments
The raw coronagraphic performance of current high-contrast imaging
instruments is limited by the presence of a quasi-static speckle (QSS)
background, resulting from instrumental non-common path errors (NCPEs). Rapid
development of efficient speckle subtraction techniques in data reduction has
enabled final contrasts of up to 10-6 to be obtained, however it remains
preferable to eliminate the underlying NCPEs at the source. In this work we
introduce the coronagraphic Modal Wavefront Sensor (cMWS), a new wavefront
sensor suitable for real-time NCPE correction. This pupil-plane optic combines
the apodizing phase plate coronagraph with a holographic modal wavefront
sensor, to provide simultaneous coronagraphic imaging and focal-plane wavefront
sensing using the science point spread function. We first characterise the
baseline performance of the cMWS via idealised closed-loop simulations, showing
that the sensor successfully recovers diffraction-limited coronagraph
performance over an effective dynamic range of +/-2.5 radians root-mean-square
(RMS) wavefront error within 2-10 iterations. We then present the results of
initial on-sky testing at the William Herschel Telescope, and demonstrate that
the sensor is able to retrieve injected wavefront aberrations to an accuracy of
10nm RMS under realistic seeing conditions. We also find that the cMWS is
capable of real-time broadband measurement of atmospheric wavefront variance at
a cadence of 50Hz across an uncorrected telescope sub-aperture. When combined
with a suitable closed-loop adaptive optics system, the cMWS holds the
potential to deliver an improvement in raw contrast of up to two orders of
magnitude over the uncorrected QSS floor. Such a sensor would be eminently
suitable for the direct imaging and spectroscopy of exoplanets with both
existing and future instruments, including EPICS and METIS for the E-ELT.Comment: 14 pages, 12 figures: accepted for publication in Astronomy &
Astrophysic
Quantum information processing with space-division multiplexing optical fibres
The optical fibre is an essential tool for our communication infrastructure
since it is the main transmission channel for optical communications. The
latest major advance in optical fibre technology is spatial division
multiplexing (SDM), where new fibre designs and components establish multiple
co-existing data channels based on light propagation over distinct transverse
optical modes. Simultaneously, there have been many recent developments in the
field of quantum information processing (QIP), with novel protocols and devices
in areas such as computing, communication and metrology. Here, we review recent
works implementing QIP protocols with SDM optical fibres, and discuss new
possibilities for manipulating quantum systems based on this technology.Comment: Originally submitted version. Please see published version for
improved layout, new tables and updated references following review proces
BICEP2 II: Experiment and Three-Year Data Set
We report on the design and performance of the BICEP2 instrument and on its
three-year data set. BICEP2 was designed to measure the polarization of the
cosmic microwave background (CMB) on angular scales of 1 to 5 degrees
(=40-200), near the expected peak of the B-mode polarization signature of
primordial gravitational waves from cosmic inflation. Measuring B-modes
requires dramatic improvements in sensitivity combined with exquisite control
of systematics. The BICEP2 telescope observed from the South Pole with a 26~cm
aperture and cold, on-axis, refractive optics. BICEP2 also adopted a new
detector design in which beam-defining slot antenna arrays couple to
transition-edge sensor (TES) bolometers, all fabricated on a common substrate.
The antenna-coupled TES detectors supported scalable fabrication and
multiplexed readout that allowed BICEP2 to achieve a high detector count of 500
bolometers at 150 GHz, giving unprecedented sensitivity to B-modes at degree
angular scales. After optimization of detector and readout parameters, BICEP2
achieved an instrument noise-equivalent temperature of 15.8 K sqrt(s). The
full data set reached Stokes Q and U map depths of 87.2 nK in square-degree
pixels (5.2 K arcmin) over an effective area of 384 square degrees within
a 1000 square degree field. These are the deepest CMB polarization maps at
degree angular scales to date. The power spectrum analysis presented in a
companion paper has resulted in a significant detection of B-mode polarization
at degree scales.Comment: 30 pages, 24 figure
Study of optoelectronic switch for satellite-switched time-division multiple access
The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix
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