Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-11-24
2002-07-23
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06424439
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wavelength division multiplexed channel tagging and more particularly to a method of and apparatus for tagging channels in return to zero systems such as soliton systems.
BACKGROUND OF THE INVENTION
Channel tagging or identification is an essential part of an optical network management function in order to be able to simply track wavelength channels through various network elements such as optical cross connects, add-drop nodes and optical amplifiers. Clearly there are a number of different methods by which the individual wavelength channels can be differentiated. For example, channel tagging is commonly carried out by imposing an analogue amplitude modulation on the optical envelope of the optical channel, to identify that channel uniquely, as seen in FIG.
1
. In this method of tagging the optical envelope for each channel is modulated at a different frequency. In soliton systems, or other return to zero systems, the optical pulses or solitons tend to converge to a standard amplitude, centre frequency and phase, within the bit period. Therefore, any analogue modulation imposed on the optical envelope will be removed as the optical envelope is propagated along the fibre and as such this form of conventional channel tag will be lost.
Another known method of channel tagging is to incorporate a channel identification code in a block of data between payload sections of the data, these codes being read at the channel data rate.
FIG. 2
schematically illustrates a data stream incorporating a channel identification code as described above. The problem with this method of coding a channel is the fact that the identification code must be read at the data bit rate. At present it is not clear how soliton data will be formatted. However, the very high bit rates envisaged for soliton transmissions (in the order of 100 Gbits/second) would favour bit interleaving of a plurality of separate channels at a lower rate (e.g. 5 times 20 Gbps). This not only means that the channel identification code would have to be read at a very high rate, it also means that this form of frame dependent tagging scheme would have to accommodate the frame shuffling introduced by the interleaving process.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide a wavelength division multiplexed optical channel tag without utilising envelope analogue modulation techniques in accordance with the prior art.
It is a further object of the present invention to produce a wavelength division multiplexed channel tag suitable for use with return to zero systems such as soliton systems.
It is a further object of the present invention to provide a wavelength division multiplexed channel tag that is independent of any data framing or formatting system.
It is a further object of the present invention to provide a wavelength division multiplexed channel tag which may be detected utilising equipment which operates at a low frequency in comparison to the data rate of the optical channel being tagged.
It is a further object of the present invention to provide a wavelength division multiplexed channel tag which enables tagging of a channel without necessitating the determination of the wavelength of the channel being tagged.
According to a first aspect of the present invention there is provided a method of tagging individual wavelength division multiplexed channels within a plurality of said channels, comprising 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 being arranged in a different manner to provide a characteristic tag for each tagged channel.
Preferably, the periodicity of the tagging pulses in a tagged channel is such as to produce said analogue spectral line with a frequency at least an order of magnitude less than the data rate of data being transmitted within said channel.
More preferably, the data rate of the channel lies in the GHz range and the frequency of the spectral line lies in the MHz range.
Preferably, each channel tag is modulated so as to have a different spectral line frequency.
Alternatively, each tagged channel includes a plurality of tagging pulses, which are configured to produce a characteristic binary channel identifying code, which is readable at the analogue spectral line frequency.
Alternatively, each channel tag is modulated to have a different phase. This is possible as the tag modulation is low frequency compared to the data rate, so that the relative phase of channels should be fairly well preserved down a fibre link.
According to a second aspect of the present invention there is provided an optical transmission system comprising:
a data buffer having inputs and outputs, the inputs of which are connected to a source of a series of individual untagged electronic channels,
a light source adapted to provide wavelength division multiplexed optical signals for each of said channels, the light source being connected to the outputs of said buffer,
the data buffer being adapted to provide a data stream in respect of each channel to be tagged with a series of uniformly spaced time slots,
and modulation means adapted to apply a characteristic series of tagging pulses in selected ones of said time slots to produce a tagging tone in each of said tagged channel in the form of an analogue spectral line tone.
Preferably, the modulator interrupts the data stream in order to insert additional time slots.
Alternatively, the modulator reserves time slots by treating the tagging bits as an additional low data rate tributary which is interleaved with the payload data tributaries at the bit interleaving stage.
Preferably, the modulator is arranged to provide the tagging pulses with a periodicity such that the analogue spectral line has a frequency at least an order of magnitude less than that of the data rate of the channel.
In one embodiment the modulator is arranged to modulate each channel tag by changing the frequency of the spectral line tone.
Alternatively, the modulator is arranged to produce a characteristic binary channel identifying code, which is readable at the analogue spectral line tone frequency.
Alternatively, the modulator is arranged to modulate each channel tag by changing the phase of the analogue spectral line tone on the channel.
According to a third aspect of the present invention there is provided an optical communications system comprising:
an optical transmission system comprising: a data buffer having inputs and outputs, the inputs of which are connected to a source of a series of individual untagged electronic channels, a light source adapted to provide wavelength division multiplexed optical signals for each of said channels, the light source being connected to the outputs of said buffer, the data buffer being adapted to provide a data stream in respect of each channel to be tagged with a series of uniformly spaced time slots, and modulation means adapted to apply a characteristic series of tagging pulses in selected ones of said time slots to produce a tagging tone in each of said tagged channel in the form of an analogue spectral line tone;
a multiplexer and a demultiplexer coupled via a fibre link;
and a tagging tone detector connected to said demultiplexer and adapted to distinguish individual tagging tones in order to demultiplex said tagged channels. .
Preferably, the detector includes correlation electronics adapted to distinguish individual tag identifying codes.
Alternatively, the detector is adapted to detect the analogue spectral line tone frequency of each channel tag utilising a phase locked loop detector.
Alternatively, the detector is adapted to detect the analogue spectral line frequency of each channel tag utilising a narrow band amplifier.
According to a fourth aspect of the present invention there is provided an optical wavelength division multiplexed chann
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
Pascal Leslie
Singh Dalzid
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