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Investigation of group delay ripple distorted signals transmitted through all-optical 2R regenerators

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We investigate the use of all-optical regenerators to correct pulse distortions introduced by group delay ripple. Group delay ripple creates unwanted satellite pulses and intensity fluctuations. By placing an all-optical regenerator after a device that introduces group delay ripple, we show that the signal distortions can be effectively reduced. This has the benefit of opening the signal eye at the receiver. The performances of both self-phase modulation and four-wave mixing based regenerators in reducing ripple induced system penalties are examined. We find that the regenerator based on four-wave mixing achieves better suppression of group delay ripple distortions than the self-phase modulation based alternative. The eye closure penalty introduced by group delay ripple is reduced by the four-wave mixing based regenerator by 1dB.

©2004 Optical Society of America

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Figures (9)

Fig. 1.
Fig. 1. Using all-optical regeneration to correct group delay ripple induced pulse degradation. Point A: dispersed pulses, Point B: dispersion compensated but group delay ripple distorted pulses and Point C: regenerated pulses.
Fig. 2.
Fig. 2. Effect of harmonic group delay ripple (dotted line) on an isolated pulse, whose power spectrum (solid line) is shown on the left. The resulting temporal pulse shape is shown on the right. pr and 1/pr are the ripple period and frequency, respectively.
Fig. 3.
Fig. 3. SPM-based (left) and FWM-based (right) optical regenerators. Their power transfer functions are shown as solid lines. Powers are normalised to the nominal integrated input power. Timing jitter shown as dashed lines is normalised to the 25 ps bit period. The input pulse full-width at half maximum is 8.25 ps. The top diagrams show the spectral content of the signal after the DS-HNLF in both regenerators.
Fig. 4.
Fig. 4. Regenerator’s tolerance to intensity (left-hand column) and pulse-width fluctuations (right-hand column). Top: Before regeneration, middle: regenerated via SPM, bottom: via FWM.
Fig. 5.
Fig. 5. Intensity-dependent timing jitter in the SPM-based regenerator..Pulse shapes at various stages of the SPM-based regenerator are shown as solid lines, frequency chirp as dotted lines, and the filter passband as grey band. Point A: input pulses with intensity fluctuation, point B: pulses under the effects of SPM and normal dispersion, and Point C: output pulses with timing jitter.
Fig. 6.
Fig. 6. Harmonic ripple analysis: Eye-closure penalty (dB) before and after each regenerator. Darker regions represent higher penalty. Top and bottom rows illustrate the cases for ϕr = 0 and ϕr = π/2, respectively. Contour lines are spaced by 0.5 dB. Ripple amplitude and period are normalised to the bit-period (T) and the bit-rate (1/T), respectively.
Fig. 7.
Fig. 7. Measured group delay ripple. Dotted line shows the spectrum of a 8.25 ps unchirped Gaussian pulse.
Fig. 8.
Fig. 8. Realistic ripple analysis: (Partial) pulse sequences, optical eye diagrams and eye-closure penalty before and after each regenerator. Shaded rectangles representing the eye-closures are used in the calculation of Ceye .
Fig. 9.
Fig. 9. Eye-closure penalty before (filled circles) and after (open circles) the FWM-based regenerator for a range of input wavelength drifts.

Tables (1)

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Table 1. Parameters of the SPM-based and FWM-based optical regenerators

Equations (1)

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Δ τ g ( ν ) = a r 2 cos ( 2 π ν p r + φ r )


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