We report on a direct experimental observation of dynamic localization (DL) of light in sinusoidallycurved Lithium-Niobate waveguide arrays which provides the optical analog of DL for electrons in periodic potentials subjected to ac electric fields as originally proposed by Dunlap and Kenkre [D.H. Dunlap and V.M. Kenkre, Phys. Rev. B 34, 3625 (1986)]. The theoretical condition for DL in a sinusoidal field is experimentally demonstrated.PACS numbers: 42.82. Et, 63.20.Pw, 42.25.Bs The quantum motion of an electron in a periodic potential subjected to an external field has provided since a long time a paradigmatic model to study fascinating and rather universal coherent dynamical phenomena. These include the long-predicted Bloch oscillations (BO) for dc fields [1], i.e. an oscillatory motion of the wave packet related to the existence of a Wannier-Stark ladder energy spectrum, and the more recently-predicted dynamic localization (DL) for ac fields [2], in which a localized particle periodically returns to its initial state following the periodic change of the field. In recent years, BO have been experimentally observed in a wide variety of systems including semiconductor superlattices [3], atoms in accelerated optical lattices [4], and optical waveguide arrays with a transverse refractive index gradient [5,6,7]. DL is a phenomenon similar to BO which occurs when the electron is subjected to an ac field. The condition for DL, as originally predicted by Dunlap and Kenkre [2] in the nearest-neighbor tight-binding (NNTB) approximation and for a sinusoidal driving field E(t) = F sin(ωt), is that J 0 (Γ) = 0, where Γ = eaF/ ω and a is the lattice period. DL has been shown to be related to the collapse of the quasienergy minibands [8], and the general conditions for DL beyond the NNTB approximation and for generalized ac fields have been identified [9]; DL under the action of both ac and dc fields has been also studied [10], and the influence of excitonic and many-body effects on DL in semiconductor superlattices has been considered (see, e

We report on an experimental demonstration of light transfer in an engineered triple-well optical waveguide structure which provides a classic analog of coherent tunneling by adiabatic passage (CTAP) recently proposed for coherent transport in space of neutral atoms or electrons among tunneling-coupled optical traps or quantum wells [A. D. Greentree et al., Phys. Rev. B 70, 235317 (2004); K. Eckert et al., Phys. Rev. A 70, 023606 (2004)]. The direct visualization of CTAP wave-packet dynamics enabled by our simple optical system clearly shows that in the counterintuitive passage scheme light waves tunnel between the two outer wells without appreciable excitation of the middle well

We describe a novel approach for the fabrication of optical waveguides by focused lowrepetition-rate femtosecond laser pulses. This approach overcomes the main limitation of the technique, i.e., the strong asymmetry of the waveguide profile. By use of an astigmatic beam and suitably controlling both beam waist and focal position in tangential and sagittal planes, it is possible to shape the focal volume in such a way as to obtain waveguides with a circular transverse profile and of the desired size. This technique is applied to the fabrication of active waveguides in Er:Yb-doped glass substrates. The waveguides are single mode at 1.5 m and exhibit propagation losses of 0.25 dB/cm and an internal gain of 1.4 dB at 1534 nm.