Journal of Nonlinear Optical Physics & Materials

A theoretical analysis of the condition of scalar phase-matched second harmonic generation and optical parametric oscillation (OPO) in single-crystalline samples Zn_0.52Mg_0.48Se is presented. The calculated range of pumping for second harmonic generation with phase matching is 5.1-13 μm. The tuning range of the optical parametric oscillator based on Zn_0.52Mg_0.48Se is determined. The combination of active media and nonlinear converter for OPO in the same optical element are proposed.

Polarization insensitive second harmonic generation (SHG) is proposed in an electro-optic (EO) tunable periodically poled Lithium Niobate (PPLN). The PPLN consists of four sections. External electric fields could be selectively applied to them to induce polarization rotation between the ordinary and extraordinary waves. If the domain structure is well-designed, the fundamental wave with an arbitrary polarization state can be frequency doubled efficiently in this special PPLN.

The third order nonlinear optical properties of two different sized carboxylate-modified microspheres are investigated at different pump powers. The nonlinear absorption (NLA) is measured at 532 nm using 10 Hz, 7 ns pulses from the second harmonic generated from a Q-switched Nd-YAG laser in an open aperture Z-scan setup. The nonlinear response is size-dependent, and switching from reverse saturable absorption (RSA) to saturable absorption (SA) is observed as the size increases.

We investigated the signal output efficiency of a singly-resonant ns-optical parametric oscillator based on LiNbO₃ with the double-pass pump as a function of reflectance (R) of the output coupler. The measured signal output exhibited a broad maximum around R ~ 35% at a fixed pump energy of 100 mJ/pulse, yielding a maximum signal output efficiency of ~ 38%. The experimental results were well-supported by the numerical calculation using a split-step beam propagation model. We also found that the same beam propagation model with one-dimensional diffraction predicts nearly the same results, enabling fast numerical determination of the optimum reflectance of the output coupler.

We have investigated the interaction of two level atom with time varying quadrature squeezed light field. Jaynes-Cummings model is used for solving the atom radiation interaction. Time evolution of the system for different squeezing parameter and phase have been studied. There are no well-defined revivals in population inversion when the squeezed phase is π and the squeezing parameter is greater than 0.5. Using a time varying frequency for the light field, it is found that the randomness of the population inversion and the collapse revival phenomena can be controlled. Frequency modulation of the field can thus be used as a tool for manipulating the squeezed light atom interaction.

The propagation behavior of an optical pulse is investigated at the interface of two different nonlinear bi-dispersive waveguide arrays. It is found that the peak power has a great impact on the propagation of the pulse. When the peak power is high enough, the major part of the initial pulse can be guided and confined in the interface of this waveguide array. Because of the interplay between asymmetry discrete diffraction, dispersion and Kerr nonlinearity of hetero-structure waveguide array, the output pulse develops a rectangular-like intensity profile with richer bandwidth, and its power spectrum in the frequency domain is rather uniform, i.e., less modulated. Therefore, the output pulse from the hetero-structure waveguide array can be compressed more efficiently than that of a homogeneous element.

Concentration dependent optical properties of the various types of porphyrin compounds were studied using optical absorbance and Z-scan measurements. Enhanced absorbance width of the Soret and Q-bands have been observed by blending three different porphyrin molecules in Nafion column matrix membrane. This is an important development towards achieving efficient photon-harvesting medium for possible application in photonic devices. Moreover, new evidences have been found on the concentration dependance of the nonlinear absorption coefficient (β) of the VTPP in Nafion.

We report results from investigations of the nonlinear refractive index and nonlinear absorption coefficient of (2E)-3-[4-(Dimethylamino)phenyl]-1-(2,5-dimethylthiophen-3-yl)prop-2-en-1-one and (2E)-3-(3,4-Dimethoxyphenyl)-1-(2,5-dimethylthiophen-3-yl) prop-2-en-1-one using Z-scan technique with a continuous wave (cw) laser at wavelengths 488 nm and 514 nm. The nonlinear refractive index and nonlinear absorption coefficient of both samples were evaluated. The origin of the nonlinear effects was discussed. Optical limiting based on light induced nonlinear refractive index variation is demonstrated. The limiting thresholds were estimated for both samples. The results suggested that these materials offer promise as candidates for optical limiting and optical devices in the low power regime.

We introduce a model of resonant optical systems: a waveguide array doped periodically with resonant four-level N-type atoms. The dopant atoms are driven by external fields which induce the effect of the electromagnetically induced transparency (EIT). In this resonant waveguide arrays (RWA) system, the optical field propagates as quasi-discrete diffraction, breathing beam or stable spatial soliton when different initial amplitude and width of the probe are given. The critical values representing these transformations are obtained by the numerical simulations. In a further study of the oblique incidence, the soliton loses a portion of its energy while a kick (i.e., a transverse wave vector) is initially introduced. As the value of the kick becomes larger than a critical value, the soliton collapses.

In this paper, an all-optical switch based on self-assembled GaAs/AlAs quantum dots (QDs) within a vertical cavity is designed and proposed. Two essential aspects of this novel device have been investigated, which include the QD/cavity nonlinearity with appropriately designed mirrors and the intersubband carrier dynamics inside QDs. The vertical-reflection-type switches have been investigated with an asymmetric cavity that consists of 12 periods of GaAs/Al_0.8Ga_0.2As and 25 periods for the front and back mirrors, respectively. The thicknesses of the GaAs and AlGaAs layers are chosen to be 89 and 102 nm, respectively. To give a dot-in-a-well (DWELL) structure, the 65 nm dimension of Si was recommended to deposit within a 20 nm AlAs QW. Results obtained have shown that all-optical switching via the QD excited states has been achieved with a time constant down to 275-fs and over 29.5 nm tunable wavelengths. These results demonstrated that QDs within a vertical cavity have great potential to realize low-power, consumption polarization-insensitive and micrometer-sized switching devices for future optical communication and signal processing systems.

In a butt-joint coupling system, a fiber is coupled to a slab waveguide by a fiber ended micro-lens (FEML), so that the electromagnetic field emerging from the FEML is completely different from the fiber mode. The conventional method for calculations of the coupling efficiency, such as the overlap integral method, is not valid. In this paper, a Monte Carlo model for the coupling system is proposed, based not only on the principles of reflection and refraction at media interface plane, but also on the diffractions of micro lens. This model incorporates the geometrical surface of both the fiber end-face micro-lens and slab waveguide, the relative position of the fiber and slab waveguide, and also takes into consideration both the aberration and diffraction effects. The propagation characteristics and coupling efficiencies of the system are simulated. The losses caused by misalignment of the system are also discussed.

The third-order optical nonlinearities of three planar transition metal (Ni, Cu and Pd) compounds with rigid quadridentate Schiff base derived from S-benzyl dithiocarbazate, were investigated systematically by Z-scan technique with picosecond laser pulses at 1064 nm. The three compounds exhibit both strong two-photon absorption and effective self-focusing performance. Due to the heavy atom effect, the second hyperpolarizability of PdZ molecule (〈γ〉 = 1.2 × 10^-29 esu) was found to be the highest compared to that of the other two molecules. The optical limiting properties were also measured, and the results suggest that PdZ may be a promising candidate for the application to optical limiting in the near-infrared region.