Nortel Networks Corporation

Northern Telecom Limited

Bookham Technology Limited

Jonathan Paul King

Alan Robinson

Richard E Epworth

Simon P Parry

Martyn Fice

Maurice M O'Sullivan

Kevan Peter Jones

Robert William Keys

Andrew Niall Robinson

Mark R Hinds

Kevin J Cordina

Nigel Edward Jolley

Barrie Flintham

Ian Hardcastle

Kevin John Warbrick

Christopher R Fludger

Joanne Wakefield

Stephen Wilson

James Regan

Mark E Bray

Martin P Poettcker

Robert A Baker

Roger M Gibb

Martin J Fice

Toby J Reid

Alan A Solheim

Joseph Mun

Benoit Charbonnier

Henry John Harvey

Marco Cavallari

A structure for an optical packet for transmission over an optical network comprises a packet header () and a packet payload (). The header comprises first and second sections (). The first section () comprises a series of clock pulses () at the data rate of the second section of the packet header, or a multiple or sub-multiple thereof. This header structure enables the clock pulses in the first section () to be used to control the timing instants when the header information in the second section () is read. The header information can thus be read using the data in the header alone, without needing to alter the structure of the packet payload. The clock pulses can be delayed in order to enable them to be used to control the reading of data in the second section of the packet header. The invention ca be used in optical communications networks.

Packet-based optical communications networks

An optical amplifier comprises a doped fiber core and a cladding layer surrounding the core. The mode field diameter of the fiber is greater than 8 &#x3bc;m and the refractive index difference between the core and the cladding layer is selected such that the cut-off wavelength at which the fiber becomes single mode lies in the range 1000-1550 nm. This amplifier uses a large made field diameter fiber, which reduces the intensity for a specified output power. This results in reduced filtering of the low frequency components of the signal. The refractive index difference between the core and cladding is selected such that the fiber is multi-mode at 980 nm, which enables bend performance to be improved.

Optical fiber amplifier

A structure for an optical packet has a packet header ( ) and a digitally encoded packet payload ( ). Information is encoded in the header by modulation of a signal comprising a plurality of pulses aligned with regularly occurring timing instants, the payload digits also being aligned with the regularly occurring timing instants. The header information is encoded at a rate lower than the frequency of the timing instants. This structure enables simplified opto-electric circuitry to be used to read the packet header, and also enables the packet header to be used to derive the clock information required to read the high data rate information from the packet payload. This avoids the need for the initial bits of the packet payload to be used to synchronize the clock. The structure is used in an optical communications network.

An apparatus for reshaping optical pulses divides an incoming optical signal ( ) into a first ( ) and a second ( ) path. The signal in the second path ( ) is converted into an electrical signal which provides information concerning the pulse power of individual pulses. An optical modulator ( ) is provided in the first, purely optical path ( ) for modifying the optical signal so as to attenuate the pulses by an amount which depends on the power of the pulses, higher power pulses being attenuated more than lower power pulses. This helps maintain a constant signal to noise ratio within the system and can extend the number of optical spans of an optical signal before it requires full electrical regeneration.

Apparatus for reshaping optical pulses

A method of reading and updating a packet header of an optical packet for transmission over an optical network involves dividing the input signal into two paths. The signal in one path ( ) is converted into an electrical signal and the header information is read. The data stored in the packet header is removed optically in the other path ( ) by constraining the packet header signal to have a constant amplitude. Updated header information is used to modify the constant amplitude signal using a modulator ( ). An apparatus is provided for implementing the method. The header is thus read in the electrical domain, but it is updated optically.

Apparatus and method for reading data from an optical packet header

An optical equaliser, for use in an optical communications system, comprises a plurality of concatenated, fixed modulation depth, periodic filters. Each of the filters may be individually dynamically wavelength tuned in order to optimise optical equalisation of an optical signal transmitted by an optical element in the optical communications system.

Optical equalizer

An apparatus for reshaping optical pulses comprises an N&times;N optical coupler having N ports on each side of the coupler, where N&lE;3. An input and an output of the apparatus are defined by two of the N ports on one side of the optical coupler, and a length of optical fibre connects two of the N ports on the other side of the optical coupler. The function of transmission versus input power has a negative gradient at the power level of the optical pulses. By virtue of phase shifts within the coupler, the transmission function is selected such that higher power pulses are attenuated more than lower power pulses, which tends to even out pulse powers to a constant level. This helps maintain a constant signal to noise ratio within a system and can extend the number of optical spans of an optical signal before it requires full electrical regeneration.

