[Show abstract][Hide abstract] ABSTRACT: The theory of molecular nonlinear optics based on the sum-over-states (SOS) model is reviewed. The interaction of radiation with a single wtpisolated molecule is treated by first-order perturbation theory, and expressions are derived for the linear (αij) polarizability and nonlinear (βijk, γijkl) molecular hyperpolarizabilities in terms of the properties of the molecular states and the electric dipole transition moments for light-induced transitions between them. Scale invariance is used to estimate fundamental limits for these polarizabilities. The crucial role of the spatial symmetry of both the single molecules and their ordering in dense media, and the transition from the single molecule to the dense medium case (susceptibilities χ1ij, χ2ijk, χ3ijkl), is discussed. For example, for βijk, symmetry determines whether a molecule can support second-order nonlinear processes or not. For asymmetric molecules, examples of the frequency dispersion based on a two-level model (ground state and one excited state) are the simplest possible for βijk and examples of the resulting frequency dispersion are given. The third-order susceptibility is too complicated to yield simple results in terms of symmetry properties. It will be shown that whereas a two-level model suffices for asymmetric molecules, symmetric molecules require a minimum of three levels in order to describe effects such as two-photon absorption. The frequency dispersion of the third-order susceptibility will be shown and the importance of one and two-photon transitions will be discussed.
Full-text · Article · Mar 2013 · Advances in Optics and Photonics
[Show abstract][Hide abstract] ABSTRACT: Very few nonlinear optical materials are actually useful for high throughput all-optical devices. However, AlGaAs does satisfy all of the nonlinear optical figures of merit when used with photons of energy less than one half the semiconductor bandgap. Here we review our measurements of the pertinent nonlinear coefficients in waveguides and various device applications to all-optical switching in the communications band around 1550 nm.
No preview · Article · Apr 2012 · Journal of Nonlinear Optical Physics & Materials
[Show abstract][Hide abstract] ABSTRACT: The recent theoretical predictions and experimental observations of discrete surface solitons propagating along the interface between a one- or two-dimensional continuous medium and a one- or two-dimensional waveguide array are reviewed. These discrete solitons were found in second order (periodically poled lithium niobate) and third order nonlinear media, including AlGaAs, photorefractive media and glass, respectively.
No preview · Article · Jan 2012 · Journal of Nonlinear Optical Physics & Materials
[Show abstract][Hide abstract] ABSTRACT: In this paper we review the progress made in implementing nonlinear directional couplers as potential all-optical switching devices. We will discuss the operation of the coupler and its application as an all-optical multiplexing, demultiplexing element and consider the possibility of integrating more than one nonlinear switching element. The limitation of dispersion and nonlinear absorption will also be addressed.
No preview · Article · Jan 2012 · Journal of Nonlinear Optical Physics & Materials
[Show abstract][Hide abstract] ABSTRACT: The exact formula is derived from the "sum over states" (SOS) quantum mechanical model for the frequency dispersion of the nonlinear refractive index coefficient n₂ for centrosymmetric molecules in the off-resonance and non-resonant regimes. This expression is characterized by interference between terms from two-photon transitions from the ground state to the even-symmetry excited states and one-photon transitions between the ground state and odd-symmetry excited states. When contributions from the two-photon terms exceed those from the one-photon terms, the non-resonant intensity-dependent refractive index n₂>0, and vice versa. Examples of the frequency dispersion for the three-level SOS model are given. Comparison is made with other existing theories.
[Show abstract][Hide abstract] ABSTRACT: Using the sum-over-states model for linear symmetric molecules we derive expressions for the frequency dispersion of n_2 of air molecules. The measured sign of non-resonant n_2 shows the recently published extended Miller formula is incorrect.
[Show abstract][Hide abstract] ABSTRACT: A widespread interest in all-optical networks for telecommunications has generated a great deal of activity towards approaches
for efficient channel shifting in systems based on wavelength-division-multiplexing (WDM). A key issue, namely the possibility
of transferring an incoming stream of data from a given channel or wavelength to another, has been addressed using several
techniques ranging from gain saturation in semiconductor amplifiers  to four-wave-mixing  to parametric generation . Since available bandwidth, transparence to the modulation format, possibility of gain and amount of crosstalk are important
characteristics of such a wavelength shifter, parametric processes are considered rather appealing. With the advances in periodically
poled crystals for efficient second-harmonic-generation (SHG) and difference frequency generation (DFG) , a quadratic approach in guided-wave configurations appears quite affordable in terms of required powers.
