Showing papers on "Optical Transport Network published in 1996"

PHASAR-based WDM-devices: Principles, design and applications

Abstract: Wavelength multiplexers, demultiplexers and routers based on optical phased arrays play a key role in multiwavelength telecommunication links and networks. In this paper, a detailed description of phased-array operation and design is presented and an overview is given of the most important applications.

Optical networking update

Abstract: This paper presents an inventory of the current state and future prospects for networks in which signal paths between end user nodes remain entirely in optical form without intervening electronic conversions. The emphasis is on wavelength-division multiplexing (WDM). The applications and system aspects are stressed relative to details of the supporting technologies. The case to be made for optical networks as the basis of an entire possible future generation of networking is examined, after which the various architectural choices are discussed. Next, the limits on what can be achieved, mostly arising from limitations within the available technology, are treated. After a review of the history of all-optical networking, the paper concludes with speculations about where the applications, the technology and the architectural character of these systems will be going in the years ahead.

Bidirectional WDM optical communication systems with bidirectional optical amplifiers

Abstract: The present invention provides a bidirectional WDM optical communication system with bidirectional optical amplifiers for optically amplifying two counter-propagating WDM optical signals. The bidirectional system includes two sets of optical transmitters for respectively creating a set of west-east optical channels and a set of counter-propagating east-west optical channels. The respective channel sets are multiplexed by optical combiners and output to an optical transmission path. A bidirectional optical amplifier positioned in the optical transmission path amplifies the west-east and east-west WDM signals. In an exemplary embodiment, the amplifier includes at least two optical circulators with at least first, second, and third circulating ports. A gain block interconnects the circulators for optically amplifying the WDM signals. Bragg gratings configured to reflect either the west-east or the east-west channel band are positioned in optical paths which optically communicate with the optical circulators. The bidirectional WDM optical system further includes two receiving systems for demultiplexing the WDM signals and routing the individual optical channels to their respective receivers.

Advanced optical fiber communications network

Abstract: An advanced optical fiber communications network comprises a multimode optical fiber connection (one fiber or two) from a central office to an intelligent interface device in the subscriber's premises The central office includes at least a narrowband switch and a broadband switch The narrowband switch provides voice grade telephone service routing The broadband switch provides routing for video services and may comprise an ATM switch, an optical switch or the like The intelligent interface device provides a connection to the optical fiber and performs two-way wavelength division multiplexing and demultiplexing as well as any necessary signal format conversions The network has media access control functionality and utilizes a dynamic media access control procedure The optical fiber loop to the subscriber's premises has the capacity to carry at least three different wavelengths Bandwidth on the optical fiber loop is dynamically allocated to individual services on demand, and the allocation of bandwidth includes wavelength selection as well as bit rate allocation

Distributed network control for wavelength routed optical networks

Abstract: This paper describes an architecture for adding an underlying wavelength-routed optical layer to a standard ATM network. The optical layer provides reconfigurable lightpaths that serve as links between electronic ATM switches. A lightpath is carried on a particular wavelength and path in the underlying optical wavelength-routed network. This work focuses on the mechanisms for controlling the optical layer. Distributed control protocols are provided for setting up and taking down lightpaths reliably and for updating the topology of the network, including the lightpaths. These protocols allow lightpath originators to obtain resources with high probability by minimizing reservation conflicts, allow lightpaths to stay up even if controllers along the path in the network fail, ensure that controllers in the network have a consistent view of the state of each lightpath, and ensure that all resources taken up by a lightpath are released once the lightpath is taken down.

A modular optical cross-connect architecture with optical wavelenght switching

Abstract: An optical cross-connect node architecture interfaces plural optical fiber input and output links, each link containing plural wavelength channels. In one embodiment, the input links are connected to a single optical coupler, or alternatively, to an associated one of plural optical couplers. Pairs of tunable optical filters and optical wavelength converters are each connected to an output port of the optical coupler, or to each of the plural optical couplers, and perform wavelength channel routing and switching in the wavelength domain, i.e., without the need for any optical space switch. In other embodiments, an additional input wavelength converter is connected to each input fiber link to convert the plural wavelength channels on each link to different, non-interferring wavelengths. This prevents wavelength contention in the optical coupler to which the input wavelength converters are connected. New fiber links may be added in modular fashion without significant impact on the pre-existing optical cross-connect structure. Similarly, new wavelength channels may also be multiplexed onto existing fibers to provide wavelength modularity without having to reconfigure the node.

