Search results for "Polar"
showing 10 items of 3817 documents
Field-free molecular alignment of asymmetric top molecules using elliptically polarized laser pulses
2008
International audience; We show theoretically that a short specific elliptically polarized laser pulse driving an asymmetric top molecule can induce postpulse revivals of three-dimensional (3-D) alignment. By choosing the field ellipticity resulting in the best compromise between the alignment of two molecular axes, we demonstrate that efficient 3-D alignment can be achieved at low temperature. In the experiment, the field-free alignment of moderately cool ethylene molecules is probed by using a technique based on the optical Kerr effect. Control of 3-D field-free alignment opens the door to a large range of applications in chemistry as well as in molecular optics.
Spatial and spectral nonlinear shaping of multimode waves
2016
We demonstrate a novel nonlinear dynamics of multimode fibers that reshapes their spectral and spatial beam profiles, based on spatiotemporal modulation instability. Sidebands ranging from the visible to the near-infrared are carried by one and the same spatial bell-shaped profile.
High repetition rates and high quality optical pulse train generator based on solitons over finite background
2013
This work proposes to fully exploit the nonlinear evolution undergone by a sinusoidal modulation with a finite background propagating along an optical fiber. For the original method to overcome this major drawback is to exploit the π phase shift that exists between the pulsed part and the background. By using a simple delay-line interferometer, it is possible to simultaneously double the repetition rate of the pulse train and to annihilate the deleterious background by imprinting a controlled π phase shift.
Experimental investigation of a polarization attractor at telecommunication wavelengths
2008
We report the experimental observation of a polarization attraction process taking place in an optical fiber around 1550 nm and based on a nonlinear interaction between two counter-propagating waves.
Complete nonlinear polarization control in an optical fiber system.
2010
International audience; We consider the counterpropagating interaction of a signal and a pump beam in an isotropic optical fiber. On the basis of recently developed mathematical techniques, we show that an arbitrary state of polarization of the signal beam can be converted into any other desired state of polarization. On the other hand, an unpolarized signal beam may be repolarized into two specific states of polarization, without loss of energy. Both processes of repolarization and polarization conversion may be controlled by adjusting the polarization state of the backward pump.
Optical gratings induced by field-free alignment of molecules
2006
We analyze the alignment of molecules generated by a pair of crossed ultra-short pump pulses of different polarizations by a technique based on the induced time-dependent gratings. Parallel polarizations yield an intensity grating, while perpendicular polarizations induce a polarization grating. We show that both configurations can be interpreted at moderate intensity as an alignment induced by a single polarized pump pulse. The advantage of the perpendicular polarizations is to give a signal of alignment that is free from the plasma contribution. Experiments on femtosecond transient gratings with aligned molecules were performed in CO2 at room temperature in a static cell and at 30 K in a …
Modal attraction on low order modes by Kerr effect in a graded refractive index multimode fiber
2018
Modal attraction towards low order modes in a GRIN multimode fiber was experimentally observed at high power and characterized, thus enriching the dynamics of the Kerr self-cleaning effect leading to quasi fundamental mode generation.
Optical flip-flop memory and data packet switching operation based on polarization bistability in a telecommunication optical fiber
2013
We report the experimental observation of bistability and hysteresis phenomena of the polarization signal in a telecommunication optical fiber. This process occurs in a counterpropagating configuration in which the optical beam nonlinearly interacts with its own Bragg-reflected replica at the fiber output. The proof of principle of optical flip–flop memory and 10 Gbit/s routing operation is also reported based on this polarization bistability. Finally, we also provide a general physical understanding of this behavior on the basis of a geometrical analysis of an effective model of the dynamics. Good quantitative agreement between theory and experiment is obtained.
Active reduction of fluctuations in fourth-order modulation instability
2012
International audience; We experimentally study the fluctuation properties of a scalar fourth-order modulation instability process obtained by pumping a photonic crystal fiber in the normal dispersion region. We observe large wavelength-dependant pulse-to-pulse fluctuations which cannot be significantly reduced by stimulating the process with a single seed. Their reduction requires two seeds slightly detuned from the maximum gain frequency in order to also stimulate the second-order modulation instability process cascaded from the fourth-order one. This concept is validated by experiments and numerical simulations.
Self-polarization effect in the middle point of an optical fiber
2019
In this paper, we report both numerically and experimentally an unexpected phenomenon of self-polarization occurring in the middle point of an isotropic optical fiber when two uncorrelated partially polarized waves are simultaneously injected at the ends of the fiber. More precisely, we demonstrate that two counterpropagating waves of equal intensity exhibit a spontaneous organization of their polarization states around two pools of attraction just in the middle point of propagation, and then both recover a partially polarized state at their respective fiber outputs. The self-polarization effect then remains hidden within the optical fiber in the sense that no apparent sign of this process …