Optical Amplification and Slow Light Based on Two-Wave Mixing at Large Modulation Depth

Based on Kukhtarev＇s equations, we derive the formulae of intensity-coupling coefficient, the phase-coupling coefficient and the group velocity at large modulation depth. It is theoretically shown that the signal beam can be amplified after passing through the photorefractive crystal and the group velocity reduced to m/s, even cm/s. Meanwhile, we also analyse the influence of the thermal excitation rate and the large signal effects on optical amplification and reduction of light propagation in photorefractive two-wave mixing.     

Polarization-anisotropic scattering lines in LiNbO3

Lines of light-induced scattering with extraordinary polarization from two ordinary polarized pump waves in LiNbO₃:Fe crystals are observed. A nonlinear mixing of four copropagating waves in the crystal with photovoltaic charge transport is shown to be the reason for parametric amplification of the seed radiation scattered from optical imperfections of the sample.     

Giant and negative bistable shifts for one-dimensional photonic crystal containing a nonlinear metamaterial defect

In this Letter, we investigate giant and negative bistable lateral shifts for a light beam transmitted through a one-dimensional photonic crystal containing a nonlinear metamaterial defect. It is shown that there exists a typical S-shaped curve of the normalized input-output intensity. The hysteresis of lateral shift, resulting from the reshaping effect (constructive and destructive interferences of each plane wave components undergoing different phase shifts) is dependent on the nonlinear defect, the incident intensity and incidence angle. Numerical simulations are also made for the validity of stationary phase approach. All these phenomena lead to potential applications in integrated optics and optical switches.     

Mirrorless parametric oscillation in BaTiO3

We report on the first observation of mirrorless oscillation in BaTiO₃ pumped by two nearly counterpropagating mutually incoherent light waves, both containing an ordinary and an extraordinary component. The oscillation waves appear at a certain angle defined by the phase matching condition for four-wave mixing of orthogonally polarized waves.     

Optical hyperlens composed of multilayered metallodielectric nanofilms

We present a study of the properties of metamaterial consisting of multilayered nanofilms and numerically demonstrate the subwavelength imaging effect. We find that a point source placed in the vicinity of the structure can form an image in the opposite side of the slab, even when the permittivity of metal and dielectric materials is not matched. When light is incident obliquely on the interface, the intensity of transmitted field is smaller than the one when light is incident upon the structure, and the image becomes blurred. This structure verifies that the multilayered metallodielectric structure can act as optical hyperlens.     

Tunable Pair Transmission in One-Dimensional Photonic Crystals Consisting of Single-Negative Materials

We study the transmission of one-dimensional photonic crystals consisting of single-negative permittivity and single-negative permeability media by using transfer matrix method. A pair of transmission modes is found in the gap. The transmission modes are dependent only on the ratio of the thicknesses of the two alternating layers. The separation of a pair of transmission modes can be tuned by varying the thickness of the defect layer or the ratio of thicknesses of the two alternating layers.     

The Sommerfeld precursor in photonic crystals

We calculate the Sommerfeld precursor that results after transmission of a generic electromagnetic plane wave pulse with transverse electric polarization, through a one-dimensional rectangular N-layer photonic crystal with two slabs per layer. The shape of this precursor equals the shape of the precursor that would result from transmission through a homogeneous medium. However, amplitude and period of the precursor are now influenced by the spatial average of the plasma frequency squared instead of the plasma frequency squared for the homogeneous case.     

The effect of doping and processing conditions on the optical performance of Rh:BaTiO3

We demonstrate the advantages of using high levels of rhodium (2000–3200 ppm) to dope barium titanate for achieving finite absorption coefficients (0.36 cm^-1), high two-beam coupling gain (11.5 cm^-1), and acceptable response time (7 s) at 1.06 μm. We also report on the mass spectroscopy measurements on Rh:BaTiO₃ samples indicating a small segregation coefficient for rhodium (below 0.01) and the presence of a relatively large concentration (6000 ppm) of unintentionally added strontium. Received: 20 November 1998 / Revised version: 25 January 1999 / Published online: 12 April 1999     

Magnetic response of dendritic structures at infrared frequencies

We propose a quasi-periodic dendritic resonant magnetic model that can be used for the realization of the negative permeability at infrared frequencies. The numerical simulation exhibits a magnetic response when the incident light is perpendicular to the plane of the model. The copper dendritic structures are prepared by the electro-deposition method. And the transmission spectrum of this dendritic structure shows a magnetic response at infrared frequencies with a maximum transmission −7.95 dB. Further studies demonstrate that the magnetic response relate to the fractal dimension of the dendritic structure to a certain extent.     