Fault detection for all-optical add-drop multiplexer

Abstract: A fault detecting apparatus and method for a network node of an optical transmission system receives a wavelength division multiplexed (WDM) optical signal which includes a group of optical channels. The network node includes an optical demultiplexer, optical switch, optical multiplexer, and an optical channel add/drop device. Supervisory optical signals having a different wavelength than the wavelengths of the group of optical channels are generated and spliced with each optical channel by the optical demultiplexer. The supervisory channel optical power is tapped off at various points in the network node, such as the output optical channels of the demultiplexer, dropped optical channel outputs, output optical channels from the optical switch, and the output WDM optical signal of the multiplexer. The supervisory channels are monitored by a wavemeter for bypass lightpaths and dropped lightpaths. Added optical channels are monitored by monitoring a portion of the signal power in the added lightpath of the added optical channel. If the wavemeter detects the absence of the supervisory signal, or the portion of the added optical channel, this indicates a fault condition and the network control is notified to effect correction of the fault.

Semiconductor optical space switches

Abstract: This paper reviews the various optical space switch structures on III-V semiconductor material. Their characteristics are discussed in the context of optical transport and switching network applications exploiting wavelength division multiplexing.

Results from the COST 239 project. Ultra-High Capacity Optical Transmission Networks

Abstract: The objective of COST 239 (Ultra-High Capacity Optical Transmission Networks) is to evaluate the feasibility of an optical overlay network interconnecting major cities within Europe. This European Optical Network employs wavelength routing to provide the required interconnection between network nodes. The study has a number of key activities and achievements relating to traffic modelling, transmission, network topologies and dimensioning, and protection strategies. In this paper the emphasis is on network rather than transmission aspects.

WDM Optical communication systems with remodulators and remodulating channel selectors

Abstract: The present invention provides a WDM optical communication system with remodulators at the transmission input and remodulating channel selectors adjacent the optical receivers, providing complete control over the interfaces with optical transmission equipment. In an exemplary embodiment, the WDM system includes optical transmitters which input transmitted optical signals into optical remodulators. The optical remodulators place the information from each of the transmitted signals onto separate optical channels in the WDM system channel plan. The optical channels are multiplexed onto an optical waveguide. At the receive end, remodulating channel selectors each receive a portion of the WDM optical signal, select a particular optical channel, and place the information from the selected channel onto a newly-generated optical signal. This newly-generated optical signal is output to a receiver or to a further WDM optical system.

Method and system for optical restoration tributary switching in a fiber network

Abstract: A method and system for restoration of a fiber communication network through optical tributary switching. Multi-port optical cross-switches switch traffic at the tributary side of lightwave terminal equipment in the event of a network failure. Optical tributary switching is implemented in a variety of all-optical core network architectures including separate disjoint path, link-based mesh, and path-based mesh configurations. Network resiliency is enhanced without introducing loss over a high-speed fiber line or trunk.

Method and apparatus for signal routing in an optical network and an ATM system

Abstract: A method and apparatus for optical signal routing in an optical network that includes one or more optical fibers to carry multiplexed signals. Each optical fiber may include a plurality of optical carriers with each optical carrier operating at a different wavelength. The optical network includes an optical network routing apparatus to receive the multiplexed signals from the optical fiber, to categorize the multiplexed signals as local signals or as non-local signals, to drop the local signals to a local switch, and to transmit the non-local signals to the optical fiber for further routing in the optical network. Advantageously, the transport of multiplexed signals on optical carriers of different wavelengths on a single optical fiber multiples by the number of optical carriers the bandwidth capacity of the optical fiber. Further, the optical network routing apparatus routes signals through the optical network, routes signals to a local switch associated with the optical network, and/or adds signals from the local switch to the optical network. The optical network routing apparatus includes an optical wavelength division demultiplexor to demultiplex multiplexed signals into signals based on wavelength. A type check categorizes the signals as local signals or as non-local signals. The type check transmits the local signals to a local switch based on signal type and/or wavelength. The type check also transmits the non-local signals to an optical wavelength division multiplexor, which multiplexes the non-local signals for further routing through the optical network.

