Abstract
We experimentally demonstrate the impact of equalization-enhanced phase noise (EEPN) on the performance of 56 Gbaud dual-polarization (DP) QPSK long haul transmission systems. Although EEPN adds additional noise to the received symbols, we show that this reduces the phase variance introduced by the LO laser, and therefore should be considered when designing the carrier phase recovery (CPR) algorithms and estimating system performance. Further, we experimentally demonstrate the performance degradation caused by EEPN when a LO laser with a large linewidth is used at the receiver. When using a 2.6 MHz linewidth distributed feedback (DFB) laser instead of a ~100 kHz linewidth external-cavity laser (ECL) as a LO, the transmission distance is reduced from 4160 km to 2640 km due to EEPN. We also confirm the reduction of the phase variance of the received symbols for longer transmission distances showing its impact on the CPR algorithm optimization when a DFB laser is used at the receiver. Finally, the relationship between the EEPN-induced penalty versus the signal baud rate and the LO laser linewidth is experimentally evaluated, and numerically validated by simulations.
Highlights
Equalization-enhanced phase noise (EEPN) is a non-negligible impairment in dispersionunmanaged single carrier transmission systems when inexpensive local oscillator (LO) lasers are used at the receiver [1,2,3,4]
With the distributed feedback (DFB) laser as the LO, we experimentally show that the symbol phase variance decreases as the transmission distance increases, which affects the optimization of the carrier phase recovery (CPR) algorithm
We investigated the equalization-enhanced phase noise (EEPN) for 56 Gbaud dual-polarization (DP) quadrature phase shift keying (QPSK) long haul systems
Summary
Equalization-enhanced phase noise (EEPN) is a non-negligible impairment in dispersionunmanaged single carrier transmission systems when inexpensive local oscillator (LO) lasers (with large linewidths) are used at the receiver [1,2,3,4]. EEPN-induced performance degradation has been experimentally demonstrated for 28 Gbaud dual-polarization (DP) quadrature phase shift keying (QPSK) systems over a 3000 km transmission distance [4]. This penalty scales with the signal baud rate and transmission distance [1,2]. We show that EEPN increases the noise variance of the received symbols it reduces the variance of the symbol phase drift because of the chromatic dispersion (CD)-induced correlation between symbols This should be considered in designing and optimizing carrier phase recovery (CPR) algorithms, and/or estimating system performance. We calculate the EEPN-induced Q-factor penalty versus the signal baud rate and the LO laser linewidth, through both experiments and simulations
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