Nortel Networks Corporation

Ciena Corporation

Northern Telecom Limited

Delphi Technologies IP Limited

Delphi International Operations Luxembourg S.a.r.l.

Nigel Baker

Robert Friskney

Duncan John Forbes

James St Harley

Alan Glen Solheim

Kim Byron Roberts

Richard A Habel

Maurice Stephen O'Sullivan

Robert William Spagnoletti

Ian Hardcastle

Giuseppe Bordogna

Peter D Roorda

David John Danagher

Fiona Davis

Takis Hadjifotiou

Bipin Patel

Christopher Phillips

Song Dong

Alan Frank Graves

Nigel Lawrence Bragg

Adrian Paul Sparks

Siraj Nour Elahmadi

Louisa J Perryman

Kesavamurthy Nagaraj

Ross Alexander Saunders

Paul Arthur Bullock

Douglas Fisher

Steven Martin

Martin Sykes

A method for determining a path in an optical network, implemented by one or more controllers associated with a control layer, includes receiving a path request specifying start and end points, an associated bandwidth, and a longevity parameter providing an anticipated length during which the path is required; determining a route in the optical network through a routing algorithm executed by the controller, wherein the routing algorithm utilizes the start and end points, the associated bandwidth, and the longevity parameter to determine the path; and provisioning the path through a plurality of switches along the route.

Methods and apparatus for determining a path in a communications network

Typically paths are provisioned in a network with a margin which allows for component variations and failures in the network and so on. By providing more information about the requirements of the link in a path request, it is possible to more efficiently calculate a route for the path through the network. The efficiency gain allows greater network utilization which in turn saves costs for the network service provider.

A multiplexed frame based client signal comprising a payload and a client overhead is transported between first and second client networks over a plurality of signal paths by inverse multiplexing the client signal into a plurality of lower rate signals each containing a respective payload and client overhead; attaching a carrier overhead to each said lower rate signal; transmitting the lower rate signals over the plurality of paths from the first client network to the second client network; and, at the second network, discarding the carrier overhead from each lower rate signal, and reassembling the lower rate signals so as to recover the client signal. The method enables bandwidth trading utilising virtual concatenation of synchronous optical channels, such that transparent transmission of a customers signals over any variety of intermediate networks can be achieved without requiring that the intermediate networks support virtual concatenation.

Concatenated transmission of synchronous data

A system and method for transmitting and restoring an optical signal in an optical ring is presented. The optical ring comprises a plurality of nodes, each node containing an optical cross connect switching fabric coupled to a data switch. The optical cross connect switching fabric and the data switch are coupled to a short reach side of a wavelength translation device. A long reach side of the wavelength translation device is coupled to a dense wave division multiplex (DWDM) coupler. The optical cross connect switching fabric and the data switch include a protect channel and a working channel for transporting the optical signal. The wavelength translation device receives the optical signal at a high speed rate, where the optical signal is a short reach optical signal and originates from a high speed interface on the data switch. The wavelength translation device then maps the short reach optical signal into a long reach DWDM optical signal at the high speed rate and forwards, via the DWDM coupler, the long reach optical signal to an adjacent DWDM coupler located at an adjacent node. If a link failure occurs and has not recovered, and the protect channel is not available, optical cross connect switching fabrics at adjacent nodes on each side of the failed link switch the optical signal to an alternate diverse protect port. An optical pass through of the switched optical signal between any transit nodes in the optical ring is then configured resulting in a restoration path for the working channel.

System and method for transmitting and restoring an optical signal

To provide improved protection bandwidth efficiency for a fast recovery from a fault in an optical network, a protection ring for sharing between some of the protection paths has a pre-configured route so as to overlap on a given one of the links, with other protection paths or other rings. A selector for the given link selects which of the overlapping secondary paths is allocated to the given link at any time. Thus, two types of sharing of protection paths are combined to achieve more efficient use of protection bandwidth. The link selector can be controlled locally and so can operate more rapidly. The local control, essentially independent of the switches used to set up the secondary path through the network, makes the combination easier to scale to larger, more complex networks than shared rings alone.

Constrained optical mesh protection for transmission systems

A cross-connect switch for switching optical signals, in particular, Dense Wavelength Division Multiplexed (DWDM) signals is disclosed. The switch includes a switching matrix for each of the predetermined wavelengths of the DWDM signals. The switching matrices include Micro-Electro-Mechanical (MEM) systems which have optically reflective elements, typically mirrors, arranged in rows and columns for switching an incoming optical signal travelling along a row of such elements to an output port aligned with a column of the elements. The switch has input demultiplexers to split an incoming DWDM signal into its component channel wavelengths, each of which is directed to a switching matrix where it is switched to an output port and recombined into an outgoing DWDM signal by a multiplexer before being transmitted out of the switch. A wavelength-converting switch, connected across the switching matrices, is also included for switching channels between wavelengths.

Switch for optical signals

Wave division multiplexers and demultiplexers utilizing fused fiber couplers and similar devices are expensive to implement. This is a barrier to deployment of optical networks particularly in the metro and access areas. The invention provides a cheaper design scheme to help overcome this problem. The invention provides an apparatus arranged to demultiplex a predetermined range and number of wavelengths comprising a plurality of devices each having at least one input port and two output ports, the output ports of each device having a periodic and complimentary series of minimum attenuation wavelength peaks, wherein the devices are arranged such that each demultiplexes a unique series of wavelengths, and wherein the apparatus comprises at least one device having a series of minimum attenuation wavelength peaks which do not correspond to the unique series of wavelengths the device is arranged to demultiplex.

Optical demultiplexer architecture

An add/drop multiplexer/demultiplexer (ADM) for switching, modulating and attenuating optical signals in a fiber optic network employing wavelength division multiplexing (WDM) is disclosed. The ADM is equipped an optical multiplexer for splitting an input WDM signal into individual optical signals, leading to respective 2.times.2 switches. Each switch has another input originating from a plurality of 'add lines', and selects one of its inputs to be dropped and the other to continue along a main signal path. The retained signals may be modulated and attenuated prior to being tapped and finally multiplexed together by a WDM multiplexer. The tapped signals are optoelectronically converted and fed back to a controller, preferably a digital signal processor running a software algorithm, which controls the switching, modulation and attenuation. This permits remote control of the ADM functions by encoding instructions for the controller into a low-frequency dither signal that is embedded within the individual optical signals. The ADM can accordingly be instructed to reroute traffic, dynamically equalize or otherwise change optical channel power levels, and add or remove dither, all in real time. A specific optical channel may be reserved for control purposes, allowing a network administrator to 'log in' to the ADM to override the controller software algorithm. Optionally, the optical signals can be tapped upon entry to the ADM. A bidirectional ADM can be constructed from two unidirectional ADMs, and may share the same controller. Also, a single, general multi-input multi-output switch can be used to provide an arbitrary mapping between individual input and output optical signals.

Optical add/drop multiplexer/demultiplexer

An optical interferometer incorporating a signal strength modulated optical phase delay, such as a Kerr effect element in one of its arms is employed to improve the cross-talk isolation/extinction ratio of an optical switch, amplitude modulator, or amplitude modulated optical transmitter. The Kerr element is constructed so that its intensity dependent optical path length is such as to provide destructive interference at the interferometer output when the light input to the interferometer is low, and constructive interference when the input is high. The place of the Kerr effect element can alternatively be taken by an electro-optic modulator driven with an electrical version of the data modulation appearing on the optical signal.

Optical switches, modulators and transmitters

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Harlow, United Kingdom

Nigel Baker