All-optical wavelength conversion in optical multicarrier networks

Abstract: The authors analyze the use of all optical wavelength conversion in the optical layer of a high-capacity transport network and compare different technological solutions. The analysis is based on the evaluation of the transmission performance of a generic signal path through the network. At least two technologies have been discovered allowing the realization of all-optical wavelength converters suitable for use in the considered application, providing high performance. In particular, for networks covering long distances, wavelength conversion based on four-wave-mixing in semiconductor amplifiers seems to be a very interesting solution.

Operation and maintenance for an all-optical transport network

Abstract: For the enhancement of the existing electrical transport network a new one based on optical frequency division multiplexing (or wavelength division multiplexing) will be added to the existing one. This article focuses on the system/network supervision and operation and maintenance, which are of great importance for the success of the optical transport network. For a better understanding of these topics, it is necessary to derive a layered network model for the optical transport network and to make a workable definition of the term "network transparency." The proposed operation and maintenance concept deals with the identification of its related functions, the supervision of the optical regenerators, the maintenance signals required for failure localization, and the difficulty of defining a suitable mechanism for performance monitoring in transparent networks. Appropriate realization aspects are discussed too. Possible solutions for failure detectors are described. For transferring the individual maintenance signals between the associated network elements, a communication channel with a suitable structure is proposed.

Photonic transport network OAM technologies

Abstract: The optical path concept was proposed to realize ubiquitous B-ISDN. It can make quantum leaps in both transmission capacity and cross-connect throughput simultaneously by exploiting WDM (wavelength division multiplexing) transmission and the wavelength routing capabilities of paths. Since the optical path is a new concept, new operation and management (OAM) systems and related technologies need to be developed before it can be fully utilized. This article discusses some of the key OAM-related issues and identifies the technical points necessary for future developments. The issues include optical path realization technologies, optical path accommodation design problems, a newly proposed optical transport network layer architecture, and the optical transport module for the network node interface.

2/sup n/ prime-sequence codes and coding architecture for optical code-division multiple-access

Abstract: Recent study shows that optical code-division multiple-access (CDMA) networks cannot be evaluated or designed by only considering the performance (i.e., correlation properties) of the optical pseudo-orthogonal codes selected. The structures of optical encoders and decoders are another important factors to consider and are needed to coordinate with the selected optical codes as much as possible. A special family of 2/sup n/ codes, so-called 2/sup n/ prime-sequence codes, is constructed. A general theorem on the cardinality of the new codes is provided. The properties and performance of the codes are also studied. Since these codes pose the algebraic properties of both prime-sequence and 2/sup n/ codes, new optical encoding and decoding structures are designed to optimize the system parameters (e.g., power budget and cost) of these optical CDMA networks. This new configuration is particularly attractive for ultrafast optical processing and waveguide implementation for tile future high-capacity, low-loss, all-optical CDMA networks.

OA&M framework for multiwavelength photonic transport networks

Abstract: Photonic networks based on wavelength division multiplexing (WDM) and optical path technologies are expected to realize flexible, transparent, and cost-effective transport networks with a large transmission capacity. This paper explores the design framework of photonic transport networks taking into consideration the operation administration and maintenance (OA&M) functions required for the successful introduction of WDM systems based on the optical path concept. From the view point of network maintenance, clear distinction is made between the optical path layer and the optical section layer to facilitate accurate and smooth failure localization. The digital multiplexing span between physical multiplexing interfaces at the end-to-end digital nodes should have the same maintenance span as the corresponding optical path. We argue that cooperative maintenance by OA&M functions at both the digital and optical layers can be a practical way of network supervision. A supervisory (SV) signal transfer method and a configuration that is suitable for the terrestrial trunk network are also indicated. As an example, a practical SV system design methodology and an actual procedure developed for a single channel optical transmission system based on optical in-line amplifiers are introduced. Furthermore, application of the developed SV system and network restoration schemes is discussed for future WDM-based photonic networks. The OA&M aspects introduced will be valuable for creating future photonic network systems.

