Optical transmission of OFDM NQAM signals by direct laser modulation

The OFDM modulation method is widely used in several wireless applications because they are robust against multi-path distortions in the radio channel. However OFDM is sensitive to the channel nonllnearities. The OFDM signals are usually transmitted over an optical link to the wireless link. In this method the radio signals are transposed into the optical domain. In low cost systems direct laser modulation is applied. The nonlinearity of this type of modulation can cause distortion and this way limitation on the optical transmission. In this paper we present investigations on the limitations by simulations and experiments with the result of conditions for optimum operation.