54 research outputs found
Quantum measurements of spatial conjugate variables: Displacement and tilt of a Gaussian beam
We consider the problem of measurement of optical transverse profile
parameters and their conjugate variable. Using multi-mode analysis, we
introduce the concept of detection noise-modes. For Gaussian beams,
displacement and tilt are a pair of transverse profile conjugate variables. We
experimentally demonstrate their optimal encoding and detection with a spatial
homodyning scheme. Using higher order spatial mode squeezing, we show the
sub-shot noise measurements for the displacement and tilt of a Gaussian beam.Comment: 3 page
Optimum Small Optical Beam Displacement Measurement
We derive the quantum noise limit for the optical beam displacement of a
TEM00 mode. Using a multimodal analysis, we show that the conventional split
detection scheme for measuring beam displacement is non-optimal with 80%
efficiency. We propose a new displacement measurement scheme that is optimal
for small beam displacement. This scheme utilises a homodyne detection setup
that has a TEM10 mode local oscillator. We show that although the quantum noise
limit to displacement measurement can be surpassed using squeezed light in
appropriate spatial modes for both schemes, the TEM10 homodyning scheme
out-performs split detection for all values of squeezing.Comment: 13 pages, 7 figure
Generation of Squeezing in Higher Order Hermite-Gaussian Modes with an Optical Parametric Amplifier
We demonstrate quantum correlations in the transverse plane of continuous
wave light beams by producing -4.0 dB, -2.6 dB and -1.5 dB of squeezing in the
TEM00, TEM10 and TEM20 Hermite- Gauss modes with an optical parametric
amplifier, respectively. This has potential applications in quantum information
networking, enabling parallel quantum information processing. We describe the
setup for the generation of squeezing and analyze the effects of various
experimental issues such as mode overlap between pump and seed and nonlinear
losses.Comment: 7 pages, 4 figure
Continuous-wave phase-sensitive parametric image amplification
We study experimentally parametric amplification in the continuous regime
using a transverse-degenerate type-II Optical Parametric Oscillator operated
below threshold. We demonstrate that this device is able to amplify either in
the phase insensitive or phase sensitive way first a single mode beam, then a
multimode image. Furthermore the total intensities of the amplified image
projected on the signal and idler polarizations are shown to be correlated at
the quantum level.Comment: 14 pages, 7 figures, submitted to Journal of Modern Optics, Special
Issue on Quantum Imagin
Quantum limits in image processing
We determine the bound to the maximum achievable sensitivity in the
estimation of a scalar parameter from the information contained in an optical
image in the presence of quantum noise. This limit, based on the Cramer-Rao
bound, is valid for any image processing protocol. It is calculated both in the
case of a shot noise limited image and of a non-classical illumination. We also
give practical experimental implementations allowing us to reach this absolute
limit.Comment: 4 pages, two figure
A quantum study of multi-bit phase coding for optical storage
We propose a scheme which encodes information in both the longitudinal and
spatial transverse phases of a continuous-wave optical beam. A split
detector-based interferometric scheme is then introduced to optimally detect
both encoded phase signals. In contrast to present-day optical storage devices,
our phase coding scheme has an information storage capacity which scales with
the power of the read-out optical beam. We analyse the maximum number of
encoding possibilities at the shot noise limit. In addition, we show that using
squeezed light, the shot noise limit can be overcome and the number of encoding
possibilities increased. We discuss a possible application of our phase coding
scheme for increasing the capacities of optical storage devices.Comment: 8 pages, 7 figures (Please email author for a PDF file if the
manuscript does not turn out properly
TEM10 homodyne detection as an optimal small displacement and tilt measurements scheme
We report an experimental demonstration of optimal measurements of small
displacement and tilt of a Gaussian beam - two conjugate variables - involving
a homodyne detection with a TEM10 local oscillator. We verify that the standard
split detection is only 64% efficient. We also show a displacement measurement
beyond the quantum noise limit, using a squeezed vacuum TEM10 mode within the
input beam.Comment: 9 pages, 8 figure
Quantum Noise in Multipixel Image Processing
We consider the general problem of the quantum noise in a multipixel
measurement of an optical image. We first give a precise criterium in order to
characterize intrinsic single mode and multimode light. Then, using a
transverse mode decomposition, for each type of possible linear combination of
the pixels' outputs we give the exact expression of the detection mode, i.e.
the mode carrying the noise. We give also the only way to reduce the noise in
one or several simultaneous measurements.Comment: 8 pages and 1 figur
Programmable unitary spatial modes manipulation
Free space propagation and conventional optical systems such as lenses and
mirrors all perform spatial unitary transforms. However, the subset of
transforms available through these conventional systems is limited in scope. We
present here a unitary programmable mode converter (UPMC) capable of performing
any spatial unitary transform of the light field. It is based on a succession
of reflections on programmable deformable mirrors and free space propagation.
We first show theoretically that a UPMC without limitations on resources can
perform perfectly any transform. We then build an experimental implementation
of the UPMC and show that, even when limited to three reflections on an array
of 12 pixels, the UPMC is capable of performing single mode tranforms with an
efficiency greater than 80% for the first 4 modes of the TEM basis
Real-time distance measurement immune from atmospheric parameters using optical frequency combs
We propose a direct and real-time ranging scheme using an optical frequency
combs, able to compensate optically for index of refraction variations due to
atmospheric parameters. This scheme could be useful for applications requiring
stringent precision over a long distance in air, a situation where dispersion
becomes the main limitation. The key ingredient is the use of a mode-locked
laser as a precise source for multi-wavelength interferometry in a homodyne
detection scheme. By shaping temporally the local oscillator, one can directly
access the desired parameter (distance) while being insensitive to fluctuations
induced by parameters of the environment such as pressure, temperature,
humidity and CO content
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