[Show abstract][Hide abstract] ABSTRACT: Improved methods for the growth and polymerization of single crystals of polydiacetylene PTS, poly bis(p-toluene sulfonate)
of 2,4-hexadiyne-1,6-diol, have allowed new optical measurements to be made. The absorption spectrum, and typical Z-scans
for measuring the optical nonlinearity up to fourth order are described.
[Show abstract][Hide abstract] ABSTRACT: Spatial solitons are beams which do not diffract on propagation in a material due to the presence of some optical nonlinearity.
Their properties were first documented by John Scott Russell when he reported his observations on non-spreading water waves
which consisted of a single “hump” propagating in a canal in Scotland.[l] In the very early days of nonlinear optics, interest was quickly evoked by what were then called “self-focused filaments”,
initiated by observations of self-focusing of powerful lasers in optical media, frequently leading to stable filaments or
even material damage. [2,3] However it was not until the late 1990s that systematic experimental research into spatial solitons was initiated.  Since then there has been a surge of activity and many new solitons have been observed. [5–16]
[Show abstract][Hide abstract] ABSTRACT: The goal of this paper is to summarize findings on different oxide-based glasses that have been engineered for their potential application as Raman gain media. Recent results have shown that phosphate-based glasses can provide Raman amplification bandwidths of up to 40 THz, an improvement of almost 5 times the bandwidth of SiO2. On the other hand, tellurite-based glasses appear to be promising candidates for high Raman gain applications, providing peak Raman gain coefficients of up to 50 times higher than SiO2.
[Show abstract][Hide abstract] ABSTRACT: The recent interpretation of experiments on the nonlinear non-resonant birefringence induced in a weak probe beam by a high intensity pump beam in air and its constituents has stimulated interest in the non-resonant birefringence due to higher-order Kerr nonlinearities. Here a simple formalism is invoked to determine the non-resonant birefringence for higher-order Kerr coefficients. Some general relations between nonlinear coefficients with arbitrary frequency inputs are also derived for isotropic media. It is shown that the previous linear extrapolations for higher-order birefringence (based on literature values of n2 and n4) are not strictly valid, although the errors introduced in the values of the reported higher- order Kerr coefficients are a few percent.
[Show abstract][Hide abstract] ABSTRACT: The Rayleigh acoustic waves of sputter-deposited Cu/Co, Ag/Pd and Cu/Pd sup-erlattice films were studied using Brillouin scattering. All three of these systems are fcc/fcc superlattices. The dependence of the Rayleigh wave velocities for these films on the superlattice modulation wavelength is discussed.
No preview · Article · Jan 2011 · MRS Online Proceeding Library
[Show abstract][Hide abstract] ABSTRACT: We provide an in-depth treatment of the various mechanisms by which an inci-dent light beam can produce an intensity-or flux-dependent change in the re-fractive index and absorption coefficient of different materials. Whenever pos-sible, the mechanisms are initially traced to single-atom and -molecule effects in order to provide physical understanding. Representative values are given for the various mechanisms. Nine different mechanisms are discussed, starting with the Kerr effect due to atoms and/or molecules with discrete states, includ-ing organic materials such as molecules and conjugated polymers. Simplified two and/or three-level models provide useful information, and these are sum-marized. The nonlinear optics of semiconductors is reviewed for both bulk and quantum-confined semiconductors, focusing on the most common types II–VI and III–V. Also discussed in some detail are the different nonlinear mechanisms that occur in liquid crystals and photorefractive media. Additional nonlinear material systems and mechanisms such as glasses, molecular reorientation of single molecules, the electrostrictive effect, the nuclear effect (vibrational con-tributions), cascading, and the ever-present thermal effects are quantified, and representative tables of values are given.
Full-text · Article · Mar 2010 · Advances in Optics and Photonics
[Show abstract][Hide abstract] ABSTRACT: In the paper a simple formula for the non-resonant and off-resonant nonlinearity in symmetric linear molecules and conjugated polymers made from such molecules is presented. Obtained results agree with experimental data known from the literature.
Preview · Article · Dec 2009 · Photonics Letters of Poland
[Show abstract][Hide abstract] ABSTRACT: Discrete optics opens up new opportunities in manipulating light flow. We provide an overview of recent experimental and theoretical developments in this area. The effects of discreteness on linear and nonlinear optical interactions are discussed.