Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
1999-12-15
2004-05-11
Pascal, Leslie (Department: 2733)
Optical communications
Multiplex
Wavelength division or frequency division
C398S037000, C398S038000, C398S094000, C398S157000, C359S337130, C359S341300, C359S349000
Reexamination Certificate
active
06735394
ABSTRACT:
FIELD OF THE INVENTION
The invention is in the field of optical telecommunications, and more particularly, pertains to an optical communication system in which individual channel output power levels are equalized independent of channel wavelength and input power level.
BACKGROUND OF THE INVENTION
In Wavelength Division Multiplexed (WDM) optical links it is difficult to assure that signals arriving at each channel's photodetector have a power level that is within the receiver's dynamic range. Even for simple point-to-point links, flattening filters are used in the Erbium Doped Fiber Amplifiers (EDFA's), MUX/DEMUX components' profiles of attenuation vs. wavelength must be trimmed, and the system must be carefully monitored to ensure that large inter-channel differences in concatenated connector and splice losses are not accumulated.
Typically, all WDM channels are amplified in a single amplifier, with the single amplifier being optimized for gain flatness. However, there are different power levels in each channel due to differences in accumulated channel losses at different frequencies. Variable Optical Attenuators (VOA's) are used in the respective channels to compensate for the losses. The VOA's require frequent adjustment to maintain required power levels, and if the power level in a given channel drops below a minimum level, a transponder is required in the line to increase the power level to the required level.
Thus, there is a need to be able to automatically readjust the power level on a per-channel basis so that the photodetector at the optical receiver receives a signal with an adequate Optical Signal to Noise Ratio (OSNR) and amplitude to achieve a desired Bit Error Rate (BER), but not so high a power level that the optical receiver or the electronics to follow are saturated.
SUMMARY OF THE INVENTION
In view of the above, it is an aspect of the invention to adjust the power levels in an optical communication system on a per-channel basis.
It is another aspect of the invention to adjust the power levels in an optical communication system on a per-channel basis by including in each channel an optical amplifier which is operated in the saturation mode.
It is yet another aspect of the inventions to adjust the power levels in an optical communication system on a per-channel basis by including in each channel an optical amplifier, with each such amplifier receiving a predetermined pump power for operating each such amplifier in the saturation mode.
It is still another aspect of the invention to connect Optical Line Terminals (OLT's) back-to-back at their respective pass-through interface channels, with each channel including an optical amplifier, with each such amplifier receiving a predetermined pump power for operating each such amplifier in the saturation mode.
It is still yet another aspect of the invention to adjust the power levels in each output channel from a demultiplexer in a WDM optical communication system on a per-channel basis, with each such output channel including an optical amplifier, with each such amplifier receiving a predetermined pump power for operating each such amplifier in the saturation mode, with the pump power being provided from either a predetermined power per-channel pump for each amplifier, or a single shared pump which supplies the predetermined power to each channel amplifier, wherein one or more of the pumps also are referred to as a “controller”.
It is a further aspect of the invention to adjust the power levels in each input channel to a multiplexer in a WDM optical communication system on a per-channel basis, with each such input channel including an optical amplifier, with each such amplifier receiving a predetermined pump power for operating each such amplifier in the saturation mode, with the pump power being provided from either a predetermined power per-channel pump for each amplifier, or a single shared pump which supplies the same predetermined power to each channel amplifier.
It is yet another further aspect of the invention to maximize the number of optical hops in an optical ring network by equalizing the output power level in the respective channels due operating the respective channel amplifiers at a predetermined power level by operating the amplifiers in the saturation mode.
It is still yet another further aspect of invention to prevent lasing in an optical ring network by operating an amplifier in each channel at a predetermined power level which can't be exceeded, such that one channel can't rob another channel of power due to the one channel's wavelength traversing the loop without being dropped.
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Green Paul
Yue Chaoyu
Fitzpatrick ,Cella, Harper & Scinto
Pascal Leslie
Tellabs Operations Inc.
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