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In the last decade, the bit rates achieved on fiber broadband networks have increased multiple times and every new generation of passive optical network (PON) technologies must unlock more of fiber’s potential and must be backward compatible to ensure easy and iterative upgrade of operator’s networks. In this paper we present two novel dynamic wavelength (in the case of multichannel system) and bandwidth allocation models for realization of fully QoS (Quality of Service)-aware single-channel i.e. multichannel Ethernet passive optical network (EPON). The both presented models include a novel approach for inter/intra –ONU (Optical Network Unit) scheduling mechanism as well as advanced support for multimedia and business-related services. Moreover, the single channel system could be upgraded to multichannel system on per-need basis i.e., only nodes with higher traffic demands could be upgraded. The aim of this approach is twofold. On the one side we hope to avoid the implementation of additional, complex algorithms usually related to QoS support in the access segment and on the other side to develop a solution in which new and old EPON technologies are able to coexist. This approach would eliminate the need for complex migrations, complicated and time consuming procedures as well as possible service outages in the access network. We present detailed simulation experiments with the aim of conducting a study of the performances of both presented approaches and validate both of them in the terms of the future application, further service development and implementation in the next generation broadband networks (NGNs).

In this article, the impact of surface recombination on the J–V characteristics of organic solar cells (OSC) was analyzed. The investigation was carried out using the drift-diffusion model in which the surface recombination of holes and electrons on both electrodes, anode and cathode, were taken into account through boundary conditions. In order to perceive the individual influence of the surface recombination, the equilibrium thermionic concentrations for holes and electrons on contact interfaces were neglected. As the reference point of our analysis, the measured In2O5Sn/ poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/ poly(3-hexylthiophene-2,5-diyl): indene-C60 bisadduct /Al solar cell J–V curve was reproduced by our model. The surface recombination velocities (SRVs) for electrons and holes on both contacts were further varied and J–V curves were generated. For simplicity, it was assumed that diffusion current dominates at contacts. For the sake of systematization, three categories of SRV values were introduced, S —small for blocking contact, L —large for conductive contact, and M —medium for contact which is neither blocking nor conductive. The analysis was conducted for different ratios of electron and hole mobilities. It was established that in order to obtain regular J-shape J–V characteristics in OSCs, both contacts should be conductive, for both holes and electrons. This implies that the concept of contact selectivity in OSCs should be reexamined in terms of its physical description and relation to the SRVs values.

The steady state drift-diffusion model (DDM) of organic solar cells that considers the surface recombination processes for majority and minority carriers, as well as their thermionic emission on both electrodes, is presented in this paper. When the full Robin boundary conditions (BCs) and the popular finite difference method with Schaffeter-Gummel discretization (FDSG) were applied, significant instabilities were observed when surface recombination velocities (SRVs) for majority carriers on one or both electrodes were reduced. To analyze this problem and perceive the independent impacts of electron and hole contact processes, the model was simplified by assuming a constant electric field in the device and by solving the electron and hole continuity equations separately. The stability of numerical DDM solutions obtained by the FDSG and Discontinuous Galerkin (DG) methods for three different types of BCs (Dirichlet and two mixed BCs) was examined. The DG method showed a better stability when majority carriers SRVs were reduced. The current density versus voltage (J-V) characteristic calculated by the DDM with Dirichlet BCs using the DG method was compared to the measured ITO/PEDOT:PSS/P3HT:PCBM/Al solar cell J-V curve for the model validation.

The standard drift–diffusion model (DDM) was used for calculation of organic solar cells’ (OSCs) J–V characteristics under different assumption sets. One analytical (DDMA) and two numerical (DDMN1, DDMN2) solutions were obtained. In the DDMA, a Beer–Lambert absorption profile, a constant electric field and a monomolecular charge carrier recombination were used. Interference effects as well as space charge effects were included in numerical models. The monomolecular recombination mechanism was applied in the DDMN1, while the Langevin bimolecular recombination was assumed in the DDMN2. Simulated and measured J–V curves are compared for ITO/PEDOT:PSS/P3HT:PCBM/Al solar cells in the dark regime and under illumination. Experimentally obtained dark J–V curves are best reproduced by the DDMA, while the DDMN2 gives the best prediction for J–V characteristics under illumination. Additionally, it was shown that the recombination of holes and electrons can be neglected in the dark mode and a simple Shockley-like J(V) expression was derived from the DDMA. From our analysis, it can be concluded that in the dark regime the electric field in OSCs is homogeneous and electrons and holes recombine monomolecularly, although to a negligible extent. When the OSC is illuminated, the space charge effects become significant in the active layer, as well as the charge carrier recombination, which gains the bimolecular Langevine character.

