Faster-than-light effects and negative group delays in optics and electronics, and their applications

Recent manifestations of apparently faster-than-light effects confirmed our predictions that the group velocity in transparent optical media can exceed c. Special relativity is not violated by these phenomena. Moreover, in the electronic domain, the causality principle does not forbid negative group delays of analytic signals in electronic circuits, in which the peak of an output pulse leaves the exit port of a circuit before the peak of the input pulse enters the input port. Furthermore, pulse distortion for these superluminal analytic signals can be negligible in both the optical and electronic domains. Here we suggest an extension of these ideas to the microelectronic domain. The underlying principle is that negative feedback can be used to produce negative group delays. Such negative group delays can be used to cancel out the positive group delays due to transistor latency (e.g., the finite RC rise time of MOSFETS caused by their intrinsic gate capacitance), as well as the propagation delays due to the interconnects between transistors. Using this principle, it is possible to speed up computer systems.Comment: 13 pages, 5 figures, 2001 Photonic West Plenary Tal

Zener tunneling in two-dimensional photonic lattices

We discuss the interband light tunneling in a two-dimensional periodic photonic structure, as was studied recently in experiments for optically-induced photonic lattices [H. Trompeter et al., Phys. Rev. Lett. \textbf{96}, 053903 (2006)]. We identify the Zener tunneling regime at the crossing of two Bloch bands, which occurs in a generic case of the Bragg reflection when the Bloch index crosses the edge of the irreducible Brillouin zone. Similarly, the higher-order Zener tunneling involves four Bloch bands when the Bloch index passes through a high-symmetry point on the edge of the Brillouin zone. We derive simple analytical models that describe the tunneling effect, and calculate the corresponding tunneling probabilities.Comment: 6 pages, 6 figures, submitted to Phys Rev E; changes: band structure added (fig1) and the error estimates for the Landau-Zener model (fig 6

Nonlocal Nonlinear Optical Response of Ionic Liquids under Violet Excitation

The nonlocal nonlinearity under violet excitation of ionic liquids was investigated using the Z-scan technique. The bis(trifluoromethylsulfonyl)imide (Tf2N−) was employed as anionic part, while the cationic part consisted of four different imidazolium (, with , 6, 8, and 10) derivatives. The thermooptical coefficients, nonlinear refractive indexes of thermal origin, and degree of nonlocality were obtained for laser excitation tuned at 410 nm. Our results indicate that ionic liquids can be exploited as very efficient nonlinear media with large nonlocal character under violet excitation

Probing the reciprocal lattice associated with a triangular slit to determine the orbital angular momentum for a photon

The orbital angular momentum conservation of light reveals different diffraction patterns univocally dependent on the topological charge of the incident light beam when passing through a triangular aperture. It is demonstrated that these patterns, which are accessed by observing the far-field measurement of the diffracted light, can also be obtained using few photon sources. In order to explain the observed patterns, we introduce an analogy of this optical phenomenon with the study of diffraction for the characterization of the crystal structure of solids. We demonstrate that the finite pattern can be associated with the reciprocal lattice obtained from the direct lattice generated by the primitive vectors composing any two of the sides of the equilateral triangular slit responsible for the diffraction. Using the relation that exists between the direct and reciprocal lattices, we provide a conclusive explanation as to why the diffraction pattern of the main maxima is finite. This can shed a new light on the investigation of crystallographic systems

Resonant Zener tunneling in two-dimensional periodic photonic lattices

We study Zener tunneling in two-dimensional photonic lattices and derive, for the case of hexagonal symmetry, the generalized Landau–Zener–Majorana model describing resonant interaction between high symmetry points of the photonic spectral bands. We demonstrate that this effect can be employed for the generation of Floquet–Bloch modes and verify the model by direct numerical simulations of the tunneling effect.This work has been supported by the Australian Research Council and by the National Council for Scientific and Technological Development (CNPq) of Brazil

Coherent soliton propagation through doped optical fibers: cloning, breakup, and soliton interactions

The simultaneous propagation of two optical pulses through a doped nonlinear dispersive medium modelled by a resonant three-level system was investigated numerically, within the framework of a pair of coupled extended nonlinear Schrödinger equations. These included the contribution of the dopant resonances whose dynamics is governed by Bloch equations. In this work, we review the interesting possibilities on the manipulation of fields such as cloning, breakup and soliton interactions, that the combination of coherent population trapping with nonlinear dispersive media offers

Femtosecond nonlinear optical properties of tellurite glasses

The third-order nonlinear optical properties of tellurite glasses with different compositions were investigated in the femtosecond regime at 810 nm. Using the I-scan technique, positive nonlinear refractive indices of similar to 10(-15) cm(2)/W were measured. The authors also determined that nonlinear absorption was negligible for all studied samples. This result, added to their good chemical stability, indicates that tellurite glasses are promising materials for ultrafast photonic applications. (c) 2006 American Institute of Physics

Third-order nonlinear optical response of colloidal gold nanoparticles prepared by sputtering deposition

The nonlinear optical responses of gold nanoparticles dispersed in castor oil produced by sputtering deposition were investigated, using the thermally managed Z-scan technique. Particles with spherical shape and 2.6 nm of average diameter were obtained and characterized by transmission electron microscopy and small angle X-ray scattering. This colloid was highly stable, without the presence of chemical impurities, neither stabilizers. It was observed that this system presents a large refractive third-order nonlinear response and a negligible nonlinear absorption. Moreover, the evaluation of the all-optical switching figures of merit demonstrated that the colloidal nanoparticles prepared by sputtering deposition have a good potential for the development of ultrafast photonic devices