Abstract
The potential for higher spectral efficiency has increased the interest in all-optical orthogonal frequency division multiplexing (OFDM) systems. However, the sensitivity of all-optical OFDM to fiber non-linearity, which causes nonlinear phase noise, is still a major concern. In this paper, an analytical model for estimating the phase noise due to self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in an all-optical OFDM system is presented. The phase noise versus power, distance, and number of subcarriers is evaluated by implementing the mathematical model using Matlab. In order to verify the results, an all-optical OFDM system, that uses coupler-based inverse fast Fourier transform/fast Fourier transform without any nonlinear compensation, is demonstrated by numerical simulation. The system employs 29 subcarriers; each subcarrier is modulated by a 4-QAM or 16-QAM format with a symbol rate of 25 Gsymbol/s. The results indicate that the phase variance due to FWM is dominant over those induced by either SPM or XPM. It is also shown that the minimum phase noise occurs at -3 dBm and -1 dBm for 4-QAM and 16-QAM, respectively. Finally, the error vector magnitude (EVM) versus subcarrier power and symbol rate is quantified using both simulation and the analytical model. It turns out that both EVM results are in good agreement with each other.
Highlights
Due to their promising potentials, all-optical orthogonal frequency division multiplexing (OFDM) techniques have been recently studied for optical transmission system applications [1,2,3]
We develop an analytical model that evaluates linear and nonlinear phase noises induced by the interaction of amplified spontaneous emission (ASE) with selfphase modulation (SPM), XPM, and four-wave mixing (FWM) in both 4-QAM and 16-QAM all-optical OFDM transmission systems
In contrast to wavelength-division multiplexing (WDM) optical transmission systems [18] the nonlinear phase noise induced by FWM dominates other factors in all-optical OFDM systems
Summary
Due to their promising potentials, all-optical orthogonal frequency division multiplexing (OFDM) techniques have been recently studied for optical transmission system applications [1,2,3]. It is very important to discuss the phase noise in this system in the future With this analytical model, we are able to quantify the nonlinear phase noise variation induced by SPM, XPM, and FWM due to variations in sub-carrier peak power, number of subcarriers, fiber length, and channel index. In contrast to WDM optical transmission systems [18] the nonlinear phase noise induced by FWM dominates other factors in all-optical OFDM systems This phenomenon is likely due to the subcarriers of all-optical OFDM systems modulated from optical frequency combs, where the interaction is derived from the same laser source. The analytical and simulation results are presented, where the impacts of fiber dispersion, number of subcarriers, fiber length, and subcarrier peak power on the variance of the total phase noise are studied.
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