Elementary photonic switching modules in three divisions

Abstract: In three-divisional photonic switching networks, data is interchanged among channels that are formed in space, time, and wavelength This paper presents several techniques for designing the architectures of small photonic switching modules that switch in three divisions In one technique, Marcus' (1970) classical transformation from a space-only Clos network to a time-space-time architecture is generalized to the wavelength division and extended to three divisions In another technique, Hunter's (see IEEE J Lightwave Technol, vol11, no3, p495-511, 1993) space-time transformation is also generalized and extended to three divisions It is illustrated on several classical network architectures, including the most elementary case of a three-division photonic switching module based on the Benes (1965) architecture: an eight-by-eight network in which each side has two fibers and each fiber has two wavelengths and two timeslots

The super-PON concept and its technical challenges

Abstract: This paper describes the architecture and the technical challenges for the design of a large-split and long-range Passive Optical Network (PON) intended for Fiber-To-The-Home (FTTH) deployment. The system, called Super-PON, can support a splitting factor of 1024 (or more but with a more complex and hence costly implementation) and a range of 100 km. The overall network capacity is 2.5 Gbps TDM downstream and 300 Mbps ATM-based TDMA upstream. As compared with already designed PON systems, the proposed Super-PON requires the introduction of optical amplifiers along the fiber paths. The presence of these optical amplifiers brings new technical challenges especially for burst mode amplification in the upstream direction of transmission. Analysis and potential solutions to solve these problems while allowing further capacity upgrades using WDM/VDMA techniques are described in this paper along with a discussion of network survivability issues.

Optical amplifiers transform long-distance lightwave telecommunications

Abstract: Optical amplifiers and wavelength-multiplexing technology are transforming lightwave communications by providing cost-effective upgrades that will increase immensely the transmission capacity of long-distance telecommunications networks. A new generation of undersea cable systems using fiber optical amplifiers as repeaters has been developed for transoceanic applications, yielding a capacity almost ten times larger than conventional systems using opto-electronic regenerators. Terrestrial long-haul networks will benefit significantly from amplified wavelength-multiplexed transmission systems designed to access the large inherent bandwidth in the installed fiber. Successful deployment of these advanced systems requires a thorough understanding of optical amplifiers and the optical fiber medium, as their requirements interrelate through optical bandwidth, noise, dispersion, optical nonlinearities, and their impact on signal transmission. While the first commercial WDM amplified lightwave systems are deployed for point-to-point applications, optical transparency and wavelength multiplexing will be exploited for networking leading to the higher functionality and improved cost-effectiveness expected of photonic networks.

An all-optical network architecture

Abstract: A novel photonic network, MATRIX (for multi-wavelength all-optical transparent information exchange), is proposed in this paper. The all-optical multihop network supports wavelength continuity and provides a very high network capacity. Spatial reuse of wavelengths as well as the multiplicity of fibers in optical fiber cables are exploited and enable the interconnection of N/sup 2/ network nodes with merely N wavelengths. The node structure is simple since neither tunable devices nor wavelength converters are required. Packets are routed through the network by photonic fast packet switching as well as by wavelength and experience a maximum hop number of two. Multiple optical paths between any pair of nodes provide a good network survivability.

Effect of cascaded misaligned optical (de)multiplexers on multiwavelength optical network performance

Abstract: In this paper we use computer simulation techniques to evaluate the performance degradation of a multiwavelength optical network with a cascade of 2 to 100 perfectly aligned or randomly misaligned (de)multiplexers taking into consideration laser misalignment, and laser chirp. For lightwave systems using WDM technology with 200 GHz or more channel spacing, cross talk is small enough to be neglected in this study.

