Long haul transmission links evolve with the advent of new multiplexing and modulation schemes. We propose a new approach of dispersion compensated coherent optical orthogonal frequency division multiplexing scheme which is combined with quadrature amplitude modulation to double the data rate and spectral efficiency as transmitted in an optical OFDM system. Quadrature amplitude modulation (QAM) technique is used for data mapping in the OFDM system. In-phase and quadraturephase signal are modulated with two different Mach Zehnder modulators with a laser source of 1550nm wavelength and transmitted through a standard single mode fiber. Though the addition of cyclic prefix minimizes the effect of dispersion the use of various dispersion compensation techniques improved the bit error rate performance enabling long distance transmission.