Abstract
We show that dispersion-enhanced phase noise (DEPN) induces performance degradations in both conventional CO-OFDM systems and reduced-guard-interval (RGI) CO-OFDM systems employing RF-pilot phase compensation. After analytically studying DEPN, we show that DEPN causes a 2 to 6 dB optical signal-to-noise ratio (OSNR) penalty at transmission distances of 3200 km and 1600 km for 28 and 56 Gbaud QPSK systems, respectively, using lasers with 2 MHz linewidths. At such distances, DEPN reduces the linewidth tolerance at 1 dB OSNR penalty to 250-500 kHz while in the back-to-back case the tolerance is 1-3 MHz for both systems. When fiber nonlinearity is included, we observe similar performance degradations.
Highlights
Coherent optical orthogonal frequency-division multiplexing (CO-OFDM) has been extensively studied because of its advantages such as high spectral efficiencies, low required sampling rates, and flexible bandwidth scalability and allocation [1]
We investigate the impact of dispersion-enhanced phase noise (DEPN) on both 28 Gbaud dual polarization (DP) QPSK (112 Gb/s) and 56 Gbaud DP-QPSK (224 Gb/s) systems
We show that using 2 MHz distributed feedback (DFB) lasers only induces approximately 1 dB optical signal-to-noise ratio (OSNR) penalties at bit error rates (BERs) = 10−3 for both 28 and 56 Gbaud DP-QPSK systems in the back-to-back case, the OSNR penalty is increased by 2-6 dB after 3200 km and 1600 km transmission for the 28 and 56 Gbaud systems respectively
Summary
Coherent optical orthogonal frequency-division multiplexing (CO-OFDM) has been extensively studied because of its advantages such as high spectral efficiencies, low required sampling rates, and flexible bandwidth scalability and allocation [1]. Using RF-pilot phase compensation, which was proposed in [7] to combat ICI, it has been demonstrated that the laser linewidth tolerances can be increased to several MHz [7,8,9] This enables the use of lowcost distributed feedback (DFB) lasers without inducing large performance degradations. We show that using 2 MHz DFB lasers only induces approximately 1 dB optical signal-to-noise ratio (OSNR) penalties at bit error rates (BERs) = 10−3 for both 28 and 56 Gbaud DP-QPSK systems in the back-to-back case, the OSNR penalty is increased by 2-6 dB after 3200 km and 1600 km transmission for the 28 and 56 Gbaud systems respectively At such transmission distances, the laser linewidth tolerance of the RF-pilot compensation scheme at 1 dB OSNR penalty is reduced from 1-3 MHz to 250-500 kHz for both systems because of DEPN. We find that DEPN induced penalties in conventional CO-OFDM systems cannot be mitigated whereas DEPN-induced penalties in RGI CO-OFDM systems can be mitigated using maximum-likelihood algorithms [10, 16]
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