Improved performance analysis of Gigabit passive optical networks

Gigabit passive optical networks (GPON) provide a capacity boosts in both the total bandwidth and bandwidth efficiency through the use of larger variable-length packets in Passive Optical Networks technology. In this paper, we have described a purely-passive GPON compatible reach extender using distributed Raman amplification and reported the improved investigation through implementation of a square root module by a distance of 60 km at data rate of 2.5 Gbps. An efficient improvement in Q factor is achieved with square root module, which further helps in increasing the length of GPON.     

Elasto-plastic vibrational analysis of tapered bars under uniform axial loading considering shear deformation and rotary inertia

The analysis of structures in the plastic regime is important in order to develop an adequate and competitive design in engineering. This paper presents a study of the small-amplitude free vibration of tapered bars under pre-stress in the post-elastic regime due to a uniform axial loading. The plastic behavior is taken into account using an energy approach. The method does not require an iterative procedure, unlike conventional methods used in plasticity. The Timoshenko beam theory and the dynamic version of the principle of virtual work are used to derive the eigenvalue problem. The solution is carried out using beam finite elements. The results are validated using 3D finite element software and results from the open literature. A variety of numerical results are given in order to analyze the influence of plastic behavior for various bar geometries and material parameters. The combined effect of the stiffening due to the axial loading and the plastic softening may produce an increase or decrease of the natural frequencies as the tensile load increases. The plastic softening effect is seen to be pronounced for short bars and for high taper ratios. In addition, axial normal modes are more affected than bending modes.     

Magnetically assisted gas-solid fluidization in a tapered vessel: Part Ⅱ Dimensionless bed expansion scaling

The article presents an effort to create dimensionless scaling correlations of the overall bed porosity in the case of magnetically assisted fluidization in a tapered vessel with external transverse magnetic field. This is a stand of portion of new branch in the magnetically assisted fluidization recently created con-cerning employment of tapered vessels. Dimensional analysis based on "pressure transform" of the initial set of variables and involving the magnetic granular Bond number has been applied to develop scaling relationships of dimensionless groups representing ratios of pressures created by the fluid flow, gravity and the magnetic field over an elementary volume of the fluidized bed. Special attention has been paid on the existing data correlations developed for non-magnetic beds and the links to the new ones especially developed for tapered magnetic counterparts. A special dimensionless variable Xp = (Ar△DbL)1/3(√RgMQ) combining Archimedes and Rosensweig numbers has been conceived for porosity correlation. Data cor-relations have been performed by power-law, exponential decay and asymptotic functions with analysis of their adequacies and accuracies of approximation.     

Magnetically assisted gas-solid fluidization in a tapered vessel： Part II Dimensionless bed expansion scaling

The article presents an effort to create dimensionless scaling correlations of the overall bed porosity in the case of magnetically assisted fluidization in a tapered vessel with external transverse magnetic field. This is a stand of portion of new branch in the magnetically assisted fluidization recently created concerning employment of tapered vessels. Dimensional analysis based on ＂pressure transform＂ of the initial set of variables and involving the magnetic granular Bond number has been applied to develop scaling relationships of dimensionless groups representing ratios of pressures created by the fluid flow, gravity and the magnetic field over an elementary volume of the fluidized bed. Special attention has been paid on the existing data correlations developed for non-magnetic beds and the links to the new ones especially developed for tapered magnetic counterparts. A special dimensionless variable Xp = （Ar△Dbt）1/3√RgMQ combining Archimedes and Rosensweig numbers has been conceived for porosity correlation. Data correlations have been performed by power-law, exponential decay and asymptotic functions with analysis of their adequacies and accuracies of approximation.     

Loss Behavior of Single-mode Optical Fiber Microbend Sensors

Periodic microbending has been studied to develop an insight into the loss behavior of single-mode microbend sensors by using the finite-difference beam propagation method. Loss sensitivity variations with wavelength are examined, as well as the optical loss dependence on the number of microbends and the modal field perturbations caused by the microbending.     

