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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.

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In this paper, we propose nanodiamond (ND) material as a saturable absorber (SA) to generate short pulses from a mode-locked erbium-doped fiber laser (EDFL). The ND-SA is fabricated by the drop-casting method using polyvinyledenedifluoride–trifluoroethylene as a host polymer and methyl ethel ketone as a solvent liquid. The SA, which possesses 20% ND concentration, has a 5.46% modulation depth with 2000 M W / c m 2 saturation intensity. Sequentially, the performance of the EDFL is investigated after integrating an ND-SA within the laser ring. The results reveal that the presented ND-SAs produce stable ultrashort laser pulses. Moreover, the fabricated ND film is a promising solid film for many photonic schemes. The proposed mode-locked EDFL-based ND-SA starts a mode-locking operation at a pumped power of 116 mW. The generated mode-locked pulses have a pulse duration of 0.84 ps, a repetition rate of 1.93 MHz, and a power of 0.517 mW, at a pumped power of 187 mW. Finally, to the best of our knowledge, this is the first time that the ND-SA has been used as a mode locker within the EDFL as a thin film and with the suggested fabrication method.