Serial-mode optical multicast based on active vertical coupler optical crosspoint switch matrix

This paper investigates a novel optical multicast scheme without excess optical splitting loss to be realized using an active vertical coupler (AVC)-based optical switch matrix, due to the optical gain available in the AVC switch cells. Theoretical analysis and computer simulation have been carried out regarding the operational principle and switching characteristics of this scheme. Computer simulation further suggests that the amplified spontaneous emission (ASE)-limited scalability of the scheme can be as high as more than 40. Experiments using an existing 4 /spl times/ 4 switch-matrix device successfully demonstrated the predicted multicast switching operation. Measured switching characteristics and the optical signal-to-noise ratio (OSNR) values are in good agreement with simulation predictions. High switched-signal Q-factor values of 1-to-2 and 1-to-3 multicasting configurations indicate that the scale of the multicasting scheme can be further increased significantly.

The optical switch matrix is the one of the key elements in constructing optical switching systems. Many types of optical switch matrix architectures have been proposed1 to improve their characteristics and to construct devices with larger switch dimensions. However, since the substrate for fabricating the optical switch matrix is limited in size, the switching voltage of these structures was still relatively high. In addition, crosstalk characteristics degraded with increasing the number of output and input ports. The architecture wich can be obtained3 by simplifying the structure of tree-structure,2 wich we propose is one of the candidates for solving these problems. We report on the basic characteristics of this structure and some measured results from devices fabricated on LiNbO3 by indiffusion of Ti.

Packet-switching characteristics are optimized across an integrated 4 x 4 optical cross-point switch matrix based on active vertical coupler switch cells. Optical gain is demonstrated across the entire matrix with a <3-dB difference between the shortest and longest switching paths.

Large-scale optical switching matrix is the core technology of automatically switched optical network. With the significant increase of the matrix size, the study showed that the nonlinear factors, such as the correlation of the wavelength, phase and polarization between the optical switches have major impacts for the system performance. Because the full-size optical simulation is not available now, the research will be a great significance that we establish an overall model with not only considering the performance of optical switch unit, but also reflecting the structural characteristics of the network.In this paper, we calculated the transmission field of 2×2 Mach –Zehnder(MZI) silica on silicon thermo optic(TO) switch with different structure by using the finite difference beam propagation method(BPM). On the basis of optimization design, we constructed and simulated the large-scale 16×16 MZI silicon-based SiO2 Silica on silicon thermo switching matrix. The results are: In TE Mode, for Crossbar and banyan structures, insertion losses are 13.35 dB and 4.3638 dB; crosstalk losses are 27.125~29.0173 dB and 42.2318-43.7159 dB; extinction ratios are 29.57 dB and 26.79 dB respectively.

Active optical switches based on polarization-tuned guided-mode resonance filters for optical communication

At a switching node in an optical packet switching (OPS) network, packet contention occurs whenever two or more packets try to reach the same output port of the node at the same wavelength, consequently it degrades network performance. Previous works on optical packet switching flourishingly adopted optical buffering with optical fibre delay line (FDL), wavelength conversion, or deflection routing to resolve packet contention. In this paper, we focus on the optical fibre delay line approach, especially the selection of proper length of FDL under asynchronous variable length packet traffic. As the length of fibre coils equipped in a FDL optical buffering system is impossible to be reconfigured frequently, a proper length of FDL should be determined during manufacture. The motivation is to observe the impact factors on FDL optical system performance in a WDM network scenario, and provide the empirical data as supports to select the proper length of FDL in an OPS node system.

Packet contention is a major issue in optical packet switching network. To resolve contention, optical buffering approach is used using Fiber Delay Lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output-port and free FDLs. This paper proposes a selective minimum delay value algorithm (SMDV) to resolve contention for shared FDL buffering architecture in order to ensure the availability of output-port for the contended packet after coming out from FDL. Simulation result shows that proposed scheme can achieve a packet loss rate of ~ even at heavy traffic load 0.9 for 32×32 switch using 32 variable length FDL.

A folding rearrangeable nonblocking 4×4 optical matrix switch was designed and fabricated on silicon-on-insulator wafer. To compress chip size, switch elements (SEs) were interconnected by total internal reflection (TIR) mirrors instead of conventional S-bends. For obtaining smooth interfaces, potassium hydroxide anisotropic chemical etching of silicon was utilized to make the matrix switch for the first time. The device has a compact size of 20×1.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a fast response of 7.5 μs. The power consumption of each 2×2 SE and the average excess loss per mirror were 145 mW and -1.1 dB, respectively. Low path dependence of /spl plusmn/0.7 dB in total excess loss was obtained because of the symmetry of propagation paths in this novel matrix switch.

Optical Burst Switching (OBS) is a new paradigm for future all-optical networks. It has been noted that performance of an OBS node depends on the wavelength assignment algorithm that is used. In this paper we present a new class of wavelength allocation algorithms called cost-based algorithms. We note that bursts compete for more types of resources than wavelengths alone. For example if a given burst is to be allocated successfully, a Fiber Delay Line (FDL) or a wavelength converter may have to be used. It can be expected, however, that the set of available resources will be limited. If at a given time all the converters are used, then any arriving burst will have to be allocated on the same wavelength - if it is available. Similarly, the unavailability of FDLs will decrease the probability of a burst being accepted. In a cost-based algorithm, each resource is assigned a metric (or price). Channels are priced according to their suitability for a particular burst. When a control packet arrives at a core node, all the possible ways of handling the corresponding burst are found (the outgoing channel, with or without a FDL or wavelength converter), and the one with a lowest metric is chosen. To show how the performance of a cost-based algorithm compares to other algorithms we present the results of our simulations for a node with full conversion capability and a shared FDL.