Terahertz Time Domain Spectroscopy for the Identification of Two Cellulosic Fibers with Similar Chemical Composition

The distinct terahertz spectra of ramie and bamboo fibers were obtained by means of terahertz time-domain spectroscopy. Numerical simulation for glucose based on density functional theory has been performed to interpret the observed THz features theoretically. The results indicate that the intramolecular motions do make partial contribution to experimental features of cellulosic fibers, but most of the features are attributed to intermolecular modes. The investigation suggests that THz spectroscopy is a promising candidate for distinguishing bamboo and ramie fibers, and this will open new prospect to identify textile fibers especially those with similar chemical composition.     

Computational fluid dynamics and experimental study of the hydrodynamics of a gas–solid tapered fluidized bed

In the present work, experimental and numerical studies for the hydrodynamics in a gas–solid tapered fluidized bed have been carried out. The experimental results obtained by carrying out experiments in a tapered fluidized bed for glass bead (spherical) of 2.0 mm and dolomite (non-spherical particles) of 2.215 mm in diameter, were compared with the computational fluid dynamics (CFD) simulation results, using a commercial CFD software package, Fluent. The gas–solid flow was simulated using the Eulerian–Eulerian model and applying the kinetic theory of granular flow for solid particles. The Gidaspow drag model was used to calculate the gas–solid momentum exchange coefficients. Pressure drops predicted by the CFD simulations agreed reasonably well with experimental measurements for both types (spherical and non-spherical) of particles. Good agreement was also obtained between experimental and CFD predicted bed expansion ratios for both types of particles. Present study provides a useful basis for further works on the CFD of tapered fluidized bed.     

Higher order mode propagation in an optical nanofiber

The propagation of higher modes, such as the LP₁₁ mode, in optical nanofibers using the exponentially tapered optical fiber as a basic model is investigated. In order to preserve the LP₁₁ mode in the downtaper as far as the nanofiber waist, the effect of varying the cladding-core radius ratio on the LP₁₁ adiabatic criterion is modeled. A Laguerre-Gaussian beam is created in free space using a spatial light modulator (SLM) and coupled to a few-mode fiber. This device allows convenient switching between the fundamental and LP₁₁ fiber modes. By selecting a few-mode fiber with a relatively low cladding-core ratio, the propagation of the LP₁₁ mode down to a submicron waist has been maintained. Furthermore, by observing the transmission profile during tapering, it is possible to decisively terminate the pulling process in order to eliminate the two degenerate HE₂₁ modes of the LP₁₁ mode. As a result, a nanofiber can be fabricated through which only the TE₀₁ and TM₀₁ components of the LP₁₁ mode propagate. Such a nanofiber has promising applications in the area of mode interference for controlled particle trapping sites.     

Mechanically induced long-period fiber gratings on tapered fibers

The characteristics of a mechanically induced long-period fiber grating (MLPFG) made by pressing a pair of grooved plates over single-mode fiber tapers are analyzed. Fiber tapers with a waist length of 80 mm and diameter ranging from 90 to 125 μm, fabricated using the heating and puling method, were used. We observed that the resonance wavelengths shift toward shorter wavelengths as the fiber taper waist diameter is reduced. A maximum shift of 254 nm in the position of the resonance peaks was observed when the fiber diameter was reduced to 90 μm. This technique is particularly suitable for tuning the resonance wavelengths to shorter wavelengths below the limit imposed by the grooved plate period.     

Mesoscopic effect of spectral modulation for the light transmitted by a SNOM tip

The effect of a tapered metal-coated optical fiber terminated by a sub-wavelength aperture (SWA) on the spectrum of the transmitted light is investigated experimentally. Under certain conditions a remarkable spectral modulation of the transmitted light can be observed. This effect is of a mesoscopic origin, occurring only for a certain interval of SWA diameters. One can conclude that a noticeable modulation appears when the number of the transmitted fiber modes is small but exceeds unity, thus indicating the presence of a phase shift between different modes. To discern between two possible sources of such phase shift, the fiber length dependence of the output spectrum has been studied. According to the results obtained for the used sample of 200 nm SNOM tip, the observed phase shift is mostly caused rather by the inherent modal dispersion of the multimode fiber than by the mode-dependent light slowdown in the tapered region close to SWA due to the coupling to surface plasmons of the metal coating. The SWA acts here mainly as an effective mode filter.