In order to manage Quality of Service (QoS) and energy efficiency in the optical access network, an online Dynamic Bandwidth Allocation (DBA) algorithm with adaptive sleep cycle is presented. This DBA algorithm has the ability to allocate an additional bandwidth to the end user within a single sleep cycle whose duration changes depending on the current buffers occupancy. The purpose of this DBA algorithm is to tune the duration of the sleep cycle depending on the network load in order to provide service to the end user without violating strict QoS requests in all network operating conditions.

This paper presents a comprehensive techno-economic evaluation of the hybrid fiber-coax (HFC) networks and the multichannel Ethernet passive optical networks (EPONs) as two main next generation broadband technologies. The focus within this study is the comparison of these technologies in the case of their deployment in the rural area. Moreover, this paper analyzes how these technologies could be profitably deployed and what could be the optimal migration path for the operators in Europe.

Infrared (IR) aircraft signature has been studied out of many reasons. Someone of them are related to quality monitoring during the technological development, the other one to the possibility of tracking the aircraft in real time, the third to the formation of the appropriate standard target and so forth. Of particular importance are the procedures for tracking the small point aircraft targets at distances up to 20 km from the point of observation, because these targets may have relatively large changes in the effective radiations when compared to the immediate background. This work is related to the methodology for forming standard target aircraft taking into account: the sizes of some parts and the dimensions of the aircraft, simplified geometry which corresponds to the spatial frequency rate of the our model (Johnson’s criteria) for the representative type of the aircraft and the effective temperature difference between the total infrared signature of an aircraft, for a chosen geometry, in relation to the cold background of the clear sky (without cloudiness).

In this paper we make comparison between a well-known theoretical model of light propagation through racetrack resonator and experimentally obtained results. Observed differences are studied and some original modifications are made in the existing model so as to achieve better alignment with experiment. The influence of several geometric parameters on racetrack’s response is used for further adjustments to be performed. This procedure opens up the possibility to estimate the free spectral range and resonant wavelength for different geometric parameters and consequently to predict resonator functionality and working conditions, as well as functionality of complex photonic devices based on resonant structures.

Energy-efficiency and green communications have become dominant topics related to access network implementation, since their energy consumption is a major contributor of energy consumption within the Internet. In this paper we analyze an implementation of a new energy-efficient dynamic bandwidth algorithm in a four-channel Wavelength Division Multiplexing Ethernet Passive Optical Network (WDM EPON), in which wavelength assignments take place per service class and not per Optical Network Unit (ONU). The improved Dynamic Bandwidth Allocation (DBA) algorithm introduces independent bandwidth allocation for each wavelength, which results in efficient bandwidth management and utilization. The mathematical model for new DBA algorithm is described, as are changes to the Multi-Point Control Protocol (MPCP), necessary for its implementation. The obtained results show that the redefined DBA algorithm improves Key Performance Indicators (KPIs) and as a consequently enables delivery of enhanced services to end-users. Significant energy savings are achieved without Quality of Service (QoS) degradation, and without network or equipment architecture changes.

For evaluating quality of optical systems, different parameters are measured. One of the most important is optical transfer function. This paper shows a method for digital measurement of modulation transfer function of optical systems. Starting with analog device ODETA V, on which Moire analyzer was replaced by CMOS sensor, influence of image digitalization on a result was analyzed and methods for correction of some of artifacts was suggested.

In order to manage Quality of Service (QoS) and energy efficiency in the optical access network, an online Dynamic Bandwidth Allocation (DBA) algorithm with adaptive sleep cycle is presented. This DBA algorithm has the ability to allocate an additional bandwidth to the end user within a single sleep cycle whose duration changes depending on the current buffers occupancy. The purpose of this DBA algorithm is to tune the duration of the sleep cycle depending on the network load in order to provide service to the end user without violating strict QoS requests in all network operating conditions. In conditions of increased network load, the DBA algorithm initiates a decrease in the duration of the sleep cycle, which results in less energy savings. Under low load conditions, an increase in the duration of the sleep cycle results in significant energy savings, while QoS is still maintained.

Temperature dependence of polymer solar cell with a poly (3-hexylthiophene) : indene-C60 bisadduct (P3HT:ICBA) active layer were investigated from 15°C to 50°C to evaluate their application in standard working conditions. A standard drift-diffusion model including the temperature dependent hole mobility was used as a starting point to simulate measured I-V curves. Temperature induced solar cell parameters changes indicate that there is a significant optical interference influence in the device. In order to include these effects into the simulation, a new integral absorption coefficient parameter was introduced. Simulations of experimental data were conducted for temperature dependent mobility only, and in conjunction with integral absorption coefficient. The latter simulation results are in a better agreement with the experiment.

