Head Process Research Articles

A method of developing frequency encoded multi-bit optical data comparator using semiconductor optical amplifier

Optical data comparator is the part and parcel of arithmetic and logical unit of any optical data processor and it is working as a building block in a larger optical circuit, as an optical switch in all optical header processing and optical packet switching based all optical telecommunications system. In this article the author proposes a method of developing an all optical single bit comparator unit and subsequently extending the proposal to develop a n-bit comparator exploiting the nonlinear rotation of the state of polarization of the probe beam in semiconductor optical amplifier (SOA). Here the dataset to be compared are taken in frequency encoded/decoded form throughout the communication. The major advantages of frequency encoding over all other conventional techniques are that as the frequency of any signal is fundamental one so it can preserve its identity throughout the communication of optical signal and minimizes the probability of bit error problem. For frequency routing purpose optical add/drop multiplexer (ADM) is used which not only route the pump beams properly but also to amplify the pump beams efficiently. Switching speed of ‘MZI-SOA switch’ as well as SOA based switches are very fast with good on–off contrast ratio and as a result it is possible to obtain very fast action of optical data comparator.

All-optical router with pulse-position modulation header processing in high-speed photonic packet switching networks

In future high-speed photonic packet switching networks, it is highly desirable to carry out robust all-optical header recognition to provide high-throughput routing. The authors present a pulse-position modulation header processing (PPM-HP) scheme, offering significantly reduced routing table size and employing a single bit-wise AND operation to carry out correlation of the packet header with the entire routing table entries. The downsized routing table also offers multiple transmission modes (unicast, multicast and broadcast) in the optical layer and improves core network scalability where the number of core/edge nodes could be altered without the need for changing the number of routing table entries. The authors present modelling and simulation of the packet switching router based on PPM-HP. Noise propagation and crosstalk incurred in a multiple-hop routing scenario are investigated. The simulation results are presented and compared with the theoretical calculations.

Optical Packet Header Processing Using Time-to-Wavelength Mapping in Semiconductor Optical Amplifiers

A new approach for optical packet header processing based on a time-to-wavelength converter is proposed. The processing is composed of transferring, through an all-optical and-gate, the header data bits into the successive single optical pulses at different wavelengths. The and-gate is performed by the semiconductor optical amplifier (SOA) and makes use of either cross-polarization modulation or four-wave mixing (FWM). Both implementations are compared. In order to improve the scalability of the design and to overcome the polarization sensitivity of the FWM solution, we propose the use of a spectrum-sliced incoherent light in generating the wavelength bits. The FWM process in this specific case is studied. The 10-Gb/s demonstrations of the various elements are presented.

The Control-Plane Stability Constraint in Optical Burst Switching Networks

In this letter, we consider the performance of optical burst switching networks with electronic header processing. We find that the finite processing capacity of the electronic core-node header processors can have a significant impact on the maximum throughput and minimum burst length that can be supported. We derive necessary conditions for control-plane stability in OBS networks in terms of the physical design parameters of the system. Based on this analysis, we present a general design procedure and expressions for determining the minimum average burst length to ensure that the control-plane does not become the throughput bottleneck of the OBS system

Demonstration of 40-Gb/s Packet Routing Using All-Optical Header Processing

We show simultaneous forwarding of two optical packets through a 2times2 spatial switch at 40 Gb/s using only two ultrafast nonlinear interferometers. This demonstrates a scalable all-optical header processing architecture applicable for general network topologies and can lead to reduced size, weight, and power requirements as compared with electronic solutions. Clear open eye diagrams were observed and a packet error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> , comparable with current electronic router error rates, was measured for the entire system

Design and performance evaluation of a Programmable Packet Processing Engine (PPE) suitable for high-speed network processors units

In this paper, we present a Programmable Packet Processing Engine suitable for deep header processing in high-speed networking systems. The engine, which has been – fabricated as part of a complete network processor, consists of a typical RISC-CPU, whose register file has been modified in order to support efficient context switching, and two simple special-purpose processing units. The engine can be used in a number of network processing units (NPUs), as an alternative to the typical design practice of employing a large number of simple general purpose processors, or in any other embedded system designed to process mainly network protocols. To assess the performance of the engine, we have profiled typical networking applications and a series of experiments were carried out. Further, we have compared the performance of our processing engine to that of two widely used NPUs and show that our proposed packet-processing engine can run specific applications up to three times faster. Moreover, the engine is simpler to be fabricated, less complex in terms of hardware complexity, while it can still be very easily programmed.

