Optical waveguides – With optical coupler – Plural
Reexamination Certificate
1999-07-13
2001-07-17
Sanghavi, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Plural
C359S199200, C359S199200
Reexamination Certificate
active
06263130
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to wave division optical networks and, more particularly, to a wideband optical service channel for such networks.
BACKGROUND OF THE INVENTION
An optical multiplexer is a device that combines several input optical signals, each at a different wavelength (frequency), and each entering the device from separate optical fiber inputs, into one output optical signal on one output optical fiber. Similarly, an optical demultiplexer is a device that separates several input optical signals, each at a different wavelength and entering the device via a single optical fiber, into several optical fiber outputs, one for each wavelength. The same device can be used either as an optical multiplexer or as an optical demultiplexer.
In typical wavelength-division multiplexed (WDM) optical networks, a plurality of signals, each at a separate wavelength, are multiplexed by means of one or more optical multiplexers onto a single optical fiber. After being transmitted over the fiber, the signals are separated by means of an optical demultiplexer and directed to individual receivers. In most point-to-point and star WDM networks, multiplexers are distributed among network nodes.
In WDM networks, one or more optical service channels are employed to convey OAM&P (operation, administration, maintenance and provisioning) information between the network nodes and optical amplifier sites. The optical service channels typically use an optical source at a wavelength that is distinct from the wavelengths of the various signals. The bandwidth or data rate of the service channel is typically smaller than the signal bandwidth or data rate.
Generally, one filter is used to add an optical service channel and another is used to drop the optical service channel. Such an optical service channel implementation is disclosed in U.S. Pat. No. 5,113,459 issued May 12, 1992 to Grasso et al., wherein a wavelength substantially different from the wavelength used for the signals is used for optical service channel transmission. Such an implementation is also shown in U.S. Pat. Nos. 5,291,326 (issued Mar. 1, 1994 to Heidemann) and U.S. Pat. No. 5,532,864 (issued Jul. 2, 1996 to Alexander et al.), where a laser outside of the EDFA (Erbium Doped Fiber Amplifier) band is employed. The purported advantage of such a laser is that the service channel survives an amplifier fault.
Numerous additional systems and methods have been proposed. However, these typically add ancillary components (such as filters), escalate the cost of the system, or compromise bandwidth.
For a particular link, the qualities of the transmitter and receiver may be summarised in a single number, called a “link budget”. The link budget represents the amount of allowable attenuation of a signal over the link, say 30 dB. If an ancillary component is included in a link, for instance for service channel transmission, additional attenuation may be introduced. If a component reduces signal power by 1 dB, the link budget would then be 29 dB. The 1 dB reduction in link budget is called a “link budget penalty”.
It would be desirable to have a method of transmitting information between nodes in a network using a multiplexer and an optical source where no link budget penalty is realized and where a more economical optical source could be employed.
SUMMARY OF THE INVENTION
The present invention provides a method for transmitting OAM&P (operation, administration, maintenance and provisioning) information between network nodes in a wavelength division multiplex network. OAM&P information is transmitted using a spectrally broad service channel signal transmitted over the unused portion of the optical spectrum.
In accordance with an aspect of the present invention there is provided a method of transmitting information between nodes in a network using a multiplexer and an optical source, the method including providing a plurality of WDM optical signal sources, each at a distinct wavelength and modulated by an independent information source and providing an optical service channel source with a wide optical spectrum which overlaps the optical spectrum of the WDM signal sources. Further, this method includes modulating the optical service channel source with an information source, the information source for conveying network OAM&P information, and providing the following: a wave-division multiplexer having a plurality of input signal ports; means for communication with the WDM signal sources; a service channel input port having means for communicating with the optical service channel source; and a signal output port having means for transmitting multiplexed signals and the service channel over a common optical fiber. This method also includes filtering the WDM signal sources from the multiplexer input signal port to the signal output port, filtering a remaining portion of the optical spectrum from the multiplexer service channel input port to the output port, transmitting the information on the WDM signal sources and the service channel between network nodes over a common optical fiber, providing a wave division demultiplexer having a signal input port and means for receiving the multiplexed signals and the service channel transmitted over the common optical fiber, a plurality of output signal ports having means for communication with the WDM signal receivers, a service channel output port having means for communication with the optical service channel receiver, filtering the WDM signal sources from the input port to the plurality of output WDM signal ports, filtering a remaining portion of the optical spectrum from the input port to the output optical service channel port, providing means for detecting the WDM signal information and detecting the optical service channel OAM&P information.
In accordance with a further aspect of the present invention there is provided a transmission system including a multiplexer including a plurality of filters, one of the filters having an upgrade port, a plurality of input signal ports, each of the said ports connected to one of the filters, a service channel input port, connected to said upgrade port and a signal output port for transmitting the combined output of said filters. The transmission system also includes a transmitting node including a plurality of information transmitters, each of the said transmitters connected to one of the input signal ports and a service channel transmitter connected to said service channel input port. The transmission system also includes a demultiplexer including a signal output port for receiving said combined information and service signal, a plurality of filters, one of the filters having an upgrade port, a plurality of output signal ports, each of said output signal ports connected to one of the filters and a service channel output port connected to said upgrade port. The transmission system also includes a receiving node including a plurality of receivers, each said receiver connected to one said output signal port and a service channel receiver connected to said service channel output port.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
REFERENCES:
patent: 5661585 (1997-08-01), Feldman et al.
patent: 5712932 (1998-01-01), Alexander et al.
patent: 5777764 (1998-07-01), Kohn
patent: 6002503 (1999-12-01), Mizrahi
patent: 0 905 937 A2 (1999-03-01), None
patent: WO 98/36302 (1998-08-01), None
Nortel Networks Limited
Rojas Omar
Sanghavi Hemang
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