Optical: systems and elements – Optical amplifier – Beam combination or separation
Reexamination Certificate
2001-06-06
2004-02-24
Black, Thomas G. (Department: 3663)
Optical: systems and elements
Optical amplifier
Beam combination or separation
C359S199200, C359S199200, C359S341320, C359S341330, C359S199200
Reexamination Certificate
active
06697193
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to optical communications systems and more particularly to amplification in optical communications systems.
The explosion of communications services, ranging from video teleconferencing to electronic commerce, has spawned a new era of personal and business interactions. As evident in the rapid growth of Internet traffic, consumers and businesses have embraced broadband services, viewing them as a necessity. However, this enormous growth in traffic challenges the telecommunication industry to develop technology that will greatly expand the bandwidth limitations of existing communications systems. Further improvements in optical communications hold great promise to meet the demands for greater and greater bandwidth.
Wavelength Divisional Multiplexing (WDM) technology permits the concurrent transmission of multiple channels over a common optical fiber, thus expanding available bandwidth and providing other advantages in implementation. When it is necessary to recover data from the WDM signal, the individual wavelength components are isolated from one another and converted to electrical form by optical receivers. These optical receivers only operate correctly when the power level of their inputs is within a specified dynamic range. Typically amplification must be provided to bring the power level of the optical signals up to the necessary level due to losses in transmission and elsewhere.
FIG. 1
depicts a prior art approach to amplification within a WDM receiver system
100
. WDM receiver system
100
has as its input a composite WDM signal
102
that includes, e.g., up to 200 wavelength components located on WDM channels spaced 25 GHz apart. An optical wavelength router (OWR)
104
incorporates a first deinterleaving block
106
that divides the 25 GHz grid into two grids having 100 WDM channels at 50 GHz spacings. Deinterleaving blocks
108
and
110
then further divide these two grids into four grids of 50 channels each at 100 GHz spacings. Each such grid is equipped with an amplifier
112
to bring the signal power level up to the level needed for correct optical receiver operation. A set of demultiplexers
114
then complete the separation of the WDM signal into its individual wavelength components.
Due to various wavelength-selective effects in the WDM link and demultiplexing components, there must be a way of varying gain across the overall grid. Otherwise, certain groups of WDM channels will have power levels outside the required dynamic range. This is particularly true when the dynamic range is relatively narrow as is the case with high data rate systems where the individual wavelength components are each modulated by 10 Gbps data streams or even higher data rate streams. Furthermore, these wavelength-selective effects are dependent on the particular installation and will vary over time. Unfortunately, each of amplifiers
112
may provide flat gain across the entire spectrum occupied by the 200 channel grid with no provision for adaptive equalization.
One way to vary gain across the spectrum to assure optimal receiver performance would be to install a variable gain optical amplifier with its own pump for each channel following demultiplexers
114
. By controlling the pump powers of the individual pumps, an optical equalization function may be performed. Alternatively, a variable optical attenuator (VOA) may be installed for each channel. Unfortunately, these approaches are both very expensive and space-inefficient. Their expense and cumbersomeness increase further as the number of channels increases.
What is needed is an amplification architecture for WDM receiver systems that provides an appropriate amount of amplification for each WDM channel while economizing on component cost and space consumption.
SUMMARY OF THE INVENTION
One embodiment of the present invention provides an amplification architecture for WDM receiver systems. The WDM channel grid is divided into groups of adjacent channels. A separate optical amplifier is provided for each channel with a single pump being shared among the channels of each group. The, gain experienced by channels of a given group may be adjusted by varying the power of the group's pump. This approach allows equalization of received channel power such that all channels fall within the desired dynamic range. The amplification architecture may be implemented in a space-efficient manner at low cost.
A first aspect of the present invention provides apparatus for amplifying a plurality of optical signals in a WDM communications system carrying a plurality of WDM channels. The apparatus includes a first group of optical amplifiers, each of the first group of amplifiers amplifying a selected optical signal being carried by one of a first group of adjacent WDM channels, a second group of optical amplifiers each of the second group of amplifiers amplifying a selected optical signal being carried by one of a second group of adjacent WDM channels, the first optical energy source providing pump energy to amplifiers of the first group of optical amplifiers, and a second optical energy source providing pump energy to amplifiers of the second group of optical amplifiers.
A second aspect of the present invention provides a WDM receiver system in a WDM communications system carrying a plurality of WDM channels. The WDM receiver system includes: a demultiplexer that receives a composite optical signal and isolates components thereof corresponding to the plurality of WDM channels, a first group of optical amplifiers, each of the first group of amplifiers amplifying a selected optical signal being carried by one of a first group of adjacent WDM channels, a second group of optical amplifiers, each of the second group of amplifiers amplifying a selected optical signal being carried by one of a second group of adjacent WDM channels, a first optical energy source providing pump energy to amplifiers of the first group of optical amplifiers, a second optical energy source providing pump energy to amplifiers of the second group of optical amplifiers, and a plurality of receivers for recovering information transmitted via the plurality of WDM channels.
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Yamada et al., “Broadband and Gain-Flattened amplifier composed of a 1.55 um-band and a 1.58 um-band Er3+ doped fibre amplifier in a parallel configuration.” Elect. Lett. 33: Apr. 8, 1997, pp. 710-711.
Castagnetti Roberta
Grasso Giorgio
Meli Fausto
Black Thomas G.
Cisco Technology Inc.
Cunningham Stephen
Ritter Lang & Kaplan LLP
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