Band 35, Heft 4

Dependence of chirp parameter of a coupled double quantum well electroabsorption modulator at wavelength 1.55 µm on the structural parameters such as wells widths and strain of wells is studied. For this purpose, we calculate the absorption of structure under applied electric fields and then solve the Kramers-Kronig relation to obtain field-induced refractive index changes. Results show that the chirp parameter is strongly dependent on the first well width and strain variation. The wider well with the compressive strain results in reduction of chirp parameter. The second well parameters effect is weaker than that of the first well. Results show that by proper design of absorption region, all negative chirp can be achieved.

Based on the simple power series formulation of fundamental mode developed by Chebyshev formalism in the low V region, we prescribe analytical expression for effective core area of graded index fiber. Taking step and parabolic index fibers as examples, we estimate the effective core areas as well as effective refractive index for different normalized frequencies (V number) having low values. We also show that our estimations match excellently with the available exact results. The concerned predictions by our method require little computation. Thus, this simple but accurate formalism will be user friendly for the system engineers.

We study dynamics in an opto-electronic delayed feedback two-section semiconductor laser. We predict theoretically that the system can result in bistability and bifurcation. We analyze numerically the route to chaos from stability to bifurcation by varying the delayed time, feedback strength and two in-currents. The system displays the four distinct types or modes of stable, periodic pulsed or self-pulsing, undamped oscillating or beating, and chaos. The frequency and intensity varying with the delayed time in the self-pulsation regions are discussed detailedly to find that the pulsing frequency is reduced with the long delayed time while the pulsing intensity is added. And the chaotic pulsing frequency is increased with the large in-current J a . The laser relaxation oscillation frequency is decreased with the large in-current J b . One in-current characterize dynamics in the laser to conduce to stable, periodic pulsed, beating and chaotic states by altering its values. The other in-current characterize dynamics in the chaotic laser to be controlled to a stable state after a road to quasi-period by adding the values.

Multicast routing based on network coding can save large wavelength channels with high network coding operation costs for the all-optical WDM network. An optical multicast routing algorithm based on minimum network coding cells to reach the multicast max-flow is proposed in the paper. The algorithm selects path in the K shortest paths from source to each destination which meets the two criteria. One is to select paths making the least probability of dropping multicast max-flow. The other is to make the path lowest potential path coding cells in the K shortest paths. We investigate that the previously proposed multicast algorithms based on network coding choose the shortest paths or link-disjoint highest shared links to construct network coding sub-graph which may result in the large coding operation cost and decrease the possibility of getting the maximal multicast flow. The simulation results show that the proposed algorithm can effectively reduce the network coding cells and improve the possibility of achieving the multicast max-flow by using our designed two path selection criteria. In addition, the proposed multicast algorithm deteriorates a very limited multicast link costs which is very close to the lowest link costs. So, the proposed algorithm can get the cost-effective multicast routing for the optical networks.

In this paper we propose to use an iterative algorithm for optimizing the fixed-alternate shortest path routing in the dynamic routing and wavelength assignment (RWA) problem in wavelength routing optical networks. The algorithm performance is compared, in terms of blocking probability, with the Dijkstra and Yen traditional algorithms, as well as with the recently proposed best among the shortest routes (BSR) algorithm. The results suggest that it is feasible to choose an appropriate set of routes for each pair of nodes (source, destination), among the shortest paths and efficiently balance the network load. For all studied scenarios, the proposed heuristic achieved superior performance.

Due to various desirable features of optical code division multiple access (OCDMA), it is believed this technique once developed and commercially available will be an integral part of optical access networks. Optical CDMA system suffers from a problem called multiple access interference (MAI) which limits the number of active users, it occurs when number of active users share the same carriers. The aim of this paper is to review successive interference cancellation (SIC) scheme based on optical CDMA system. The paper also reviews the system performance in presence of shot noise, thermal noise, and phase–induced intensity noise (PIIN). A comprehensive review on the mathematical model of SIC scheme using direct detection (DS) and spectral amplitude coding (SAC) were presented in this article.

