Crosstalk-free Conjugate Networks for Optical Multicast Switching

High-speed photonic switching networks can switch optical signals at the rate of several terabits per second. However, they suffer from an intrinsic crosstalk problem when two optical signals cross at the same switch element. To avoid crosstalk, active connections must be node-disjoint in the switching network. In this paper, we propose a sequence of decomposition and merge operations, called conjugate transformation, performed on each switch element to tackle this problem. The network resulting from this transformation is called conjugate network. By using the numbering-schemes of networks, we prove that if the route assignments in the original network are link-disjoint, their corresponding ones in the conjugate network would be node-disjoint. Thus, traditional nonblocking switching networks can be transformed into crosstalk-free optical switches in a routine manner. Furthermore, we show that crosstalk-free multicast switches can also be obtained from existing nonblocking multicast switches via the same conjugate transformation.Comment: 10 page

Symmetric rearrangeable networks and algorithms

A class of symmetric rearrangeable nonblocking networks has been considered in this thesis. A particular focus of this thesis is on Benes networks built with 2 x 2 switching elements. Symmetric rearrangeable networks built with larger switching elements have also being considered. New applications of these networks are found in the areas of System on Chip (SoC) and Network on Chip (NoC). Deterministic routing algorithms used in NoC applications suffer low scalability and slow execution time. On the other hand, faster algorithms are blocking and thus limit throughput. This will be an acceptable trade-off for many applications where achieving ”wire speed” on the on-chip network would require extensive optimisation of the attached devices. In this thesis I designed an algorithm that has much lower blocking probabilities than other suboptimal algorithms but a much faster execution time than deterministic routing algorithms. The suboptimal method uses the looping algorithm in its outermost stages and then in the two distinct subnetworks deeper in the switch uses a fast but suboptimal path search method to find available paths. The worst case time complexity of this new routing method is O(NlogN) using a single processor, which matches the best known results reported in the literature. Disruption of the ongoing communications in this class of networks during rearrangements is an open issue. In this thesis I explored a modification of the topology of these networks which gives rise to what is termed as repackable networks. A repackable topology allows rearrangements of paths without intermittently losing connectivity by breaking the existing communication paths momentarily. The repackable network structure proposed in this thesis is efficient in its use of hardware when compared to other proposals in the literature. As most of the deterministic algorithms designed for Benes networks implement a permutation of all inputs to find the routing tags for the requested inputoutput pairs, I proposed a new algorithm that can work for partial permutations. If the network load is defined as ρ, the mean number of active inputs in a partial permutation is, m = ρN, where N is the network size. This new method is based on mapping the network stages into a set of sub-matrices and then determines the routing tags for each pair of requests by populating the cells of the sub-matrices without creating a blocking state. Overall the serial time complexity of this method is O(NlogN) and O(mlogN) where all N inputs are active and with m < N active inputs respectively. With minor modification to the serial algorithm this method can be made to work in the parallel domain. The time complexity of this routing algorithm in a parallel machine with N completely connected processors is O(log^2 N). With m active requests the time complexity goes down to (logmlogN), which is better than the O(log^2 m + logN), reported in the literature for 2^0.5((log^2 -4logN)^0.5-logN)<= ρ <= 1. I also designed multistage symmetric rearrangeable networks using larger switching elements and implement a new routing algorithm for these classes of networks. The network topology and routing algorithms presented in this thesis should allow large scale networks of modest cost, with low setup times and moderate blocking rates, to be constructed. Such switching networks will be required to meet the bandwidth requirements of future communication networks

Devices and networks for optical switching

This thesis is concerned with some aspects of the application of optics to switching and computing. Two areas are dealt with: the design of switching networks which use optical interconnects, and the development and application of the t-SEED optical logic device. The work on optical interconnects looks at the multistage interconnection network which has been proposed as a hybrid switch using both electronics and optics. It is shown that the architecture can be mapped from one dimensional to two dimensional format, so that the machine makes full use of the space available to the optics. Other mapping rules are described which allow the network to make optimum use of the optical interconnects, and the endpoint is a hybrid optical-electronic machine which should be able to outperform an all-electronic equivalent. The development of the t-SEED optical logic device is described, which is the integration of a phototransistor with a multiple quantum well optical modulator. It is found to be important to have the modulator underneath rather than on top of the transistor to avoid unwanted thyristor action. In order for the transistor to have a high gain the collector must have a low doping level, the exit window in the substrate must be etched all the way to the emitter layer, and the etch must not damage the emitter-base junction. A real optical gain of 1.6 has been obtained, which is higher than has ever been reached before but is not as high as should be possible. Improvements to the device are suggested. A new model of the Fabry-Perot cavity is introduced which helps considerably in the interpretation of experimental measurements made on the quantum well modulators. Also a method of improving the contrast of the multiple quantum well modulator by grading the well widths is proposed which may find application in long wavelength transmission modulators. Some systems which make use of the t-SEED are considered. It is shown that the t-SEED device has the right characteristics for use as a neuron element in the optical implementation of a neural network. A new image processing network for clutter removal in binary images is introduced which uses the t-SEED, and a brief performance analysis suggests that the network may be superior to an all-electronic machine

