Nortel Networks Corporation

Chris Wilhelm Barnard

Chung Y Wu

Alan Glen Solheim

Farideh Khaleghi

A method of equalizing the channels of a WDM link comprises identifying an error threshold level BER,for the BER defined for each signal S(j) in accordance with the channel rate, and determining the attenuation A(j) of, for example, the power P(j) of each signal S(j) transmitted over the WDM link. The transmitter powers are adjusted taking into account the attenuations determined for all channels. The attenuation A(j) for channel (j) is determined by first setting the power P(j) of all signals S(j) to a maximum P,, attenuating the power P(j) of channel (j) until the BER reaches the threshold value BER,, measuring the power corresponding to the BER,for that channel, and calculating the difference between the P,and P(j),. The transmitter powers are then set according to the relationship P(j)&equals;P,&minus;&eegr;(A(j)&minus;A,), where &eegr; is 0.8 for a system with 3-4 channels. The method may be used for multi-channel systems with intermediate nodes where channels are added and dropped.

Methods for equalizing WDM systems

A method of equalizing the channels of a WDM link comprises identifying an error threshold level BER.sub.Fail for the BER defined for each signal S(j) in accordance with the channel rate, and determining the attenuation A(j) of, for example, the power P(j) of each signal S(j) transmitted over the WDM link. The transmitter powers are adjusted taking into account the attenuations determined for all channels. The attenuation A(j) for channel (j) is determined by first setting the power P(j) of all signals S(j) to a maximum P.sub.Max, attenuating the power P(j) of channel (j) until the BER reaches the threshold value BER.sub.Fail, measuring the power corresponding to the BER.sub.Fail for that channel, and calculating the difference between the P.sub.Max and P(j).sub.Fail. The transmitter powers are then set according to the relationship P(j)=P.sub.Max -.eta.(A(j)-A.sub.Min), where .eta. is 0.8 for a system with 3-4 channels. The method may be used for multi-channel systems with intermediate nodes where channels are added and dropped.

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.

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Orleans, Canada

Chris Wilhelm Barnard