Orthogonal Frequency Division Multiplexing (OFDM) is a baseband wired and wireless communication system which has proffered an effective solution to transmission impairment like nonlinearity in fiber, fading, Chromatic Dispersion (CD) which resulted in intersymbol and intercarrier interferences. The urge for a very high speed transmission has lead to a dramatic increase of interest in OFDM based optical communication system in recent years. This paper gives a tutorial overview of O-OFDM detection techniques namely; Direct Detection O-OFDM (DDO-OFDM) and Coherent O-OFDM (CO-OFDM) from the basis, outlining their similarities and differences in their performance. The only different in the conceptual diagram of DDO-OFDM and CO-OFDM is replacing MZM and PIN detector in DDO-OFDM with optical IQ modulator and coherent receiver respectively, although the DSP requirement, Cyclic Prefix (CP), DACs and ADCs design for both will depend on the choice of the designer. The building architecture of direct detection is much cheaper as compared to coherent receiver system, but with the robust implementation of DSP in the transceiver circuit as the signal volume increases, the cost of the coherent receiver will equally come down drastically.