Leonora Ursini

All-optical signal processing using dynamic Brillouin gratings

The manipulation of dynamic Brillouin gratings in optical fibers is demonstrated to be an extremely flexible technique to achieve, with a single experimental setup, several all-optical signal processing functions. In particular, all-optical time differentiation, time integration and true time reversal are theoretically predicted, and then numerically and experimentally demonstrated. The technique can be exploited to process both photonic and ultra-wide band microwave signals, so enabling many applications in photonics and in radio science.

Raman Nonlinear Polarization Pulling in the Pump Depleted Regime in Randomly Birefringent Fibers

The polarization evolution of the pump and signal in Raman copropagating amplifiers is numerically investigated, by considering the nonlinear polarization rotation and the pump depletion effects. The signal and pump quality at the fiber output is evaluated. The intrinsic limitations of the nonlinear polarization pulling effect are determined.

Enhancing Chaotic Communication Performances by Manchester Coding

A numerical analysis of an optical chaotic transmission system, based on the synchronization of two chaotic lasers, in a master-slave closed loop configuration is presented. At the transmitter, the master chaotic wave is superposed on the information message; at the receiver, the message is recovered by subtracting the synchronized slave chaotic wave from the received signal. The performances are analyzed in terms of the Q-factor, considering two different message modulation formats: the nonreturn-to-zero and the Manchester coding. The Manchester coding shows enhanced performances due to the shift of the signal spectrum to higher frequencies.

Polarized Backward Raman Amplification in Randomly Birefringent Fibers

In this paper, a model describing the vector interaction of an intense backward-propagating Raman pump and a weak forward-propagating Stokes signal in randomly birefringent fibers is proposed. The model accounts for the losses, the Raman interaction, and the linear and nonlinear birefringence. Realistic characteristics of the backward-propagation-birefringence vector have been originally accounted for. Numerical solutions show that polarized-backward-Raman amplifiers can have gain fluctuations larger than previously reported because of linear- and nonlinear-birefringence effects. Moreover, the gain mean depends on the signal and pump state of polarization imposed at the amplifier input or output. Simple formulas are derived for predicting the gain mean when nonlinear effects can be neglected

Polarized Brillouin Amplification in Randomly Birefringent and Unidirectionally Spun Fibers

Polarized Brillouin amplification in randomly birefringent spun fibers is theoretically and numerically studied. For unspun fibers, the mean gain is theoretically determined. For unidirectionally spun fibers, the potential of providing high gain with low uncertainty is numerically demonstrated.

Polarization Attraction in Counterpropagating Fiber Raman Amplifiers

Polarization attraction in counterpropagating, randomly birefringent, fiber Raman amplifiers is numerically investigated, including the effects of nonlinear polarization rotation, pump depletion and orthogonal Raman gain. The analysis determines the limitations of the pulling efficiency, and shows that the maximum achievable mean degree of polarization is a function of the mean gain.

Polarization-Dependent Brillouin Gain in Randomly Birefringent Fibers

An extensive study of the alignment between the pump, the signal, and the polarization-dependent gain (PDG) vectors in stimulated Brillouin amplification in randomly birefringent fibers is realized by numerically integrating the equations governing the propagation. At the fiber output, the signal tends to align to the PDG vector for large pump power because of the nonlinear polarization pulling effect. The PDG vector, for large random birefringence, aligns to a state that has the same linear component of the pump but opposite circular component.

Dynamic Brillouin gratings permanently sustained by chaotic lasers

A method to induce only one permanent and localized dynamic Brillouin grating in polarization maintaining optical fibers is introduced. The generation of the grating exploits the thumbtack correlation of the chaotic laser signals. A numerical calculation, corroborated by a theoretical analysis, is performed and the grating properties, length, and reflectance determined.

Polarized Backward Raman Amplification in Unidirectionally Spun Fibers

The vector interaction of an intense, backward-propagating, Raman pump and a weak, forward-propagating, Stokes signal in randomly birefringent, unidirectionally spun fibers is theoretically and numerically studied. The governing equations account for losses, Raman interaction, random linear birefringence, nonlinearity, and spinning. A model of birefringence, previously proposed for determining the polarization properties of unidirectionally spun fibers, is applied to the Raman amplifier confirming that this particular spin generates an equivalent circular birefringence. Numerical solutions show that, for rapid spinning, random birefringence effects are greatly reduced, Raman gain can be enhanced, and its fluctuations are minimized.

Applications of the Dynamic Brillouin Gratings to Ultrawideband Communications

Unconventional signal processing, such as all-optical signal time differentiation and true time reversal, can be realized on sub-nanosecond pulses, by exploiting dynamic Brillouin gratings in optical fibers. The performance of such optical processors, to generate ultrawideband (including high-order) Gaussian pulses and to implement an ultrawideband time reversal mirror, is numerically assessed.