In this work, simulative investigation to evaluate the performance of OFDM-RoF transmission links using ODSB and OSSB modulation schemes at high transmission rate is reported. Further, the results have been reported by compensating the degradations introduced by fiber dispersion using DC fiber for the proposed SSB-OFDM-RoF transmission links and a comparison is presented for evaluating the performance of such systems with and without DC fiber. Our result shows that the OSSB performs better than ODSB modulation scheme as the later severely suffered with fading problems due to fiber dispersion. In case of OSSB with DC fiber dispersion compensation technique, an improvement in SNR ratio and total power received is achieved in comparison to OSSB without DC fiber.

WDM/TDM (wavelength-division multiplexing/time-division multiplexing) PON (passive optical network) appears to be an attractive solution for the next generation optical access networks. Dynamic bandwidth allocation (DBA) plays a crucial role in efficiently and fairly allocating the bandwidth among all users in WDM/TDM PON. In this paper, two dynamic bandwidth allocation schemes (DBA1 and DBA2) are proposed to eliminate the idle time of polling cycles (i.e. polling interval), improve bandwidth utilization and make full use of bandwidth resources. The two DBA schemes adjust the time slot of sending request information and make fair scheduling among users to achieve the effective utilization of polling interval in WDM/TDM PON. The simulation and theoretical analyses verify that the proposed schemes outperform the conventional DBA scheme. We also make comparisons between the two schemes in terms of bandwidth utilization and average packet delay to further demonstrate the effectiveness of the scheme of DBA2.

In this paper, we investigate the performance of a Free Space Optic (FSO) link considering the impairments caused by the presence of various weather conditions such as very clear air, drizzle, haze, fog, etc., and turbulence in the atmosphere. Analytic expression for the outage probability is derived using the gamma-gamma distribution for turbulence and accounting the effect of weather conditions using the Beer-Lambert's law. The effect of receiver diversity schemes using aperture averaging and array receivers on the outage probability is studied and compared. As the aperture diameter is increased, the outage probability decreases irrespective of the turbulence strength (weak, moderate and strong) and weather conditions. Similar effects are observed when the number of direct detection receivers in the array are increased. However, it is seen that as the desired level of performance in terms of the outage probability decreases, array receiver becomes the preferred choice as compared to the receiver with aperture averaging.

Complementing wireless radio networks with free-space optics (FSO) achieves high data rates by modulating radio subcarriers over an optical carrier without expensive optical fiber cabling, enabling a pervasive platform for reaching underserved areas. In this paper, we review the main features of FSO for terrestrial and inter-satellite communications. Simulations of 1 Gbps data transmission through FSO links in both terrestrial and inter-satellite communications have been investigated to highlight potential atmospheric challenges in FSO.

The multicanonical method is applied to the calculation of the symbol error ratio (SER) as a function of the optical signal to noise ratio (OSNR) at the receiver for a polarization multiplexed quadrature phase shift keying (PM-QPSK) wavelength division multiplexed (WDM) system. We improve upon previous calculations by including polarization mode dispersion (PMD) and subsequently verifying the numerical accuracy of our calculations. Our numerical studies demonstrate that acceptable accuracy can be achieved even when advancing the polarization through the fiber with relatively large propagation step lengths.

We have studied bidirectional lump Raman amplification (LRA) for upgrading the existing passive optical network (PON). We focus on the upgrading to TWDM-PON (or WDM/TDM-PON) systems economically. First of all, we investigate properties of a bidirectional LRA theoretically considering the co-use of 10 G-EPON and TWDM-PON. Then, we investigate them experimentally using a dispersion-shift fiber (DSF) and a high-nonlinear fiber (HNLF). Finally, we made fundamental bit error rate (BER) experiments to confirm the feasibility of the co-use method.

Performances of QoS in Gigabit Ethernet passive optical network (GEPON) upward service is the most critical factor for practical application. This article proposes a novel of dual-clocking algorithm basing on studying in the existing dynamic bandwidth. The improved algorithm both guarantees EF high priority service and supports burst BE data traffic, in the meanwhile conspicuously enhances GEPON network efficiency. The article has confirmed the lgorithm feasibility and the improved properties through the simulation.