Compact header processing circuit for optical DPSK packets

By means of only one SOA a compact all-optical circuit that simultaneously extracts the header information and produces a sequence of multiwavelength coloured pulses from the DPSK packets is demonstrated. Combined with an optical demultiplexer, this realises a highly scalable all-optical header processor based on time-to-wavelength conversion. Experimental results demonstrate operation on packets with eight different DPSK headers at 10 Gbit/s. The system requires low optical power, can potentially operate at high speed, is asynchronous and suitable for photonic integration in a single chip.

Exploiting time-to-wavelength conversion for all-optical label processing

We propose a novel asynchronous all-optical header processor based on time-to-wavelength conversion. It always requires only four optical functional blocks, i.e., the whole complexity does not linearly scale with the number of possible headers. The scheme is experimentally demonstrated at 10.9 Gb/s and four different headers are distinguished at four distinct outputs. The limited amount of switches (four), the low optical power operation, and the potential photonic integration of each switch in a single chip make the system highly scalable and, therefore, suitable for devising an all-optical packet switch.

Optical tunable delay lines using fiber ring with acousto-optic frequency shifters and EDFAs: I. experimental demonstration

Optical buffers are key components in optical packet switching network systems that prevent packet collision along the same virtual path and wait for header processing time. Conventional fiber loops for optical buffers present the drawback of unexpected oscillation at gain peak wavelength of the fiber loop. In this paper, an optical tunable delay line using a fiber ring with an acousto-optic frequency shifter and an erbium-doped fiber amplifier (EDFA) are demonstrated experimentally. The frequency shifter plays the role of preventing unexpected oscillation. Clear eye heights are visible in data packets through the delay line.

Architectures and Buffering for All-Optical Packet-Switched Cross-Connects

This paper considers the performance of an all-optical packet-switched cross-connect. All-optical header processing and all-optical routing are implemented in the cross-connect architectures. The main metric considered to measure the performance is the packet loss ratio for the buffering. This is influenced primarily by three factors. The first is the cross-connect architecture: feedback or feed-forward buffering, incorporating wavelength domain contention resolution. The second is the selection of the fibre delay line distribution: degenerate or non-degenerate distributions. And the third is the traffic load together with the traffic model used for the performance analysis: a Poisson distribution or a self-similar model. It is shown that the optimal implementation of a feedback buffer requires a technique such as overflow buffering as well as the superior performance of an all-optical switch in order to maintain signal quality through multiple recirculations.

A scalable explicit multicast protocol for MANETs

Group oriented multicast applications are becoming increasingly popular in mobile ad hoc networks (MANETs). Due to dynamic topology of MANETs, stateless multicast protocols are finding increased acceptance since they do not require maintenance of state information at intermediate nodes. Recently, several multicast schemes have been proposed which scale better with the number of multicast sessions than traditional multicast strategies. These schemes are also known as explicit multicast (Xcast; explicit list of destinations in the packet header) or small group multicast (SGM). In this paper, we propose a new scheme for small group multicast in MANETs named extended explicit multicast (E2M), which is implemented on top of Xcast and introduces mechanisms to make it scalable with number of group members for a given multicast session. Unlike other schemes, E2M does not make any assumptions related to network topology or node location. It is based on the novel concept of dynamic selection of Xcast forwarders (XFs) between a source and its potential destinations. The XF selection is based on group membership and the processing overhead involved in supporting the Xcast protocol at a given node. If the number of members in a given session is small, E2M behaves just like the basic Xcast scheme with no intermediate XFs. As group membership increases, nodes may dynamically decide to become an XF. This scheme, which can work with few E2M aware nodes in the network, provides transparency of stateless multicast, reduces header processing overhead, minimizes Xcast control traffic, and makes Xcast scalable with the number of group members.

Network design and cost optimization for label switched multilayer photonic IP networks

Dealing with the explosive increase in the amount of Internet traffic requires high-speed and huge capacity Internet protocol (IP) backbone networks. Existing IP backbone networks are constructed using point-to-point wavelength-division-multiplexing (WDM) transmission systems, where all the wavelengths are terminated link-by-link, so that rather expensive optical/electrical conversions are necessary at every node. In these systems, since every IP packet is routed at each intermediate node based on the header information, a header processing bottleneck will occur when the node input traffic exceeds several hundreds of gigabits per second. In order to mitigate these problems, an optical cross-connect (OXC) function that employs wavelength routing of the optical paths (OPs) will provide an effective solution. This paper proposes a network design method where electrical and photonic multiprotocol label switching (MPLS) technologies are used; the network is referred to as a photonic IP network. We first propose new algorithms that minimize the network cost in a multilayered network comprising electrical label switched paths (LSPs) and optical LSPs (optical paths that are controlled using the MPLS mechanism). The particular point of the proposed algorithms is that they include different cost minimization scenarios appropriate for the different OLSP provisioning conditions that are chosen as the first step in the design stage. The effectiveness of the proposed algorithms and the benefits of the OLSPs are quantitatively evaluated through various simulations.

