Mitigating the effect of pulse distortions along an optical fiber communications link
OwnerAndrew Ellisinventor
Life of this patent
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Abstract
A method of mitigating the effect of deterministic (only slowly changing) pulse distortions along an optical fiber communications link transmitting a train of pulses, and apparatus for performing it. Plural copies of the pulse train are made and are all coherently added together with the original train after delaying each copy by a different amount. The amplitude and phase of each copy are independently adjusted, normally by a computer, to optimize the resulting pulse shape. The technique is capable of mitigating (not totally eliminating) distortions of diverse origin, including but not limited to polarization mode dispersion, chromatic dispersion, multiple reflections, and self-phase modulation, even if they interact with each other.
Claims20
A method of mitigating the effect of deterministic pulse distortions along an optical fiber communications link transmitting a train of pulses which comprises, at at least one intermediate point of the link, making plural copies of said pulse train, delaying each said copy by a different amount, coherently adding said copies to said pulse train, and adjusting the amplitude and phase of each said copy to optimize the resulting pulse shape.
An all-optical homodyne distortion compensator comprising:
- an input optical fiber for receiving a modulated carrier signal having a distorted pulse train which resulted from propagation of the modulated carrier signal through an optical link;
- a first plurality of beam steering elements and couplers for splitting the distorted pulse train of the modulated carrier signal into multiple fractions as copies for optical propagation;
- a parallel array of adaptive amplitude and phase controls for providing adjustable amplitude and adjustable phase of each of the copies of the distorted modulated carrier signal;
- a parallel configuration of incrementally delayed lines starting from an undelayed path for coupling the first plurality of beam steering elements and couplers to the parallel array of adaptive amplitude and phase controls, wherein the delayed lines have an increment time delay between the lines of at least 10% of the pulse length of the modulated carrier signal for incrementally delaying the amplitude adjustable and phase adjustable copies of the distorted pulse train of the modulated carrier;
- a second plurality of beam steering elements and couplers interferometrically combines the optical fields of the amplitude adjustable and phase adjustable delayed copies and the undelayed copy of the split distorted pulse train of the modulated carrier for providing an output signal;
- a computer controlled by a frequency impulse response (FIR) algorithm chosen to optimize the pulse shape resulting from the optical field addition of the copies to the undelayed fraction of the pulse train of the modulated carrier by controlling the parrallel array of amplitude and phase elements in response to a feedback control portion of the output signal;
- and
- an output fiber for coupling the output signal as a restored version of the modulated carrier signal with the optimized pulse shape having distortion mitigated.
Apparatus for mitigating the effect of deterministic pulse distortions along an optical fiber communications link transmitting a train of pulses which comprises:
- (a) a splitter array for separating said train of pulses into multiple fractions
- (b) for each said fraction except one
- (i) at least one amplitude adjusting means selected from the group consisting of variable optical amplifiers and variable optical attenuators and
- (ii) phase adjusting means
- to enable the production of respective copies of said train of pulses modified in amplitude and phase;
- (c) an interferometric adder for coherently adding said copies to said one fraction, optical path lengths from said splitter to said interferometric adder being such that each said copy is delayed by a different length of time relative to said one fraction.
An optical fiber communication link comprising an optical digital transmitter for generating a train of optical pulses, a receiver for said pulse train, at least one optical fiber connecting said transmitter to said receiver for conveying said pulse train and, for mitigating the effect of deterministic pulse distortions along said optical fiber communications link at least one apparatus which comprises:
- (a) a splitter array for separating said train of pulses into multiple fractions
- (b) for each said fraction except one
- (i) at least one amplitude adjusting means selected from the group consisting of variable optical amplifiers and variable optical attenuators and
- (ii) phase adjusting means
- to enable the production of respective copies of said train of pulses modified in amplitude and phase;
- and
- (c) an interferometric adder for coherently adding said copies to said one fraction, optical path lengths from said splitter to said interferometric device being such that each said copy is delayed by a different length of time relative to said one fraction.
Dependencies are inferred from the claim text.