Abstract: 

The main motivation in the employment of the orthogonal frequency division multiplexing (OFDM) modulation technique in long haul optical communications system (Optical-OFDM) is mainly due to its ability to electronically compensate the chromatic (CD) and polarization mode dispersions (PMD). High spectral efficiency is also provided due to the orthogonality of the OFDM subcarriers which increased the utilization of the optical bandwidth. The implementations of the optical OFDM system have been demonstrated based on two optical receiver design; the coherent (CO-OFDM) and the direct detection optical OOFDM (DDO-OFDM). 

In this study, the noise impairments in the DDO-OFDM system will be investigated. The noise due to the active devices used and the mixing of the noise with the signal components will be evaluated. The noise contributions from the laser source such as the relative intensity noise (RIN) and the linewidth will be investigated. The laser source characteristics required for the minimum acceptable system performance will be identified. For long haul optical communications, the effects of the conversion from the phase to the intensity fluctuations due to dispersion will introduce penalty to the system performance. For the use of the optical amplifiers, the noise contribute in the system will mix with the other signal components and the distortion products when detected at photodiode. This study will investigate the effect of the noise with the employment of the erbium doped fiber amplifier (EDFA) and the Raman amplifier. For the external modulator, the issues on the nonlinearity, the signal imbalance at the upper and lower branches and the clipping effects of the modulator will be investigated. The additional noise due to the DAC will be also investigated for the overall noise analysis of the DDO-OFDM system. Finally, the technique to mitigate the noise will be identified and employed at the device and system level. The performance of the DDO-OFDM system with the noise mitigation will be investigated for transmission of high data rate of 100 Gb/s.

About the Speaker:  Zuraidah is a postgraduate research student with the department of Electrical and Computer Systems Engineering at Monash University, Clayton Campus