14,967 research outputs found
Controlling Light Through Optical Disordered Media : Transmission Matrix Approach
We experimentally measure the monochromatic transmission matrix (TM) of an
optical multiple scattering medium using a spatial light modulator together
with a phase-shifting interferometry measurement method. The TM contains all
information needed to shape the scattered output field at will or to detect an
image through the medium. We confront theory and experiment for these
applications and we study the effect of noise on the reconstruction method. We
also extracted from the TM informations about the statistical properties of the
medium and the light transport whitin it. In particular, we are able to isolate
the contributions of the Memory Effect (ME) and measure its attenuation length
Hanbury-Brown-Twiss measurements at large rapidity separations, or can we measure the proton radius in p-A collisions?
We point out that current calculations of inclusive two-particle correlations
in p-A collisions based on the Color Glass Condensate approach exhibit a
contribution from Hanbury-Brown-Twiss correlations. These HBT correlations are
quite distinct from the standard ones, in that they are apparent for particles
widely separated in rapidity. The transverse size of the emitter which is
reflected in these correlations is the gluonic size of the proton. This raises
an interesting possibility of measuring the proton size directly by the HBT
effect of particle pairs produced in p-A collisions.Comment: 11 pages, 3 eps figures; v2: comments, discussions, references and
acknowledgements added, conclusions unchanged, final versio
Beamforming and Multiuser Detection in CDMA Systems with External Interferences
Multiuser detection has been investigated to mitigate the near-far effect in CDMA systems. Antenna arrays have been shown to provide spatial diversity and cancel undesired signals. In this paper we consider the synergy of both multiuser detection and antenna arrays for the base station of a CDMA system. The receiver we proposed consists of the known multiuser decorrelator, which cancels multiple-access interferences followed by a beamformer for each user, which cancels the external interferences. This receiver adds an extra branch to the decorrelator. This additional branch, corresponding to a fictitious user with an unused code and zero power, allows to estimate the external interference signal subspace and compute a suitable beamforming weight-vector that cancels the external interferences. The receiver is also extended to the asynchronous case and all of this without any training signal or any a priori spatial information.Peer ReviewedPostprint (published version
Nonlinear propagation in multi-mode fibers in the strong coupling regime
In spite of the massive interest that the generalized Manakov equation has
attracted in the past two decades, no physical system which is quantitatively
described by this equation has been reported so far. In this paper we show that
propagation in a group of degenerate modes of a multi-mode optical fiber
satisfies this equation in the presence of random mode coupling. Consequently,
this is the first reported physical system that admits true multi-component
soliton solutions. The reported formalism constitutes the starting point for
future studies of nonlinear effects in multi-mode fiber transmission
Spatial coherence of forward-scattered light in a turbid medium
We study spatially coherent forward-scattered light propagating in a turbid medium of moderate optical depth (0-9 mean free paths). Coherent detection was achieved by using a tilted heterodyne geometry, which desensitizes coherent detection of the attenuated incident light. We show that the degree of spatial coherence is significantly higher for light scattered only once in comparison with that for multiply scattered light and that it approaches a small constant value for large numbers of scattering events
Recognition and reconstruction of coherent energy with application to deep seismic reflection data
Reflections in deep seismic reflection data tend to be
visible on only a limited number of traces in a common
midpoint gather. To prevent stack degeneration,
any noncoherent reflection energy has to be removed.
In this paper, a standard classification technique in
remote sensing is presented to enhance data quality. It
consists of a recognition technique to detect and extract
coherent energy in both common shot gathers and fi-
nal stacks. This technique uses the statistics of a picked
seismic phase to obtain the likelihood distribution of its
presence. Multiplication of this likelihood distribution
with the original data results in a âcleaned upâ section.
Application of the technique to data from a deep seismic
reflection experiment enhanced the visibility of all
reflectors considerably.
Because the recognition technique cannot produce an
estimate of âmissingâ data, it is extended with a reconstruction
method. Two methods are proposed: application
of semblance weighted local slant stacks after recognition,
and direct recognition in the linear tau-p domain.
In both cases, the power of the stacking process to increase the signal-to-noise ratio is combined with the direct selection of only specific seismic phases. The joint
application of recognition and reconstruction resulted in
data images which showed reflectors more clearly than
application of a single technique
Hybrid Coding Technique for Pulse Detection in an Optical Time Domain Reflectometer
The paper introduces a novel hybrid coding technique for improved pulse detection in an optical time domain reflectometer. The hybrid schemes combines Simplex codes with signal averaging to articulate a very sophisticated coding technique that considerably reduces the processing time to extract specified coding gains in comparison to the existing techniques. The paper quantifies the coding gain of the hybrid scheme mathematically and provide simulative results in direct agreement with the theoretical performance. Furthermore, the hybrid scheme has been tested on our self-developed OTDR
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