E. Seve

Observation of induced modulational polarization instabilities and pulse-train generation in the normal-dispersion regime of a birefringent optical fiber

Four-photon mixing in a low-birefringence fiber is strongly influenced by the orientation of the pump and signal waves with respect to the fiber axes. We experimentally investigated the dependence of the modulational gain spectra on pump power and polarization by mixing orthogonal pump and probe light beams in a birefringent optical fiber. With a pump on the fast fiber axis, a cascade of sidebands was generated in the regime of normal fiber dispersion. These sidebands are shown to correspond to 0.2–0.3-THz trains of pulses with complex polarization profiles. The analysis reveals that, at particular values of the input pump and probe powers and signal frequency detuning, trains of dark-solitonlike pulses can be generated on the axis orthogonal to the pump.

Dark-soliton-like pulse-train generation from induced modulational polarization instability in a birefringent fiber

Theory and experiments show that the nonlinear development of the modulational polarization instability of an intense light beam in a normally dispersive, low-birefringence optical fiber leads to ultrashort dark-soliton-like trains with repetition rates in the terahertz range in the polarization orthogonal to the pump.

Demonstration of a nonlinear gap in the modulational instability spectra of wave propagation in highly birefringent fibers

We investigate modulational instability in normally dispersive highly birefringent fibers. By means of a technique based on a two-frequency pump field we are able to provide evidence for strong nonlinear dependence of the modulational instability spectra. This dependence manifests itself by the appearance of a nonlinear spectral gap in which modulational instability vanishes.

Generation of vector dark-soliton trains by induced modulational instability in a highly birefringent fiber

We present a set of experimental observations that demonstrate the generation of vector trains of dark-soliton pulses in the orthogonal axes of a highly birefringent optical fiber. We generated dark-soliton trains with terahertz repetition rate in the normal group-velocity dispersion regime by inducing a polarization modulational instability by mixing two intense, orthogonal continuous laser beams. Numerical solutions of the propagation equations were used to optimize the emission of vector dark pulses at the fiber output.

Buildup of terahertz vector dark-soliton trains from induced modulation instability in highly birefringent optical fiber.

We present the experimental observation of generation of vector dark-soliton pulse trains with terahertz repetition rates in the normal dispersion regime of an optical fiber. The polarization solitons build up from induced cross-phase modulation instability of two orthogonal pumps in a highly birefringent fiber.

Large-signal enhanced frequency conversion in birefringent optical fibers: theory and experiments

Strong frequency conversion among light waves propagating in a low-birefringence optical fiber in the normal-dispersion regime is experimentally investigated. Modulational gain spectra are obtained by injection of a signal orthogonally polarized with respect to a pump beam aligned with the slow fiber axis. Measurements reveal that, for signal power levels above a certain threshold value, peak conversion is obtained at pump signal frequency detunings far from the phase-matching condition. The large-signal three-wave mixing regime is well described by integrable nonlinear coupled-wave equations.

Failure of phase-matching concept in large-signal parametric frequency conversion

Four-wave mixing experiments in a low-birefringence optical fiber reveal an unexpected sudden increase of the conversion efficiency as the signal power crosses a threshold value. In this regime, peak frequency conversion is achieved outside the small-signal parametric gain spectrum. A nonlinear model of wave mixing fits the measured data well.

Raman-assisted three-wave mixing of non-phase-matched waves in optical fibres: application to wide-range frequency conversion

Abstract We analyse theoretically and experimentally the Raman-assisted parametric coupling between non-phase-matched waves propagating in normally dispersive single-mode fibres. We perform a careful analysis of the wave-coupling behaviour, which shows that scalar and vector three-wave mixing (TWM) interactions induce a relatively small periodic power flow between a central-frequency pump at frequency ω0 and a pair of up-shifted (anti-Stokes) and down-shifted (Stokes) sidebands at frequencies ω 0 +Ω and ω 0 −Ω , respectively. For sufficiently high pump powers, the stimulated Raman scattering enters into play, causing a unilateral transfer of energy from higher to lower frequency waves. This energy transfer destroys the spatial periodicity of the parametric energy-exchange process. As a result, parametric seeding and subsequent Raman amplification of a Stokes idler wave is achieved by mixing a strong pump with a weak anti-Stokes signal. This Raman-induced Stokes power-gain enhancement leads to efficient anti-Stokes → Stokes frequency conversion, with frequency detunings which can be relatively large (typically, from 7 to 30 THz), even for very short parametric coherence. Raman-assisted TWM thus overcomes the strict spectral limitation usually imposed by the phase-matching condition, leading to broadband frequency conversion processes that are inaccessible with a pure parametric interaction.

Vector Modulational Instabilities and Soliton Experiments

In optical fibers, the interaction between nonlinear and dispersive effects leads to phenomena such as modulational instability (MI)[1, 2, 3, 4, 5, 6], in which a continuous or quasi-continuous wave undergoes a modulation of its amplitude or phase in the presence of noise or any other small perturbation. The perturbation can originate from quantum noise (spontaneous-MI) or from a frequency shifted signal wave (induced-MI). MI has been observed for the first time for a single pump wave propagating in a standard non birefringe.nt fiber (scalar MI)[7]. It has been shown that scalar MI only occurs when the group velocity dispersion (GVD) is negative (anomalous dispersion regime).

Generation of High-Repetition-Rate Dark Soliton Trains and Frequency Conversion in Optical Fibers

Induced modurational polarization instability in birefringent fibers leads to trains of dark soliton-like pulses. Optimal large-signal cw and soliton frequency conversion is also analysed.