Petar S. Matavulj

Implementation of Intra-ONU Scheduling for Quality of Service Support in Ethernet Passive Optical Networks

The Ethernet passive optical network (EPON) is a reliable cost effective, high bit-rate point-to-multipoint optical access network. With new applications and services that emerged in last decade, the quality of service support in EPON has become a major concern. In our work, we analyze the performance of dynamic bandwidth allocation algorithms and intra-ONU scheduling algorithms, and further investigate how a combination these algorithms can be implemented in EPON in order to efficiently support the transmission of multimedia traffic and improve the performance of the low priority traffic at the same time. The system model separates the transmission of high priority traffic from the transmission of lower priority traffic and introduces the implementation of intra-ONU scheduling algorithms for lower traffic class transmission. Numerical results show a slight degradation of transmission characteristics for high priority traffic but on the other side, significant improvement of the lower priority traffic transmission parameters has been detected.

Silicon photonic waveguides for different wavelength regions

In this paper, we present our work on three silicon waveguide structures that are suitable for three different wavelength regions: near-, mid- and far-infrared. Design rules for standard rib SOI waveguides are given. Both single mode and polarization independence in these waveguides are discussed. A hollow-core waveguide suitable for gas-sensing applications in the mid-infrared wavelength region is also analysed. Finally, fabrication and experimental results for free standing waveguides, which may find application in the mid- and perhaps far-infrared wavelength regions, are presented.

Design Rules for Single-Mode and Polarization-Independent Silicon-on-Insulator Rib Waveguides Using Stress Engineering

There is a trend towards miniaturization of silicon photonic circuits due to superior performance and small cost. Design rules that must be imposed on the geometry of optical waveguides to make them behave as polarization-independent and single-mode devices are well known for waveguides with relatively large cross sections and for some small cross-sectional rib waveguides with vertical sidewalls and an air top cladding. The influence of the top oxide cover on waveguide birefringence was analyzed recently, but only for relatively large cross-sectional waveguides. This paper reports simulations for both single-mode and polarization-independent behavior for small cross-sectional waveguides with variable rib width, etch depth, top oxide cover thickness, and side-wall angle. The results show that the stress-induced effects must be taken into account to satisfy both requirements. Design rules to maintain birefringence-free operation and to satisfy single-mode behavior for small rib silicon-on-insulator (SOI) waveguides are presented.

The influence of nonstationary carrier transport on the bandwidth of p-i-n photodiode

The influence of nonstationary carrier transport on the bandwidth and the bandwidth quantum efficiency product of p-i-n photodiodes is analyzed using the complete phenomenological model for two-valley semiconductors. The analysis has been made for various submicron and micron dimensions, for different bias voltages and for several energies of incident pulse excitation, including the variation of the active area of the p-in photodiode. The analysis shows that, as the thickness of the absorption layer varies, the bandwidth could have more than one maximum, especially for smaller bias voltages. The optimal thickness of the absorption layer versus bias voltage and device area is determined, providing maximal bandwidth and maximal bandwidth-quantum efficiency product.

Analysis of blocking probability in optical burst switched networks

In this article, we study the blocking probability in a wavelength division multiplexing (WDM) based asynchronous bufferless optical burst switched (OBS) network, equipped with a bank of wavelength converters. Our analysis encloses two wavelength reservation schemes JIT (just-in-time) and JET (just-enough-time), and two-class data rate. The contribution of our work includes: (i) derivation of an accurate model for blocking probability of lower priority bursts in case of a non-preempted model; (ii) provision of the analytical model for blocking probability calculation in the OBS network, which includes these variables: two signaling schemes, partial wavelength conversion, two-class data, traffic intensity, cross-connect speed, number of wavelengths in WDM fiber, number of fibers in the node, number of wavelength converters, and number of nodes in the path; (iii) simulation results, which show that partial wavelength conversion provide quite satisfactory quality of service. We compare performance in a single OBS node, under various sets of parameter values. The OBS network shows great flexibility in terms of used multiclass data, and there is no dependence on the used higher layer protocol.

