Clock recovery for optical transmission systems
AssigneeCisco Technology, Inc.
InventorChristopher Fludger
Life of this patent
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Abstract
A receiver for an optical communications system which corrects distortion of a received signal. A clock recovery system utilizing a feedback and feedforward system are provided. The feedback loop comprises a phase detector and a clock source, while the feedforward loop comprises the phase detector and a delay element for delaying the output of distortion correction system. The feedback loop has a significantly lower bandwidth than the feedforward path. There are also provided methods of optimizing tap weights and of acquiring initial tap weights.
Claims20
A method of initially acquiring tap weights for a finite impulse response (FIR) filter used to correct distortion in an optical communication receiver, the method comprising:
- acquiring and storing a series of samples of a received optical signal, the series of samples being acquired in an order in time;
- applying a blind optimization algorithm to the series of samples to obtain first estimated tap weights for the FIR filter in order to equalize the received optical signal, wherein the blind optimization algorithm is applied to the series of samples alternately in the order that the series of samples is acquired and in a reverse order that the series of samples is acquired in a digital processing system;
- activating a clock recovery system in the optical communication receiver based on the first estimated tap weights to remove a clock offset for subsequent samples;
- after the clock recovery system is activated, acquiring and storing a further series of samples of the received optical signal, wherein the clock offset is removed from the further series of samples;
- and
- applying the blind optimization algorithm to the further series of samples to obtain second estimated tap weights having an accuracy higher than the first estimated tap weights.
An apparatus comprising:
- an optical receiver configured to acquire and store a series of samples of a received optical signal, the series of samples being acquired in an order in time;
- a clock recovery system;
- a digital signal processor configured to:
- apply a blind optimization algorithm to the series of samples to obtain first estimated tap weights, wherein the digital signal processor applies the blind optimization algorithm to the series of samples alternately in the order that the series of samples is acquired and in a reverse order that the series of samples is acquired;
- wherein the optical receiver is further configured to activate the clock recovery system based on the first estimated tap weights to remove a clock offset for subsequent samples;
- wherein, after the clock recovery system is activated, the optical receiver is configured to acquire and store a further series of samples of the received optical signal and the clock offset is removed from the further series of samples;
- wherein the digital signal processor is further configured to apply the blind optimization algorithm to the further series of samples to obtain second estimated tap weights having an accuracy higher than the first estimated tap weights;
- and
- a finite impulse response (FIR) filter configured to equalize the received optical signal with the second estimated tap weights.
One or more non-transitory computer readable storage media encoded with computer readable instructions which, when executed by a processor, cause the processor to:
- acquire and store a series of samples of a received optical signal, the series of samples being acquired in an order in time;
- apply a blind optimization algorithm to the series of samples to obtain first estimated tap weights for a finite impulse response (FIR) filter in order to equalize the received optical signal, wherein the blind optimization algorithm is applied to the series of samples alternately in the order that the series of samples is acquired and in a reverse order that the series of samples is acquired in a digital processing system;
- activate a clock recovery system in an optical communication receiver based on the first estimated tap weights to remove a clock offset for subsequent samples;
- after the clock recovery system is activated, acquire and store a further series of samples of the received optical signal, wherein the clock offset is removed from the further series of samples;
- and
- apply the blind optimization algorithm to the further series of samples to obtain second estimated tap weights having an accuracy higher than the first estimated tap weights.
Dependencies are inferred from the claim text.