Roman Malendevich

Spatial modulation instability in a Kerr slab waveguide

We report the observation of noise-initiated modulational instability in AlGaAs slab waveguides at 1.55 microm . Experiments were performed with the local, ultrafast Kerr nonlinearity at half the bandgap. The agreement between experiment and theory for the periodicity versus intensity was good.

Spatial modulational instability in one-dimensional lithium niobate slab waveguides

We report an experimental study of the breakup through modulational instability of broad fundamental beams near the phase-matching condition for second-harmonic generation in lithium niobate slab waveguides. Two mechanisms for initiating modulational instability, waveguide imperfections and noise on the input beam, are identified.

Two-dimensional type I quadratic spatial solitons in KNbO 3 near noncritical phase matching

Experiments on the properties of quadratic, two-dimensional spatial soliton properties in KNbO(3) near and at noncritical phase matching (NCPM) are reported. The NCPM geometry leads to unique features such as a large angular bandwidth for soliton generation, weak dependence of soliton composition on intensity and incidence angle, and unique multisoliton-generation properties.

Effects of anisotropic diffraction on quadratic multisoliton excitation in noncritically phase-matched crystals

The generation of multiple quadratic spatial solitons aligned approximately along a crystal axis in a biaxial noncritically phase-matched crystal is shown theoretically and experimentally to be the consequence of anisotropic diffraction.

Radiation-related Polarization Instability of Kerr Spatial Vector Solitons

We report the experimental observation and numerical simulations of a polarization instability of spatial vector solitons in an AlGaAs slab waveguide. At power levels where the nonlinear index change becomes comparable to the birefringence, the fast soliton becomes unstable. The instability is related to coupling of the fast soliton to the slow radiation modes through phase matching. The combined effects of bifurcation and radiation coupling are the processes ultimately limiting the stability of any single-polarization (fast and slow) Kerr soliton.

Radiation related polarization instability of fast Kerr spatial solitons in slab waveguides

We report the observation of a power-dependent polarization conversion from a fast spatial soliton-like beam into the orthogonal polarization in an AlGaAs slab waveguide at power levels below which the nonlinear index change becomes comparable to the birefringence. The slow soliton, however, shows no polarization conversion. We interpret these results in terms of the previously predicted polarization instability of a fast soliton into orthogonally polarized radiation. The experimental results are in qualitative agreement with theory.

Nonlinear beam dynamics in chi2 waveguides

The evolution from diffraction, to single and then multiple quadratic soliton generation, and finally the onset of modulational instability were observed for wide fundamental beams in both birefringence and quasi-phase matched LiNbO3 slab waveguides.

Fission of narrow high power beams into multiple solitons in a second-order nonlinear slab waveguide

Summary form only given. One of the first nonlinear effects observed was the break-up of wide, high intensity, beams into filaments due to spatial noise present on the beam, known as modulational instability (MI), that generally occurs in any media with nonlinearities which lead to self-focusing. We have recently reported observation of MI near the phase-matching condition for second-harmonic generation in LiNbO/sub 3/ slab waveguides. For narrow beams, a different phenomenon can occur at lower intensities than MI, namely the fission of the beam into multiple solitons. For spatial solitons, the peak soliton intensity varies inversely with the solitons spatial width, so that if the input beam contains sufficient intensity to generate multiple solitons, fission occurs. Here we report experimental observation of the break-up of high intensity beams into multiple components at thresholds consistent with soliton fission.

Periodic spatial instabilities of high intensity beams in nonlinear waveguides

Summary form only given. In self-focusing media a plane wave of infinite extent breaks-up into a periodic array of individual intensity maxima. This has been reported in bulk quadratic and photorefractive media, but not in slab waveguides for which analytical theories exist. Modulational instability (MI) leading to periodic structures has been demonstrated for SHG in LiNbO/sub 3/ slab waveguides, in excellent agreement with theory. Furthermore, by seeding the periodic patterns, the MI gain coefficients were measured, and again good agreement with theory.

Experiments on Seeded and Noise Initiated Modulational Instability in LiNbO3 Slab Waveguides

We report the experimental study of seeded and noise initiated modulational instability (MI) during second harmonic generation in a LiNbO3 slab waveguide. In the non-seeded case, two MI initiating mechanisms were identified, namely random noise on the input beam and waveguide imperfections. We also measured the MI gain coefficient as a function of periodicity and beam intensity employing a small, well-defined periodic perturbation (seeding). Excellent agreement with theory was obtained.