Nonlinear pulse response of p-i-n photodiode caused by the change of the bias voltage

An analytical expression is derived for nonlinear response of a p-i-n photodiode, commonly used in optical communications. Nonlinearity is caused only by the change of bias voltage, in case of pulse light excitation. The response time increases slowly with increasing the incident pulse power as a result of this nonlinearity. It is assumed in calculations that the optical excitation is not so strong to cause space charge redistribution.

Resonant cavity-enhanced Schottky photodiode - modelling and analysis

The theoretical analysis of the linear pulse responses of homostructure GaAs conventional and resonant cavity-enhanced (RCE) Schottky photodiodes is presented in this paper. The results have been obtained by numerical simulation of the complete phenomenological model for a two-valley semiconductor. Besides the drift, as the dominant mechanism of the transport, the model takes into account the diffusion, the influence of the electric field due to the spatial and temporal redistribution of the photogenerated carriers within the absorption layer, the influence of the parasitic time constant and the electron intervalley transfer. The behaviour of the bandwidths and bandwidth-quantum efficiency products when the active area, the width of the absorption layer and the reverse bias voltage change has been investigated. It is shown that conventional and RCE Schottky photodiodes with exactly the same operating parameters have practically identical frequency responses, i.e. bandwidths. For certain thicknesses of the absorption layer the bandwidth-quantum efficiency products have been increased more than fivefold. In comparison with the RCE P-i-N photodetectors having the same operating parameters, the RCE Schottky photodiodes exhibited approximately twofold increased bandwidths.

Novel wavelength and bandwidth allocation algorithms for WDM EPON with QoS support

Ethernet passive optical networks (EPONs) have been considered as the one of the most promising candidates for next-generation access networks. However, the EPON architecture although cost effective is bandwidth limited and quality of service (QoS) support is still a major concern. In this paper, we propose a cost-efficient wavelength division multiplexing (WDM) EPON architecture. We present two wavelength and bandwidth allocation algorithms with full QoS support to fulfill all requirements of new application and services in a converged triple play network. We analyze and compare the presented models and algorithms in terms of delay, jitter, queue occupancy, throughput and overall system performance. We conduct detailed simulation experiments to study the performance and validate the effectiveness of the proposed architecture and algorithms.

A Model for the Current–Voltage Characteristics of ITO/PEDOT:PSS/MEH-PPV/Al Photodetectors

We have developed a model of current-voltage (I-V) characteristic for an ITO/PEDOT:PSS/MEH-PPV/Al photodetector. The model is based on the solution of the continuity and drift-diffusion equation for hole polarons. Detailed analysis of the generation process is carried out through the investigation of the internal quantum efficiency (QE) dependence on incident photon flux density, incident light wavelength, and applied electric field. An excellent agreement between the simulated and measured I-V characteristics has been achieved in the maximum external QE wavelength range of the photodetector for a wide range of bias voltages from 0 to -8 V.

Highly flexible and efficient model for QoS provisioning in WDM EPON

The recent development of new applications and services, primarily multimedia applications, has driven the need for higher bandwidth and a faster access network, but these cannot be fully realized with the conventional single-channel Ethernet passive optical network (EPON). In such circumstances, the realization of WDM EPONs is the best solution for the implementation of converged triple-play networks. In this paper we present a novel algorithm dynamic wavelength priority bandwidth allocation with traffic class hopping for wavelength and bandwidth allocation with quality of service (QoS) support that incorporates both offline and modified online scheduling. In order to implement QoS support, we present an approach in which wavelength assignment takes place per service class and not per optical network unit, as suggested by the common approach in literature. The presented algorithm can guarantee both the priority and fairness of the differentiated traffic classes. Apart from the theoretical analysis, we studied and evaluated the performance of the presented model through detailed simulation experiments. An original network model is developed in MATLAB and incorporates all key parameters of the real network environment, such as queuing, transmission and packet processing delay, round-trip time, and framing overhead. The simulation results confirm the excellent performance of the presented model in terms of average packet delay, jitter, and packet loss.