20 research outputs found
Optical fiber systems are convectively unstable
We theoretically and experimentally evidence that fiber systems are convective systems since their nonlocal inherent properties, such as the dispersion and Raman effects, break the reflection symmetry. Theoretical analysis and numerical simulations carried out for a fiber ring cavity demonstrate that the third-order dispersion term leads to the appearance of convective and absolute instabilities. Their signature is an asymmetry in the output power spectrum. Using this criterion, experimental evidence of convective instabilities is given in a fiber cavity pumped by a pulsed laser
All-fiber tunable optical delay line
We present a tunable optical delay line based on the use of a
single chirped fiber Bragg grating written into a standard single mode
optical fiber. In the proposed scheme, the delay is induced through the
Bragg grating differential group delay curve. This is achieved by launching
orthogonally polarized optical pulses in both directions into the Bragg
grating and by controlling its local birefringence. This bidirectional
propagation allows to compensate the second-order dispersion. The setup is
suitable to delay pulses with a spectral width just less than the grating
reflection bandwidth, which is particularly useful in the context of
forthcoming wavelength division multiplexing ultra-high bit rate lightwave
systems. In this work, the performances of the setup are investigated using a
pulsed laser delivering 6.3 ps Fourier transform limited pulses at 1548 nm.
A maximum delay of 120 ps (about 20 times the pulse width) is reported
experimentally
Average patterns and coherent phenomena in wide aperture lasers
Using a realistic model of wide aperture, weakly astigmatic lasers we develop a framework to analyze experimental average intensity patterns. We use the model to explain the appearance of patterns in terms of the modes of the cavity and to show that the breaking of the symmetry of the average intensity patterns is caused by overlaps in the frequency spectra of nonvanishing of modes with different parity. This result can be used even in systems with very fast dynamics to detect experimentally overlaps of frequency spectra of modes.<br/
Experimental focusing shocklike dynamics in a nonlocal optical stochastic Kerr medium
International audienceWe experimentally study the propagating of an optical intensity jump discontinuity in a nonlocal stochastic Kerr focusing nematic liquid crystal cell. We show both theoretically and experimentally that nonlocality opens a route towards beam steering in our system. Indeed, the discontinuity trajectory follows a curve that bends with the injected power. Despite the stochastic nature of the medium and the constant presence of transverse instabilities, the development of a focusing shocklike dynamics is shown to survive. The distance Zs for the focusing shock to occur follows a power law with the beam power P according to Zs∝Pχ, with χ=−4/3, as for shock dynamics in self-defocusing media
Noisy precursors in one-dimensional patterns
International audienc
Optical fiber systems are convectively unstable
International audienceWe theoretically and experimentally evidence that fiber systems are convective systems since their nonlocal inherent properties, such as the dispersion and Raman effects, break the reflection symmetry. Theoretical analysis and numerical simulations carried out for a fiber ring cavity demonstrate that the third-order dispersion term leads to the appearance of convective and absolute instabilities. Their signature is an asymmetry in the output power spectrum. Using this criterion, experimental evidence of convective instabilities is given in a fiber cavity pumped by a pulsed laser