The optical orthogonal frequency division multiplexing (OFDM) signal is affected by impairments introduced by electrical filters and optical chromatic dispersion. An enhanced fourth-power algorithm for phase estimation with frequency separation is used to estimate and compensate the phase rotation of OFDM subcarriers. The performance of the proposed phase estimation algorithm is evaluated on a 4-Gb/s OFDM signal at different frequencies. Experimental results using the proposed algorithm show a 1.8-dB received power sensitivity improvement at a bit error rate of 1×10-4 after a 100-km standard single-mode fiber transmission, compared with the conventional technique.