Interleavers form an important component in Optical Interleave Division Multiple Access (OIDMA) systems that help in reducing the impact of Multiple Access Interference (MAI). This paper highlights the performance comparison of OIDMA system with coded OIDMA systems based on Tree-based and Random interleavers at different values of processing gains. The OIDMA system studied in this paper utilizes FEC encoding for its efficient functioning. OIDMA system is basically the amalgamation of spreading and interleaving techniques in order to facilitate multiuser communication. The effectiveness of spreading and interleaving processes in reducing MAI and noise impacts lies in the value of processing gain. The performance of OIDMA system is evaluated in terms of BER for different numbers of users.