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Abstract
We propose--as a modification of the optical (RF) pilot scheme--a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within ½ orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper.
Highlights
Chromatic dispersion (CD) and laser phase noise severely impact the performance of high speed optical fiber transmission systems [1,2]
First we look at the effect of this on constellation diagrams for optical signal-to-noise ratio (OSNR) = 35 dB i.e. when enhanced phase noise (EEPN) generates a phase noise error-rate-floor
In this paper we propose a balanced phase modulation between two orthogonal polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations
Summary
Chromatic dispersion (CD) and laser phase noise severely impact the performance of high speed optical fiber transmission systems [1,2]. In [15], the carrier phase is extracted using an optical (RF) pilot tone in the orthogonal polarization relative to the QPSK modulated signal and the Viterbi-Viterbi algorithm is applied for reducing EEPN influence. Based upon a leading order Taylor expansion of the laser phase noise it is possible to associate the EEPN effect with an effective laser linewidth [13,22,23] It has been verified in brute force simulation results for the Bit-Error-Rate (BER) that this linewidth predicts resulting BER floors for differential QPSK systems well even when the EEPN influence is dominating [22,23].
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