Segmented-clad fiber design for inherently gain-flattened L/sup +/-band TDFA

We present here an efficient design for high gain, inherently gain-flattened L/sup +/-band thulium-doped fluoride fiber amplifier (TDFA), based on a novel segmented clad fiber refractive index profile. Detailed simulations show that the designed amplifier is able to achieve 20-dB gain, with /spl plusmn/0.7-dB gain ripple over 40-nm bandwidth (1600-1640) nm. Performance comparisons of the proposed module with an L/sup +/-TDFA based on conventional W-fiber designs and on a conventional step-index fiber have also been carried out.     

A novel numerical technique for solving the one-dimensionalSchroedinger equation using matrix approach-application to quantum wellstructures

A numerical technique that allows straightforward determination of bound-state and quasi-bound-state energy eigenvalues (and lifetimes of the latter) for arbitrary one-dimensional potentials is presented. The method involves straightforward multiplication of 2×2 matrices and does not involve any iterations. The applicability of the technique to analysis of the quantum-well structures is also shown. Since the Schroedinger equation for a spherically symmetric potential can be transformed to a one-dimensional equation, all such problems can also be solved using this method     

The local absorption technique: A straightforward characterization method for many optical devices

A new technique is analyzed and demonstrated to characterize integrated optical directional couplers. It is based on the locally induced absorption caused by a sliding Mercury drop. This technique works at any wavelength, does not rely on specific material properties, and leads to very fast knowledge of the characteristic parameters of the directional couplers.     

Resonant tunneling three-waveguide polarization splitter

A design for a novel and highly efficient all-dielectric, three-waveguide polarization splitter based on the phenomenon of resonant tunneling is proposed. By considering a glass waveguide structure with an intermediate high-index guiding layer (such as silicon), it is shown that extinction ratios better than -33 dB in both the outer waveguides at a particular thickness of the high-index layer can be obtained. The tolerance required with respect to the separation between the middle and outside guides and the thickness of the high-index layer of such a device is estimated. The design should be of interest in the realization of in-line fiber-optic polarization splitters and in integrated optics     

Recombinant botulinum neurotoxin A heavy chain-based delivery vehicles for neuronal cell targeting

The long half-life of botulinum neurotoxin serotype A (BoNT/A) in cells poses a challenge in developing post-exposure therapeutics complementary to existing antitoxin strategies. Delivery vehicles consisting of the toxin heavy chain (HC), including the receptor-binding domain and translocation domain, connected to an inhibitory cargo offer a possible solution for rescuing intoxicated neurons in victims paralyzed from botulism. Here, we report the expression and purification of soluble recombinant prototype green fluorescent protein (GFP) cargo proteins fused to the entire BoNT/A-HC (residues 544-1295) in Escherichia coli with up to a 40 amino acid linker inserted between the cargo and BoNT/A-HC vehicle. We show that these GFP-HC fusion proteins are functionally active and readily taken up by cultured neuronal cells as well as by neuronal cells in mouse motor nerve endings.     

Coherent tunnelling adiabatic passage in optical fibres using superimposed long-period fiber gratings

Abstract

In this paper, we present the optical analogue of stimulated Raman adiabatic passage (STIRAP) technique for three level atomic system in optical fibre geometry. Considering linearly polarized modes of an optical fibre, it is shown that using a pair of superimposed long-period gratings with peak refractive index perturbation varying spatially along the propagation axis, light can be transferred adiabatically from one core mode to another core mode via an intermediate cladding mode which itself does not get appreciably excited; thus acting like a dark mode. We compare the transmission spectrum of superimposed long-period gratings involved in adiabatic transfer with the transmission spectrum of conventional long-period grating. The analogue output is further analysed for its tolerance to the changes in the ambient refractive index, temperature and other fabrication parameters.     

Synthesis and characterization of lacquers based on styrene acrylic copolymers for applications in leather industry

Radical copolymerization of styrene with butylacrylate and/or maleic anhydride was carried out at 70°C, using benzoyl peroxide as an initiator in benzene/ethylacetate in order to prepare lacquers for top coats for use in leather industry. Copoly(styrene–butylacrylate) was characterized using IR and ¹³C-NMR spectroscopy. Thermal properties of the polymers were studied using thermogravimetric analysis and evaluated the integral procedural decomposition temperatures of polymers. The order of reaction and the activation energy for the thermal degradation of polystyrene, poly(ST-co-MAn) and St–BA–MAn terpolymer at different temperatures were calculated. Molecular weights were determined from gel permeation chromatography and viscosity measurements. Physical properties of the films were studied and compared with standard lacquers available for top coats in leather industry.     

Equivalent step index (ESI) model for elliptic core fibers

We present empirical relations describing the spectral dependence of the spot sizes of the fundamental mode (along the major and minor axes) in a homogeneous elliptic core fiber. These relations are obtained by modeling the fundamental mode by a Gaussian distribution. Using these relations, we present a method for the determination of the equivalent step index (ESI) parameters of a monomode elliptic Core fiber. The applicability of the proposed method is shown through a) calculation of the cutoff wavelengths of a parabolic index elliptic core fiber and b) calculations of various fiber parameters like the core radii and index difference of an elliptic core fiber from recently reported experimental data.     

Polarization characteristics of side-pit and side-tunnel fibers using the effective index method

The effective index method has been used to determine the polarization characteristics of side-pit and side-tunnel fibers. The results obtained by the present method compare quite well with those reported by using the finite element method.