Comparative Study on Large and Small Signal Theory for Intensity Modulation Response of Semiconductor Lasers Including Higher-Order Dispersion Terms

In this article, the comparison of large signal theory and small signal theory has been done with dispersive propagation of optical signal with IMDD (Intensity Modulation Direct Detection) systems for semiconductor lasers with higher-order dispersion terms. The expressions for an exact large signal theory and small signal theory including higher-order dispersion terms for propagation of an optical wave with sinusoidal amplitude and frequency modulation in a dispersive fiber have been derived. It is observed that small signal theory is more sensitive compared to large signal theory in terms of intensity modulation/direct detection systems. Also, it is reported that for large signal analysis the higher-order effects of dispersion can be ignored, whereas for small signal theory, the higher-order effects can be ignored for lower modulation frequencies only. The variation in the transfer function for various values of modulation indices are greater for small signal analysis than for large signal analysis. Also, as the intensity modulation index is increased, there is a decrease in the value of transfer function. The large signal model approximates the small signal model for lower values of the intensity modulation index.     

Approximate and Exact Small Signal Analysis for Single-Mode Fiber Near Zero Dispersion Wavelength with Higher Order Dispersion

This article presents the comparison of approximate and exact small-signal theories for analyzing the influence of the higher-order dispersion terms on dispersive optical communication systems operating near zero dispersion wavelength for linear single-mode fiber. For the approximate theory, the generalized conversion matrix has been reported and gives the transfer function of intensity and phase from the fiber input to fiber output for a laser source including the influence of any higher-order dispersion term. In addition, expressions for the small-signal frequency response and the relative intensity noise (RIN) response of an ultrafast laser diode including noises are derived. However, it is observed that the approximation assumed for the second-order dispersion term for the approximate analysis is not valid. From the approximate theory, the exact generalized conversion matrix and exact expressions for small-signal frequency response and relative intensity noise (RIN) are obtained. We show that for the exact theory, the second-order dispersion term has no effect on intensity and frequency response even at large modulating frequencies and large propagation distances contrary to the approximate theory as reported by other authors. But we show that third-order dispersion term certainly has some minute impact on the frequency and RIN response for long distance links at high modulating frequencies.     

Characterization of nanostructured hollow polymer spheres with small-angle neutron scattering (SANS)

Hollow polymer spheres synthesized from a vesicle-directed polymerization can be dried and redispersed in water using a variety of nonionic ethoxylated alcohol surfactants as stabilizers. The final dispersions consist of both polymer shells and surfactant micelles, which remain together in colloidal suspension for at least several months. Small-angle neutron scattering (SANS) is used to measure the polymer shell thickness (63 A) and core radius (560 A) of the surfactant-stabilized hollow polymer spheres in the presence of surfactant micelles. Characterization by SANS provides information about the surfactant bilayer and polymer shell thicknesses which were previously unattainable.     

Combined Path and Maximum Empty Static Routing Algorithms with Wavelength Assignment for Future Transport Networks

Abstract

In this article, two static routing algorithms have been proposed and compared to some of the existing algorithms on the basis of blocking probability. The two proposed static routing and wavelength assignment algorithms reduce the blocking probability to maximize the utilization of the network. All of these algorithms are analyzed and compared with four wavelength assignment schemes, which are first-fit, random, most used, and least used. It is shown that our proposed static algorithms give the best performance for first-fit wavelength assignment and most used wavelength assignment strategies with reduced complexity. For least used wavelength assignment and random wavelength assignment, 1 fixed and 2 alternate routing algorithm gives the lowest blocking probability.     

Performance evaluation of VCSEL through single and multi mode fibers

This paper presents influence of the change in temperature of a vertical cavity surface emitting laser (VCSEL) on its output power. It is observed that with increase in temperature of laser its output power decrease. It is also observed that with decrease in threshold voltage of the laser output power increase. Decrease in output power due to increase in temperature can be compensated by increasing driving current. But increase in drive current decrease life of the laser. So a laser with lower threshold voltage can be used to operate at high temperature with long life. Propagation of VCSEL through single mode and multimode fiber is also studied. In single mode fiber only one propagation mode exists due to which signal can be transmitted to longer distances.     

