On the impact of the clipping techniques on the performance of optical OFDM

Recently, OFDM modulations are being considered for both optical fiber and wireless optical communications, specially due to their efficiency to combat the inter-symbol interference. Between the modifications of the standard OFDM that meet the requirements of the incoherent OFDM optical communications such as the ones that consider intensity modulation/direct detection, the asymmetric clipping optical OFDM and the DC biased optical OFDM techniques are the most popular but both involve an asymmetric clipping operation. Therefore, due to the high sensitivity of OFDM signals to nonlinearities, the nonlinear distortion effects introduced by the asymmetric clipping in the form of in and out-band-distortion should not be neglected. In fact, in order to address the performance of such systems, these distortion effects must be accurately characterized. In this work, by making use of a Gaussian approximation, we study analytically the impact of the asymmetric clipping in the performance of optical OFDM techniques by deriving theoretical expressions for the power spectral density and for the distortion at the subcarrier level, which is a key step to understand the potential performance of these systems.