Robert Fischer

Broadband femtosecond frequency doubling in random media

The authors demonstrate broadband femtosecond phase-matched noncollinear second-harmonic generation (SHG) in strontium barium niobate crystals with random ferroelectric domains. The process is similar to femtosecond SHG in ultrathin crystals, but it results in higher efficiency and exact mapping of the spectrum of the fundamental field into the spectrum of the second harmonics, even for pulses with complex spectral profiles. The observed parametric conversion process can be used as an efficient frequency mapping from infrared to visible for the femtosecond pulse monitoring.

Reduced-Symmetry Two-Dimensional Solitons in Photonic Lattices

We demonstrate theoretically and experimentally a novel type of localized beam supported by the combined effects of total internal and Bragg reflection in nonlinear two-dimensional square periodic structures. Such localized states exhibit strong anisotropy in their mobility properties, being highly mobile in one direction and trapped in the other, making them promising candidates for optical routing in nonlinear lattices.

Monitoring ultrashort pulses by transverse frequency doubling of counterpropagating pulses in random media

The authors study experimentally the transverse second-harmonic generation of counterpropagating pulses by a quasi-phase-matching in a medium with a random ferroelectric domain structure. The authors show that this parametric process results in a direct realization of the cross correlation of two optical signals and, therefore, it can be employed for direct characterizations of ultrashort pulses including their temporal structure and pulse front tilt.

Observation of light localization in modulated Bessel optical lattices

We generate higher-order azimuthally modulated Bessel optical lattices in photorefractive crystals by employing a phase-imprinting technique. We report on the experimental observation of self-trapping and nonlinear localization of light in such segmented lattices in the form of ring-shaped and single-site states. The experimental results agree well with numerical simulations accounting for an anisotropic and spatially nonlocal nonlinear response of photorefractive crystals.

Nonlinear Bloch modes in two-dimensional photonic lattices

We generate experimentally different types of two-dimensional Bloch waves of a square photonic lattice by employing the phase imprinting technique.We probe the local dispersion of the Bloch modes in the photonic lattice by analyzing the linear diffraction of beams associated with the high-symmetry points of the Brillouin zone, and also distinguish the regimes of normal, anomalous, and anisotropic diffraction through observations of nonlinear self-action effects.

Observation of spatial shift in interaction of dark nonlocal solitons

We study experimentally and theoretically a two- dimensional interaction of dark solitons in thermal defocusing medium. We report on the experimental observation of a spatial shift occurring at the intersection of obliquely interacting dark solitons. Numerical modeling reveals that this new effect is due to the nonlocal character of thermal nonlinearity.

Broadband second harmonic parametric scattering in ferroelectric crystals with random domains structure

We report the results of an experimental study on broadband second-harmonic (SH) parametric scattering in an un-poled strontium barium niobate (SBN) crystal with random-size ferroelectric domains. We consider different geometries of the interacting waves. The observed spatial distribution of the SHG is due to the larger facility to achieve phase matching conditions in the presence of disorder, and the polarization of the SH light can be both ordinary and extraordinary. The nonlinear coefficients of the crystal may be determined from the measurement of the SHG as a function of the fundamental beams polarization. The experimental results are in very good agreement with the predictions of our theoretical model.

Polychromatic Gap Solitons and Breathers in Nonlinear Waveguide Arrays

We predict the spatial localization of multiple wavelength components in the form of stationary polychromatic gap solitons and dynamic multi-gap breathers, and observe experimentally tunable spatio-spectral trapping of supercontinuum radiation in nonlinear periodic photonic structures.

Directional nonlinear wave transport in photonic lattices

We demonstrate theoretically and experimentally directional wave transport in two-dimensional perfectly periodic photonic structures. This effect is associated with the anisotropic mobility of nonlinear localized modes formed by the combined effects of total-internal and Bragg reflection.

Light localization in Bessel photonic lattices

We report on the experimental observation of nonlinear localization of light in azimuthally modulated Bessel photonic lattices. These lattices are optically induced in a photorefractive crystal and resemble multiple-core highly nonlinear micro-structured fibers.