Abstract
A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.
Highlights
Coherent detection together with digital signal processing offers a promising solution in terms of receiver sensitivity, dispersion resilience, and the phase noise tolerance [1,2,3]
We show with a frequency domain analysis that the enhanced phase noise (EEPN) results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator
In coherent optical systems with electronic dispersion compensation (EDC), it is observed that the received constellation, even after digital signal processing, remains influenced by enhanced noise commonly known as equalization-enhanced phase noise (EEPN) originating from the phase noise of the local oscillator (LO) [5]
Summary
Coherent detection together with digital signal processing offers a promising solution in terms of receiver sensitivity, dispersion resilience, and the phase noise tolerance [1,2,3]. In coherent optical systems with electronic dispersion compensation (EDC), it is observed that the received constellation, even after digital signal processing, remains influenced by enhanced noise commonly known as equalization-enhanced phase noise (EEPN) originating from the phase noise of the local oscillator (LO) [5]. In order to understand the influence of LO frequency noise on this enhanced noise we perform a frequency domain analysis of a coherent optical system with electronic dispersion compensation. The findings of the frequency domain analysis are validated through system simulations using quadrature phase shift keying (QPSK) and 16-quadrature amplitude modulation (QAM) for different symbol rates, accumulated dispersion and LO linewidths. The results of the paper indicate how EEPN can be effectively mitigated, thereby enabling the use of conventional semiconductor lasers with a Lorentzian linewidth up to 10 MHz as LO lasers in these systems
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