Following the extensive discussion from the previous section, we may now conclude that WDMtechnologies can be used to dramatically increase the throughput of EPONs. However, the probability of constructing a new WDM EPON network is very small, considering the large investments that would follow the construction of such a system.

As defined in the IEEE 802.3 standard, EPON is a PON-based network that carries data traffic encapsulated in Ethernet frames. According to the IEEE 802.3 standard [50], Ethernet MAC can operate in one of the two modes: CSMA/CD (Carrier-Sense Multiple Access with Collision Detection) mode or full-duplex mode. The standard defines two basic modes of operation for an Ethernet network

In order to transfer the various applications and services that exist in the triple-play network, it is necessary to provide resources and different levels of performance so that the end-users would get a satisfactory level of service.

Surface changes created by interaction of transversely excited atmospheric carbon dioxide (TEA CO2) laser with titanium target/implant in nitrogen and carbon dioxide gas were studied. TEA CO2 laser operated at 10.6 mu m, pulse length of 100 ns and fluence of similar to 17 J/cm(2) which was sufficient for inducing surface modifications. Induced changes depend on the gas used. In both gases the grain structure was produced (central irradiated zone) but its forms were diverse, (N-2: irregular shape; CO2: hill-like forms). Hydrodynamic features at peripheral zone, like resolidified droplets, were recorded only in CO2 gas. Elemental analysis of the titanium target surface indicated that under a nitrogen atmosphere surface nitridation occurred. In addition, irradiation in both gases was followed by appearance of plasma in front of the target. The existence of plasma indicates relatively high temperatures created above the target surface offering a sterilizing effect.

Information and communication security are one of the most global security issues. As a solution of this problem emerge quantum key distribution, technology that guarantees security by the laws of physics. But without authentication this technology is also subjected to cyberattacks. In this paper physical model for authentication of B92 protocol is proposed and explained. Based on analogy with optical chaotic systems this model gives advanced security in comparison to so far proposed systems.

Achieving energy savings in Ethernet passive optical networks (EPONs) becomes key factor for further development of optical access networks since energy usage increases rapidly. In recent years various energy-saving technics have been proposed among which enabling optical network units (ONUs) sleep time has been recognized as very promising approach for achieving energy savings in green EPONs. However, introduction of additional mechanisms can jeopardize the quality of service (QoS) performance of the network and as a result limit the deployment of green EPONs. In this work we suggest modification of multi-point control protocol (MPCP) in order to make communication between OLT and ONUs more efficient and to achieve energy efficiency and high-level of QoS performances in the same time. In order to evaluate our research, we also present simulation results of Green WDM EPON in the form of additional packet delay induced by packets buffering and the achieved service bandwidth. Obtained results confirm that putting ONU unit in energy efficient operation mode does not degrade guaranteed QoS.

In order to obtain the energy saving WDM EPON it is necessary to reduce an ONU’s electrical power consumption to the lower level and it is very important to achieve this without any compromising the implemented QoS. In this paper we present energy efficient WDM EPON model which is based on WDM EPON-FWPBA model and which supports QoS implementation. The simulations show that it is possible to save at least 3MWh per year in one WDM EPON with 64 ONUs (users).

Quantum key distribution (QKD) is not secure without an authentication protocol running together. The aim of the authentication protocol is to guarantees the identity of legitimate users, avoiding the man-in-the-middle attack. An authentication protocol requires an initially shared secret and it can be realized by software or by a physical system. In the first case a pseudo-random number generator (PRNG) is used while in the second case synchronized optical chaotic systems can be employed. In this direction, the present work considers both cases. Firstly, we show how to implement an authenticated polarization-based B92 QKD protocol using a PRNG. Its security is analyzed taking into account the number of bits of the pre-shared secret. Following, we describe a chaos-based authenticated B92 QKD protocol: We consider a chaotic system whose output is a light polarization state that changes chaotically and the synchronization of two of such systems. The Stokes’ parameter S1 of the output field is used to obtain a pseudo-random bit sequence that is used to implement the authentication. We emphasize functional limits for these two implementations.

This paper deals with a relatively new SPICE model of a P-i-N photodiode. The model includes a change of velocities of electrons and holes, due to the voltage drop on the edges of the photodiode, which depends on the time form of input excitation. We have derived the model of the P-i-N photodiode for digital input excitation i.e. for Heaviside’s square wave time excitation. The model is incorporated in SPICE program and simulated with it. The model and the limitations of the model itself are observed. The output results are compared with the similar ones. It is suggested when it is practical to use the model, and determined the photodiode working domain regime when the model gives accurate results.

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.

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.