Are ternary halides useful materials for nonlinear optical applications?

Ternary halides are potential materials for nonlinear optical applications in the mid infrared because of their transparency. We discuss physical, chemical and crystallographic aspects and develop a concept for preparing nonlinear optical halides. Based on the bond-charge model optical hyperpolarizabilities are calculated for more than one hundred A-X bonds where X = Cl, Br or I. The calculations are tested as far as possible by a comparison with experimental data. The tests show that the listed hyperpolarizabilities are a sound basis for the calculation of nonlinear optical susceptibilities in halides. A list of cations is given which form bonds with large hyperpolarizabilities and which show the tendency to form acentric structures. Phase diagrams of the two selected systems TII-AsI₃ and TII-BiI₃ are studied experimentally. Large single crystals of the new acentric compound Tl₇Bi₃I₁₆ and of Tl₃PbCl₅ are prepared. In both crystals twinning prevents an effective SHG effect.     

A precise data processing method for extracting χ from Z-scan technique

We present a precise data processing method, in the Z-scan experiments using a Gaussian beam and trimmed Airy beam, for directly extracting nonlinear refraction from the closed aperture Z-scan trace with the aid of the open aperture Z-scan trace when the materials exhibit nonlinear refraction and nonlinear absorption simultaneously. This method is still applicable when the nonlinear absorption is dominant and the closed aperture Z-scan curve degenerates into a single valley configuration, which is a salient advantage over other methods. In addition, we give gracefully empirical formulas with very high precision, which have good practicability for characterizing the optical nonlinearities of materials by use of the Gaussian beam and trimmed Airy beam Z-scan technique, respectively.     

Phase control of group velocity in one-dimensional photonic crystal with a dispersive defect layer

Propagation of an electromagnetic pulse through one-dimensional photonic crystal doped with three-level ο-type atomic systems is discussed. It is found that in the presence of quantum interference and incoherent pump, the transmitted pulse becomes completely phase dependent. So, the group velocity of the transmitted pulse can be switched from subluminal to superluminal light propagation just by adjusting the relative phase of applied fields.     

Photonic nanojet modulation by elliptical microcylinders

The detailed analysis of localized photonic nanojets generated at the shadow side surfaces of dielectric elliptical microcylinder illuminated by a plane wave is reported. We have studied the distribution of the electric energy density within and in the vicinity outside an elliptical microcylinder by using finite-difference time-domain calculation with high resolution. The location of photonic nanojet depends on the radius ratio of the microcylinder. We have further analyzed the effect of the rotation angle of elliptical microcylinder upon the focal length of photonic nanojets. The horizontal and vertical shifts of photonic nanojet can be changed by rotating the rotation angle of elliptical microcylinder. The mechanisms of elliptical microcylinder may supply a new ultra-lens approach to distinguish nanoscale targets such as nanoparticles, optical gratings, and nanoscale surface roughness.     

Dielectric photonic crystal as medium with negative electric permittivity and magnetic permeability

We show that the two-dimensional photonic crystal (PC) made from a non-magnetic dielectric is a left-handed material in the sense defined by Veselago. Namely, it has negative values for both the electric permittivity ? and the magnetic permeability μ in some frequency range. This follows from a recently proven general theorem. The negative values of ? and μ are found by a numerical simulation. Using values |?| and |μ| for the medium surrounding the PC slab we simulate the Veselago lens, a unique optical device predicted by Veselago. An approximate analytical theory is proposed to calculate the values of ? and μ from the PC band structure. It gives the results that are close to those obtained by the numerical simulation. The theory explains how a non-zero magnetization arises in a non-magnetic PC.