Performance analysis of an integrated scheme in optical burst switching high-speed networks

A new integrated scheme based on resource-reservation and adaptive network flow routing to alleviate contention in optical burst switching networks is proposed. The objective of the proposed scheme is to reduce the overall burst loss in the network and at the same time to avoid the packet out-of-sequence arrival problem. Simulations are carried out to assess the feasibility of the proposed scheme. Its performance is compared with that of contention resolution schemes based on conventional routing. Through extensive simulations, it is shown that the proposed scheme not only provides significantly better burst loss performance than the basic equal proportion and hop-length based traffic routing algorithms, but also is void of any packet re-orderings.     

A novel optical burst switching architecture for high speed networks

A novel optical burst switching （OBS） high speed network architecture has been proposed. To verify its feasibility and evaluate its performance, just-enough-time （JET） signaling has been considered as a high performance protocol. In the proposed architecture, to avoid burst losses, firstly, a short-prior- confirmation-packet （SPCP） is sent over the control channel that simulates the events that the actual packet will experience. Once SPCP detects a drop at any of the intermediate nodes, the actual packet is not sent but the process repeats. In order to increase network utilization, cost effectiveness and to overcome some limitations of conventional OBS, inherent codes （e.g., orthogonal optical codes （OOC））, which are codified only in intensity, has been used. Through simulations, it shows that a decrease in burst loss probability, cost effectiveness and a gain in processing time are obtained when optical label processing is used as compared with electronic processing.     

Theory of Frequency-Dependent Polarization of General Planar Electrodes with Zeta Potentials of Arbitrary Magnitude in Ionic Media

Electrode polarization effects have long aggravated the efforts of low frequency analysis, particularly those investigations carried out on biological material or in highly conductive media. Beginning from elementary equations of electrostatics and hydrodynamics, a comprehensive model is devised to account for the screening of a general planar electrode by an ionic double layer. The surface geometry of the planar electrode is left unspecified to include any type of micromachined array. Building on the previous work by DeLacey and White (1982, J. Chem. Soc. Faraday Trans. 2 78, 457) using a variational theorem, we extend their numerical results with compact analytic solutions, analogous to the Debye-Hückel potential for dc systems, but applicable now to dynamic ac experiments. The variational approach generates functions that are not restricted by perturbation expansions or numerical convergence, representing optimal approximations to the exact solutions. Copyright 2000 Academic Press.     

Tuning intermicellar potential of Triton X-100-anthranilic acid mixed micelles

Structural parameters of micelles formed by Triton X-100 in the presence of solubilized anthranilic acid at different pH values was investigated using light scattering and small angle neutron scattering. Analysis of the SANS data indicate that micelles are oblate ellipsoidal in nature with little variation in the dimensions, in the investigated pH range (from 0.5 to 6.0). The interaction potential of the micelles shows a minimum closer to the isoelectric point of anthranilic acid. A similar variation is observed in the cloud point of the micelles with pH. The observed variation in the interaction potential with pH of the micellar solution can be explained in terms of the reversal of charge on anthranilic acid due to shift in the acid-base equilibrium. The variation in interaction potential and cloud point with pH is modelled using Coulombic repulsion of charged molecules at the micelle interface.      

Generic routing and wavelength assignment algorithm for a wavelength-routed WDM network

In this paper, we have developed a simple mathematical model which is used for the calculation of blocking probability of network. A generic routing and wavelength assignment algorithm has also been proposed for the optimization and minimization of blocking probability. The implementation of the proposed model has less complexity and the computation used in this model is quite efficient. This paper suggests an optimum path and assigns wavelength to that path, as a solution to routing and wavelength assignment problem to have least blocking probability. This model can be implemented on different network topologies. Further, the model is also used to evaluate the blocking performance of a 6-node simple network topology and hence used to improve its performance on the basis of blocking probability.