All-optical header processing system based on time-to-wavelength conversion for pure DPSK packets

Presented is a novel asynchronous all-optical header processing system for pure DPSK packets based on time-to-wavelength conversion of the header information that requires only four optical functions independently of the number of headers. Experimental results at 12.5 Gbit/s demonstrate that four DPSK headers are distinguished at four distinct outputs. The system requires low optical power, is highly scalable, and allows for potentially high-speed operation and photonic integration in a single chip.

1/spl times/4 all-optical packet switch at 10 gb/s

We demonstrated a 1/spl times/4 all-optical packet switch with all-optical header processing at a header rate of 5 Gb/s and payload rate of 10 Gb/s using injection-locking in a single Fabry-Pe/spl acute/rot laser diode at each output port of the switch.

A Minimalist Approach to All-Optical Packet Switching

By retaining only the most essential packet-switching functions in the optical domain, a single Fabry Perot Laser Diode can function as an all-optical on/off switch with all-optical header processing, and an all-optical add/drop node can be used to construct an all-optical ring network.

All-optical header processing using an injection-locked Fabry-Pérot laser diode

Simultaneous all-optical header processing and control-packet switching are demonstrated by using multiwavelength injection-locking in a single Fabry–Pérot laser diode. A special two-level control packet is used to process the header of the data packet at 5 Gb/s. The entire control packet is all optically switched ON or OFF. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 342–345, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20629

Integrated optical 2 /spl times/ 2 switch for wavelength multiplexed interconnects

A highly compact integrated optical switch is proposed and demonstrated for broadband optical switching applications. Routing of 8 /spl times/ 10 Gb/s data channels is demonstrated using a low-cost 1250-Mb/s control scheme. The advantages of lossless operation, broad optical bandwidth, and nanosecond switching times are leveraged. Multichannel wavelength is exploited for reduced latency, enhanced capacity, and functionality, while retaining compatibility with existing off-the-shelf electronics and transceiver technology. The requirements for optical header processing, wavelength translation, and optical buffering are avoided. Low-penalty multiwavelength transmission is demonstrated for a highly compact sub-mm/sup 2/ amplifying 2 /spl times/ 2 switch. Pattern dependent gain and amplified spontaneous emission are minimized to facilitate 0.0-0.4 dB penalty. Mitigation techniques compatible with the architecture are deployed to reduce the penalty under adverse operating conditions. Control schemes are proposed and demonstrated to facilitate 8 /spl times/ 10 Gb/s optically switched networking.

All-optical header processing using control signals generated by direct modulation of a DFB laser

On-the-fly all-optical header processing and control signal generation were simultaneously realized using a dual-wavelength injection-locked Fabry–Pérot laser diode. The special two-level input control signal was generated by direct modulation of a distributed feedback laser. The header processing rate is 2.5 Gb/s, the payload data rate is 10 Gb/s, and the packet length is 25.6 ns. The switching ratio for the switched control signals measured spectrally was improved from 3 dB to over 20 dB by using a polarizer.

All-optical packet header processor based on cascaded SOA-MZIs

A novel scheme for all-optical packet header processing is proposed. The highly scalable photonic-integrated architecture is comprised of cascaded SOA-based Mach-Zehnder interferometers. The simulation results show its feasibility to recognise bit patterns at 10 Gbit/s and beyond. The maximum number of header bits that can be all-optically processed is dependent on the ASE noise, but the approach is still valid for all-optical label swapping networks.

High capacity all-optical networks capable of supporting bandwidth on demand

Dynamic high-speed access to optical fiber can be achieved by transmitting data at a very high bit rate in a packet-switched manner. Access nodes, which are able to process high-speed optical packets and to provide fast switching in the optical domain, are the scope of this paper. All-optical techniques for short pulse generation and transmission, dispersion compensation, data rate conversion, clock recovery and header processing are described and discussed.