Abstract
In coherent optical systems with electronic dispersion compensation (EDC) after digital signal processing (DSP) the received constellation remains impacted by enhanced noise commonly known as equalization-enhanced phase noise (EEPN) [1]. The enhanced noise is mainly generated due to low frequency noise of the local oscillator as shown in [2]. This impairment limits to achieve higher capacity and/or longer reach. Therefore, it is essential for the system designer to be able to estimate the impact of EEPN in order to make an informed choice between a system configuration with tolerable penalty (e.g. by using better LO laser, lower constellation etc.) or a mitigation technique such as one proposed in [3], [4]. In [5], we show that EEPN is due to the interference of multiple delayed versions of the dispersed signal, generated by the intermixing of the signal with the LO noise side bands in the photodetectors. The estimate of the impact of EEPN on the system performance having LO with white frequency noise can be described in terms of optical signal to noise ratio (OSNR). We show that in coherent optical systems utilizing EDC, this noise corresponds to multipath fading in wireless communication systems. Closed form expressions of necessary LO linewidth and/or mitigation bandwidth for a general system configuration and specified OSNR penalty are given.
Published Version
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