This paper studies the frequency domain equalization scheme for single carrier optical intensity modulation direct detection system.Through theoretical analysis on the relationship between the time and frequency domain inter-symbol interference for single carrier signal

a time domain clipping based channel equalizer with new tap updating method is proposed to reduce the effect of noise.The optimal clipping position and symbol number are selected through numerical simulations.The simulation results show that compared with conventional time domain channel equalization

the required OSNR can be reduced by almost 2dB through frequency domain channel equalization after 100 km transmission of 10Gbit/s NRZ-OOK signals.