In Intensity-Modulated Direct Detection Optical Orthogonal Frequency Division Multiplexing (IM/DD-OOFDM) communication systems, a lower Peak-to-Average Power Ratio (PAPR) is essential for improving system performance. In order to reduce the high PAPR, a Discrete Forest Optimization Algorithm (DFOA) is integrated with the classical Selective Mapping (SLM) method in IM/DD-OFDM system. This approach successfully optimizes the values of phase factors, minimizes the search numbers, and reduces computational complexity. To evaluate the impact of the DFOA-SLM method on PAPR reduction, the parameters of the DFOA-SLM method play a crucial role in decreasing the PAPR in an IM/DD optical OFDM system. The DFOA-SLM method demonstrates improved Bit Error Rate (BER) performance, power spectral density (PSD), and power saving performance compared to other PAPR reduction methods.