Journal of Nonlinear Optical Physics & Materials

The birefringence and natural ability to form periodic structures make cholesteric liquid crystalline (CLC — chiral nematics) materials particularly attractive as 1D photonic band gap systems. If a CLC is doped with dye fluorescent molecules, in such a way that the maximum peak of fluorescence matches one of the edges of the selective stop band, laser action is expected at that spectral position. By confining the helical super-structure of chiral liquid crystals in polymeric micro-cavity channels, a tunable microcavity laser array was achieved. In multiple scattering systems, the propagation of the light waves is quite different, as optical scattering may induce a phase transition in the photon transport behavior. Beyond a critical scattering level, the system makes a transition into a strongly localized state and light transmission is inhibited. This effect can be used as a photon trapping mechanism to obtain laser action in the presence of a gain medium. Random lasing modes come from interference effects which survive in disordered systems and open a particular chapter in the study of the interplay between localization and amplification. Here, experiments performed on systems having different order degree and confinement are presented and possible technological implications are discussed.

Nematic liquid crystal (NLC) is a material that features a large nonlinear optical response. The nonlinearity can be enhanced by doping a dye agent into a NLC host. In this paper, we review the nonlinear phenomena recently observed for dye-doped liquid crystal (DDLC) films measured using the Z-scan technique, which is a simple, yet powerful method for measuring nonlinear refractive indices (optical Kerr constant) n₂ and nonlinear absorption coefficients β. The nonlinear effects of liquid crystals (LCs) include the electronic polarization effect, electrostriction effect, thermal effect and reorientation effect. When LCs are doped with dye agents, the dye-induced orientational effect, photoisomerization effect, and light-induced thermal effect come about to enhance LC nonlinearity. The dominant effect depends strongly upon the spatial, temporal and polarization properties of the excitation laser beam. Generally speaking, the nonlinear effects resulted from the electronic polarization and photoisomerization effects arise from a laser pulse on picosecond duration scale, while electrostriction, thermal and reorientation effects occur on nanosecond ~ microsecond, nanosecond ~ millisecond and millisecond ~ second duration scales, respectively. In this paper, the causation of nonlinear refractive index n₂ into various different experimental conditions is summarized, including the changes of the external electric field, external optical field, polarization of pump beam, temperature and the use of deuterated materials. The mechanisms, which influence the nonlinear effect in dye-doped liquid crystal films, are also discussed.

The generalized Thomas-Kuhn sum rules are used to characterize the nonlinear optical response of organic chromophores in terms of fundamental parameters that can be measured experimentally. The nonlinear optical performance of organic molecules is evaluated from the combination of hyper-Rayleigh scattering measurements and the analysis in terms of the fundamental limits. Different strategies for the enhancement of nonlinear optical behavior at the molecular and supramolecular level are evaluated and new paradigms for the design of more efficient nonlinear optical molecules are proposed and investigated.

In this paper, three kinds of controllable nonlinear left-handed materials (DNLHMs) are proposed and analyzed, which are designed by introducing inductors and capacitors into the traditional nonlinear left-handed materials (NLHMs) as inhomogeneous doped elements. Due to such changes, several new transmission properties have been presented through finite-difference time-domain (FDTD) simulations. These have brought new features to our DNLHMs. On one hand, the original passband in the traditional nonlinear left-handed material is narrowed after introducing inductors. In addition, a new passband, which does not exist in doped linear LHMs, is generated. On the other hand, through introducing capacitors, the original passband of the nonlinear left-handed material can be shifted, resonance frequency can be changed, and a new passband can be generated. When capacitors and inductors are introduced simultaneously, the material properties, such as the number of passbands, the characteristic resonance frequency, and the bandwidth, can also be changed. Noting these characteristics, the values of the introduced inductors and capacitors are varied to investigate the spectrum changes of DNLHMs. Then, a series of controllable properties of the DNLHMs can be retrieved. And more importantly, the designed DNLHMs give the adjustability of suppressing high harmonics, which is not possible in the past materials.

By using the three-dimensional complex Ginzburg–Landau equation with the cubic-quintic nonlinearity, the energy exchange of stable dissipative optical bullets is investigated for bullets launched with zero velocities and with non-zero velocities numerically in dissipative system. It is found that there are two primary factors in the energy exchange process: (i) the relative phase of dissipative optical bullets, which is crucial for energy exchange between bullets, and (ii) the initial velocities of them, which influence interaction and energy exchange between bullets and external source greatly. In addition, some interesting phenomena accompanied by energy exchange, such as asymmetric lateral deflection, bullet fusion and bullet disappearance, are also demonstrated.

