Direct Form I Realization of Active Photonic Filters

Abstract

An integrated photonic architecture is introduced and used to realize an optical filter with direct form I realization. The architecture offers gain from semiconductor optical amplifiers, and this gain results in an active optical filter whose filter response depends on the individual gains. The presence of gain provides advantages in filter performance, and tunable and adaptive functionality. The optical filter is modeled as a discrete time system and the z-transform is used in its analysis and design. A low-pass filter design example is presented and the filter coefficients are derived in terms of gains and coupler splitting ratios. The region of stable operations is derived by applying the Schur-Cohn stability test.     

Global existence and uniform stability of solutions for a quasilinear viscoelastic problem

In this paper the nonlinear viscoelastic wave equation in canonical form with Dirichlet boundary condition is considered. By introducing a new functional and using the potential well method, we show that the damping induced by the viscoelastic term is enough to ensure global existence and uniform decay of solutions provided that the initial data are in some stable set. Copyright © 2006 John Wiley & Sons, Ltd.     

Influence of Fano interference and incoherent processes on optical bistability in a four-level quantum dot nanostructure

Role of Fano interference and incoherent pumping field on optical bistability in a four-level designed In Ga N/Ga N quantum dot nanostructure embedded in a unidirectional ring cavity are analyzed. It is found that intensity threshold of optical bistability can be manipulated by Fano interference. It is shown that incoherent pumping fields make the threshold of optical bistability behave differently by Fano interference. Moreover, in the presence of Fano interference the medium becomes phase-dependent. Therefore, the relative phase of applied fields can affect the behaviors of optical bistability and intensity threshold can be controlled easily.     

Enhanced Kerr nonlinearity in a quantized four-level graphene nanostructure

In this paper, a new model is proposed for manipulating the Kerr nonlinearity of right-hand circular probe light in a monolayer of graphene nanostructure. By using the density matrix equations and quantum optical approach, the third-order susceptibility of probe light is explored numerically. It is realized that the enhanced Kerr nonlinearity with zero linear absorption can be provided by selecting the appropriate quantities of controllable parameters, such as Rabi frequency and elliptical parameter of elliptical polarized coupling field. Our results may be useful applications in future all-optical system devices in nanostructures.     

Synthesis,characterization and cytotoxicity of new 2‐isonicotinoyl‐N‐phenylhydrazine‐1‐carbothioamide and its metal complexes

The reaction of the newly synthesized ligand, 2‐isonicotinoyl‐N‐phenylhydrazine‐1‐carbothioamide (H₃L), with acetate salt of Co (II), Cu (II),Ni (II) and Zn (II) led to isolation of four solid complexes. The ligand and complexes structure elucidation were based on elemental analyses, spectral analyses (IR, UV–Visible, ¹H and¹³C‐NMR, MS and ESR), TGA, molar conductivity and magnetic moments measurements. The results indicated that the ligand exists in the thioketo form, while on coordination to the metal ions; it behaves as mono‐negative bidentate chelate and exists in enol form. The optical band gap measurements of the ligand and its metal complexes are in the range 3.83–4.48 eV indicating their semi‐conducting character. The cytotoxicity examination of H₃L and its Zn (II) complex showed that the ligand have very strong cytotoxicity against both HCT‐116 and HEPG‐2 cell lines while, Zn (II) complex has moderate activity.     

Structural Elucidation of {[(CH3)2SnCl2·H2O]2·18-crown-6} n and its Hydrogen Bonding in Solution by HMBC Spectroscopy

Behavior of {[(CH₃)₂SnCl₂·H₂O]₂·18-crown-6}_n in solution have been investigated by HMBC NMR. The results show that coordination of water to tin containing species and its hydrogen bonding to crown ether remains intact in non-coordinating solvent in contrast to coordinating solvent. H-NMR reveals that the chemical shift of water in complex varies by solvent of crystallization.     

Manganese porphyrins/mesoporous amberlyst 15 nanocomposites: Robust biomimetic catalysts for aqueous oxidation of olefins

In this study, the manganese complexes of N-methylated meso-tetra(2-, 3-, or 4 pyridyl)porphyrins, immobilized into the pores of the sodium salt of mesoporous amberlyst 15 nanoparticles (nanoAmbSO₃Na), nanoAmbSO₃@MnT(2-MePy)P (OAc), nanoAmbSO₃@MnT(3-MePy)P (OAc), and nanoAmbSO₃@MnT(4-MePy)P (OAc), were synthesized and characterized by field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), thermal gravimetric analysis (TGA), nitrogen adsorption/desorption porosimetry analysis, and diffuse reflectance UV–vis spectroscopy. FESEM images revealed a particle size less than ~40 nm for the nanocomposites. The results of BET are in accord with the occupation of the larger pores of the polymer matrix in the case of MnT(2-MePy)P (OAc) as the most sterically demanding metalloporphyrin of the series, and the smaller pores in the case of the other ones. The immobilized manganese porphyrins were used as catalysts for the oxidation of olefins with sodium periodate in the presence of imidazole (ImH) as the co-catalyst. The negligible oxidative destructions of the immobilized manganese porphyrins under the oxidative conditions allowed the comparison of the inherent catalytic activity of the metalloporphyrins, decreased as nanoAmbSO₃@MnT(4-MePy)P (OAc) > nanoAmbSO₃@MnT(3-MePy)P (OAc) ≫ nanoAmbSO₃@MnT(2-MePy)P (OAc). Contrary to the general belief that electron-deficient metalloporphyrins are more efficient catalysts than the electron-rich ones, the most electron-deficient metalloporphyrin of the series, that is, nanoAmbSO₃@MnT(2-MePy)P (OAc), showed the lowest catalytic activity. Due to the high oxidative stability of the immobilized manganese porphyrins, ring opening of epoxide competes with the epoxidation reaction to decrease the yield of epoxide at longer reaction times than the optimized one.     

A new diphenylphosphinite ionic liquid (IL-OPPh2) as reagent and solvent for highly selective bromination, thiocyanation or isothiocyanation of alcohols and trimethylsilyl and tetrahydropyranyl ethers

A new diphenylphosphinite ionic liquid (IL-OPPh₂) is introduced. This ionic liquid is used as both a reagent and a solvent to convert alcohols and trimethylsilyl and tetrahydropyranyl (THP) ethers into their corresponding alkyl bromides, thiocyanates or isothiocyanates in the presence of Br₂ and SCN⁻ at 80 °C. In this ionic liquid, bromination and thiocyanation of alcohols occurs highly selectively in the presence of trimethylsilyl and THP-ethers and also between different classes of alcohols. The use of this ionic liquid allows easy separation of the desired products from the phosphinate by-product.     

Investigation of the structural directing effect of (2-hydroxyethyl)trimethylammonium on distribution of the silicate anions using 29Si NMR spectroscopy

The effect of (2-hydroxyethyl)trimethylammonium (2-HETMA) cation on the equilibrium of silicate oligomers in aqueous alkaline silicate solutions was investigated using (29)Si NMR spectra. The results indicate role of structural directing of 2-HETMA in which it particularly directs the silicate species to the Q(4)(1)Q(4)(3)Q(4)(4) silicate anion. Results reveal that composition of the alcohols in solution affect the distribution of anionic species. The effect of methanol concentration is also discussed.