31 research outputs found
A universal optical all-fiber omnipolarizer
Wherever the polarization properties of a light beam are of concern, polarizers and polarizing beamsplitters (PBS) are indispensable devices in linear-, nonlinear-and quantum-optical schemes. By the very nature of their operation principle, transformation of incoming unpolarized or partially polarized beams through these devices introduces large intensity variations in the fully polarized outcoming beam(s). Such intensity fluctuations are often detrimental, particularly when light is post-processed by nonlinear crystals or other polarization-sensitive optic elements. Here we demonstrate the unexpected capability of light to self-organize its own state-of-polarization, upon propagation in optical fibers, into universal and environmentally robust states, namely right and left circular polarizations. We experimentally validate a novel polarizing device-the Omnipolarizer, which is understood as a nonlinear dual-mode polarizing optical element capable of operating in two modes-as a digital PBS and as an ideal polarizer. Switching between the two modes of operation requires changing beam's intensity
A connection between optimal control theory and adiabatic passage techniques in quantum systems
This work explores the relationship between optimal control theory and
adiabatic passage techniques in quantum systems. The study is based on a
geometric analysis of the Hamiltonian dynamics constructed from the Pontryagin
Maximum Principle. In a three-level quantum system, we show that the Stimulated
Raman Adiabatic Passage technique can be associated to a peculiar Hamiltonian
singularity. One deduces that the adiabatic pulse is solution of the optimal
control problem only for a specific cost functional. This analysis is extended
to the case of a four-level quantum system.Comment: 19 pages, 6 figure
Saturation of a spin 1/2 particle by generalized Local control
We show how to apply a generalization of Local control design to the problem
of saturation of a spin 1/2 particle by magnetic fields in Nuclear Magnetic
Resonance. The generalization of local or Lyapunov control arises from the fact
that the derivative of the Lyapunov function does not depend explicitly on the
control field. The second derivative is used to determine the local control
field. We compare the efficiency of this approach with respect to the
time-optimal solution which has been recently derived using geometric methods.Comment: 12 pages, 4 figures, submitted to new journal of physics (2011
The FALCON concept: multi-object adaptive optics and atmospheric tomography for integral field spectroscopy. Principles and performances on an 8 meter telescope
Integral field spectrographs are major instruments to study the mechanisms
involved in the formation and the evolution of early galaxies. When combined
with multi-object spectroscopy, those spectrographs can behave as machines used
to derive physical parameters of galaxies during their formation process. Up to
now, there is only one available spectrograph with multiple integral field
units, e.g. FLAMES/GIRAFFE on the VLT. However, current ground based
instruments suffer from a degradation of their spatial resolution due to
atmospheric turbulence. In this article we describe the performance of FALCON,
an original concept of a new generation multi-object integral field
spectrograph with adaptive optics for the ESO Very Large Telescope. The goal of
FALCON is to combine high angular resolution (0.25 arcsec) and high spectral
resolution (R > 5000) in J and H bands over a wide field of view (10x10
arcmin2) in the VLT Nasmyth focal plane. However, instead of correcting the
whole field, FALCON will use multi-object adaptive optics (MOAO) to perform
locally on each scientific target the adaptive optics correction. This requires
then to use atmospheric tomography in order to use suitable natural guide stars
for wavefront sensing. We will show that merging MOAO and atmospheric
tomography allows us to determine the internal kinematics of distant galaxies
up to z=2 with a sky coverage of 50%, even for objects observed near the
galactic pole. The application of such a concept to Extremely Large Telescopes
seems therefore to be a very promising way to study galaxy evolution from z = 1
to redshifts as high as z = 7.Comment: Monthly Notices of the Royal Astronomical Society, accepte
Line of polarization attraction in highly birefringent optical fibers
We investigate the phenomenon of polarization attraction in a highly birefringent fiber. This polarization process originates from the nonlinear interaction of two counter-propagating beams. We show that all polarization states of the forward (signal) beam are attracted toward a specific line of polarization states on the surface of the Poincaré sphere, whose characteristics are determined by the polarization state of the injected backward (pump) beam. This phenomenon of polarization attraction takes place without any loss of energy for the signal beam. The stability of different stationary solutions is also discussed through intensive numerical simulations. On the basis of mathematical techniques recently developed for the study of Hamiltonian singularities, we provide a detailed description of this spontaneous polarization process. In several particular cases of interest, the equation of the line of polarization attraction on the Poincaré sphere can be obtained in explicit analytical form
FALCON: Extending adaptive corrections to cosmological fields
International audienceWe present FALCON which is an original concept for a next generation instrument which could be used on the ESO very large telescope (VLT) and on the future extremely large telescopes (ELT). It is a multi-object integral field spectrograph with multiple small integral field units (IFUs). Each of them integrates a tiny adaptive optics system coupled with atmospheric tomography to solve the sky coverage problem. This therefore allows to reach spatial (∼0.25 arcsec) and spectral ( R ⩾ 5000) resolutions suitable for distant galaxy studies in the 0.8-1.8 μm wavelength range. In the FALCON concept, the adaptive optics correction is only applied to small and discrete areas selected within a large field. This approach implies to develop miniaturized devices, such as deformable mirrors (DM) and wavefront sensors (WFS) for wavefront correction