Optical Interconnections based on Microring Resonators

Projecte fet en col.laboració amb la Facoltà di Ingegneria dell’Informazione. Politecinco de TorinoThe aim of this thesis is to present and analyse optical interconnection architectures based on microring resonators. The trend of meeting large bandwidth and strict latency requirements in both global on-chip and off-chip communication face critical challenges in maintaining a sustainable performance-per-watt. Optical technologies support the immense bandwidth allowed by wavelength division multiplexed (WDM) while could offer a significant power saving switching capabilities. Microring resonators have received considerable attention as promising technologies for realizing photonic integrated circuits. Their small footprint and their capacity for processing high-bandwidth WDM data can lead these devices become the key elements for the switch nodes in next-generation telecommunication networks. This thesis firstly describes the basic principles of operation of a microring resonator defining 1x2 basic switching element (1B-SE). Then, the 2x2 basic SE (2B-SE) based on two 1B-SEs jointly controlled and the new 2x2 mirrored SE (2M-SE) are characterised as atomic building elements for interconnection architectures. The severe asymmetric behaviour presented by those SEs could limit the scalability of classical optical switching fabrics and we aim at balancing the complexity and optical signal level. In a second stage, the well-known switching theory is revised in order to classify the interconnection architectures according to their characteristics when using that SEs as building element. It is applied an exhaustive procedure to obtain the performance of classical Crossbar and Benes structures and of the newly proposed Mirroring and HBC structures. Thereafter, using as a starting point for each analysed structure the characterisation previously obtained, the scalability response of larger switching fabrics is explored. Then we define a construction rule for the new proposed architectures of which we assess the complexity in terms of used microring

Optical Interconnections based on Microring Resonators

Projecte fet en col.laboració amb la Facoltà di Ingegneria dell’Informazione. Politecinco de TorinoThe aim of this thesis is to present and analyse optical interconnection architectures based on microring resonators. The trend of meeting large bandwidth and strict latency requirements in both global on-chip and off-chip communication face critical challenges in maintaining a sustainable performance-per-watt. Optical technologies support the immense bandwidth allowed by wavelength division multiplexed (WDM) while could offer a significant power saving switching capabilities. Microring resonators have received considerable attention as promising technologies for realizing photonic integrated circuits. Their small footprint and their capacity for processing high-bandwidth WDM data can lead these devices become the key elements for the switch nodes in next-generation telecommunication networks. This thesis firstly describes the basic principles of operation of a microring resonator defining 1x2 basic switching element (1B-SE). Then, the 2x2 basic SE (2B-SE) based on two 1B-SEs jointly controlled and the new 2x2 mirrored SE (2M-SE) are characterised as atomic building elements for interconnection architectures. The severe asymmetric behaviour presented by those SEs could limit the scalability of classical optical switching fabrics and we aim at balancing the complexity and optical signal level. In a second stage, the well-known switching theory is revised in order to classify the interconnection architectures according to their characteristics when using that SEs as building element. It is applied an exhaustive procedure to obtain the performance of classical Crossbar and Benes structures and of the newly proposed Mirroring and HBC structures. Thereafter, using as a starting point for each analysed structure the characterisation previously obtained, the scalability response of larger switching fabrics is explored. Then we define a construction rule for the new proposed architectures of which we assess the complexity in terms of used microring

Efficient parallel processing with optical interconnections

With the advances in VLSI technology, it is now possible to build chips which can each contain thousands of processors. The efficiency of such chips in executing parallel algorithms heavily depends on the interconnection topology of the processors. It is not possible to build a fully interconnected network of processors with constant fan-in/fan-out using electrical interconnections. Free space optics is a remedy to this limitation. Qualities exclusive to the optical medium are its ability to be directed for propagation in free space and the property that optical channels can cross in space without any interference. In this thesis, we present an electro-optical interconnected architecture named Optical Reconfigurable Mesh (ORM). It is based on an existing optical model of computation. There are two layers in the architecture. The processing layer is a reconfigurable mesh and the deflecting layer contains optical devices to deflect light beams. ORM provides three types of communication mechanisms. The first is for arbitrary planar connections among sets of locally connected processors using the reconfigurable mesh. The second is for arbitrary connections among N of the processors using the electrical buses on the processing layer and N2 fixed passive deflecting units on the deflection layer. The third is for arbitrary connections among any of the N2 processors using the N2 mechanically reconfigurable deflectors in the deflection layer. The third type of communication mechanisms is significantly slower than the other two. Therefore, it is desirable to avoid reconfiguring this type of communication during the execution of the algorithms. Instead, the optical reconfiguration can be done before the execution of each algorithm begins. Determining a right configuration that would be suitable for the entire configuration of a task execution is studied in this thesis. The basic data movements for each of the mechanisms are studied. Finally, to show the power of ORM, we use all three types of communication mechanisms in the first O(logN) time algorithm for finding the convex hulls of all figures in an N x N binary image presented in this thesis

Space Communications: Theory and Applications. Volume 3: Information Processing and Advanced Techniques. A Bibliography, 1958 - 1963

Annotated bibliography on information processing and advanced communication techniques - theory and applications of space communication