Massimiliano Guasoni

Fast and Chaotic Fiber-Based Nonlinear Polarization Scrambler

We report a simple and efficient all-optical polarization scrambler based on the nonlinear interaction in an optical fiber between a signal beam and its backward replica which is generated and amplified by a reflective loop. When the amplification factor exceeds a certain threshold, the system exhibits a chaotic regime in which the evolution of the output polarization state of the signal becomes temporally chaotic and scrambled all over the surface of the Poincaré sphere. We numerically derive some design rules for the scrambling performances of our device which are well confirmed by the experimental results. The polarization scrambler has been successfully tested on a 10-Gb/s On/Off Keying Telecom signal, reaching scrambling speeds up to 500-krad/s, as well as in a wavelength division multiplexing configuration. A different configuration based on a following cascade of polarization scramblers is also discussed numerically, which leads to an increase of the scrambling performances.

Polarization domain walls in optical fibres as topological bits for data transmission

Domain walls are topological defects which occur at symmetry-breaking phase transitions. While domain walls have been intensively studied in ferromagnetic materials, where they nucleate at the boundary of neighbouring regions of oppositely aligned magnetic dipoles, their equivalent in optics have not been fully explored so far. Here, we experimentally demonstrate the existence of a universal class of polarization domain walls in the form of localized polarization knots in conventional optical fibres. We exploit their binding properties for optical data transmission beyond the Kerr limits of normally dispersive fibres. In particular, we demonstrate how trapping energy in well-defined train of polarization domain walls allows undistorted propagation of polarization knots at a rate of 28 GHz along a 10 km length of normally dispersive optical fibre. These results constitute the first experimental observation of kink-antikink solitary wave propagation in nonlinear fibre optics.

Polarization chaos and random bit generation in nonlinear fiber optics induced by a time-delayed counter-propagating feedback loop

In this manuscript, we experimentally and numerically investigate the chaotic dynamics of the state-of-polarization in a nonlinear optical fiber due to the cross-interaction between an incident signal and its intense backward replica generated at the fiber-end through an amplified reflective delayed loop. Thanks to the cross-polarization interaction between the two-delayed counter-propagating waves, the output polarization exhibits fast temporal chaotic dynamics, which enable a powerful scrambling process with moving speeds up to 600-krad/s. The performance of this all-optical scrambler was then evaluated on a 10-Gbit/s On/Off Keying telecom signal achieving an error-free transmission. We also describe how these temporal and chaotic polarization fluctuations can be exploited as an all-optical random number generator. To this aim, a billion-bit sequence was experimentally generated and successfully confronted to the dieharder benchmarking statistic tools. Our experimental analysis are supported by numerical simulations based on the resolution of counter-propagating coupled nonlinear propagation equations that confirm the observed behaviors.

Random bit generation through polarization chaos in nonlinear optical fibers

Nowadays, cryptographic applications are becoming of paramount importance in order to guarantee ultimately secure communications. Performances of classical and quantum key distribution and encryption algorithms are strongly dependent on the used Random Number Generator (RNG). A good RNG must produce unpredictable, unreproducible and unbiased sequences of numbers. For this reason, many true random number generators relying on chaotic physical phenomena, such as chaotic oscillations of high-bandwidth lasers [1, 2] or polarization chaos from a VCSEL diode [3], have been developed. In this work, we propose a RNG implementation based on a different physical mechanism than the ones previously used in literature: the polarization chaos induced in an optical fiber by the nonlinear interaction between a forward beam and its amplified backward replica. Basically, we operate the device called Omnipolarizer, originally used in our previous works as an all-optical polarization attractor or beam splitter [4], in an additional operating mode, namely the chaotic mode [5].

Dataset for Intermodal four-wave mixing and parametric amplification in kilometer-long multimode fibers

We theoretically and numerically investigate intermodal four-wave mixing in kilometer-long fibers, where random birefringence fluctuations are present along the fiber length. We identify several distinct u2009regimes that depend on the relative magnitude between the length scale of the random fluctuations and the beat lengthsu2009 of the interacting quasi-degenerate modes. In addition, we analyze the impact of mode dispersion and weu2009 demonstrate that random variations of the core radius, which are typically encountered during the drawing stage of the fiber, can represent the major source of bandwidth impairment. These results set a boundary on the limits of validity of the classical Manakov model and may be useful for the design of multimode parametric amplifiers and wavelength converters, as well as for the analysis of nonlinear impairments in long-haul spatial division multiplexed transmission.