Ordered Au nanoparticle arrays were fabricated on fused quartz substrates using nanosphere lithography. Linear and nonlinear optical properties of triangular Au nanoparticle arrays were investigated. Two LSPR peaks due to the surface plasmon resonance of Au particles were observed. The nonlinear optical properties were measured using the Z-scan technique at a wavelength of 532 nm and pulse duration of 10 ns. The nanoparticle arrays exhibit distinct nonlinear absorption saturation behavior, the absorption coefficient was determined to be –3.5 × 10³ (cm/GW).

Comparator determines whether a number is greater than, equals to or less than another number. It plays a significant role in fast central processing unit in all-optical scheme. In all-optical scheme here 1-bit binary comparator is proposed and described by Terahertz Optical Asymmetric Demultiplexer (TOAD) based interferometric switch. Simulation result by Mathcad-7 is also given. Cascading technique of building up the n-bit binary comparator with this 1-bit comparator block is also proposed here.

This paper describes a new model for the breakdown voltage of SiO₂ fiber coupler using the Pockel effect and empirical equation. The model is evaluated by using the coupling coefficient and the changes in the refractive index. We found that the breakdown voltage is in the order of 10² volt corresponding to coupling coefficient by the order of mm^-1. Increasing the value of coupling coefficient between the electrodes leads to a reduction in the breakdown voltage.

We investigate the transmission properties of a metamagnetic structure, the so-called cut-wire pair (CWP), using the transfer-matrix method and the finite integration technique. The electric and magnetic resonances of the CWP structure are demonstrated by the effective medium analyses. The corresponding effective permittivity and permeability are calculated from the complex scattering parameters using the standard retrieval procedure. Importantly, the dependence of transmission properties and resonance frequencies on the periodicities as well as the shape of CWP are systematically examined.

The amplifier separation and channel separation has conflicting effects on the noise generated due to the fiber non-linear effects (Stimulated Raman scattering SRS and Four wave mixing FWM) and the Amplified spontaneous emission (ASE) noise introduced by inline optical amplifications. While designing an efficient Dense Wavelength Division Multiplexing (DWDM) system, optimization of the channel separation and amplifier separation are required to minimize the non-linear effects (FWM and SRS) along with the ASE noise. In this paper, theoretical investigations of the optical DWDM systems have been presented to minimize the bit error rate (BER) by optimizing inter-channel separation and inter-amplifier separation at different data rates considering the combined effect of SRS, FWM, ASE, receiver and beat noises.

The nonlinearity effects of photonic crystal fiber (PCF) in a ring resonator for different lengths of Bismuth erbium-doped fiber (Bi-EDF) as the Brillouin gain medium is investigated. Bi-EDF (215 cm) itself has high stimulated Brillouin effect at 150 mW that is generated at 1480 nm pump power. The proposed Brillouin fiber laser (BFL) with PCF operates at 1559 nm for 49 cm Bi-EDF, which is upshifted by 0.08 nm from the Brillouin pump with a side-mode suppression ratio more than 12 dB. As a result of using reduced length of PCF and two long Bi-EDF, the BFL is stable at room temperature and compact in this report.

This paper studies the optical bistability in a degenerate three-level Λ-type atomic system in a unidirectional optical ring cavity. The effect of quantum interference on the phase control of the optical bistabilty is then discussed. It is shown that the optical bistability changes with the intensity of coupling and the rate of an incoherent pumping field. The possibility of creating an optical multistability (OM) by the intensity of coupling field relative phase between the applied fields, and the rate of an incoherent pump field has also been discussed.

Femtosecond laser pulse propagation in monomode optical fibers is demonstrated and investigated numerically (by simulations) and experimentally in this paper. A passively mode locked Nd:glass laser giving a pulse duration of about 200 fsec at 1053 nm wavelength and 120 mW average optical power with 100 MHz repetition rate is used in the experimental work. Numerical simulations are done by solving the nonlinear Schrödinger equation with the aid of Matlab program. The results show that self phase modulation (SPM) leads to compression of the spectral width from 5 nm to 2.1 nm after propagation of different optical powers (34, 43, 86 and 120 mW) in fibers of different length (5, 15, 35 m). The varying optical powers produced a varying phase shift. The output spectral width also changed with the fiber length at a given peak power.