An optical fiber amplifier or laser comprises an optical housing having a diffusive reflective inner surface and at least one opening for receiving pump light. An optical fiber having a doped core is at least partially contained within the optical housing. The optical fiber can be pumped by an optical source without the need for any complex or expensive optical couplers. Lateral illumination of the fiber core with pump light enables many fibers to be pumped by the same pump source, so that a separate dedicated coupler is no longer required to couple the pump light into each optical cable.

Optical fiber device

A hybrid optical fiber comprises a first fiber section comprising a fiber or a concatenation of fibers having first dispersion characteristics at a predetermined operating wavelength and a second fiber section coupled to the first fiber section to form the hybrid fiber. The first fiber dispersion characteristics are selected to maintain the signal dispersion within desired limits, whereas the second fiber is optimised for low loss. Dispersion compensation is provided in the first section of the fiber span where the signal intensity is highest, and therefore the region of the fiber span where these non-linearities have greatest effect. In the second section of the fiber span, the non-linear effects can be ignored, so it is optimised for low loss rather than for dispersion compensation.

Dispersion managed fiber optic cable and system

A method of tagging individual wavelength division multiplexed channels within a plurality of said channels. The method comprises the step of creating a tagging tone in the form of an analogue spectral line tone, by providing a series of regularly spaced time slots substantially throughout each of said tagged channels for receipt of binary tagging pulses. The binary tagging pulses in each tagged channel are arranged in a different manner to provide a characteristic tag for each tagged channel.

Wavelength division multiplexed channel tagging

A pulse interleaver splits an input pulse train into at least two optical branches ( ). A first one of the branches ( ) carries a first signal, and is terminated with a mirror ( ) and a device ( ) for manipulating the state of polarization. The reflected signal is re-combined at a combiner ( ) with a second signal on a second one of the branches ( ). The effective path lengths for the first and second signals between the input and the combiner are selected such that the input pulse train is interleaved with itself thereby providing an output with increased frequency. The mirror ( ) and the device for manipulating the state of polarization ( ) provide a predetermined relationship between the polarization of pulses in the output pulse train derived from an individual pulse of the input pulse train.

Pulse interleaver

An optical equalizer comprises a plurality of serially concatenated filter elements the phase and modulation depth of which can be individually tuned. The filter elements are tuneable in order to generate a desired optical equalization function. Each of the filter elements is a three arm interferometer and each is fabricated utilizing integrated waveguide technology.

A method and apparatus for determining control signals of a filter for optimization of the gain profile of an amplifier, particularly though not exclusively for use in optical communications systems, and a system incorporating the same. The method is for calculating at least one control signal for at least one periodic filter arranged to alter the output gain profile of an amplifier, in which at least one of the phase and amplitude of the filter response are tuneable. The method includes the steps of: determining an error profile from the amplifier output gain profile and a predetermined target output gain profile; determining the dot product of the error profile and a first function of similar period and form to the response of the filter; determining the dot product of the error profile and a second function of similar period and form to the response of the filter, said second function being substantially orthogonal to said first; and determining at least one control signal for tuning of said filter from the calculated dot products.

Amplifier control

In a WDM optical transmission system employing optical amplifiers in its transmission path, a supervisory signal channel, used for monitoring and controlling the operation of the amplifiers and spectrally separated from the data transmission, may be multiplexed with the data. A construction of amplifier is disclosed which is capable of being upgraded with an upgrade of the transmission system to include additional data handling capacity, for instance data transmission in an additional waveband and/or in the opposite direction, without interruption of the pre-upgrade data transmission path through the amplifiers. This is accomplished by the use of channel dropping and insertion filters disposed so that the amplifying data transmission path extends via the drop/insertion channel of those filters.

Optical amplifiers

A multi-mode pump laser having an output, and an optical fiber coupler. The optical fiber coupler has a first section and a second section. The first section of the optical fiber coupler comprises a multi-mode fiber which is optically coupled to the pump laser output. The second section of the fiber coupler comprises a plurality of single mode optical fibers each of which has an input which is optically coupled to the multi-mode fiber. The source further comprises a pump drive which is controllable to dither the optical center frequency of the light produced by the pump laser, so as to scramble modal power distribution at the inputs of the single mode optical fibers.

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Epping, United Kingdom

Jonathan Paul King