Intermodal four-wave mixing and parametric amplification in kilometer-long multimode fibers

We theoretically and numerically investigate intermodal four-wave mixing in kilometer-long fibers, where random birefringence fluctuations are present along the fiber length. We identify several distinct u2009regimes that depend on the relative magnitude between the length scale of the random fluctuations and the beat lengthsu2009 of the interacting quasi-degenerate modes. In addition, we analyze the impact of mode dispersion and weu2009 demonstrate that random variations of the core radius, which are typically encountered during the drawing stage of the fiber, can represent the major source of bandwidth impairment. These results set a boundary on the limits of validity of the classical Manakov model and may be useful for the design of multimode parametric amplifiers and wavelength converters, as well as for the analysis of nonlinear impairments in long-haul spatial division multiplexed transmission.

Theoretical Model for Pattern Engineering of Harmonic Generation in All-Dielectric Nanoantennas

We develop a novel theoretical model for the study of harmonic generation in cylindrical structures of finite height. Our technique is based on the decomposition of the electromagnetic field over the complete set of modes of the corresponding infinite cylinder. Differently from previous works, in our model no constraints are given neither on the cross section nor on the refractive index of the cylinder. We then apply our approach in the special case of frequency doubling in tall AlGaAs nanodisks, where radiative modes can be neglected. Our results open new perspectives for optimization and engineering of the radiation pattern in harmonic generation processes at the nanoscale.

40GHz picosecond pulse source based on a cross-phase modulation induced orthogonal focusing in normally dispersive optical fibers(Conference Presentation)

The generation of picosecond pulse trains has become of great interest for many scientific applications. However, even though different techniques of nonlinear compression have been developed for optical fibers in the anomalous dispersion regime, only a few exist for normally dispersive fibers. Here, we describe a new method based on the generation of a strong nonlinear focusing effect induced by the cross phase modulation of a high power 40-GHz beat-signal on its orthogonally polarized interleaved weak replica. More precisely, while the normally dispersive defocusing regime induced a nonlinear reshaping of a high power 40-GHz sinusoidal signal into successively parabolic then broad and sharp square pulses, it also progressively close a singularity at its null point characterized by steeper and steeper edges. Here we show that the cross phase modulation induced by this nonlinear dark structure on a weak interleaved orthogonally polarized replica then turns out the normally dispersive regime into a focusing dynamics. This phenomenon is similar to the polarization domain wall effect for which the energy of a domain is strongly localized and bounded by the commutation of both orthogonally polarized waves. In other words, since a particle in a gradually collapsing potential, the energy contained in the weak interleaved component is found to be more and more bounded and is thus forced to temporally compress along the fiber length, thus reshaping the initial beat-signal into a train of well-separated short pulses. We have experimentally validated the present method by demonstrating the temporal compression of an initial 40-GHz beat-signal into a train of well separated pulses in different types of normally dispersive fibers. To this aim, an initial 40-GHz beat-signal is first split into 2 replica for which one is half-period delayed and 10-dB attenuated before polarization multiplexing in such a way to generate a strongly-unbalanced orthogonally-polarized interleaved signal. The resulting signal is then amplified and injected into the fiber under-test. In first fibers of 1 and 2 km (D = -15 ps.km-1.nm-1, γ = 2.3 W-1.km-1, α = 0.2 dB.km-1), we have observed the nonlinear focusing of the initial 40-GHz sinusoidal signal input into a train of 5.5-ps pulses. By decreasing the dispersion coefficient down to D = -2.5 ps.km-1.nm-1 in such a way to exacerbate the nonlinear defocusing effect of the strongest component far beyond the wave breaking, we have successfully compressed the orthogonally polarized 40-GHz beat-signal into well-separated 2.5-ps pulses after 5 km of propagation for a total input power of 28 dBm. We then studied the effect of total power on the compression ratio, and showed that compression is more efficient with higher total power, even after the wave breaking phenomenon. We followed by showing that the power ratio between the two polarization axes is closely linked to the compression factor, as the higher the power difference between the two axes, the better compression. Finally, our experimental results are in excellent agreement with our numerical predictions.

Giant Collective Incoherent Shock Waves in Strong Turbulence

Contrary to conventional coherent shocks, we show theoretically and experimentally that nonlocal turbulent flows lead to the emergence of large-scale incoherent shock waves, which constitute a collective phenomenon of the incoherent field as a whole.