Optical switching network and control method for same

Abstract: The object of the present invention is to provide an optical switching network and control method that can reduce latency required for passage of signals through switches as well as reduce the overhead of circuit connection processes and electro-optical conversion generated up to the start of transmission of optical signals. The optical switching network and control method employ a plurality of data transmitters that each include a network interface circuit that divides transmitted messages into control packets and data packets, respective transmission buffers for the storage of the control packets and data packets, respective retry buffers for the temporary shunting and storage of control packets and data packets, a queue control circuit for controlling the transmission buffers and retry buffers, an optical transmitter for electro-optical conversion of data packets and output of the result to an optical transmission path, an optical receiver for photoelectric conversion of optical signals inputted from the optical transmission path, and a reception buffer for storage of the output of the optical receiver as reception data; and an optical switching device that includes an optical switch that performs a routing process on data packets transmitted from the optical transmitter and an arbiter that performs management of line connection information, processing of control packets from the data transmitter, transmission of control signals to the queue control circuit, and switching control of the optical switch.

Large scale photonic transport network design based on optical paths

Abstract: Optical path (OP) technologies such as the WP (wavelength path) and the VWP (virtual wavelength path) will be the key to create advanced photonic transport networks The problem of assigning wavelengths to paths is NP-complete and significantly complicates the path accommodation process for a transmission facility network An OP accommodation design tool that can heuristically set-up OPs within a feasible time is needed to realize OP networks This paper demonstrates effective OP accommodation design tools applicable to large scale network design The proposed tools not only set-up OPs, but also determine the amount of network resources such as optical fibers and cross-connect system scale needed to accommodate OPs Some OP accommodation design results are demonstrated that elucidate the difference between the WP and VWP schemes in terms of required resources

Transmission limitations in the all-optical network

Abstract: All-optical networks are of considerable interest as flexible, high-capacity communication networks, but generally they do have transmission limitations due to the non-idealities of their building blocks Some transmission limitations are typical for networks, or more complicated in networks than in point-to-point links, eg crosstalk and channel power equalisation, whereas others are common to networks and point-to-point links, eg dispersion Because of the accumulation of impairments in all-optical networks, it will probably be difficult to implement networks with a large number of optical nodes and full end-to-end transparency for all connections; instead, there might be need for electrical "isolation" between different parts or levels of the optical network The optimum placement of this border between all-optical and OEO networks remains to be determined

Network architecture and management concepts for optical transport networks

Abstract: This paper proposes a layered network architecture for optical transport networks and the concept of optical path network management. First, the WDM (wavelength division multiplex) based optical path network concept and realization techniques such as the WP (wavelength path) and the VWP (virtual WP) are presented. Second, a new layered architecture for WDM based transport networks is proposed. The proposed network architecture retains maximum commonality with existing B-ISDN networks. Finally, optical transport network management functions such as configuration, performance and fault management, are discussed.

Feasibility issues of a high-speed photonic packet switching fabric based on WDM subnanosecond optical gates

Abstract: The broadcast-and-select matrix has been tested in a switching configuration at 2.5 Gbit/s. Up to 16/spl times/16 inputs/outputs and 32 buffer positions are feasible thanks to fast WDM optical gates and all optical wavelength converters.

Electrophotonic computer networks with strictly nonblocking and self-routing functions

Abstract: Three-stage optical interconnection networks for use in massively parallel processors are proposed. Wavelength-division- and space-division-multiplexing switches used in these networks are described, and free-space optics to assist in the construction of networks that are small and provide high throughput are discussed.

Optical WDM (wavelength division multiplexing) transmission system and method for configuring the same

Abstract: An optical WDM transmission system formed by integrating by using an optical WDM device at least two point-to-multipoint optical transmission systems which provide independent services by using optical signals of different wavelengths. It provides a plurality of user terminals with optical signals obtained by splitting with an optical splitter an optical signal which is wavelength multiplexed by the WDM device. The splitting numbers of optical splitters placed ahead of or behind the WDM device are set such that a loss from the center terminal to the user terminals of each optical transmission system falls within an allowed loss of each system. Since the splitting numbers of the optical system of each system can be set independently, each system can accommodate a maximum number of user terminals per center terminal within the allowed loss of the system.