WDM optical network with passive pass-through at each node

• US 20030215238A1
• Filed: 12/20/2002
• Published: 11/20/2003
• Est. Priority Date: 08/27/1997
• Status: Active Grant

• Current Assignee: Ciena Corporation
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Milton, David, Liu, Kexing, Valis, Tomas, Pigeon, Michel, Totti, Gino
• Granted Patent: US 6,892,032 B2
• Time in Patent Office: Days
• US Class Current: 398/83
• CPC Class Codes: H04J 14/0206 Express channels arrangements
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements
• CPC Class Codes: H04J 14/0226 Fixed carrier allocation, e.g. according to service
• CPC Class Codes: H04J 14/0227 Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
• CPC Class Codes: H04J 14/0241 Wavelength allocation for communications one-to-one, e.g. unicasting wavelengths
• CPC Class Codes: H04J 14/0246 using one wavelength per ONU
• CPC Class Codes: H04J 14/025 using one wavelength per ONU, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
• CPC Class Codes: H04J 14/028 WDM bus architectures
• CPC Class Codes: H04J 14/0282 WDM tree architectures
• CPC Class Codes: H04J 14/0283 WDM ring architectures
• CPC Class Codes: H04J 14/0284 WDM mesh architectures
• CPC Class Codes: H04J 14/0289 Optical multiplex section protection
• CPC Class Codes: H04J 14/0291 Shared protection at the optical multiplex section (1:1, n:m)
• CPC Class Codes: H04J 14/0298 with sub-carrier multiplexing [SCM]
• CPC Class Codes: H04Q 11/0062 Network aspects

Abstract

A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

Claims

1. A communications network employing wavelength division multiplexing comprising:

a plurality of nodes;

an optical transmission medium interconnecting said nodes, said transmission medium being capable of a carrying a plurality of wavelengths organized into bands; and

an interface at each node for dropping a band associated therewith, adding band carrying traffic for another node, and passively forwarding other bands;

whereby communication can be established directly between a pair of nodes in said network sharing a common band without the active intervention of any intervening node.

2. A communications network as claimed in claim 1, wherein said interface includes a filter that passively reflects bands other than the band(s) to be dropped at the node.

3. A communications network as claimed in claim 2, wherein said filter is an interference filter.

4. A communications network as claimed in claim 3, wherein each node further comprises a fine filter acting as a demultiplexer for subdividing wavelengths within a band dropped by said filter.

5. A communications network as claimed in claim 4, wherein said interface comprises photodetectors associated with said respective subdivided wavelengths for producing electrical signals.

6. A communications network as claimed in claim 5, wherein said interface further comprises lasers for generating wavelengths in said band to be added, said lasers being directed into a multiplexer for combining individual wavelengths into a band.

7. A communications network as claimed in claim 6, wherein said interference filter further acts a multiplexer multiplexing said band to be added with bands that are passively passed through said interface unit.

8. A communications network as claimed in claim 1, wherein at least some of the nodes further comprise a cross-connect switch for selectively connecting desired wavelengths with a payload signal.

9. A communications network as claimed in claim 8, wherein said cross connect switch is an electrical switch and electro-optical couplers are provided between said switch and said interface.

10. A communications network as claimed in claim 8, wherein said cross connect switch is an optical switch, and said payload signal is an optical signal.

11. A communications network as claimed in claim 8, wherein the wavelengths within a band have approximately 1.6 nm separation.

12. A communications network as claimed in claim 11, wherein the bands are separated by approximately 9.6 nm including guard space.

13. A communications network as claimed in claim 11, wherein the passband of each band is approximately 6.4 nm.

14. A communications network as claimed in claim 1, wherein said nodes are physically arranged in a ring.

15. A communications network as claimed in claim 14, wherein said ring is a bi-directional ring.

16. A communications network as claimed in claim 15, wherein said nodes are connected in a hub arrangement by said bands of wavelengths.

17. A communications network as claimed in claim 15, wherein said nodes are connected in a mesh pattern by said bands of wavelengths.

18. A communications network as claimed in claim 15, wherein said bi-directional ring is based on a single strand optical fibre.

