Nortel Networks Corporation

Chung Y Wu

Matthew D Brown

Chris Wilhelm Barnard

Ping Wai Wan

Colin Geoffrey Kelly

Michel Pigeon

Marc A Nadeau

James Moser

A system for recovering a clock signal from a data signal is described. The system uses an oscillator adapted to generate an oscillator output signal, a first detecting circuit for obtaining a coarse frequency-lock condition between the data signal and a recovered clock signal, a second detecting circuit for obtaining a phase-locked condition between the data signal and the recovered clock signal, a lock-detecting circuit responsive to the first detecting circuit for detecting an out-of-lock condition between the data signal and the recovered clock signal, and a control circuit responsive to the lock-detecting circuits and adapted to control the oscillator to generate an oscillator output signal on the basis of the first detecting circuit during an out-of-lock condition, and otherwise to generate the oscillator output signal on the basis of the second detecting circuit. The advantages include a much wider pull-in range for frequency acquisition, and an accurate and robust measure of a quality of received data.

Method and apparatus for clock recovery and data qualification

A method and apparatus for performing optical channel performance management on a WDM system while in operation is disclosed in which each transmitter and receiver uses forward error-correction schemes to improve the BER performance of the channel in a known relation to the performance before error-correction. The receiver measures the BER performance before error-correction in real-time and communicates it to a system manager which determines, from this data, the appropriate launch power of each transmitter in the system, which it commands each transmitter to adopt, thereby ensuring relative launch powers which optimize the overall BER performance of the WDM multiplexed signal.

Method and apparatus for performance management of a multiplexed transmission system

A method and apparatus for filtering phase noise or jitter from a reference signal that may be of any arbitrary rate. By using a synthesizer to convert a signal at the output of a low noise signal source to a signal with frequency similar to a high speed output rate with desired relationship to the reference signal, a limitation normally caused by the narrow tuning range of a VCXO (a typical low noise signal source) can be overcome. Conversely, the desired high speed output rate may be converted to one similar to the VCXO frequency.

Method and apparatus for agile phase noise filtering using phase locked loops

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.

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Kanata, Canada

Chung Y Wu