Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
2003-03-17
2004-05-18
Tweel, John (Department: 2636)
Optical communications
Multiplex
Wavelength division or frequency division
C398S080000, C398S066000, C398S175000, C455S078000
Reexamination Certificate
active
06738581
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical communication networks generally, and more particularly to optical communication networks which utilize wavelength division multiplexing.
BACKGROUND OF THE INVENTION
Today, a growing demand for telecommunication services is experienced by the telecommunication industry and the demand is further expected to grow in the future. One of the ways to meet such demand is by expanding capacity of information carried over fiber optic cables in optical communication systems through use of wavelength division multiplexing (WDM).
The use of WDM enables simultaneous transmission of multiple signals at different wavelengths over the same fiber optic cable. The multiple signals at the different wavelengths are combined and transmitted in a combined form along the fiber optic cable to a receiving end. At the receiving end the multiple signals are received and separated, and the data carried over each separate channel wavelength is regenerated.
Basic elements of a WDM based system, such as wide band optical amplifiers, multiplexers/demultiplexers, optical transmitters, optical receivers and tunable optical filters, exist today and are commercially available. However, there are still several network control and management problems that have to be resolved in order to provide efficient WDM based optical communication networks.
Some aspects of technologies and art related to WDM based optical communication systems and to elements of WDM based optical communication systems are described in the following publications:
an article titled “Mining the Optical Bandwidth for a Terabit per Second”, by Alan Eli Willner, in IEEE Spectrum, April 1997, pp. 32-41;
an article titled “Record Data Transmission Rate Reported at ECOC 96”, by Paul Mortensen, Laser Focus World, November 1996, pp. 40-42;
an article titled “Multiple Wavelengths Exploit Fiber Capacity”, by Eric J. Lerner, Laser Focus World, July 1997, pp. 119-125;
an article titled “Advances in Dense WDM Push Diode-Laser Design”, by Diana Zankowsky, Laser Focus World, August 1997, pp. 167-172;
an article titled “Multistage Amplifier Provides Gain Across 80 nm”, by Kristin Lewotesky, Laser Focus World, September 1997, pp. 22-24;
an article titled “Optical switching promises cure for telecommunications logjam”, by Jeff Hecht, Laser Focus World, September 1998;
The Communications Handbook, CRC Press & IEEE Press, 1997, Editor-in-Chief Jerry D. Gibson, Section 65, pp. 883-890;
an article titled “WDM Local Area Networks”, by Kazovsky et al., IEEE LTS, May 1992, pp. 8-15;
an article titled “Optical Switches Ease Bandwidth Crunch”, by Rien Flipse, EuroPhotonics, August/September 1998, pp. 44-45;
an article titled “Speed Demons: Is “Faster Better and Cheaper?”, by Stephanie A. Weiss, Photonics Spectra, February 1999, pp. 96-102;
an article titled “Wavelength Lockers Keeps Lasers in Line”, by Ed Miskovic, Photonics Spectra, February 1999, pp. 104 -110;
an article titled “Optical switches pursue crossconnect markets”, by Hassaun Jones-Bay, Laser Focus World, May 1998, pp. 153-162;
a conference review titled “Optical amplifiers revolutionize communications”, Laser Focus World, September 1998, pp. 28-32;
an article titled “Combining gratings and filters reduces WDM channel spacing”, by J. J. Pan and Y. Shi, Optoelectronics World, September 1998, pp. S
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an article titled “Demand triggers advances in dense WDM components”, by Raymond Nering, Optoelectronics World, September 1998, pp. S
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an article titled “Optical Networks Seek Reconfigurable Add/Drop Options”, by Hector E. Escobar, Photonics Spectra, December 1998, pp. 163-167;
an article titled “Ultrafast Optical Switch Unveiled”, by Michael D. Wheeler, Photonics Spectra, December 1998, pp. 42;
an article titled “Data express Gigabit junction with the next-generation Internet”, by John C. Collins, Joel Dunn, Phil Emer and Mark Johnson, IEEE Spectrum February 1999, pp. 18-25; and
an article titled “Designing Broadband Fiber Optic Communication Systems”, by Juan F. Lam, Communication Systems Design, February 1999.
Additionally, in U.S. Pat. No. 5,170,273 to Nishio there is described a cross-talk reducing optical switching system which receives electrical digital signals at its input terminal.
U.S. Pat. No. 5,191,457 to Yamazaki describes a WDM optical communication network in which optical beams are modulated by channel discrimination signals of different frequencies.
U.S. Pat. No. 5,194,977 to Nishio describes a wavelength division switching system with reduced optical components using optical switches.
U.S. Pat. No. 5,557,439 to Alexander et al. describes wavelength division multiplexed optical communication systems configured for expansion with additional optical signal channels.
U.S. Pat. No. 5,680,490 to Cohen et al. describes a comb splitting system which demultiplexes and/or multiplexes a plurality of optical signal channels at various wavelengths.
U.S. Pat. No. 5,712,932 to Alexander et al. describes reconfigurable wavelength division multiplexed systems which include configurable optical routing systems.
U.S. patent application Ser. No. 09/126,378 filed on Jul. 30, 1998, now U.S. Pat. No. 6,404,522, describes improvements in communication performance of an optical communication system which communicates data via N different channel wavelengths using WDM.
The disclosures of all references mentioned above and throughout the present specification are hereby incorporated herein by reference.
SUMMARY OF THE INVENTION
The present invention seeks to improve performance of WDM based communication networks.
In the present invention, a network control system may be used to control and manage communication and to improve communication performance of a communication network. In a preferred embodiment of the present invention, the network control system is embodied in a node serving terminal and is employed to limit a number of channel wavelengths actually used for substantially simultaneously communicating the optical signals via a fiber optic cable to an end node to a highest number N of separable channel wavelengths at the end node. Thus, channel wavelengths that cannot be separated at the end node due to, for example, limitations of separation equipment at the end node, are not used for communication with the end node and are therefore not able to generate crosstalk among channel wavelengths or other types of interference which may degrade communication performance.
The network control system may include a passive element, such as a filter, to limit the number of channel wavelengths actually used for communication. The filter may block transmission of channel wavelengths outside a selected pass-band, or a few selected pass-bands. Channel wavelengths of optical signals carried over channel wavelengths which are not transmitted by the filter may be reflected and converted to at least one channel wavelength within at least one pass-band transmitted by the filter thereby forming converted optical signals.
The converted optical signals may be transmitted via a separate route to another node serving terminal which may communicate the converted optical signals to the end node via a separate link and a separate route.
Alternatively, the converted optical signals may be transmitted to the end node over the at least one channel wavelength within the at least one pass-band transmitted by the filter after a delay time period. The delay time period may be provided by a delay generator.
Further alternatively, the converted optical signals may be combined with non-converted optical signals carried over the N channel wavelengths and transmitted in a combined form to the end node if a data rate of data carried over each of the N channel wavelengths resulting from the combination of the converted optical signals with the non-converted optical signals does not exceed a channel data rate threshold determined, for example, by a maximum channel capacity.
The network control system may alternatively include a controller which actively limits the number
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