19. A communications network as claimed in claim 1, wherein said nodes are physically arranged in an open-loop or a point-to-point manner.

20. A communications network as claimed in claim 19, wherein said network is bi-directional.

21. A communications network as claimed in claim 19, wherein said network is based on a single strand of optical fibre.

22. A method of establishing communication over an optical network employing wavelength division multiplexing and having a plurality of nodes interconnected by an optical transmission medium capable of carrying a plurality of wavelengths organized into bands, comprising the steps of:

sending traffic destined for a remote node in a band associated with the remote node;

passively forwarding said band at any intervening nodes; and

dropping said band at said remote node to extract said traffic destined therefor.

23. A method as claimed in claim 22, wherein said nodes are physically arranged in the form of a bi-directional ring.

24. A method as claimed in claim 22, further comprising the step of adding a band of wavelengths at a node for transmission over said network to a remote node dropping that band.

25. A method as claimed in claim 24, further comprising the step of performing wavelength switching at a node to transfer data between bands.

27. An interface device as claimed in claim 25, wherein said multiplexer and demultiplexer comprise an optical filter that extracts said dropped waveband and reflects said other wavebands.

26. An interface device for use in an optical network employing wavelength division multiplexing, comprising a demultiplexer for dropping a predetermined waveband from the network at a node, means for converting optical input signals from said demultiplexer to electrical output signals, means for generating optical output signals from electrical input signals, a multiplexer for adding a said optical output signals in a predetermined waveband to the network, said demultiplexer and multiplexer being arranged to forward passively optical signals in bands other than said band that is dropped.

28. An interface device as claimed in claim 26, wherein said optical filter is an interference filter.

29. A fiber optic wavelength division multiplexed ring comprising a plurality of switching nodes, means for generating a plurality of wavelengths organized in to bands on said ring, and means for transmitting maintenance channel data on at least one of said wavelengths as a pilot tone.

30. A fiber optic wavelength division multiplexed ring as claimed in claim 29, wherein said transmitting means for transmitting maintenance channel data modulates the bias current of said means for generating a plurality of wavelengths.

31. A fiber optic wavelength division multiplexed ring as claimed in claim 30, wherein said transmitting means FSK modulates the maintenance channel data onto said at least one wavelength.

32. A fiber optic wavelength division multiplexed ring as claimed in claim 31, wherein said transmitting means QAM modulates the maintenance channel data onto said at least one wavelength.

33. A fiber optic wavelength division multiplexed ring as claimed in claim 30, wherein said transmitting means OFDM modulates the maintenance channel data onto said at least one wavelength.

34. A fiber optic wavelength division multiplexed ring as claimed in claim 29, wherein said maintenance channel has a modulation depth such that it matches the bit error rate (BER) or waterfall curve performance of the data channel so that the system can determine the performance of the data channel by monitoring the maintenance channel data and without looking at the maintenance channel payload.

35. A distributed high speed packet switch comprising a plurality of switching components distributed over a geographic area;

a fiber optic wavelength division multiplexed ring interconnecting said switching components, said fiber optic ring carrying a plurality of wavelengths organized into bands; and

means for adding/dropping a band at each switching component associated therewith, said adding/dropping means passively forwarding other bands, and pairs of said switching components forming part of said switch directly communicating on wavelengths in bands associated therewith.

36. A distributed high speed packet switch as claimed in claim 35, wherein said switch is an ATM switch.

37. In a communications network employing wavelength division multiplexing comprising a plurality of nodes, and an optical transmission medium interconnecting said nodes via individual links, a method of optimizing the individual link performance (received signal quality, power level, bit error rate) between any communicating nodes in the network comprising sending data over maintenance channel links.

38. In a communications network employing wavelength division multiplexing comprising a plurality of nodes, and an optical transmission medium interconnecting said nodes via individual links, a method of determining whether a data channel is carrying valid traffic or noise comprising verifying the consistency of the bit rate of the data channel.

39. In a communications network employing wavelength division multiplexing comprising a plurality of nodes, and an optical transmission medium interconnecting said nodes via individual links, a method of determining whether pulse retiming is required and controlling a frequency agile clock recovery and jitter filter circuit comprising measuring the bit rate of a data channel.