In this paper we investigate charge carrier recombination processes in polymer based photodetector ITO/PEDOT:PSS/MEH-PPV/Al. The major carriers are the hole polarons created by the photoexcitation in the active MEH-PPV film. The model used in this paper is based on the continuity equation and drift-diffusion equation for hole polarons. We assume the Poole-Frenkel expression for field dependence of the hole polaron mobility. The internal quantum efficiency dependence on incident photon flux density, incident light wavelength and applied electric field is included in the model. The simulated photocurrent density spectra for two different, assumed, recombination mechanisms, linear (monomolecular) and square (bimolecular) is compared with our experimental results. The bimolecular recombination mechanism applied in our model is assumed to be of Langevin type. The agreement between the measured and the calculated data unambiguously indicate that the hole polaron recombination mechanism in the MEH-PPV film is bimolecular with bimolecular rate constant depending on the external electric field. For the established recombination mechanism the theoretical prediction of the photocurrent density spectra shows excellent agreement with the measured spectra in wide range of inverse bias voltages (from 0 to -8 V).

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.

Significant changes in quantum well laser performances when current leakage is not neglected are reported. Leakage effect is included extending three-level rate equations. Derived SPICE model is used to optimize and improve the most important parameters of single quantum well lasers: threshold current, cutoff frequency, and turn-on delay time. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 479–483, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23121

In this paper we investigate the most popular silicon waveguide structures in the form of a silicon-on-insulator (SOI) rib waveguide. Single mode and birefringence free conditions in these relatively small waveguides are discussed and the influence of the top oxide cladding stress is analyzed. Field profiles for a wide range of waveguide cross section shapes and dimensions are systematically considered. Design guidelines for this type of SOI waveguides are presented.

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.

An equivalent electric circuit of a P-i-N photodiode, for the case of the pulse-light excitation, is derived and incorporated using SPICE. We consider only nonlinearity, which is the result of the change of the photodiode's reverse-bias voltage. We compare our SPICE model with a previously published analytical model. The results obtained prove the superiority of the derived model, which has potential application in comprehensive OEIC modeling. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 468–471, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20174

A new advanced model of the single quantum well laser (SQWL), based on tree-level rate equations, was developed from SPICE simulations of carrier dynamics emphasizing carrier leakage effect in SQWLs are presented. Different frequency responses are obviously apparent.

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.

High-power illumination of a p-i-n photodiode results in nonlinear operating conditions and, of course, in nonlinear electric response. This article presents an investigation and comparison of the nonlinear response of conventional and resonant cavity enhanced (RCE) p-i-n photodiodes constructed using a two-valley semiconductor (GaAs). The presented results are obtained through numerical simulation of the complete phenomenological model for a two-valley semiconductor in the submicron region for several bias voltages and several values of Dirac pulse optical powers. The nonlinear behavior is analyzed through carrier transit and response time. Nonstationary effects exist in two-valley semiconductors in the presence of adequate perturbation of the electric field in the absorption layer. The present investigation shows that the RCE p-i-n photodiode reaches the nonlinear operating regime for smaller incident optical irradiances.

This paper presents linear pulse response of a Resonant Cavity Enhanced (RCE) P-i-N fotodiode. The RCE P-i-N photodiode designed for high-speed aplication is analysed for various submicron thicknesses of absorption layer, bias voltages, active areas and incident pulse optical excitations. The results are obtained by numerical simulation of the complete phenomenological model for two valley semiconductor. Great enhancement of the quantum efficiency and the product bandwidth-quantum efficiency, is obvious from obtained results for this photodiode type.

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.

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.

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.

International audience; This paper addresses WDM optical packet rings which present a single control channel and multiple data chan- nels. These rings are intended as transport networks in metro areas, i.e. are considered as replacement for the traditional SONET/SDH or Ethernet rings. These networks are thus ex- pected to deliver a lossless and low latency service. In the considered transfer mode, time is slotted, traffic insertion is opportunistic and transit traffic always has priority over new traffic which ensures optical transparency. The present work assesses the impact on delay performance of the two configuration characteristics of these rings: scheduling mechanism and number of data channels. We compare two Max-Weight scheduling policies (Oldest Packet First, OPF and the originally proposed Largest Virtual Waiting Time First, LVWTF) with the commonly used, non Max-Weight, Round-Robin (RR) scheduling in order to assess the respective Fairness performances of LVWTF and RR. It is shown that unless the ring is heavily loaded, RR is as fair, or fairer than LVWTF. In the second part of the paper, we have analyzed the performance of an optical packet ring with uniform and complete traffic matrix configured with LVWTF scheduling. The mean delay performance is quantified, and shown to depend both on the number of data channels and on the number of nodes in the ring. In particular, it is shown that for a given number nodes, and a given load, the delay presents a minimum for a finite number of data channels, which shows that increasing resources (number of data channels) may indeed degrade QoS (delay).