Method and apparatus for channel equalization in wavelength division multiplexed systems
First Claim
1. A method of equalizing performance of a first channel transmitting a first signal from a first transmitter along a first transmission path with respect to performance of a second channel transmitting a second signal from a second transmitter along a second transmission path the equalization being effective at a predetermined location in an optical wavelength division multiplexed system and the location being downstream of an optical amplifier in the first path and downstream of an optical amplifier in the second path, the method comprising:
- measuring the optical power of the first signal and the second signal at the inputs of each optical amplifier that is upstream of said location; and
adjusting the optical power of the first transmitter by an amount dependent upon the sum of the reciprocal of the first signal optical power measurements relative to the sum of the reciprocal of the second signal optical power measurements.
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Abstract
A method and apparatus for channel performance equalization in wavelength division multiplexed (WDM) systems is disclosed. Performance of the channels is estimated from optical power measurements of each signal transmitted by the channels. The measurements are taken at the inputs of optical amplifiers in the transmission path of the system. The channels are equalized by adjusting the optical power of the channel transmitters. The method is applicable to point-to-point networks as well as more complex network configurations such as those having an add-drop multiplexer (ADM) for inserting and extracting channels from the transmission path. The method can compensate for signals having different bit rates by applying an offset to the amount of optical power adjustment of the channel transmitters. Furthermore, if different types of optical amplifiers are used in the transmission path, the method can accommodate different noise characteristics of the amplifiers by using their noise figures in determining the amount of optical power adjustment of the transmitters that is required to equalize channel performance.
170 Citations
13 Claims
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1. A method of equalizing performance of a first channel transmitting a first signal from a first transmitter along a first transmission path with respect to performance of a second channel transmitting a second signal from a second transmitter along a second transmission path the equalization being effective at a predetermined location in an optical wavelength division multiplexed system and the location being downstream of an optical amplifier in the first path and downstream of an optical amplifier in the second path, the method comprising:
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measuring the optical power of the first signal and the second signal at the inputs of each optical amplifier that is upstream of said location; and adjusting the optical power of the first transmitter by an amount dependent upon the sum of the reciprocal of the first signal optical power measurements relative to the sum of the reciprocal of the second signal optical power measurements. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An apparatus for equalizing performance of a first channel transmitting a first signal from a first transmitter along a first transmission path with respect to performance of a second channel transmitting a second signal from a second transmitter along a second transmission path the equalization being effective at a predetermined location in an optical wavelength division multiplexed system and the location being downstream of an optical amplifier in the first path and downstream of an optical amplifier in the second path the apparatus comprising:
- a receiving means for receiving optical power measurements of said signals taken at the inputs of each optical amplifier that is upstream of said location;
a storing means for storing said optical power measurements; a calculating means for calculating an amount of transmitter optical power adjustment of the first transmitter from the optical power measurements; a communicating means for communicating the amount of transmitter optical power adjustment to the first transmitter; and an offset calculating means for calculating an offset to be added to the amount of transmitter optical power adjustment to obtain a resultant amount of transmitter adjustment for adjusting the optical power of the first transmitter, said offset being dependent upon the difference between the bit rate of the first signal and the second signal. - View Dependent Claims (10, 11, 12, 13)
- a receiving means for receiving optical power measurements of said signals taken at the inputs of each optical amplifier that is upstream of said location;
Specification