Optical packet switching (OPS) is being considered as one of the switching technologies for a future optical internet. For contention resolution in an optical packet switching (OPS) system, the wavelength dimension is generally used in combination with a fibre delay line (FDL) buffer. In this study, the authors propose to reduce the number of tunable wavelength converters (TWCs) by sharing TWCs for cost-effective design of an asynchronous OPS system with a shared or an output FDL buffer. Asynchronous and variable-length packets are considered in the OPS system design. To investigate the number of TWCs needed for the OPS system, an algorithm is proposed, which searches for an available TWC and an unused internal wavelength, as well as an outgoing channel. This algorithm is applied to an OPS system with a shared or an output FDL buffer. Also, the number of internal wavelengths (i.e. the conversion range of the TWC) needed for an asynchronous OPS system is presented for cost reduction of the OPS system.

The prospects of Optical Burst Switching (OBS) as a cost-effective switching paradigm for future all-optical transport networks could greatly benefit from avoiding the use of complex and expensive all-optical wavelength converters at the network nodes. However, contention resolution is essential to achieve reasonable bandwidth utilization efficiency in OBS networks and replacing the wavelength converters by Fiber Delay Line (FDL) buffers requires huge numbers of FDLs and large space switches, thus also rendering complex network nodes. This paper proposes combining the use of a priority-based wavelength assignment and burst scheduling strategy at the ingress nodes, which minimizes the probability of contention, with the use of shared FDL buffers at the core nodes to resolve the unavoidable contentions. The objective is to design OBS networks employing only moderate numbers of simple FDL buffers while matching the performance of a network using full-range wavelength converters. Simulation results using a reference network topology show that this goal is feasible. Moreover, the FDL buffer requirements are shown to depend on the offered traffic load, the number of wavelengths per link, and the maximum burst delay at the ingress node.

In order to achieve service differentiation, especially loss differentiation, in optical burst switching (OBS) networks, we propose a dynamic fiber delay line (FDL) partitioning algorithm, which divides FDLs into several groups over a feed-forward output buffering architecture. In the proposed scheme, a plurality of traffic classes and FDL groups can be considered, and each FDL group is assigned to traffic classes, so that the target loss probabilities of classes are guaranteed. Also, the optimal number of FDLs for each FDL group by the proposed algorithm is decided in Poisson traffic environments. The extensive simulation results validate the effectiveness of the proposed dynamic FDL partitioning algorithm for the loss differentiation in OBS networks.

Optical burst switching (OBS) is a promising paradigm for the next-generation Internet. In OBS, a key problem is to schedule bursts on wavelength channels, whose bandwidth may become fragmented with the so-called void (or idle) intervals, using both fast and bandwidth efficient algorithms so as to reduce burst loss. To date, two well-known scheduling algorithms, called Horizon and LAUC-VF, have been proposed in the literature, which trade off bandwidth efficiency for fast running time and vice versa, respectively. In this paper, we propose a set of novel burst scheduling algorithms for OBS networks with and without fiber delay lines (FDLs) utilizing the techniques from computational geometry. In networks without FDLs, our proposed minimum-starting-void (Min-SV) algorithm can schedule a burst in O(logm) time, where m is the total number of void intervals, as long as there is a suitable void interval. Simulation results suggest that our algorithm achieves a loss rate which is at least as low as LAUC-VF, but can run much faster. In fact, its speed can be almost the same as Horizon (which has a much higher loss rate). In networks with FDLs, our proposed batching FDL algorithm considers a batch of FDLs to find a suitable FDL to delay a burst which would otherwise be discarded due to contention, instead of considering the FDLs one by one. The average running time of this algorithm is therefore significantly reduced from that of the existing burst scheduling algorithms. Our algorithms can also be used as algorithmic tools to speed up the scheduling time of many other void-filling scheduling algorithms.

SOI (Silicon on Insulator) based photonic devices has attracted more and more attention in the recent years. Integration of SOI optical switch matrix with isolating grooves, total internal reflection (TIR) mirrors and spot size converter (SSC) was studied. A folding re-arrangeable non-blocking 4times4 optical switch matrix and a blocking 16times16 matrix with TIR mirrors and SSC were fabricated on SOI wafer. The performances, including extinction ratio and the crosstalk, are better than before. The insertion loss and the polarization dependent loss (PDL) at 1.55mum increase slightly with longer device length, more bend and intersecting waveguides. The insertion losses decrease 2-3 dB when anti-reflection films are added in the ends of the devices. The rise and fall times of the devices are 2.1mus and 2.3mus, respectively

Optical Packet Switching (OPS) has emerged as a promising candidate for the future all-optical core network. A crucial issue in such networks is how the packet length distribution (PLD) influences the performance under different traffic scenarios. In this paper we investigate how a deterministic, empirical and exponential PLD influences the Packet Loss Rate (PLR) in an optical packet switch in the case of a Poisson arrival process and a bursty Hyperexponential arrival process. We consider optical packet switches with and without Fibre Delay Line (FDL) contention buffers. Our results show that in the case of OPS without FDL buffering and with a Hyperexponential arrival process, the empirical PLD yields the lowest PLR. However, in the case of OPS with FDL buffering, the deterministic PLD yields the lowest PLR.